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Chapter 19Functions of the Blood Vessels

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Introduction• The circulatory system performs five main

functions.

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Functions as a Delivery System• The circulatory system delivers oxygen and

nutrients to the cells.• The circulatory system picks up waste from

the cells and delivers it to the organs of excretion.

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Regulates Blood Pressure• The circulatory system maintains a blood

pressure to ensure an adequate flow of blood to the body.

• The normal blood pressure is 120/80 mm Hg; 120 is the systolic reading, and 80 is the diastolic reading.

• Blood pressure varies throughout the circulatory system; it is highest in the aorta and lowest in the venae cavae.

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Regulates Blood Pressure - cont’d

• Blood pressure is determined by the action of the heart and blood vessels. The heart affects blood pressure by increasing or decreasing cardiac output. The blood vessels affect blood pressure by constricting or dilating the arterioles.

• Blood pressure is regulated on a day-to-day basis by the baroreceptor reflex. Other mechanisms can correct blood pressure more slowly. The most important is the renin-angiotensin-aldosterone mechanism.

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Acts as Exchange Vessel• The capillaries are the site of exchange of nutrients and waste

between the blood and tissue fluid.• Factors that make the capillaries ideal exchange vessels are the

thin capillary walls with many pores, millions of capillaries, and a slow rate of blood flow through the capillaries.

• Water and dissolved substances move out of the capillary into the tissue spaces by diffusion and filtration. The capillary pressure pushes water out of the capillaries. Water and dissolved waste move from the tissue fluid into the capillaries by osmosis.

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Distributes Blood• Distributes blood according to need

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Regulates Body Temperature• Vasodilation of the blood vessels of the skin

encourages heat loss.• Vasoconstriction of the blood vessels of the

skin decreases heat loss.

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Introduction• The circulatory system is a series of blood

vessels, or hollow tubes, that begin and end in the heart. The circulatory system delivers blood to all the body’s cells and then returns the blood to the heart.

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Circles, Circuits, and Circulations• The heart and blood vessels form a circle.• Two circulations: pulmonic and systemic.

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Blood Vessels • Naming the Blood Vessels– Arteries carry blood away from the heart; the

smallest arteries are the arterioles.– Capillaries connect arteries and veins; a capillary is

close to every cell in the body.– Veins carry blood back to the heart; small veins

are called venules.

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Blood Vessels - cont’d

• Layers of Blood Vessels– The tunica intima is the smooth innermost layer.– The tunica media is the middle layer that contains

elastic tissue and smooth muscle.– The tunica adventitia is the outermost layer of

connective tissue.

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Blood Vessels - cont’d

• Blood Vessels: What They Do– Arteries conduct blood from the heart to the organs and

are called conductance vessels.– The arterioles constrict and dilate, thereby determining

resistance to the flow of blood. The arterioles are called resistance vessels.

– Capillaries are concerned with the exchange of water and dissolved substances between the blood and tissue fluid. Capillaries are called exchange vessels.

– Veins and venules return blood to the heart from the body. The veins also store blood and are therefore called capacitance vessels.

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Major Arteries of the Systemic Circulation

• The major arteries include the aorta and the arteries arising from the aorta.

• See Figure 18-4 for the names and locations of the major arteries.

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Major Veins of the Systemic Circulation

• The major veins include the venae cavae and the veins that empty into them.

• See Figure 18-5 for the names and locations of the major veins.

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Special Circulations• The head and brain are supplied by two sets of

arteries: the carotid arteries and the vertebral arteries. The internal carotid arteries and the basilar artery form the circle of Willis. Blood from the head and brain drains into the jugular veins.

• The blood supply of the liver is composed of the portal vein, hepatic artery, and hepatic veins. The hepatic artery brings oxygen-rich blood to the liver.

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Special Circulations - cont’d

• The portal vein carries blood from the digestive tract to the liver. The hepatic veins carry blood from the liver to the inferior vena cava.

• The fetal circulation has several unique features. The fetus uses the placenta as lungs. The umbilical blood vessels carry blood between the placenta and the fetus. Three special structures are the ductus venosus, foramen ovale, and ductus arteriosus.

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The Pulse• The pulse is due to the alternating expansion

and recoil of the artery creating a pressure wave (similar to vibration).

• The pulse is often described as a “heartbeat that can be felt at the wrist.”

• Figure 18-9 identifies the pulse points.

