EXPLAIN HUMAN HEART/FUNCTIONS OF HUMAN HEART

EXPLAIN HUMAN HEART/FUNCTIONS OF HUMAN HEART

Heart is a muscular organ responsible for pumping blood through blood vessels by repeated contractions. The term ''cardiac'' means ''related to the heart''. The bulk of the walls of heart chambers is made of cardiac muscles.

In human body, heart is situated between lungs, in the middle of chest cavity ( thorax ) under breastbone. Heart is enclosed in a sac known as pericardium. There is a fluid, known as pericardial fluid, between pericardium and heart walls. it reduces friction between pericardium and heart, during heart contractions.

Human heart consist of four chambers, like the heart of birds and other mammals. The upper thin-walled chambers are called left and right atria ( singular 'atrium' ), and the lower thick-walled chambers are called left and right ventricles. Left ventricle is the largest and strongest chamber in heart.

Human heart works as a double pump. It receives de-oxygenated ( with less oxygen ) blood from body and pumps it to lungs. At the same time, it receive oxygenated ( with more oxygen ) blood from lungs and pumps it to all body. Inside heart chambers the de-oxygenated and oxygenated bloods are kept separated. Here is a brief  description of the circulation of blood inside heart to show its double-pump mechanism.

Right atrium receive de-oxygenated blood from body via the main veins i.e. superior and inferior vena cavae. When right atrium contracts it is passes the de-oxygenated blood to right ventricle. The opening between right atrium and right ventricle is guarded by a valve known as tricuspid valve ( because it has 3 flaps ). When right ventricle contract, the blood is passed to pulmonary trunk, which carries blood to lungs. Tricuspid valve prevents the backflow of blood from right ventricle to right atrium. At the base of pulmonary trunk , pulmonary semilunar valve is present which prevents the backflow of blood from pulmonary trunk to right ventricle.

The oxygenated blood from lungs is brought by pulmonary veins to left atrium. Left atrium contracts and pump this blood to left ventricle. The opening between left atrium and left ventricle is guarded by a valve known as bicuspid valve ( because it has two flaps ). When left ventricle contracts, it pumps the oxygenated blood in aorta, which carries blood to all parts of body from left ventricle to left atrium. At the base of aorta, aertic semilunar valve is present which prevents the backflow of blood from aorta to left ventricle.

Pulmonary and systemic circulation

We see that right side of heart collects de-oxygenated blood from body and distributes it to lungs while left side collects oxygenated blood from lungs and distributes it to body. The pathway on which de-oxygenated blood is carried from heart to lungs and in return oxygenated blood is carried  from lungs to heart is called pulmonary circulation or circuit. Similarly, the pathway on which oxygenated blood is carried from heart to body tissues and in return de-oxygenated blood is carried from body tissues to heart is called systemic circulation or circuit.

Heartbeat

The relaxation of heart chambers fills them with blood and contraction of chambers propels blood out of them. the alternating relaxation and contraction make up the cardiac cycle and one complete cardiac cycle makes one heartbeat. Complete cardiac cycle consist of the following steps.

* Atria and ventricles relax and blood is filled in atria. this period is called cardiac diastole. Immediately after their filling both atria contract and pump blood towards ventricles. This period in cardiac cycle is called atrial systole.Now both ventricles contract and pump blood towards body and lungs. The period of ventricular contraction is called ventricular systole. in one heartbeat diastole lasts about 0.4 seconds atria systole takes about 0.1 seconds, and ventricular systole lasts about 0.3 seconds.

When ventricles contract tricuspid and bicuspid valves close and ''lubb'' sound is produced. Similarly when ventricles relax, the semilunar valves close and ''dubb'' sound is produced. Lubb-dubb can be heard with the help of stethoscope.

Heart rate and pluse rate

Heart rate is the number of times the heart beats per minute. activities, the normal heart rate is 70 times per minute in men and 75 times per minute in women. The heart rate fluctuates a lot depending on factors such as activity level and stress level.

Heart rate can be measured by feeling the pluse. Pluse is the rhythmic expansion and contraction of an artery as blood is forced through it by the regular contraction of heart. pluse can be felt at areas where artery is closed to skin for example at wrist, neck groin or top of foot. Most commonly people measure their pluse in their wrist.