Chapter 019

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.

Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights

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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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Chapter 019

Health & Medicine