HSSLIVE Plus One Zoology Chapter 7: Body Fluids and Circulation Notes – Hsslive | Hsslive.co.in | Hss Live

Circulatory systems transport essential materials throughout multicellular organisms. This chapter investigates the composition of blood and lymph, and the structure and function of the human cardiovascular system. It explains the cardiac cycle, blood pressure regulation, and the formation of tissue fluid and lymph. The chapter also compares different types of circulatory systems found across the animal kingdom, from open circulatory systems in invertebrates to the complex four-chambered hearts of mammals and birds.

Chapter 7: Body Fluids and Circulation

Body Fluids

Blood

Blood is a specialized connective tissue consisting of a fluid matrix called plasma and formed elements.

Composition of Blood:

Plasma (55%): Straw-colored fluid component
- Water (90-92%): Main component
- Proteins (7-8%): Albumins, globulins, fibrinogen
- Nutrients: Glucose, amino acids, lipids, vitamins
- Waste products: Urea, uric acid, creatinine
- Gases: Oxygen, carbon dioxide
- Hormones, enzymes, ions
Formed Elements (45%):
- Erythrocytes (RBCs): 5-6 million/mm³, biconcave discs without nucleus
  - Function: Transport oxygen (contain hemoglobin)
  - Formation: Bone marrow (erythropoiesis)
  - Lifespan: 120 days
- Leukocytes (WBCs): 5000-9000/mm³, nucleated cells
  - Granulocytes: Neutrophils, eosinophils, basophils
  - Agranulocytes: Lymphocytes, monocytes
  - Function: Defense against infections
- Platelets (Thrombocytes): 150,000-350,000/mm³, cell fragments
  - Function: Blood clotting

Blood Groups

ABO System: Based on presence/absence of antigens A and B on RBC surface
- Type A: Antigen A, antibody anti-B
- Type B: Antigen B, antibody anti-A
- Type AB: Both antigens, no antibodies
- Type O: No antigens, both antibodies
Rh System: Based on presence/absence of Rh factor (Rh antigen)
- Rh⁺: Have Rh factor
- Rh⁻: Lack Rh factor

Blood Coagulation (Clotting)

Process preventing excessive blood loss through formation of clot:

Platelets + damaged tissue release thromboplastin
Thromboplastin + Ca²⁺ converts prothrombin to thrombin
Thrombin converts soluble fibrinogen to insoluble fibrin
Fibrin forms mesh trapping blood cells = clot

Lymph

Clear, colorless fluid derived from tissue fluid
Composition similar to plasma but less protein
Contains lymphocytes (WBCs)
Functions:
- Returns proteins from tissues to blood
- Transports fats from intestine to blood
- Provides immune defense

Circulatory System

Types of Circulation

Open Circulation: Blood flows through open spaces (sinuses) rather than vessels
- Example: Arthropods, molluscs (except cephalopods)
Closed Circulation: Blood flows through closed vessels
- Example: Annelids, cephalopods, vertebrates

Human Circulatory System

Consists of heart, blood vessels, and blood.

Heart

Located in thoracic cavity between lungs
Size: About the size of a clenched fist
Protected by pericardium (double-layered membrane)
Chambers:
- Two atria (upper chambers): Receive blood
- Two ventricles (lower chambers): Pump blood
Valves:
- Tricuspid valve: Between right atrium and ventricle
- Bicuspid/Mitral valve: Between left atrium and ventricle
- Semilunar valves: At the base of aorta and pulmonary artery

Cardiac Cycle

Sequence of events in one heartbeat:

Atrial Systole (0.1 sec): Atria contract, blood flows to ventricles
Ventricular Systole (0.3 sec): Ventricles contract, blood flows to arteries
Cardiac Diastole (0.4 sec): All chambers relax

Total duration: 0.8 seconds
Heart rate: About 72 beats per minute

Electrocardiogram (ECG)

Graphical representation of electrical activity of heart:

P wave: Atrial depolarization (before atrial contraction)
QRS complex: Ventricular depolarization (before ventricular contraction)
T wave: Ventricular repolarization (recovery)

Double Circulation

Blood passes through the heart twice in one complete circuit:

Pulmonary Circulation: Right heart → Lungs → Left heart
- Deoxygenated blood from body → right heart → lungs → oxygenated blood to left heart
Systemic Circulation: Left heart → Body tissues → Right heart
- Oxygenated blood from left heart → body tissues → deoxygenated blood to right heart

Blood Vessels

Arteries: Carry blood away from heart
- Thick, elastic walls, no valves
- Carry oxygenated blood (except pulmonary artery)
Veins: Carry blood toward heart
- Thinner walls, have valves
- Carry deoxygenated blood (except pulmonary vein)
Capillaries: Connect arterioles and venules
- Single layer of cells for exchange of materials
- Site of exchange between blood and tissues

Major Blood Vessels

Arteries:
- Aorta: Largest artery, from left ventricle
- Pulmonary artery: From right ventricle to lungs
- Coronary arteries: Supply heart muscle
Veins:
- Venae cavae (superior and inferior): Return blood to right atrium
- Pulmonary veins: From lungs to left atrium
- Hepatic portal vein: From intestine to liver

Regulation of Cardiac Activity

Intrinsic Regulation:
- Sinoatrial node (SA node): Pacemaker, initiates heartbeat
- Atrioventricular node (AV node): Delays impulse before ventricular contraction
- Purkinje fibers: Conduct impulse throughout ventricles
Extrinsic Regulation:
- Autonomic nervous system:
  - Sympathetic: Accelerates heartbeat
  - Parasympathetic (vagus nerve): Slows heartbeat
- Hormones: Adrenaline increases heart rate

Disorders of Circulatory System

Hypertension: High blood pressure (>140/90 mmHg)
Coronary Artery Disease: Narrowing of coronary arteries
Angina Pectoris: Chest pain due to insufficient oxygen to heart muscle
Heart Attack (Myocardial Infarction): Death of heart muscle due to blocked blood supply
Rheumatic Heart Disease: Damaged heart valves following streptococcal infection
Anemia: Reduced hemoglobin or RBC count
Leukemia: Cancer of blood-forming tissues

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