Circulatory System

Circulatory System

Introduction

·       The circulatory system, also known as the cardiovascular system, is a complex network responsible for the transportation of blood, nutrients, gases, hormones, and waste products throughout the body.

·       It is essential for maintaining homeostasis, cellular respiration, immunity, and temperature regulation.

·       It consists of three main components:

1.     Blood – the fluid connective tissue.

2.     Heart – the muscular pump.

3.     Blood Vessels – the network of channels for blood distribution (arteries, veins, capillaries).

Blood

Composition of Blood

1. Plasma (55%) – straw-colored fluid containing:
• Water (90–92%)
• Plasma proteins (7–8%) → Albumin, Globulins, Fibrinogen.
• Other solutes – electrolytes (Na⁺, K⁺, Cl⁻), nutrients (glucose, amino acids, lipids), hormones, waste products (urea, uric acid).
2. Formed Elements (45%) – cellular components:
• Erythrocytes (RBCs)
• Leukocytes (WBCs)
• Thrombocytes (Platelets)

Functions of Blood

• Transport: O₂ from lungs to tissues, CO₂ from tissues to lungs, nutrients from GIT, hormones, waste products to kidneys/liver.
• Regulation: Maintains pH, osmotic balance, body temperature, fluid distribution.
• Protection: WBCs defend against infection, platelets aid in clotting, antibodies provide immunity.

Types of Blood Corpuscles

1. Erythrocytes (RBCs):
• Biconcave, non-nucleated cells in humans; life span ~120 days.
• Contain hemoglobin (Hb) for O₂ and CO₂ transport.
• Produced in red bone marrow (erythropoiesis stimulated by erythropoietin).
• Count: ~5–5.5 million/µL in males, 4.5–5 million/µL in females.
2. Leukocytes (WBCs):
• Nucleated, colorless, defensive cells.
• Normal count: 4,000–11,000/µL.
• Types:
• Granulocytes: Neutrophils (phagocytosis), Eosinophils (allergic response, parasitic defense), Basophils (histamine release).
• Agranulocytes: Lymphocytes (B-cells – antibody production, T-cells – cell-mediated immunity), Monocytes (phagocytes).
3. Thrombocytes (Platelets):
• Small, irregular fragments without nuclei.
• Normal count: 150,000–400,000/µL.
• Essential for blood clotting and prevention of blood loss.

Blood Groups

• Based on the presence of antigens (agglutinogens) on RBC membrane.

1. ABO System:
• A → Antigen A, Anti-B antibody.
• B → Antigen B, Anti-A antibody.
• AB → Antigens A & B, no antibody (universal recipient).
• O → No antigen, both antibodies (universal donor).
2. Rh Factor:
• Rh⁺ (antigen present) or Rh⁻ (absent).
• Clinical significance in hemolytic disease of the newborn (HDN) and transfusion reactions.

Coagulation of Blood

• A protective mechanism to prevent excessive bleeding after injury.
• Involves a cascade of clotting factors leading to the conversion of:
• Prothrombin → Thrombin (by prothrombin activator & Ca²⁺).
• Fibrinogen → Fibrin (by thrombin).
• Fibrin forms a meshwork trapping blood cells, creating a clot.
• Platelets release serotonin (vasoconstriction) and thromboplastin (clot initiation).
• Normal clotting time: 3–8 minutes.

Heart

Structure

• Muscular, hollow, four-chambered organ (~300 g).
• Located in mediastinum between lungs.
• Chambers:
• Right atrium → receives deoxygenated blood from superior & inferior vena cava.
• Right ventricle → pumps blood to lungs via pulmonary artery.
• Left atrium → receives oxygenated blood from lungs via pulmonary veins.
• Left ventricle → pumps blood to body via aorta (thickest wall).
• Valves:
• Atrioventricular (AV): Tricuspid (right), Bicuspid/Mitral (left).
• Semilunar: Pulmonary, Aortic.
• Heart wall layers: Endocardium, Myocardium, Epicardium.
• Covered by pericardium (fibrous + serous).

Cardiac Cycle

• Sequence of events in one heartbeat (~0.8 sec at 72 bpm).

1. Atrial systole (0.1 sec): Atria contract, blood pushed to ventricles.
2. Ventricular systole (0.3 sec): Ventricles contract, AV valves close (lub sound), blood ejected into arteries.
3. Joint diastole (0.4 sec): Both atria & ventricles relax, blood flows in passively.

Heartbeat

• Normal: ~70–72 beats/min at rest.
• Controlled by SA node (pacemaker).
• Sounds:
• Lub (S1): Closure of AV valves.
• Dub (S2): Closure of semilunar valves.

ECG (Electrocardiogram)

• A graphic record of electrical activity of heart.
• Waves:
• P wave: Atrial depolarization.
• QRS complex: Ventricular depolarization.
• T wave: Ventricular repolarization.
• Diagnostic tool for arrhythmias, MI, conduction defects.

Blood Pressure

• Force exerted by blood against arterial walls.
• Normal: 120/80 mmHg.
• Systolic (120): Ventricular contraction.
• Diastolic (80): Ventricular relaxation.
• Hypertension: >140/90 mmHg.
• Hypotension: <90/60 mmHg.

Pulse

• Rhythmic expansion of arteries due to ventricular systole.
• Normal rate: 70–72/min.
• Common sites: radial artery, carotid artery, femoral artery.

Conducting System of Heart

• Specialized auto-rhythmic fibers:
1. SA node (pacemaker): Initiates impulse, controls heartbeat.
2. AV node: Receives impulse, slight delay.
3. Bundle of His: Conducts impulse to interventricular septum.
4. Purkinje fibers: Spread impulse to ventricular walls, causing contraction.

Blood Vessels

1. Arteries:
• Thick-walled, elastic, carry blood away from heart (usually oxygenated except pulmonary artery).
• Small arteries branch into arterioles.
2. Capillaries:
• Microscopic, one-cell-thick walls.
• Exchange of gases, nutrients, and wastes between blood and tissues.
3. Veins:
• Thin-walled, less elastic, carry blood toward heart (usually deoxygenated except pulmonary veins).
• Contain valves to prevent backflow.

Video Description

·        Don’t forget to do these things if you get benefitted from this article

·        Visit our Let’s contribute page https://keedainformation.blogspot.com/p/lets-contribute.html

·        Follow our page

·        Like & comment on our post

·