The Circulatory System

 OVERVIEW  OF THE CARDIOVASCULAR SYSTEM

The circulatory system, often referred to as the cardiovascular system, is a complex network that plays a vital role in sustaining life. It functions as the body’s transportation highway, delivering oxygen, nutrients, hormones, and removing waste products. A healthy circulatory system is essential for maintaining homeostasis, optimal cellular function, and overall health.

The circulatory system consists of a network of  blood vessels and the heart.

Blood Vessels 

These are of 3 types.

i. Arteries – These carries blood away from the heart

ii. Veins – Returns blood to the heart

iii. Capillaries – These links the arteries and the veins  

Circulatory system 

  Capillaries are tiny blood vessels with tiny thin walls consisting of only one layer of cells.

 They are the sites of exchange of substances between the blood and body tissues. Eg oxygen, nutrients & cellular waste products. Blood vessels forms a network that transports blood to:

a. The lungs (pulmonary circulation) where oxygen is absorbed from the air in the lungs & at the same time Co2 is excreted from the blood into the air.

b. Cells in all other parts of the body (systemic/general circulation)

The heart: This is a muscular sac which pumps blood round the body & maintains the blood pressure. The cardiac muscle is not under conscious control (involuntary). At rest, the heart contracts about 65-75 times per minute. The rate is increased during exercise. The rate at which the heart beats can be counted by taking the pulse.

 The heart is composed of 3 layers of tissues. Viz: Pericardium, Myocardium & Endocardium from outside to within.

Blood Flow Through the Heart:

   The 2 largest veins of the body – Superior & Inferior venea cavaeempty their contents into the Rt. atrium. This blood passes via the Rt. atrioventricular valve into the Rt. Ventricle & from there is pumped into the pulmonary artery (the only artery that carries deoxygenated blood).

 After leaving the heart, the pulmonary artery divides into Lt. & Rt. Pulmonary arteries which carries the venous blood to the lungs for oxygenation. 2 pulmonary veins from each lung carries oxygenated blood back to the Lt. atrium. Blood then passes through the Lt. atrioventricular valve into the Lt. ventricle & then pumped into the aorta, the 1st artery of the general circulation.

   From these sequence of events, it can be seen that the blood flows from the Rt. to the Lt. side of the heart via the lungs (pulmonary circulation). However, it should also be noted that both atria contracts at the same time followed by the simultaneous contraction of both ventricles.

The atria usually assisted by gravity to propel the blood through the atrioventricular vavle (AVV) into the ventricles, whereas the ventricles actively pumps the blood to the lungs and round the whole body.