B3.2 Transport - A Complete Overview PDF

B3.2 Transport: A Complete Overview Components of blood and their functions Erythrocytes (Red Blood Cells) transport oxygen from the lungs to respiring cells and carry carbon dioxide from respiring cells to the lungs. Plasma acts as a solvent, transporting nutrients (from the g...

B3.2 Transport: A Complete Overview Components of blood and their functions Erythrocytes (Red Blood Cells) transport oxygen from the lungs to respiring cells and carry carbon dioxide from respiring cells to the lungs. Plasma acts as a solvent, transporting nutrients (from the gut to the liver), hormones, urea (from the liver to the kidneys), dissolved proteins, antibodies, gases, and waste. Thrombocytes (Platelets) play a role in the blood clotting mechanism, which is important for wound healing. Leukocytes (White Blood Cells) have major roles in the immune system. Lymphocytes form antibodies, and other leukocytes (phagocytes) ingest bacteria or cell fragments. B3.2.1 Adaptations of Capillaries for the Exchange of Materials Capillaries are the narrowest blood vessels, with a diameter of about 10μm. They branch and rejoin repeatedly to form a capillary network with a huge total length. This extensive branching creates a large surface area, which facilitates efficient material exchange. The narrow diameters of the capillaries increase the contact between blood and the surrounding tissues. Capillaries transport blood through almost all tissues in the body. Two exceptions are the lens and the cornea of the eye, which must be transparent and therefore lack blood vessels. Having many narrow capillaries results in a total surface area greater than that of fewer wider blood vessels. This large surface area of the capillary network in any tissue enhances the scope for diffusion between the blood and tissue cells. The density of capillary networks varies in different tissues depending on the needs of the cells, ensuring that all active cells in the body are close to a capillary. The capillary wall consists of one layer of endothelium cells with a coating of extracellular fibrous proteins crosslinked to form a gel called the basement membrane. This membrane acts as a filter, allowing small or medium-sized particles to pass through while blocking macromolecules. There are pores between the endothelium cells, making the capillary wall very permeable. These pores permit part of the blood plasma, but not the red blood cells, to leak out through the basement membrane. The fluid that leaks out, known as tissue fluid, is similar but not identical to blood plasma. Tissue fluid contains oxygen, glucose, and other substances found in blood plasma, except for large protein molecules, which are too large to pass through the basement membrane. This fluid flows between the cells in a tissue, allowing them to absorb useful substances and excrete waste products, before re-entering the capillary network. In some tissues, capillaries have a greater number of fenestrations (large pores), called fenestrated capillaries. These allow larger volumes of tissue fluid to be produced, which speeds up the exchange between tissue cells and blood. The glomerulus (filter unit) of the kidney has fenestrated capillaries to produce large volumes of filtrate in the first stage of urine production. This adaptation of capillaries with large surface area, narrow diameters, thin walls, and fenestrations facilitates efficient and rapid exchange of materials between blood and tissues. B3.2.2 Structure of Arteries and Veins The structures of arteries and veins reflect their functions in the circulatory system. Arteries, which carry blood away from the heart under high pressure, have thick, elastic walls. In contrast, veins return blood to the heart under much lower pressure. Students should be able to distinguish arteries and veins in micrographs from the structure of a vessel wall and its thickness relative to the diameter of the lumen. Structure of Arteries and Veins: Arteries carry pulses of high-pressure blood away from the heart to the organs of the body. Veins carry a stream of low-pressure blood from the organs to the heart. Because of the difference in function, these two types of blood vessels have different structures to their walls. Key Differences: Arteries have thicker walls relative to their lumen to withstand and maintain the high pressures exerted by the heart's pumping action. Veins have thinner walls relative to their lumen as they transport blood under lower pressure. When examining micrographs, the thickness of the vessel wall compared to the diameter of the lumen is a critical indicator that helps distinguish arteries from veins. B3.2.3 Adaptations of Arteries for the Transport of Blood Students should understand how the layers of muscle and elastic tissue in the walls of arteries help them to withstand and maintain high blood pressures. Adaptations of Arteries for the Transport of Blood Away from the Heart: The wall of the artery is