What is the primary function of blood in the human body?

The primary function of blood is multifaceted, acting as the body's main transport system. It delivers oxygen from the lungs and nutrients from the digestive tract to all cells, while simultaneously carrying metabolic waste products like carbon dioxide and urea to the lungs and kidneys for excretion. Beyond transport, blood plays a crucial role in regulating body temperature, maintaining pH balance, and protecting against pathogens through its immune cells and clotting factors, ensuring overall physiological stability and defense.

Why are red blood cells biconcave and anucleated?

Red blood cells are biconcave (concave on both sides) to maximize their surface area-to-volume ratio, which enhances the efficiency of oxygen and carbon dioxide diffusion across their membrane. This shape also provides flexibility, allowing them to squeeze through narrow capillaries without rupturing. They are anucleated (lack a nucleus) in their mature form, which frees up space to pack more hemoglobin, the protein responsible for oxygen transport, thereby significantly increasing their oxygen-carrying capacity.

What is the difference between serum and plasma?

Plasma is the liquid component of blood that contains all clotting factors, including fibrinogen. When blood clots, fibrinogen is converted into insoluble fibrin, which forms the meshwork of the clot. Serum is the clear, yellowish fluid that remains after blood has clotted and the formed elements, along with the clotting factors (like fibrinogen), have been removed. Essentially, serum is plasma minus the clotting proteins.

How does blood clotting prevent excessive blood loss?

Blood clotting, or coagulation, is a vital hemostatic mechanism. When a blood vessel is injured, platelets aggregate at the site to form a temporary plug. Simultaneously, a complex cascade of clotting factors, primarily plasma proteins, is activated. This cascade ultimately converts prothrombin into thrombin, which then transforms soluble fibrinogen into insoluble fibrin threads. These fibrin threads form a strong, stable mesh that traps red blood cells and platelets, sealing the wound and preventing further blood loss.

What is the significance of ABO and Rh blood grouping in transfusions?

ABO and Rh blood grouping are critical for safe blood transfusions to prevent potentially fatal immune reactions. The ABO system classifies blood based on A and B antigens on RBCs and corresponding antibodies in plasma. Transfusing incompatible blood leads to agglutination (clumping) of recipient's RBCs. The Rh system considers the presence or absence of the Rh antigen. An Rh- person exposed to Rh+ blood can develop antibodies, leading to severe reactions in subsequent exposures, particularly relevant in pregnancy (erythroblastosis fetalis).

Blood

Biology

NEET UG

Version 1Updated 22 Mar 2026

Explore This Topic

Definition Deep Explanation Core Principles NEET Importance Problem Strategy Practice Problems MCQ Practice Quick Revision

Blood is a specialized connective tissue, unique among tissues for its fluid matrix, known as plasma, in which various cellular elements, collectively termed formed elements, are suspended. It circulates throughout the cardiovascular system, driven by the pumping action of the heart, performing vital functions such as the transport of gases, nutrients, hormones, and waste products. Beyond transpor…

Quick Summary

Blood is a vital fluid connective tissue, comprising about 7-8% of body weight. It consists of a liquid matrix, plasma (55%), and formed elements (45%). Plasma, mostly water, carries proteins (albumin, globulins, fibrinogen), nutrients, hormones, and waste.

Formed elements include Red Blood Cells (RBCs/erythrocytes) for oxygen transport via hemoglobin, White Blood Cells (WBCs/leukocytes) for immunity, and Platelets (thrombocytes) for blood clotting. RBCs are biconcave, anucleated, and live for ~120 days.

WBCs are diverse, categorized into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes), each with specific defensive roles. Platelets are cell fragments crucial for hemostasis.

Blood groups (ABO, Rh) are determined by antigens on RBCs and are critical for safe transfusions. Blood coagulation is a complex cascade involving clotting factors, culminating in fibrin clot formation to prevent blood loss.

All blood cells originate from hematopoietic stem cells in bone marrow.

Vyyuha

Your 6-Month Blueprint, Updated Nightly

AI analyses your progress every night. Wake up to a smarter plan. Every. Single.…

Key Concepts

ABO Blood Group System and Transfusion Compatibility

The ABO blood group system is based on the presence or absence of two antigens, A and B, on the surface of…

Hemoglobin Structure and Function

Hemoglobin (Hb) is the primary protein within red blood cells, responsible for their distinctive red color…

Role of Fibrinogen in Blood Coagulation

Fibrinogen is a large, soluble plasma protein (Factor I) synthesized by the liver, and it is absolutely…

Blood Composition — Plasma (55%) + Formed Elements (45%).

Plasma — 90-92% water, 6-8% proteins (Albumin, Globulins, Fibrinogen).

RBCs (Erythrocytes) — Biconcave, anucleated,

5-5.5,\text{million/mm}^3

. Contain Hemoglobin (Hb) for

O_2

transport. Life span ~120 days.

WBCs (Leukocytes) — Nucleated,

6000-8000/\text{mm}^3

. Immune function. Types:

- Granulocytes: Neutrophils (phagocytic, 60-65%), Eosinophils (allergy/parasites, 2-3%), Basophils (histamine/heparin, 0.5-1%). - Agranulocytes: Lymphocytes (specific immunity, 20-25%), Monocytes (macrophages, 6-8%).

Platelets (Thrombocytes) — Cell fragments,

1.5-3.5,\text{lakh/mm}^3

. Blood clotting.

Blood Groups (ABO) — Antigens on RBCs, Antibodies in plasma. O = Universal Donor (no antigens), AB = Universal Recipient (no antibodies).

Rh Factor — Rh+ (antigen present), Rh- (antigen absent). Rh- mother + Rh+ fetus

\rightarrow

Erythroblastosis fetalis.

Coagulation — Platelets

\rightarrow

Prothrombin

\rightarrow

Thrombin

\rightarrow

Fibrinogen

\rightarrow

Fibrin (clot).

To remember the order of WBC abundance (Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils - from most to least):

Never Let Monkeys Eat Bananas