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Fig. 13.5 Copyright © McGraw-Hill Education. Permission required for reproduction or display. CO2 O2 Brain Circulation to brain and tissues of head Aorta Circulation to upper limbs CO2 Pulmonary arteries O2 Pulmonary trunk Pulmonary vein O2 CO2 Heart Pulmonary circulation Digestive tract circulation Liver circulation Kidney Renal circulation Circulation to lower limbs CO2 O2 Fig. 13.1-2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tunica adventitia Tunica media (elastic tissue and smooth muscle) Connective tissue Endothelium and basement membrane Tunica intima (a) Elastic arteries. The tunica media is mostly elastic connective tissue. Elastic arteries recoil when stretched, which prevents blood pressure from falling rapidly. Tunica adventitia Elastic connective tissue Smooth muscle Elastic connective tissue Connective tissue Endothelium and basement membrane (b) Muscular arteries. The tunica media is a thick layer of smooth muscle. Muscular arteries regulate blood flow to different regions of the body. Tunica media Tunica intima Fig. 13.34 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Endothelium Vessel wall Atherosclerotic plaque Fig. 13.1-4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tunica adventitia Tunica media (elastic tissue and smooth muscle) Connective tissue Endothelium and basement membrane Tunica intima (a) Elastic arteries. The tunica media is mostly elastic connective tissue. Elastic arteries recoil when stretched, which prevents blood pressure from falling rapidly. Tunica adventitia Elastic connective tissue Smooth muscle Elastic connective tissue Connective tissue Endothelium and basement membrane Tunica media Tunica intima (b) Muscular arteries. The tunica media is a thick layer of smooth muscle. Muscular arteries regulate blood flow to different regions of the body. Tunica adventitia Tunica media Tunica intima (c) Arterioles. All three tunics are present; the tunica media consists of only one or two layers of circular smooth muscle cells. Endothelium (d) Capillaries. Walls consist of only a simple endothelium surrounded by delicate loose connective tissue. Fig. 13.3 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Arteriole Precapillary sphincters Capillaries Capillary network Venule Fig. 13.1 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Tunica adventitia Tunica adventitia Tunica media (elastic tissue and smooth muscle) Tunica media Connective tissue Connective tissue Tunica intima Endothelium and basement membrane Endothelium and basement membrane (a) Elastic arteries. The tunica media is mostly elastic connective tissue. Elastic arteries recoil when stretched, which prevents blood pressure from falling rapidly. Tunica intima (g) Large veins. All three tunics are present. The tunica media is thin but can regulate vessel diameter because blood pressure in the venous system is low. The predominant layer is the tunica adventitia. Tunica adventitia Elastic connective tissue Smooth muscle Elastic connective tissue Connective tissue Endothelium and basement membrane Tunica adventitia Tunica media Tunica media Tunica intima Connective tissue Endothelium and basement membrane (b) Muscular arteries. The tunica media is a thick layer of smooth muscle. Muscular arteries regulate blood flow to different regions of the body. (f) Small and medium veins. All three tunics are present. Tunica adventitia Tunica intima Tunica media Tunica intima (c) Arterioles. All three tunics are present; the tunica media consists of only one or two layers of circular smooth muscle cells. (e) Venules. Only the tunica intima resting on a delicate layer of dense connective tissue is present. Endothelium (d) Capillaries. Walls consist of only a simple endothelium surrounded by delicate loose connective tissue. Tunica intima Fig. 13.2 Copyright © McGraw-Hill Education. Permission required for reproduction or display. V A LM 250x Tunica intima Tunica media Tunica adventitia ©Ed Reschke/Photolibrary/Getty Images Fig. 13.4 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Valve closed Vein Valve open Direction of blood flow Fig. 13.21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 When the cuff pressure is high enough to keep the brachial artery closed, no blood flows through it, and no sound is heard. Degree to which brachial artery is open during: 300 Systole 250 2 3 4 When cuff pressure decreases and is no longer able to keep the brachial artery closed, blood is pushed through the partially opened brachial artery, producing turbulent blood flow and a sound. Systolic pressure is the pressure at which a sound is first heard. As cuff pressure continues to decrease, the brachial artery