NEET Exam > NEET Notes > Short Notes > Short Notes Body Fluids and Circulation - Short Notes for NEET
Short Notes Body Fluids and Circulation - Short Notes for NEET
Composition of Blood
General Features
- Blood is a fluid connective tissue
- pH: 7.4 (slightly alkaline)
- Volume: 5-6 liters in average adult human
- Constitutes 6-8% of body weight
- Two main components: Plasma (55%) and Formed Elements (45%)
1. Plasma (55%)
- Straw-colored, fluid matrix
- Water: 90-92%
- Proteins:6-8%
- Albumins: Maintain osmotic pressure
- Globulins: Immune response (antibodies = immunoglobulins)
- Fibrinogen: Blood clotting
- Prothrombin: Blood clotting
- Other substances: Glucose, amino acids, lipids, hormones, enzymes, vitamins, minerals (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, HCO₃⁻), waste products (urea, uric acid, creatinine)
- Serum: Plasma without clotting factors (fibrinogen)
2. Formed Elements (45%)
| Cell Type | Count | Structure | Function | Lifespan |
|---|---|---|---|---|
| Erythrocytes (RBC) | 5-5.5 million/mm³ | • Biconcave, disc-shaped • No nucleus (in mammals) • Contains haemoglobin • Formed in red bone marrow | Transport O₂ and CO₂ | 120 days Destroyed in spleen (graveyard of RBCs) |
| Leucocytes (WBC) | 6000-8000/mm³ | • Nucleated • Colorless • Amoeboid | Immune defense; fight infections | Varies (few days to years) |
| Platelets (Thrombocytes) | 1.5-4 lakh/mm³ | • Cell fragments • No nucleus • Formed from megakaryocytes in bone marrow | Blood clotting; release clotting factors | 5-10 days |
Types of Leucocytes (WBCs)
| Type | % of WBC | Features & Functions |
|---|---|---|
| A. GRANULOCYTES (with granules in cytoplasm) | ||
| Neutrophils | 60-65% | • Most abundant WBC • Phagocytic; engulf bacteria • First responders to infection |
| Eosinophils | 2-3% | • Resist infections • Associated with allergic reactions • Combat parasitic infections |
| Basophils | 0.5-1% | • Least abundant WBC • Secrete histamine, serotonin, heparin • Involved in inflammatory response |
| B. AGRANULOCYTES (without granules) | ||
| Lymphocytes | 20-25% | • B-lymphocytes: Produce antibodies (humoral immunity) • T-lymphocytes: Cell-mediated immunity • Second most abundant WBC |
| Monocytes | 6-8% | • Largest WBC • Phagocytic; transform into macrophages in tissues |
Blood Groups
ABO Blood Group System
- Discovered by Karl Landsteiner
- Based on presence/absence of antigens (A and B) on RBC surface
- Plasma contains corresponding antibodies (anti-A and anti-B)
| Blood Group | Antigens on RBC | Antibodies in Plasma | Can Donate To | Can Receive From |
|---|---|---|---|---|
| A | A | Anti-B | A, AB | A, O |
| B | B | Anti-A | B, AB | B, O |
| AB | A and B | None | AB only | A, B, AB, O (Universal recipient) |
| O | None | Anti-A and Anti-B | A, B, AB, O (Universal donor) | O only |
Rh Blood Group System
- Named after Rhesus monkey (discovered by Landsteiner and Wiener)
- Based on Rh antigen (D antigen) on RBC surface
- Rh positive (Rh⁺): Rh antigen present (~80% population)
- Rh negative (Rh⁻): Rh antigen absent (~20% population)
- Erythroblastosis foetalis:
- Rh⁻ mother + Rh⁺ fetus
- Mother develops anti-Rh antibodies (after first pregnancy)
- In subsequent pregnancies, antibodies attack fetal RBCs
- Causes hemolysis, jaundice, anemia in newborn
- Prevention: Anti-D injection (RhoGAM) given to mother
Coagulation of Blood (Blood Clotting)
Mechanism
- Prevents excessive blood loss
- Complex cascade involving clotting factors (I to XIII)
Steps of Clotting
Step 1: Injury to blood vessel → Platelets adhere and release clotting factors
Step 2: Formation of Prothrombinase(Thromboplastin)
- Extrinsic pathway: Tissue damage releases thromboplastin
- Intrinsic pathway: Blood contacts damaged vessel wall
- Both require Ca²⁺ ions
- Step 3: Prothrombinase converts Prothrombin → Thrombin (requires Ca²⁺ and Vitamin K)
- Step 4: Thrombin converts soluble Fibrinogen → Insoluble Fibrin threads
- Step 5: Fibrin forms mesh; traps blood cells → forms clot (thrombus)
- Clot retraction: Serum is squeezed out
Important Points
- Heparin: Anticoagulant produced by basophils and mast cells
- Vitamin K: Essential for synthesis of clotting factors
- Calcium ions: Required at multiple steps
- Haemophilia: Genetic disorder; deficiency of clotting factors (Factor VIII or IX); excessive bleeding
Composition of Lymph and its Function