composed of several layers that help it withstand and maintain high blood pressures: Tunica Externa: A tough outer layer of connective tissue with collagen fibres, providing structural support and flexibility. Tunica Media: A thick layer containing smooth muscle and elastic fibres made of the protein elastin. This layer is crucial for maintaining high blood pressure as it allows the artery to stretch and recoil. Tunica Intima: A smooth endothelium forming the lining of the artery, which minimizes friction for blood flow. In some arteries, this layer also includes a layer of elastic fibres, aiding in the elastic recoil and maintaining blood pressure. Each time the ventricles of the heart pump, a burst of blood under high pressure enters the arteries and flows along them. The pressure then declines until the next heartbeat. Arteries have relatively narrow lumens, which helps them to maintain high blood pressures and high velocities of blood flow. Artery walls are relatively thick and contain elastic fibres and tough collagen fibres. The elastic fibres are proteins that can stretch and then recoil. Collagen fibres are tough, rope-like proteins with high tensile strength. These features make arteries strong enough to withstand high and variable blood pressures without bulging outwards (known as an aneurysm) or bursting. Elastic fibres make up as much as 50% of the dry mass of artery walls. Peak pressure in an artery (systolic pressure) causes the wall of an artery to be pushed outwards, widening the lumen and stretching the wall. When stretched, elastic fibres store potential energy. At the end of each heartbeat, the pressure in arteries falls and the stretched elastic fibres return the energy by recoiling and squeezing the blood in the lumen. In this way, the elastic fibres help to reduce the amount of energy expended in transporting blood to the organs of the body. When the elastic fibres are recoiling and pushing on blood in an artery, the semilunar valves at the exit of the ventricles are closed. This means that blood cannot flow back towards the heart; it is forced onwards towards the organs. Elastic fibres therefore help to pump blood along the arteries and prevent the minimum pressure inside the artery (diastolic pressure) from becoming too low. They help to even out blood flow in the arteries. Artery walls also contain smooth muscle cells with a particularly high density in the branches of arteries (called arterioles). The smooth muscle cells are circular, so when they contract, the diameter of the lumen is narrowed. This is called vasoconstriction and it reduces the flow of blood along an artery or arteriole. When the smooth muscle cells relax, the lumen widens, and blood flow is increased. This is vasodilation. The smooth muscle cells respond to hormone and neural signals, enabling the body to adjust the flow rate of blood to tissues in each organ depending on availability and need.  Arteries Veins Lumen The space inside the artery Relatively wide (inside space) through which blood flows - relatively narrow Tunica intima Smooth endothelium, Smooth endothelium, no sometimes with elastic fibres elastic fibres Tunica media Thick layer of smooth muscle Thinner layer of elastic tissue and elastic fibres and and collagen fibres collagen fibres Tunica externa Thick layer of connective Thinner layer of connective tissue with collagen fibres tissue with fewer collagen fibres B3.2.4 Measurement of Pulse Rates Students should be able to determine heart rate by feeling the carotid or radial pulse with fingertips. Traditional methods could be compared with digital ones. Measurement of Pulse Rates: Every time the heart beats, a wave of blood under high pressure passes along the arteries. Where an artery is close to the body surface, this pressure wave can be felt as a pulse. This happens because the artery wall becomes stretched and then recoils. Traditional Method: ○ Pulse Rate and Heart Rate: There is one pulse per beat of the heart, so measurement of pulse rate allows heart rate to be deduced. Pulse and heart rate are counted in beats per minute. ○ Locations: The wrist (radial artery) and the neck (carotid artery) are two parts of the body where the pulse can often be felt. Two or three fingertips are pressed lightly against the skin where the artery is located. The thumb should not be used because it has a pulse that could cause confusion. Digital Method:  ○ Pulse Oximeters: These devices are usually clipped to a fingertip. They have LEDs that shine red and infrared light through the finger and detectors to measure how much of the light passes through the tissues of the finger. This enables detection of variations in the amount of blood in the tissues each time the heart beats, and from this, the heart rate is calculated. ○ Oxygen Saturation: The percentage saturation of the blood with oxygen can also be deduced because deoxygenated blood absorbs red light, whereas oxygenated blood absorbs infrared light. B3.2.5 Adaptations of