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I
Ch
ap
ter 50
The
Cir
cula
tory
Sys
tem
Ch
ap
ter
Ou
tlin
e
50
.1
Th
e C
om
po
nen
ts o
f B
loo
d
50
.2
Inve
rteb
rate
Cir
cula
tory
Sys
tem
s
50
.3
Ver
teb
rate
Cir
cula
tory
Sys
tem
s
50
.4
Th
e F
ou
r-C
ham
ber
ed H
eart
an
d t
he
Blo
od
Ves
sels
50
.5
Ch
arac
teri
stic
s o
f B
loo
d V
esse
ls
50
.6
Reg
ula
tio
n o
f B
loo
d F
low
an
d B
loo
d P
ress
ure
Intr
od
uc
tio
n
In m
ult
ice
llu
lar
org
an
ism
s, o
xyg
en o
bta
ined
by
the
resp
ira
tory
sys
tem
an
d n
utr
ien
ts p
roce
ssed
by
the
dig
esti
ve s
yste
m m
ust
be
tra
nsp
ort
ed t
o c
ells
th
rou
gh
ou
t th
e b
od
y. C
on
vers
ely,
ca
rbo
n d
ioxi
de
an
d o
ther
wa
ste
pro
du
cts
pro
du
ced
wit
hin
th
e ce
lls m
ust
be
retu
rned
to
th
e re
spir
ato
ry, d
iges
tive
, an
d u
rin
ary
sys
tem
s fo
r el
imin
ati
on
fro
m t
he
bo
dy.
Th
ese
task
s a
re t
he
resp
on
sib
ility
of t
he
circ
ula
tory
sys
tem
. All
mu
ltic
ellu
lar
org
an
ism
s h
ave
a h
eart
th
at
pu
mp
s !
uid
s th
rou
gh
th
e b
od
y. M
an
y in
vert
ebra
tes
ha
ve a
n o
pen
syst
em in
wh
ich
! u
ids
mo
ve t
hro
ug
h t
he
bo
dy
cavi
ty. V
erte
bra
tes
als
o h
ave
a s
yste
m li
ke t
his
th
at
mo
ves
lym
ph
th
rou
gh
the
bo
dy;
ho
wev
er, t
he
pri
ma
ry c
ircu
lato
ry !
uid
is b
loo
d, w
hic
h m
ean
s th
rou
gh
a c
lose
d s
yste
m o
f blo
od
ves
sels
.
pla
tele
ts,
alth
ou
gh
in
clu
ded
in
fig
ure
50
.1,
are
no
t co
mp
lete
ce
lls;
rat
her
, th
ey a
re f
rag
men
ts o
f ce
lls
that
are
pro
du
ced
in t
he
bo
ne
mar
row
. (W
e d
escr
ibe
the
acti
on
of
pla
tele
ts i
n b
loo
d
clo
ttin
g l
ater
in
th
is s
ecti
on
.)
Cir
cula
tin
g b
loo
d h
as m
any
fun
ctio
ns:
Tra
nsp
ort
atio
n.
1.
All
of
the
sub
stan
ces
esse
nti
al f
or
cell
ula
r m
etab
oli
sm a
re t
ran
spo
rted
by
blo
od
. Red
blo
od
ce
lls
tran
spo
rt o
xyg
en a
ttac
hed
to
hem
og
lob
in;
nu
trie
nt
mo
lecu
les
are
carr
ied
in
th
e p
lasm
a, s
om
etim
es b
ou
nd
to
ca
rrie
rs;
and
met
abo
lic
was
tes
are
elim
inat
ed a
s b
loo
d
pas
ses
thro
ug
h t
he
live
r an
d k
idn
eys.
Reg
ula
tio
n.
2.
Th
e ca
rdio
vasc
ula
r sy
stem
tra
nsp
ort
s re
gu
lato
ry h
orm
on
es f
rom
th
e en
do
crin
e g
lan
ds
and
als
o
5
0.1
Th
e C
om
po
nen
ts o
f Blo
od
Le
arn
ing
Ou
tco
me
s
De
scri
be
the
fun
ctio
ns
of
circ
ula
tin
g b
loo
d.
1.
Dis
tin
gu
ish
be
twe
en
th
e ty
pe
s o
f fo
rme
d e
lem
en
ts.
2.
De
lin
ea
te t
he
pro
cess
of
blo
od
clo
ttin
g.
3.
Blo
od
is
a co
nn
ecti
ve t
issu
e co
mp
ose
d o
f a
flu
id m
atri
x, c
alle
d
pla
sma,
an
d s
ever
al d
iffe
ren
t ki
nd
s o
f ce
lls
and
oth
er f
orm
ed
ele
men
ts t
hat
cir
cula
te w
ith
in t
hat
flu
id (
fig
ure
50
.1) .
Blo
od
CH
AP
TE
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Fig
ure
50
.1
Co
mp
osi
tio
n o
f b
loo
d.
par
tici
pat
es i
n t
emp
erat
ure
reg
ula
tio
n. C
on
trac
tio
n a
nd
d
ilat
ion
of
blo
od
ves
sels
nea
r th
e su
rfac
e o
f th
e b
od
y,
ben
eath
th
e ep
ider
mis
, hel
ps
to c
on
serv
e o
r to
dis
sip
ate
hea
t as
nee
ded
.P
rote
ctio
n.
3.
Th
e ci
rcu
lato
ry s
yste
m p
rote
cts
agai
nst
in
jury
an
d f
ore
ign
mic
rob
es o
r to
xin
s in
tro
du
ced
in
to
the
bo
dy.
Blo
od
clo
ttin
g h
elp
s to
pre
ven
t b
loo
d l
oss
w
hen
ves
sels
are
dam
aged
. Wh
ite
blo
od
cel
ls, o
r le
uko
cyte
s, h
elp
to
dis
arm
or
dis
able
in
vad
ers
such
as
viru
ses
and
bac
teri
a (s
ee c
hap
ter
52
).
Blo
od
pla
sma
is a
" u
id m
atr
ix
Blo
od
pla
sma
is t
he
mat
rix
in w
hic
h b
loo
d c
ells
an
d p
late
lets
are
su
spen
ded
. In
ters
titi
al (
extr
acel
lula
r) f
luid
s o
rig
inat
e fr
om
th
e fl
uid
pre
sen
t in
pla
sma.
A
lth
ou
gh
pla
sma
is 9
2%
wat
er, i
t al
so c
on
tain
s th
e fo
llo
w-
ing
so
lute
s:
Nu
trie
nts
, w
aste
s, a
nd
ho
rmo
nes.
1.
Dis
solv
ed w
ith
in
the
pla
sma
are
all
of
the
nu
trie
nts
res
ult
ing
fro
m
dig
esti
ve b
reak
do
wn
th
at c
an b
e u
sed
by
cell
s, i
ncl
ud
ing
glu
cose
, am
ino
aci
ds,
an
d v
itam
ins.
Als
o d
isso
lved
in
th
e p
lasm
a ar
e w
aste
s su
ch a
s n
itro
gen
co
mp
ou
nd
s an
d C
O2
pro
du
ced
by
met
abo
lizi
ng
cel
ls. E
nd
ocr
ine
ho
rmo
nes
re
leas
ed f
rom
gla
nd
s ar
e al
so c
arri
ed t
hro
ug
h t
he
blo
od
to
th
eir
targ
et c
ells
.Io
ns.
2.
Blo
od
pla
sma
is a
dil
ute
sal
t so
luti
on
. Th
e p
red
om
inan
t p
lasm
a io
ns
are
Na+
, Cl–
, an
d b
icar
bo
nat
e io
ns
(HC
O3–).
In
ad
dit
ion
, pla
sma
con
tain
s tr
ace
amo
un
ts o
f o
ther
io
ns
such
as
Ca2+
, Mg
2+
, Cu
2+
, K+
, an
d Z
n2+
.P
rote
ins.
3.
As
men
tio
ned
ear
lier
, th
e li
ver
pro
du
ces
mo
st o
f th
e p
lasm
a p
rote
ins,
in
clu
din
g al
bu
min
, w
hic
h c
on
stit
ute
s m
ost
of
the
pla
sma
pro
tein
; th
e al
ph
a (α
) an
d b
eta
(β)
glo
bu
lin
s, w
hic
h s
erve
as
carr
iers
of
lip
ids
and
ste
roid
h
orm
on
es; a
nd
" b
rin
ogen
, w
hic
h is
req
uir
ed f
or
blo
od
cl
ott
ing.
Blo
od
pla
sma
wit
h t
he
! b
rin
oge
n r
emo
ved
is
call
ed s
eru
m.
Fo
rme
d e
lem
en
ts in
clu
de
circ
ula
tin
g c
ell
s a
nd
pla
tele
ts
Th
e fo
rmed
ele
men
ts o
f b
loo
d c
ells
an
d c
ell
frag
men
ts i
ncl
ud
e re
d b
loo
d c
ells
, w
hit
e b
loo
d c
ells
, an
d p
late
lets
. E
ach
ele
men
t h
as
a sp
ecif
ic
fun
ctio
n
in
mai
nta
inin
g
the
bo
dy’
s h
ealt
h
and
ho
meo
stas
is.
Ery
thro
cyte
s
Eac
h m
icro
lite
r o
f b
loo
d c
on
tain
s ab
ou
t 5
mil
lio
n r
ed
blo
od
ce
lls,
or
ery
thro
cyte
s. T
he
frac
tio
n o
f th
e to
tal
blo
od
vo
lum
e th
at i
s o
ccu
pie
d b
y er
yth
rocy
tes
is c
alle
d t
he
blo
od
’s h
emat
ocri
t;
in h
um
ans,
th
e h
emat
ocr
it i
s ty
pic
ally
aro
un
d 4
5%
.
Eac
h e
ryth
rocy
te r
esem
ble
s a
do
ug
hn
ut-
shap
ed d
isk
wit
h
a ce
ntr
al d
epre
ssio
n t
hat
do
es n
ot
go
all
th
e w
ay t
hro
ug
h. M
a-tu
re m
amm
alia
n e
ryth
rocy
tes
lack
nu
clei
. T
he
eryt
hro
cyte
s o
f ve
rteb
rate
s co
nta
in
hem
og
lob
in,
a p
igm
ent
that
b
ind
s an
d
tran
spo
rts
oxy
gen
. (H
emo
glo
bin
was
des
crib
ed m
ore
fu
lly
in
the
pre
vio
us
chap
ter
wh
en w
e d
iscu
ssed
res
pir
atio
n. )
In
ver
te-
bra
tes,
hem
og
lob
in i
s fo
un
d o
nly
in
ery
thro
cyte
s. I
n i
nve
rte-
bra
tes,
th
e o
xyg
en-b
ind
ing
pig
men
t (n
ot
alw
ays
hem
og
lob
in)
is
also
pre
sen
t in
pla
sma.
Le
uk
ocy
tes
Les
s th
an 1
% o
f th
e ce
lls
in h
um
an b
loo
d a
re w
hit
e b
loo
d
cell
s, o
r le
uko
cyte
s; t
her
e ar
e o
nly
1 o
r 2
leu
kocy
tes
for
ever
y 1
00
0 e
ryth
rocy
tes.
Leu
kocy
tes
are
larg
er t
han
ery
thro
cyte
s an
d
hav
e n
ucl
ei.
Fu
rth
erm
ore
, le
uko
cyte
s ar
e n
ot
con
fin
ed t
o t
he
blo
od
as
eryt
hro
cyte
s ar
e, b
ut
can
mig
rate
ou
t o
f ca
pil
lari
es
thro
ug
h t
he
inte
rcel
lula
r sp
aces
in
to t
he
surr
ou
nd
ing
in
ters
ti-
tial
(ti
ssu
e) f
luid
.
Leu
kocy
tes
com
e in
sev
eral
var
ieti
es, e
ach
of
wh
ich
pla
ys
a sp
ecif
ic r
ole
in
def
end
ing
ag
ain
st i
nva
din
g m
icro
org
anis
ms
and
o
ther
fo
reig
n
sub
stan
ces,
as
d
escr
ibed
in
ch
apte
r 5
2.
Gra
nu
lar
leu
ko
cyte
s in
clu
de
neu
tro
ph
ils,
eo
sin
op
hil
s, a
nd
ba-
sop
hil
s, w
hic
h a
re n
amed
acc
ord
ing
to
th
e st
ain
ing
pro
per
ties
o
f g
ran
ule
s in
th
eir
cyto
pla
sm.
No
ng
ran
ula
r le
uko
cyte
s in
-cl
ud
e m
on
ocy
tes
and
lym
ph
ocy
tes.
In
hu
man
s, n
eutr
op
hil
s ar
e th
e m
ost
nu
mer
ou
s o
f th
e le
uko
cyte
s, f
oll
ow
ed in
ord
er b
y ly
m-
ph
ocy
tes,
mo
no
cyte
s, e
osi
no
ph
ils,
an
d b
aso
ph
ils.
cha
pte
r 5
0
Th
e C
ircu
lato
ry S
yste
m
10
19
ww
w.r
av
en
bio
log
y.c
om
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lls
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d t
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du
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me
nts
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10
20
p
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VII
An
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rm a
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Fu
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Pla
tele
ts
Pla
tele
ts a
re c
ell
frag
men
ts t
hat
pin
ch o
ff f
rom
lar
ger
cel
ls i
n
the
bo
ne
mar
row
. T
hey
are
ap
pro
xim
atel
y 3
μm
in
dia
met
er,
and
fo
llo
win
g a
n i
nju
ry t
o a
blo
od
ves
sel,
the
live
r re
leas
es p
ro-
thro
mbi
n i
nto
th
e b
loo
d. I
n t
he
pre
sen
ce o
f th
is c
lott
ing
fac
tor,
fi
bri
no
gen
is
con
vert
ed i
nto
in
solu
ble
th
read
s o
f fi
bri
n.
Fib
rin
th
en a
gg
reg
ates
to
fo
rm t
he
clo
t.
Fo
rme
d e
lem
en
ts a
rise
fro
m s
tem
ce
lls
Th
e fo
rmed
ele
men
ts o
f b
loo
d e
ach
hav
e a
fin
ite
life
sp
an a
nd
th
eref
ore
mu
st b
e co
nst
antl
y re
pla
ced
. M
any
of
the
old
cel
l fr
agm
ents
are
dig
este
d b
y p
hag
ocy
tic
cell
s o
f th
e sp
leen
; h
ow
-ev
er, m
any
pro
du
cts
fro
m t
he
old
cel
ls, s
uch
as
iro
n a
nd
am
ino
ac
ids,
are
in
corp
ora
ted
in
to n
ew f
orm
ed e
lem
ents
. T
he
cre-
atio
n o
f n
ew f
orm
ed e
lem
ents
beg
ins
in t
he
bo
ne
mar
row
(se
e ch
apte
r 4
7).
A
ll o
f th
e fo
rmed
ele
men
ts d
evel
op
fro
m p
luri
po
ten
t st
em
cell
s (s
ee c
hap
ter
19
). T
he
pro
du
ctio
n o
f b
loo
d c
ells
oc-
curs
in
th
e b
on
e m
arro
w a
nd
is
call
ed h
em
ato
po
iesi
s. T
his
p
roce
ss g
ener
ates
tw
o t
ypes
of
stem
cel
ls w
ith
a m
ore
res
tric
ted
fa
te:
a ly
mp
ho
id s
tem
cel
l th
at g
ives
ris
e to
lym
ph
ocy
tes
and
a
mye
loid
ste
m c
ell
that
giv
es r
ise
to t
he
rest
of
the
blo
od
cel
ls
(fig
ure
50
.2) .
W
hen
th
e o
xyg
en a
vail
able
in
th
e b
loo
d d
ecre
ases
, th
e ki
dn
ey c
on
vert
s a
pla
sma
pro
tein
in
to t
he
ho
rmo
ne
ery
thro
-p
oie
tin
. E
ryth
rop
oie
tin
th
en
stim
ula
tes
the
pro
du
ctio
n
of
eryt
hro
cyte
s fr
om
th
e m
yelo
id s
tem
cel
ls t
hro
ug
h a
pro
cess
ca
lled
ery
thro
po
iesi
s .
In m
amm
als,
mat
uri
ng
eryt
hro
cyte
s lo
se t
hei
r n
ucl
ei p
rio
r to
rel
ease
in
to c
ircu
lati
on
. In
co
ntr
ast,
th
e m
atu
re e
ryth
rocy
tes
of
all o
ther
ver
teb
rate
s re
mai
n n
ucl
eate
d. M
egak
aryo
cyte
s are
ex-
amp
les
of
com
mit
ted
cel
ls f
orm
ed i
n b
on
e m
arro
w f
rom
ste
m
cell
s. P
iece
s o
f cy
top
lasm
are
pin
ched
off
th
e m
egak
aryo
cyte
s to
fo
rm t
he
pla
tele
ts.
Inq
uir
y q
ue
stio
n
?
Wh
y d
o y
ou
th
ink
th
e u
se o
f e
ryth
rop
oie
tin
as
a d
rug
is
ba
nn
ed
in t
he
Oly
mp
ics
an
d in
so
me
oth
er
spo
rts?
