1. Chapter 18 Blood Vessels and Circulation Inner Surface of an Artery
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2. Functions of the Peripheral Circulation
The heart provides the major force that causes blood to circulate
The peripheral circulation
Carries blood
Exchanges nutrients, waste products, and gases with tissues
Helps regulate blood pressure
Directs blood flow to tissues

3. General Features of Blood Vessels
Arteries carry blood away from the heart toward capillaries, where exchange between the blood and interstitial fluid occurs
Blood flows from the heart through elastic arteries, muscular arteries, and arterioles to the capillaries
Veins carry blood from the capillaries toward the heart
Blood returns to the heart from the capillaries through venules, small veins, and large veins

4. Fig. 18.2

5. General Features of Blood Vessels
Blood vessels, except for capillaries, have three layers
Inner: tunica intima
Consists of endothelium (simple squamous epithelium), basement membrane, and internal elastic lamina
Middle: tunica media
Contains circular smooth muscle and elastic and collagen fibers
Outer: tunica adventitia
connective tissue
The thickness and the composition of the layers vary with blood vessel type and diameter

6. Fig. 18.1

7. Arteries Large elastic arteries Muscular (distributing) arteries
Thick-walled with large diameters
Tunica media has many elastic fibers and little smooth muscle
Muscular (distributing) arteries
Thick-walled with small diameters
Tunica media has abundant smooth muscle and some elastic fibers
Arterioles
Smallest arteries
Tunica media consists of one or two layers of smooth muscle cells and a few elastic fibers

8. Arteries
Fig. 18.2

9. Capillaries Capillaries consist only of endothelium
A capillary bed is a network of capillaries
Thoroughfare channels carry blood from arterioles to venules
Blood can pass rapidly through thoroughfare channels
Precapillary sphincters regulate the flow of blood into capillaries

10. Fig. 18.3

11. Fig. 18.4

12. Veins
Venules connect to capillaries and are like capillaries, except they are larger in diameter
Large venules and all veins have all three layers
Valves prevent the backflow of blood in the veins

13. Veins
Fig. 18.2

14. Fig. 18.2

15. Aging of the Arteries
Arteriosclerosis results from a loss of elasticity in the aorta, large arteries, and coronary arteries
Atherosclerosis is the deposition of materials in arterial walls to form plaques

16. Fig. 18.5

17. Pulmonary Circulation
Moves blood to and from the lungs
Pulmonary trunk arises from the right ventricle and divides to form the pulmonary arteries, which project to the lungs
From the lungs, four pulmonary veins return blood to the left atrium

18. Systemic Circulation: Arteries
Arteries carry blood from the left ventricle of the heart to all parts of the body
Fig. 18.6

19. Aorta Leaves the left ventricle to form the
Ascending aorta
Aortic arch
Descending aorta
Consists of the thoracic aorta and the abdominal aorta
Coronary arteries branch from the aorta and supply the heart

20. Aorta
Fig. 18.7

21. Arteries to the Head and the Neck
The following arteries branch from the aortic arch to supply the head and the upper limbs
Brachiocephalic
Divides to form the right common carotid and the right subclavian arteries
Left common carotid
Left subclavian
Vertebral arteries branch from the subclavian arteries

22. Arteries to the Head and the Neck
The common carotid arteries and the vertebral arteries supply the head
The common carotid arteries divide to form the
external carotids: supply the face and mouth
internal carotids: supply the brain
Vertebral arteries join within the cranial cavity to form the basilar artery, which supplies the brain
The internal carotids and basilar arteries contribute to the cerebral arterial circle

23. Arteries to the Head and the Neck
Fig. 18.9

24. Major Arteries of the Head and Thorax
Fig. 18.8

25. Fig

26. Arteries of the Upper Limb
The subclavian artery continues (without branching) as the axillary artery and then as the brachial artery. The brachial artery divides into the radial and ulnar arteries
The radial artery supplies the deep palmar arch
The ulnar artery supplies the superficial palmar arch
Both arches give rise to the digital arteries

27. Fig

28. Fig

29. Branches of the Aorta
Fig

30. Thoracic Aorta/Branches
The thoracic aorta has
Visceral branches that supply the thoracic organs
Parietal branches that supply the thoracic wall
Fig

31. Abdominal Aorta/Branches
The abdominal aorta has
Visceral branches that supply the abdominal organs
Parietal branches that supply the abdominal wall
Fig

32. Abdominal Aorta/Branches
The visceral branches are paired and unpaired
The unpaired arteries supply the stomach, spleen, and liver (celiac trunk); the small intestine and upper part of the large intestine (superior mesenteric); and the lower part of the large intestine (inferior mesenteric)
The paired arteries supply the kidneys, adrenal glands, and gonads

