What is the primary difference between blood plasma and serum?

Blood plasma is the liquid matrix of blood that contains all the clotting factors, including fibrinogen. When blood clots, these clotting factors are used up to form the clot. The remaining clear, yellowish fluid after the clot has formed and retracted is called serum. Therefore, the primary difference is that serum is plasma without the clotting factors, particularly fibrinogen. Serum is often used in diagnostic tests because it lacks these factors, which could interfere with certain assays.

Why are RBCs biconcave and anucleated in mammals?

The biconcave shape of mammalian RBCs increases their surface area-to-volume ratio, which enhances the efficiency of gas exchange (oxygen and carbon dioxide). This shape also provides flexibility, allowing them to squeeze through narrow capillaries. Being anucleated (lacking a nucleus) means they cannot synthesize proteins or divide, but it allows for more space to be dedicated to hemoglobin, maximizing oxygen-carrying capacity. This adaptation comes at the cost of a shorter lifespan (approx. 120 days).

How does the lymphatic system contribute to immunity?

The lymphatic system is a critical component of the immune system. It transports lymphocytes (a type of white blood cell) throughout the body. Lymph nodes, which are strategically located along lymphatic vessels, act as filters, trapping pathogens, foreign particles, and cellular debris from the lymph. Within the lymph nodes, lymphocytes proliferate and mount immune responses against these trapped invaders. This ensures that the body can effectively detect and fight infections.

What is the significance of the Rh factor in blood transfusions and pregnancy?

The Rh factor, specifically the D antigen, is crucial because an Rh-negative individual does not naturally have anti-Rh antibodies but can develop them upon exposure to Rh-positive blood. In transfusions, an Rh-negative recipient receiving Rh-positive blood for the first time might not show an immediate reaction, but will produce antibodies, leading to a severe reaction if exposed again. In pregnancy, if an Rh-negative mother carries an Rh-positive fetus, her immune system can become sensitized and produce anti-Rh antibodies. In subsequent Rh-positive pregnancies, these antibodies can cross the placenta and attack the fetal RBCs, leading to a severe condition called erythroblastosis fetalis or hemolytic disease of the newborn.

Explain the role of platelets in blood clotting.

Platelets, or thrombocytes, are essential for hemostasis (stopping bleeding). When a blood vessel is injured, platelets are activated by exposed collagen. They adhere to the site of injury, change shape, and release various chemicals that attract more platelets, forming a temporary 'platelet plug.' This plug provides the initial seal. Furthermore, activated platelets provide a surface for the assembly of clotting factors, accelerating the coagulation cascade that ultimately leads to the formation of a stable fibrin clot, reinforcing the platelet plug and permanently sealing the wound.

Body Fluids

Biology

NEET UG

Version 1Updated 22 Mar 2026

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Body fluids are the aqueous solutions that circulate throughout the body, providing a medium for the transport of nutrients, oxygen, hormones, metabolic wastes, and other essential substances. They are crucial for maintaining the internal environment, known as homeostasis, which is the stable condition necessary for the proper functioning of cells, tissues, and organs. The primary body fluids in h…

Quick Summary

Body fluids are the essential internal liquids that circulate throughout the human body, maintaining a stable internal environment (homeostasis) crucial for cell and organ function. The primary body fluids are blood, lymph, and interstitial fluid.

Blood, a specialized connective tissue, circulates within vessels, transporting oxygen, nutrients, hormones, and waste, and playing a vital role in defense and clotting. It consists of plasma (fluid matrix) and formed elements (RBCs, WBCs, platelets).

Blood groups (ABO, Rh) are determined by antigens on RBCs and are critical for safe transfusions. Lymph is formed from interstitial fluid that enters lymphatic vessels. It circulates through the lymphatic system, returning excess fluid to the bloodstream, absorbing fats, and playing a central role in immunity by transporting lymphocytes and filtering pathogens in lymph nodes.

Interstitial fluid directly bathes cells, facilitating the exchange of substances between blood and cells. The intricate balance and interaction of these fluids are fundamental for overall physiological health and are frequently tested in NEET.

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Key Concepts

Blood Plasma Composition and Function

Blood plasma is the non-cellular, liquid component of blood, making up roughly 55% of its total volume. It's…

Formed Elements: RBCs, WBCs, and Platelets

The formed elements are the cellular components of blood, suspended in the plasma, and constitute about 45%…

ABO Blood Grouping and Transfusion Reactions

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

Blood: — Plasma (55%) + Formed Elements (45%).\n- Plasma: 92% water, 8% proteins (Albumin - osmotic balance, Globulins - immunity, Fibrinogen - clotting).\n- Formed Elements:\

\quad - RBCs (Erythrocytes): $5-5.5 \times 10^6/mm^3$ , biconcave, anucleated, hemoglobin, 120-day lifespan.\ \quad - WBCs (Leukocytes): $6000-8000/mm^3$ , immune function. Granulocytes (Neutrophils - phagocytic, most abundant; Eosinophils - allergy/parasites; Basophils - inflammation) & Agranulocytes (Lymphocytes - specific immunity; Monocytes - macrophages).

\ \quad - Platelets (Thrombocytes): $1.5-3.5 \times 10^5/mm^3$ , clotting.\ - Blood Groups (ABO): Antigens on RBCs, Antibodies in plasma. O is universal donor, AB is universal recipient.\ - Rh Factor: D antigen.

Rh- mother + Rh+ fetus = erythroblastosis fetalis.\ - Coagulation: Platelets \rightarrow Prothrombinase \rightarrow Prothrombin \xrightarrow{\text{Thrombin}} Thrombin \rightarrow Fibrinogen \xrightarrow{\text{Thrombin}} Fibrin clot.

\ - Lymph: Interstitial fluid + Lymphocytes. Low protein, no RBCs. Functions: fluid return, fat absorption, immunity.

For WBC abundance (most to least): Never Let Monkeys Eat Bananas.\nNeutrophils (60-65%)\nLymphocytes (20-25%)\nMonocytes (6-8%)\nEosinophils (2-3%)\nBasophils (0.5-1%)