opens even more during systole. At first, the artery is closed during diastole, but as cuff pressure continues to decrease, the brachial artery partially opens during diastole. Turbulent blood flow during systole produces Korotkoff sounds, although the pitch of the sounds changes as the artery becomes more open. Eventually, cuff pressure decreases below the pressure in the brachial artery, and it remains open during systole and diastole. Nonturbulent flow is reestablished, and no sounds are heard. Diastolic pressure is the pressure at which the sound disappears. No sound 1 Diastole Blocked 200 2 150 Systolic pressure (120 mm Hg) Korotkoff sounds 100 Diastolic pressure (80 mm Hg) 50 Arm Elbow 3 Blocked or partially open Sound disappears. No sound 0 Pressure cuff Sound is first heard. 4 Open Fig. 13.22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 140 Pulse pressure 120 Systolic pressure 100 Mean blood pressure Pressure (mm Hg) 80 60 40 20 Diastolic pressure Fig. 13.24 Copyright © McGraw-Hill Education. Permission required for reproduction or display. 1 2 3 At the arterial end of the capillary, the movement of fluid out of the capillary due to blood pressure is greater than the movement of fluid into the capillary due to osmosis. At the venous end of the capillary, the movement of fluid into the capillary due to osmosis is greater than the movement of fluid out of the capillary due to blood pressure. Approximately nine-tenths of the fluid that leaves the capillary at its arterial end reenters the capillary at its venous end. About one-tenth of the fluid passes into the lymphatic capillaries. One-tenth volume passes into lymphatic capillaries. 3 Nine-tenths volume returns to capillary. Net movement of fluid out of the capillary into the interstitial space Outward movement of fluid due to blood pressure Inward movement of fluid due to osmosis Inward movement of fluid due to osmosis Outward movement of fluid due to blood pressure 1 2 Blood flow Arterial end Venous end Net movement of fluid into the capillary from the interstitial space Fig. 13.3 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Arteriole Precapillary sphincters Capillaries Capillary network Venule Fig. 13.25 Copyright © McGraw-Hill Education. Permission required for reproduction or display. 1 Blood flow increases Smooth muscle of precapillary sphincter relaxes. 2 Blood flow decreases Smooth muscle of precapillary sphincter contracts. Blood flow Blood flow 1 Relaxation of precapillary sphincters. Precapillary sphincters relax as the tissue concentration of O2 and nutrients, such as glucose, amino acids, and fatty acids, decreases. The precapillary sphincters also relax as CO2 concentration increases and pH decreases. 2 Contraction of precapillary sphincters. Precapillary sphincters contract as the tissue concentration of O2 and nutrients, such as glucose, amino acids, and fatty acids, increases. The precapillary sphincters also contract as the CO2 concentration decreases and pH increases. Fig. 13.26 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Vasomotor center in medulla oblongata Spinal cord Sympathetic nerve fibers Blood vessels Sympathetic chain Fig. 13.27 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Carotid sinus baroreceptors 1 Baroreceptors in the carotid sinus and aortic arch monitor blood pressure. 2 Sensory nerves conduct action potentials to the cardioregulatory and vasomotor centers in the medulla oblongata. 3 2 3 Increased parasympathetic stimulation of the heart decreases the heart rate. 4 Increased sympathetic stimulation of the heart increases the heart rate and stroke volume. Cardioregulatory and vasomotor centers in the medulla oblongata 4 Sympathetic nerves 5 Increased sympathetic stimulation of blood vessels increases vasoconstriction. Sympathetic chain 5 Blood vessels 1 Aortic arch baroreceptors Fig. 13.28 Copyright © McGraw-Hill Education. Permission required for reproduction or display. 3 4 Actions Reactions Baroreceptors in the carotid arteries and aorta detect an increase in blood pressure. The cardioregulatory center and the vasomotor center in the brain alter activity of the heart and blood vessels (baroreceptor reflex), and the adrenal medulla decreases secretion of epinephrine. Homeostasis Disturbed: Blood pressure increases. Start here Homeostas is Restored: Blood pressure decreases. 