Formation
- Formed from tissue fluid/interstitial fluid
- When tissue fluid enters lymphatic capillaries, it becomes lymph
- Also called "extracellular fluid"
Composition
- Similar to blood plasma but:
- No RBCs
- Fewer proteins (only small proteins that escape from capillaries)
- Contains lymphocytes
- Less oxygen, more CO₂
- Contains water, minerals, glucose, amino acids, fatty acids (especially after fat digestion)
Functions
- Returns interstitial fluid to blood (maintains fluid balance)
- Transport of nutrients, especially fats from intestine (via lacteals)
- Immune function: Lymphocytes destroy pathogens
- Removal of waste products from tissues
- Filters foreign particles through lymph nodes
Lymphatic System
- Components: Lymphatic capillaries → Lymphatic vessels → Lymph nodes → Lymphatic ducts
- Major ducts:
- Right lymphatic duct: Drains right side of head, thorax, right arm
- Thoracic duct: Drains rest of body
- Both empty into subclavian veins
- Lymph nodes: Filter lymph; contain lymphocytes and macrophages
- Other lymphoid organs: Spleen, thymus, tonsils, Peyer's patches
Human Circulatory System
General Features
- Closed circulatory system: Blood flows through vessels
- Double circulation: Blood passes through heart twice in one complete cycle
- Components: Heart, Blood vessels (arteries, veins, capillaries), Blood
Structure of Human Heart
Location and Protection
- Located in thoracic cavity, slightly left of midline
- Protected by rib cage
- Size: Fist-sized; weight ~300 grams
- Covered by pericardium(double-layered membrane)
- Outer fibrous pericardium
- Inner serous pericardium (parietal and visceral layers)
- Pericardial fluid reduces friction
Chambers
- Four-chambered heart: 2 atria (upper) + 2 ventricles (lower)
- Right atrium: Receives deoxygenated blood from body via superior and inferior vena cava
- Right ventricle: Pumps deoxygenated blood to lungs via pulmonary artery
- Left atrium: Receives oxygenated blood from lungs via pulmonary veins
- Left ventricle: Pumps oxygenated blood to body via aorta; has thickest wall
- Inter-atrial septum: Separates two atria
- Inter-ventricular septum: Separates two ventricles
- Fossa ovalis: Remnant of foramen ovale (opening in fetal heart)
Valves
| Valve | Location | Function |
|---|---|---|
| Tricuspid valve | Between right atrium and right ventricle | Prevents backflow from RV to RA; has 3 cusps |
| Bicuspid/Mitral valve | Between left atrium and left ventricle | Prevents backflow from LV to LA; has 2 cusps |
| Pulmonary semilunar valve | At opening of pulmonary artery from RV | Prevents backflow from pulmonary artery to RV |
| Aortic semilunar valve | At opening of aorta from LV | Prevents backflow from aorta to LV |
- Chordae tendineae: Fibrous cords attached to AV valves
- Papillary muscles: Muscles that prevent valve eversion
Wall of Heart
- Epicardium: Outer layer (visceral pericardium)
- Myocardium: Middle, thick muscular layer; cardiac muscles
- Endocardium: Inner endothelial lining
Coronary Circulation
- Coronary arteries: Supply oxygenated blood to heart muscle
- Coronary veins: Drain deoxygenated blood into coronary sinus → right atrium
Blood Vessels
| Feature | Arteries | Veins | Capillaries |
|---|---|---|---|
| Function | Carry blood away from heart | Carry blood to heart | Exchange of materials between blood and tissues |
| Blood type | Oxygenated (except pulmonary artery) | Deoxygenated (except pulmonary vein) | Both types |
| Wall thickness | Thick, elastic, muscular | Thin, less elastic | Very thin (single layer of endothelium) |
| Lumen | Narrow | Wide | Very narrow |
| Pressure | High | Low | Decreasing |
| Valves | Absent (except at base) | Present (prevent backflow) | Absent |
| Blood flow | Rapid, pulsatile | Slow, non-pulsatile | Very slow |
Types
- Arteries → Arterioles → Capillaries → Venules → Veins
- Aorta: Largest artery
- Vena cava: Largest vein (superior and inferior)
Cardiac Cycle
Definition
- One complete heartbeat = one cardiac cycle
- Involves sequential contraction (systole) and relaxation (diastole) of chambers
- Duration: ~0.8 seconds (at 72 beats/min)
Phases of Cardiac Cycle
| Phase | Duration | Events |
|---|---|---|
| 1. Atrial Systole (Ventricular Diastole) | 0.1 sec | • Atria contract • AV valves open • Blood flows from atria to ventricles • Ventricles fill (~70% filled passively before this) • Semilunar valves closed |
