Chapter 15b Blood Flow and the Control of Blood Pressure

Arteriolar Resistance Arteriolar resistance is influenced by both local and systemic control mechanisms Local control Sympathetic reflexes Hormones

Arteriolar Resistance Table 15-2

Arteriolar Resistance Myogenic autoregulation Paracrines Active hyperemia Reactive hyperemia Sympathetic control SNS: norepinephrine Adrenal medulla: epinephrine

Hyperemia is a Locally Mediated Increase in Blood Flow Figure 15-11a

Hyperemia is a Locally Mediated Increase in Blood Flow Figure 15-11b

Norepinephrine Tonic control of arteriolar diameter Figure 15-12

Distribution of Blood Distribution of blood in the body at rest Figure 15-14

Blood Flow Blood flow through individual blood vessels is determined by vessel’s resistance to flow Figure 15-15a

Blood Flow Flow  1/resistance Figure 15-15b

Precapillary Sphincters Figure 15-16a

Precapillary Sphincters Figure 15-16b

Capillaries: Exchange Plasma and cells exchange materials across thin capillary wall Capillary density is related to metabolic activity of cells Capillaries have the thinnest walls Single layer of flattened endothelial cells Supported by basal lamina Bone marrow, liver and spleen do not have typical capillaries but sinusoids

Two Types of Capillaries Figure 15-17a Basement membrane Endothelial cell junctions Transcytosis vesicles Endothelial cells Nucleus (a) Continuous capillaries have leaky junctions.

Two Types of Capillaries Basement membrane (cut) Basement membrane Endothelial cell junction junction Transcytosis vesicles Fenestrated pores (b) Fenestrated capillaries have large pores. Fenestrations or pores Figure 15-17b

Velocity of Blood Flow Velocity of flow depends on total cross- sectional area of the vessels Figure 15-18

Capillary Exchange Exchange between plasma and interstitial fluid occurs by paracellular pathway or endothelial transport Small dissolved solutes and gasses move by diffusion Larger solutes and proteins move by vesicular transport In most capillaries, large proteins are transported by transcytosis

Capillary Exchange Bulk flow Mass movement as a result of hydrostatic or osmotic pressure gradients Absorption: fluid movement into capillaries Net absorption at venous end Filtration: fluid movement out of capillaries Caused by hydrostatic pressure Net filtration at arterial end

Fluid Exchange at a Capillary Hydrostatic pressure and osmotic pressure regulate bulk flow Figure 15-19a

Autoregulation and Capillary Dynamics PLAY Interactive Physiology® Animation: Cardiovascular System: Autoregulation and Capillary Dynamics

Lymphatic System Returning fluid and proteins to circulatory system Picking up fat absorbed and transferring it to circulatory system Serving as filter for pathogens

Fluid Exchange at a Capillary Figure 15-19b Arteriole Net absorption Lymph vessels Net filtration Venule (b) Relationship between capillaries and lymph vessels

Lymphatic System Figure Thoracic (left lymph) duct Axillary lymph nodes Lymphatics of mammary gland Spleen Pelvic lymph nodes Inguinal lymph nodes Thoracic duct Thymus Right lymph duct Cervical lymph nodes Blind-end lymph capillaries in the tissues remove fluid and filtered proteins. Lymph fluid empties into the venous circulation. Lymphatics of upper limb Lumbar lymph nodes Lymphatics of lower limb

Edema Two causes Inadequate drainage of lymph Filtration far greater than absorption Disruption of balance between filtration and absorption Increase in hydrostatic pressure Decrease in plasma protein concentration Increase in interstitial proteins

Blood Pressure Components of the baroreceptor reflex Figure Medullary cardiovascular control center Carotid and aortic baroreceptors Change in blood pressure Parasympathetic neurons Sympathetic neurons Veins Arterioles Ventricles SA node Integrating center Stimulus Efferent path Effector Sensory receptor KEY

Change in blood pressure Integrating center Stimulus Efferent path Effector Sensory receptor KEY Blood Pressure Figure (1 of 10)

Carotid and aortic baroreceptors Change in blood pressure Integrating center Stimulus Efferent path Effector Sensory receptor KEY Blood Pressure Figure (2 of 10)

Medullary cardiovascular control center Carotid and aortic baroreceptors Change in blood pressure Integrating center Stimulus Efferent path Effector Sensory receptor KEY Blood Pressure Figure (3 of 10)

