Physiological Structure and Life Process

Blood Circulation System

The system formed with the heart, blood, and the network of arteries, veins, and capillaries is called the Blood Circulation System. The heart is the central and the most important organ in the system. The heart circulates the blood through the network of arteries, veins, and capillaries in the human body. 
 

Structure of Blood

Blood is a red, thick, liquid connective tissue. A healthy adult typically has about 5.5 liters of blood, with a slightly alkaline pH between 7.35 and 7.45.

Composition of Blood

Blood consists of two main parts: Plasma (55%) and Blood Cells (45%).

1. Plasma: A pale yellow, transparent liquid. It is 80–90% water and contains proteins (albumin, globulin, and fibrinogen), nutrients, hormones, and enzymes. It helps regulate body temperature and water balance.

2. Red Blood Cells (Erythrocytes): These circular, disc-shaped cells contain hemoglobin, which gives blood its red color and carries oxygen. They live for 90 to 120 days.

3. White Blood Cells (Leucocytes): Known as the "soldiers of the body," they fight off germs and infections to keep us healthy

4. Platelets (Thrombocytes): These are the smallest blood cells. Their primary job is to clot blood when we get a cut, preventing excessive bleeding.
 

Blood Groups

Human blood is categorized into four main groups—A, B, AB, and O—based on antigens found on the surface of red blood cells. Additionally, the Rh factor determines if a blood group is Positive (+) or Negative (-)

• Group O is the most common blood group worldwide
• It is critical to match blood groups correctly during a blood transfusion to avoid life-threatening complications
   

Blood Vessels

The blood vessels are the path to the blood, through which blood flows. There are three types of blood vessels Artery, Vein, and Capillaries.

1. Artery

• Aorta: This is the largest artery in the human body. It carries pure blood from the heart's left ventricle to the body's different parts.
• Pulmonary Artery: They carry impure blood (Deoxygenated blood) from the heart's right ventricle to the lungs for purification. 

2. Vein

• Venacave: This is the largest vein in the human body. It carries impure blood (with Carbon dioxide) from different parts of the body to the right auricle.
• Pulmonary Veins: They carry pure blood (Oxygenated blood) from the lung to the left auricle of the heart.

3. Capillaries

• Capillaries are very fine networks of blood vessels. They connect the arteries to the veins and capillaries provide a definite path for the flow of blood.

Blood Circulation

The process of the body which helps in the transportation of nutrients, oxygen, and hormones to different parts of the body and collects their waste products like carbon dioxide is called blood circulation. There are two types of blood circulation in the human body Systemic blood circulation and Pulmonary blood circulation. 

1. Systemic Blood Circulation

The circulation of blood between the heart and different parts of the body except the lungs is called systemic blood circulation. Which means blood circulation from the Left ventricle to the Right auricle through the different body parts.

2. Pulmonary Blood Circulation

The circulation of blood between the heart and lungs is called pulmonary blood circulation. Which means blood circulation from the right ventricle to the left auricle through the lung. 

Heart Rate and Pulse Rate

The rhythmic contraction and relaxation of the heart is called heartbeat. Pulse rate, also known as heart rate, is the number of times a heart beats in a minute.

Blood Pressure

Human Heart External

Human Heart Internal