The heart is a hollow muscular organ responsible for
the pumping of blood in the system. The heart lies in the thoracic cavity in
the mediastinium between the lungs. Two-third (2/3) of the heart lies left of
the chest mid line (sternum). It is a cone shaped in structure and inverted
with its apex below and the base above. The base extend from the 2nd
rib and apex terminates at the 5th inter coastal space. It is the
size of a fist of man. Surrounding the heart are organs which are in
association with the heart;
the pumping of blood in the system. The heart lies in the thoracic cavity in
the mediastinium between the lungs. Two-third (2/3) of the heart lies left of
the chest mid line (sternum). It is a cone shaped in structure and inverted
with its apex below and the base above. The base extend from the 2nd
rib and apex terminates at the 5th inter coastal space. It is the
size of a fist of man. Surrounding the heart are organs which are in
association with the heart;
Superiorly: The aorta (the largest artery)
pulmonary artery and vein, superior vena cava (SVC).
pulmonary artery and vein, superior vena cava (SVC).
Inferiorly: The central tendon of the
diaphragm where the apex rest
diaphragm where the apex rest
Anteriorly: Sternum, ribs and the
inter-costal muscles
inter-costal muscles
Posteriorly: The oesophagus, trachea,
left and right bronchus, descending aorta, inferior vena cava and throacic
vertebra
left and right bronchus, descending aorta, inferior vena cava and throacic
vertebra
Laterally: The lungs (both sides)
structurally.
structurally.
Layers of the Heart
The heart is made up of
three (3) layers of tissue namely pericardium, myocardium, and endocardium.
three (3) layers of tissue namely pericardium, myocardium, and endocardium.
Pericardium: The heart lies in the
conical sac called the pericardium. These consist of an inner serous
pericardium and an outer serous pericardium. The inner serous pericardium is
composed of two smooth layers, the visceral and parietal. The visceral layer
attached to the heart with the parietal layer of the fibrous sac. Those smooth
layers allow the heart to beat in the mediastinum. With minimal friction, it
prevent over distension of the heart during the cardiac cycle.
conical sac called the pericardium. These consist of an inner serous
pericardium and an outer serous pericardium. The inner serous pericardium is
composed of two smooth layers, the visceral and parietal. The visceral layer
attached to the heart with the parietal layer of the fibrous sac. Those smooth
layers allow the heart to beat in the mediastinum. With minimal friction, it
prevent over distension of the heart during the cardiac cycle.
Myocardium: This is made up of
specialized muscle known as the cardiac muscle it is found exclusively in the
heart and having inter laying fibrous that enable impulse to be distributed
evenly around the heart. The muscle fibrous is branched and lies side by side.
specialized muscle known as the cardiac muscle it is found exclusively in the
heart and having inter laying fibrous that enable impulse to be distributed
evenly around the heart. The muscle fibrous is branched and lies side by side.
Endocardium: This form a cover to the
myocardium and the valves. It is a tin, smooth, glistering membrane which
permits easy flow of blood within cardiac muscle. The layers correspond to the
tunica intimal of the blood vessel.
myocardium and the valves. It is a tin, smooth, glistering membrane which
permits easy flow of blood within cardiac muscle. The layers correspond to the
tunica intimal of the blood vessel.
Interiors of the Heart
It is made up of four
chambers-two atrial and two ventricular chambers. The atrial chamber is
sometime refers to as upper chamber while the ventricular the lower chamber.
i.e. there is right and left atrium also right and left ventricle respectively.
chambers-two atrial and two ventricular chambers. The atrial chamber is
sometime refers to as upper chamber while the ventricular the lower chamber.
i.e. there is right and left atrium also right and left ventricle respectively.
The right chamber (RA, RV)
are separated from the left chamber (LA, LV) by a brand of myocardium referred
to as the septum. Opening into the right atrium and right ventricule is guarded
by the right arterioventricular valve. The pulmonary valve guards the opening
between the right ventricule and the pulmonary artery. To the left, the opening
between left (LA) atrium and left (LV) ventricle is guarded by the left
arterioventricular valve. The valve opening and close in respond to pressure in
any of the chamber preventing the back flow of blood in opposite direction. The
valve are passive structure, i.e. they do not contain any muscle tissue, in
case any disease it might replace by valve transplant.
are separated from the left chamber (LA, LV) by a brand of myocardium referred
to as the septum. Opening into the right atrium and right ventricule is guarded
by the right arterioventricular valve. The pulmonary valve guards the opening
between the right ventricule and the pulmonary artery. To the left, the opening
between left (LA) atrium and left (LV) ventricle is guarded by the left
arterioventricular valve. The valve opening and close in respond to pressure in
any of the chamber preventing the back flow of blood in opposite direction. The
valve are passive structure, i.e. they do not contain any muscle tissue, in
case any disease it might replace by valve transplant.
