Lecture 15.pdf

About This Chapter 15.1 The Blood Vessels 15.2 Blood Pressure 15.3 Resistance in the Arterioles 15.4 Distribution of Blood to the Tissues 15.5 Regulation of Cardiovascular Function 15.6 Exchange at the Capillaries 15.7 The Lymphatic System Copyright © 2019, 2016, 2013 Pearson Education...

About This Chapter 15.1 The Blood Vessels 15.2 Blood Pressure 15.3 Resistance in the Arterioles 15.4 Distribution of Blood to the Tissues 15.5 Regulation of Cardiovascular Function 15.6 Exchange at the Capillaries 15.7 The Lymphatic System Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 15.3 Resistance in the Arterioles Local control: matches tissue blood flow to metabolic needs of tissue In heart and skeletal muscle, often take precedence over reflex control by CNS • Arteriolar resistance is influenced by both local and systemic control reflexes: CNS, maintain mean arterial pressure and determine blood distribution to mechanisms Sympathetic various tissues to meet homeostatic needs like temperature regulation particularly those regulating salt and water – Local control, sympathetic reflexes, hormones Hormones: excretion by kidneys influence blood pressure by acting • Myogenic autoregulation adjusts blood flow directly non arterioles and by altering autonomic reflex control – Vascular smooth muscle regulates its own state of contraction – Stretched vascular smooth muscle mechanically-gated Ca2+ channels Cation entry depolarizes cell —> opens Ca2+ channels —> Ca2+ flows into cell ▪ Contracts to resist stretching down its gradient + calmodulin —> activates myosin light chain kinase (MLCK) —> increases myosin ATPase activity and cross bridge activity —> contraction • Paracrine signals influence vascular smooth muscle by by – Secreted vascular epithelium or nearby cells which arterioles are supplying blood ▪ Active hyperemia vs. reactive hyperemia figure 15.10 drugs used to treat erectile dysfunction prolong NO activity in endogenous NO activity suspected to play a role in hypertension and ▪ Nitric oxide Decreases preeclampsia (elevated blood pressure in pregnancy) ▪ Kinins and histamine are potent vasodilators play a role in inflammation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Table 15.2 Chemicals Mediating Vasoconstriction and Vasodilation Vasoconstriction Chemical Physiological Role Source Type Norepinephrine (α-receptors) Baroreceptor reflex Sympathetic neurons Neurotransmitter Serotonin Platelet aggregation, smooth muscle contraction Neurons, digestive tract, platelets Paracrine signal, neurotransmitter Endothelin Local control of blood flow Vascular endothelium Paracrine Vasopressin Increases blood pressure in hemorrhage Posterior pituitary Neurohormone Angiotensin II Increases blood pressure Plasma hormone Hormone Vasodilation Chemical Physiological Role Source Type Epinephrine (β2-receptors) Increase blood flow to skeletal muscle, heart, liver Adrenal medulla Neurohormone Acetylcholine Erection reflex (indirectly through NO production) Parasympathetic neurons Neurotransmitter Nitric oxide (NO) Local control of blood flow Endothelium Paracrine signal Bradykinin (via NO) Increases blood flow Multiple tissues Paracrine signal Adenosine Increases blood flow to match metabolism Hypoxic cells Paracrine signal  O2 ,  CO2 ,  H+ ,  K + Increase blood flow to match metabolism Cell metabolism Paracrine molecule Histamine Increases blood flow Mast cells Paracrine signal Natriuretic peptides (example: ANP) Reduce blood pressure Atrial myocardium, brain Hormone, neurotransmitter Vasoactive intestinal peptide Digestive secretion, relax smooth muscle Neurons Neurotransmitter, neurohormone Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 15.10 Hyperemia Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Sympathetic Branch Controls Most Vascular Smooth Muscle • Sympathetic control – Sympathetic innervation of most systemic arterioles ▪ Exception: vasculature of erectile tissue (penis and clitoris) ▪ Norepinephrine maintains arteriolar tone – Binds α receptors → vasoconstriction – Adrenal medulla releases epinephrine into blood ▪ Binds α receptors with very low affinity → vasoconstriction Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 15.4 Distribution of Blood to the Tissues • Blood distribution varies according to metabolic need of individual tissues • Governed by • • – Local control mechanisms – Homeostatic reflexes Possible because arterioles are arranged in parallel – Flow in aorta = Flow in all arterioles – Individual arterioles regulate own flow, compensated by remaining arterioles Cerebral blood flow stays nearly constant Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 15.12 Distribution of blood in the body at rest Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 15.13 Blood flow through individual blood vessels is determined by the vessel’s resistance to flow Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 15.5 Regulation of Cardiovascular Function • Cardiovascular control center (CVCC) • The baroreceptor reflex controls blood pressure – – Baroreceptors (mechanoreceptors) in carotid arteries and aorta ▪ Produce continuous (tonic) action potential to brainstem ▪ Changes in pressure reflected changes in frequency of action potential Always functioning Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 15.14(a) Cardiovascular Control Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 15.6 Exchange at the Capillaries • Plasma and cells exchange materials across thin capillary walls – Most cells are located within 0.1 mm of the nearest capillary • Capillary density is related to metabolic activity of cells • Capillaries have the thinnest walls – Single layer of flattened endothelial cells – Supported by basal lamina • • most common ones, in muscle, connective tissue, and neural tissue (BBB) Continuous capillaries vs. fenestrated capillaries endothelial cells are joined to one another with leaky junction large pores that allow high volumes of fluid to pass rapidly between plasma and interstitial fluid kidney and intestine (associated with absorptive transporting epithelia) times wider than a capillary Sinusoids 5have fenestrations, may be gaps between cells – Modified capillary vessel where blood cells and plasma proteins need to cross the – Bone marrow, liver, and spleen locations endothelium to enter blood Liver: sinusoidal endothelium lacks basal lamina which allows more free exchange between plasma and interstitial fluid Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 15.16 Capillaries Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 15.17(a-b) Velocity of blood flow Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Most Capillary Exchange Takes Place by Diffusion and Transcytosis • • • Exchange between plasma and interstitial fluid occurs by – paracellular pathway movement between endothelial cells – endothelial transport movement through cells Movement by diffusion – Small dissolved solutes and gases – Depending on lipid solubility and concentration gradient Vesicular transport – Larger solutes and proteins – In most capillaries, large molecules (including selected proteins) are transported by transcytosis Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Capillary Filtration and Absorption Takes Place by Bulk Flow • Bulk flow is mass movement as a result of hydrostatic or osmotic pressure gradients • Filtration: fluid movement out of capillaries – Caused by hydrostatic pressure (PH); IF hydrostatic pressure (PIF) is negligible ▪ PH decreases over length of capillary due to friction as energy is lost • Absorption: fluid movement into capillaries – Caused by colloid osmotic pressure (π), also called oncotic pressure ▪ Due to presence of proteins in fluid and capillaries have plasma causes oncotic proteins (πcap = 25 mm Hg), IF has none (πIF = 0 mm Hg. this pressure • Net pressure determines direction of bulk flow; PNET = PH - π – Net filtration at arterial end (PH > π) + : net filtration -: net absorption 7 mm Hg – Net absorption at venous end (PH < π) -10 mm Hg Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 15.18(a) Capillary fluid exchange Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 15.18(b) Capillary fluid exchange Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 15.7 Lymphatic System • Returns fluid and proteins to circulatory system • Picks up fat absorbed and transferring it to circulatory system • Serves as filter for pathogens • Allows for one-way movement of interstitial fluid into the circulatory system • – Lymph – Lymph capillaries are blind-ended – Lymph vessels with semilunar valves empty into venous circulation – nodules of tissue with a fibrous outer capsule and an internal collection of immunologically Lymph nodes bean-shaped active cells, including lymphocytes and macrophages clear fluid lie close to all blood capillaries except those in kidney and CNS Edema is accumulation of fluid in the interstitial space – Inadequate drainage of lymph or filtration greater than absorption Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Key words • perfusion, elastic recoil, pressure reservoir, arterioles, volume reservoir, endothelium, tunica intima, vascular smooth muscle, vasoconstriction, vasodilation, muscle tone, microcirculation, arterioles, metarterioles, precapillary sphincters, driving pressure, systolic pressure, diastolic pressure, pulse, pulse pressure, venous return, skeletal muscle pump, respiratory pump, mean arterial pressure (MAP), myogenic autoregulation, active hyperemia, reactive hyperemia, atrial natriuretic peptide, angiotensin II (ANGII), cardiovascular control center (CVCC), baroreceptors, baroreceptor reflex, continuous capillaries, blood-brain barrier, fenestrated capillaries, sinusoids, total cross-sectional area, bulk flow, absorption, filtration, colloid osmotic pressure (π, also called oncotic pressure), hydrostatic pressure (PH), lymph, lymph nodes, lymph capillaries. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved