Cardiovascular System: Vessels Chapter 20 – Lecture Notes to accompany Anatomy and Physiology: From Science to Life textbook by Gail Jenkins, Christopher Kemnitz, Gerard Tortora

Chapter Overview 20.1 Arterial Blood Flow Overview 20.2 Capillaries 20.3 Venules and Veins 20.4 Capillary Exchange 20.5 Blood Flow 20.6 Blood Pressure Regulation 20.7 Pulse 20.8 Systemic and Pulmonary Circuits

Essential Terms artery blood vessel carrying blood away from the heart vein vessel carrying blood toward the heart capillaries smallest vessels that function in exchange of nutrients and wastes between blood and body cells

Introduction Blood vessels transport materials throughout body carry nutrients to cells carry wastes away for excretion From heart to arteries to arterioles to capillaries to venules to veins to heart

Concept 20.1 Arteries

Arteries Two main types Three coats elastic arteries muscular arteries Three coats tunic interna endothelium, basement membrane, internal elastic lamina tunica media elastic fibers and smooth muscle fibers tunic externa elastic and collagen fibers Innervated by sympathetic fibers of ANS

Figure 20.1ab

Figure 20.1c

Figure 20.1d

Figure 20.1e

Elastic Arteries largest diameter highest proportion of elastic fibers in tunica media help propel blood onward while ventricles are relaxing stretch with surge of blood recoil when pressure decreases

Figure 20.2

Muscular Arteries medium-sized arteries tunica media has more smooth muscle and fewer elastic fibers than elastic arteries adjust blood flow capable of greater vasoconstriction and vasodilation most named arteries are muscular arteries

Arterioles muscular arteries divide into smaller arteries smaller arteries divide into arterioles arterioles feed capillaries tunics minimize as they near capillary beds regulate resistance contraction of smooth muscle increases resistance can significantly affect blood pressure

Figure 20.3

Concept 20.2 Capillaries

Capillaries microscopic vessels that connect arterioles to venules exchange vessels fed by metarterioles found near almost every cell in the body number varies with metabolic activity of tissue they serve center vessel is thoroughfare channel all others have precappillary sphincters that can constrict and restrict flow

Figure 20.3

Three Capillary Types From least leaky to most leaky continuous fenestrated sinusoids If blood passes from one capillary network to another through a vein vein is called portal vein second network is called portal system

Figure 20.4a

Figure 20.4b

Figure 20.4c

Concept 20.3 Venules and Veins

Venules capillaries unite to form venules drain into veins tunica interna and tunica media

Veins venules unite to form veins return blood to the heart tunica interna, media, and externa thinner than arteries many have valves to prevent back flow low pressure system

Figure 20.5

Veins venules unite to form veins return blood to the heart tunica interna, media, and externa thinner than arteries many have valves to prevent back flow low pressure system

Table 20.1

Blood Reservoirs about 64% of blood is in systemic veins and venules at any given moment brain stem can vasoconstrict these vessels allowing greater blood flow to skeletal muscles

Figure 20.6

Concept 20.4 Capillary Exchange

Capillary Exchange exchange mechanisms include diffusion transcytosis bulk flow Hydrostatic pressure influences exchange Blood colloid osmotic pressures helps blood retain fluid in vessels resisted by interstitial fluid osmotic pressure

Figure 20.7

Filtration and Reabsorption pressure driven movement of fluid and solutes FROM blood into interstitial fluid reabsorption pressure driven from interstitial fluid INTO blood vessels net filtration pressure (NFP) difference between filtration pressure and reabsorption pressure is

Figure 20.7

Concept 20.5 Blood Flow

Blood Pressure hydrostatic pressure exerted by blood on walls of blood vessel measured in mm Hg systolic blood pressure highest pressure attained in arteries during systole diastolic blood pressure lowest pressure during diastole mean arterial pressure average of systolic and diastolic pressures useful when considering blood flow