Veins for the Return of Blood Include valves to prevent backflow and the flexibility of the wall to allow it to be compressed by muscle action. Adaptations of Veins for the Return of Blood to the Heart: Veins collect blood from all organs of the body and convey it back to the heart. Blood drains out of capillaries into veins continuously, which means there is no pulse. The wall of a vein contains far fewer elastic fibres than the wall of an artery. There are also fewer smooth muscle cells because veins are not used to adjust blood flow to different parts of the body. Lower Pressure: Blood in veins is at much lower pressure than in arteries, so the wall does not need to be thick to prevent bursting. Valves to Prevent Backflow: To maintain circulation, veins contain pocket valves. These consist of three cup-shaped flaps of tissue projecting into the vein in the direction of blood flow. ○ If blood starts to flow backwards, it gets caught in the flaps of the pocket valve, which fill with blood and close the valve. This blocks the lumen of the vein. ○ When blood flows towards the heart, it pushes the flaps to the sides of the vein. The pocket valve therefore opens and blood can flow freely. Flexible Walls: Blood flow in veins is assisted by gravity and by pressures exerted by adjacent tissues, especially skeletal muscles. Contraction makes a muscle shorter and wider, so it squeezes on adjacent veins like a pump. The relatively thin walls of veins help because they allow a vein to be squeezed into a flatter shape. Walking, sitting, or even just fidgeting greatly improves venous blood flow. Around 80% of the blood in a person at rest is in the veins, but this is reduced during vigorous exercise.  Capillaries Arteries Veins How are these blood - Single layer of endothelial - Narrow lumen relative to - Wider lumen relative to vessels cells (very thin walls) - wall thickness - Thick walls wall thickness - Thinner adapted to their Extremely narrow lumen, just with three layers: - Tunica walls compared to arteries function? large enough for a single red Intima: Smooth endothelial - Valves present to prevent blood cell to pass through lining with elastic fibres - backflow - Thin layer of Refer to the structural Tunica Media: Thick layer smooth muscle (tunica features to Exchange of materials: The of smooth muscle and media) - Thin layer of explain how each thin walls allow for efficient elastic fibres - Tunica connective tissue (tunica vessel is diffusion of oxygen, carbon Externa: Thick layer of externa) adapted to its dioxide, nutrients, and waste connective tissue with function. products between blood and collagen fibres - Return blood to the tissues. - Small lumen: heart: Wider lumen Reduces the diffusion - Withstand high pressure: accommodates a larger distance, enhancing the Thick walls, especially the volume of blood at lower efficiency of material tunica media with smooth pressure. - Valves: Prevent exchange. - Permeability: muscle and elastic fibers, backflow of blood, Allows plasma to filter help withstand and maintain ensuring unidirectional through into tissue spaces. high blood pressure from the flow towards the heart. - heart. - Elasticity and Thin walls and flexibility: stretch: Elastic fibres allow Allow veins to be the artery to stretch and compressed by surrounding recoil, maintaining skeletal muscles, aiding continuous blood flow. - venous return through the Regulate blood flow: muscle pump action. Smooth muscle can constrict or dilate the artery to control blood flow and pressure. B3.2.6 Causes and Consequences of Coronary Artery Occlusion Students should be able to evaluate epidemiological data relating to the incidence of coronary heart disease. Consequences of Occlusion of the Coronary Arteries: The aorta carries blood pumped by the left side of the heart to all organs of the body apart from the lungs. Two arteries branch off from the aorta close to its origin at the semilunar valve. They are the right coronary artery, which supplies the right side of the heart, and the left coronary artery, which branches into two arteries that supply the left anterior and left posterior regions of the heart wall. There are thus three main coronary arteries, each of which branches repeatedly to provide oxygenated blood to all parts of the muscular wall of the heart. The coronary arteries can become narrowed or totally blocked by fatty deposits known as atheroma (plaque), leading to an occlusion. These deposits build up in the wall of the artery and contain a variety of lipids including cholesterol. They restrict blood flow to the downstream region of the heart wall, often causing chest pain (angina) or shortness of breath, especially during exercise. Fatty deposits in the artery wall can become impregnated with calcium salts, which harden the artery and make the inner surface rough. This can trigger the formation of a blood clot (thrombosis). Hypertension (high blood pressure) increases the risk of thrombosis. Blood clots can