Blo
od
clo
ttin
g is
an
ex
am
ple
of
an
en
zym
e c
asc
ad
e
Wh
en a
blo
od
ves
sel i
s b
roke
n o
r cu
t, s
mo
oth
mu
scle
in t
he
ves-
sel
wal
ls c
on
trac
ts, c
ausi
ng t
he
vess
el t
o c
on
stri
ct. P
late
lets
th
en
accu
mu
late
at
the
inju
red
sit
e an
d f
orm
a p
lug b
y st
icki
ng t
o o
ne
ano
ther
an
d t
o t
he
surr
ou
nd
ing t
issu
es (
figu
re 5
0.3
) . A
cas
cad
e o
f en
zym
atic
rea
ctio
ns
is t
rigger
ed b
y th
e p
late
lets
, pla
sma
fac-
tors
, an
d m
ole
cule
s re
leas
ed f
rom
th
e d
amag
ed t
issu
e.
On
e o
f th
e re
sult
s o
f th
is c
asca
de
is t
hat
fib
rin
og
en, n
or-
mal
ly d
isso
lved
in
th
e p
lasm
a, c
om
es o
ut
of
solu
tio
n i
n a
rea
c-ti
on
th
at f
orm
s fi
bri
n. T
he
pla
tele
t p
lug
is
then
rei
nfo
rced
by
fib
rin
th
read
s, w
hic
h c
on
trac
t to
fo
rm a
tig
hte
r m
ass.
Th
e ti
gh
t-en
ing
plu
g o
f p
late
lets
, fi
bri
n,
and
oft
en t
rap
ped
ery
thro
cyte
s co
nst
itu
tes
a b
loo
d c
lot.
O
nce
th
e ti
ssu
e d
amag
e is
hea
led
, th
e ca
refu
l p
roce
ss o
f d
isso
lvin
g t
he
blo
t cl
ot
beg
ins.
Th
is p
roce
ss i
s si
gn
ific
ant
be-
cau
se i
f a
clo
t b
reak
s lo
ose
an
d t
rave
ls i
n t
he
circ
ula
tory
sys
-te
m, i
t m
ay e
nd
up
blo
ckin
g a
blo
od
ves
sel i
n t
he
bra
in, c
ausi
ng
a
stro
ke, o
r in
th
e h
eart
, cau
sin
g a
hea
rt a
ttac
k.
Le
arn
ing
Ou
tco
me
s R
ev
iew
50
.1Th
e ci
rcul
ator
y sy
stem
func
tion
s in
tran
spor
t of m
ater
ials
, reg
ulat
ion
of
tem
pera
ture
and
bod
y pr
oces
ses,
and
pro
tect
ion
of th
e bo
dy. F
orm
ed
elem
ents
in b
lood
incl
ude
red
bloo
d ce
lls, w
hite
blo
od c
ells
, and
pla
tele
ts.
Blo
od c
lott
ing
invo
lves
a c
asca
de o
f enz
ymat
ic re
acti
ons
trig
gere
d by
plat
elet
s an
d pl
asm
a fa
ctor
s to
pro
duce
inso
lubl
e fi
brin
from
fi br
inog
en.
■
H
ow
do
es
a b
loo
d c
lot
form
?
Fig
ure
50
.3 B
loo
d c
lott
ing
. F
ibri
n i
s fo
rmed
fro
m a
so
lub
le p
rote
in,
! b
rin
og
en,
in t
he
pla
sma.
Th
is r
eact
ion
is
cata
lyze
d b
y th
e
enzy
me
thro
mb
in,
wh
ich
is
form
ed f
rom
an
in
acti
ve e
nzy
me
call
ed p
roth
rom
bin
. T
he
acti
vati
on
of
thro
mb
in i
s th
e la
st s
tep
in
a c
asca
de
of
enzy
mat
ic r
eact
ion
s th
at p
rod
uce
s a
blo
od
clo
t w
hen
a b
loo
d v
esse
l is
dam
aged
.
cha
pte
r 5
0
Th
e C
ircu
lato
ry S
yste
m
10
21
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en
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igu
re 5
0.4
Cir
cula
tory
sy
ste
ms
of
the
an
ima
l k
ing
do
m.
a.
Sp
on
ges
(le
ft p
anel
) d
o n
ot
hav
e a
sep
arat
e ci
rcu
lato
ry s
yste
m.
Th
ey
circ
ula
te w
ater
usi
ng
man
y in
curr
ent
po
res
and
on
e ex
curr
ent
po
re.
Th
e g
astr
ova
scu
lar
cavi
ty o
f a
hyd
ra (
mid
dle
pan
el )
serv
es a
s b
oth
a
dig
esti
ve a
nd
a c
ircu
lato
ry s
yste
m,
del
iver
ing
nu
trie
nts
dir
ectl
y to
th
e ti
ssu
e ce
lls
by
dif
fusi
on
fro
m t
he
dig
esti
ve c
avit
y. T
he
nem
ato
de
(rig
ht
pan
el )
is t
hin
en
ou
gh
th
at t
he
dig
esti
ve t
ract
can
als
o b
e u
sed
as
a ci
rcu
lato
ry s
yste
m.
Lar
ger
an
imal
s re
qu
ire
a se
par
ate
circ
ula
tory
sys
tem
to
carr
y n
utr
ien
ts t
o a
nd
was
tes
away
fro
m t
issu
es. b.
In t
he
op
en c
ircu
lati
on
of
an i
nse
ct, h
emo
lym
ph
is
pu
mp
ed f
rom
a t
ub
ula
r h
eart
in
to
cavi
ties
in
th
e in
sect
’s b
od
y; t
he
hem
oly
mp
h t
hen
ret
urn
s to
th
e b
loo
d v
esse
ls s
o t
hat
it
can
be
reci
rcu
late
d. c.
In
th
e cl
ose
d c
ircu
lati
on
of
the
eart
hw
orm
, b
loo
d p
um
ped
fro
m t
he
hea
rts
rem
ain
s w
ith
in a
sys
tem
of
vess
els
that
ret
urn
s it
to
th
e h
eart
s. A
ll v
erte
bra
tes
also
hav
e cl
ose
d
circ
ula
tory
sys
tem
s.
5
0.2
In
vert
ebra
te C
ircu
lato
ry
Syst
ems
Le
arn
ing
Ou
tco
me
s
Dis
tin
gu
ish
be
twe
en
op
en
an
d c
lose
d c
ircu
lato
ry s
yste
ms.
1.
De
fin
e h
em
oly
mp
h.
2.
Th
e n
atu
re o
f th
e ci
rcu
lato
ry s
yste
m i
n m
ult
icel
lula
r in
vert
e-b
rate
s is
dir
ectl
y re
late
d t
o t
he
size
, co
mp
lexi
ty, a
nd
lif
esty
le o
f th
e o
rgan
ism
in
qu
esti
on
. Sp
on
ges
an
d m
ost
cn
idar
ian
s u
tili
ze
wat
er f
rom
th
e en
viro
nm
ent
as a
cir
cula
tory
flu
id.
Sp
on
ges
p
ass
wat
er t
hro
ug
h a
ser
ies
of
chan
nel
s in
th
eir
bo
die
s, a
nd
H
ydra
an
d
oth
er
cnid
aria
ns
circ
ula
te
wat
er
thro
ug
h
a g
astr
ova
scu
lar
cavi
ty (
fig
ure
50
.4a)
. Bec
ause
th
e b
od
y w
all
in
Hyd
ra s
pec
ies
is o
nly
tw
o c
ell
laye
rs t
hic
k, e
ach
cel
l la
yer
is i
n
dir
ect
con
tact
wit
h e
ith
er t
he
exte
rnal
en
viro
nm
ent
or
the
gas
-tr
ova
scu
lar
cavi
ty.
P
seu
do
coel
om
ate
inve
rteb
rate
s (r
ou
nd
wo
rms,
ro
tife
rs)
use
th
e fl
uid
s o
f th
e b
od
y ca
vity
fo
r ci
rcu
lati
on
. Mo
st o
f th
ese
inve
rteb
rate
s ar
e q
uit
e sm
all
or
are
lon
g a
nd
th
in,
and
th
ere-
fore
ad
equ
ate
circ
ula
tio
n is
acc
om
pli
shed
by
mo
vem
ents
of
the
bo
dy
agai
nst
th
e b
od
y fl
uid
s, w
hic
h a
re i
n d
irec
t co
nta
ct w
ith
th
e in
tern
al t
issu
es a
nd
org
ans.
Lar
ger
an
imal
s, h
ow
ever
, hav
e ti
ssu
es t
hat
are
sev
eral
cel
l la
yers
th
ick,
so
th
at m
any
cell
s ar
e
10
22
p
art
VII
An
ima
l Fo
rm a
nd
Fu
nct
ion
Apago PDF Enhancer
Systemic
capillaries
Respiratory
capillaries
Gills
Sinus
venosus
Ventricle
Conus
arteriosus
Atrium
Body
5
0.3
V
erte
bra
te C
ircu
lato
ry S
yste
ms
Le
arn
ing
Ou
tco
me
s
Tra
ce t
he
evo
luti
on
of
the
cha
mb
ere
d h
ea
rt f
rom
1.
la
nce
lets
to
bir
ds
an
d m
am
ma
ls.
De
lin
ea
te t
he
flo
w o
f b
loo
d t
hro
ug
h t
he
circ
ula
tory
2
. sy
ste
m in
bir
ds
an
d m
am
ma
ls.
Fig
ure
50
.5 T
he
he
art
an
d c
ircu
lati
on
of
a #
sh
. D
iag
ram
of
a !
sh h
eart
, sh
ow
ing t
he
stru
ctu
res
in s
erie
s w
ith
eac
h o
ther
(sin
us
ven
osu
s; a
triu
m; ve
ntr
icle
s; c
on
us
arte
rio
sus)
th
at f
orm
tw
o
pu
mp
ing
ch
amb
ers.
Blo
od
is
pu
mp
ed b
y th
e ve
ntr
icle
th
rou
gh
th
e
gil
ls a
nd
th
en t
o t
he
bo
dy.
Blo
od
ric
h i
n o
xyg
en (
oxy
gen
ated
) is
sho
wn
in
red
; b
loo
d l
ow
in
oxy
gen
(d
eoxy
gen
ated
) is
sh
ow
n i
n b
lue.
too
far
aw
ay f
rom
th
e b
od
y su
rfac
e o
r d
iges
tive
cav
ity
to d
i-re
ctly
exc
han
ge
mat
eria
ls w
ith
th
e en
viro
nm
ent.
In
stea
d, o
xy-
gen
an
d n
utr
ien
ts a
re t
ran
spo
rted
fro
m t
he
envi
ron
men
t an
d
dig
esti
ve c
avit
y to
th
e b
od
y ce
lls
by
an i
nte
rnal
flu
id w
ith
in a
ci
rcu
lato
ry s
yste
m.
Op
en
cir
cula
tory
sy
ste
ms
mo
ve
" u
ids
in a
on
e-w
ay
pa
th
Th
e tw
o m
ain
typ
es o
f ci
rcu
lato
ry s
yste
ms
are
open
an
d c
lose
d.
In a
n o
pen
cir
cula
tory
sys
tem
, su
ch a
s th
at f
ou
nd
in
mo
st m
ol-
lusk
s an
d i
n a
rth
rop
od
s (f
igu
re 5
0.4
b),
ther
e is
no
dis
tin
ctio
n
bet
wee
n t
he
circ
ula
tin
g f
luid
an
d t
he
extr
acel
lula
r fl
uid
of
the
bo
dy
tiss
ues
. Th
is f
luid
is
thu
s ca
lled
hem
oly
mp
h.
In
in
sect
s, a
mu
scu
lar
tub
e, o
r h
ear
t, p
um
ps
hem
oly
mp
h
thro
ug
h a
net
wo
rk o
f ch
ann
els
and
cav
itie
s in
th
e b
od
y. T
he
flu
id t
hen
dra
ins
bac
k in
to t
he
cen
tral
cav
ity.
Clo
sed
cir
cula
tory
sy
ste
ms
mo
ve
" u
ids
in a
loo
p
In a
clo
sed
cir
cula
tory
sys
tem
, th
e ci
rcu
lati
ng
flu
id,
blo
od
, is
al
way
s en
clo
sed
wit
hin
blo
od
ves
sels
th
at t
ran
spo
rt it
aw
ay fro
m
and
bac
k to
th
e h
eart
(fi
gu
re 5
0.4
c). S
om
e in
vert
ebra
tes,
su
ch a
s ce
ph
alo
po
d m
oll
usk
s an
d a
nn
elid
s (s
ee c
hap
ter
34
), a
nd
all
ver
-te
bra
tes
hav
e a
clo
sed
cir
cula
tory
sys
tem
.
In a
nn
elid
s su
ch a
s ea
rth
wo
rms,
a d
ors
al v
esse
l co
ntr
acts
rh
yth
mic
ally
to
fu
nct
ion
as
a p
um
p.
Blo
od
is
pu
shed
th
rou
gh
fi
ve s
mal
l co
nn
ecti
ng
art
erie
s, w
hic
h a
lso
fu
nct
ion
as
pu
mp
s, t
o
a ve
ntr
al v
esse
l, w
hic
h t
ran
spo
rts
the
blo
od
po
ster
iorl
y u
nti
l it
ev
entu
ally
ree
nte
rs t
he
do
rsal
ves
sel.
Sm
alle
r ve
ssel
s b
ran
ch
fro
m e
ach
art
ery
to s
up
ply
th
e ti
ssu
es o
f th
e ea
rth
wo
rm w
ith
o
xyg
en a
nd
nu
trie
nts
an
d t
o r
emo
ve w
aste
pro
du
cts.
Le
arn
ing
Ou
tco
me
s R
ev
iew
50
.2In
inve
rteb
rate
s, o
pen
circ
ulat
ory
syst
ems
pum
p he
mol
ymph
into
tiss
ues,
from
whi
ch it
then
dra
ins
into
a c
entr
al c
avit
y. C
lose
d ci
rcul
ator
y sy
stem
s
mov
e fl
uid
in a
loop
to a
nd fr
om a
mus
cula
r pum
ping
regi
on s
uch
as a
hea
rt.
Hem
olym
ph (i
nver
tebr
ates
) is
iden
tica
l to
the
extr
acel
lula
r fl u
id in
the
tiss
ues.
■
In
th
e o
pe
n c
ircu
lato
ry s
yste
m o
f in
sect
s, h
ow
do
es
he
mo
lym
ph
ge
t b
ack
to
th
e h
ea
rt?
Th
e ev
olu
tio
n o
f la
rge
and
co
mp
lex
hea
rts
and
clo
sed
cir
cula
-to
ry s
yste
ms
pu
t a
pre
miu
m o
n e
ffic
ien
t ci
rcu
lati
on
. In
re-
spo
nse
, ver
teb
rate
s h
ave
evo
lved
a r
emar
kab
le s
et o
f ad
apta
tio
ns
inex
tric
ably
lin
kin
g c
ircu
lati
on
an
d r
esp
irat
ion
, w
hic
h h
as f
a-ci
lita
ted
div
ersi
fica
tio
n t
hro
ug
ho
ut
aqu
atic
an
d t
erre
stri
al h
ab-
itat
s an
d p
erm
itte
d t
he
evo
luti
on
of
larg
e b
od
y si
ze.
In #
she
s, m
ore
e$
cie
nt
circ
ula
tio
n
de
ve
lop
ed
co
ncu
rre
ntl
y w
ith
gil
ls
Ch
ord
ates
an
cest
ral
to t
he
vert
ebra
tes
are
tho
ug
ht
to h
ave
had
si
mp
le t
ub
ula
r h
eart
s, s
imil
ar t
o t
ho
se n
ow
see
n in
lan
cele
ts (
see
chap
ter
35
). T
he
hea
rt w
as l
ittl
e m
ore
th
an a
sp
ecia
lize
d z
on
e o
f th
e ve
ntr
al a
rter
y th
at w
as m
ore
hea
vily
mu
scle
d t
han
th
e re
st o
f th
e ar
teri
es;
it c
on
trac
ted
in
sim
ple
per
ista
ltic
wav
es.
T
he
dev
elo
pm
ent
of
gil
ls b
y fi
shes
req
uir
ed a
mo
re e
ffi-
cien
t p
um
p,
and
in
fi
shes
w
e se
e th
e ev
olu
tio
n
of
a tr
ue
cham
ber
-pu
mp
hea
rt. T
he
fish
hea
rt i
s, i
n e
ssen
ce, a
tu
be
wit
h
fou
r st
ruct
ure
s ar
raye
d o
ne
afte
r th
e o
ther
to
fo
rm t
wo
pu
mp
-in
g c
ham
ber
s (f
igu
re 5
0.5
) . T
he
firs
t tw
o s
tru
ctu
res—
the
sin
us
ven
osu
s an
d a
triu
m—
form
th
e fi
rst
cham
ber
; th
e se
con
d t
wo
, th
e ve
ntr
icle
an
d c
on
us
arte
rio
sus,
fo
rm t
he
seco
nd
ch
amb
er.
Th
e si
nu
s ve
no
sus
is t
he
firs
t to
co
ntr
act,
foll
ow
ed b
y th
e at
riu
m,
the
ven
tric
le, a
nd
fin
ally
th
e co
nu
s ar
teri
osu
s.
