chapter 15b
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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
Basementmembrane
Endothelial celljunctions
Transcytosisvesicles
Endothelial cells
Nucleus
(a) Continuous capillaries have leaky junctions.
Two Types of Capillaries
Basementmembrane (cut)
Basementmembrane
Endothelial celljunctionjunction
Transcytosis vesicles
Fenestratedpores
(b) Fenestrated capillaries have large pores.
Fenestrationsor 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
Netabsorption
Lymphvessels
Netfiltration
Venule
(b) Relationship between capillaries and lymph vessels
Lymphatic System
Figure 15-20
Thoracic (left lymph) duct
Axillary lymph nodes
Lymphatics ofmammary gland
Spleen
Pelviclymph nodesInguinallymph nodes
Thoracic ductThymus
Right lymph duct
Cervicallymph nodes
Blind-end lymphcapillaries in the tissuesremove fluid and filteredproteins.
Lymph fluid empties into the venous circulation.
Lymphatics ofupper limb
Lumbarlymph nodes
Lymphaticsof 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 15-22
Medullarycardiovascularcontrol center
Carotid and aorticbaroreceptors
Change inblood
pressure
Parasympatheticneurons
Sympatheticneurons
Veins
Arterioles
Ventricles
SA node
Integrating center
Stimulus
Efferent path
Effector
Sensory receptor
KEY
Change inblood
pressure
Integrating center
Stimulus
Efferent path
Effector
Sensory receptor
KEY
Blood Pressure
Figure 15-22 (1 of 10)
Carotid and aorticbaroreceptors
Change inblood
pressure
Integrating center
Stimulus
Efferent path
Effector
Sensory receptor
KEY
Blood Pressure
Figure 15-22 (2 of 10)
Medullarycardiovascularcontrol center
Carotid and aorticbaroreceptors
Change inblood
pressure
Integrating center
Stimulus
Efferent path
Effector
Sensory receptor
KEY
Blood Pressure
Figure 15-22 (3 of 10)
Medullarycardiovascularcontrol center
Carotid and aorticbaroreceptors
Change inblood
pressure
Parasympatheticneurons
Integrating center
Stimulus
Efferent path
Effector
Sensory receptor
KEY
Blood Pressure
Figure 15-22 (4 of 10)
Medullarycardiovascularcontrol center
Carotid and aorticbaroreceptors
Change inblood
pressure
Parasympatheticneurons
Sympatheticneurons
Integrating center
Stimulus
Efferent path
Effector
Sensory receptor
KEY
Blood Pressure
Figure 15-22 (5 of 10)
Medullarycardiovascularcontrol center
Carotid and aorticbaroreceptors
Change inblood
pressure
Parasympatheticneurons
Sympatheticneurons SA node
Integrating center
Stimulus
Efferent path
Effector
Sensory receptor
KEY
Blood Pressure
Figure 15-22 (6 of 10)
Medullarycardiovascularcontrol center
Carotid and aorticbaroreceptors
Change inblood
pressure
Parasympatheticneurons
Sympatheticneurons SA node
Integrating center
Stimulus
Efferent path
Effector
Sensory receptor
KEY
Blood Pressure
Figure 15-22 (7 of 10)
Medullarycardiovascularcontrol center
Carotid and aorticbaroreceptors
Change inblood
pressure
Parasympatheticneurons
Sympatheticneurons
Ventricles
SA node
Integrating center
Stimulus
Efferent path
Effector
Sensory receptor
KEY
Blood Pressure
Figure 15-22 (8 of 10)
Medullarycardiovascularcontrol center
Carotid and aorticbaroreceptors
Change inblood
pressure
Parasympatheticneurons
Sympatheticneurons
Arterioles
Ventricles
SA node
Integrating center
Stimulus
Efferent path
Effector
Sensory receptor
KEY
Blood Pressure
Figure 15-22 (9 of 10)
Medullarycardiovascularcontrol center
Carotid and aorticbaroreceptors
Change inblood
pressure
Parasympatheticneurons
Sympatheticneurons
Veins
Arterioles
Ventricles
SA node
Integrating center
Stimulus
Efferent path
Effector
Sensory receptor
KEY
Blood Pressure
Figure 15-22 (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 15-25
(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 accumulatesFibrous scar tissue
Smooth muscle cells
Calcifications are depositedwithin 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 depositedwithin 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
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