TOPIC 1. CLASSIFICATION KINGDOM FUNGI

The heart has four chamber right auricle, right ventricle, left auricle and left ventricle. The auricles are also called atria (singular: atrium). The walls of the ventricles are thicker than those of the auricles. This is because the ventricles pump blood to a greater distance than the auricles. Auricles pump blood to the ventricles. Ventricles pump blood to all other parts of the body. The left ventricle is thicker than the right ventricle   because the right ventricle pumps blood to the lungs while the left ventricle pumps blood to the rest of the body.

The heart has several valves. Valves have flaps that ensure that blood flows in one direction only. The tricuspidvalve is found between the right auricle and right ventricle. The bicuspid valve is found between the left auricle and left ventricle. Semi lunar valves are located at the bases of the pulmonary artery and aorta to prevent blood from flowing back into the ventricles.

Valves close when blood tries to flow back.

The left and right sides of the heart are separated by the septum. The septum is a thick muscular wall that prevents mixing of oxygenated and deoxygenated blood.

The flow of blood through the heart;

The vena cava brings deoxygenated blood to the heart. Deoxygenated blood contains low amounts of oxygen.

The vena cava has two branches:

The superior vena cava which transports deoxygenated blood from the upper parts of the body such as head, neck and upper limbs.

The inferior   vena   cava   which   transports deoxygenated blood from the lower parts of body such as the lower limbs, kidney, liver, stomach and intestines.

The inferior vena cava and the superior vena cava unite to form the vena cava; the vena cava is connected to the right auricle.

When the right auricle relaxes, it fills up with deoxygenated blood from the vena cava. There is increased pressure in the right auricle when the muscles contract. This pushes the blood trough the tricuspid valve. The muscles of the

Right ventricles relax and it fills up with blood. The tricuspid valve closes to prevent blood from owing back into the right auricle. When the right ventricle is full, the increased pressure causes the muscles to contract and the Semi lunar valve in the pulmonary artery to open. The blood flows into lie pulmonary artery and the bicuspid valve closes prevent back flow of blood.

The pulmonary artery transports blood to the lungs. Blood absorbs more oxygen in the lungs, and thus becomes oxygenated.

Oxygenated blood flows to the heart through the pulmonary vein. This vein is connected to the left auricle. When the left auricle relaxes, the semi lunarvalve opens and blood from the pulmonary veinflows in. Pressure increases in the left auricle as itfills up with blood. The pressure causes the musclesof the auricle to contract and pump blood throughthe bicuspid valve into the left ventricle.

The muscles of the left ventricle contract, allowing blood to flow in. The bicuspid valve closes to prevent blood from flowing back into the left auricle. Pressure builds up in the left ventricle as blood flows in.

The muscles of the left ventricle contract, pumping blood through the semi lunar valve into the aorta. The aorta branches into smaller arteries that transport blood to all parts of the body. The heart beats in such a way that when the auricles contract, the ventricles relax and vice versa.

In the right atrium, there is a small patch of muscle called the sinoatrial node (SAN). This node acts as a pacemaker, setting the time and rate of cardiac muscle contraction.

Adaptations of the heart to its functions

Table below shows how the heart is adapted to its functions.

Adaptations of the heart

      

Adaptation	Function
Muscular walls	Contract to pump blood
Cardiac muscle	Contract and relax continuously without being fatigued. This ensures continuous pumping of blood
Valves	Ensure blood flows in only one direction
Septum	Separates oxygenated blood from deoxygenated blood
Connection to large blood vessels	Enables transportation of deoxygenated blood from all parts of the body to the heart and transportation of oxygenated blood from the heart to all parts of the body
Sinoatrial node	Sets time and rate of contraction of cardiac muscle
Coronary artery and coronary vein	The coronary artery nourishes the heart and supplies it with oxygen,     The coronary vein removes wastes which would harm the heart if left to accumulate

Blood vessels

Mammals have three types of blood vessels: arteries, veins and capillaries.

Arteries

Arteries are thick-walled, muscular and elastic vessels that transport blood from the heart to all parts of the body. All arteries transport oxygenated blood, except the pulmonary artery which transports deoxygenated blood from the heart to the lungs