Des
pit
e sh
ifts
in
th
e re
lati
ve p
osi
tio
ns
of
thes
e st
ruct
ure
s,
this
hea
rtb
eat
seq
uen
ce i
s m
ain
tain
ed i
n a
ll v
erte
bra
tes.
In
fis
h,
the
elec
tric
al i
mp
uls
e th
at p
rod
uce
s th
e co
ntr
acti
on
is
init
iate
d
in t
he
sin
us
ven
osu
s; in
oth
er v
erte
bra
tes,
th
e el
ectr
ical
imp
uls
e is
in
itia
ted
by
a st
ruct
ure
ho
mo
log
ou
s to
th
e si
nu
s ve
no
sus—
the
sin
oat
rial
(S
A)
no
de.
A
fter
blo
od
lea
ves
the
con
us
arte
rio
sus,
it
mo
ves
thro
ug
h
the
gil
ls,
bec
om
ing
oxy
gen
ated
. B
loo
d l
eavi
ng
th
e g
ills
th
en
flo
ws
thro
ug
h a
net
wo
rk o
f ar
teri
es t
o t
he
rest
of
the
bo
dy,
fi-
nal
ly r
etu
rnin
g t
o t
he
sin
us
ven
osu
s. T
his
sim
ple
lo
op
has
on
e se
rio
us
lim
itat
ion
: in
pas
sin
g t
hro
ug
h t
he
cap
illa
ries
in
th
e g
ills
, blo
od
pre
ssu
re d
rop
s si
gn
ific
antl
y. T
his
slo
ws
circ
ula
tio
n
fro
m t
he
gil
ls t
o t
he
rest
of
the
bo
dy
and
can
lim
it o
xyg
en d
e-li
very
to
tis
sues
.
cha
pte
r 5
0
Th
e C
ircu
lato
ry S
yste
m
10
23
ww
w.r
av
en
bio
log
y.c
om
Apago PDF Enhancer
a.
b.
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S ��� �� �Y �� �� ���� �� ��� #� �� ��L �� �� ��
In a
mp
hib
ian
s a
nd
mo
st r
ep
tile
s, lu
ng
s
req
uir
ed
a s
ep
ara
te c
ircu
lati
on
Th
e ad
ven
t o
f lu
ng
s in
am
ph
ibia
ns
(see
ch
apte
r 4
9)
invo
lved
a
maj
or
chan
ge
in t
he
pat
tern
of
circ
ula
tio
n,
a se
con
d p
um
pin
g
circ
uit
. Aft
er b
loo
d i
s p
um
ped
by
the
hea
rt t
hro
ug
h t
he
pulm
o-n
ary
arte
ries
to
th
e lu
ng
s, it
do
es n
ot
go
dir
ectl
y to
th
e ti
ssu
es o
f th
e b
od
y. I
nst
ead
, it
is
retu
rned
via
th
e pu
lmon
ary
vein
s to
th
e h
eart
. B
loo
d l
eave
s th
e h
eart
a s
eco
nd
tim
e to
be
circ
ula
ted
th
rou
gh
oth
er ti
ssu
es. T
his
syst
em is
term
ed d
ou
ble
cir
cula
tio
n:
On
e sy
stem
, th
e p
ulm
on
ary
circ
ula
tio
n, m
ove
s b
loo
d b
etw
een
h
eart
an
d l
un
gs,
an
d a
no
ther
, th
e sy
stem
ic c
ircu
lati
on
, m
ove
s b
loo
d b
etw
een
th
e h
eart
an
d t
he
rest
of
the
bo
dy.
Am
ph
ibia
n c
ircu
lati
on
Op
tim
ally
, o
xyg
enat
ed b
loo
d f
rom
lu
ng
s w
ou
ld g
o d
irec
tly
to
tiss
ues
, ra
ther
th
an b
ein
g m
ixed
in
th
e h
eart
wit
h d
eoxy
gen
-at
ed b
loo
d r
etu
rnin
g f
rom
th
e b
od
y. T
he
amp
hib
ian
hea
rt h
as
two
str
uct
ura
l fe
atu
res
that
sig
nif
ican
tly
red
uce
th
is m
ixin
g
(fig
ure
50
.6) .
Fir
st,
the
atri
um
is
div
ided
in
to t
wo
ch
amb
ers:
T
he
rig
ht
atri
um
rec
eive
s d
eoxy
gen
ated
blo
od
fro
m t
he
sys-
tem
ic
circ
ula
tio
n,
and
th
e le
ft
atri
um
re
ceiv
es
oxy
gen
ated
b
loo
d f
rom
th
e lu
ng
s. T
hes
e tw
o t
ypes
of
blo
od
, th
eref
ore
, do
n
ot
mix
in
th
e at
ria.
B
ecau
se a
n a
mp
hib
ian
hea
rt h
as a
sin
gle
ven
tric
le,
the
sep
arat
ion
of
the
pu
lmo
nar
y an
d s
yste
mic
cir
cula
tio
ns
is i
n-
com
ple
te.
Th
e ex
ten
t o
f m
ixin
g w
hen
th
e co
nte
nts
of
each
at
riu
m e
nte
r th
e ve
ntr
icle
is
red
uce
d b
y in
tern
al c
han
nel
s cr
e-at
ed b
y re
cess
es i
n t
he
ven
tric
ula
r w
all.
Th
e co
nu
s ar
teri
osu
s is
p
arti
ally
sep
arat
ed b
y a
div
idin
g w
all,
wh
ich
dir
ects
deo
xyg
en-
ated
blo
od
in
to t
he
pu
lmo
nar
y ar
teri
es a
nd
oxy
gen
ated
blo
od
in
to t
he
aort
a, t
he
maj
or
arte
ry o
f th
e sy
stem
ic c
ircu
lati
on
.
Am
ph
ibia
ns
livi
ng
in
wat
er c
an o
bta
in a
dd
itio
nal
oxy
gen
b
y d
iffu
sio
n t
hro
ug
h t
hei
r sk
in. T
hu
s, a
mp
hib
ian
s h
ave
a pu
lmo-
cuta
neo
us
circ
uit
th
at s
end
s b
loo
d t
o b
oth
th
e lu
ng
s an
d t
he
skin
. C
uta
neo
us
resp
irat
ion
is a
lso
see
n in
man
y aq
uat
ic r
epti
les
such
as
tu
rtle
s.
Re
pti
lia
n c
ircu
lati
on
Am
on
g r
epti
les,
ad
dit
ion
al m
od
ific
atio
ns
hav
e fu
rth
er r
edu
ced
th
e m
ixin
g o
f b
loo
d in
th
e h
eart
. In
ad
dit
ion
to
hav
ing
tw
o s
ep-
arat
e at
ria,
rep
tile
s h
ave
a se
ptu
m t
hat
par
tial
ly s
ub
div
ides
th
e ve
ntr
icle
. Th
is s
epar
atio
n i
s co
mp
lete
in
on
e o
rder
of
rep
tile
s,
the
cro
cod
ilia
ns,
wh
ich
hav
e tw
o s
epar
ate
ven
tric
les
div
ided
by
a co
mp
lete
sep
tum
(se
e th
e fo
llo
win
g s
ecti
on
). A
no
ther
ch
ang
e in
th
e ci
rcu
lati
on
of
rep
tile
s is
th
at t
he
con
us
arte
rio
sus
has
b
eco
me
inco
rpo
rate
d i
nto
th
e tr
un
ks o
f th
e la
rge
arte
ries
lea
v-in
g t
he
hea
rt.
Fig
ure
50
.6 T
he
he
art
an
d c
ircu
lati
on
of
an
am
ph
ibia
n.
a.
Th
e fr
og
has
a t
hre
e-ch
amb
ered
hea
rt w
ith
tw
o a
tria
bu
t o
nly
on
e
ven
tric
le, w
hic
h p
um
ps
blo
od
bo
th t
o t
he
lun
gs
and
to
th
e b
od
y. b
. D
esp
ite
the
po
ten
tial
fo
r m
ixin
g, t
he
oxy
gen
ated
an
d d
eoxy
gen
ated
blo
od
s
(red
an
d b
lue
lin
es, re
spec
tive
ly)
mix
lit
tle
as t
hey
are
pu
mp
ed t
o t
he
bo
dy
and
lu
ng
s. O
xyg
enat
ion
of
blo
od
als
o o
ccu
rs b
y g
as e
xch
ang
e
thro
ug
h t
he
skin
.
10
24
p
art
VII
An
ima
l Fo
rm a
nd
Fu
nct
ion
Apago PDF Enhancer
Head
Body
Lungs
Systemic
capillaries
Pulm
onary
artery
Pulm
onary
semilu
nar va
lve
Inferior
vena cava
Superior
vena cava
Aorta
Tricuspid valve
Right ve
ntricle
Left
ventricle
Right atrium
Pulm
onary
veins
Left atrium
Bicuspid
mitral
valve
Systemic
capillaries
Pulm
onary
artery
Superior
vena cava
Inferior
vena cava
Artery
Pulm
onary
vein
Aorta
Respiratory
capillaries
a.
b.
Ma
mm
als
, bir
ds,
an
d c
roco
dil
ian
s h
av
e t
wo
com
ple
tely
se
pa
rate
d c
ircu
lato
ry s
yst
em
s
Mam
mal
s, b
ird
s, a
nd
cro
cod
ilia
ns
hav
e a
fou
r-ch
amb
ered
hea
rt
wit
h t
wo
sep
arat
e at
ria
and
tw
o s
epar
ate
ven
tric
les
(fig
ure
50
.7) .
T
he
hea
rts
of
bir
ds
and
cro
cod
iles
exh
ibit
so
me
dif
fere
nce
s, b
ut
ove
rall
are
qu
ite
sim
ilar
, w
hic
h i
s n
ot
surp
risi
ng
giv
en t
hei
r cl
ose
evo
luti
on
ary
rela
tio
nsh
ip (
fig
ure
50
.8) .
Ho
wev
er,
the
ex-
trem
e si
mil
arit
y o
f th
e h
eart
s o
f b
ird
s an
d m
amm
als—
so a
like
th
at a
sin
gle
ill
ust
rati
on
can
su
ffic
e fo
r b
oth
(se
e fi
gu
re 5
0.7
)—is
a r
emar
kab
le c
ase
of
con
verg
ent
evo
luti
on
(se
e fi
gu
re 5
0.8
).
In
a f
ou
r-ch
amb
ered
hea
rt,
the
rig
ht
atri
um
rec
eive
s d
e-o
xyg
enat
ed b
loo
d f
rom
th
e b
od
y an
d d
eliv
ers
it t
o t
he
rig
ht
ven
tric
le, w
hic
h p
um
ps
the
blo
od
to
th
e lu
ng
s. T
he
left
atr
ium
re
ceiv
es o
xyg
enat
ed b
loo
d f
rom
th
e lu
ng
s an
d d
eliv
ers
it t
o t
he
left
ven
tric
le, w
hic
h p
um
ps
the
oxy
gen
ated
blo
od
to
th
e re
st o
f th
e b
od
y (s
ee f
igu
re 5
0.7
).
Th
e h
eart
in
th
ese
vert
ebra
tes
is a
tw
o-c
ycle
pu
mp
. Bo
th
atri
a fi
ll w
ith
blo
od
an
d s
imu
ltan
eou
sly
con
trac
t, e
mp
tyin
g
thei
r b
loo
d i
nto
th
e ve
ntr
icle
s. B
oth
ven
tric
les
also
co
ntr
act
at
the
sam
e ti
me,
pu
shin
g b
loo
d s
imu
ltan
eou
sly
into
th
e p
ulm
o-
nar
y an
d s
yste
mic
cir
cula
tio
ns.
T
he
incr
ease
d e
ffic
ien
cy o
f th
e d
ou
ble
cir
cula
tory
sys
tem
in
mam
mal
s an
d b
ird
s is
th
ou
gh
t to
hav
e b
een
im
po
rtan
t in
th
e ev
olu
tio
n o
f en
do
ther
my.
Mo
re e
ffic
ien
t ci
rcu
lati
on
is
nec
es-
sary
to
su
pp
ort
th
e h
igh
met
abo
lic
rate
req
uir
ed f
or
mai
nte
-n
ance
of
inte
rnal
bo
dy
tem
per
atu
re a
bo
ut
a se
t p
oin
t.
Th
rough
out t
he
evolu
tion
ary
his
tory
of t
he
vert
ebra
te h
eart
, th
e si
nus
ven
osu
s h
as s
erve
d a
s a
pac
emak
er,
the
site
wh
ere
the
impuls
es t
hat
in
itia
te t
he
hea
rtbea
t ori
gin
ate.
Alt
hough
th
e si
nus
ven
osu
s co
nst
itute
s a
maj
or
cham
ber
in t
he
fish
hea
rt, i
t is
red
uce
d
in s
ize
in a
mph
ibia
ns
and i
s fu
rth
er r
educe
d i
n r
epti
les.
In
mam
-m
als
and b
irds,
th
e si
nus
ven
osu
s is
no lo
nge
r pre
sen
t as
a s
epar
ate
cham
ber
, al
though
som
e of
its
tiss
ue
rem
ain
s in
th
e w
all
of
the
righ
t at
rium
. Th
is t
issu
e, t
he
sin
oat
rial
(S
A)
node,
is
still
the
site
w
her
e ea
ch h
eart
bea
t ori
gin
ates
as
det
aile
d la
ter
in t
he
chap
ter.
Le
arn
ing
Ou
tco
me
s R
ev
iew
50
.3
The
chor
date
hea
rt h
as e
volv
ed fr
om a
mus
cula
r reg
ion
of a
ves
sel,
to th
e
two-
cham
bere
d he
art o
f fi s
h, th
e th
ree-
cham
bere
d he
art o
f am
phib
ians
and
mos
t rep
tile
s, a
nd th
e fo
ur-c
ham
bere
d he
art o
f cro
codi
lians
, bir
ds, a
nd
mam
mal
s. D
eoxy
gena
ted
bloo
d tr
avel
s in
the
pulm
onar
y ci
rcui
t fro
m th
e
righ
t atr
ium
into
the
righ
t ven
tric
le a
nd th
en to
the
lung
s; it
retu
rns
to
the
left
atr
ium
. Oxy
gena
ted
bloo
d tr
avel
s in
the
syst
emic
cir
cuit
from
the
left
atr
ium
into
the
left
ven
tric
le a
nd th
en to
the
body
; it r
etur
ns to
the
righ
t atr
ium
.
■
W
ha
t is
th
e p
hys
iolo
gic
al a
dva
nta
ge
of
ha
vin
g
sep
ara
ted
ve
ntr
icle
s?
Fig
ure
50
.7T
he
he
art
an
d c
ircu
lati
on
of
ma
mm
als
an
d b
ird
s.
a.
Th
e p
ath
of
blo
od
th
rou
gh
th
e fo
ur-
cham
ber
ed h
eart
. b.
Th
e
rig
ht
sid
e o
f th
e h
eart
rec
eive
s d
eoxy
gen
ated
blo
od
an
d p
um
ps
it t
o t
he
lun
gs;
th
e le
ft s
ide
of
the
hea
rt r
ecei
ves
oxy
gen
ated
blo
od
an
d p
um
ps
it
to t
he
bo
dy.
In
th
is w
ay,
the
pu
lmo
nar
y an
d s
yste
mic
cir
cula
tio
ns
are
kep
t co
mp
lete
ly s
epar
ate.
cha
pte
r 5
0
Th
e C
ircu
lato
ry S
yste
m
10
25
ww
w.r
av
en
bio
log
y.c
om
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F 16H)- )' +d5 +(I 1331- +e .*'- )+f 34(5g5 16+; *,H,95-5 16+J h.131' )+85 *9 +
Fig
ure
50
.8
Ev
olu
tio
n o
f th
e
he
art
in
ve
rte
bra
tes.
Des
pit
e th
eir
sim
ilar
ity,
the
fou
r-ch
amb
ered
hea
rts
of
mam
mal
s
and
bir
ds
evo
lved
con
verg
entl
y.
5
0.4
Th
e Fo
ur-
Ch
am
ber
ed H
eart
a
nd
th
e B
loo
d V
esse
ls
Le
arn
ing
Ou
tco
me
s
Exp
lain
th
e ca
rdia
c cy
cle
.1.
De
scri
be
the
role
of
au
torh
yth
mic
ce
lls
of
the
SA
no
de
.2
.
De
fin
e b
loo
d p
ress
ure
an
d h
ow
it is
me
asu
red
3.
As
men
tio
ned
ear
lier
, th
e h
eart
of
mam
mal
s, b
ird
s, a
nd
cro
co-
dil
ian
s g
oes
th
rou
gh
tw
o c
on
trac
tio
n c
ycle
s, o
ne
of
atri
al c
on
-tr
acti
on
to
sen
d b
loo
d t
o t
he
ven
tric
les,
an
d o
ne
of
ven
tric
ula
r co
ntr
acti
on
to
sen
d b
loo
d t
o t
he
pu
lmo
nar
y an
d s
yste
mic
cir
-cu
its.
Th
ese
two
co
ntr
acti
on
s p
lus
the
rest
ing
per
iod
bet
wee
n
thes
e m
ake
up
th
e co
mp
lete
car
dia
c cy
cle
en
com
pas
sed
by
the
hea
rtb
eat.
