Vertebrates Circulatory System #2
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Transcript of Vertebrates Circulatory System #2
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Bird Circulatory System
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` 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
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`
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
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` 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
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` 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
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` 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
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`
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
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` 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
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Tricuspid valve
± atrioventricular valve on the right side
± has three flaps
Bicuspid valve
± atrioventricular valve on the left side
± has two flaps
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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
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Internal and External Structure of the Human Heart
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` 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
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` 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
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-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)
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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
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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
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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
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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
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` 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
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` 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
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` 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
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Human Circulatory System
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` 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
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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
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` 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
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` 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
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1. Arteries
- aorta (largest artery, 25 mm wide)- arterial wall has 3 layers:
inner layer
± endothelium with connectivetissue basement membrane;
± contains elastic fibers
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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
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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
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` 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
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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
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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
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Chicken¶s Heart Human¶s Heart
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` 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