Notes on Body Fluids and Circulation
15.1 Blood
Blood is a connective tissue that circulates throughout the body, composed of two main components: plasma and formed elements.
15.1.1 Plasma
- Plasma constitutes about 55% of blood and is primarily composed of water (90-92%).
- Proteins in plasma (6-8%) include:
- Fibrinogen: Essential for blood clotting.
- Globulins: Play a role in immune defenses.
- Albumins: Maintain the osmotic balance.
- Contains minerals, nutrients, and waste products.
- Serum is plasma without clotting factors.
15.1.2 Formed Elements
- Made up of Erythrocytes (RBCs), Leucocytes (WBCs), and Platelets (Thrombocytes), which account for about 45% of blood.
- Erythrocytes:
- Most abundant cell type, primarily involved in gas transport (O2 and CO2).
- Contains hemoglobin that gives blood its red color.
- Lifespan is around 120 days; destroyed in the spleen.
- Leucocytes:
- Less abundant, crucial for immune response.
- Two categories: Granulocytes (neutrophils, eosinophils, basophils) and Agranulocytes (lymphocytes and monocytes).
- Neutrophils are the most common type (60-65%).
- Platelets:
- Fragments involved in blood clotting, produced from megakaryocytes; healthy blood has about 150,000-350,000 per mm³.
15.1.3 Blood Groups
- Blood groups are classified mainly into ABO and Rh systems:
- ABO groups are determined by the presence of antigens (A and B) on the surface of RBCs.
- The Rh factor is another antigen that can determine compatibility.
- Group O: Universal donor; Group AB: Universal recipient.
15.1.4 Coagulation of Blood
- Coagulation occurs to prevent blood loss from injuries and involves:
- Fibrin formation: Inactive fibrinogen gets converted to fibrin by thrombin.
- Sequence of reactions (cascade) involving various clotting factors, often begins with the activation of platelets.
- Calcium ions play a crucial role in this process.
15.2 Lymph (Tissue Fluid)
- Interstitial fluid seeps out of blood capillaries, known as tissue fluid, and comprises minerals similar to plasma.
- Lymph is collected by lymphatic vessels:
- Carries nutrients, hormones, and assists in immune response via lymphocytes.
- Lymphatic system collects excess tissue fluid and returns it to the blood.
15.3 Circulatory Pathways
- Open vs. Closed Circulatory Systems:
- Open: Found in arthropods and mollusks, where blood bathes internal organs directly.
- Closed: Blood circulates within a system of vessels; observed in annelids and vertebrates (more efficient).
- Heart Structures:
- Fish: Two-chambered heart (1 atrium, 1 ventricle).
- Amphibians/Reptiles: Three-chambered heart (2 atria, 1 ventricle).
- Birds/Mammals: Four-chambered heart (2 atria, 2 ventricles).
- Circulation Types:
- Single circulation in fish.
- Double circulation in birds/mammals (pulmonary and systemic circulation).
15.3.1 Human Circulatory System
- Comprises heart, blood vessels, and blood.
- Heart has four chambers: two atria and two ventricles separated by septa and valves for unidirectional blood flow.
15.3.2 Cardiac Cycle
- Defined as the sequence of events during one heartbeat needing about 0.8 seconds for each cycle.
- Comprises both systole (contraction) and diastole (relaxation) phases for atria and ventricles.
- Cardiac output: Volume of blood pumped per minute (about 5 liters in a healthy adult).
15.3.3 Electrocardiograph (ECG)
- Measures the heart's electrical activity during the cycle, identifying areas of depolarization and repolarization among the cardiac muscle which indicates heart health.
15.4 Double Circulation
- Discusses the systemic (oxygenated blood from heart to body tissues) and pulmonary (deoxygenated blood to lungs for oxygenation) pathways.
- Includes specialized circulatory routes, like the hepatic portal system.
15.5 Regulation of Cardiac Activity
- Intrinsic regulation by the nodal tissue; influenced by the autonomic nervous system adjusting heart rate and contraction strength (sympathetic = increase; parasympathetic = decrease).
15.6 Disorders of Circulatory System
- Overview of conditions like Hypertension, Coronary Artery Disease, Angina, and Heart Failure, their significance, and impacts on health.
Summary
The chapter effectively provides a comprehensive understanding of blood composition, circulatory mechanisms, and the pathophysiology of various circulatory disorders. All vertebrates utilize a sophisticated circulatory system for the transport of vital substances and waste removal, facilitated by the protective structures of the heart and blood vessels.
Understanding these concepts forms a crucial foundation for knowledge in biology and medicine as they demonstrate essential life processes vital for maintaining homeostasis.