Th
e c
ard
iac
cycl
e d
riv
es
the
ca
rdio
va
scu
lar
syst
em
Th
e h
eart
has
tw
o p
airs
of v
alve
s. O
ne
pai
r, th
e at
riove
ntr
icu
lar
(AV
) va
lves,
mai
nta
ins
un
idir
ecti
on
al b
loo
d f
low
bet
wee
n t
he
atri
a an
d v
entr
icle
s. T
he
AV
val
ve o
n t
he
rig
ht
sid
e is
th
e tr
icu
spid
val
ve, a
nd
th
e A
V v
alve
on
th
e le
ft is
th
e b
icu
spid
, or
mit
ral,
valv
e.
An
oth
er
pai
r o
f va
lves
, to
get
her
ca
lled
th
e se
mil
un
ar v
alve
s, e
nsu
re o
ne-
way
flo
w o
ut
of
the
ven
tric
les
to
the
arte
rial
sys
tem
s. T
he
pu
lmo
nar
y va
lve
is lo
cate
d a
t th
e ex
it
of
the
rig
ht
ven
tric
le, a
nd
th
e ao
rtic
val
ve i
s lo
cate
d a
t th
e ex
it
of
the
left
ven
tric
le.
Th
ese
valv
es o
pen
an
d c
lose
as
the
hea
rt
go
es t
hro
ug
h it
s cy
cle.
Th
e cl
osi
ng
of
thes
e va
lves
pro
du
ces
the
“lu
b-d
ub
” so
un
ds
hea
rd w
ith
a s
teth
osc
op
e.
T
he
card
iac
cycl
e is
po
rtra
yed
in
fig
ure
50
.9 . I
t b
egin
s as
b
loo
d r
etu
rns
to t
he
rest
ing
hea
rt t
hro
ug
h v
ein
s th
at e
mp
ty
into
th
e ri
gh
t an
d l
eft
atri
a. A
s th
e at
ria
fill
an
d t
he
pre
ssu
re i
n
them
ris
es,
the
AV
val
ves
op
en a
nd
blo
od
flo
ws
into
th
e ve
n-
tric
les.
Th
e ve
ntr
icle
s b
eco
me
abo
ut
80
% f
ille
d d
uri
ng
th
is
tim
e. C
on
trac
tio
n o
f th
e at
ria
top
s u
p t
he
fin
al 2
0%
of
the
80
mL
of
blo
od
th
e ve
ntr
icle
s re
ceiv
e, o
n a
vera
ge,
in
a r
esti
ng
p
erso
n. T
hes
e ev
ents
occ
ur
wh
ile
the
ven
tric
les
are
rela
xin
g,
a p
erio
d c
alle
d v
entr
icu
lar
dia
sto
le.
A
fter
a s
ligh
t d
elay
, th
e ve
ntr
icle
s co
ntr
act,
a p
erio
d c
alle
d
ven
tric
ula
r sy
sto
le.
Co
ntr
acti
on
of
each
ven
tric
le i
ncr
ease
s th
e p
ress
ure
wit
hin
eac
h c
ham
ber
, ca
usi
ng t
he
AV
val
ves
to f
orc
e-fu
lly
clo
se (
the
“lu
b”
sou
nd
), p
reve
nti
ng b
loo
d f
rom
bac
kin
g u
p
into
th
e at
ria.
Im
med
iate
ly a
fter
th
e A
V v
alve
s cl
ose
, th
e p
res-
sure
in t
he
ven
tric
les
forc
es t
he
sem
ilu
nar
val
ves
op
en a
nd
blo
od
fl
ow
s in
to t
he
arte
rial
sys
tem
s. A
s th
e ve
ntr
icle
s re
lax,
clo
sin
g o
f th
e se
mil
un
ar v
alve
s p
reve
nts
bac
kflo
w (
the
“du
b”
sou
nd
).
Co
ntr
act
ion
of
he
art
mu
scle
is
init
iate
d b
y a
uto
rhy
thm
ic c
ell
s
As
in o
ther
typ
es o
f m
uscl
e, c
ontr
acti
on o
f h
eart
mus
cle
is s
tim
u-la
ted
by m
embr
ane
depo
lari
zati
on (s
ee c
hap
ters
44
and
47).
In s
kel-
etal
mus
cles
, on
ly n
erve
impu
lses
from
mot
or n
euro
ns ca
n n
orm
ally
in
itia
te d
epol
ariz
atio
n. T
he
hea
rt, b
y co
ntr
ast,
con
tain
s sp
ecia
lized
“s
elf-
exci
tabl
e” m
uscl
e ce
lls c
alle
d au
torh
yth
mic
fib
ers,
wh
ich
can
in
itia
te p
erio
dic
acti
on p
oten
tial
s w
ith
out
neu
ral a
ctiv
atio
n.
T
he
mo
st i
mp
ort
ant
gro
up
of
auto
rhyt
hm
ic c
ells
is
the
sin
oat
rial
(S
A)
no
de,
des
crib
ed e
arli
er (
fig
ure
50
.10
) . L
oca
ted
in
th
e w
all
of
the
rig
ht
atri
um
, th
e S
A n
od
e ac
ts a
s a
pac
emak
er
for
the
rest
of
the
hea
rt b
y p
rod
uci
ng
sp
on
tan
eou
s ac
tio
n p
o-
ten
tial
s at
a f
aste
r ra
te t
han
oth
er a
uto
rhyt
hm
ic c
ells
. T
hes
e sp
on
tan
eou
s ac
tio
n p
ote
nti
als
are
du
e to
a c
on
stan
t le
akag
e o
f N
a+ io
ns
into
th
e ce
ll t
hat
dep
ola
rize
th
e m
emb
ran
e. W
hen
th
e
10
26
p
art
VII
An
ima
l Fo
rm a
nd
Fu
nct
ion
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�=? �L C� �L
���F
igu
re 5
0.9
Th
e c
ard
iac
cy
cle
. a.
Co
ntr
acti
on
an
d r
elax
atio
n o
f th
e at
ria
and
ven
tric
les
mo
ves
blo
od
th
rou
gh
th
e h
eart
. b.
Blo
od
pre
ssu
re a
nd
vo
lum
e ch
ang
es t
hro
ug
h t
he
card
iac
cycl
e, s
ho
wn
her
e fo
r th
e le
ft v
entr
icle
.
thre
sho
ld i
s re
ach
ed,
an a
ctio
n p
ote
nti
al o
ccu
rs. A
t th
e en
d o
f th
e ac
tio
n p
ote
nti
al,
the
mem
bra
ne
is a
gai
n b
elo
w t
hre
sho
ld
and
th
e p
roce
ss b
egin
s ag
ain
. Th
e ce
lls
of
the
SA
no
de
gen
erat
e an
act
ion
po
ten
tial
eve
ry 0
.6 s
ec, e
qu
ival
ent
to a
bo
ut
10
0 a
min
-u
te. A
s w
e w
ill
see
late
r in
th
e ch
apte
r, t
he
auto
no
mic
ner
vou
s sy
stem
can
mo
du
late
th
is r
ate.
E
ach
dep
ola
riza
tio
n in
itia
ted
by
this
pac
emak
er is
tra
nsm
it-
ted
th
rou
gh t
wo
pat
hw
ays:
on
e to
th
e ca
rdia
c m
usc
le f
iber
s o
f th
e le
ft a
triu
m,
and
th
e o
ther
to
th
e ri
ght
atri
um
an
d t
he
atri
ove
n-
tric
ula
r (A
V)
no
de.
On
ce in
itia
ted
, dep
ola
riza
tio
ns
spre
ad q
uic
kly
fro
m o
ne
mu
scle
fib
er to
an
oth
er in
a w
ave
that
en
velo
ps
the
righ
t an
d l
eft
atri
a n
earl
y si
mu
ltan
eou
sly.
Th
e ra
pid
sp
read
of
dep
ola
r-iz
atio
n i
s m
ade
po
ssib
le b
ecau
se s
pec
ial
con
du
ctin
g fi
ber
s ar
e p
rese
nt a
nd
bec
ause
the
card
iac
mu
scle
cel
ls a
re c
ou
ple
d b
y gr
ou
ps
of
gap
jun
ctio
ns
loca
ted
wit
hin
inte
rcal
ated
dis
ks (
see
chap
ter
44 ).
A
sh
eet
of
con
nec
tive
tis
sue
sep
arat
ing
th
e at
ria
fro
m t
he
ven
tric
les
blo
cks
the
spre
ad o
f ex
cita
tio
n t
hro
ug
h m
usc
le f
iber
s fr
om
on
e ch
amb
er t
o t
he
oth
er. T
he
AV
no
de
pro
vid
es t
he
on
ly
pat
hw
ay f
or
con
du
ctio
n o
f th
e d
epo
lari
zati
on
fro
m t
he
atri
a to
th
e ve
ntr
icle
s. T
he
fib
ers
of
the
AV
no
de
slo
w d
ow
n t
he
con
-d
uct
ion
of
the
dep
ola
rizi
ng
sig
nal
s, d
elay
ing
th
e co
ntr
acti
on
of
the
ven
tric
le b
y ab
ou
t 0
.1 s
ec.
Th
is d
elay
per
mit
s th
e at
ria
to
fin
ish
co
ntr
acti
ng
an
d e
mp
tyin
g t
hei
r b
loo
d i
nto
th
e ve
ntr
icle
s b
efo
re t
he
ven
tric
les
con
trac
t.
Fro
m t
he
AV
no
de,
th
e w
ave
of
dep
ola
riza
tio
n i
s co
n-
du
cted
rap
idly
ove
r b
oth
ven
tric
les
by
a n
etw
ork
of
fib
ers
call
ed
the
atri
ove
ntr
icu
lar
bu
nd
le, o
r b
un
dle
of
His
. Th
ese
fib
ers
rela
y th
e d
epo
lari
zati
on
to
Pu
rkin
je f
iber
s, w
hic
h d
irec
tly
stim
ula
te
the
myo
card
ial
cell
s o
f th
e le
ft a
nd
rig
ht
ven
tric
les,
cau
sin
g
thei
r al
mo
st s
imu
ltan
eou
s co
ntr
acti
on
.
Th
e st
imula
tion
of
myo
card
ial
cells
pro
duce
s an
act
ion
po-
ten
tial
th
at le
ads
to c
on
trac
tion
. Con
trac
tion
is c
on
trolled
by
Ca2+
an
d t
he
tropon
in/t
ropom
yosi
n s
yste
m s
imilar
to s
kele
tal
musc
le
(see
ch
apte
r 47
), but
the
shap
e of
the
acti
on
pote
nti
al i
s dif
fere
nt.
T
he
init
ial r
isin
g ph
ase
due
to a
n in
flux
of N
a+ fr
om
volt
age-
gate
d
Na+
ch
ann
els
is f
ollow
ed b
y a
pla
teau
ph
ase
that
lea
ds
to m
ore
su
stai
ned
con
trac
tion
. Th
e pla
teau
ph
ase
is d
ue
to t
he
open
ing
of
volt
age-
gate
d C
a2+ c
han
nel
s. T
he
resu
ltin
g in
flux
of
Ca2+
kee
ps
the
mem
bra
ne
dep
ola
rize
d w
hen
th
e N
a+ c
han
nel
s in
acti
vate
. T
his
, in
turn
, le
ads
to m
ore
volt
age-
gate
d C
a2+ c
han
nel
s in
th
e sa
rcopla
smic
ret
iculu
m o
pen
ing.
Th
e ad
dit
ion
al C
a2+ in
th
e cy
to-
pla
sm
pro
duce
s a
more
su
stai
ned
co
ntr
acti
on
. T
he
Ca2+
is
cha
pte
r 5
0
Th
e C
ircu
lato
ry S
yste
m
10
27
ww
w.r
av
en
bio
log
y.c
om
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F ig
ure
50
.10
Th
e p
ath
of
ele
ctr
ica
l e
xci
tati
on
in
th
e
he
art
. T
he
even
ts o
ccu
rrin
g d
uri
ng
co
ntr
acti
on
of
the
hea
rt a
re
corr
elat
ed w
ith
th
e m
easu
rem
ent
of
elec
tric
al a
ctiv
ity
by
an
elec
tro
card
iog
ram
(E
CG
als
o c
alle
d E
KG
). T
he
dep
ola
riza
tio
n/
con
trac
tio
n o
f th
e at
riu
m i
s sh
ow
n i
n g
reen
ab
ove
an
d c
orr
esp
on
ds
to t
he
P w
ave
of
the
EC
G (
also
in
gre
en).
Th
e d
epo
lari
zati
on
/
con
trac
tio
n o
f th
e ve
ntr
icle
is
sho
wn
in
red
ab
ove
an
d c
orr
esp
on
ds
to t
he
QR
S w
ave
of
the
EC
G (
also
in
red
). T
he
T w
ave
on
th
e E
CG
corr
esp
on
ds
to t
he
rep
ola
riza
tio
n o
f th
e ve
ntr
icle
s. T
he
atri
al
rep
ola
riza
tio
n i
s m
aske
d b
y th
e Q
RS
wav
e.
rem
ove
d f
rom
th
e cy
topla
sm b
y a
pum
p i
n t
he
sarc
opla
smic
re-
ticu
lum
sim
ilar
to s
kele
tal m
usc
le, a
nd a
n a
ddit
ion
al c
arri
er in
th
e pla
sma
mem
bra
ne
pum
ps
Ca2+
into
th
e in
ters
titi
al s
pac
e.
Th
e el
ectr
ical
act
ivit
y o
f th
e h
eart
can
be
reco
rded
fro
m
the
surf
ace
of
the
bo
dy
wit
h e
lect
rod
es p
lace
d o
n t
he
lim
bs
and
ch
est.
Th
e re
cord
ing,
ca
lled
an
el
ectr
oca
rdio
gram
(E
CG
o
r E
KG
), s
ho
ws
ho
w t
he
cell
s o
f th
e h
eart
dep
ola
rize
an
d r
epo
lari
ze
du
rin
g th
e ca
rdia
c cy
cle
(see
fig
ure
50.
10). D
epo
lari
zati
on
cau
ses
con
trac
tio
n o
f th
e h
eart
, an
d r
epo
lari
zati
on
cau
ses
rela
xati
on
.
Th
e fi
rst
pea
k in
th
e re
cord
ing
, P, i
s p
rod
uce
d b
y th
e d
e-p
ola
riza
tio
n o
f th
e at
ria,
an
d i
s as
soci
ated
wit
h a
tria
l sy
sto
le.
Th
e se
con
d,
larg
er p
eak,
QR
S,
is p
rod
uce
d b
y ve
ntr
icu
lar
de-
po
lari
zati
on
; du
rin
g t
his
tim
e, t
he
ven
tric
les
con
trac
t (v
entr
icu
-la
r sy
sto
le).
T
he
last
p
eak,
T
, is
p
rod
uce
d
by
ven
tric
ula
r re
po
lari
zati
on
; at
th
is t
ime,
th
e ve
ntr
icle
s b
egin
dia
sto
le.
Art
eri
es
an
d v
ein
s b
ran
ch t
o
an
d f
rom
all
pa
rts
of
the
bo
dy
Th
e ri
ght
and
lef
t p
ulm
on
ary
arte
ries
del
iver
oxy
gen
-dep
lete
d
blo
od
fro
m t
he
rig
ht
ven
tric
le t
o t
he
rig
ht
and
lef
t lu
ng
s. A
s
10
28
p
art
VII
An
ima
l Fo
rm a
nd
Fu
nct
ion
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Ù
Ú
Fig
ure
50
.11
Me
asu
rem
en
t o
f b
loo
d p
ress
ure
. T
he
blo
od
pre
ssu
re c
uff
is
tigh
ten
ed t
o s
top
th
e b
loo
d !
ow
th
rou
gh
th
e b
rach
ial
arte
ry. A
s th
e cu
ff i
s lo
ose
ned
, th
e m
axim
al (
syst
oli
c) p
ress
ure
bec
om
es g
reat
er t
han
th
e cu
ff p
ress
ure
an
d b
loo
d c
an m
om
enta
rily
pas
s th
rou
gh
,
pro
du
cin
g a
pu
lse
that
can
be
hea
rd w
ith
a s
teth
osc
op
e. T
he
pre
ssu
re a
t th
is p
oin
t is
rec
ord
ed a
s th
e sy
sto
lic
pre
ssu
re. A
s th
e cu
ff p
ress
ure
con
tin
ues
to
dro
p, b
loo
d p
ress
ure
is
gre
ater
th
an c
uff
pre
ssu
re f
or
larg
er p
ort
ion
s o
f th
e ca
rdia
c cy
cle.
Eve
ntu
ally
, eve
n t
he
min
imu
m p
ress
ure
du
rin
g t
he
cycl
e is
gre
ater
th
an t
he
cuff
pre
ssu
re, a
t w
hic
h t
ime
the
blo
od
ves
sel
is n
o l
on
ger
dis
tort
ed a
nd
sil
ent
lam
inar
! o
w r
etu
rns,
rep
laci
ng
the
pu
lsin
g s
ou
nd
. Th
e d
iast
oli
c p
ress
ure
is
reco
rded
as
the
pre
ssu
re a
t w
hic
h a
so
un
d i
s n
o l
on
ger
hea
rd.
pre
vio
usl
y m
enti
on
ed, t
he
pu
lmo
nar
y ve
ins
retu
rn o
xyg
enat
ed
blo
od
fro
m t
he
lun
gs
to t
he
left
atr
ium
of
the
hea
rt.