33. Branches of the Aorta
Fig

34. of the Abdomen and Pelvis
Major Arteries
of the Abdomen and Pelvis
Fig
Fig

35. Arteries of the Pelvis
The common iliac arteries arise from the abdominal aorta, and the internal iliac arteries branch from the common iliac arteries
The visceral branches of the internal iliac arteries supply the pelvic organs
The parietal branches supply the pelvic wall and floor and the external genitalia

36. Arteries of the Lower Limb
The external iliac arteries branch from the common iliac arteries
The external iliac artery continues (without branching) as the femoral artery and then as the popliteal artery
The popliteal artery divides to form the anterior and posterior tibial arteries
The posterior tibial artery gives rise to the fibular (peroneal) and plantar arteries
The plantar arteries form the plantar arch, from which the digital arteries arise

37. Arteries of the Pelvis and Lower Limb
Fig

38. Major Arteries of the Lower Limb
Fig

39. Systemic Circulation: Veins
The three major veins returning blood to the heart are the
Superior vena cava (head, neck, thorax, and upper limbs)
Inferior vena cava ( abdomen, pelvis, and lower limbs)
Coronary sinus (heart)
Veins are of three types:
Superficial veins
Deep veins
Sinuses

40. Major Veins
Fig

41. Veins of the Head and Neck
The internal jugular veins drain the dural venous sinuses and the veins of the anterior head, face, and neck
The external jugular veins and the vertebral veins drain the posterior head and neck

42. Fig

43. Fig

44. Fig

45. Veins of the Upper Limb
The deep veins are the small ulnar and radial veins of the forearm, which join the brachial veins of the arm. The brachial veins drain into the axillary vein
The superficial veins are the basilic, cephalic, and median cubital
The basilic vein becomes the axillary vein, which then becomes the subclavian vein. The cephalic vein drains into the axillary vein
The median cubital connects the basilic and cephalic veins at the elbow

46. Fig

47. Fig

48. Veins of the Thorax
The left and right brachiocephalic veins and the azygos veins return blood to the superior vena cava
Fig

49. Veins of the Abdomen and Pelvis
Ascending lumbar veins from the abdomen join the azygos and hemiazygos veins
Veins from the kidneys, adrenal glands, and gonads directly enter the inferior vena cava
Veins from the stomach, intestines, spleen, and pancreas connect with the hepatic portal vein
The hepatic portal vein transports blood to the liver for processing. Hepatic veins from the liver join the inferior vena cava

50. Fig

51. Fig

52. Fig

53. Veins of the Lower Limb
The deep veins are the fibular (peroneal), anterior tibial, posterior tibial, popliteal, femoral, and external iliac veins
The superficial veins are the small and great saphenous veins

54. Fig

55. Fig

56. Physiology of Circulation
Blood Pressure
A measure of the force exerted by blood against the blood vessel wall. Blood moves through vessels because of blood pressure
Can be measured by listening for Korotkoff sounds produced by turbulent flow in arteries as pressure is released from a blood pressure cuff

57. Fig

58. Fig

59. Physiology of Circulation
Blood Flow Through a Blood Vessel
The amount of blood that moves through a vessel in a given period.
Directly proportional to pressure differences and is inversely proportional to resistance
Resistance is the sum of all the factors that inhibit blood flow. Resistance increases when blood vessels become smaller and viscosity increases
Viscosity is the resistance of a liquid to flow. Most of the viscosity of blood results from red blood cells. The viscosity of blood increases when the hematocrit increases or plasma volume decreases

60. Physiology of Circulation
Blood Flow Through the Body
Mean arterial pressure equals cardiac output times peripheral resistance
Vasomotor tone is a state of partial contraction of blood vessels. Vasoconstriction increases vasomotor tone and peripheral resistance, whereas vasodilation decreases vasomotor tone and peripheral resistance
Blood pressure averages 100 mm Hg in the aorta and drops to 0 mm Hg in the right atrium. The greatest drop occurs in the arterioles and capillaries

61. Physiology of Circulation
Pulse Pressure and Vascular Compliance
Pulse pressure is the difference between systolic and diastolic pressures. Pulse pressure increases when stroke volume increases or vascular compliance decreases
Vascular compliance is a measure of the change in volume of blood vessels produced by a change in pressure
Pulse pressure waves travel through the vascular system faster than the blood flows. Pulse pressure can be used to take the pulse

62. Fig

63. Physiology of Circulation
Blood Pressure and the Effect of Gravity
In a standing person, hydrostatic pressure caused by gravity
Increases blood pressure below the heart
Decreases pressure above the heart

