Download Walls of the Heart

Histology 2016-2017
Department of Anatomy &Histology:
Dr.Rajaa Ali
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Cardiovascular System
Introduction
The human body is made up of 70 to 80 trillion cells. All of these cells need
to be fed oxygen and nutrients. These are provided by the cardiovascular
system (CVS), (fig. ).
The body’s cells must also get rid of waste materials. The CVS does this job
too, at the same time it delivers oxygen and nutrients.
12.1 Major Organs of the Cardiovascular System
The heart pumps blood. It beats 60 to 90 times every minute for whole life.
Each beat pumps blood throughout the body. The blood flows through blood
vessels.
12.2 Structures of the Heart
1. superior vena cava (VE-nah KAY-vah)
2. pulmonary semilunar valve (POOL-mon-ayr-ee seh-me-LOO-nar VALV)
3. right atrium (AY-tree-um)
4. tricuspid valve (trigh-KUS-pid)
5. right ventricle (VEN-trih-kul)
6. inferior vena cava (VE-nah KAY-vah)
7. septum (SEP-tum)
8. left ventricle (VEN-trih-kul)
9. bicuspid (bye-KUS-pid) or mitral (MY-tral) valve
10. aortic semilunar valve (ay-OR-tick seh-mee-LOO-nar VALV)
11. left atrium
12. aorta (ay-OR-tah)
The large blood vessels include the aorta, superior vena cava (SVC), inferior
vena cava (IVC), and pulmonary artery.
Heart Chambers
The heart contains four cavities. They are called
chambers. The upper chambers are called atria (singular is atrium). The
lower chambers are called ventricles (singular is ventricle).
Figure also illustrates that the heart is separated into the right and left
sections.
The wall dividing them is called the septum.
In Brief
Atria are the upper chambers.
Ventricles are the lower chambers.
Septum separates the right and left sides of the heart.
Heart Valves
There are four valves in the heart. They open to let blood in, and then they
close tightly to ensure there is no backward flow of blood (Figure ).
Two of the valves are called semilunar valves (Figure 12-4A). The
semilunar valve at the entrance of the pulmonary artery is called the
pulmonary semilunar valve.
The one at the entrance of the aorta is called the aortic semilunar valve.
In Brief
Semilunar valves
pulmonary valve
aortic valve
Atrioventricular (AV) valves
tricuspid valve
bicuspid valve
Walls of the Heart
The heart has three walls (Figure ). The outer wall is the epicardium
um).
The middle wall is the myocardium . It is composed of the muscle that
contracts the ventricles, pumping the blood out of the heart. The inner
wall is the endocardium .
Pericardium: The heart is surrounded by a sac called the pericardium.
(Figure). It has two layers. Pericardial fluid lies between the layers. This
fluid prevents friction between the two layers when the heart beats.
In Brief
Epicardium outermost wall of the heart
Myocardium muscle wall of the heart
Endocardium innermost wall of the heart
Pericardium sac surrounding the heart
How the Heart Beats
Electrical impulses stimulate the heart to beat. Unlike other nerve impulses,
they do not come from the brain. They are created in special tissue in the
atrium called the pacemaker.
They then follow a trail through the heart to the Purkinje fibers, which
extend throughout the ventricles. When the impulses reach the Purkinje
fibers, the ventricles contract and push blood out of the heart into arteries.
The trail the impulses follow from the pacemaker to the ventricles is called
the conduction pathway. It is illustrated in Figure . When the electrical
impulses follow the conduction pathway properly, the heart will beat in a
regular way, 60 to 90 beats per minute. This is called normal sinus rhythm.
The electrical activity of the heart can be recorded in a procedure called
electrocardiography (Figure). The record of such a test is called an
electrocardiogram . It is usually referred to as an ECG or EKG. Figure
shows a record of a normal ECG. The spikes or waves on the record
represent the strength of contraction of the atria and ventricles.
In Brief
Electrical impulses travel through the heart from the pacemaker to the
Purkinje fibers, causing the ventricles to contract and the heart to beat. An
ECG monitors the electrical impulses as they travel through the heart.
Blood Pressure and Pulse
On each ventricular contraction, blood is pumped through an artery. It
pushes on the artery wall. The pressure this creates is called blood pressure
(BP).
Blood pressure is measured with an instrument called a sphygmomanometer.
When the blood pressure (BP) is taken manually, as shown in Figure 12-9, a
stethoscope is used to listen to blood sounds. When using a digital
sphygmomanometer, which is automated, no stethoscope is used.
A normal blood pressure reading is written like this: 115/75 mm Hg. The
first number is the systolic (SIS-tohl-ick) pressure, the pressure against the
arterial wall when the ventricles contract and pumps blood out of the heart.
The second number is the diastolic pressure, the pressure against the
arterial wall when the ventricles relax. High blood pressure is called
hypertension (high-per-TEN-shun).
Low blood pressure is called hypotension . If high blood pressure affects
the heart, the condition is called hypertensive heart disease.
A BP reading between 120/80 to 139/89 is considered prehypertension.
A reading over 140/90 is hypertension. BP of 90/60 is hypotension.
Many experts now suggest that 115/75 is the optimum. The arteries dilate
and constrict in unison with the heartbeat. These movements, known
as a pulse, can be readily detected at several sites. Figure 12-10 illustrates
the following pulse sites: temporal, carotid, brachial, radial, femoral,
popliteal, and dorsalis pedis.
In Brief
Sphygmomanometer
A device used to measure blood pressure. Optimum blood pressure reading
is 115/75 mm Hg.
In Brief