Zoology Assignment Help >> Heart, Parts of Heart, Ventricles, Working of Heart in Body Systems

HEART

Heart is a highly modified blood vessel which has the capacity to contract and expand. It pumps the blood into the arteries and receives the blood through the veins. It has all the three layers present in the blood vessel as follows-

(1) Epicardium: Similar to tunica extema

(2) Mesocardium: Similar to tunica media

(3) Endocardium: Similar to tunica intema

Generally heart can be of the following types-

(i) Venous heart: When only impure blood (i.e. venous blood) is pumped by the heart. e.g. fishes.

(ii) Mixed heart: In the heart of amphibians and most of the reptiles, the oxygenated and deoxygenated blood is mixed. Such type of heart is mixed heart.

(iii) Double circulatory heart: In the heart of crocodile (reptilia), birds and mammals, oxygenated and deoxygenated blood are not mixing in any part of auricle and ventricle. There is a separation of blood circulation completely in the heart. The left half of the heart contains oxygenated and right one contains deoxygenated blood. Thus there is a double circulation in the heart.

Vasa vasorum: Blood vessels supplying blood to the walls of blood vessels are called vasa vasorum.

Structure of heart of man: It pumps the blood to the different organs via blood vessels. The wall of the heart which is made up of cardiac muscles, is known as myocardium.

The heart is enclosed in the membranous pericardium which encloses a cavity known as pericardial cavity. This cavity is filled with pericardial fluid.

Parts of heart: Two parts-

(i) Auricla

(ii) Ventricle.

Chambers of heart: Four chambered heart-

Auricle - 2 chambers

Ventricle - 2 chambers Auricles:

(1) Auricles are thin-walled, sac like structures, separated by a septum known as inter-auricular septum.

(2) Left auricle receives oxygenated blood (pure blood) by four pulmonary veins.

(3) Right auricle receives deoxy¬genated blood from different parts of the body via two pre-caval (right and left) and one post-caval from anterior and posterior body parts respectively.

(4) The right auricle opens into right ventricle through right auriculo-ventricular aperture which is guarded by a right AV valve called tricuspid valve.

(5) The left auricle opens into left ventricle through left auriculo-ventricular aperture which is guarded by a left AV valve called bicuspid valve or mitral valve.

(6) These valves are attached to the papillary muscles on the inner wall of ventricles by means of chordae tendinae.

Ventricles:

(1) The wall of ventricle is more thick in comparison to auricle.

(2) The cavity of ventricle is unequally divided into two by an oblique septum known as inter-ventricular septum.

(3) Left ventricle receives oxygenated blood from left auricle.

(4) Right ventricle receives deoxy¬genated blood from right auricle.

(5) The wall of left ventricle is more thick in comparison to that of right one.

(6) The inter-ventricular septum is provided with 'bundle of His' and wall of ventricle is provided with Purkinje's fibres.

(7) From right ventricle the pulmonary arch arises which takes deoxygenated blood for the oxygenation to the lungs.

(8) The carotico systemic aorta or arch originates from the left ventricle and supplies the oxygenated blood to the different parts of the body. After its origination the carotico systemic aorta turns towards left side.

(9) At the origin of the aortic arches from the ventricle, three semilunar valves are present which prevent the backflow of blood.

WORKING OF HEART

(1) Human heart beats approximately 72 times in a minute.

(2) There are two centres of contraction present in the heart of man. One in the right auricle known as sinu¬auricular node (SA node). It is also known as pacemaker. The other is present at the junction of right and left ventricle known as atrio-ventricular node (AV node).

(3) Both of these nodes are modified cardiac muscles and supplied with the parasympathetic 'and sympathetic nerves.

(4) Workins of heart is myogenic.

(5) When heart beat starts, the auricles and the ventricles are in relaxed form. This stage is known as joint diastole. In this stage blood comes in the auricle.

(6) Then comes the systolic phase. In this phase contraction of auricle takes place which forces pumping of blood into their respective ventricle.

(7) The above action is due to the excitation' of the SA node which sends the waves of contraction. These waves contract the right auricle first then they go towards the left auricle and contract.

(8) After the contraction of the left auricle the waves of contraction are centralised at the AV node.

(9) This causes the stimulation of AV node and this node sends the electrical stimulation to the apex of ventricle via 'bundle of His'.

(10) When this stimulation reaches at the apex of ventricle, these are given to the Purkinje fibres present in the wall of ventricle. From its apex the contraction reaches towards the anterior side and thus blood is pumped into the aorta or arches originating from ventricle.

(11) After the systolic phase the diastole starts.

Sound of murmur: Sounds are due to disorder of heart valves. It may be due to-

1. Valvular insufficiency

2. Stenosis

Sounds of heart: The sounds are produced due to the closure of valves of heart.

First sound: It is due to the closure of atrioventricular valves. This sound is like LUBB.

Second sound: It is due to the sudden closure of semilunar valves present at the opening (origin) of aorta or arches from the ventricles. This sound is like DUP.

Thus sound of heart is LUBB-DUP and a pause and again LUBB-DUP will develop.

Blood pressure: The pressure by which blood flows in the arteries is called blood pressure. It is measured by sphygmomanometer.

Normal systolic pressure = 125-130 mm Hg

Normal diastolic pressure = 70-90 mm Hg

Electrocardiogram: An instrument measuring different stages of potential in the form of a graph known as E.C.G. A typical E.C.G. has-

1. P-wave: Depolarization of auricle.

2. Q.R.S. complex: Depolarization of ventricle.

3. T-wave: Repolarization of ventricle.

Cardiac output: The volume of blood pumped by the heart in a minute is known as cardiac output.

C.O. = Heart rate x Stroke volume

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