Human Blood Circulation System Structure and Function

1. The Blood Circulatory System

Blood Vessels and Heart

1.1 Composition of Blood

Blood is a reddish liquid composed of:

• Plasma: Constitutes 55% of the blood. It is a yellowish liquid consisting of water, mineral salts, proteins, glucose, etc.
• Blood Cells: Constitute 45% of the blood.

Blood Cells:

• Red Blood Cells (or Erythrocytes/Hamaties): Transport oxygen ($\text{O}_2$). They contain hemoglobin.
• White Blood Cells (or Leukocytes): Defend the body.
• Platelets (or Thrombocytes): Prevent bleeding.

1.3 Functions of Blood

• Transporting nutrients (via red blood cells).
• Transporting gases.
• Controlling bleeding (via platelets).
• Distributing body heat.

2. Diseases

Anemia

• Symptoms: Paleness, tiredness, spots on nails, nosebleeds.
• Grounds: Lack of iron, resulting in insufficient production of red blood cells or hemoglobin.
• Cure: Dietary changes (lentils and pâté) and medications.

Leukemia

• Symptoms: Fatigue, high number of leukocytes.
• Grounds: Blood cancer, characterized by few red blood cells because the bone marrow is flawed.
• Healing: Marrow transplantation.

Haemophilia

• Symptoms: Non-stop bleeding.
• Reasons: Platelets do not form sufficiently; it is a hereditary condition located on the X chromosome.
• Healing: There is no cure.

3. Blood Vessels

Arteries

These are the blood vessels that carry blood from the heart to the organs.

Characteristics: Thin but elastic walls. They must withstand much pressure.

Veins

These carry blood from the organs back to the heart.

Characteristics: Thin walls, thinner than those of the arteries, and carry blood under low pressure. They possess valves to prevent blood from flowing backward.

Capillaries

These are very fine-walled blood vessels that allow the exchange of substances with the cells.

The circulatory system is closed.

4. The Heart

The heart is a body organ about the size of a fist, located toward the left side within the ribcage.

Parts of the Wall:

• Myocardium (MI): Heart muscle tissue that allows the heart to contract.

4.1 Parts of the Heart:

4.2 The Heartbeat:

• Systole: Contraction.
• Diastole: Relaxation.

Cardiac Cycle:

These are the stages that allow the movement of the heartbeat:

• Atrial Systole: The atria contract and pass 30% of the blood into the ventricles.
• Ventricular Diastole: The ventricles relax and allow all the blood from the atria to pass into them.
• Ventricular Systole: The ventricles contract, and blood passes through the semilunar valves into the arteries.
• Atrial Diastole: The atria relax, and blood returns to fill them again.

Vascular Circuits (3 Types):

• Minor or Pulmonary Circulation: Where the blood is oxygenated.
• Greater or Systemic Circulation: Where $\text{O}_2$ is delivered and $\text{CO}_2$ is removed.