1. Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
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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 atria of heart
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Blood Vessels
Three layers (tunica): external, middle, inner
Arteries: thicker
Elastic: large
Arterioles:
smooth muscle helps regulate blood pressure
Sympathetic activity to smooth muscle  vasoconstriction (narrowing)
Decreased sympathetic activity or NONE causes relaxation (dilation)
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4. Capillaries lack muscle fibers
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Metarteriole
connects arteriole directly to venule
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6. Walls of Artery and Vein
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7. Blood Vessel Structure: Arteries, Veins
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8. Blood Vessel Structure: Arteries, Veins
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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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Capillary Network
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11. 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
Autoregulation: ability of a tissue to adjust blood flow into the area according to demands
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12. Exchange in the Capillaries
water and other substances leave capillaries because of net outward pressure at the capillaries’s arteriolar ends
water enters capillaries’ at the 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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Capillary Details
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Capillary Details
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Capillary Exchange
Colloid osmotic pressure (pulls into capillary)
Plasma proteins create this “pulling” pressure
Causes reabsorption of fluid from outside to inside
Excess fluid returned via lymphatic system
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Capillary Exchange
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17. Blood Vessel Structure: Veins
Larger lumen, thinner walls
Valves prevent backflow
Venules
Very thin, no valves
Blood enters veins at very low pressure
Inadequate to overcome gravity and return blood to heart
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Venous Valves
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19. Venous Return: Two Mechanisms
Skeletal muscle contractions
Especially in lower limbs
squeeze veins - emptying them
Because of valves, flow is  heart
Systemic venules and veins serve as blood reservoirs
hold ~ 64% total blood volume
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20. Venous Return: Two Mechanisms
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21. Venous Return: Two Mechanisms
Respiratory pump
Inhalation decreases thoracic pressure
& increases abdominal pressure
 blood to heart
Exhalation allows refilling of abdominal veins
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22. Blood Flow Through Vessels
BP highest in aorta: 110/70 mm Hg
Pulse in large arteries
BP declines as flows through more vessels
Arterioles: major drop in BP due to smooth muscle contraction  vasoconstriction
Capillary beds ~ mm Hg 
16 mm Hg at venules  0 at right atrium
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23. Blood Flow Through Vessels
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24. Factors that regulate blood flow and BP
Blood volume and ventricular contraction  cardiac output
Under control of cardiovascular (CV) center (medulla)
Vascular resistance:
lumen diameter
Smaller lumen (with vasoconstriction)  greater resistance
vessel length
Greater vessel length (with weight gain)  greater resistance
blood viscosity
Higher viscosity (as with high hematocrit)  greater resistance
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25. Cardiovascular Center
Located in medulla
Helps regulate
Heart rate
Stroke volume
Blood pressure
Blood flow to specific tissues
Mechanisms
By neural mechanisms
By hormonal mechanisms
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26. Input to Cardiovascular Center (Medulla)
Input from different parts of brain
Cerebral cortex: thoughts, decisions
Limbic system: emotions
Hypothalamus: changes in temperature or blood volume  blood flow adjusted accordingly
Input from sensory receptors and nerves
Proprioceptors, baroreceptors, chemoreceptors
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27. Input to Cardiovascular Center (Medulla)
Proprioceptors:
Cause  heart rate as exercise begins   cardiac output (CO)   BP
Baroreceptors in aorta and carotid: if BP 
 sympathetic stimulation   CO   BP
 parasympathetic   CO   BP
Chemoreceptors in aorta and carotid bodies
If low O2, high CO2, or high H+ (acidity)   resistance by  vasoconstriction   BP
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28. Input to Cardiovascular Center (Medulla)
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29. Output to Cardiovascular Effectors
ANS nerves to heart
 Sympathetic  HR and  force of contraction   cardiac output (CO)   BP
 Parasympathetic   HR  CO   BP
Vasomotor (sympathetic nerves)
To arterioles contract smooth muscle   vasomotor tone   vascular resistance   BP
To veins contract smooth muscle  move blood to heart   BP
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30. Hormone Regulation of Blood Flow + BP
Renin-angiotensin aldosterone (RAA) system
Angiotensin II  vasoconstriction   BP
 aldosterone  retain Na++ water   BP
Epinephrine + norepinephrine   CO  BP
ADH = vasopressin
 vasoconstriction   BP
Thirst + water retention in kidney   BP
ANP from cells in atria
Vasodilation, loss of Na+ water in urine  BP
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31. Hormone Regulation of Blood Flow + BP
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32. Arterial Blood Pressure
Blood Pressure – force the blood exerts against the inner walls of the blood vessels
rises when ventricles contract
falls when ventricles relax
systolic pressure – maximum pressure
diastolic pressure – minimum pressure
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33. Checking Circulation: Pulse
Pulse in arteries = heart rate (HR)
Press artery against bone or muscle.
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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Pulse
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35. Central Venous Pressure
pressure in the right atrium
weakly beating heart increases central venous pressure
increase in central venous pressure causes blood to back up into peripheral vein
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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
Lower pressure further until sound become faint
Diastolic BP
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
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Circulatory Routes
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39. Circulatory Routes: Aorta
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40. Circulatory Routes: Aorta
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41. Circulatory Routes: Aorta
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42. Circulatory Routes: Aorta
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43. Circulatory Routes: Pelvis, Lower Limb
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44. Circulatory Routes: Principle Veins
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45. Circulatory Routes: Principle Veins of the Hands and Neck
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46. Circulatory Routes: Principle Veins of the Right Upper Limb
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47. Circulatory Routes: Principle Veins of the Pelvis and Lower Limbs
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48. Pulmonary Circulation
Carries blood from right side of heart to lungs to get O2 and eliminate CO2
Right ventricle (RV)  pulmonary trunk  R + L pulmonary arteries  both lungs 
Carry “blue blood” 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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Pulmonary Circuit
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50. 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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51. Cerebral Arterial Circle
Circle of Willis
formed by anterior and posterior cerebral arteries, which join the internal carotid arteries
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52. Hepatic Portal Circulation
Portal vein: transports blood from one organ’s capillary bed to another
GI organs 
Splenic and superior mesenteric veins 
Hepatic portal vein (“blue blood”) 
Sinusoids (“leaky capillaries” in liver) 
Mixes “blue blood” with “red blood”
Hepatic vein  inferior vena cava (IVC)
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53. Hepatic Portal Circulation
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54. Copyright 2010, John Wiley & Sons, Inc.
Hepatic Portal Vein
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55. Hepatic Portal Circulation
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Fetal Circulation
Specialized for exchange of materials with maternal blood/bypass lungs
Exchange in placenta  umbilical vein
 ductus venosus (bypasses liver)
 inferior vena cava  R atrium (mixes with deoxygenated blood from lower body)
 foramen ovale  L atrium
Or  R Ventricle  pulmonary trunk  ductus arteriosus  aorta  internal iliac arteries  umbilical arteries  placenta
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Fetal Circulation
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Changes at Birth
Umbilical arteries  medial umbilical ligaments
Umbilical vein  ligamentum teres
Ductus venosus  ligamentum venosum
Placenta expelled after
Foramen ovalis closes  fossa ovale
Ductus arteriosus  ligamentum arteriosum
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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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