T
he
aort
a an
d a
ll i
ts b
ran
ches
are
sys
tem
ic a
rter
ies,
car
-ry
ing
oxy
gen
-ric
h b
loo
d f
rom
th
e le
ft v
entr
icle
to
all
par
ts o
f th
e b
od
y. T
he
coro
nar
y ar
teri
es
are
the
firs
t b
ran
ches
off
th
e ao
rta;
th
ese
sup
ply
oxy
gen
ated
blo
od
to
th
e h
eart
mu
scle
its
elf
(see
fig
ure
50
.7b )
. O
ther
sys
tem
ic a
rter
ies
bra
nch
fro
m t
he
aort
a as
it m
akes
an
arc
h a
bo
ve t
he
hea
rt a
nd
as
it d
esce
nd
s an
d
trav
erse
s th
e th
ora
cic
and
ab
do
min
al c
avit
ies.
T
he
blo
od
fro
m t
he
bo
dy’
s o
rgan
s, n
ow
lo
wer
in
oxy
gen
, re
turn
s to
th
e h
eart
in
th
e sy
stem
ic v
ein
s. T
hes
e ev
entu
ally
em
pty
in
to t
wo
maj
or
vein
s: t
he
sup
eri
or
ven
a ca
va,
wh
ich
d
rain
s th
e u
pp
er b
od
y, a
nd
th
e in
feri
or
ven
a ca
va, w
hic
h d
rain
s th
e lo
wer
bo
dy.
Th
ese
vein
s em
pty
in
to t
he
rig
ht
atri
um
, co
m-
ple
tin
g t
he
syst
emic
cir
cula
tio
n.
T
he
flo
w o
f b
loo
d t
hro
ug
h t
he
arte
ries
, ca
pil
lari
es,
and
ve
ins
is d
rive
n b
y th
e p
ress
ure
gen
erat
ed b
y ve
ntr
icu
lar
con
-tr
acti
on
. T
he
ven
tric
les
mu
st c
on
trac
t fo
rcef
ull
y en
ou
gh
to
m
ove
th
e b
loo
d t
hro
ug
h t
he
enti
re c
ircu
lato
ry s
yste
m.
Art
eri
al b
loo
d p
ress
ure
ca
n b
e m
ea
sure
d
As
the
ven
tric
les
con
trac
t, g
reat
pre
ssu
re i
s g
ener
ated
wit
hin
th
em a
nd
tra
nsf
erre
d t
hro
ug
h t
he
arte
ries
on
ce t
he
aort
ic
valv
e o
pen
s. T
he
pu
lse
that
yo
u c
an d
etec
t in
yo
ur
wri
st o
r
nec
k r
esu
lts
fro
m c
han
ges
in
pre
ssu
re a
s el
asti
c ar
teri
es e
x-p
and
an
d c
on
trac
t w
ith
th
e p
erio
dic
blo
od
flo
w.
Do
cto
rs u
se
blo
od
p
ress
ure
as
an
g
ener
al
ind
icat
or
of
card
iova
scu
lar
hea
lth
bec
ause
a v
arie
ty o
f co
nd
itio
ns
can
cau
se i
ncr
ease
s o
r d
ecre
ases
in
pre
ssu
re.
A
sph
ygm
oman
omet
er m
easu
res
the
blo
od
pre
ssu
re i
n t
he
bra
chia
l ar
tery
fo
un
d o
n t
he
insi
de
par
t o
f th
e ar
m, a
bo
ve t
he
elb
ow
(fi
gu
re 5
0.1
1) .
A c
uff
wra
pp
ed a
rou
nd
th
e u
pp
er p
art
of
the
arm
is
tig
hte
ned
en
ou
gh
to
sto
p t
he
flo
w o
f b
loo
d t
o t
he
low
er p
art
of
the
arm
. As
the
cuff
is
slo
wly
lo
ose
ned
, ev
entu
-al
ly t
he
blo
od
pre
ssu
re p
rod
uce
d b
y th
e h
eart
is
gre
ater
th
an
the
con
stri
ctin
g p
ress
ure
of
cuff
an
d b
loo
d b
egin
s p
uls
atin
g
thro
ug
h t
he
arte
ry,
pro
du
cin
g a
so
un
d t
hat
can
be
det
ecte
d
usi
ng
a s
teth
osc
op
e. T
he
po
int
at w
hic
h t
his
pu
lsin
g s
ou
nd
b
egin
s m
arks
th
e p
eak
pre
ssu
re,
or
syst
oli
c p
ress
ure
, at
w
hic
h v
entr
icle
s ar
e co
ntr
acti
ng
. A
s th
e cu
ff i
s lo
ose
ned
fu
r-th
er,
the
po
int
is r
each
ed w
her
e th
e p
ress
ure
of
the
cuff
is
low
er t
han
th
e b
loo
d p
ress
ure
th
rou
gh
ou
t th
e ca
rdia
c cy
cle,
at
wh
ich
tim
e th
e b
loo
d v
esse
l is
no
lo
ng
er d
isto
rted
an
d t
he
pu
lsin
g s
ou
nd
sto
ps.
Th
is p
oin
t m
arks
th
e m
inim
um
pre
ssu
re
bet
wee
n h
eart
bea
ts o
r d
iast
oli
c p
ress
ure
, at
wh
ich
th
e ve
n-
tric
les
are
rela
xed
.
Th
e b
loo
d p
ress
ure
is
wri
tten
as
a ra
tio
of
syst
oli
c o
ver
dia
sto
lic
pre
ssu
re, a
nd
fo
r a
hea
lth
y p
erso
n i
n h
is o
r h
er t
wen
-ti
es, a
typ
ical
blo
od
pre
ssu
re is
12
0/7
5 (
mea
sure
d in
mil
lim
eter
s
cha
pte
r 5
0
Th
e C
ircu
lato
ry S
yste
m
10
29
ww
w.r
av
en
bio
log
y.c
om
Apago PDF Enhancer
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a.
b.
c.
Fig
ure
50
.12
Th
e
stru
ctu
re o
f b
loo
d
ve
sse
ls.
Art
erie
s (a
)
and
vei
ns
(b)
hav
e th
e
sam
e ti
ssu
e la
yers
, b
ut
the
smo
oth
mu
scle
lay
er
in a
rter
ies
is m
uch
thic
ker
and
th
ere
are
two
ela
stic
lay
ers.
c. C
apil
lari
es a
re
com
po
sed
of
on
ly a
sin
gle
lay
er o
f
end
oth
elia
l ce
lls.
(No
t to
sca
le.)
of
mer
cury
, o
r m
m
Hg
).
Th
e m
edic
al
con
dit
ion
ca
lled
h
ypert
en
sio
n (
hig
h b
loo
d p
ress
ure
) is
def
ined
as
eith
er a
sys
-to
lic
pre
ssu
re g
reat
er t
han
15
0 m
m H
g o
r a
dia
sto
lic
pre
ssu
re
gre
ater
th
an 9
0 m
m H
g.
Le
arn
ing
Ou
tco
me
s R
ev
iew
50
.4Th
e ca
rdia
c cy
cle
cons
ists
of s
ysto
le a
nd d
iast
ole;
the
vent
ricl
es c
ontr
act
at s
ysto
le a
nd re
lax
at d
iast
ole.
The
SA
node
in th
e ri
ght a
triu
m in
itia
tes
wav
es o
f dep
olar
izat
ion
that
sti
mul
ate
fi rs
t the
atr
ia a
nd th
en tr
avel
to th
e
AV n
ode,
whi
ch s
tim
ulat
es th
e ve
ntri
cles
. Blo
od p
ress
ure
is e
xpre
ssed
as
the
rati
o of
sys
tolic
pre
ssur
e ov
er d
iast
olic
pre
ssur
e an
d is
mea
sure
d w
ith
a
devi
ce c
alle
d a
sphy
gmom
anom
eter
.
■
W
ha
t w
ou
ld h
ap
pe
n w
ith
ou
t a
de
lay
be
twe
en
au
ricu
lar
an
d v
en
tric
ula
r co
ntr
act
ion
?
5
0.5
C
ha
ract
eris
tics
of B
loo
d V
esse
ls
Le
arn
ing
Ou
tco
me
s
De
scri
be
the
fou
r ti
ssu
e la
yers
in b
loo
d v
ess
els
.1.
Exp
lain
th
e d
isti
nct
ion
s a
mo
ng
art
eri
es,
ca
pil
lari
es,
2
. a
nd
ve
ins.
De
scri
be
ho
w t
he
lym
pa
thic
sys
tem
op
era
tes.
3.
Yo
u a
lrea
dy
kno
w t
hat
blo
od
lea
ves
the
hea
rt t
hro
ugh
ves
sels
kn
ow
n a
s ar
teri
es. T
hes
e co
nti
nu
ally
bra
nch
, fo
rmin
g a
ho
llo
w
“tre
e” t
hat
en
ters
eac
h o
rgan
of t
he
bo
dy.
Th
e fi
nes
t, m
icro
sco
pic
b
ran
ches
of
the
arte
rial
tre
e ar
e th
e ar
teri
ole
s. B
loo
d f
rom
th
e ar
teri
ole
s en
ters
th
e ca
pil
lari
es,
an e
lab
ora
te l
atti
cew
ork
of
very
n
arro
w,
thin
-wal
led
tu
bes
. A
fter
tra
vers
ing
the
cap
illa
ries
, th
e b
loo
d is
co
llec
ted
into
mic
rosc
op
ic v
enu
les,
wh
ich
lead
to
larg
er
vess
els
call
ed v
ein
s, a
nd
th
ese
carr
y b
loo
d b
ack
to t
he
hea
rt.
La
rge
r v
ess
els
are
co
mp
ose
d
of
fou
r ti
ssu
e la
ye
rs
Art
erie
s, a
rter
iole
s, v
ein
s, a
nd
ven
ule
s al
l h
ave
the
sam
e b
asic
st
ruct
ure
(fi
gu
re 5
0.1
2 ).
Th
e in
ner
mo
st l
ayer
is
an e
pit
hel
ial
shee
t ca
lled
th
e en
doth
eliu
m. C
ove
rin
g t
he
end
oth
eliu
m is
a t
hin
la
yer
of
elas
tic
fib
ers,
a s
mo
oth
mu
scle
lay
er,
and
a c
on
nec
tive
ti
ssu
e la
yer.
Th
e w
alls
of
thes
e ve
ssel
s, t
her
efo
re,
are
thic
k en
ou
gh
to
sig
nif
ican
tly
red
uce
exc
han
ge
of
mat
eria
ls b
etw
een
th
e b
loo
d a
nd
th
e ti
ssu
es o
uts
ide
the
vess
els.
T
he
wal
ls o
f ca
pil
lari
es, i
n c
on
tras
t, a
re c
om
po
sed
on
ly o
f en
do
thel
ium
, so
mo
lecu
les
and
io
ns
can
lea
ve t
he
blo
od
pla
sma
by
dif
fusi
on
, b
y fi
ltra
tio
n t
hro
ug
h p
ore
s b
etw
een
th
e ce
lls
of
the
cap
illa
ry w
alls
, an
d b
y tr
ansp
ort
th
rou
gh
th
e en
do
thel
ial
cell
s. T
her
efo
re,
exch
ang
e o
f g
ases
an
d m
etab
oli
tes
bet
wee
n
the
blo
od
an
d t
he
inte
rsti
tial
flu
ids
and
cel
ls o
f th
e b
od
y ta
kes
pla
ce t
hro
ug
h t
he
cap
illa
ries
.
Art
eri
es
an
d a
rte
rio
les
ha
ve
ev
olv
ed
to
wit
hst
an
d p
ress
ure
Th
e la
rger
art
erie
s co
nta
in m
ore
ela
stic
fib
ers
in t
hei
r w
alls
th
an o
ther
blo
od
ves
sels
, all
ow
ing
th
em t
o r
eco
il e
ach
tim
e th
ey
rece
ive
a vo
lum
e o
f b
loo
d p
um
ped
by
the
hea
rt. S
mal
ler
arte
r-ie
s an
d
arte
rio
les
are
less
el
asti
c,
bu
t th
eir
rela
tive
ly
thic
k sm
oo
th m
usc
le l
ayer
en
able
s th
em t
o r
esis
t b
urs
tin
g.
T
he
nar
row
er t
he
vess
el,
the
gre
ater
th
e fr
icti
on
al r
esis
-ta
nce
to
flo
w.
In f
act,
a v
esse
l th
at i
s h
alf
the
dia
met
er o
f an
-o
ther
has
16
tim
es t
he
fric
tio
nal
res
ista
nce
. Res
ista
nce
to
blo
od
fl
ow
is
inve
rsel
y p
rop
ort
ion
al t
o t
he
fou
rth
po
wer
of
the
rad
ius
of
the
vess
el. T
her
efo
re, w
ith
in t
he
arte
rial
tre
e, t
he
smal
l art
er-
ies
and
art
erio
les
pro
vid
e th
e g
reat
est
resi
stan
ce t
o b
loo
d f
low
.
Co
ntr
acti
on
of
the
smo
oth
mu
scle
lay
er o
f th
e ar
teri
ole
s re
sult
s in
vas
oco
nst
rict
ion
, w
hic
h g
reat
ly i
ncr
ease
s re
sist
ance
an
d d
ecre
ases
flo
w.
Rel
axat
ion
of
the
smo
oth
mu
scle
lay
er r
e-su
lts
in
vaso
dil
atio
n,
dec
reas
ing
re
sist
ance
an
d
incr
easi
ng
b
loo
d f
low
to
an
org
an. C
hro
nic
vas
oco
nst
rict
ion
of
the
arte
ri-
ole
s ca
n r
esu
lt i
n h
yper
ten
sio
n, o
r h
igh
blo
od
pre
ssu
re.
10
30
p
art
VII
An
ima
l Fo
rm a
nd
Fu
nct
ion
a.
b.
° ��¬����£ �¢ ��ª § �����¬����¥£� �¬¤£ �Ó ��¬����£ �¢ ��ª § �����¬����¥£� �¬¤£ �æ àìíîíèìê äâ îêâ íè ë ¥£� �¬¤£ � �� ¦§ �« ¬ª�¬£ �§ � Î �¥£§§ �¬ ¯� ¬���¥£§§ �¬ ¯ �¥¢£ ��ª�¬¹ ���ª¬��ª��º � ¬���¥£§§ �¬ ¯ �¥¢£ ��ª�¬¹ ¬�§ � ï��º«£ ¬�¬ ��ª�¬
æ àìíðâã àêâ íè
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Fig
ure
50
.13
Re
gu
lati
on
of
he
at
ex
cha
ng
e.
Th
e am
ou
nt
of
hea
t g
ain
ed o
r lo
st a
t th
e b
od
y’s
surf
ace
can
be
reg
ula
ted
by
con
tro
llin
g t
he
! o
w o
f b
loo
d t
o t
he
surf
ace.
a.
Co
nst
rict
ion
of
surf
ace
blo
od
ves
sels
lim
its
! o
w a
nd
hea
t lo
ss w
hen
th
e an
imal
is
war
mer
th
an t
he
surr
ou
nd
ing
air
; w
hen
th
e an
imal
is
coo
ler
than
the
surr
ou
nd
ing
air
(n
ot
sho
wn
her
e),
con
stri
ctio
n m
inim
izes
hea
t
gai
n; (b
) d
ilat
ion
of
thes
e ve
ssel
s in
crea
ses
! o
w a
nd
hea
t ex
chan
ge.
V
aso
con
stri
ctio
n a
nd
vas
od
ilat
ion
are
im
po
rtan
t m
ean
s o
f re
gu
lati
ng
bo
dy
hea
t in
bo
th e
cto
ther
ms
and
en
do
ther
ms
(fig
ure
50
.13
) . B
y in
crea
sin
g b
loo
d f
low
to
th
e sk
in, a
n a
nim
al
can
in
crea
se t
he
rate
of
hea
t ex
chan
ge,
wh
ich
is
ben
efic
ial
for
gai
nin
g o
r lo
sin
g h
eat.
Co
nve
rsel
y, s
hu
nti
ng
blo
od
aw
ay f
rom
th
e sk
in i
s ef
fect
ive
wh
en a
n a
nim
al n
eed
s to
min
imiz
e h
eat
exch
ang
e, a
s m
igh
t h
app
en i
n c
old
wea
ther
.
Ca
pil
lari
es
form
a v
ast
ne
two
rk
for
ex
cha
ng
e o
f m
ate
ria
ls
Th
e h
ug
e n
um
ber
an
d e
xten
sive
bra
nch
ing
of
the
cap
illa
ries
en
sure
th
at e
very
cel
l in
th
e b
od
y is
wit
hin
10
0 m
icro
met
ers
( μm
) o
f a
cap
illa
ry. O
n t
he
aver
age,
cap
illa
ries
are
ab
ou
t 1
mm
lo
ng
an
d 8
μm
in
dia
met
er, t
his
dia
met
er i
s o
nly
sli
gh
tly
larg
er
than
a r
ed b
loo
d c
ell
(5 t
o 7
μm
in
dia
met
er).
Des
pit
e th
e cl
ose
fi
t,
no
rmal
re
d
blo
od
ce
lls
are
flex
ible
en
ou
gh
to
sq
uee
ze
thro
ug
h c
apil
lari
es w
ith
ou
t d
iffi
cult
y.
