The study of body fluids and circulation explains how essential substances like oxygen, nutrients, hormones, and waste products are transported throughout the body. This is a central topic in human physiology, vital for understanding the cardiovascular system. For NEET and other competitive exams, this chapter is extremely important as it combines structural, functional, and clinical aspects of biology.
Introduction to Body Fluids and Circulation
The circulatory system ensures that every cell in the body receives oxygen and nutrients while waste products are efficiently removed. The two major components are:
1. Body Fluids – Blood and lymphTogether, these maintain homeostasis, immunity, and life processes.
Body Fluids
Blood
Blood is a fluid connective tissue with plasma and formed elements.
Plasma: Straw-colored fluid containing water, proteins (albumin, globulin, fibrinogen), hormones, nutrients, gases, and waste products.Formed Elements:
- RBCs (Erythrocytes) – Transport oxygen via hemoglobin.
- WBCs (Leukocytes) – Provide immunity; types include neutrophils, eosinophils, basophils, lymphocytes, monocytes.
- Platelets (Thrombocytes) – Help in blood clotting.
Lymph
Lymph is a colorless fluid derived from interstitial fluid. It helps in transporting nutrients, immunity, and maintaining tissue fluid balance.
Human Circulatory System
Heart Structure
- Muscular, four-chambered organ.
- Right side handles deoxygenated blood, left side handles oxygenated blood.
- Valves ensure unidirectional flow.
Blood Vessels
- Arteries – Carry blood away from heart.
- Veins – Carry blood to heart.
- Capillaries – Thin vessels for exchange of gases, nutrients, and wastes.
Types of Circulation
- Systemic Circulation – Oxygenated blood from the left ventricle is distributed to tissues and deoxygenated blood returns to the right atrium.
- Pulmonary Circulation – Deoxygenated blood from the right ventricle goes to the lungs and returns oxygenated to the left atrium.
- Coronary Circulation – Blood supply to the heart muscle itself.
Cardiac Cycle
The cardiac cycle is the sequence of events in one heartbeat (~0.8 seconds).
- Atrial systole – Contraction of atria.
- Ventricular systole – Contraction of ventricles.
- Joint diastole – Relaxation of both chambers.
The heart sound “lub-dub” is due to closure of valves.
Regulation of Cardiac Activity
- Controlled by autonomic nervous system and nodal tissue.
- SA node (pacemaker) initiates the heartbeat.
- AV node, Bundle of His, Purkinje fibers spread impulse.
ECG (Electrocardiogram)
ECG records electrical activity of the heart.
- P wave – Atrial depolarization
- QRS complex – Ventricular depolarization
- T wave – Ventricular repolarization
Abnormal ECG indicates heart disorders.
Disorders of Circulatory System
- Hypertension – Elevated blood pressure
- Coronary Artery Disease (CAD) – Blockage in coronary arteries
- Angina Pectoris – Chest pain due to poor oxygen supply
- Heart Failure – Inefficient pumping of blood
- Leukaemia – Abnormal increase in WBCs
Comparative Table – Blood Components
| Component | Function | Example |
|---|---|---|
| RBCs | Oxygen transport | Hemoglobin |
| WBCs | Immunity | Lymphocytes, Neutrophils |
| Platelets | Blood clotting | Thrombocytes |
| Plasma | Transport of substances | Albumin, Globulin |
| Lymph | Immune defense, nutrient transport | Lymphocytes |
Importance of Body Fluids and Circulation
- Maintains homeostasis and nutrient supply.
- Protects against infections and blood loss.
- Essential for survival and clinical understanding.
- NEET frequently tests concepts like cardiac cycle, ECG interpretation, and blood groups.
FAQs on Body Fluids and Circulation
Q1. What are the two main body fluids in humans?
Blood and lymph are the two main body fluids.
Q2. Which chamber of the heart pumps oxygenated blood?
The left ventricle pumps oxygenated blood into systemic circulation.
Q3. What is the role of hemoglobin?
Hemoglobin binds oxygen for transport to tissues.
Q4. What does the “lub-dub” sound signify?
It represents closure of heart valves during the cardiac cycle.
Q5. Why is ECG important?
It diagnoses electrical activity and disorders of the heart.