| 2. Ventricular Systole (Atrial Diastole) | 0.3 sec | • Ventricles contract • AV valves close (produces 1st heart sound "Lub") • Pressure in ventricles increases • Semilunar valves open • Blood ejected into aorta and pulmonary artery • Atria relax and start filling |
| 3. Joint Diastole (Complete Cardiac Diastole) | 0.4 sec | • Both atria and ventricles relax • Semilunar valves close (produces 2nd heart sound "Dup") • AV valves open • Blood from veins fills atria • Passive filling of ventricles begins |
Heart Sounds
- "Lub" (1st sound): Closure of AV valves (tricuspid and bicuspid) at beginning of ventricular systole
- "Dup" (2nd sound): Closure of semilunar valves at beginning of ventricular diastole
- Heard using stethoscope
Important Values
- Stroke volume (SV): Volume of blood pumped by each ventricle per beat = ~70 mL
- Heart rate (HR): Number of heartbeats per minute = ~72 bpm
- Cardiac output (CO):Volume of blood pumped by each ventricle per minute
- CO = SV × HR = 70 mL × 72 = ~5000 mL/min (5 L/min)
- End Diastolic Volume (EDV): Volume in ventricle at end of diastole = ~120-130 mL
- End Systolic Volume (ESV): Volume remaining in ventricle after systole = ~50-60 mL
Electrocardiogram (ECG/EKG)
Definition
- Graphical recording of electrical activity of heart
- Recorded by electrocardiograph
- Invented by Willem Einthoven (Nobel Prize)
Normal ECG Waves
| Wave/Complex | Represents |
|---|---|
| P wave | Atrial depolarization (contraction of atria) |
| QRS complex | Ventricular depolarization (contraction of ventricles); also represents atrial repolarization |
| T wave | Ventricular repolarization (relaxation of ventricles) |
Segments and Intervals
- P-Q/P-R interval: Time from start of atrial depolarization to start of ventricular depolarization
- S-T segment: Period when ventricles are contracted
- Q-T interval: Duration of ventricular systole
Clinical Significance
Detects arrhythmias, myocardial infarction, heart blocks, chamber enlargement
Double Circulation
Definition
- Blood passes through heart twice in one complete circuit
- Two pathways: Pulmonary circulation and Systemic circulation
- Prevents mixing of oxygenated and deoxygenated blood
- Ensures efficient oxygen delivery
1. Pulmonary Circulation
- Right ventricle → Pulmonary artery → Lungs → Pulmonary veins → Left atrium
- Deoxygenated blood from RV goes to lungs for oxygenation
- Oxygenated blood returns to LA
- Pulmonary artery carries deoxygenated blood (exception)
- Pulmonary veins carry oxygenated blood (exception)
2. Systemic Circulation
- Left ventricle → Aorta → Body tissues → Vena cava → Right atrium
- Oxygenated blood from LV distributed to body
- Deoxygenated blood returns to RA via superior and inferior vena cava
- Supplies oxygen and nutrients; removes CO₂ and wastes
Complete Pathway
RA → RV → Pulmonary artery → Lungs → Pulmonary veins → LA → LV → Aorta → Body → Vena cava → RA
Regulation of Cardiac Activity
Nodal Tissue (Autorhythmic Cells)
- Heart is myogenic (contractions generated within heart muscle itself)
- Specialized cardiac muscle fibers form nodal tissue
Components of Nodal Tissue
| Structure | Location | Function |
|---|---|---|
| Sino-Atrial Node (SAN) | Upper right atrium near opening of superior vena cava | • Pacemaker of heart • Generates rhythmic impulses (~72/min) • Initiates heartbeat |
| Atrio-Ventricular Node (AVN) | Lower right atrium near inter-atrial septum | • Receives impulse from SAN • Delays impulse (~0.1 sec) to allow atrial contraction • Passes impulse to ventricles |
| Bundle of His (AV Bundle) | Passes through inter-ventricular septum | • Conducts impulse from AVN to ventricles • Divides into right and left bundle branches |
| Purkinje Fibers | Spread throughout ventricular myocardium | • Rapidly distribute impulse to all parts of ventricles • Cause ventricular contraction |
Sequence of Impulse Conduction
SAN → Atrial muscles → AVN → Bundle of His → Bundle branches → Purkinje fibers → Ventricular muscles
Neural Regulation
- Cardiovascular center in medulla oblongata regulates heart rate
- Sympathetic nerves: Increase heart rate and contractility (norepinephrine/epinephrine)
- Parasympathetic nerves (Vagus nerve): Decrease heart rate (acetylcholine)
- Baroreceptors: In aortic arch and carotid sinus; monitor blood pressure
