The Human Body in Health and Illness, 4 th edition Barbara Herlihy Chapter 19: Functions of the Blood Vessels
The Human Body in Health and Illness, 4th edition
Barbara Herlihy
Chapter 19:Functions of the Blood Vessels
Lesson 19-1 Objectives
• List five functions of the blood vessels.• Describe the factors that determine
blood pressure.• Explain the baroreceptor reflex.
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Five Functions of Blood Vessels
• Act as a delivery system• Regulate blood pressure• Engage in the exchange of nutrients and
waste between the capillaries and cells• Redistribute blood in response to changing
body needs• Help regulate body temperature
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The Blood Vessels Deliver • Blood vessels deliver nutrients to the cell and
pick up waste.• Inadequate blood flow = Ischemia• “Five Cool Ps” assess adequacy of blood flow
– Pain– Pulselessness– Pallor– Paresthesia– Paralysis– Coolness
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Blood Pressure: Terminology
• Blood pressure: The force of blood against vessel walls (e.g., 118/76 mm Hg)
• Systolic pressure: Pressure in large arteries at the peak of systole (top number)
• Diastolic pressure: Pressure in large arteries during diastole (bottom number)
• Pulse pressure: Difference between systolic and diastolic pressures (42 mm Hg in this example)
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Blood Pressure: Ranges
• Normal range: <120 mm Hg (systolic) and <80 mm Hg (diastolic)
• Consequences of hypertension: Stroke, strain on the heart, other end-organ dysfunction
• Consequences of hypotension: Inadequate perfusion to all organs, especially heart and brain
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Measuring Blood Pressure
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Blood Pressure in Different Vessels
• Highest in aorta• Lowest in venae
cavae• High pressure
(aorta) pushes blood to low pressure (venae cavae)
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Aids to Venous Return
• Skeletal muscle pump
• Respiratory pump• Venoconstriction
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Heart and Blood Vessels Determine Blood Pressure
• Heart: Cardiac output (CO)• Vessels: Systemic vascular resistance (SVR)• BP = CO x SVR • BP = HR x SV x SVR
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Blood Pressure: Cardiac Component
• Plunger elevates pressure in barrel and pushes H2O out.
• Heart (plunger) elevates pressure in aorta and pushes blood through systemic circulation.
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Blood Pressure: Blood Vessel Component
• Resistance to flow– Nozzles (A and B)
change resistance to flow.
– Arterioles (C and D) act as nozzles, changing resistance to flow (vasodilation and vasoconstriction)
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Mechanisms of BP Regulation
• Rapidly acting mechanism: Baroreceptor reflex• Slowly acting mechanisms: Hormones
– Renin-angiotensin-aldosterone– Antidiuretic hormone (ADH)– Atrial natriuretic peptide (ANP)– Brain natriuretic peptide (BNP)
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Baroreceptor Reflex: Components
• Baroreceptors– Aortic arch and
carotid sinus
• Sensory nerves– CN IX, CN X
• Medulla oblongata• Motor nerve • Effector response
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Baroreceptor Reflex: Response• Stimulus: BP • Activate receptors• Sensory
information along CN IX, X
• Medulla interprets• Sympathetics fire
HR, SV, SVR BP
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Lesson 19-2 Objectives
• Describe the factors that determine capillary exchange.
• Describe mechanisms of edema formation.• Explain how the blood vessels respond to
changing body needs.• Describe the role of the blood vessels in the
regulation of body temperature.
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Blood Vessels Act as Exchange Vessels
• Waiters bring food to the table and take waste away.
• Capillaries bring oxygen and nutrients to cells, and carry away waste.
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Capillaries: Good Exchange Vessels
• Thin capillary walls– Facilitate diffusion across capillary walls
• Millions of capillaries– Increase surface area for diffusion – Place a capillary near each cell
• Slow velocity of blood flow– Increases time available for diffusion
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Capillaries Slow the Velocity of Flow
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Capillary Exchange: Forces • Outward force
– Filtration – Caused by blood
pressure– Aided by diffusion
• Inward force– Oncotic pressure – Caused by plasma
proteins– Lymphatic drainage
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Mechanisms: Edema and Dehydration
Edema• Fluid floods interstitial
space.• Pressure of outward
filtration exceeds inward oncotic pressure.
• Dependent edema– “Pitting”
Dehydration• Fluid of interstitial space
is depleted. • Inward oncotic pressure
exceeds pressure of outward filtration.
• Poor skin turgor– “Tenting”
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Edema Formation: Loss of Albumin
• Mechanism– Loss of albumin decreases plasma oncotic
pressure– Fluid accumulates in interstitial space
• Examples– Nephrotic syndrome (albuminuria and
hypoalbuminemia)– Severe burns
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Edema Formation: Poor Lymphatic Drainage
• Mechanism– Lymphatic capillaries help
drain interstitial space.– When blocked or removed,
fluid accumulates.
• Example– Lymphedema after removal
of axillary lymph nodes
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Edema Formation: Excess Blood Volume
• Mechanism – Excess blood volume increases filtration pressure
in capillaries.– Excess fluid accumulates in interstitial space.
• Examples– Heart failure– Overhydration
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Causes of Dehydration
• Mechanism– Low blood volume causes low filtration pressure in
the capillaries.– Plasma oncotic pressure pulls fluid from the
interstitial space.
• Examples– Excess vomiting and/or diarrhea– Exercise in high-temperature environment– Blood loss
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Blood Vessels Distribute Blood Flow in Rest and Exercise
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Blood Vessels Regulate Body Temperature
• During exercise, blood vessels dissipate heat.– Vasodilation
• During cold weather, blood vessels conserve heat.– Vasoconstriction
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