Meaning of the human blood circulatory system

Blood Circulatory System

The blood circulatory system is responsible for transporting blood, nutrients, and waste products throughout the body. It consists of three main components: blood, blood vessels, and the heart. The heart acts as a pump, propelling blood through the blood vessels to various parts of the body.

Parts of the Human Blood Circulatory System

1. Blood

   Blood is a fluid tissue composed of:

   • Plasma:

     • Makes up 55% of the total blood volume.
     • Contains water, proteins, antibodies, and dissolved salts.
     • Transports nutrients, hormones, and waste products.
     • Regulates body temperature, aids in clotting, and fights diseases.

   • Red Blood Cells (RBCs):

     • Round, biconcave cells without a nucleus.
     • Contain hemoglobin, which transports oxygen and carbon dioxide.
     • Live for about four months and are formed in the bone marrow.
     • Old RBCs are destroyed in the liver, which recycles iron for new RBC production.
     

   • White Blood Cells (WBCs):

     • Irregularly shaped cells with a nucleus.
     • Formed in the bone marrow and lymph nodes.
     • Protect the body against diseases.
     

   • Platelets:

     • Small, irregularly shaped cells without a nucleus.
     • Produced in the bone marrow.
     • Prevent bleeding by clotting blood when vessels are damaged.
     

2. The Heart

   • A muscular organ located in the chest, slightly to the left.

   • Pumps blood throughout the body.

     

     External structure of the mammalian heart

     

     Internal structure of a mammalian heart

   • Structure:

     • Divided into two sides (left and right), each with two chambers: atria (upper) and ventricles (lower).
     • Left ventricle has thicker walls than the right ventricle as it pumps blood to the entire body.
     • Contains valves to prevent the backflow of blood:
       • Valves between atria and ventricles.
       • Valves at the connection points of the aorta and pulmonary artery.

   • Function:

     • Contraction and relaxation of the heart chambers create heartbeats, which pump blood.
     • Blood flow:
       • Left side: Pumps oxygenated blood to the body via the aorta.
       • Right side: Pumps deoxygenated blood to the lungs via the pulmonary artery.
     • Normal pulse rate: 70 beats per minute.

3. Blood Vessels

   Blood vessels are hollow tubes that transport blood throughout the body. They include:

   • Arteries:

     • Carry oxygenated blood from the heart to the body (except the pulmonary artery, which carries deoxygenated blood to the lungs).
     • The largest artery is the aorta.
     • Pulmonary artery is the only artery with valves to prevent backflow.

   • Veins:

     • Carry deoxygenated blood from the body to the heart (except the pulmonary vein, which carries oxygenated blood from the lungs to the heart).
     • Contain valves to prevent backward blood flow due to low pressure.

   • Capillaries:

     • Small blood vessels connecting arteries and veins.
     • Facilitate diffusion of nutrients, oxygen, and waste products between blood and cells.

How the Heart Pumps Blood

1. Heart chambers contract and relax in turns.
2. When atria contract:
   • Blood flows into the ventricles as valves between atria and ventricles open.
3. When ventricles contract:
   • Blood is pumped to the lungs (right ventricle) or the rest of the body (left ventricle).
   • Valves close to prevent backflow into the atria.
4. The continuous contraction and relaxation create heartbeats, ensuring constant circulation of blood.