Body Fluids and Circulation: Complete Class 11 NCERT Guide

Composition and Functions of Body Fluids

Body fluids mainly include blood and lymph, essential for transporting nutrients, gases, hormones, and waste products. Blood is a connective tissue composed of plasma (a fluid matrix) and formed elements (cells and cell fragments).

Formed elements:

• Red Blood Cells (RBCs): Transport oxygen from lungs to tissues using haemoglobin.
• White Blood Cells (WBCs): Defend the body against infections.
• Platelets: Help in blood clotting to prevent excessive bleeding.

Plasma is a pale yellow fluid containing water, plasma proteins, nutrients, hormones, and waste. Plasma proteins include albumins (maintain osmotic pressure), globulins (immune functions), and fibrinogen (blood clotting).

Together, these components maintain homeostasis, transport substances, and protect the body.

Understanding Blood Groups: ABO and Rh Systems

Human blood groups are classified based on specific antigens on the surface of RBCs. The two main systems are:

ABO Blood Group System

• Group A: Has A antigen; plasma contains anti-B antibodies.
• Group B: Has B antigen; plasma contains anti-A antibodies.
• Group AB: Has both A and B antigens; no antibodies (universal recipient).
• Group O: No antigens; both anti-A and anti-B antibodies (universal donor).

Rh Blood Group System

• Presence (+) or absence (-) of Rh antigen.
• Rh+ individuals have Rh antigen; Rh- do not.
• Important for transfusions and pregnancy compatibility.

Rh incompatibility between an Rh- mother and Rh+ fetus can cause erythroblastosis foetalis, a serious condition where maternal antibodies destroy fetal RBCs. This is preventable by administering anti-Rh antibodies to the mother after the first delivery.

Functions and Importance of Plasma Proteins

Plasma proteins play crucial roles in maintaining blood and body functions:

• Albumins: Maintain osmotic pressure, preventing fluid loss from blood vessels.
• Globulins: Act as antibodies, helping in immune defense.
• Fibrinogen: Essential for blood clotting by forming fibrin threads.

Besides these, plasma proteins transport hormones, vitamins, and drugs through the bloodstream. They also help maintain the pH balance of blood, ensuring proper enzyme activity and metabolism.

Understanding plasma proteins is key to grasping how blood maintains homeostasis and protects the body from infections and injuries.

Circulation in Humans: Pulmonary and Systemic Circulation

Circulation is the movement of blood through the heart and blood vessels, supplying oxygen and nutrients and removing wastes.

Pulmonary Circulation

• Carries deoxygenated blood from the right ventricle to the lungs via pulmonary arteries.
• Blood gets oxygenated in the lungs and returns to the left atrium via pulmonary veins.

Systemic Circulation

• Carries oxygenated blood from the left ventricle to all body parts through the aorta.
• Deoxygenated blood returns to the right atrium via the superior and inferior vena cava.

The heart’s pumping action involves two phases:

• Systole: Contraction phase, pumping blood out.
• Diastole: Relaxation phase, filling chambers with blood.

This continuous circulation maintains oxygen supply and removes carbon dioxide and other wastes efficiently.

Differences Between Blood and Lymph

Blood and lymph are two vital body fluids but differ in composition and function:

Lymph helps in maintaining fluid balance and immunity, while blood performs broader transport and protective roles.

Why Blood is Considered a Connective Tissue

Blood is classified as a connective tissue because:

• It has a fluid extracellular matrix called plasma.
• It connects various body parts by transporting nutrients, gases, hormones, and wastes.
• It originates from mesenchymal cells during development, like other connective tissues.
• It contains cells (RBCs, WBCs, platelets) suspended in plasma, similar to cells in other connective tissues.

This classification highlights blood’s role in linking body systems and maintaining internal stability.