NEET 2026 Body Fluids & Circulation in One-Shot by Samapti Ma’am

Preparing Human Physiology for NEET requires conceptual clarity and systematic revision. Among all physiology chapters, Body Fluids and Circulation is considered highly scoring but concept-intensive. The NEET 2026 Body Fluids & Circulation in one-shot by Samapti Ma’amm focuses on strengthening fundamentals through clear explanations and logical connections.

This chapter explains how blood, heart, blood vessels, and lymph work together to transport substances, regulate body functions, and maintain internal balance. In this article, the entire chapter is explained in simple language, strictly following the NCERT framework, making it ideal for quick revision before NEET 2026.

Introduction to Body Fluids and Circulation

All living cells require oxygen and nutrients for survival, while waste materials such as carbon dioxide must be continuously removed. In humans, this exchange of materials is made possible by specialized body fluids.

Blood and lymph are the main transport fluids in the body. Circulation of these fluids helps maintain body temperature, supports immunity, and ensures proper functioning of organs. Without an efficient circulatory system, cells would fail to survive.

Need for a Circulatory System

Human cells are not in direct contact with the external environment. Therefore, they depend on an internal transport system to meet their needs.

The circulatory system helps in:

• Transporting oxygen from the lungs to the body tissues

• Carrying nutrients from the digestive system

• Removing metabolic waste products

• Transporting hormones to target organs

• Providing protection through immune cells

While simple organisms rely on diffusion, higher organisms like humans require a well-developed circulatory system to support complex body functions.

Composition of Blood

Blood is a specialized connective tissue consisting of two major components: plasma and formed elements.

Plasma

Plasma forms about 55% of blood volume. It is a straw-colored fluid mainly composed of water and dissolved substances. Plasma proteins such as albumins help maintain osmotic balance, while globulins play a role in immunity.

Formed Elements

Formed elements constitute around 45% of blood volume and include:

• Red Blood Cells (RBCs)

• White Blood Cells (WBCs)

• Platelets

White blood cells are further classified into granulocytes and agranulocytes, with neutrophils being the most abundant and actively involved in destroying pathogens.

Blood Groups and Coagulation

Understanding blood groups is essential for the NEET 2026 Body Fluids & Circulation syllabus, especially from a clinical perspective.

ABO Blood Group System

The ABO system is based on the presence or absence of antigens on the surface of RBCs.

• Group O acts as a universal donor as it lacks antigens

• Group AB acts as a universal recipient, as it lacks antibodies

Rh Factor

The Rh system depends on the presence of the Rh antigen. Rh incompatibility during pregnancy can lead to Erythroblastosis Fetalis, a condition in which maternal antibodies destroy fetal RBCs. This condition is prevented by administering anti-Rh antibodies to the mother after the first delivery.

Human Heart and Cardiac Cycle

The human heart is a myogenic organ, meaning the heartbeat originates within the heart muscle itself. The SA node acts as the pacemaker and initiates electrical impulses.

The cardiac cycle lasts 0.8 seconds and consists of:

• Joint Diastole (0.4 s): All chambers are relaxed

• Atrial Systole (0.1 s): Atria contract

• Ventricular Systole (0.3 s): Ventricles contract

During one cardiac cycle, two heart sounds are heard:

• Lub: Closure of atrioventricular valves

• Dub: Closure of semilunar valves

The electrical activity of the heart is recorded using an ECG, represented by the P wave, QRS complex, and T wave.

Circulatory Pathways and Disorders

Humans exhibit double circulation, where blood passes through the heart twice during one complete cycle.

• Pulmonary circulation: Between the heart and the lungs

• Systemic circulation: Between the heart and body tissues

This chapter also includes important circulatory disorders:

• Hypertension: Persistently high blood pressure

• Atherosclerosis: Narrowing of arteries due to deposits

• Heart Failure: Inability of the heart to pump sufficient blood

Plasma

Plasma is the liquid matrix of blood that acts as a transport medium for cells and dissolved substances. It helps maintain blood volume, osmotic balance, and pH.

Composition of Plasma

Water (90–92%): Acts as a solvent and transport medium.

Plasma Proteins (6–8%)

Other Solutes: Include nutrients, gases, electrolytes, hormones, and metabolic wastes.

Serum

Serum is obtained after blood coagulation. Since it lacks clotting factors like fibrinogen and prothrombin, it cannot clot and is commonly used in diagnostic tests.

Formed Elements

Formed elements are the cellular components of blood derived from hematopoietic stem cells. They are involved in transport, immunity, and blood clotting.

Erythrocytes (Red Blood Cells)

RBCs are the most abundant blood cells and are specialized for oxygen transport.

• Count: 5–5.5 million/mm³

• Shape: Biconcave

• Nucleus: Absent in mammals (camel and llama are exceptions)

• Lifespan: ~120 days

• Destroyed in: Spleen

• Vitamins required: Vitamin B₁₂ and B₉

Leukocytes (White Blood Cells)

WBCs are defensive cells that protect the body against infections.

• Count: 6,000–8,000/mm³

• Special property: Diapedesis

• Disorder: Leukemia

Classification of Leukocytes

Leukocytes are the defensive cells of the blood that protect the body against infections and foreign substances. Based on the presence or absence of cytoplasmic granules, leukocytes are classified into two main groups.

Granulocytes

Granulocytes are white blood cells that contain distinct cytoplasmic granules and usually have a lobed nucleus. They play an important role in innate immunity and inflammatory responses.

Agranulocytes

Agranulocytes lack visible cytoplasmic granules and have a single, large nucleus. They are mainly involved in specific immune responses and phagocytosis.

Platelets (Thrombocytes)

Platelets are cell fragments essential for blood clotting.

• Count: 1.5–3.5 lakh/mm³

• Origin: Megakaryocytes

• Lifespan: ~7 days

• Disorder: Thrombocytopenia

Blood Clotting (Coagulation)

Blood clotting prevents excessive blood loss at injury sites.

Steps of Clotting: Injury → Thromboplastin → Thrombokinase → Thrombin → Fibrin → Clot formation

Tissue Fluid and Lymph

Tissue fluid forms the internal environment for cells. When it enters lymphatic vessels, it is called lymph.

• Tissue fluid: Plasma without proteins and cells

• Lymph: Helps maintain fluid balance and immunity

Circulatory Systems

Animals show different circulatory systems based on complexity.

Human Heart

The human heart is a muscular organ responsible for pumping blood.

• Origin: Mesodermal

• Chambers: Four

• Nature: Myogenic

Conducting System of the Heart

The conducting system regulates rhythmic contraction.

Cardiac Cycle

The cardiac cycle represents one complete heartbeat lasting 0.8 seconds.

Heart Sounds

Heart sounds are produced due to valve closures:

• Lub: AV valve closure

• Dub: Semilunar valve closure

Disorders of the Circulatory System

Circulatory disorders affect blood flow and heart efficiency. Important conditions include hypertension, coronary artery disease, angina pectoris, heart attack, heart failure, and cardiac arrest.