1. Chapter 16 The Cardiovascular System: Blood Vessels and Circulation

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Blood Vessels
Arteries: carry blood away from heart
Elastic: large
Arterioles: distribution to capillaries
Their smooth muscle helps regulate blood pressure
Capillaries: thin-walled for diffusion of oxygen and nutrients to cells
Veins: carry blood back to heart
Venules: from capillaries
Veins from tissues  vena cava  heart
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3. Blood Vessel Structure: Arteries, Veins
Three layers (tunica): external, middle, inner
Arteries: thicker tunica media
Elastic tissue and/or muscle
Arterioles
Arterioles: control blood pressure
Veins
Larger lumen, thinner walls
Valves to prevent backflow
Venules
Venules: very thin, no valves
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4. Blood Vessel Structure: Arteries, Veins
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5. Blood Vessel Functions
Muscular arteries, arterioles regulate flow from the heart to the body
Arterioles adjust flow into capillaries
Capillaries: sites of gas and nutrient/waste exchange
Veins: return blood back to the heart from the body against the push of gravity using valves in the veins
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Capillary Details
Capillaries composed of endothelium
Very thin cells: allows for easy diffuse
Connected from arterioles  venules in networks
Sometimes direct route from arteriole to venule
Capillary filling controlled by small arterioles and precapillary sphincters
Autoregulation: ability of a tissue to adjust blood flow into the area according to demands
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Capillary Details
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Capillary Details
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Capillary Exchange
Slowest rate of flow is through capillaries
Allows time for gas and nutrient exchange through wall
Blood pressure (BP) (pushes out of capillary)
Permits filtration of fluid out of capillary
Mostly in first half of capillary network
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10. Venous Return: Two Mechanisms
Blood enters veins at very low pressure
Inadequate to overcome gravity and return blood to heart
Skeletal muscle contractions
Contracting skeletal muscles (especially in lower limbs) squeeze veins emptying them
Because of venous valves, flow is  heart
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11. Venous Return: Two Mechanisms
Respiratory pump has similar action
Inhalation decreases thoracic pressure and increases abdominal pressure  blood to heart
Exhalation allows refilling of abdominal veins
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12. Venous Return: Two Mechanisms
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13. Blood Flow Through Vessels
From high pressure area to lower pressure area, that is, down pressure gradient
Greater gradient  greater flow
BP is highest in aorta: 110/70 mm Hg
Note pulse in large arteries
BP declines as flows through more vessels
Arterioles: major drop in BP due to smooth muscle contraction  vasoconstriction
Capillary beds ~35-16 mm Hg 
16 mm Hg at venules  0 at right atrium
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14. Blood Flow Through Vessels
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15. Blood Flow Through Vessels
Factors that regulate blood flow and BP
Blood volume and ventricular contraction  cardiac output
Vascular resistance: opposition to flow (depends on lumen diameter + vessel length + blood viscosity)
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16. Checking Circulation: Pulse
Pulse in arteries = heart rate (HR). Press artery against bone or muscle. Sites used
Radial artery (thumb side of wrist)
Carotid artery (neck)
Brachial artery (arm)
Tachycardia: rapid resting HR (>100 bpm)
Bradycardia= slow resting HR (<50 bpm)
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Blood Pressure
Device used: sphygmomanometer
Usually on brachial artery
Inflate cuff to raise pressure > systolic BP
Briefly stop blood flow there
Lower pressure in cuff until flow just starts
First sound indicates systolic BP (contraction of ventricles)
Lower pressure further until sound become faint
Diastolic BP (when the ventricles are relaxed)
Normal BP values <120 mm Hg for systolic and < 80 mm Hg for diastolic
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Circulatory Routes
Two main routes: systemic + pulmonary
Systemic circulation
Oxygenated blood travels from heart throughout body, deoxygenating as it goes
All systemic arteries branch from aorta
All systemic veins empty into superior vena cava, inferior vena cava, or the coronary sinus
Deoxygenated blood returns to heart
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Circulatory Routes
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20. Circulatory Routes: Aorta
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21. Circulatory Routes: Aorta
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22. Circulatory Routes: Aorta
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23. Circulatory Routes: Pelvis, Lower Limb
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24. Circulatory Routes: Principle Veins
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25. Circulatory Routes: Principle Veins of the Hands and Neck
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26. Circulatory Routes: Principle Veins of the Right Upper Limb
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27. Circulatory Routes: Principle Veins of the Pelvis and Lower Limbs
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28. Pulmonary Circulation
Carries blood from right side of heart to lungs to get O2 and eliminate CO2
Route: (R = right, L = left)
Right ventricle (RV)  pulmonary trunk  R + L pulmonary arteries  both lungs 
Carry “blue blood” (actually a dark red color in the body) low O2 in and high in CO2
Pulmonary capillaries: gas exchange 
R and L pulmonary veins  L atrium
Carry “red blood” (high in O2 in and low in CO2)
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Aging
Stiffening of aorta
Loss of cardiac muscle strength
Reduced CO & increased systolic pressure
Higher risk for
Coronary artery disease (CAD)
Congestive heart failure (CHF)
Atherosclerosis
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30. Common Heart Disorders
1. Mitral valve prolapse- mitral valve flaps extend back into the left atrium causing leakage. Severe chest pains and fatigue in some patients.
2. Myocardial Infarction – heart attack
3. Atherosclerosis – “heardening of the arteries”, build up of plaque inside the vessel wall
4. Angina Pectoris – severe chest pain
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5. Congestive Heart Failure – failure of left ventricle to pump adequately, so blood is not leaving the heart at a fast enough rate to deliver to the body
6. Varicose Veins – enlarged veins where blood pools instead of continue on to the heart
7. Hemorrhoids (piles) – varicose veins of the anal canal brought on by straining (defecation, child birth, etc.)
8. Heart Murmur – abnormal heart sound that may indicate valvular insufficiency
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Mitral Valve Prolapse
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Atherosclerosis
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Vericose Veins
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