Functions and disease of the Heart

Functions and disease of the  Heart

Heart is a central pumping organ.It receives pumps out blood to the whole body.
1.Shape:Conical or roughly heart shaped.
2.Size:12cm from base to apex.
        6cm antero-posteriorly.
 
Situation:Situated in the middle mediastinum in between the two lungs,obliquely placed behind the body of sternum and the cartilages:about one third of it is on the right side and two third of it on the left side on the middle.

Explain:During diastole of heart,cardiac muscles are relaxed,intramural tension decreases and coronary blood vessels are less compressed.So,blood can easilyenters into coronary vessels and supply blood.On the other hand,during systole,due to increase cardic muscular tension,coronary vessels are compressed.So,heart gets its blood supply during diastole

Fuction of valves:Valves help in the flow of blood in one direction.Prevent regurgitation of back flow of blood by their direction during opening and closure.They are concerned with the production of heart sound.

Syncytium: It means a group of cells in which the protoplasm of one cell is continuous with that of adjoining cells such as the mesenchyme cells of embroys, striated muscle fibre.Heart muscle cells are large and branching.They are connected to each other by angulated dark areas crossing the cardiac muscles fibre are called intercalated discs; however, they are actually cell membranes that separate individual cardiac muscle cells from each other. That is cardiac muscle fibres are made up of many individual cells connected in series with each other the intercalated disc exerts a very little resistance, which resembles that there is no membrane fuse with each other and from very permeable junctions that allow relatively free diffusion of ions.
Therefore,from a functional point of view,ions move with ease along the axes of the cardiac muscle fibres so that action potentials travel from one cardiac muscle cell to another, past the intercalated dises, with only slight hindrance.Therefore, cardiac muscle is a syncytium.The heart is composed of two separate syncytiums; the atrial syncytium that constitute the walls of two atria and the ventricular syncytium that constitute the wall of two venticule.      

Heart sound:The vibration of the taut valves immediately motion of heart produced during the different events of cardiac cycle conducts through the structure surrounding the heartand produces special audible sound called heart sound. Classification of heart sound:Heart sound is classified into four in number

First heart sound:It is a low,slightly prolonged lub caused by vibrations set up by the sudden closure of the mitral and tricuspid valves at the start of ventricular systole.
Duration:About 0.15 second.
Fequency:24-45 Hz.
It is soft when the heart rate is low,beacuse the ventricles are well filled with blood and the leftlets of the AV valves float together before systole.The vibrations travel through the adjacent tissues to the chest wall,where they can be heard as sound by the stethoscope.

second heart  sound:It is a shorter,high-pitched dup caused by vibration associated with closure of the aortic and pulmonary valves just after the end of ventricular systole.
Duration:About 0.12 second.
Frequency:50 Hz
It is loud and sharp when the diastolic pressure in the aorta or pulmonary artery is elevated,causing the respective valves toshut briskly at the end of systole.The interval between aortic pulmonary valve closure during inspiration is frequently long anough for the second sound to be reduplicated.

Third heart sound:A soft,low -pitched third sound is heard about one-third of the way through diastole in many normal young individuals.It coincides with the period of rapid ventricular filling and is probably due to vibration set up by the inrush of blood.
Duration:The third sound has a duration of 0.1 second.

Fourth heart sound:It can sometimes be heard immediately before the first sound when atrial pressure is high or the ventricle is stif in conditions such as ventricular hypertrophy.It is due to ventricular filling and is rarely heart in normal adults.

What is heart block?

Occasionally transmission of the impules throgh the herat is blocked at a critical point in the conduetive system is called heart block.

Classification or types of heart block:There are three types of heart block-
1.Sinno-atrial heart block.Atrio-ventricular (A-V) heart block.Bundle branch block and hemi block.

Describe A-V type of heart block
Definition:When comduction of impules between atria and ventricle is blocked.
cause:Localized damage depression of A-V node..Excessive stimulation of vagus nerve..Localized destruction of AVbundle as a result of coronary infract.Pressure on the AV bundle by arteriosclerotic paques.Depression caused by various drug. Dgrees of AV heart block :First dgree heart block:All atrial impulses reaches the ventricle  but the P-R interval is abnormaly long. 2nd degree heart block:Not all atrial impulses are conducted to ventricles.There may be,for example,a ventricles brst following every second or every third atrial beat.Complete heart block:When no impules passes from atria to ventricle.It causes the"droped beat".Here the atrial rate is faster then the ventricle,for this reason, ventricle escape from the control of atria.  
Stokes Adams syndrome:When AV block occurs that is, when the cardiac impulse fails to pass from the atria into the ventricles through the AV nodal and bundle system-the atria continue to beat at the normal rate of rhythmof the sinus node, while a new pacemaker develops in the purkinje system does not minute at a new rate somewhere between 15 and 40 beats per minute.After a sudden block, the purkinje system does not begin to emit its rhythmical impulses until 5 to 30 seconds later because, before the blockage, the purkinje fibers had been ''overdriven'' by the rapid sinus impules and consequently, are in a suppressed state .
During these 5 to 30 seconds, the ventricles fail to pump blood, and the person faints after the first 4 to 5 seconds because of lack of blood flow to the brain.This delayed pick up of the heart beat is called stokes adams syndrome. If the delay period is too long it can lead to death.   


In bundle branch block:The duration of QRS is more than 0.11 second.Ppresence of RSR(in V1) pattern denotes right bundle branch block.Whereas a slurred and broad QRS in V5 and V6 denote left bundle branch block. Bundle of his block: Here the conduction of impules from AV node to bundle of his is impaired.It may be right or left bundle block.

SA Heart block :Here SA node fails to generate or fail to transmit the impules from SA node to the atrial muscle.
Causes:1.Over vagal stimulation.Vasovagal syndrom.Severe myocardial diseases.