Understanding the Circulatory System: Blood, Heart, and Components

Blood

Blood is a viscous, red fluid that circulates inside the blood vessels.

An adult usually has about five liters of blood, representing 8% of their body mass. Blood volume varies with age, sex, height, and weight.

Functions of Blood

• Nutrition: Transports nutrients from the digestive system to all body cells.
• Respiration: Carries oxygen from the lungs to the cells and carbon dioxide from the cells to the lungs.
• Excretion: Collects waste products produced by cells and transports them to the excretory system for elimination.
• Defense: Carries the body's defense cells.
• Thermoregulation: Participates in the regulation of body temperature, heating or cooling.

Composition of Blood

Plasma

Plasma is a yellowish liquid, up to 90% water. It contains a variety of substances, including proteins, carbohydrates, lipids, minerals, and gases. Most of its properties are due to blood proteins called serum. The process by which plasma solidifies is called clotting.

Blood Cells

There are three types of blood cells: red blood cells, white blood cells, and platelets. All are derived from cells found in the red bone marrow within the bones of the skeleton.

Red Blood Cells (Erythrocytes)

Red blood cells are elastic and deformable, allowing them to penetrate even the smallest capillaries. Their red color is due to hemoglobin. They carry oxygen from the lungs and also eliminate carbon dioxide. A healthy person has between 4.5 and 5.5 million red blood cells per microliter of blood.

White Blood Cells (Leukocytes)

White blood cells are larger than red blood cells. There are five types: neutrophils, eosinophils, basophils, lymphocytes, and monocytes. All are involved in defensive functions against infections.

Platelets (Thrombocytes)

Platelets are small, irregular-shaped cells that play a crucial role in blood clotting.

The Heart

The heart is a muscular organ that pumps blood through blood vessels. It is located in the center of the chest between the lungs. The heart's walls are made of muscle tissue called the myocardium.

The interior of the heart is divided into two halves, right and left, separated by a muscular septum. Each half has two chambers: an upper chamber called the atrium and a lower chamber called the ventricle. The ventricles' walls are thicker than the atria's.

Heart Valves

The atria and ventricles communicate through the atrioventricular valves.

• Mitral Valve: Connects the left atrium and left ventricle. It has two leaflets.
• Tricuspid Valve: Connects the right atrium and right ventricle. It has three leaflets.

These valves open and close, allowing the passage of blood from the atria to the ventricles, but preventing backflow.