- Chemoreceptors: Monitor O₂, CO₂, H⁺ levels
Hormonal Regulation
- Epinephrine and Norepinephrine: Increase heart rate and contractility
- Thyroid hormones: Increase heart rate
- Ions (Ca²⁺, K⁺, Na⁺): Affect heart function
Disorders of Circulatory System
| Disorder | Description | Causes/Features |
|---|---|---|
| Hypertension (High BP) | Blood pressure consistently above 140/90 mm Hg | • Stress, obesity, smoking, high salt intake • Can lead to heart disease, stroke, kidney damage • Often called "silent killer" |
| Coronary Artery Disease (CAD) | Narrowing of coronary arteries due to plaque deposition | • Atherosclerosis: Buildup of cholesterol, fats, Ca²⁺ in artery walls • Reduces blood supply to heart muscle • Risk factors: high cholesterol, smoking, diabetes, sedentary lifestyle |
| Angina Pectoris | Chest pain due to inadequate oxygen supply to heart muscle | • Usually during physical exertion or stress • Due to partial blockage of coronary arteries • Warning sign of heart disease |
| Heart Failure | Heart unable to pump sufficient blood to meet body's needs | • Congestive heart failure: Blood backs up in veins; fluid accumulation • Weakness, fatigue, shortness of breath • Can be left-sided or right-sided |
| Myocardial Infarction (Heart Attack) | Death of heart muscle due to complete blockage of coronary artery | • Blood clot blocks artery • Severe chest pain, sweating, nausea • Medical emergency |
Additional Disorders (Brief)
- Stroke: Interruption of blood supply to brain; brain tissue damage
- Arteriosclerosis: Hardening and thickening of arterial walls
- Arrhythmia: Irregular heartbeat
- Congenital heart defects: Structural abnormalities present at birth (e.g., ventricular septal defect)
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FAQs on Short Notes Body Fluids and Circulation - Short Notes for NEET
| 1. What are the main components of blood in the human body? |  |
Ans. The main components of blood are plasma, red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). Plasma is the liquid portion that carries nutrients, hormones, and waste products. Red blood cells transport oxygen using haemoglobin, while white blood cells are crucial for the immune response, and platelets aid in blood clotting.
| 2. How does the circulatory system function in the human body? | |
Ans. The circulatory system, also known as the cardiovascular system, functions by transporting blood throughout the body via a network of arteries, veins, and capillaries. The heart acts as a pump, propelling oxygenated blood from the left ventricle into the aorta, which branches into smaller arteries, delivering oxygen and nutrients to tissues. Deoxygenated blood returns to the heart through veins to be re-oxygenated in the lungs.
| 3. What role do platelets play in the body's response to injury? | |
Ans. Platelets play a crucial role in the body's response to injury by initiating the process of blood clotting. When a blood vessel is damaged, platelets adhere to the site of injury and aggregate to form a temporary plug. They release chemical signals that attract more platelets and promote the coagulation cascade, ultimately leading to the formation of a stable blood clot to prevent excessive bleeding.
| 4. What is the significance of the lymphatic system in body fluids? | |
Ans. The lymphatic system is significant in regulating body fluids, maintaining fluid balance, and supporting the immune system. It collects excess interstitial fluid from tissues, returning it to the bloodstream, thus preventing swelling. Additionally, the lymphatic system transports lymph, which contains white blood cells, and plays a vital role in filtering pathogens and foreign particles through lymph nodes.
| 5. How do the lungs and heart work together in circulation? | |
Ans. The lungs and heart work together in circulation by facilitating the exchange of gases. Deoxygenated blood from the body enters the right atrium of the heart, is pumped to the right ventricle, and then sent to the lungs via the pulmonary arteries. In the lungs, carbon dioxide is exchanged for oxygen. The oxygenated blood returns to the left atrium of the heart, is pumped into the left ventricle, and then circulated to the rest of the body, delivering oxygen to tissues.
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