5 6 Blood pressure (normal range) 1 Blood pressure (normal range) 2 Effectors Respond: Heart rate and stroke volume decrease; blood vessels dilate. Homeostasis Disturbed: Blood pressure decreases. Actions Homeostasis Restored: Blood pressure increases. Reactions Baroreceptors in the carotid arteries and aorta detect a decrease in blood pressure. The cardioregulatory center and the vasomotor center in the brain alter activity of the heart and blood vessels (baroreceptor reflex), and the adrenal medulla increases secretion of epinephrine (adrenal medullary mechanism). Effectors Respond: Heart rate and stroke volume increase; blood vessels constrict. Fig. 13.29 Copyright © McGraw-Hill Education. Permission required for reproduction or display. 1 Chemoreceptors in the carotid and aortic bodies monitor blood O2, CO2, and pH. 1 Aortic body chemoreceptors 2 Chemoreceptors in the medulla oblongata monitor blood CO2 and pH. 3 2 3 Decreased blood O2, increased CO2, and decreased pH decrease Chemoreceptors parasympathetic stimulation in the medulla of the heart, which oblongata increases the heart rate. 4 Decreased blood O2, increased CO2, and decreased pH increase sympathetic stimulation of the heart, which increases the heart rate and stroke volume. 5 Decreased blood O2, increased CO2, and decreased pH increase sympathetic stimulation of blood vessels, which increases vasoconstriction. Carotid body chemoreceptors 4 Cardioregulatory and vasomotor centers in the medulla oblongata Sympathetic nerves Sympathetic chain 5 Fig. 13.30 Copyright © McGraw-Hill Education. Permission required for reproduction or display. 1 Increased stimulation 1 The same stimuli that increase sympathetic stimulation of the heart and blood vessels cause action potentials to be carried to the medulla oblongata. 2 Descending pathways from the medulla oblongata to the spinal cord increase sympathetic stimulation of the adrenal medulla, resulting in secretion of epinephrine and some norepinephrine. Medulla oblongata Spinal cord 2 Epinephrine and norepinephrine Sympathetic nerve fiber Sympathetic chain Adrenal medulla Fig. 13.31 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Liver Decreased blood pressure 1 1 The kidneys detect decreased blood pressure, resulting in increased renin secretion. Angiotensinogen Renin 2 Renin converts angiotensinogen, a protein secreted from the liver, to angiotensin I. 2 Kidney Angiotensin I 6 3 Angiotensin-converting enzyme in the lungs converts angiotensin I to angiotensin II. Aldosterone 3 Angiotensin-converting enzyme in lung capillaries 4 Angiotensin II is a potent vasoconstrictor, resulting in increased blood pressure. 5 Angiotensin II Adrenal cortex 4 5 Angiotensin II stimulates the adrenal cortex to secrete aldosterone. Vasoconstriction 6 Aldosterone acts on the kidneys to increase Na+ reabsorption. As a result, urine volume decreases and blood volume increases, resulting in increased blood pressure. Increases water reabsorption and decreases urine volume Increased blood pressure Fig. 13.32 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Hypothalamic nerve cells detect increased osmotic pressure. Baroreceptors (aortic arch, carotid sinus) detect decreased blood pressure. Hypothalamic nerve cell Posterior pituitary ADH Increased reabsorption of water Blood vessel Kidney Vasoconstriction Increased blood volume Increased blood pressure Fig. 18.16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Increased blood pressure in right atrium ANH Kidney ANH secretion Increased Na+ excretion and increased water loss result in decreased BP. Fig. 13.33 Copyright © McGraw-Hill Education. Permission required for reproduction or display. 3 4 Actions Atrial natriuretic mechanism: Cardiac muscle cells detect increased atrial blood pressure; secretion of atrial natriuretic hormone increases. Renin-angiotensin-aldosterone mechanism: The kidneys detect increased blood pressure; production of angiotensin II and secretion of aldosterone from the adrenal cortex decrease. Effectors Respond: Vasodilation decreases peripheral resistance to blood flow. More Na+ and water are lost in the urine, decreasing blood volume. Homeostasis Disturbed: Blood pressure increases. Start here Homeostasis Restored: Blood pressure decreases. 5 6 Blood pressure (normal range) 1 Blood pressure (normal range) 2 Reactions Homeostasis Disturbed: Blood pressure decreases. Actions Renin-angiotensin-aldosterone mechanism: The kidneys detect decreased blood pressure; production of angiotensin II and secretion of aldosterone from the adrenal cortex increase. ADH (vasopressin) mechanism: Baroreceptors detect decreased blood pressure, resulting in decreased stimulation of the hypothalamus and increased ADH secretion by the posterior pituitary. Homeostasis Restored: Blood pressure increases. Reactions Effectors Respond: Vasoconstriction increases peripheral resistance to blood flow. Less Na+ and water are lost in the urine, increasing blood volume. Fig. 13.34 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Endothelium Vessel wall Atherosclerotic plaque