T
he
rate
of
blo
od
flo
w t
hro
ug
h v
esse
ls i
s g
ove
rned
by
hyd
rod
ynam
ics.
Th
e sm
alle
r th
e cr
oss
-sec
tio
nal
are
a o
f a
ves-
sel,
the
fast
er f
luid
mo
ves
thro
ug
h i
t. G
iven
th
is,
flo
w i
n t
he
cap
illa
ries
wo
uld
be
exp
ecte
d t
o b
e th
e fa
stes
t in
th
e sy
stem
. T
his
wo
uld
no
t b
e id
eal
for
dif
fusi
on
, an
d i
s ac
tual
ly n
ot
the
case
. Alt
ho
ug
h e
ach
cap
illa
ry i
s ve
ry n
arro
w,
so m
any
of
them
ex
ist
that
th
e ca
pil
lari
es h
ave
the
gre
ates
t to
tal
cro
ss-s
ecti
on
al
area
of
any
oth
er t
ype
of
vess
el.
Co
nse
qu
entl
y, b
loo
d m
ovi
ng
th
rou
gh
cap
illa
ries
go
es m
ore
slo
wly
an
d h
as m
ore
tim
e to
ex-
chan
ge
mat
eria
ls w
ith
th
e su
rro
un
din
g e
xtra
cell
ula
r fl
uid
. B
y th
e ti
me
the
blo
od
rea
ches
th
e en
d o
f a
cap
illa
ry, i
t h
as r
elea
sed
so
me
of
its
oxy
gen
an
d n
utr
ien
ts a
nd
pic
ked
up
car
bo
n d
ioxi
de
and
oth
er w
aste
pro
du
cts.
Blo
od
lo
ses
pre
ssu
re a
nd
vel
oci
ty a
s it
mo
ves
thro
ug
h t
he
arte
rio
les
and
cap
illa
ries
, b
ut
as c
ross
-se
ctio
nal
are
a d
ecre
ases
in
th
e ve
no
us
sid
e, v
elo
city
in
crea
ses.
Ve
nu
les
an
d v
ein
s h
av
e
less
mu
scle
in t
he
ir w
all
s
Ven
ule
s an
d v
ein
s h
ave
the
sam
e ti
ssu
e la
yers
as
arte
ries
, b
ut
they
hav
e a
thin
ner
lay
er o
f sm
oo
th m
usc
le.
Les
s m
usc
le i
s n
eed
ed b
ecau
se t
he
pre
ssu
re i
n t
he
vein
s is
on
ly a
bo
ut
on
e-te
nth
th
at i
n t
he
arte
ries
. Mo
st o
f th
e b
loo
d i
n t
he
card
iova
scu
-la
r sy
stem
is
con
tain
ed w
ith
in v
ein
s, w
hic
h c
an e
xpan
d t
o h
old
ad
dit
ion
al a
mo
un
ts o
f b
loo
d. Y
ou
can
see
th
e ex
pan
ded
vei
ns
in
you
r fe
et w
hen
yo
u s
tan
d f
or
a lo
ng
tim
e.
Th
e ve
no
us
pre
ssu
re a
lon
e is
no
t su
ffic
ien
t to
ret
urn
b
loo
d t
o t
he
hea
rt f
rom
th
e fe
et a
nd
leg
s, b
ut
seve
ral
oth
er
sou
rces
of
pre
ssu
re p
rovi
de
hel
p.
Mo
st s
ign
ific
antl
y, s
kele
tal
mu
scle
s su
rro
un
din
g t
he
vein
s ca
n c
on
trac
t to
mo
ve b
loo
d b
y sq
uee
zin
g t
he
vein
s, a
mec
han
ism
cal
led
th
e ve
no
us
pu
mp
. B
loo
d m
ove
s in
on
e d
irec
tio
n t
hro
ug
h t
he
vein
s b
ack
to t
he
hea
rt w
ith
th
e h
elp
of
ven
ou
s va
lves
(fig
ure
50
.14
). W
hen
a
Fig
ure
50
.14
On
e-w
ay
! o
w o
f
blo
od
th
rou
gh
ve
ins.
V
eno
us
valv
es
ensu
re t
hat
blo
od
mo
ves
thro
ug
h t
he
vein
s in
on
ly o
ne
dir
ecti
on
, b
ack
to
the
hea
rt.
cha
pte
r 5
0
Th
e C
ircu
lato
ry S
yste
m
10
31
ww
w.r
av
en
bio
log
y.c
om
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Fig
ure
50
.15
Re
lati
on
ship
be
twe
en
blo
od
, ly
mp
h, a
nd
inte
rsti
tia
l !
uid
. a.
Ves
sels
of
the
circ
ula
tory
an
d l
ym
ph
atic
syst
ems
wit
h a
rro
ws
ind
icat
ing
th
e d
irec
tio
n o
f !
ow
of
! u
id i
n t
he
vess
els.
b.
Pla
sma
! u
id, m
inu
s p
rote
ins,
is
" lt
ered
ou
t o
f ca
pil
lari
es,
form
ing
in
ters
titi
al !
uid
th
at b
ath
es t
issu
es. M
uch
of
this
! u
id i
s
retu
rned
to
th
e ca
pil
lari
es b
y o
smo
sis
du
e to
th
e h
igh
er p
rote
in
con
cen
trat
ion
in
pla
sma.
Exc
ess
inte
rsti
tial
! u
id d
rain
s in
to
op
en-e
nd
ed l
ym
ph
atic
cap
illa
ries
, w
hic
h u
ltim
atel
y re
turn
th
e !
uid
to t
he
card
iova
scu
lar
syst
em.
per
son
’s v
ein
s ex
pan
d t
oo
mu
ch w
ith
blo
od
, th
e ve
no
us
valv
es
may
no
lo
ng
er w
ork
an
d t
he
blo
od
may
po
ol
in t
he
vein
s. V
ein
s in
th
is c
on
dit
ion
are
kn
ow
n a
s va
rico
se v
ein
s.
Th
e ly
mp
ha
tic
syst
em
ha
nd
les
! u
ids
tha
t le
av
e t
he
ca
rdio
va
scu
lar
syst
em
Th
e ca
rdio
vasc
ula
r sy
stem
is
con
sid
ered
a c
lose
d s
yste
m b
e-ca
use
all
its
ves
sels
are
co
nn
ecte
d w
ith
on
e an
oth
er—
no
ne
are
sim
ply
op
en-e
nd
ed. B
ut
a si
gn
ific
ant
amo
un
t o
f w
ater
an
d s
ol-
ute
s in
th
e b
loo
d p
lasm
a fi
lter
th
rou
gh
th
e w
alls
of
the
cap
illa
r-ie
s to
fo
rm t
he
inte
rsti
tial
(ti
ssu
e) f
luid
. Mo
st o
f th
e fl
uid
lea
ves
the
cap
illa
ries
nea
r th
eir
arte
rio
lar
end
s, w
her
e th
e b
loo
d p
res-
sure
is
hig
her
; it
is r
etu
rned
to
th
e ca
pil
lari
es n
ear
thei
r ve
nu
lar
end
s (f
igu
re 5
0.1
5).
Flu
id r
etu
rns
by
osm
osi
s (s
ee c
hap
ter
5).
Mo
st o
f th
e p
lasm
a p
rote
ins
can
no
t es
cap
e th
rou
gh
th
e ca
pil
lary
po
res
be-
cau
se o
f th
eir
larg
e si
ze,
and
so
th
e co
nce
ntr
atio
n o
f p
rote
ins
in t
he
pla
sma
is g
reat
er t
han
th
e p
rote
in c
on
cen
trat
ion
in
th
e in
ters
titi
al f
luid
. Th
e d
iffe
ren
ce i
n p
rote
in c
on
cen
trat
ion
pro
-d
uce
s an
osm
oti
c p
ress
ure
gra
die
nt
that
cau
ses
wat
er t
o m
ove
in
to t
he
cap
illa
ries
fro
m t
he
inte
rsti
tial
sp
ace.
H
igh
cap
illa
ry b
loo
d p
ress
ure
can
cau
se t
oo
mu
ch i
nte
r-st
itia
l flu
id t
o a
ccu
mu
late
. In
pre
gn
ant
wo
men
, fo
r ex
amp
le, t
he
enla
rged
ute
rus,
car
ryin
g t
he
fetu
s, c
om
pre
sses
vei
ns
in t
he
ab-
do
min
al c
avit
y, t
her
eby
add
ing
to
th
e ca
pil
lary
blo
od
pre
ssu
re
in t
he
wo
man
’s l
ow
er l
imb
s. T
he
incr
ease
d i
nte
rsti
tial
flu
id c
an
cau
se s
wel
lin
g o
f th
e ti
ssu
es, o
r ed
em
a, o
f th
e fe
et.
E
dem
a m
ay a
lso
res
ult
if
the
pla
sma
pro
tein
co
nce
ntr
a-ti
on
is
too
lo
w.
Flu
ids
do
no
t re
turn
to
th
e ca
pil
lari
es,
bu
t re
-m
ain
as
inte
rsti
tial
flu
id.
Lo
w p
rote
in c
on
cen
trat
ion
in
th
e p
lasm
a m
ay b
e ca
use
d e
ith
er b
y li
ver
dis
ease
, b
ecau
se t
he
live
r p
rod
uce
s m
ost
of
the
pla
sma
pro
tein
s, o
r b
y in
suff
icie
nt
die
tary
p
rote
in s
uch
as
occ
urs
in
sta
rvat
ion
.
Eve
n u
nd
er n
orm
al c
on
dit
ion
s, t
he
amo
un
t o
f fl
uid
fil
-te
red
ou
t o
f th
e ca
pil
lari
es i
s g
reat
er t
han
th
e am
ou
nt
that
re-
turn
s to
th
e ca
pil
lari
es
by
osm
osi
s.
Th
e re
mai
nd
er
do
es
even
tual
ly r
etu
rn t
o t
he
card
iova
scu
lar
syst
em b
y w
ay o
f an
o
pen
cir
cula
tory
sys
tem
cal
led
th
e ly
mp
hat
ic s
yste
m.
T
he
lym
ph
atic
sys
tem
co
nsi
sts
of
lym
ph
atic
cap
illa
r-ie
s, l
ymp
hat
ic v
esse
ls,
lym
ph
no
des
, an
d l
ymp
hat
ic o
rgan
s,
incl
ud
ing
th
e sp
leen
an
d t
hym
us.
Exc
ess
flu
id i
n t
he
tiss
ues
d
rain
s in
to b
lin
d-e
nd
ed l
ymp
h c
apil
lari
es w
ith
hig
hly
per
-m
eab
le w
alls
. Th
is f
luid
, no
w c
alle
d l
ym
ph
, p
asse
s in
to p
ro-
gre
ssiv
ely
larg
er l
ymp
hat
ic v
esse
ls,
wh
ich
res
emb
le v
ein
s an
d
hav
e o
ne-
way
va
lves
(s
imil
ar
to
fig
ure
5
0.1
4).
T
he
lym
ph
eve
ntu
ally
en
ters
tw
o m
ajo
r ly
mp
hat
ic v
esse
ls, w
hic
h
dra
in i
nto
th
e le
ft a
nd
rig
ht
sub
clav
ian
vei
ns
loca
ted
un
der
th
e co
llar
bo
nes
.
Mo
vem
ent
of
lym
ph
in
mam
mal
s re
sult
s as
ske
leta
l m
us-
cles
sq
uee
ze a
gai
nst
th
e ly
mp
hat
ic v
esse
ls, a
mec
han
ism
sim
ilar
to
th
e ve
no
us
pu
mp
th
at m
ove
s b
loo
d t
hro
ug
h v
ein
s. I
n s
om
e ca
ses,
th
e ly
mp
hat
ic v
esse
ls a
lso
co
ntr
act
rhyt
hm
ical
ly. I
n m
any
fish
es,
all
amp
hib
ian
s an
d r
epti
les,
bir
d e
mb
ryo
s, a
nd
so
me
adu
lt b
ird
s, m
ove
men
t o
f ly
mp
h i
s p
rop
elle
d b
y ly
mp
h h
ear
ts.
A
s th
e ly
mp
h m
ove
s th
rou
gh
lym
ph
no
des
an
d l
ymp
hat
ic
org
ans,
it
is m
od
ifie
d b
y p
hag
ocy
tic
cell
s (s
ee c
hap
ter
4)
that
li
ne
the
chan
nel
s o
f th
ose
org
ans.
In
ad
dit
ion
, th
e ly
mp
h n
od
es
10
32
p
art
VII
An
ima
l Fo
rm a
nd
Fu
nct
ion
Apago PDF Enhancer
a.
b.
c.
® µ
¤®¶ µ
¤� µ
¤
Fig
ure
50
.16
Ath
ero
scle
rosi
s.
a.
Th
e co
ron
ary
arte
ry s
ho
ws
on
ly m
ino
r b
lock
age.
b.
Th
e ar
tery
exh
ibit
s se
vere
ath
ero
scle
rosi
s—
mu
ch o
f th
e p
assa
ge
is b
lock
ed b
y b
uil
du
p o
n t
he
inte
rio
r w
alls
of
the
arte
ry. c.
Th
e co
ron
ary
arte
ry i
s es
sen
tial
ly c
om
ple
tely
blo
cked
.
and
lym
ph
atic
org
ans
con
tain
ger
min
al c
ente
rs,
wh
ere
the
acti
-va
tio
n a
nd
pro
life
rati
on
of
lym
ph
ocy
tes
occ
urs
.
Ca
rdio
va
scu
lar
dis
ea
ses
a#
ect
th
e d
eli
ve
ry s
yst
em
Car
dio
vasc
ula
r d
isea
ses
are
the
lead
ing
cau
se o
f d
eath
in
th
e U
nit
ed S
tate
s; m
ore
th
an 8
0 m
illi
on
peo
ple
hav
e so
me
form
of
card
iova
scu
lar
dis
ease
. M
any
dis
ease
co
nd
itio
ns
resu
lt f
rom
p
rob
lem
s in
art
erie
s, s
uch
as
blo
ckag
e o
r ru
ptu
re.
A
thero
scle
rosi
s, o
r h
ard
en
ing
of
the a
rteri
es,
is
an
accu
mu
lati
on
wit
hin
th
e ar
teri
es o
f fa
tty
mat
eria
ls, a
bn
orm
al
amo
un
ts o
f sm
oo
th m
usc
le, d
epo
sits
of
cho
lest
ero
l o
r fi
bri
n,
or
vari
ou
s k
ind
s o
f ce
llu
lar
deb
ris.
T
hes
e ac
cum
ula
tio
ns
cau
se a
n in
crea
se in
vas
cula
r re
sist
ance
, wh
ich
imp
edes
blo
od
fl
ow
(fi
gu
re 5
0.1
6) .
Th
e lu
men
(in
teri
or)
of
the
arte
ry m
ay
be
furt
her
nar
row
ed b
y a
clo
t th
at f
orm
s as
a r
esu
lt o
f th
e at
her
osc
lero
sis.
In
th
e se
vere
st c
ases
, th
e ar
tery
bec
om
es
com
ple
tely
blo
cked
.
Th
e ac
cum
ula
tio
n o
f ch
ole
ster
ol
in v
esse
ls i
s af
fect
ed b
y a
nu
mb
er o
f fa
cto
rs i
ncl
ud
ing
to
tal
seru
m c
ho
lest
ero
l an
d t
he
leve
ls o
f d
iffe
ren
t ch
ole
ster
ol
carr
ier
pro
tein
s. B
ecau
se c
ho
-le
ster
ol
is n
ot
very
wat
er-s
olu
ble
, it
is
carr
ied
in
blo
od
in
th
e fo
rm o
f li
po
pro
tein
co
mp
lexe
s. T
wo
mai
n f
orm
s ar
e o
bse
rved
th
at d
iffe
r in
den
sity
: lo
w-d
ensi
ty l
ipo
pro
tein
s (L
DL
) an
d
hig
h-d
ensi
ty l
ipo
pro
tein
s (H
DL
) —o
ften
cal
led
“b
ad c
ho
les-
tero
l” a
nd
“g
oo
d c
ho
lest
ero
l,” r
esp
ecti
vely
. T
he
reas
on
fo
r th
is i
s th
at H
DL
s te
nd
to
tak
e ch
ole
ster
ol
ou
t o
f ci
rcu
lati
on
, tr
ansp
ort
ing
it
to t
he
live
r fo
r el
imin
atio
n,
and
LD
L i
s th
e ca
rrie
r th
at b
rin
gs
cho
lest
ero
l to
all
cel
ls i
n t
he
bo
dy.
Th
e p
rob
lem
ar
ises
w
hen
ce
lls
hav
e en
ou
gh
ch
ole
ster
ol.
T
his
ca
use
s a
red
uct
ion
in t
he
amo
un
t o
f L
DL
rec
epto
rs, l
ead
ing
to
h
igh
lev
els
of
circ
ula
tin
g L
DL
s, w
hic
h c
an e
nd
up
bei
ng
de-
po
site
d i
n b
loo
d v
esse
ls.
