NEET Biology - Unit 5- Body fluids and circulation- Study Notes - New Syllabus
NEET Biology – Unit 5- Body fluids and circulation- Study Notes – New Syllabus
Key Concepts:
- Body fluids and circulation: Composition of blood, blood groups, coagulation of blood; Composition of lymph and its function; Human circulatory system-Structure of human heart and blood vessels; Cardiac cycle, cardiac output, ECG, Double circulation; Regulation of cardiac activity; Disorders of circulatory system-Hypertension, Coronary artery disease, Angina pectoris, Heart failure.
Body Fluids and Circulation
🩸Composition of Blood
Blood is a fluid connective tissue that transports substances throughout the body.
It has two main components:
📌 A. Plasma
- Pale yellow, fluid part of blood
- Makes about 55 percent of blood
- Mostly water (90 to 92 percent)
- Contains:
- Proteins
- Albumins: maintain osmotic pressure
- Globulins: defense (antibodies)
- Fibrinogen: blood clotting
- Minerals: Na+, Ca2+, Mg2+, HCO3–
- Nutrients: glucose, amino acids, lipids
- Waste products: urea, uric acid
- Hormones and enzymes
Function: Helps transport materials, maintain pH and osmotic balance.
📌 B. Formed Elements
Make up 45 percent of blood.
Includes RBCs, WBCs and Platelets.
1. RBCs (Erythrocytes)
- Most abundant blood cells
- Formed in red bone marrow
- Biconcave, no nucleus
- Contain haemoglobin (Hb)
- Carry O₂ and CO₂
- Lifespan: 120 days
2. WBCs (Leucocytes)
- Nucleated, colourless
- Provide immunity
- Two types:
Granulocytes
- Neutrophils: most abundant, phagocytic
- Eosinophils: allergy response
- Basophils: least abundant, release histamine/serotonin during inflammation
Agranulocytes
- Lymphocytes: B and T cells (antibody formation and immunity)
- Monocytes: largest WBC, phagocytic
3. Platelets (Thrombocytes)
- Small cell fragments
- Essential for blood clotting
- Low count leads to excessive bleeding
🧬 Blood Groups
Blood grouping is mainly based on ABO system and Rh system.
A. ABO Blood Group System
Based on the presence or absence of A and B antigens on RBCs.
| Blood Group | Antigen on RBC | Antibody in Plasma | Can Receive | Can Donate |
|---|---|---|---|---|
| A | A | Anti-B | A, O | A, AB |
| B | B | Anti-A | B, O | B, AB |
| AB | A and B | None | All | AB |
| O | None | Anti-A + Anti-B | O | All |
O = universal donor
AB = universal recipient
B. Rh Factor (Positive / Negative)
- Rh antigen present → Rh+
- Rh antigen absent → Rh−
🔶 Rh Incompatibility
- Occurs when Rh− mother carries Rh+ fetus.
- First pregnancy safe
- During delivery → mixing of blood → mother forms anti-Rh antibodies
- Second Rh+ pregnancy → antibodies attack fetal RBCs
This causes Erythroblastosis Foetalis (fetal anemia + jaundice).
Prevented by giving anti-Rh antibodies to mother after 1st delivery.
🩹Coagulation of Blood (Blood Clotting)
Blood clotting prevents excessive blood loss after injury.
Steps in Clotting
- Injury to blood vessel → platelets release clotting factors
- Prothrombin (inactive) → gets converted to Thrombin (requires Thrombokinase + Ca2+)
- Thrombin converts Fibrinogen → Fibrin
- Fibrin forms a mesh that traps RBCs → forms a clot
Vitamin K is essential for making clotting proteins.
Calcium ions (Ca2+) activate various clotting steps.
📘 Quick Recap
Blood = plasma + formed elements
Plasma contains proteins (albumin, globulin, fibrinogen), nutrients, minerals
RBC: haemoglobin, O₂ transport, no nucleus
WBC: immunity (neutrophils phagocytic, lymphocytes antibody production)
Platelets: clotting
ABO groups: based on A/B antigens
Rh system important in pregnancy
Coagulation: prothrombin → thrombin → fibrin → clot
Lymph: Composition and Functions
🧪 Introduction
Lymph is a pale, slightly yellow fluid flowing inside lymphatic vessels.
It forms when some part of the fluid leaks out of blood capillaries into tissues.
The lymphatic system collects this leaked fluid and returns it to the bloodstream.