Medullary cardiovascular control center Carotid and aortic baroreceptors Change in blood pressure Parasympathetic neurons Integrating center Stimulus Efferent path Effector Sensory receptor KEY Blood Pressure Figure (4 of 10)

Medullary cardiovascular control center Carotid and aortic baroreceptors Change in blood pressure Parasympathetic neurons Sympathetic neurons Integrating center Stimulus Efferent path Effector Sensory receptor KEY Blood Pressure Figure (5 of 10)

Medullary cardiovascular control center Carotid and aortic baroreceptors Change in blood pressure Parasympathetic neurons Sympathetic neurons SA node Integrating center Stimulus Efferent path Effector Sensory receptor KEY Blood Pressure Figure (6 of 10)

Medullary cardiovascular control center Carotid and aortic baroreceptors Change in blood pressure Parasympathetic neurons Sympathetic neurons SA node Integrating center Stimulus Efferent path Effector Sensory receptor KEY Blood Pressure Figure (7 of 10)

Medullary cardiovascular control center Carotid and aortic baroreceptors Change in blood pressure Parasympathetic neurons Sympathetic neurons Ventricles SA node Integrating center Stimulus Efferent path Effector Sensory receptor KEY Blood Pressure Figure (8 of 10)

Medullary cardiovascular control center Carotid and aortic baroreceptors Change in blood pressure Parasympathetic neurons Sympathetic neurons Arterioles Ventricles SA node Integrating center Stimulus Efferent path Effector Sensory receptor KEY Blood Pressure Figure (9 of 10)

Medullary cardiovascular control center Carotid and aortic baroreceptors Change in blood pressure Parasympathetic neurons Sympathetic neurons Veins Arterioles Ventricles SA node Integrating center Stimulus Efferent path Effector Sensory receptor KEY Blood Pressure Figure (10 of 10)

Blood Pressure The baroreceptor reflex: the response to increased blood pressure Figure 15-23

Blood Pressure The baroreceptor reflex: the response to orthostatic hypotension Figure 15-24

Blood Pressure Regulation PLAY Interactive Physiology® Animation: Cardiovascular System: Blood Pressure Regulation

CVD: Risk Factors Not controllable Sex Age Family history Controllable Smoking Obesity Sedentary lifestyle Untreated hypertension

CVD: Risk Factors Uncontrollable genetic but modifiable lifestyle Blood lipids Leads to atherosclerosis HDL-C versus LDL-C Diabetes mellitus Metabolic disorder contributes to development of atherosclerosis

LDL and Plaque The development of atherosclerotic plaques Figure (a) Normal arterial wall (b) Fatty streak (c) Stable fibrous plaque (d) Vulnerable plaque Endothelial cells Elastic connective tissue Smooth muscle cells Macrophages Smooth muscle cells A lipid core accumulates Fibrous scar tissue Smooth muscle cells Calcifications are deposited within the plaque. Platelets Macrophages LDL cholesterol accumulates

LDL and Plaque Figure 15-25a (a) Normal arterial wall Endothelial cells Elastic connective tissue Smooth muscle cells

LDL and Plaque Figure 15-25b (b) Fatty streak Macrophages Smooth muscle cells LDL cholesterol accumulates

LDL and Plaque Figure 15-25c (c) Stable fibrous plaque A lipid core accumulates Fibrous scar tissue Smooth muscle cells Calcifications are deposited within the plaque.

LDL and Plaque Figure 15-25d (d) Vulnerable plaque Platelets Macrophages

Hypertension The risk of developing cardiovascular disease doubles with each 20/10 mm Hg increase in blood pressure Essential hypertension has no clear cause other than hereditary Figure 15-26

Hypertension Carotid and aortic baroreceptors adapt Risk factor for atherosclerosis Heart muscle hypertrophies Pulmonary edema Congestive heart failure Treatment Calcium channel blockers, diuretics, beta- blocking drugs, and ACE inhibitors

Summary Blood vessels Vascular smooth muscle, metarterioles, venules, and angiogenesis Measuring blood pressure Systolic pressure, diastolic pressure, pulse pressure, MAP, and Korotkoff sounds Resistance in the arterioles Myogenic autoregulation, active hyperemia, and reactive hyperemia

Summary Distribution of blood Capillary exchange Continuous capillaries, fenestrated capillaries, bulk flow, filtration, absorption, and colloid osmotic pressure Lymphatic system Blood pressure regulation Baroreceptors, baroreceptor reflex, and cardiovascular control center Cardiovascular disease