Physiological Structure and Life Processes: Blood Circulation in Human Body

1. Circulatory System

Definition: The system that transports blood, oxygen, nutrients, hormones, and wastes throughout the body.
Main organ: Heart
Other components: Blood vessels (arteries, veins, capillaries), blood

Function:

1. Transports oxygen, nutrients, hormones to all cells
2. Removes wastes (CO₂, urea) to excretory organs
3. Connects other organ systems (digestive, respiratory, endocrine)

2. Blood

Definition: Red-colored connective tissue that circulates in the body.
Composition:

Plasma (55%): pale yellow liquid, 80–90% water + dissolved substances (proteins, carbs, salts, hormones, enzymes)

Blood cells (45%): Red blood cells, White blood cells, Platelets

Functions:

1. Transportation: Oxygen, CO₂, nutrients, hormones, wastes
2. Regulation: Body temperature, water balance, pH
3. Protection: WBCs fight infection, platelets clot blood

Blood Corpuscles

a. Red Blood Cells (RBC / Erythrocytes)

1. Biconcave, nucleus-free, red
2. Contain hemoglobin (iron + protein globin) → binds O₂ and CO₂
3. Life span: 90–120 days
4. Produced in bone marrow, destroyed in liver & spleen
5. Deficiency → Anemia; Excess → Polycythemia

b. White Blood Cells (WBC / Leucocytes)

1. Larger, nucleated, no hemoglobin

Types:

• Granular: Neutrophil, Eosinophil, Basophil
• Non-granular: Lymphocytes, Monocytes

1. Life span: ~2 weeks
2. Function: Fight infections → “soldiers of the body”
3. Deficiency → Leukopenia, Excess → Leukemia

c. Platelets (Thrombocytes)

1. Smallest, non-nucleated
2. Function: Blood clotting (with fibrinogen)
3. Deficiency → Hemophilia, Excess → Thrombocytosis

3. Blood Groups

1. Determined by antigens on RBC surface: A, B, AB, O
2. Also contains Rh factor (D antigen) → Positive (+) / Negative (–)
3. Total blood groups = 8 (A+, A–, B+, B–, AB+, AB–, O+, O–)
4. Importance: Compatibility in blood transfusions

4. Heart

Definition: Muscular organ that pumps blood to all parts of the body.

1. Size: About a fist, ~300 g
2. Location: Thoracic cavity, slightly left
3. Protected by pericardium (double-layered membrane)

Structure:

1. Four chambers: Right & Left Auricle (atrium), Right & Left Ventricle
2. Septum: Prevents mixing of oxygenated & deoxygenated blood
3. Valves: Tricuspid, Bicuspid/Mitral, Pulmonary, Aortic
4. Blood vessels:

• Veins → bring blood to heart (superior & inferior vena cava, pulmonary veins)
• Arteries → carry blood from heart (aorta, pulmonary artery)
• Function: Pump blood → supplies oxygen/nutrients and removes wastes

Blood Circulation

1. Systemic Circulation:

Oxygenated blood → Left ventricle → aorta → body → deoxygenated blood → right auricle via veins

2. Pulmonary Circulation:

Deoxygenated blood → Right ventricle → pulmonary artery → lungs → oxygenated blood → left auricle via pulmonary veins

5. Heartbeat & Pulse

1. Heartbeat: Rhythmic contraction & relaxation of heart
2. Pulse: Expansion of artery walls as blood flows
3. Normal rate: 60–100/min
4. Bradycardia: <60/min, Tachycardia: >100/min

6. Blood Vessels

1. Arteries: Thick, muscular, no valves, carry blood away from heart
2. Veins: Thin-walled, valves prevent backflow, carry blood to heart
3. Capillaries: Microscopic, allow exchange of gases, nutrients, and wastes

7. Blood Pressure

1. Definition: Pressure exerted by blood on artery walls
2. Systolic: During ventricular contraction
3. Diastolic: During ventricular relaxation
4. Normal: 120/80 mmHg
5. High BP (Hypertension): >140/90 mmHg
6. Causes: Obesity, stress, salty/fatty food, smoking, lack of exercise
   Prevention: Healthy diet, exercise, stress management

8. Heart Attack (Myocardial Infarction)

1. Definition: Sudden blockage of blood flow to heart → tissue damage
   Causes: Narrowed coronary arteries due to cholesterol/fat deposits (plaque)
   Symptoms: Chest pain, shortness of breath, cold sweat, nausea
   Treatment:

Medical: Oxygen supply, blood thinners

Surgical: Angioplasty & stenting, Coronary artery bypass

9. Disorders Related to Blood Circulation

• Diabetes (Hyperglycemia): High blood sugar due to insufficient insulin
• Symptoms: Thirst, frequent urination, blurred vision
• Prevention: Balanced diet, exercise, active lifestyle
• High Uric Acid (Hyperuricemia): Excess uric acid → joint pain, kidney stones
• Causes: Purine-rich diet, low water intake
• Prevention: Exercise, water intake, avoid fatty foods
• Hypertension: High blood pressure
• Prevention: Healthy lifestyle, avoid alcohol & smoking, exercise

3. Blood Circulation 

A. Systemic Circulation

Left Ventricle → Aorta → Arteries → Capillaries (body cells) → Veins → Vena Cava → Right Auricle

Function: Deliver O₂ & nutrients to cells, remove CO₂ & wastes

B. Pulmonary Circulation

Right Ventricle → Pulmonary Artery → Lungs → Pulmonary Vein → Left Auricle

Function: Exchange CO₂ for O₂ in lungs

4. Blood Vessel Types

Heart → Artery → Arteriole → Capillaries → Venule → Vein → Heart