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3
Location of Heart
• posterior to sternum• medial to lungs• anterior to vertebral column• base lies beneath 2nd rib• apex at 5th intercostal space• lies upon diaphragm
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Heart Chambers
Right Atrium• receives blood from
• inferior vena cava• superior vena cava• coronary sinus
Left Atrium• receives blood from
pulmonary veins
Right Ventricle• receives blood from
right atrium
Left Ventricle• receives blood from
left atrium
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Cardiac Cycle
Atrial Systole/Ventricular Diastole
• blood flows passively into ventricles
• remaining 30% of blood pushed into ventricles
• A-V valves open/semilunar valves close
• ventricles relaxed
• ventricular pressure increases
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Cardiac Cycle
Ventricular Systole/Atrial diastole
• A-V valves close
• chordae tendinae prevent cusps of valves from bulging too far into atria
• atria relaxed
• blood flows into atria
• ventricular pressure increases and opens semilunar valves
• blood flows into pulmonary trunk and aorta
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Heart Sounds
Lubb• first heart sound • occurs during ventricular systole• A-V valves closing
Dupp• second heart sound• occurs during ventricular diastole• pulmonary and aortic semilunar valves closing
Murmur – abnormal heart sound
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Cardiac Muscle Fibers
Cardiac muscle fibers form a functional syncytium
• group of cells that function as a unit• atrial syncytium• ventricular syncytium
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Electrocardiogram
• recording of electrical changes that occur in the myocardium• used to assess heart’s ability to conduct impulses
P wave – atrial depolarizationQRS wave – ventricular depolarizationT wave – ventricular repolarization
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Regulation of Cardiac Cycle
Autonomic nerve impulses alter the activities of the S-A and A-V nodes
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Regulation of Cardiac Cycle
• physical exercise• body temperature• concentration of various ions
• potassium• calcium
• parasympathetic impulses decrease heart action• sympathetic impulses increase heart action• cardiac center regulates autonomic impulses to the heart
Additional Factors that Influence HR
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Blood Vessels
• arteries• carry blood away from ventricles of heart
• arterioles• receive blood from arteries• carry blood to capillaries
• capillaries• sites of exchange of substances between blood
and body cells• venules
• receive blood from capillaries• veins
• carry blood toward ventricle of heart
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Arteries and Arterioles
Artery• thick strong wall • endothelial lining• middle layer of smooth
muscle and elastic tissue• outer layer of connective
tissue• carries blood under
relatively high pressure
Arterioles• thinner wall than artery• endothelial lining• some smooth muscle
tissue• small amount of
connective tissue• helps control blood flow
into a capillary
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Arteriole
• smallest arterioles only have a few smooth muscle fibers• capillaries lack muscle fibers
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Capillaries• smallest diameter blood vessels• extensions of inner lining of arterioles• walls are endothelium only• semipermeable• sinusoids – leaky capillaries
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Regulation of Capillary Blood Flow
Precapillary sphincters
• may close a capillary
• respond to needs of the cells
• low oxygen and nutrients cause sphincter to relax
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Exchange in the Capillaries• water and other substances leave capillaries because of net outward
pressure at the capillaries’ arteriolar ends
• water enters capillaries’ venular ends because of a net inward pressure
• substances move in and out along the length of the capillaries according to their respective concentration gradients
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Venules and Veins
Venule• thinner wall than arteriole• less smooth muscle and elastic tissue than arteriole
Vein• thinner wall than artery• three layers to wall but middle layer is poorly developed• some have flaplike valves• carries blood under relatively low pressure• serves as blood reservoir
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Arterial Blood Pressure
Blood Pressure – force the blood exerts against the inner walls of the blood vessels
Arterial Blood Pressure• rises when ventricles contract• falls when ventricles relax• systolic pressure – maximum pressure• diastolic pressure – minimum pressure
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Control of Blood Pressure
Controlling cardiac output and peripheral resistance regulates blood pressure
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Control of Blood Pressure
If blood pressure rises, baroreceptors initiate the cardioinhibitory reflex, which lowers the blood pressure
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Venous Blood Flow
• not a direct result of heart action
• dependent on • skeletal muscle
contraction• breathing• venoconstriction
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Central Venous Pressure
• pressure in the right atrium
• factors that influence it alter flow of blood into the right atrium
• affects pressure within the peripheral veins
• weakly beating heart increases central venous pressure
• increase in central venous pressure causes blood to back up into peripheral vein
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Pulmonary Circuit
• consists of vessels that carry blood from the heart to the lungs and back to the heart
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Blood Flow Through Alveoli
• cells of alveolar wall are tightly joined together• the high osmotic pressure of the interstitial fluid draws
water out of them
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Systemic Circuit
• composed of vessels that lead from the heart to all body parts (except the lungs) and back to the heart
• includes the aorta and its branches
• includes the system of veins that return blood to the right atrium
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Cerebral Arterial Circle• Circle of Willis• formed by anterior and posterior cerebral arteries, which
join the internal carotid arteries
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Veins from the Abdominal Viscera:Hepatic Portal Vein
Hepatic portal vein drains one set of capillaries and leads to another set
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Life-Span Changes• cholesterol deposition in blood vessels
• heart enlargement
• death of cardiac muscle cells
• increase in fibrous connective tissue of the heart
• increase in adipose tissue of the heart
• increase in blood pressure
• decrease in resting heart rate