Blood Supply to the Heart
The blood supply is from
the coronary artery, which is the branch of the aortic artery
the coronary artery, which is the branch of the aortic artery
Nerve Supply
Parasympathetic and
sympathetic nerves supply the heart. The sympathetic nerves increase the
activity of the heart (heart rate) while parasympathetic decreases the activity
of the heart (heart rate)
sympathetic nerves supply the heart. The sympathetic nerves increase the
activity of the heart (heart rate) while parasympathetic decreases the activity
of the heart (heart rate)
Factors Affecting Heart
Rate
Rate
Autonomic Nervous system: This originates in the
medulla oblongata, the centre controlling the autonomic action. The rate of the
heart is a balance of the sympathetic and parasympathetic activity and it is
the most important in determining the heart rate
medulla oblongata, the centre controlling the autonomic action. The rate of the
heart is a balance of the sympathetic and parasympathetic activity and it is
the most important in determining the heart rate
Circulating Chemicals: Hormones like Adrenaline
and noradrenaline have same effect as sympathetic stimulation.Thyroxine also
increase the heart rate. Some drugs either increase or decrease the heart rate
and noradrenaline have same effect as sympathetic stimulation.Thyroxine also
increase the heart rate. Some drugs either increase or decrease the heart rate
Position This is determine with the
position of an individual. It increases when in standing position and decreases
in sleeping positioning: During excitement or fear, the heart rate usually
increased and this is mediated by sympathetic nerve
position of an individual. It increases when in standing position and decreases
in sleeping positioning: During excitement or fear, the heart rate usually
increased and this is mediated by sympathetic nerve
Gender: The heart rate of a woman
is usually larger than that of a man
is usually larger than that of a man
Age: The heart rate of children
is normally more or high compare to adults.
is normally more or high compare to adults.
Exercise: This cause increase in
blood flow or pumping of blood into the circulation more efficiently as a
result of more forceful myocardial contraction.
blood flow or pumping of blood into the circulation more efficiently as a
result of more forceful myocardial contraction.
Properties of the Heart
Muscles
Muscles
Rhythmicity: The heart is composed of
cardiac muscle. And such muscles has the relax alternately in a rhythmical
manner. This property is developed to the greatest extends in region known as
the sinu-atrial node (S.A node) which is situated in the wall of the right
atrium near the entrance of the superior vena cava. The S.A node originate each
heart beat which is called pace-maker
cardiac muscle. And such muscles has the relax alternately in a rhythmical
manner. This property is developed to the greatest extends in region known as
the sinu-atrial node (S.A node) which is situated in the wall of the right
atrium near the entrance of the superior vena cava. The S.A node originate each
heart beat which is called pace-maker
The cardiac muscles have
three fibres which are cylindrical in shape with central nuclei and faint
cross-stration. The fibres branch to form network and cause the contraction of
the entire muscle by the spread of impulse from the S.A node. No nerve are
involved in the spread of a contraction waves through cardiac muscle cases at
the fibrous septum between the atrial and ventricule which contains the (4)
valves. The only pathway through this non-conducting septum is from the
Atrio-Ventricular Node (A.V node) down the atrio-ventricular bundle (Bundle of
His) this bundle run into the ventricule. The passage of contraction waves down
the bundle of modified cardiac muscle is not visible from the surface of this
heart and there appear to be a slight pause following the atrial contraction.
The contraction waves enter the ventricule near the apex and spread upward the
base. The blood in the ventricule is forced upward toward the base of the heart
and out through the aortic and pulmonary valves.
three fibres which are cylindrical in shape with central nuclei and faint
cross-stration. The fibres branch to form network and cause the contraction of
the entire muscle by the spread of impulse from the S.A node. No nerve are
involved in the spread of a contraction waves through cardiac muscle cases at
the fibrous septum between the atrial and ventricule which contains the (4)
valves. The only pathway through this non-conducting septum is from the
Atrio-Ventricular Node (A.V node) down the atrio-ventricular bundle (Bundle of
His) this bundle run into the ventricule. The passage of contraction waves down
the bundle of modified cardiac muscle is not visible from the surface of this
heart and there appear to be a slight pause following the atrial contraction.
The contraction waves enter the ventricule near the apex and spread upward the
base. The blood in the ventricule is forced upward toward the base of the heart
and out through the aortic and pulmonary valves.