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Introduction• The heart pumps blood through the blood

vessels, supplying the cells of the body with oxygen and nutrients and carrying away the waste products of metabolism. The heart functions in a coordinated and adaptable manner to perform its tasks.

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Part A:The Coordinated and Adaptable Pump

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Cardiac Cycle• The cardiac cycle is a sequence of events that

occurs during one heartbeat.• The events of the cardiac cycle include atrial

and ventricular systole (contraction) and diastole (relaxation).

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Heart: Autonomic Control • The autonomic nervous system (ANS) allows the

heart to respond to changing body needs.• Stimulation of the sympathetic nerves increases

heart rate (SA node), conduction velocity (AV node), and contractile force (myocardium).

• Stimulation of the parasympathetic nerves (vagus) decreases heart rate and conduction velocity.

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Cardiac Output (CO)• CO is the amount of blood pumped by the

ventricle in 1 minute.• CO is determined by heart rate and stroke

volume.• There are many factors that change HR and/or

SV.

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How Stroke Volume (SV) Can Be Changed

• SV can be changed by Starling’s law of the heart (stretch).

• SV can be changed by an inotropic effect (nonstretch).

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Part B: Heart Talk

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Heart Talk• Heart Talk: includes the definition and

description of commonly used clinical terms such as preload, afterload, ejection fraction, and inotropic effect.

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Heart Talk - cont’d

• Heart Talk: Receptor Terminology: includes the definitions of beta1-adrenergic receptor activation, beta1-adrenergic receptor blockade, muscarinic-receptor activation, and muscarinic-receptor blockade.

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Part C:

The Failing Heart: When the Heart Can’t Pump

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Left-Sided Heart Failure• The left heart can fail, producing symptoms

due to a backup of blood into the pulmonic circulation (pulmonary edema).

• The failing left heart is unable to pump adequate blood to the systemic circulation, producing S&S related to poor tissue oxygenation.

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Right-Sided Heart Failure• Blood backs up behind the failed right

ventricle, causing jugular vein distention, hepatomegaly, splenomegaly, digestive problems, and ankle edema.

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Heart Failure • Heart failure is also described as backward

heart failure and forward heart failure.

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Introduction • The heart is a four-chambered pump that

delivers blood to the lungs and the systemic circulation.

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Function, Location, and Size of the Heart

• The heart is located in the mediastinum toward the left side. It is about the size of a fist.

• The heart pumps blood throughout the body delivering nutrients and picking up waste.

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The Heart’s Layers and Covering• The heart has three layers: endocardium,

myocardium, and epicardium. • The heart is supported by a slinglike

pericardium. • Two layers of the pericardium form the

pericardial space.

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A Double Pump and Two Circulations• The right heart pumps blood to the lungs for

oxygenation (called the pulmonary circulation).

• The left heart pumps blood throughout the rest of the body (called the systemic circulation).

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The Heart’s Chambers and Great Vessels

• The heart has four chambers, two atria and two ventricles.

• The atria receive the blood, and the ventricles pump the blood.

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Heart Valves• The purpose of heart valves is to keep blood

flowing in a forward direction.• Two atrioventricular (AV) valves are the

tricuspid valve (right heart) and the bicuspid (mitral) valve (left heart).

• The two semilunar valves are the pulmonic valve (right heart) and the aortic valve (left heart).

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Heart Sounds• The heart sounds (“lubb-dupp”) are made by

the vibrations caused by closure of the valves.• The “lubb” is due to the closure of the AV

valves at the beginning of ventricular systole. The “dupp” is due to the closure of the semilunar valves at the beginning of ventricular diastole.

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Pathway: Blood Flow Through the Heart

• The right heart receives blood from the venae cavae and pumps it to the lungs for oxygenation. The left heart receives oxygenated blood from the lungs and pumps it to the systemic circulation.

• Blood flow through the heart is summarized in the flow chart (see Figure 16-7).

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Blood Supply to the Myocardium• The left and right coronary arteries supply the

myocardium with oxygen and nutrients. • The coronary veins drain the unoxygenated

blood and empty it into the coronary sinus (which empties into the right atrium).

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Cardiac Conduction System• The heart generates an electrical signal (cardiac

impulse) that moves throughout the heart in a coordinated way. The electrical signal causes the myocardium to contract.

• The pathway followed by the cardiac impulse is summarized in Figure 16-10.

• Cardiac muscle displays automaticity and rhythmicity.

• The electrical activity of cardiac muscle is recorded as an electrocardiogram.

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