Biology Chapter on Blood Circulation and Clotting

Types of Circulatory Systems in Multicellular Organisms

• Multicellular organisms need transport systems because their surface area to volume ratio is small, making diffusion inefficient for substance exchange.
• Open circulatory systems, found in invertebrates like insects and molluscs, have haemolymph that flows directly into the body cavity (haemocoel) and bathes the cells.
• Closed circulatory systems, found in vertebrates like humans and fish, have blood contained in a continuous closed network of blood vessels, ensuring efficient transport throughout the body. Blood is pumped by the heart.
• The closed system allows for higher blood pressure and efficient transport compared to open systems.
• In closed systems, exchange of substances occurs across the walls of blood capillaries.

Circulatory System of Insects

• Insects have an open circulatory system.
• Haemolymph flows from the heart into the haemocoel.
• When the heart contracts, haemolymph flows out.
• When the heart relaxes, haemolymph flows back in through tiny openings called ostia.
• This system facilitates substance exchange between the haemolymph and the cells.

Circulatory System of Fish

• Fish have a single circulatory system with two chambers.
• Blood leaves the ventricle and goes to the gills for gas exchange.
• Oxygenated blood is then transported to cells through capillaries.
• Deoxygenated blood returns to the atrium.
• Blood flows in one direction.

Circulatory System of Amphibians

• Amphibians have a double circulatory system with three chambers.
• Deoxygenated blood is pumped to the lungs and skin for gas exchange (pulmocutaneous circulation).
• The oxygenated blood returns to the heart and is then pumped to the body tissues (systemic circulation).
• Oxygenated and deoxygenated blood are mixed in the ventricle.

Circulatory System of Humans

• Humans have a double circulatory system with four chambers.
• The heart is divided into two atria and two ventricles.
• The four chambers are separated completely which avoids mixing of oxygenated and deoxygenated blood.
• Blood is pumped from the heart to the lungs for oxygenation and back to the heart from the lungs (pulmonary circulation).
• Blood is then pumped from the heart to the body tissues and back to the heart (systemic circulation).

Composition of Human Blood

• Human blood consists of plasma (55%) and blood cells (45%).
• Plasma is the liquid portion and transports substances.
• Plasma contains water, proteins (albumin, globulin, fibrinogen), nutrients, hormones, waste products, and gases.
• Blood cells include red blood cells (erythrocytes) for oxygen transport, white blood cells (leukocytes) for immune function, and platelets for blood clotting.

Blood Vessels

• Arteries carry blood away from the heart.
• Veins carry blood toward the heart.
• Capillaries are the smallest blood vessels where gas exchange occurs.
• Arteries have strong, elastic walls to withstand high pressure.
• Veins have thinner walls with valves to prevent backflow.

Blood Clotting

• Blood clotting is a series of chemical reactions that stops bleeding after an injury occurs.
• This process involves platelets, damaged cells/clotting factors in blood plasma, and chemical reactions to form a clot.
• The clotting mechanism involves conversion of prothrombin to thrombin and fibrinogen to fibrin.
• Fibrin forms a network that traps blood cells to cause the clot.

Health Issues Related to Blood Clotting

• Haemophilia: A genetic disorder affecting blood clotting factors, leading to excessive bleeding.
• Thrombosis: Formation of blood clots (thrombi) in blood vessels which can block blood flow and lead to heart attacks/strokes.
• Embolism: A blood clot (embolus) travels to another part of the body, blocking blood flow.

Blood Groups of Humans

• Blood groups are determined by antigens present on the surface of red blood cells.
• The ABO blood group system classifies blood into A, B, AB, and O types.
• Blood typing is important for safe blood transfusions.
• Rhesus factor (Rh factor) is another important blood group system that must be considered when blood transfusions occur.

Pregnancy and the Rh Factor

• Rh incompatibility can arise when an Rh-negative mother carries an Rh-positive foetus.
• The mother's immune system can produce antibodies that attack the foetus's red blood cells causing severe symptoms known as erythroblastosis fetalis.
• Anti-D injections to the mother during pregnancy can prevent this complication.

Health Issues Related to the Human Lymphatic System

• Oedema: Swelling of body tissues caused by fluid buildup.
• Pregnancy, prolonged bedridden patients, or deficiencies in plasma proteins can lead to oedema.
• Parasitic infections such as lymphatic filariasis can block the lymphatic flow leading to swelling.

Mechanism of Blood Clotting

• The body has a series of chemical reactions that occur to stop bleeding when a blood vessel has been damaged.
• It's a response to injury to maintain blood flow and homeostasis. This process involves chemical activations to convert prothrombin to thrombin with the help of calcium ions and vitamin K.
• Thrombin converts soluble fibrinogen into insoluble fibrin that forms a network to stop bleeding.

Mechanism of Heartbeat

• The heart's contraction is initiated and coordinated by a pacemaker called the sinoatrial node (SA node).
• The SA node sends electrical impulses through the atria, causing them to contract and push blood into the ventricles.
• Impulses then reach the atrioventricular node (AV node), which delays the impulse before sending it to the ventricles.
• The ventricles contract, pumping blood to the lungs and to the rest of the body.
• The sequence of electrical impulses triggers a coordinated contraction/relaxation resulting in a heartbeat.

Human Lymphatic System

• The lymphatic system plays a role in maintaining fluid balance, immune response, and lipid absorption.
• Lymph is fluid that bathes the cells and is filtered through a network of lymph capillaries.
• Lymph nodes filter lymph, trapping pathogens and immune cells.
• Lymph eventually returns to the bloodstream, completing a circulatory pathway that complements the blood circulatory system.

The Necessity of the Lymphatic System

• Returns excess fluid from tissues to blood.
• Transports fats and fat-soluble substances to the blood.
• Plays a major role in the body's immune response involving lymph nodes.