Heart (Cardiovascular) System

The Cardiovascular System (cardio=heart; vascular=blood vessels) consists of three interrelated components: blood, the heart and blood vessels.

1. Blood, the only liquid connective tissue, has three general functions:

a. Transportation: blood transports oxygen from the lungs to the cells of the body and carbon dixide from the body cells to the lungs for exhalation. It carries nutrients from the gastrointestinal tract to body cells and horrmones from endocrine glands to other body cells. Blood also transports heat and waste products to the lungs, kidneys and skin for elimination from the body.

b. Regulation: Circulating blood helps maintain homeostasisin all body fluids. Blood helps regulate pH through the heat absorbing and coolant properties of the water in plasma and its variable rate of flow through the skin, where excess heat can be lost from the blood to the environment. Blood osmotic pressure also influences the water content of cells, mainly through interactions of dissolved ions and proteins.

c. Protection: Blood can clot, which protects against its excessive loss from the cardiovascular system after an injury. In addition white blood cells protect against disease by carrying on phagocytosis. Several types of blood proteins, antibodies, such as interferons, and complement, help protect against disease in a variety of ways.

2. The heart is pump that circulates the blood.

For blood to reach body cells and exchange materials with them, it must be constantly propelled through blood vessels. The heart is pump that circulates the blood through an estimated 100,000 km (60,000 mi) of blood vessels. It beats about 100,000 times every day. Heart pumps 30 times its weight each minute, about 5 lit. to the lungs and the same volume to the rest of the body, that means it pumps 14,000 lit (3,600 gal) of blood in a day. The heart size 12 cm long X 9 cm wide X 6 cm thick and its mass averages 250 gm in adult females & 300 gm in adult males.

The wall of the heart consists of three layers : i. The epicardium (external layer) ii. The myocardium (middle layer) iii. The endocardium (inner layer).

3. The blood vessels are five types: arteries, arterioles, capillaries, venules and veins. Arteries carry blood away from the heart to other organs. Arterioles are smaller arteries. Capillaries are tiny arterioles entering a tissue. Veins are larger blood vessels that convey blood from the tissues back to the heart. Venules are groups of tiny veins within a tissue.