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Physiology
The Circulatory System
Behrouz Mahmoudi
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The Closed Circulatory System
•Humans have a closed circulatory system, typical of
all vertebrates, in which blood is confined to vessels
and is distinct from the interstitial fluid.
–The heart pumps blood into large vessels
that branch into smaller ones leading into the
organs.
–Materials are exchanged by diffusion between the
blood and the interstitial fluid bathing the cells.
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•Three Major Elements
• – Heart, Blood Vessels, & Blood
•1. The Heart- cardiac muscle tissue
–highly interconnected cells
–four chambers
•Right atrium
•Right ventricle
•Left atrium
•Left ventricle
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Circuits
•Pulmonary circuit
–The blood pathway
between the right side of
the heart, to the lungs,
and back to the left side
of the heart.
•Systemic circuit
–The pathway between
the left and right sides of
the heart.
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Blood Vessels –Arteries arterioles move away from the heart
•Elastic Fibers
•Circular Smooth Muscle
–Capillaries – where gas exchange takes place.
•One cell thick
•Serves the Respiratory System
–Veins Venules moves towards the heart
•Skeletal Muscles contract to force blood back from legs
•When they break - varicose veins form
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The Blood
A. Plasma
Liquid portion of the blood. Contains clotting factors,
hormones, antibodies, dissolved gases, nutrients and
waste
B. Erythrocytes - Red Blood
Cells
•Carry hemoglobin and oxygen.
Do not have a nucleus and live
only about 120 days.
•Can not repair themselves.
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C. Leukocytes – White Blood cells
–Fight infection and are formed in the bone marrow
–Five types – neutrophils, lymphocytes, eosinophils, basophils, and
monocytes.
D. Thrombocytes – Platelets.
•These are cell fragment that
are formed in the bone
marrow from megakaryocytes.
•Clot Blood by sticking
together – via protein fibers
called fibrin.
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Functions of the Heart
• Generating blood pressure
• Routing blood
– Heart separates pulmonary and systemic
circulations
• Ensuring one-way blood flow
– Heart valves ensure one-way flow
• Regulating blood supply
– Changes in contraction rate and force match
blood delivery to changing metabolic needs
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Pericardium
Coronary artery
The vessels that deliver oxygen-rich blood to
the myocardium are known as coronary
arteries. The vessels that remove the
deoxygenated blood from the heart muscle are
known as cardiac veins
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Heart Wall
• Three layers of tissue
– Epicardium: This serous membrane of smooth
outer surface of heart
– Myocardium: Middle layer composed of cardiac
muscle cell and responsibility for heart contracting
– Endocardium: Smooth inner surface of heart
chambers
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Heart Valves
•Atrioventricular
–Tricuspid; prevent back flow of blood into the right atrium.
–Bicuspid or mitral; lie between the atria and the ventricles of the heart and
control the flow of blood.
•Semilunar
–Aortic; When the pressure in the left ventricle rises above the pressure in the
aorta, the aortic valve opens, allowing blood to exit the left ventricle into the aorta.
–Pulmonary; At the end of ventricular systole, when the pressure in the right
ventricle falls rapidly, the pressure in the pulmonary artery will close the pulmonary
valve
•Prevent blood from flowing back
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Systemic and Pulmonary
Circulation
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Cardiac Muscle
•
•
•
•
•
Elongated, branching cells containing 1-2 centrally located nuclei
Contains actin and myosin myofilaments
Intercalated disks: Specialized cell-cell contacts
Desmosomes hold cells together and gap junctions allow action potentials
Electrically, cardiac muscle behaves as single unit
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Conducting System of Heart
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Original Impulses from S-A Node
The electrical impulses are normally generated by a group of
specialized pacemaker cells at sinoatrial (SA) node.
SA node
- located in the right
atrial wall, just inferior
to the entrance of the
superior vena cava.
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Conduction of Action Potentials from Cell to Cel
through gap junctions in intercalated discs
(electrical synapses)
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Conduction in Atria
The electrical impulses from SA node spread through the entire
right and left atrial muscle mass, triggering contraction of the right
and left atrium.
- Each electrical impulse can trigger cardiac muscle contraction normally
only once.
- A normal heart generates 60 to 100 impulses in 1 minute at resting
state.
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EELECTROCARDIOGRAPHY
((ECG)
the recording of electrical activities of the heart via
electrodes placed on body surface.
QRS: potential changes during depolarization of ventricles
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Regulation of the Heart
• Intrinsic regulation: Results from normal
functional characteristics, not on neural or
hormonal regulation
– Starling’s law of the heart
• Extrinsic regulation: Involves neural and
hormonal control
– Parasympathetic stimulation
• Supplied by vagus nerve, decreases heart rate, acetylcholine secreted
– Sympathetic stimulation
• Supplied by cardiac nerves, increases heart rate and force of contraction,
epinephrine and norepinephrine released
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Baroreceptor and Chemoreceptor
Reflexes
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Effects of Aging on the Heart
• Gradual changes in heart function, minor under
resting condition, more significant during exercise
• Hypertrophy of left ventricle
• Maximum heart rate decreases
• Increased tendency for valves to function
abnormally and arrhythmias to occur
• Increased oxygen consumption required to pump
same amount of blood
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