Figure 20–2c

Anatomy of the Heart

Pericardium & Myocardium

Figure 20–2c

Remember, the heart sits in it’s own cavity, known as the

mediastinum. The heart is surrounded by the Pericardium,

a double lining of the pericardial cavity. The pericardium and

its fluid lubricate the moving surfaces of the heart.

Figure 20–2c

The Pericardium, consists of a double lining:

Parietal pericardium

Is the tough, outer two-layered sac and is

fibrous. This sac contains pericardial fluid. It

is attached to the diaphragm, the sternum,

and the base of the heart.

Visceral (epicardium) pericardium

Is the thinner, inner layer of pericardium that

adheres tightly to the heart.

The space between the parietal and visceral

pericardium is known as the pericardial cavity

and contains the pericardial fluid.

Figure 20–2c

The parietal layer attaches to the large arteries exiting the

heart and turns and continues over the external heart

surface as the visceral layer (epicardium).

The parietal and visceral layers is the pericardial cavity

which contains a serous fluid, known as pericardial fluid.

This fluid allows the heart to glide smoothly during heart

activity in a friction-free environment.

Figure 20–2c

The visceral layer secretes the pericardial fluid.

The myocardium is the heart muscle and is composed

mainly of cardiac muscle and forms the bulk of the heart.

The endocardium (inside the heart) is a glistening white

sheet of endothelium (squamous epithelium) resting on a

thin c.t. layer.

Atria

Figure 20–2c

The atria (atrium = entryway) is the receiving chamber and is

thin-walled (relatively speaking). This is because it contracts

minimally to push blood “downstairs” into the ventricles.

Each has a little ear-shaped appendage termed the auricle

which helps increase the atrial volume.

Coronary Circulation

Although the heart is continuously filled with blood, this blood

provides little nourishment to heart tissue.

The coronary circulation is the functional blood supply of

the heart & is the shortest circulation in the body.

Figure 20–2c

The right atrium may show a slight groove, the coronary

sulcus which divides the atria and ventricles.

This groove is the location of the coronary arteries and

posteriorly the coronary sinus (vessels of cardiac muscle),

and right coronary artery.

Figure 20–2c

The arterial supply of the coronary circulation is provided by

the right and left coronary arteries, both arising from the base

of the aorta and encircling the heart in the coronary sulcus.

The left coronary artery divides to form the anterior

interventricular and left circumflex artery.

Figure 20–2c

The right coronary artery divides into two branches, the

marginal artery and the posterior interventricular artery

Complete blockage leads to tissue death and heart attack.

Angina pectoris (choked chest) is thoracic pain caused by a

fleeting deficiency in blood delivery to the myocardium.

How Coronary Heart Disease Develops

Coronary Artery Angioplasty

Figure 20–2c

After passing through the capillary beds of the myocardium,

the venous blood is collected by the cardiac veins, whose

paths roughly follow those of the coronary arteries.

These veins join together to form an enlarged vessel called

the coronary sinus, which empties the blood into the right

atrium.

Figure 20–2c

The sinus has three large tributaries: the great cardiac vein,

in the anterior interventricular sulcus; and the small cardiac

vein, running along the heart’s right inferior margin.

Additionally, several anterior cardiac veins empty directly into

the right atrium anteriorly.

The Right Atria

Figure 20–2c

Blood enters the right atrium via 3 veins, the superior and

inferior vena cava and the coronary sinus.

The posterior region of the right atrium have smooth

LOOKING muscle, but the anterior portion has pectinate

muscles (pectin = comb) which contain prominent muscular

ridges on the anterior atrial wall and inner surfaces of the

right auricle.

The right atrium shows the Foramen ovale.

Before birth, it is an opening through the interatrial

septum that connects the two atria.

This seals off at birth, forming the fossa ovalis.

AV Valves

Atrioventricular (AV) valves connects the right atrium to right

ventricle and left atrium to left ventricle

Each atrioventricular valve has cusps that are attached to a

fibrous ring around the opening

The fibrous flaps that form tricuspid (3 valves, right side) &

bicuspid (2 valves, left side) valves

Valves allow blood flow in one direction.

Atrioventricular (AV) valves: When Blood pressure

increases it closes the valve cusps during ventricular

contraction, the papillary muscles tense the chordae

tendineae, (heart strings), which prevents the valves from

swinging into the atria.

AV Valve Function

(a) The AV valves open when the blood pressure

exerted on their atrial side is greater than that exerted

on their ventricular side.

(b) The valves are forced closed when the ventricles contract &

interventricular pressure rises, moving the contained blood

superiorly. Papillary m. & chordae tendineae keeps the valve

flaps closed.

Mitral (bicuspid) Left AV Valve

Semilunar Valves

The semilunar valves (SL) guard the bases of the large

arteries coming from the ventricles (aorta & pulmonary trunk) &

prevent back flow into the associated ventricles.

Each SL valve is fashioned from 3 pocket-like cusps shaped

roughly like a crescent moon.

The SL valves open & close in response to differences in

pressure.

Semilunar Valve Function

(a) During ventricular contraction, the valves are open.

(b) When the ventricles relax, the back flowing blood closes the

valves.

Ventricular Differences

The left ventricle holds same volume as right the ventricle,

but is larger & the muscle is thicker and more powerful

Similar internally to right ventricle but does not have

moderator band

Right ventricle wall is thinner, develops less pressure than left

ventricle. Right ventricle is pouch-shaped, left ventricle is

round.

One Heartbeat

The ability of cardiac muscle to depolarize and contract is

intrinsic; that is, it is a property of heart muscle and does not

depend on the n. system.

Even if all n. connections to the heart are severed, the heart

continues to beat rhythmically, as demonstrated by

transplanted hearts.

The heart is supplied with autonomic n. fibers that can alter

the rhythm of the heart.

A cardiac cycle consists of the events occurring during one

heartbeat.

At a normal heart rate of 70-76 beats/min, a cardiac cycle

lasts 0.8 seconds.

Normal heart sounds arise chiefly from turbulent blood flow

during the closing of heart valves.

Systole = contraction of the ventricles (atria relax)

Diastole = relaxation of ventricles (atria contract)

The right and left ventricles contract causing the semilunar

valves to open and the AV valves to close = LUB (first heart

sound, S1)

The right atrium contracts and blood is pushed into the right

ventricle…at the same time, the left atrium contracts and

blood is pushed into the left ventricle.

The AV valves must be open.

As blood in the pulmonary and aorta moves backward it

causes the semilunar valves to close = DUB (Second heart

sound, S2).

Between S1 and S2 = systole, blood is

going out into the whole body.

Between S2 and S1 = diastole, blood

refilling from atrium to ventricles.

Normal Heart Sounds

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