Page 269 - Concise Pathology for Exam Preparation ( PDFDrive )

11

Disorders of the Heart

Normal Heart
• The weight of a normal heart averages approximately 250–300 g in females and
300–350 g in males.
• It is enclosed in a double–walled sac called pericardium. The pericardium consists of
an outer fibrous layer called the parietal pericardium and an inner layer called the vis-
ceral pericardium or the epicardium.
• The wall of the human heart is composed of three layers. The outer layer is the epicardium;
the middle layer is called myocardium and the innermost layer is called endocardium.
• The endocardium merges with the endothelium, which lines the blood vessels and cov-
ers heart valves (valvular endocardium). The usual thickness of free wall of right ven-
tricle is 0.3–0.5 cm and that of the left ventricle is 1.3–1.5 cm.
• Structure of the normal heart is depicted in (Fig. 11.1). An increase in cardiac weight or
size is termed cardiomegaly. Thickening of ventricular wall is called hypertrophy, and an
enlarged chamber size indicates dilation.
• The myocardium is composed of specialized muscle cells called cardiac myocytes. The
basic contractile unit of cardiac muscle is called the sarcomere, which is composed of
thick and thin filaments containing myosin and actin, respectively, along with regulatory
proteins troponin and tropomyosin. The striated appearance of cardiac myocytes is due
to a specific arrangement of sarcomeres. The sliding of the actin filaments between the
myosin filaments towards the centre of each sarcomere is the mechanism responsible for
the contractility of the cardiac muscle.
• Besides myocytes other cells that are present in heart include endothelial cells and fibro-
blasts. Cardiac myocytes contain structures called intercalated disks that join individual
cells to allow mechanical and electrical coupling.
Vascular Supply of the Heart (Fig. 11.2)

The three major epicardial coronary arteries that perfuse the heart are
(1) Anterior descending branch of the left coronary artery (LAD), which supplies most of
apex of the heart, the anterior wall of the left ventricle and the anterior two-thirds of
the ventricular septum.
(2) Circumflex branch of the left coronary artery (LCX) gives rise to posterior descending
branch (PDA) and thereby perfuses the posterior third of the septum.
(3) Right coronary artery (RCA) which supplies the right atrium, right ventricle, interven-
tricular septum and SA and AV nodes.
Majority of the perfusion of the myocardium by the coronary arteries occurs during
ventricular diastole, when there is no compression of the cardiac microcirculation due to
cardiac contraction.
Q. Enumerate the types of heart disease.

Ans. There are five major types of heart disease:
• Ischaemic heart disease (IHD)
• Hypertensive (systemic/pulmonary) heart disease
• Nonischaemic primary myocardial disease
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