biol233 - outline 5 (circulation and gas exchange)
TRANSCRIPT
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Circulation and Gas Exchange:
Readings:
Russell et al:
Chapter 37 pp. 891-896, 899-906
Chapter 42 pp. 1039-1053
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Main Topics:
Circulation:Open and closed circulatory systems
Cardiac cycle
Vasculature
Gas Exchange:Terminology: volume% and partial pressures
Ficks diffusion law
Water breathing
Air breathing
Gas transport (transport of O2 and CO2)
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Animals need to supply oxygen to the
mitochondria of the cells for oxidativemetabolismand remove waste product of
metabolism CO2.
Circulatory system provides the avenue fortransport of these gases
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Or, they have an extensive tracheal network which
allows gases to penetrate deep within body example:insects
They still have a cardiovascular
system, but its hardly used.
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Most animals, however, rely on a circulatory
system to transport gases.
Two types: closed and opened
Closed Circulating fluid (blood) is completely enclosed
within a series of blood vessels. At no time does theblood directly contact other body fluids.
Open circulating fluid (hemolymph) is allowed to enter
the body cavity and come into contact with other bodyfluids or tissue s themselves.
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Evolution of the closed circulatory system:
Given the colours (red and blue) refer to oxy- and
deoxygenated blood, what do you notice about fish heart
vs. the hearts of other vertebrates?
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Evolution of the closed circulatory system:
Fish single circuit
one atrium- one ventricle:
They pump deoxygenated blood into
the gill. In the gil, there is exchange of
O2 and CO2 Blood becomes oxygenated as it travels
through the gill
Oxygenated blood is transported to
tissues exchange of O2 and CO2 at
tissues, which deoxygenated the blood,
which returns to the heart.
Known as in-series circulatory system.
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Evolution of the closed circulatory system:
Amphibians (frog) dual circuits:
Two atria one ventricle
(Air breathers)
Known as in-parallel circulatory system.
Two atria one for deoxygenated blood, and
one for oxygenated blood.
Single ventricle pumps both oxygenated and
deoxygenated blood.
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Evolution of the closed circulatory system:
Birds, reptiles and mammals dual circuits:
Two atria-two ventricles
Turtles, lizards
The ventricle has some
septa that are
beginning to divide theventricle into two sides.
Crocdiles septum is
more apparent.
Birds/Mammals total
sepration of R and L
ventricles
Purple vessel = Shunt
Shunt of blood away from lungs during
a dive to reduce blood thats not being
ventilated.
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Evolution of the closed circulatory system:
Birds, reptiles and mammals dual circuits:
Two atria-two ventricles *Note: separation of
these two circuits.
Pulmonary circuit
- Low resistance- Low pressure
Systemic circuit
- High resistance
- High pressure
- Many more and more
extensive blood
vessels.
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Cardiac cycle: filling and emptying of the heart
Open circulatory system: Example crayfish or lobster:
Blood (hemolymph) flows into pericardial cavity
(surrounding heart) via openings in cavity
Hemolymph enter the ostia of heart during filling(diastole)
Heart muscle contracts (systole) ostia close and
blood is ejected out the arteries.
Heart is filledbysuctionValved ostia artery
^ Suspensory ^
ligament
Paricardial sac (rigid)
Paricardial cavity
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Cardiac cycle: filling and emptying of the heart
Open circulatory system: Example crayfish or lobster:
Suspensory ligaments stretch
Ostia close
Contraction forces blood out the arteries.
(Ostia is valved to prevent backflow)
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Cardiac cycle: filling and emptying of the heart
Steps in the cardiac cycle of vertebrate heart: example humanFilling occurs under pressure
rather than suction.
Diastole: pressure in atria is
greater than pressure in
ventricles get filling of
ventricles.
AV valves between atria
and ventricles which opento allow blood to fill
ventricle.
