1. What are the functions of the CVS?• Rapid transport of nutrients (oxygen, amino acids, glucose, fatty acids, water,etc.) and waste products (carbon dioxide, urea, creatinine, etc.)
• Hormonal control, by transporting hormones to their target organs and by secreting its own hormones (e.g. atrial natriuretic peptide)
• Temperature regulation, by controlling heat distribution between the body core and the skin
• Reproduction, by producing erection of the penis
• Host defence, transporting immune cells, antigen and other mediators (e.g. antibody)
2. How are the two circulations organized?The heart is double pump. It consists of two muscular pumps (the left and right ventricles). Each pump has its own reservoir (the left and the right atrium).
The two pumps each serve a different circulation. A typical blood cell flows first in one circulation and then moves into the other.
The right ventricle is the pump for the pulmonary circulation. Blood is pumped into the lungs, where it acquires oxygen and loses carbon dioxide; it then returns to the left atrium of the heart. This blood then enters the left ventricle.
The left ventricle is the pump for the systemic circulation. Blood is pumped from the left ventricle to the rest of the body. In the tissues of the body, nutrients and waste products are exchanged. Blood (which now carries less oxygen and more carbon dioxide) returns to the right atrium and then into the right ventricle.
3. How are the flow and distribution of blood through the two circulations governed?The two circulations are operating simultaneously, which blood constantly flowing in each circulation. They can be thought of as being in series, with each circulation supplied by a different pump. This one way, circular pathway for blood is brought about by the presence of valves in the heart and veins.
The circulatory system is made up of arteries, veins, capillaries and lymphatic vessels.
• Arteries transport blood from the heart to the body tissues
• Capillaries are where diffusion of nutrients and waste products take place
• Veins return blood from the tissues to the heart
• Lymphatic vessels return to the blood any excess water and nutrients that have diffused out of the capillaries
The amount of blood ejected from one ventricle during one minute is called the cardiac output. The cardiac output of each ventricle is equal overall, but there may be occasional beat-by-beat variation. The entire cardiac output of the right ventricle passes through the lungs. The cardiac output of the left ventricle passes into the aorta, and it is distributed to various organs and tissues according to their metabolic requirements or particular functions (e.g. skeletal muscle gets a larger blood supply; the kidney receives 20% of cardiac output so that its excretory function can be maintained). This distribution can be changed to supply demand (e.g. during exercise, the flow to the skeletal muscle is increased considerably).
Blood is driven along the vessels by pressure. This pressure, which is produced by the ejection of blood from the ventricles, is highest in the aorta (about 120mmHg above atmospheric pressure) and lowest in the great veins (almost atmospheric). It is this pressure difference that moves blood through the arterial tree, through the capillaries, and into the veins. In the veins, the movement of blood is aided by one-way valves.
Arterial blood flow is pulsatile, with a higher pressure during systole than diastole.
