BODY FLUIDS - Class 11 Gujarat Board Zoology

Body Fluids and Circulation

Introduction to Body Fluids

Body fluids are essential for the transport of substances in higher organisms, including humans. The main body fluid responsible for transport is blood, but lymph and cerebrospinal fluid are also present, both derived from blood. Blood is a specialized fluid connective tissue, primarily responsible for the movement of gases, nutrients, and waste products.

• Main body fluid: Blood
• Other fluids: Lymph, cerebrospinal fluid (CSF), both derived from blood
• Blood as tissue: Specialized fluid connective tissue

Composition of Blood

Blood consists of two main components: plasma (fluid part)…

Body Fluids and Circulation

Introduction to Body Fluids

Body fluids are essential for the transport of substances in higher organisms, including humans. The main body fluid responsible for transport is blood, but lymph and cerebrospinal fluid are also present, both derived from blood. Blood is a specialized fluid connective tissue, primarily responsible for the movement of gases, nutrients, and waste products.

• Main body fluid: Blood
• Other fluids: Lymph, cerebrospinal fluid (CSF), both derived from blood
• Blood as tissue: Specialized fluid connective tissue

Composition of Blood

Blood consists of two main components: plasma (fluid part) and formed elements (cellular part). Plasma makes up about 55% of blood and is mainly water, while formed elements constitute about 45% and include red blood cells (RBCs), white blood cells (WBCs), and platelets.

• Plasma: 90-92% water, 6-8% proteins (albumin, globulin, fibrinogen), ions (Na⁺, K⁺, Cl⁻, Mg²⁺, Ca²⁺, HCO₃⁻), urea, respiratory gases (O₂, CO₂), hormones, nutrients (glucose, amino acids)
• Formed elements: RBCs, WBCs, platelets

Plasma Proteins and Their Functions

Plasma proteins play critical roles in maintaining osmotic balance, immunity, and blood clotting. The three main types are albumin, globulin, and fibrinogen.

• Albumin: Maintains osmotic pressure and water balance
• Globulin: Functions in immunity (antibody formation)
• Fibrinogen and Prothrombin: Involved in blood clotting, present in inactive form

Formed Elements: RBCs, WBCs, Platelets

Formed elements are the cellular components of blood. RBCs are most numerous, followed by platelets and WBCs.

• RBCs (Erythrocytes): 5-5.5 million/mm³, biconcave, anucleate (in mammals except camel), lifespan 120 days, destroyed in spleen ("graveyard of RBCs"), contain hemoglobin for O₂ and CO₂ transport, produced in red bone marrow (erythropoiesis)
• WBCs (Leukocytes): 6,000-8,000/mm³, nucleated, immunity function, produced in red bone marrow (leukopoiesis), two main types:
  • Granulocytes: Neutrophils (60-65%, phagocytic), Eosinophils (2-3%, anti-allergic), Basophils (0.5-1%, release histamine, serotonin, heparin)
  • Agranulocytes: Monocytes (6-8%, phagocytic), Lymphocytes (20-25%, antibody production)
• Platelets (Thrombocytes): 1.5-3.5 lakh/mm³, anucleate, irregular shape, lifespan ~1 week, formed from megakaryocytes, contain thromboplastin for clotting

Blood Clotting Mechanism

Blood clotting prevents blood loss after injury. The process involves a cascade of events leading to the formation of a fibrin mesh that traps blood cells.

• Sequence:
  1. Injury activates thromboplastin from platelets
  2. Thromboplastin (with Ca²⁺) converts prothrombin (inactive) to thrombin (active)
  3. Thrombin (with Ca²⁺) converts fibrinogen (inactive) to fibrin (active)
  4. Fibrin forms a mesh at the injury site, trapping blood cells and forming a clot

Blood Groups and Transfusion

Blood groups are determined by the presence of specific antigens on RBCs and antibodies in plasma. The two main systems are ABO and Rh.

• ABO System: Four groups (A, B, AB, O) based on A/B antigens on RBCs and anti-A/anti-B antibodies in plasma
• Rh System: Presence (Rh⁺) or absence (Rh⁻) of Rh antigen; 80% are Rh⁺, 20% Rh⁻
• Transfusion rules: O is universal donor, AB is universal recipient
• Erythroblastosis fetalis: Occurs when Rh⁻ mother carries Rh⁺ fetus; anti-Rh antibodies from mother attack fetal RBCs in subsequent pregnancies, leading to jaundice, anemia, or death in fetus; prevented by giving anti-Rh antibodies to mother after first delivery

Lymph and Tissue Fluid

Lymph is derived from blood plasma and is involved in the transport of nutrients, waste, and immune cells. It is formed when plasma filters out of capillaries, minus large proteins and formed elements.