Then AV valves close to
empty ventricle.
diastole
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Cardiac cycle: filling and emptying of the heart
Steps in the cardiac cycle of vertebrate heart: example human
Systole -- Blood is ejected out
of ventricles into:
Pulmonary artery (right
side of heart) Or Aorta (left side of heart)
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Control of cardiac cycle:
Neurogenic vs. myogenic hearts
Example of neurogenic heart crustacean heart
Control is via a nerve ganglion (cardiac ganglion) that sits on
top of the heart.
It is not muscle tissue! It is nerve tissue.
This sets the pace of the heart.
Removal of cardiac ganglion heart will not beat.
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Control of cardiac cycle:
Neurogenic vs. myogenic hearts
Example of myogenic heart all vertebratehearts
The pace is set by modified muscle cells called pacemakers.
This includes SA node (primary pacemaker) and AV node
(secondary)
Heart will still beat on its own even if all neural
connections are removed.
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Control of cardiac cycle:
Pacemakers of myogenic hearts
Brown area = electrical excitation, starting at SA node. Excites
all the atria, which stimulates the AV node which excites theventricles.
AV node delay in wave of excitation so that the ventricle
doesnt contract at the same time as atria (ventricle wouldnt
have enough time to fill)
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Vasculature:
Closed system Composed of: Aorta,
arteries, arterioles,
capillaries, venules, veins
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Vessels in cross-section :
In systemic circuit:
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Surface area is
greatest at level ofcapillaries area of
nutrient and gas
exchange
Velocity of flow
slowest in capillaries
facilitates nutrient and
gas exchange
Artery Vein
ArteriolesCapillaries
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Control of flow to various capillary beds controlled by:
Vasodilation or vasoconstriction of arteriolar smoothmuscle
Opening or closing of pre-capillary sphincters
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Agents that cause arterioles and capillaries to open:
Increase in tissue fluid lactic acid Decrease in tissue fluid oxygen pressure
Increase in tissue fluid CO2 pressure
Decrease in tissue fluid pH
Ex. In a runner, more oxygenated blood goes to the limbs that
need it the most (legs) because of the above agents.
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Gas exchange O2 and CO2
Main Topics:
Terminology: volume% and partial pressuresFicks diffusion law
Water breathing
Air breathing
Gas transport (transport of O2 and CO2)
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Concepts and terms
Volume % - fraction of a gas in an atmosphere dry air
is 21% oxygen, 79% nitrogen, 0.03% CO2 (same
regardless of altitude)
Partial pressure that part of the atmospheric
pressure attributed to a particular gas
Is found by multiplying the atmospheric pressure bythe fraction of gas in the atmosphere
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Concepts and terms
For example:
the atmospheric press. at sea level is 760 mmHg
therefore the partial pressure of oxygen in theatmosphere is 0.21 x 760 = 160 mm Hg;
partial pressure of CO2 is 0.23 mm Hg;
partial pressure of nitrogen is 600 mm Hg
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In Calgary; atmospheric press. = 670 mmHg
PO2 = 141 mmHgPCO2 = 0.20 mmHg
Atmospheric press. at top ofMt. Everest = 250 mmHgPO2 = 53 mm Hg
All gas exchange in the simply gases diffusing down aconcentration gradient.
P = partial pressure
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All gas exchange occurs across a moist surface (whether aquatic or
terrestrial) and depends on Ficks Law of diffusion
Rate of diffusion depends on:mLO2/unit time
Or
mLCO2/unit time
To facilitate rate of diffusion:
1. Large surface area for gas
exchange
2. Reducing thickness of membrane
across which gas is going tomove (ex. Flatworms have very
thin skin, gases just diffuse through
membrane)
3. Keep difference between partial pressure to favour
movement of gas in that direction
Surface area^
of gas exchange
surface
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Organisms one or two cell-layers thick (like cnidarians)
do not need special respiratory organs gases simplydiffuse across cell membranes..
but multi-layered animals have to have a respiratory
organ of some sort.
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Breathing in aquatic environments:
Gills may be external (stick out into environment) or
internal (enclosed by some sort of covering)External: no energy is wasted trying to pump water over surface of
gill when water just glides over gills. But gills become exposed to
damage or predation.
