இந்தக் கட்டுரையில், TNPSC குரூப் 1, குரூப் 2, குரூப் 2A, குரூப் 4 மாநிலப் போட்டித் தேர்வுகளான TNUSRB, TRB, TET, TNEB போன்றவற்றுக்கான முறைகள் இலவசக் குறிப்புகளைப் பெறுவீர்கள்.தேர்வுக்கு தயாராவோர் இங்குள்ள பாடக்குறிப்புகளை படித்து பயன்பெற வாழ்த்துகிறோம்.
Human Heart
Structure of Human Heart
Heart is a muscular pumping organ that pumps out the blood into the blood
vessels.
Human heart is situated between the lungs, slightly tilted toward the left and
above the diaphragm in the thoracic cavity.
The heart is made of specialized type of muscle called the cardiac muscle.
The heart is enclosed in a double walled sac called pericardium.
It contains lubricating pericardial fluid which reduces friction during heart
beat and protects it from mechanical injuries.
The human heart is four chambered.
1. Autricle or atria – The two upper thin walled chambers of the heart.
2. Ventricles – two lower thick walled chambers.
The chambers are separated by partition called septum.
The septum between auricles and ventricles prevents the mixing of
oxygenated and deoxygenated blood.
The two auricles are separated from each other by interatrial septum.
The left atrium is smaller than the right atrium.
The right atrium receives deoxygenated blood from different parts of the
body through the main veins superior vena cava, inferior vena cava and
coronary sinus.
Pulmonary veins bring oxygenated blood to the left atrium from the lungs.
The right and left auricles pump blood into the right and left ventricles
respectively.
The ventricles form the lower part of the heart.
The two ventricles are separated from each other by an interventricular
septum.
The left and right ventricles have thick walls because the ventricles have
to pump out blood with force away from the heart.
From the right ventricle arises the pulmonary trunk which bifurcates to
form right and left pulmonary arteries.
The right and left pulmonary arteries supply deoxygenated blood to the
lungs of the respective side.
The left ventricle is longer and narrower than the right ventricle.
The walls are about three times thicker than the right ventricle.
The left ventricle gives rise to aorta.
The oxygenated blood is supplied by the aorta to various organs of the
body.
The coronary arteries supply blood to the heart.
Function of Heart Chambers Ventricular diastole [PHASE 1]
The pressure in the auricles increases than that of the ventricular pressure.
AV valves are open while the semi lunar valves are closed.
Blood flows from the auricles into the ventricles passively.
Atrial systole [PHASE 2]
The atria contracts while the ventricles are still relaxed.
The contraction of the auricles pushes maximum volume of blood to the
ventricles until they reach the End Diastolic Volume (EDV).
EDV is related to the length of the cardiac muscle fibre.
More the muscle is stretched, greater the EDV and the stroke volume.
Ventricular systole (isovolumetric contraction) [PHASE 3]
The ventricular contraction forces the AV valves to close and increases the
pressure inside the ventricles.
The blood is then pumped from the ventricles into the aorta without
change in the size of the muscle fibre length and ventricular chamber
volume (isovolumetric contraction).
Ventricular systole (ventricular ejection) [PHASE 4]
Increased ventricular pressure forces the semilunar valves to open and
blood is ejected out of the ventricles without backflow of blood.
This point is the End of Systolic Volume (ESV).
Ventricular diastole [PHASE 5]
The ventricles begins to relax, pressure in the arteries exceeds ventricular
pressure, resulting in the closure of the semilunar valves.
The heart returns to phase 1 of the cardiac cycle.
Valves:
The valves are the muscular flaps that regulate the flow of blood in a single
direction and prevent back flow of blood.
The heart contains three types of valves.
Right atrioventricular valve:
It is located between the right auricle and right ventricle.
It has three thin triangular leaf like flaps and therefore called tricuspid
valve.
The apices of the flaps are held in position by chordae tendinae arising
from the muscular projection of the ventricle wall known as papillary
muscles.
Left atrioventricular valve:
It is located between the left auricle and left ventricle.
