vertebrates circulatory system #2

8/7/2019 Vertebrates Circulatory System #2

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Bird Circulatory System



` Large 4-chambered heart of two atria and two

ventricles

` Completely separate pulmonary and systemic

circuits

` Right aortic arch leads to the dorsal aorta

` Main blood vessels

- arteries and veins



`

2 jugular veins in neck are connected by a crossvein (an adaptation for shunting blood from one

jugular to the other as the head rotates)

` Brachial and pectoral arteries to the wings andbreast are unusually large



` Heartbeat is extremely fast, there is an inverse

relationship between heart rate and body weight

Ex:

turkey- heart rate of about 93 beats per

minute

chicken ± heart rate of 250 beats per minute



` Blood pressure is roughly equivalent to that inmammals of similar size

` Bird¶s blood contains nucleated, biconvex

erythrocytes

Phagocytes, or mobile amoeboid cells are

very active and efficient in birds in repairing

wounds and destroying microbes



` Muscular organ located between the lungs directly

behind the sternum

` Is tilted so that the apex is oriented to the left

` Myocardium, consists of cardiac muscle tissue



`

Pericardium, a thick membranous sac thatsurrounds the myocardium

` Inner surface of heart is lined with endocardium,

which consists of connective tissue and

endothelial tissue

` Septum, a wall that separates the right side from

the left side



` 4 chambers:

2 upper thin-walled atria have auricles

2 lower chambers are thick-walled ventricleswhich pump the blood

` 4 valves which direct flow of blood andprevent its backward movement:

two valves that lie between atria andventricles are the atrioventricular valves

= supported by the chordae tendineae



Tricuspid valve

± atrioventricular valve on the right side

± has three flaps

Bicuspid valve

± atrioventricular valve on the left side

± has two flaps



remaining two valves are semilunar valvesbetween ventricles and attached vessels

Pulmonary semilunar valve

- lies between right ventricle andpulmonary trunk

Aortic semilunar valve

- lies between left ventricle and aorta



Internal and External Structure of the Human Heart



` Superior vena cava and inferior vena cava,

which carry O2-poor blood, enter the rightatrium

` Right atrium sends blood through the

tricuspid valve to the right ventricle



` blood is then pumped into the pulmonary

trunk, which divides into two pulmonary

arteries, one leading to each lung

` 4 pulmonary veins, which carry O2-rich blood,

enter the right atrium

` left atrium sends blood through bicuspid

valve to the left ventricle

` blood is pumped through the aorta to thebody proper



-called a cardiac cycle

- first 2 atria contract at the same time;

2 ventricles contract; all chambers relax- heart beats about 70 times a minute, lasts

about 0.85 second

� Systole (contraction)

� Diastole (relaxation)



Intrinsic control of heartbeat

causes rhythmical contraction of atria and ventricles

Nodal tissue located in 2 regions of the heart

SA (sinoatrial) node/pacemaker

- located in the upper dorsal wall of right atrium

- Initiates heartbeat; automatically sends out anexcitation impulse every 0.85 second that causes

atria to contract



AV (atrioventricular) node

- located in base of right atrium

- slight delay of impulses; allows atria to finish

contraction before ventricles begin contraction

- signal travels through the 2 branches of AV bundle

before reaching numerous Purkinje fibers

- AV bundle and Purkinje fibers consists of

specialized cardiac muscle fibers that efficiently

cause ventricles to contract



Extrinsic control of heartbeat

- cardiac control in medulla oblongata connects to theheart by two sets of nerves

- Impulses sent along the parasympathetic vagusnerves, apply a braking action to the heart rate

- and impulses sent along the sympathetic nerves,speed it up

- Parasympathetic system decreases S A and AV

nodal activity when we are inactive

- sympathetic system increases S A and AV nodalactivity when we are active or excited



Stages in cardiac cycle

- atria contract, ventricles are relaxed and filling

with blood

- when ventricles contract, atrioventricular valves

are closed, and blood is pumped into pulmonary

trunk and aorta

-heart is relaxed, both atria and ventricles arefilling with blood



` Systemic circuit

- path of blood begins in left ventricle, which

pumps blood into aorta

- coronary arteries are the first branches off the aorta

- venules converge to form cardiac veins,

which empty into the right atrium



` In arteries Blood pressure (pressure of blood against the wall of a

blood vessel)

x Systolic pressure

x During e jection of blood from heart

x Diastolic pressure

x Occurs while heart ventricles are relaxing



` Blood pressure decreases with distance fromthe left ventricle

Increases the total cross-sectional area of blood

vessels

Causes the blood velocity to gradually decrease as it

flows toward the capillaries



Human Circulatory System



` In capillaries

Blood moves even more slowly

Slow progress allows time for substances to be

exchanges between blood in capillaries and

surrounding tissues

` In veins

Blood pressure is minimal



Venous return depends upon 3 factors: skeletal

muscle contraction, presence of valves and veins,

and respiratory movements

` Skeletal muscle contraction

They compress the weak walls of the veins

Causes blood to move past the next valve; cannot flowbackward



` Respiration movement

Thoracic pressure falls and abdominal pressure rises

Aids the flow of venous blood back to the heart (flows

in direction of reduced pressure)

Blood velocity increases slightly in venous vessels due

to progressive reduction in cross-sectional area



` Cardiovascular system has 3 types of blood

vessels:

1. Arteries ± carry blood away from the heart to the

capillaries

2. Capillaries ± permit exchange of material with the

tissues

3. Veins ± return the blood from the capillaries to the

heart



1. Arteries

- aorta (largest artery, 25 mm wide)- arterial wall has 3 layers:

inner layer

± endothelium with connectivetissue basement membrane;

± contains elastic fibers



Middle layer

- thickest layer

- consists of smooth muscle that can contract

to regulate blood flow and blood pressure

Outer layer - fibrous connective tissue near middle layer,

but becomes loose connective tissue



2. Capillaries

- one-cell thick walls composed of endotheliumwith basement membrane

- capillary beds are present in all regions of body

-important part because exchange of substancestakes place across thin walls



` Capillary exchange

Capillaries are quite permeable to small ions,nutrients, and water

Blood pressure within a capillary tends to force

fluids out through capillary walls and into

surrounding interstitial space

a protein-free filtrate crosses for carrying

away metabolic wastes

colloid osmotic pressure, draws water backinto capillary from tissue fluid



Amount of fluid filtered fluctuates and some

excess fluid remains in interstitial spaces

This excess is collected by lymph capillaries

and lymph is returned to circulatory system

3. Veins

- take blood from the capillaries to the heart



walls have the same 3 layers of arteries butthinner than that of the artery

have valves that allows blood to flow only

toward the heart when open and preventbackward flow of blood when closed; found in

veins that carry blood against force of gravity

Acts as blood reservoir



Chicken¶s Heart Human¶s Heart



` Hickman, C. P., Larson, A., & Roberts, L.S.

(2004). Activity of life. In Integrated principles

of zoology. (12 th ed.). (pp. 662- 666). New York:

McGraw-Hill Companies, Inc.

` Circulatory System (n.d). Retrieved on February

23, 2010 from http://www.ama-

assn.org/ama1/pub/upload/images/446/circulationgeneral.gif



Kosmix� Corporation (2010) Human H eart

Pict u

re. Retrieved on February 23, 2010 fromhttp://www.righthealth.com/topic/

Human_ Heart_ Pictures/overview/wiki_deta

iled?modp=Human_heart

vertebrates circulatory system #2

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