Internal: gills are not as subject to damage, however, there needsto be a device to pump water over the gills.
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Internal gills have to be ventilated.
Cavity containing gills is ventilated by drawing or forcingwater over gills.
Gill bailer sits at the front of the gill chamber and acts like a
paddle so that water is sucked up over surface of the gills, and
water is collected and forced out through the front of theanimal. A current is created by moving the little gill bailer at
the front of the animal.
Gills are protected.
But a lot of energy is required
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For example: In crayfish, scaphognathite (gill bailer)
creates a negative pressure in gill chamber thus drawing
water over gills.
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In fish, operculum and mouth are used to move water
over gillsGreen bar = floor of mouth which can move up
and down. Flaps allow water to come in and outof mouth.
Suction phase lower floor of mouth, opens
mouth and water flows into gill.
Force pump floor of mouth moves up, squeeze
fluid out the operculum and mouth closes.
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Anatomy of fish gill:
Gill arch composed of stack of gillfilaments each gill filament has
secondary lamellae
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Countercurrent flow of water over gill:
advantage: allows for continuous diffusion gradient all along
surface of secondary lamellae.
% saturation with O2
% saturation with O2
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Breathing in terrestrial environment:
Advantages over breathing water
1. There is more O2/unit volume in air than in water at the
same temperature. Three times more O2 available in air than
in water.
2.Air is less dense, and therefore less energy is
required to move air over gas exchange surface
Problem with breathing air : desiccation (losing vapor)
Solution : Internal the gas exchange surface.
Humidify the air as it enters the animal.
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Air breathing: positive pressure ventilation of the lungs
Example: frogsInhalation:
1. Open nostrils and lower floor of
buccal cavity air moves into
buccal cavity. Glottis is closed.
2. Close nostrils and raise floor of
buccal cavity air is forced intolung. Glottis is open
(Buccal cavity is like the floor of the
mouth)
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Exhalation: elastic recoil of lung wall
forces air out of lung and through
mouth and nostrils
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Air breathing: negative pressure ventilation of the lungs
Negative pressure ventilation examples mammals and
birds ..
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Pressure more
negative than
atmosphere
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Negative pressure ventilation: in mammals
Inhalation:
1. Outward movement of rib cage (by contraction of
intercostals muscles) and diaphragm contraction expands
thorax and lung creating sub-atmospheric press. in lung
2. Air flows into lung via nasal passages and mouth because
pressure in expanding lung is less than atmospheric
3. Eventually air flow stops at point of max expansionbecause as the lung fills with air, pressure diff. between
lung and atmosphere becomes zero.
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Negative pressure ventilation: in mammals
Exhalation:
1. Intercostal muscles relax and lung recoils.
2. Air is forced out because lung pressure exceeds
atmospheric pressure.
In mammals tidal flow of air means some exhaled air is
always mixed with fresh air
Old dead air is mixed with fresh air, so air found in lung has a
lower partial pressure than in the atmosphere.
Rapid, shallow breathing is not as good as deep, slow
breathing.
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Negative pressure ventilation: in birds
Lung is a series of parallel rigid
tubes (parabronchi) connected
to air sacs on either end.
Air sacs expand and contract
with each ventilation cycle.
Air continually moves across
the lung
The lung does not expand orcontract! It stays the same size.
The air sacs are what expand
and contract.
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Negative pressure ventilation: in birds
Inhalation:
1. Outward movement of thorax (by contraction of
intercostals muscles) expands air sacs creating sub-
atmospheric pressure in air sacs.
2. Fresh air flows into posterior air sacs via nasal passages
and trachea.
3. Air in lungs is sucked into anterior air sacs.
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Negative pressure ventilation: in birds
Exhalation:
1. Fresh air (high in oxygen) from posterior air sacs moves
through the lung
2. Air in anterior air sacs is forced out of trachea and nasal
passages
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It takes two cycles (i.e.
two inspirations and
two expirations) for anair molecule to move
though both air sacs
and lung.Red = fresh air
When we breathe in, fresh air
goes to posterior sacs.
