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Chapter 18Anatomy of the

Cardiovascular System

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Heart

• Location of the heart

– Lies in the mediastinum

– Posteriorly the heart rests on the bodies of thoracic vertebrae 5 through 8

– Boundaries of the heart are clinically important as an aid in diagnosing heart disorders

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Heart• Size and shape of the heart

– At birth, is transverse and appears large in proportion to diameter of chest cavity, 1/130 body weight

– Between puberty and 25 years of age the heart attains its adult shape and weight, 1/300 body weight

– Males- 310 g– Females- 225 g

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Heart: Structure

• Pericardium- covers the heart– Function of the heart coverings—provides

protection against friction

pericardium from a normal ferret

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Heart: Structure– Wall of the heart—made up of three distinct

layers:• Epicardium

– outer layer of heart wall• Myocardium

– thick, contractile middle layer of heart wall

– compresses the heart cavities, and the blood within them, with great force

• Endocardium– delicate inner layer of endothelial tissue

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Heart: Structure

Chambers of the heart— divided into four cavities with the right and left chambers separated by the septum

• Atria– Two superior chambers, known as

“receiving chambers,” because they receive blood from veins

– Myocardial wall of each atrium is not very thick, because little pressure is needed to move blood such a small distance

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Heart: Structure

• Ventricles

– Two lower chambers, known as

“pumping chambers,” because they

push blood into the large network of

vessels

– Ventricular myocardium is thicker than myocardium of the atria, because great force must be generated to pump blood a large distance (to lungs and body)

– myocardium of left ventricle is thicker than the right, because it must push blood much further

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Right Atrium Left Atrium

Right Ventricle Left Ventricle

Lungs

Pulmonary Artery

Through bicuspid

valve

Body

Pulmonary Vein Through

tricuspid (mitral) valve

Aorta

Superior Vena Cava

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To Body

To Lungs

To Brain

Right Ventricle to the LUNGS (blue chambers)

Left Ventricle to the BODY (red chambers)

Brain & Body Right Atrium Right Ventricle Lungs Left Atrium Left Ventricle Brain & Body

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Heart: ValvesValves of the heart— devices

that permit the flow of blood

in one direction only• Atrioventricular (AV) valves—prevent blood from

flowing back into the atria from the ventricles when the ventricles contract

– Tricuspid valve (LEFT AV valve)— guards the left atrioventricular orifice with 3 flaps of endocardium

– Bicuspid, valve (RIGHT AV valve)—similar in structure to tricuspid valve except only two flaps present

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Heart: Valves

• Semilunar (SL) valves– half moon–shaped flaps growing out from the lining of the

pulmonary artery and aorta

– prevents blood from flowing back into ventricles from aorta and pulmonary artery

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Heart: Blood Supply

Artery: Carries blood AWAY from heart– Coronary arteries

– First branches to come off aorta– Ventricles receive blood from branches of both right

and left coronary arteries– Each ventricle receives blood only from a small

branch of corresponding coronary artery– Most abundant blood supply goes to myocardium of

left ventricle

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Heart: Blood Supply

Veins of the coronary circulation– As a rule, veins follow a course that closely parallels

that of coronary arteries– After going through cardiac veins, blood enters

coronary sinus to drain into right atrium– Several veins drain directly into right atrium

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Heart

– Conduction system of the heart• Sinoatrial node (SA node or pacemaker)— hundreds

of cells in right atrial wall near opening of superior vena cava- start heart beat

• Atrioventricular node (AV node)—small mass of special cardiac muscle in right atrium along lower part of interatrial septum

• Atrioventricular bundle (bundle of His) and Purkinje fibers

– Bundle of His originates in AV node, extends by two branches down the two sides of the interventricular septum, and continues as Purkinje fibers

– Purkinje fibers extend out to papillary muscles and lateral walls of ventricles

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Heart

– Nerve supply of the heart• Cardiac plexuses— made up of the combination of

excitatory and inhibitory fibers• Vagus fibers— inhibitory, or depressor, nerves

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Blood Vessels

– Arteries• Carry blood AWAY from heart—all arteries

(except pulmonary artery) carry oxygenated blood

• Elastic arteries— largest in body– Examples: aorta and its major branches– Able to stretch without injury– Accommodate surge of blood when heart

contracts and able to recoil when ventricles relax

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Blood Vessels– Arteries

• Muscular (distributing) arteries– Smaller in diameter than elastic arteries

– Muscular layer is thick

» Examples: brachial, gastric, superior mesenteric

• Arterioles (resistance vessels)– Smallest arteries

– Important in regulating

blood flow to organs

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Blood Vessels– Capillaries— primary exchange vessels

• Microscopic vessels• Carry blood from arterioles to venules• Not evenly distributed

– highest numbers in

tissues with high

metabolic rate

• may be absent in some

“avascular” tissues

such as cartilage

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Blood Vessels

• Types of capillaries – True capillaries– Continuous capillaries– Fenestrated capillaries– Sinusoids

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Blood Vessels

– Veins• Carry blood toward the heart• Act as collectors and as reservoir vessels• called capacitance vessels

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Circulatory routes

– Systemic circulation- Left Ventricle Brain & Body Right Atrium

– Pulmonary circulation- Right Atrium Right Ventricle Lungs Left Atrium

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Systemic circulation

– Systemic arteries• arteries arterioles capillaries

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Fetal circulationBasic plan of fetal

circulation— additional vessels needed to allow fetal blood to secure oxygen from maternal blood at the placenta

• Umbilical vein- returns oxygenated blood from placenta to fetus

• Foramen ovale-opening in septum between right and left atria

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Changes in circulation at birth • When umbilical cord is cut, the two umbilical arteries, the

placenta and the umbilical vein no longer function

• Umbilical vein within the baby’s body becomes the round ligament of the liver

• Foramen ovale—functionally closed shortly after a newborn’s first breath and pulmonary circulation is established; structural closure takes approximately 9 months

• Ductus arteriosus—contracts with establishment of respiration, becomes ligamentum arteriosum

Fetal circulation

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Cycle of Life: Cardiovascular Anatomy

• Birth— change from placenta-dependent system• Heart and blood vessels maintain basic structure

and function from childhood through adulthood– Exercise thickens myocardium and increases supply of

blood vessels in skeletal muscle tissue• Adulthood through later adulthood—degenerative

changes– Atherosclerosis— blockage or weakening of critical

arteries– Heart valves and myocardial tissue degenerate—

reduces pumping efficiency