It has two cusps and therefore called bicuspid or mitral valve.
Semilunar valves:
The major arteries(pulmonary artery and aorta) which leave the heart have
semilunar valves which prevent backward flow of blood into the ventricles.
They are the pulmonary and aortic semilunar valves.
Heart Beat Sound
The rhythmic closure and opening of the heart valves causes the sound of
the heart.
The first sound LUBB (0.16 – 0.9sec) is of longer duration and is
produced by the closure of the tricuspid and bicuspid valves after the
beginning of ventricular systole.
The second sound DUPP(0.10sec) is of a shorter duration and produced
by the closure of semilunar valves at the end of ventricular systole.
Heart Beat
One complete contraction (systole) and relaxation (diastole) of the
atrium and ventricles of the heart constitute heartbeat.
The heart normally beats 72 – 75 times per minute Initiation and
conduction of Heart beat
The human heart is myogenic in nature. Contraction is initiated by a
specialized portion of the heart muscle, the Sino- atrial (SA) node which
is situated in the wall of the right atrium near the opening of the superior
vena cava.
The SA node is broader at the top and tapering below. It is made up of thin
fibres.
Sino-atrial node acts as the ‘pacemaker’ of the heart because it is
capable of initiating impulse which can stimulate the heart muscles to
contract.
The impulse from the sinoatrial node spreads as a wave of contraction over
the right and left atrial wall pushing the blood through the atrioventricular
valves into the ventricles.
The wave of contraction from SA node reaches the atrioventricular (AV)
node which is stimulated to emit an impulse of contraction spreading to
the ventricular muscle via the atrioventricular bundle and the Purkinje
fibres.
Animals – Heart Chambers:
The muscular, chambered heart is found in all vertebrates.
1. 8 parallel lateral heart – earthworm
2. 2 heart chambers – fish
3. 3 heart chambers – reptiles
4. 4 heart chambers – birds, mammals, crocodile
Disorders of the circulatory system
Hypertension
Hypertension is the most common circulatory disease. The normal blood
pressure in man is 120/80 mmHg.
In cases when the diastolic pressure exceeds 90 mm Hg and the systolic
pressure exceeds 150 mm Hg persistently, the condition is called
hypertension.
Uncontrolled hypertension may damage the heart, brain and kidneys.
Coronary heart disease
Coronary heart disease occurs when the arteries are lined by atheroma.
The build-up of atheroma contains cholesterol, fibres, dead muscle and
platelets and is termed Atherosclerosis.
The cholesterol rich atheroma forms plaques in the inner lining of the
arteries making them less elastic and reduces the blood flow
Plaque grows within the artery and tends to form blood clots, forming
coronary thrombus.
Thrombus in a coronary artery results in heart attack.
Angina pectoris
Angina pectoris (ischemic pain in the heart muscles) is experienced during
early stages of coronary heart disease.
Atheroma may partially block the coronary artery and reduce the blood
supply to the heart.
As a result, there is tightness or choking with difficulty in breathing. This
leads to angina or chest pain.
Usually it lasts for a short duration of time.
Myocardial infarction (Heart failure)
The prime defect in heart failure is a decrease in cardiac muscle
contractility.
When the blood supply to the heart muscle or myocardium is remarkably
reduced it leads to death of the muscle fibres.
This condition is called heart attack or myocardial infarction.
Rheumatoid Heart Disease
Rheumatic fever is an autoimmune disease which occurs 2-4 weeks after
throat infection usually a streptococcal infection.
The antibodies developed to combat the infection cause damage to the heart.
Diagnosis and Treatment Angiogram
Angiogram is a special contrast X ray and can be used to detect an
abnormality in a blood vessel such as a narrowing of a large diseased artery.
Coronary Angiography
A local anesthesia is injected and a fine flexible catheter is passed within
the femoral artery, through the aorta and into a coronary artery.
A contrast dye is injected through the catheter and a series of x rays taken.
Coronary Angioplasty
A baloon catheter is passed up the wire and the baloon is inflated in the
narrowed area to widen it.
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