🧬 Composition of Lymph
Lymph is similar to plasma but contains fewer proteins. It has the following components:
- Water – forms the major portion
- Proteins – low concentration, mostly antibodies
- Ions – Na+, K+, Ca2+, Cl-, HCO3-
- Lymphocytes – mainly T and B cells involved in immunity
- Fats – absorbed from intestine as chyle, giving lymph a milky look
- Glucose and amino acids – similar to plasma
- Cell debris and waste materials – collected from tissues
- Very few RBCs or platelets – almost absent normally
🌟 Functions of Lymph
1. Helps in Immunity
- Rich in lymphocytes
- Lymph nodes filter bacteria and viruses
- Important in antibody formation
2. Transports Fat from Intestine
- Intestinal villi contain lacteals that absorb dietary fats
- Fats enter lymph as chylomicrons
- Released into blood circulation later
3. Maintains Fluid Balance
- Collects excess tissue fluid
- Returns it to the venous system
- Prevents swelling or edema
4. Removes Waste from Tissues
- Clears cell debris and metabolic waste
- Keeps tissue spaces clean
5. Transports Hormones
- Carries hormones from glands to target organs
- Helps coordinate body functions
6. Provides Defence at Local Sites
- Lymph nodes trap microbes
- Node swelling shows active immune response
📘 Summary Table
| Feature | Details |
|---|---|
| Main Components | Water, low proteins, ions, lymphocytes, fats, glucose, waste |
| Cells Present | Mostly lymphocytes, very few RBCs or platelets |
| Appearance | Pale yellow, milky when rich in fats |
| Key Functions | Immunity, fat transport, fluid balance, waste removal, hormone transport |
📘 Quick Recap
Lymph is leaked tissue fluid collected by lymph vessels
Low in proteins, rich in lymphocytes
Transports fats from intestine through lacteals
Maintains tissue fluid balance and prevents edema
Removes waste and cell debris
Lymph nodes filter pathogens and support immunity
Also helps carry hormones across the body
Human Circulatory System
❤️ Structure of Human Heart
The human circulatory system is a closed, double circulation system.
It includes the heart, blood vessels, and blood.
Its main role is to transport oxygen, nutrients, hormones, and waste materials throughout the body.
🌱 Basic Features
- Muscular, hollow pumping organ
- About the size of a fist
- Located slightly left in the thoracic cavity
- Enclosed in double-walled pericardium with pericardial fluid that reduces friction
🫀 Chambers of the Heart
The heart has four chambers:
1. Right Atrium
- Receives deoxygenated blood from:
- Superior vena cava
- Inferior vena cava
- Coronary sinus
- Thin-walled chamber
2. Right Ventricle
- Pumps deoxygenated blood to lungs through pulmonary artery
- Thicker walls than atrium
3. Left Atrium
- Receives oxygenated blood from lungs via pulmonary veins
- Thin-walled
4. Left Ventricle
- Thickest cardiac wall
- Pumps oxygenated blood to the entire body through aorta
📌 Why is left ventricle thicker?
It pumps blood to the entire body, so it needs stronger muscles.
🔒 Heart Valves (One-way movement)
1. Tricuspid valve
- Between right atrium and right ventricle
- Prevents backflow into right atrium
2. Bicuspid / Mitral valve
- Between left atrium and left ventricle
- Prevents backflow into left atrium
3. Semilunar valves
- Present at openings of:
- Aorta
- Pulmonary artery
- Prevent backflow into ventricles
Nodal System (Pacemaker of the Heart)
- SA Node (Sinoatrial Node) – in right atrium, generates impulse, natural pacemaker
- AV Node (Atrioventricular Node) – receives impulse from SA node, delays it for ventricular filling
- AV Bundle (Bundle of His) and Purkinje Fibres – spread impulse throughout ventricles for coordinated contraction
Impulse pathway:
SA Node → AV Node → Bundle of His → Purkinje Fibres
🫀 Blood Vessels
🌱 Types of Blood Vessels
1. Arteries
- Carry blood away from the heart
- Usually carry oxygenated blood (except pulmonary artery)
- Thick, muscular, elastic walls
- High pressure
- Narrow lumen
2. Veins
- Carry blood toward the heart
- Usually carry deoxygenated blood (except pulmonary vein)
- Thin, less elastic walls
- Contain valves to prevent backflow
- Low pressure
- Wide lumen
3. Capillaries
- Microscopic thin-walled vessels
- Connect arteries and veins
- Single layer of endothelium
- Main site for exchange of gases, nutrients, and wastes
📊 Summary Table: Arteries vs Veins vs Capillaries
| Feature | Arteries | Veins | Capillaries |
|---|---|---|---|
| Direction | Away from heart | Toward heart | Connect arteries and veins |
| Oxygen content | Mostly oxygenated | Mostly deoxygenated | Mixed exchange |
| Wall thickness | Thick, muscular | Thin, less muscular | One-cell thick |
| Pressure | High | Low | Very low |
| Valves | Absent | Present | Absent |
| Lumen | Narrow | Wide | Very narrow |
| Function | Distribution | Collection | Exchange |
📦 Quick Recap
Heart has four chambers: RA, RV, LA, LV
Tricuspid valve on right side, bicuspid valve on left
Semilunar valves guard aorta and pulmonary artery
SA node is the natural pacemaker
Arteries carry blood away, veins bring blood back
Capillaries are the exchange sites
Left ventricle has the thickest wall