• Formation: Plasma minus large proteins and formed elements becomes tissue fluid; excess tissue fluid enters lymphatic vessels, becoming lymph
• Functions: Transports O₂, nutrients, hormones; absorbs fats via lacteals in small intestine; returns excess fluid to blood

Circulatory Pathways

Circulatory systems are classified as open or closed. In open systems, blood bathes organs directly; in closed systems, blood circulates within vessels.

• Open system: Blood flows into open spaces (sinuses); found in arthropods, mollusks
• Closed system: Blood flows through arteries, veins, capillaries; found in annelids, vertebrates
• Heart types:
  • Two-chambered (fishes)
  • Three-chambered (amphibians, reptiles except crocodiles)
  • Four-chambered (birds, mammals, crocodiles)

Structure and Function of Human Heart

The human heart is a four-chambered organ, about the size of a fist, originating from the mesoderm. It has two atria (smaller, thin-walled) and two ventricles (larger, thick-walled).

• Layers: Pericardium (double-layered outer covering), three internal septa (interatrial, interventricular, atrioventricular)
• Valves: Tricuspid (right AV), bicuspid/mitral (left AV), semilunar (at exits of ventricles)
• Right side: Receives deoxygenated blood, pumps to lungs
• Left side: Receives oxygenated blood, pumps to body

Cardiac Conduction System and Cardiac Cycle

The heart's rhythmic contractions are controlled by specialized muscle fibers and nodes. The SA node (pacemaker) initiates impulses, followed by AV node, bundle of His, and Purkinje fibers.

• SA node: Located in right atrium, initiates 70-75 impulses/min
• AV node: Located in lower right atrium, receives impulse, delays, then passes to bundle of His
• Bundle of His: Conducts impulse to ventricles
• Purkinje fibers: Spread impulse throughout ventricles
• Cardiac cycle: Sequence of atrial systole (0.1s), ventricular systole (0.3s), joint diastole (0.4s); total cycle = 0.8s
• Stroke volume: 70 ml per beat
• Heart rate: 72 beats/min (average)
• Cardiac output: Heart rate × stroke volume = 72 × 70 = 5040 ml ≈ 5 liters/min

ECG and Interpretation

Electrocardiogram (ECG) records the electrical activity of the heart. Electrodes are placed on both arms and left ankle; sometimes on the chest.

• P wave: Atrial depolarization (contraction)
• QRS complex: Ventricular depolarization (contraction)
• T wave: Ventricular repolarization (relaxation)
• Heart rate determination: Count QRS complexes in a set time
• Abnormal ECG: Indicates possible heart disease or irregularity

Regulation of Cardiac Activity

Cardiac activity is regulated by the autonomic nervous system and medulla oblongata. The sympathetic system increases heart rate and force, while the parasympathetic system decreases them.

• Sympathetic (anukampi): Releases adrenaline, noradrenaline; increases heart rate and cardiac output
• Parasympathetic (paranukampi): Releases acetylcholine; decreases heart rate and cardiac output
• Medulla oblongata: Main center for cardiac regulation

Disorders of Circulatory System

Several disorders affect the circulatory system, including hypertension, coronary artery disease, angina, heart failure, cardiac arrest, and heart attack.

• Hypertension: Systolic >140 mmHg, diastolic >90 mmHg; measured by sphygmomanometer; affects heart, kidneys, brain
• Coronary artery disease (CAD): Narrowing of coronary arteries due to cholesterol, fat, or fibrous tissue deposition
• Angina pectoris: Chest pain due to insufficient oxygen to heart muscle, common in middle-aged/elderly
• Heart failure: Heart cannot pump enough blood; may cause congestion in lungs (congestive heart failure)
• Cardiac arrest: Heart stops beating
• Heart attack (myocardial infarction): Death of heart muscle due to lack of blood supply

Special Circulatory Pathways

• Double circulation: Blood passes twice through the heart in one complete cycle (pulmonary and systemic circuits)
• Hepatic portal system: Blood from digestive tract (rich in nutrients and ammonia) is transported to liver via hepatic portal vein, where ammonia is converted to urea (urea cycle), then blood returns to heart and is filtered by kidneys

This summary covers all key points, mechanisms, and exceptions as explicitly described, focusing on exam-relevant recall and clarity.