A
ther
osc
lero
sis
is p
rom
ote
d b
y g
enet
ic f
acto
rs,
smo
k-
ing
, h
yper
ten
sio
n (
hig
h b
loo
d p
ress
ure
), a
nd
th
e ef
fect
s o
f ch
ole
ster
ol
just
dis
cuss
ed.
Sto
pp
ing
sm
okin
g i
s th
e si
ng
le
mo
st e
ffec
tive
act
ion
a s
mo
ker
can
tak
e to
red
uce
th
e ri
sk o
f at
her
osc
lero
sis.
A
rteri
osc
lero
sis
occ
urs
wh
en c
alci
um
is
dep
osi
ted
in
ar
teri
al w
alls
. It
ten
ds
to o
ccu
r w
hen
ath
ero
scle
rosi
s is
sev
ere.
N
ot
on
ly d
o s
uch
art
erie
s h
ave
rest
rict
ed b
loo
d f
low
, bu
t th
ey
also
lac
k th
e ab
ilit
y to
exp
and
as
no
rmal
art
erie
s d
o. T
his
de-
crea
se i
n f
lexi
bil
ity
forc
es t
he
hea
rt t
o w
ork
har
der
bec
ause
b
loo
d p
ress
ure
in
crea
ses
to m
ain
tain
flo
w.
H
ear
t at
tack
s (m
yoca
rdia
l in
farc
tio
ns)
are
th
e m
ain
cau
se
of
card
iova
scu
lar
dea
ths
in t
he
Un
ited
Sta
tes,
acc
ou
nti
ng
fo
r ab
ou
t o
ne-
fift
h o
f al
l dea
ths.
Hea
rt a
ttac
ks r
esu
lt f
rom
an
insu
f-fi
cien
t su
pp
ly o
f b
loo
d t
o o
ne
or
mo
re p
arts
of
the
hea
rt m
usc
le,
wh
ich
cau
ses
myo
card
ial
cell
s in
th
ose
par
ts t
o d
ie.
Hea
rt a
t-ta
cks
may
be
cau
sed
by
a b
loo
d c
lot
form
ing
so
mew
her
e in
th
e co
ron
ary
arte
ries
an
d m
ay a
lso
res
ult
if
an a
rter
y is
blo
cked
by
ath
ero
scle
rosi
s. R
eco
very
fro
m a
hea
rt a
ttac
k is
po
ssib
le i
f th
e p
ort
ion
of
the
hea
rt t
hat
was
dam
aged
is
smal
l en
ou
gh
th
at t
he
hea
rt c
an s
till
co
ntr
act
as a
fu
nct
ion
al u
nit
.
An
gin
a p
ect
ori
s, w
hic
h l
iter
ally
mea
ns
“ch
est
pai
n,”
oc-
curs
fo
r re
aso
ns
sim
ilar
to
th
ose
th
at c
ause
hea
rt a
ttac
ks, b
ut
it
is n
ot
as s
ever
e. T
he
pai
n m
ay o
ccu
r in
th
e h
eart
an
d o
ften
als
o
in t
he
left
arm
an
d s
ho
uld
er. A
ng
ina
pec
tori
s is
a w
arn
ing
sig
n
that
th
e b
loo
d s
up
ply
to
th
e h
eart
is
inad
equ
ate
bu
t is
sti
ll s
uf-
fici
ent
to a
void
myo
card
ial
cell
dea
th.
S
tro
kes
are
cau
sed
by
an in
terf
eren
ce w
ith
th
e b
loo
d s
up
-p
ly t
o t
he
bra
in. T
hey
may
occ
ur
wh
en a
blo
od
ves
sel
bu
rsts
in
th
e b
rain
(h
emo
rrh
agic
str
oke
), w
hen
blo
od
flo
w i
n a
cer
ebra
l ar
tery
is
blo
cked
by
a b
loo
d c
lot
or
by
ath
ero
scle
rosi
s (i
sch
emic
st
roke
). T
he
effe
cts
of
a st
roke
dep
end
on
th
e se
veri
ty o
f th
e d
amag
e an
d w
her
e in
th
e b
rain
th
e st
roke
occ
urs
.
Le
arn
ing
Ou
tco
me
s R
ev
iew
50
.5Th
e fo
ur la
yers
of b
lood
ves
sels
are
(1) e
ndot
heliu
m, (
2) a
n el
asti
c la
yer,
(3) s
moo
th m
uscl
e, a
nd (4
) con
nect
ive
tiss
ue. I
n co
ntra
st, c
apill
arie
s ha
ve
only
end
othe
lium
. Art
erie
s ha
ve m
ore
mus
cle
in th
eir w
alls
than
do
vein
s
to h
elp
wit
hsta
nd g
reat
er p
ress
ure;
larg
e ar
teri
es a
lso
have
mor
e el
asti
c
fi be
rs fo
r rec
oil.
Exce
ss in
ters
titi
al fl
uid,
cal
led
lym
ph, i
s re
turn
ed to
the
card
iova
scul
ar s
yste
m v
ia th
e ly
mph
atic
sys
tem
, a o
ne-w
ay sy
stem
.
■
W
ha
t is
th
e co
nn
ect
ion
be
twe
en
th
e ly
mp
ha
tic
an
d
circ
ula
tory
sys
tem
s?
cha
pte
r 5
0
Th
e C
ircu
lato
ry S
yste
m
10
33
ww
w.r
av
en
bio
log
y.c
om
Apago PDF Enhancer
5
0.6
R
egu
lati
on
of B
loo
d F
low
a
nd
Blo
od
Pre
ssu
re
Le
arn
ing
Ou
tco
me
s
De
scri
be
ho
w e
xert
ion
aff
ect
s ca
rdia
c o
utp
ut.
1.
Exp
lain
ho
w h
orm
on
es
reg
ula
te b
loo
d v
olu
me
.2
.
Alt
ho
ug
h t
he
auto
no
mic
ner
vou
s sy
stem
do
es n
ot
init
iate
th
e h
eart
bea
t, it
do
es m
od
ula
te it
s rh
yth
m a
nd
fo
rce
of
con
trac
tio
n.
In a
dd
itio
n,
seve
ral
mec
han
ism
s re
gu
late
ch
arac
teri
stic
s o
f th
e ca
rdio
vasc
ula
r sy
stem
, in
clu
din
g c
ard
iac
ou
tpu
t, b
loo
d p
res-
sure
, an
d b
loo
d v
olu
me.
Th
e n
erv
ou
s sy
ste
m m
ay
sp
ee
d
up
or
slo
w d
ow
n h
ea
rt r
ate
Hea
rt r
ate
is u
nd
er t
he
con
tro
l o
f th
e au
ton
om
ic n
ervo
us
sys-
tem
. Th
e ca
rdia
c ce
nte
r o
f th
e m
edu
lla
ob
lon
gat
a (a
par
t o
f th
e h
ind
bra
in; s
ee c
hap
ter
44
) co
nsi
sts
of
two
neu
ron
al c
ente
rs t
hat
m
od
ula
te h
eart
rat
e. T
he
card
ioac
cele
rato
ry c
en
ter
sen
ds
sig
-n
als
by
way
of
the
sym
pat
het
ic c
ard
iac
acce
lera
tor
ner
ves
to t
he
SA
no
de,
AV
no
de,
an
d m
yoca
rdiu
m. T
hes
e n
erve
s se
cret
e n
or-
epin
eph
rin
e, w
hic
h i
ncr
ease
s th
e h
eart
rat
e. S
ymp
ath
etic
ner
-vo
us
syst
em s
tim
ula
tio
n c
an a
lso
in
crea
se c
on
trac
tili
ty o
f th
e h
eart
mu
scle
its
elf,
th
us
ejec
tin
g m
ore
blo
od
per
co
ntr
acti
on
(s
tro
ke v
olu
me)
.
Th
e ca
rdio
inh
ibit
ory
cen
ter
sen
ds
sig
nal
s vi
a th
e p
ara-
sym
pat
het
ic f
iber
s in
th
e va
gu
s n
erve
to
th
e S
A a
nd
AV
no
des
. T
he
vag
us
ner
ve s
ecre
tes
acet
ylch
oli
ne,
wh
ich
in
hib
its
the
de-
velo
pm
ent
of
acti
on
po
ten
tial
s an
d s
o s
low
s th
e h
eart
do
wn
.
Ca
rdia
c o
utp
ut
incr
ea
ses
wit
h e
xe
rtio
n
Car
dia
c o
utp
ut
is t
he
volu
me
of
blo
od
pu
mp
ed b
y ea
ch v
en-
tric
le p
er m
inu
te. It
is
calc
ula
ted
by
mu
ltip
lyin
g t
he
hea
rt r
ate
by
the
stro
ke v
olu
me,
wh
ich
is
the
volu
me
of
blo
od
eje
cted
by
each
ven
tric
le p
er b
eat.
Fo
r ex
amp
le, i
f th
e h
eart
rat
e is
72
bea
ts
per
min
ute
an
d t
he
stro
ke v
olu
me
is 7
0 m
L, t
he
card
iac
ou
tpu
t is
5 L
/min
, wh
ich
is
abo
ut
aver
age
in a
res
tin
g h
um
an.
C
ard
iac
ou
tpu
t in
crea
ses
du
rin
g e
xert
ion
bec
ause
of
an
incr
ease
in
bo
th h
eart
rat
e an
d s
tro
ke v
olu
me.
Wh
en e
xert
ion
b
egin
s, s
uch
as
run
nin
g, t
he
hea
rt r
ate
incr
ease
s u
p t
o a
bo
ut
10
0
bea
ts p
er m
inu
te t
o p
rovi
de
mo
re o
xyg
en t
o c
ells
in
th
e b
od
y.
As
mo
vem
ent
bec
om
es m
ore
in
ten
se, sk
elet
al m
usc
les
squ
eeze
o
n v
ein
s m
ore
vig
oro
usl
y, r
etu
rnin
g b
loo
d t
o t
he
hea
rt m
ore
ra
pid
ly.
In a
dd
itio
n,
the
ven
tric
les
con
trac
t m
ore
str
on
gly
, so
th
ey e
mp
ty m
ore
co
mp
lete
ly w
ith
eac
h b
eat.
D
uri
ng
exe
rcis
e, t
he
card
iac
ou
tpu
t in
crea
ses
to a
max
i-m
um
of
abo
ut
25
L/m
in i
n a
n a
vera
ge
you
ng
ad
ult
. Alt
ho
ug
h
the
card
iac
ou
tpu
t h
as i
ncr
ease
d f
ivef
old
, no
t al
l o
rgan
s re
ceiv
e fi
ve t
imes
th
e b
loo
d f
low
; so
me
rece
ive
mo
re, o
ther
s le
ss. A
rte-
rio
les
in s
om
e o
rgan
s, s
uch
as
in t
he
dig
esti
ve s
yste
m, c
on
stri
ct,
wh
ile
the
arte
rio
les
in t
he
wo
rkin
g m
usc
les
and
hea
rt d
ilat
e.
Th
e b
aro
rece
pto
r re
! e
x m
ain
tain
s
ho
me
ost
asi
s in
blo
od
pre
ssu
re
Th
e ar
teri
al b
loo
d p
ress
ure
(B
P)
dep
end
s o
n t
wo
fac
tors
: th
e ca
rdia
c o
utp
ut
(CO
) an
d t
he
resi
stan
ce (
R)
to b
loo
d f
low
in
th
e va
scu
lar
syst
em. T
his
rel
atio
nsh
ip c
an b
e ex
pre
ssed
as:
BP =
CO
× R
A
n i
ncr
ease
d b
loo
d p
ress
ure
, th
eref
ore
, co
uld
be
pro
-d
uce
d b
y an
in
crea
se i
n e
ith
er h
eart
rat
e o
r b
loo
d v
olu
me
(be-
cau
se b
oth
incr
ease
th
e ca
rdia
c o
utp
ut)
, or
by
vaso
con
stri
ctio
n,
wh
ich
in
crea
ses
the
resi
stan
ce
to
blo
od
fl
ow
. C
on
vers
ely,
b
loo
d p
ress
ure
fal
ls i
f th
e h
eart
rat
e sl
ow
s o
r if
th
e b
loo
d v
ol-
um
e is
red
uce
d—
for
exam
ple
, b
y d
ehyd
rati
on
or
exce
ssiv
e b
leed
ing
(h
emo
rrh
age)
.
Ch
ang
es
in
arte
rial
b
loo
d
pre
ssu
re
are
det
ecte
d
by
bar
ore
cep
tors
lo
cate
d i
n t
he
arch
of
the
aort
a an
d i
n t
he
ca-
roti
d a
rter
ies
(see
ch
apte
r 4
6).
Th
ese
sen
sors
are
str
etch
re-
cep
tors
se
nsi
tive
to
ex
pan
sio
n an
d co
ntr
acti
on
o
f ar
teri
es.
Wh
en t
he
bar
ore
cep
tors
det
ect
a fa
ll i
n b
loo
d p
ress
ure
, th
e n
um
ber
of
imp
uls
es t
o t
he
card
iac
cen
ter
is d
ecre
ased
, res
ult
-in
g i
n i
ncr
ease
d s
ymp
ath
etic
sti
mu
lati
on
an
d d
ecre
ased
par
a-sy
mp
ath
etic
sti
mu
lati
on
of
the
hea
rt a
nd
oth
er t
arg
ets.
Th
is
incr
ease
s h
eart
rat
e an
d s
tro
ke v
olu
me
to a
mp
lify
car
dia
c o
ut-
pu
t. T
his
als
o c
ause
s va
soco
nst
rict
ion
of
blo
od
ves
sels
in
th
e sk
in a
nd
vis
cera
, rai
sin
g r
esis
tan
ce. T
hes
e co
mb
ine
to i
ncr
ease
b
loo
d p
ress
ure
, cl
osi
ng
th
e fe
edb
ack
loo
p i
n t
his
dir
ecti
on
(f
igu
re 5
0.1
7, t
op
).
W
hen
bar
ore
cep
tors
det
ect
a ri
se i
n b
loo
d p
ress
ure
, th
e n
um
ber
of
imp
uls
es t
o t
he
card
iac
cen
ter
is i
ncr
ease
d. T
his
has
th
e o
pp
osi
te e
ffec
t o
f d
ecre
asin
g s
ymp
ath
etic
sti
mu
lati
on
an
d
incr
easi
ng
par
asym
pat
het
ic s
imu
lati
on
of
the
hea
rt. T
his
low
ers
hea
rt r
ate
and
str
oke
vo
lum
e to
red
uce
car
dia
c o
utp
ut.
Th
e ca
r-d
iac
cen
ter
also
sen
ds
sig
nal
s ca
usi
ng
vas
od
ilat
ion
of
blo
od
ves
-se
ls in
th
e sk
in a
nd
vis
cera
, lo
wer
ing
res
ista
nce
. Th
ese
com
bin
e to
d
ecre
ase
blo
od
p
ress
ure
cl
osi
ng
th
e fe
edb
ack
loo
p
in
this
dir
ecti
on
. T
hu
s, t
he
bar
ore
cep
tor
refl
ex f
orm
s a
neg
ativ
e fe
edb
ack
loo
p
resp
on
din
g
to
chan
ges
in
b
loo
d
pre
ssu
re
(fig
ure
50
.17
, bo
tto
m).
Blo
od
vo
lum
e is
re
gu
late
d b
y h
orm
on
es
Blo
od
pre
ssu
re d
epen
ds
in p
art
on
th
e to
tal
blo
od
vo
lum
e b
e-ca
use
th
is c
an a
ffec
t th
e ca
rdia
c o
utp
ut.
A d
ecre
ase
in b
loo
d
volu
me
dec
reas
es
blo
od
p
ress
ure
, if
al
l el
se
rem
ain
s eq
ual
. B
loo
d v
olu
me
reg
ula
tio
n in
volv
es t
he
effe
cts
of
fou
r h
orm
on
es:
(1)
anti
diu
reti
c h
orm
on
e, (
2)
ald
ost
ero
ne,
(3
) at
rial
nat
riu
reti
c h
orm
on
e, a
nd
(4
) n
itri
c o
xid
e.A
nti
diu
reti
c h
orm
on
e (
AD
H),
als
o c
alle
d v
aso
pre
ssin
,is
sec
rete
d b
y th
e p
ost
erio
r-p
itu
itar
y g
lan
d i
n r
esp
on
se t
o a
n
incr
ease
in
th
e o
smo
lari
ty o
f th
e b
loo
d p
lasm
a (s
ee c
hap
ter
46
).
Deh
ydra
tio
n, f
or
exam
ple
, cau
ses
the
blo
od
vo
lum
e to
dec
reas
e.
Osm
ore
cep
tors
in t
he
hyp
oth
alam
us
pro
mo
te t
hir
st a
nd
sti
mu
-la
te A
DH
sec
reti
on
fro
m t
he
po
ster
ior
pit
uit
ary
gla
nd
. AD
H, i
n
turn
, sti
mu
late
s th
e ki
dn
eys
to r
etai
n m
ore
wat
er i
n t
he
blo
od
, ex
cret
ing
les
s in
th
e u
rin
e. A
deh
ydra
ted
per
son
th
us
dri
nks
m
ore
an
d u
rin
ates
les
s, h
elp
ing
to
rai
se t
he
blo
od
vo
lum
e an
d
rest
ore
ho
meo
stas
is.