On the next expiration, air is
forced over the parabronchi
(parallel lines).On the next inspiration, the
air that has gone over
oxygenation, it gets sucked
into anterior sacs.
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Insects - dont have lungs or gills - use trachea to breath
Trachea series of blind-ended tubes that lead from the surface of
the abdomen to muscle tissue deep within the insect.
The opening is guarded by a spiracle which can be open or closed
when desired.
No circulatory system is necessary to deliver oxygen to tissuebecause trachea terminate right in the tissue.
Ventilation of gas exchange surface in Insects:
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Ventilation of gas exchange surface in Insects:
Tube opens up, and oxygen simplydiffuses through tube and directly
to the cells that need the oxygen
supply.
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Larger insects can increase ventilation by contracting and relaxing
abdominal muscles which squeeze the tracheal system and force air
through it.
Flight muscles increase tracheal ventilation in flying insects during
flight.
Contracting and
relaxing wing
muscles facilitates
squeezing the
trachea andincreases
ventilation. The
air moves faster.
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Gas transport:
Except for the insects that use a tracheal system to supplyoxygen to their tissues, most animals transport gases using a
circulatory system and have a respiratory pigment in the
circulating fluid that allows them to transport more gas than can
simply dissolve in the fluid.
Gas transport in animals with no resp. pigment gases are
dissolved in circulating fluid
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Gas transport:
Gas transport in animals with respiratory pigment gases aredissolved in circulating fluid, but much larger % of gas transport
via resp. pigment.
example: human blood carries about 3 mL O2
/L dissolved in
blood plasma
but as much as 200 mL of oxygen can be carried by
hemoglobin/L of blood.
therefore 1.5% of oxygen is dissolved in blood plasma and 98.5
% is carried bound to hemoglobin
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Gas transport:
Respiratory pigments include
hemoglobin, hemerythrin, hemocyanin, chlorocruorin
All vertebrates use hemoglobin as their resp.
Dont memorize all these. Just know that hemoglobin is the
most common pigment, and that there are more than one type
of respiratory pigment.
^red ^purple ^blue ^green
when oxygenated
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Gas transport:
Hemoglobin structure: made up of four protein subunits calledglobulins (alpha and beta) each with a porphyrin ring containing
iron
Four porphyrin rings each containing Fe+2 that binds a
molecule of oxygen
porphyrin ring = green thing
Curly blue and red things are
proteins.
Iron binds oxygen.
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Gas transport:
Oxygen binding:
Somewhere from 30-60 Po2, % saturation of hemoglobin
increases rapidly.
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Gas transport:
Oxygen binding:
Between
30-60
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Gas transport:
Oxygen binds cooperatively to hemoglobin (Hb) i.e. binding ofone molecule facilitates the binding of more to the Hb hence
the rapid increase in binding between 20 and 60 mm Hg.
In lung:PO2 = 100mmHg
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Gas transport:
At level of gas exchange surface (where the PO2 is 100 mmHg) Hb quickly becomes saturated with oxygen;
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Gas transport:
Bohr shift helps unload even more oxygen Increased acidity = lower pH in tissue = lower pH in blood.Red line = normal arterial blood pH
Blue line = pH of blood after picking up acid from tissues (Venus blood)
Venus blood picks up CO2, lactic acid, and other organic acids from
the tissue, which lowers the blood pH.
Increased blood CO2 =
decreased blood pH
% saturation ofhemoglobin at the
lung is not affected by
the Bohr shift.
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Gas transport:
CO2 is also carried by Hb (and is also dissolved in plasma or asHCO3
-) from tissues to gas exchange surface.
CO2 diffuses into red blood cell. Inside
the red blood cell,
CO2 + H2O H2CO3H2CO3 H+ + HCO3-
HCO3- diffuses into blood plasma.
At the lung, this whole processes is
reversed.