Figure 20.8

Vascular Resistance opposition to blood flow due to friction between blood and walls of vessels increase in resistance increases BP decrease in resistance decreases BP Systemic vascular resistance depends on three things size of lumen larger lumen less resistance blood viscosity thinner blood less resistance vessel length shorter length less resistance

Venous Return mechanisms that “pump” blood from lower body to heart skeletal muscle pump figure 20.9 respiratory pump during inhalation the diaphragm moves downward increasing pressure in abdominal cavity and decreasing pressure in thoracic cavity abdominal veins are compressed and blood forced upward

Figure 20.9

Velocity of Blood Flow Inversely related to cross-sectional area of vessel slowest where area is greatest velocity slows as blood moves into larger veins Circulation time time required for a drop of blood to pass from right atrium through pulmonary and systemic circulation back to right atrium normally about 1 minute

Figure 20.10

Concept 20.6 Blood Pressure Regulation

Cardiovascular Center in medulla oblongata controls neural and hormonal negative feedback systems input from cerebral cortex, limbic system and hypothalamus sensory receptors proprioceptors, baroreceptors, chemoreceptors output ANS sympathetic & parasympathetic neurons vasomotor nerves throughout body especially skin and abdominal visceral

Figure 20.11

Neural Regulation of BP Baroreceptor Reflexes pressure sensitive sensory receptors in aorta, internal carotid arteries in neck and chest two most important carotid sinus reflex (BP in brain) aortic reflex (BP in ascending arch of aorta) if pressure drops sympathetic stimulation increases parasympathetic stimulation decreases Chemoreceptor Reflexes monitor carbon dioxide, oxygen gas, pH

Figure 20.12

Figure 20.13

Hormonal Regulation of BP Renin-angiotensin-aldosterone system endocrine response Epinephrine and norepinephrine sympathetic nervous system ADH ANP

Table 20.2

Autoregulation of BP tissue level automatic regulation of BP to match metabolic needs Two general types of stimuli physical changes chemicals

Concept 20.7 Measuring Pulse and BP

Pulse alternate expansion and recoil of arteries rate same as heart rate strongest close to heart faintest most distally may be felt in any artery that lies near the surface of body and runs over a bone or other firm structure

Blood Pressure measured in mm Hg using sphygomanometer when pressure in cuff exceeds systolic blood pressure sounds cut off as pressure is released sounds return when pressure in cuff is equal to systolic pressure and disappears again as it is equalized with diastolic blood pressure

Figure 20.15

Concept 20.8 Systemic and Pulmonary Circulation

Figure 20.16

Circulatory Routes anastomosis end arteries union of two or more arteries that supply the same body region provide collateral circulation alternate routes for blood to reach a tissue or organ end arteries arteries that do not anastomose

Concept 20.9 Pulmonary Circulation

Pulmonary Circulation heart to lungs and back again heart to pulmonary trunk to right and left pulmonary arteries to lungs (arteries, arterioles, capillaries surrounding alveoli, to venules to pulmonary veins to left atrium blood leaves the heart deoxygenated and returns oxygenated resistance is very low in pulmonary circuit (low pressure system)

Figure 20.17a

Figure 20.17b

Concept 20.10 Systemic Circulation

Systemic Circulation all arteries and arterioles that carry blood containing oxygen and nutrients from left side of heart throughout the body and back to the right atrium via vena cava leaves through aorta returns through superior and inferior vena cava or coronary sinus

Figure 20.18a

Figure 20.18b

Figure 20.18c

Figure 20.24

Table 20.3 pt 1

Table 20.3 pt 2

Figure 20.20a

Figure 20.20b

Figure 20.20c

Figure 20.20d

Table 20.4 pt 1

Table 20.4 pt 2

Table 20.4 pt 3

Figure 20.21a

Figure 20.21b

Table 20.5

Figure 20.22a

Figure 20.22b

Figure 20.22c

Figure 20.22d

Figure 20.22e

Table 20.6 pt 1

Table 20.6 pt 2

Figure 20.23a