TOPIC 1. CLASSIFICATION KINGDOM FUNGI

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

The endothelium is the innermost layer of the artery. It has only one layer of cells. The endothelium surrounds the lumen (the central tube of the vessel). The lumen of an artery is narrow and smooth so that it can transport blood at high pressure.

The muscular layer is made of smooth muscle and elastic fibres. Smooth muscle is arranged in circles round the endothelium. This layer makes it possible for the artery to contract and relax for the efficient movement of blood.

The outermost layer is the fibrous layer made of connective tissues such as collagen. The fibres are arranged parallel to the length of the vessel. They enable the artery to withstand the pressure caused by the blood coming from the heart.

When the ventricles contract, the arteries relax allowing blood from the heart to flow into them. When the ventricles relax, the arteries contract, forcing the blood forward. This contraction and relaxation of arteries is felt as a pulse.

Pulse rate is the number of pulses per minute. The pulse rate reflects the heartbeat. An adult human’s heart beats at an average of 72 times a minute. However, this can increase or decrease due to physical activity, emotional state or health factors

Arteries branch to form arterioles. Arterioles in turn branch to form capillaries. Capillaries are joined at the other end by venules which join to form veins.

Veins

Veins are vessels that transport blood to the heart from all parts of the body. All veins transport deoxygenated blood except the pulmonary vein. The pulmonary vein transports oxygenated blood from the lungs to the heart