64. Physiology of Circulation
Capillary Exchange and Regulation of Interstitial Fluid Volume
Capillary exchange occurs through or between endothelial cells
Diffusion, which includes osmosis, and filtration are the primary means of capillary exchange
Filtration moves materials out of capillaries and osmosis moves them into capillaries
A net movement of fluid occurs from the blood into the tissues. The fluid gained by the tissues is removed by the lymphatic system

65. Fluid Exchange Across the Walls of Capillaries
Fig

66. Control of Blood Flow
Blood flow through tissues is highly controlled and matched closely to the metabolic needs of tissues
Local Control
The response of vascular smooth muscle to changes in tissue gases, nutrients, and waste products
If the metabolic activity of a tissue increases, the diameter and number of capillaries in the tissue increase over time.

67. Control of Blood Flow Nervous and Hormonal Control
The sympathetic nervous system (vasomotor center in the medulla) controls blood vessel diameter. Other brain areas can excite or inhibit the vasomotor center
Epinephrine and norepinephrine cause vasoconstriction in most tissues. Epinephrine causes vasodilation in skeletal and cardiac muscle
The muscular arteries and arterioles control the delivery of blood to tissues
The veins are a reservoir for blood
Venous return to the heart increases because of the vasoconstriction of veins, an increased blood volume, and the skeletal muscle pump (with valves)

68. Fig

69. Regulation of Mean Arterial Pressure
Mean arterial pressure (MAP) is proportional to cardiac output times peripheral resistance
Short-Term Regulation of Blood Pressure
Baroreceptors are sensory receptors sensitive to stretch
Located in the carotid sinuses and the aortic arch
The baroreceptor reflex changes peripheral resistance, heart rate, and stroke volume in response to changes in blood pressure

70. Baroreceptor Reflex Control of Blood Pressure
Fig

71. Regulation of Mean Arterial Pressure
Short-Term Regulation of Blood Pressure (cont.)
Epinephrine and norepinephrine are released from the adrenal medulla as a result of sympathetic stimulation. They increase heart rate, stroke volume, and vasoconstriction
Peripheral chemoreceptor reflexes respond to decreased oxygen, leading to increased vasoconstriction
Central chemoreceptors respond to high carbon dioxide or low pH levels in the medulla, leading to increased vasoconstriction, heart rate, and force of contraction (CNS ischemic response)

72. Adrenal Medullary Mechanism
Fig

73. Chemoreceptor Reflex Control of Blood Pressure
Fig

74. Regulation of Mean Arterial Pressure
Long-Term Regulation of Blood Pressure
Through the renin-angiotensin-aldosterone mechanism
Renin is released by the kidneys in response to low blood pressure
Promotes the production of angiotensin II, which causes vasoconstriction and an increase in aldosterone secretion
Aldosterone helps maintain blood volume by decreasing urine production
The vasopressin (ADH) mechanism causes ADH release from the posterior pituitary in response to a substantial decrease in blood pressure
ADH causes vasoconstriction and helps maintain blood volume by decreasing urine production

75. Renin-Angiotensin-Aldosterone Mechanism
Fig

76. Vasopressin (ADH) Mechanism
Fig

77. Regulation of Mean Arterial Pressure
Long-Term Regulation of Blood Pressure (cont.)
The atrial natriuretic mechanism causes atrial natriuretic hormone release from the cardiac muscle cells when atrial blood pressure increases. It stimulates an increase in urinary production, causing a decrease in blood volume and blood pressure
The fluid shift mechanism causes fluid shift, which is a movement of fluid from the interstitial spaces into capillaries in response to a decrease in blood pressure to maintain blood volume

78. Examples of Cardiovascular Regulation
Exercise
Local control mechanisms increase blood flow through exercising muscles, which lowers peripheral resistance
Cardiac output increases because of increased venous return, stroke volume, and heart rate
Vasoconstriction in the skin, the kidneys, the gastrointestinal tract, and skeletal muscle (non-exercising and exercising) increases peripheral resistance, which helps prevent a drop in blood pressure
Blood pressure increased despite an overall decrease in peripheral resistance because of increased cardiac output

79. Examples of Cardiovascular Regulation
Circulatory Shock
Baroreceptor reflexes and the adrenal medullary response increase blood pressure
The renin-angiotensin-aldosterone mechanism and the vasopressin mechanism increase vasoconstriction and blood volume. The fluid shift mechanism increases blood volume
In severe shock, the chemoreceptor reflexes increase vasoconstriction, heart rate, and force of contraction
In severe shock, despite negative-feedback mechanisms, a positive- feedback cycle of decreasing blood pressure can cause death