Heart: The heart
is a conical, hollow muscular organ.Location: It is a
situated in the middle mediastinum.
Shape & Size: It
is conical shape. The heart measures about 12x9 Cm. weighs about 250-300 Gm.
External features:
Apex – Directed down wards.
Base – Directed
backwards.
*Three surfaces – Anterior, posterior & left.
*Four borders – Upper, Lower, Right & left.
Internal features:
*Four chambers –
Left atrium, right atrium, left ventricle and right ventricle.
*Four valves -
Bicuspid or mitral, Tricuspid, pulmonary and aortic.
*Three layers -
Endocardium, Myocardium & pericardium.
Descriptions of external features are
Right Atrium
*The right atrium
receives blood from three veins, the superior vena cava, inferior vena cava,
and coronary sinus.
*The anterior posterior walls of the right atrium are very
different. The posterior wall is smooth; the anterior wall is smooth; the
anterior wall is rough due to the presence of muscular ridges called
pectinatemuscles which also extend into the auricle.
*Blood passes from the right atrium into the right ventricle
through a valve that is called the tricuspid valve because it consists of three
leaflets or cusps.
*The valves of the heart are composed of dense connective
tissue covered by endocardium.
Right ventricle
*The right ventricle is a triangular chamber which receives
blood from the right atrium and pumps it to lungs through the pulmonary
arteries.
*The right ventricle forms most of the anterior surface of
the heart. The inside of the right ventricle contains a series of ridges formed
by raised bundles of cardiac muscle fibers called trabeculae carneae.
Left Atrium
*The left atrium
forms most of the base of the base of the heart. It receives blood from the
lungs through four pulmonary veins. Like the right atrium, the inside of the
left atrium has a smooth posterior wall.
*Because pectinate muscles are confined to the auricle of
the left atrium, the anterior wall of the left atrium also is smooth.
*Blood passes from the left atrium into the left ventricle
through the bicuspid (mitral) valve, which
as its name implies has two cusps.
Left ventricle:
*The left
ventricle is a conical chamber. It is longer than the right ventricle and has
the thickest layer of myocardium.
*The left ventricle contains trabeculae carneae and has chordate
and has chordate tendinae that anchor the cusps of the bicuspid valve to
papillary muscles.
*Blood passes from the left ventricle through the aortic valve into the coronary
arteries, which branch from the ascending aorta and carry blood to the heart
wall.
Valves of the heart: Heart has four valves.
*The tricuspid valve regulates blood flow between the right
atrium and right ventricle.
*The pulmonary valve controls blood flow from the right
ventricle into the pulmonary arteries, which carry blood lungs to pick up
oxygen.
Layers of the heart wall
The wall of the heart consists of three layers:
*Epicardium/pericardium (external layer) : The outer most epicardium,Is a thin layer of
endothelium overlying a thin layer of connective tissue. It provides a smooth
lining for the chambers of the heart and covers the valves of the heart.
*Myocardium (middle layer) : The middle myocardium which is cardiac muscle tissue makes up the bulk of the
heart. It is striated like skeletal muscle: cardiac muscle is involuntary like
smooth muscle.
*Endocardium (inner layer) : The inner most endocardium is a thin layer of
endothelium overlying a thin layer of connective tissue. It provides a smooth
lining for the chambers of the heart and covers the valves of the heart.
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