10
34
p
art
VII
An
ima
l Fo
rm a
nd
Fu
nct
ion
Apago PDF Enhancer
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Fig
ure
50
.17
Ba
rore
cep
tor
ne
ga
tiv
e f
ee
db
ack
lo
op
s co
ntr
ol
blo
od
pre
ssu
re.
Bar
ore
cep
tors
fo
rm t
he
affe
ren
t p
ort
ion
of
a
feed
bac
k lo
op
co
ntr
oll
ing
blo
od
pre
ssu
re.
Th
e fr
equ
ency
of
ner
ve i
mp
uls
es f
rom
th
ese
stre
tch
rec
epto
rs c
orr
elat
es w
ith
blo
od
pre
ssu
re.
Th
is
info
rmat
ion
is
pro
cess
ed i
n t
he
card
iac
cen
ter
of
the
med
ull
a. T
he
effe
ren
t p
ort
ion
of
the
loo
p i
nvo
lves
sy
mp
ath
etic
an
d p
aras
ym
pat
het
ic
ner
ves
that
in
ner
vate
th
e h
eart
. T
his
co
ntr
ol
can
rai
se o
r lo
wer
hea
rt r
ate
and
str
oke
vo
lum
e to
rai
se a
nd
lo
wer
blo
od
pre
ssu
re i
n r
esp
on
se t
o
bar
ore
cep
tors
sig
nal
ing.
W
hen
ever
th
e ki
dn
eys
exp
erie
nce
a d
ecre
ased
blo
od
flo
w,
a g
rou
p o
f ki
dn
ey c
ells
in
itia
te t
he
rele
ase
of
an e
nzy
me
kno
wn
as
ren
in i
nto
th
e b
loo
d. R
enin
act
ivat
es a
blo
od
pro
tein
, an
gio
-te
nsi
n, w
hic
h s
tim
ula
tes
vaso
con
stri
ctio
n t
hro
ug
ho
ut
the
bo
dy
wh
ile
stim
ula
tin
g t
he
adre
nal
co
rtex
to
sec
rete
ald
ost
ero
ne.
Th
is s
tero
id h
orm
on
e ac
ts o
n t
he
kid
ney
s to
pro
mo
te t
he
re-
ten
tio
n o
f N
a+ a
nd
wat
er i
n t
he
blo
od
(se
e ch
apte
r 4
6).
W
hen
exc
ess
Na+
is
pre
sen
t, l
ess
ald
ost
ero
ne
is s
ecre
ted
b
y th
e ad
ren
als,
so
th
at le
ss N
a+ is
ret
ain
ed b
y th
e ki
dn
eys.
Na+
excr
etio
n i
n t
he
uri
ne
is p
rom
ote
d b
y an
oth
er h
orm
on
e, a
tria
l n
atri
ure
tic
ho
rmo
ne.
Th
is h
orm
on
e is
sec
rete
d b
y th
e ri
gh
t at
riu
m o
f th
e h
eart
in
res
po
nse
to
str
etch
ing
cau
sed
by
an i
n-
crea
sed
blo
od
vo
lum
e. T
he
acti
on
of
atri
al n
atri
ure
tic
ho
rmo
ne
com
ple
tes
a n
egat
ive
feed
bac
k lo
op
, lo
wer
ing
th
e b
loo
d v
olu
me
and
pre
ssu
re.
N
itri
c o
xid
e (
NO
) is
a g
as p
rod
uce
d b
y en
do
thel
ial
cell
s o
f b
loo
d v
esse
ls. A
s d
escr
ibed
in
ch
apte
r 4
6, i
t is
on
e o
f a
nu
m-
ber
of
par
acri
ne
reg
ula
tors
of
blo
od
ves
sels
. In
so
luti
on
, N
O
pas
ses
ou
twar
d t
hro
ug
h t
he
cell
lay
ers
of
the
vess
el, c
ausi
ng
th
e sm
oo
th m
usc
les
that
en
case
it
to r
elax
an
d t
he
blo
od
ves
sels
to
d
ilat
e (b
eco
me
wid
er).
Fo
r o
ver
a ce
ntu
ry,
hea
rt p
atie
nts
hav
e b
een
pre
scri
bed
nit
rog
lyce
rin
to
rel
ieve
ch
est
pai
n,
bu
t o
nly
n
ow
has
it
bec
om
e cl
ear
that
nit
rog
lyce
rin
act
s b
y re
leas
ing
ni-
tric
oxi
de.
Le
arn
ing
Ou
tco
me
s R
ev
iew
50
.6Ca
rdia
c ou
tput
is th
e he
art r
ate
tim
es th
e he
art’
s st
roke
vol
ume.
As
exer
tion
incr
ease
s, c
ardi
ac o
utpu
t inc
reas
es to
mee
t the
bod
y’s
dem
ands
. Blo
od
pres
sure
dep
ends
on
card
iac
outp
ut a
nd th
e re
sist
ance
to b
lood
fl ow
due
to
cons
tric
tion
of t
he a
rter
ies.
The
blo
od v
olum
e is
regu
late
d by
ant
idiu
reti
c
horm
one,
ald
oste
rone
, and
atr
ial n
atri
uret
ic h
orm
one;
nit
ric
oxid
e ca
uses
vaso
dila
tion
that
less
ens
resi
stan
ce.
■
W
ha
t a
re t
he
con
ne
ctio
ns
be
twe
en
re
gu
lati
on
of
he
art
ra
te a
nd
bre
ath
ing
ra
te? ch
ap
ter 5
0
Th
e C
ircu
lato
ry S
yste
m
10
35
ww
w.r
av
en
bio
log
y.c
om
Apago PDF Enhancer
Ch
ap
ter
Re
vie
w
Art
eri
es
an
d v
ein
s b
ran
ch t
o a
nd
fro
m a
ll p
art
s o
f th
e b
od
y.
Art
erie
s an
d a
rter
iole
s ca
rry
oxy
gen
ated
blo
od
to
th
e b
od
y; v
ein
s an
d
ven
ule
s re
turn
deo
xyg
enat
ed b
loo
d t
o t
he
hea
rt (
see
" g
ure
50
.7).
Art
eri
al b
loo
d p
ress
ure
ca
n b
e m
ea
sure
d.
A s
ph
ygm
om
ano
met
er m
easu
res
the
pea
k (s
ysto
lic)
an
d m
inim
um
(d
iast
oli
c) b
loo
d p
ress
ure
. Blo
od
pre
ssu
re i
s ex
pre
ssed
as
the
rati
o o
f sy
sto
lic
to d
iast
oli
c.
50
.5
Ch
ara
cte
rist
ics
of
Blo
od
Ve
sse
ls
Larg
er
ve
sse
ls a
re c
om
po
sed
of
fou
r ti
ssu
e la
yers
.
Art
erie
s an
d v
ein
s co
nsi
st o
f en
do
thel
ium
, ela
stic
" b
ers,
sm
oo
th
mu
scle
, an
d c
on
nec
tive
tis
sues
(se
e "
gu
re 5
0.1
2).
Cap
illa
ries
hav
e o
nly
on
e la
yer
of
end
oth
eliu
m.
Art
eri
es
an
d a
rte
rio
les
ha
ve
ev
olv
ed
to
wit
hst
an
d p
ress
ure
.
Art
erie
s an
d a
rter
iole
s h
ave
thic
ker
mu
scu
lar
laye
r an
d m
ore
el
asti
c "
ber
s to
co
ntr
ol
blo
od
! o
w a
nd
to
rec
oil
wit
h c
han
ges
in
b
loo
d p
ress
ure
.
Ca
pil
lari
es
form
a v
ast
ne
two
rk f
or
exc
ha
ng
e o
f m
ate
ria
ls.
Cap
illa
ries
are
th
e re
gio
n o
f th
e ci
rcu
lato
ry s
yste
m w
her
e ex
chan
ge
take
s p
lace
wit
h t
he
bo
dy’
s ti
ssu
es (
see
" g
ure
50
.13
).
Ve
nu
les
an
d v
ein
s h
av
e le
ss m
usc
le in
th
eir
wa
lls.
Th
e re
turn
of
blo
od
to
th
e h
eart
th
rou
gh
vei
ns
is f
acil
itat
ed b
y sk
elet
al m
usc
le c
on
trac
tio
ns
and
on
e-w
ay v
alve
s (s
ee "
gu
re 5
0.1
4).
Th
e ly
mp
ha
tic
syst
em
ha
nd
les
" u
ids
tha
t le
av
e t
he
ca
rdio
vasc
ula
r sy
ste
m.
Flu
id f
rom
pla
sma
" lt
ers
ou
t o
f ca
pil
lari
es, t
hen
ret
urn
s vi
a th
e se
par
ate,
on
e-w
ay l
ymp
hat
ic s
yste
m (
see
" g
ure
50
.15
).
Th
e ly
mp
hat
ic s
yste
m c
on
nec
ts w
ith
th
e b
loo
d c
ircu
lati
on
at
the
sub
clav
ian
vei
ns.
Ca
rdio
vasc
ula
r d
ise
ase
s a
# e
ct t
he
de
liv
ery
sys
tem
.
Ath
ero
scle
rosi
s is
an
acc
um
ula
tio
n o
f fa
tty
mat
eria
ls i
n a
rter
ies;
it
is
on
e ca
use
of
a h
eart
att
ack,
wh
ich
res
ult
s fr
om
an
in
suf"
cie
nt
sup
ply
o
f b
loo
d t
o h
eart
mu
scle
. Str
oke
s ar
e ca
use
d b
y b
lock
age
of
the
blo
od
su
pp
ly t
o t
he
bra
in.
50
.6
Re
gu
lati
on
of
Blo
od
Flo
w
an
d B
loo
d P
ress
ure
Th
e n
erv
ou
s sy
ste
m m
ay
spe
ed
up
or
slo
w d
ow
n h
ea
rt r
ate
.
No
rep
inep
hri
ne
fro
m s
ymp
ath
etic
neu
ron
s in
crea
ses
hea
rt r
ate;
ac
etyl
cho
lin
e fr
om
par
asym
pat
het
ic n
euro
ns
dec
reas
es t
he
rate
.
Ca
rdia
c o
utp
ut
incr
ea
ses
wit
h e
xert
ion
.
Bo
th h
eart
rat
e an
d s
tro
ke v
olu
me
incr
ease
wit
h e
xert
ion
.
Th
e b
aro
rece
pto
r re
" e
x m
ain
tain
s h
om
eo
sta
sis
in b
loo
d p
ress
ure
.
Art
eria
l b
loo
d p
ress
ure
is
mo
nit
ore
d b
y b
aro
rece
pto
rs
in t
he
aort
ic a
rch
an
d c
aro
tid
art
erie
s, w
hic
h r
elay
im
pu
lses
to
th
e ca
rdia
c ce
nte
r (s
ee "
gu
re 5
0.1
7).
Blo
od
vo
lum
e is
re
gu
late
d b
y h
orm
on
es.
Blo
od
vo
lum
e re
gu
lati
on
an
d a
rter
ial
resi
stan
ce i
nvo
lves
th
e ef
fect
s o
f fo
ur
ho
rmo
nes
: (1
) an
tid
iure
tic
ho
rmo
ne,
(2
) al
do
ster
on
e, (
3)
atri
al
nat
riu
reti
c h
orm
on
e, a
nd
(4
) n
itri
c o
xid
e.
50
.1
Th
e C
om
po
ne
nts
of
Blo
od
Blo
od
pla
sma
is a
" u
id m
atr
ix.
Pla
sma
is 9
2%
wat
er p
lus
nu
trie
nts
, ho
rmo
nes
, io
ns,
pla
sma
pro
tein
s,
and
was
tes
(see
" g
ure
50
.1).
Form
ed
ele
me
nts
incl
ud
e c
ircu
lati
ng
ce
lls
an
d p
late
lets
.
Blo
od
cel
ls i
ncl
ud
e er
yth
rocy
tes
(red
cel
ls),
leu
kocy
tes
(wh
ite
cell
s),
and
pla
tele
ts. E
ryth
rocy
tes
con
tain
hem
og
lob
in f
or
oxy
gen
tra
nsp
ort
, an
d l
euko
cyte
s ar
e p
art
of
the
imm
un
e sy
stem
. Pla
tele
ts h
elp
in
itia
te
blo
od
clo
ttin
g (
see
" g
ure
50
.3).
Form
ed
ele
me
nts
ari
se f
rom
ste
m c
ell
s.
Blo
od
cel
ls a
re d
eriv
ed f
rom
plu
rip
ote
nt
stem
cel
ls i
n b
on
e m
arro
w
by
hem
ato
po
iesi
s (s
ee "
gu
re 5
0.2
).
Blo
od
clo
ttin
g is
an
exa
mp
le o
f a
n e
nzy
me
ca
sca
de.
Up
on
in
itia
tio
n o
f cl
ott
ing
, " b
rin
og
en, n
orm
ally
dis
solv
ed i
n t
he
pla
sma,
is
turn
ed i
nto
" b
rin
, an
in
solu
ble
pro
tein
, via
an
en
zym
e ca
scad
e. A
s a
wo
un
d h
eals
, th
e cl
ot
mu
st b
e d
isso
lved
.
50
.2
Inv
ert
eb
rate
Cir
cula
tory
Sy
ste
ms
Op
en
cir
cula
tory
sys
tem
s m
ov
e "
uid
s in
a o
ne
-wa
y p
ath
.
Sp
on
ges
pas
s w
ater
th
rou
gh
ch
ann
els,
an
d c
nid
aria
ns
circ
ula
te w
ater
th
rou
gh
a g
astr
ova
scu
lar
cavi
ty. S
mal
l an
imal
s ca
n u
se b
od
y ca
vity
!
uid
s fo
r ci
rcu
lati
on
.
Clo
sed
cir
cula
tory
sys
tem
s m
ov
e "
uid
s in
a lo
op
.
Clo
sed
sys
tem
s h
ave
a d
isti
nct
cir
cula
tory
! u
id, s
uch
as
blo
od
, en
clo
sed
in
ves
sels
an
d t
ran
spo
rted
in
a l
oo
p.
50
.3
Ve
rte
bra
te C
ircu
lato
ry S
yst
em
s
In $
she
s, m
ore
e%
cie
nt
circ
ula
tio
n d
ev
elo
pe
d c
on
curr
en
tly
wit
h g
ills
.
Fis
hes
hav
e a
lin
ear
hea
rt w
ith
tw
o p
um
pin
g c
ham
ber
s to
in
crea
se
ef"
cien
cy o
f b
loo
d !
ow
th
rou
gh
th
e g
ills
; fr
om
th
e g
ills
, th
e b
loo
d
mo
ves
into
th
e re
st o
f th
e b
od
y (s
ee "
gu
re 5
0.5
).
In a
mp
hib
ian
s a
nd
mo
st r
ep
tile
s, lu
ng
s re
qu
ire
d a
se
pa
rate
cir
cula
tio
n.
Pu
lmo
nar
y ci
rcu
lati
on
pu
mp
s b
loo
d t
o t
he
lun
gs,
an
d s
yste
mic
ci
rcu
lati
on
pu
mp
s b
loo
d t
o t
he
bo
dy.
Am
ph
ibia
n h
eart
s h
ave
two
atr
ia t
hat
sep
arat
e b
loo
d !
ow
to
th
e lu
ng
s an
d b
od
y, a
nd
a s
ing
le v
entr
icle
("
gu
re 5
0.6
). T
he
hea
rt o
f m
ost
re
pti
les
has
a s
eptu
m t
hat
par
tial
ly d
ivid
es t
he
ven
tric
le, r
edu
cin
g
mix
ing
of
blo
od
fro
m t
he
atri
a.
Ma
mm
als
, bir
ds,
an
d c
roco
dil
ian
s h
av
e t
wo
co
mp
lete
ly s
ep
ara
ted
ci
rcu
lato
ry s
yste
ms.
Th
e fo
ur-
cham
ber
ed h
eart
has
tw
o v
entr
icle
s (s
ee "
gu
re 5
0.7
). T
he
extr
eme
sim
ilar
ity
bet
wee
n t
he
hea
rt o
f m
amm
als
and
bir
ds
is a
n
exam
ple
of
con
verg
ent
evo
luti
on
.
50
.4
Th
e F
ou
r-C
ha
mb
ere
d H
ea
rt
an
d t
he
Blo
od
Ve
sse
ls
Th
e c
ard
iac
cycl
e d
riv
es
the
ca
rdio
vasc
ula
r sy
ste
m.
Th
e u
nid
irec
tio
nal
! o
w o
f b
loo
d t
hro
ug
h t
he
hea
rt i
s m
ain
tain
ed
by
two
atr
iove
ntr
icu
lar
valv
es (
see
" g
ure
50
.9).
Du
rin
g d
iast
ole
ve
ntr
icle
s re
lax
and
atr
ia c
on
trac
t; d
uri
ng
sys
tole
ven
tric
les
con
trac
t.
Co
ntr
act
ion
of
he
art
mu
scle
is in
itia
ted
by
au
torh
yth
mic
ce
lls.
Co
ntr
acti
on
is
init
iate
d b
y th
e S
A n
od
e, a
nat
ura
l p
acem
aker
, an
d
imp
uls
es t
hen
tra
vel
to t
he
AV
no
de
(see
" g
ure
50
.10
).
10
36
p
art
VII
An
ima
l Fo
rm a
nd
Fu
nct
ion