block the flow of blood to part of the muscular wall of the heart, depriving it of oxygen and preventing normal contractions, leading to a heart attack. If a blockage persists, there will be tissue death and permanent damage to the heart. Tissue death in heart muscle due to inadequate blood supply is called a myocardial infarction. The conditions associated with narrowed or blocked coronary arteries are collectively known as coronary heart disease (CHD). Causes of Occlusion of the Coronary Arteries: Coronary heart disease is very common and there have been many epidemiological studies to identify risk factors and causes. Epidemiology is the study of the nature and spread of diseases in the human population. Multiple risk factors for coronary heart disease have been identified: Hypertension: Raised blood pressure increases the chance of blood clot formation. Smoking: Raises blood pressure because nicotine causes vasoconstriction. Diet: Consuming too much saturated fat and cholesterol promotes plaque formation.  Obesity: Associated with raised blood pressure and high blood cholesterol concentrations. High Salt Intake: A large quantity of sodium chloride in the diet raises blood pressure. Alcohol Consumption: Excessive alcohol intake is associated with raised blood pressure and obesity. Sedentary Lifestyle: Lack of exercise is correlated with obesity and prevents the return of venous blood from the extremities, increasing the risk of clot formation. Genetics: Some genes increase the risk of hypertension and thrombosis. Age: Blood vessels become less flexible with age. B3.2.11 Release and Reuptake of Tissue Fluid Release and Reuptake of Tissue Fluid in Capillaries: Plasma is the fluid in which blood cells are suspended. It consists of water with many different dissolved substances: glucose, amino acids, mineral ions such as chloride and sodium, vitamins, hormones, and plasma proteins. Lipids are carried in lipoprotein droplets. The structure of the capillary wall, as described in Section B3.2.1, is adapted to let part of the blood plasma leak out into spaces between the cells in a tissue. Most protein molecules are too large to pass through the basement membrane and are retained in the plasma, but other substances can pass out through the capillary wall. The aquaeous part of the plasma leaks through fenestrations and basement membrane of the capillaries forming tissue fluid. At any time, there are about 14 dm³ of this tissue fluid in the tissues of a 70kg human, so it constitutes about 20% of body mass. There is a continual process of release and reuptake of tissue fluid. Capillaries that are close to an arteriole tend to release tissue fluid because the blood supplied by the arteriole is at high pressure. This pressure filtration of plasma forms tissue fluid. Reuptake tends to happen in capillaries that are close to a venule, where the blood pressure is much lower. This lower pressure allows tissue fluid to drain back into the capillaries. B3.2.12 Exchange of Substances Between Tissue Fluid and Cells Discuss the composition of plasma and tissue fluid. Exchange of Substances Between Tissue Fluid and Cells in Tissues: Tissue fluid contains oxygen, glucose, and all other substances in blood plasma apart from large protein molecules, which cannot pass through the capillary wall. The fluid flows between the cells in a tissue, allowing the cells to absorb useful substances. Oxygen: Absorbed from the tissue fluid by diffusion because the oxygen concentration in cells is lower due to aerobic respiration. Glucose: Also used in aerobic respiration, absorbed by sodium–glucose cotransporters. Amino Acids: Growing cells absorb these by active transport. Composition of Plasma and Tissue Fluid: Plasma: The fluid in which blood cells are suspended, consisting of water with many dissolved substances such as glucose, amino acids, mineral ions (like chloride and  sodium), vitamins, hormones, and plasma proteins. Lipids are carried in lipoprotein droplets. Tissue Fluid: Similar to plasma but lacks large protein molecules, as they cannot pass through the capillary wall. Removal of Waste Products: Carbon Dioxide: Produced by cell respiration, diffuses out of cells into the tissue fluid, along with other metabolic waste products. As tissue fluid flows between the cells, it accumulates dissolved waste products. The tissue fluid then re-enters the capillary network, becoming part of the blood plasma. Capillaries merge to form venules, which carry the waste products out of the tissue. Carbon dioxide is excreted by the lungs, while other waste products are detoxified by the liver or excreted by the kidneys. B3.2.13 Drainage of Excess Tissue Fluid into Lymph Ducts Drainage of Excess Tissue Fluid into Lymph Ducts: Most of the tissue fluid released by capillaries returns to them, but some does not. Of the 20 dm³ of tissue fluid produced per day in an average adult’s body, 17 dm³ return to the capillaries. If the remaining 3 dm³ of fluid stayed in tissues, it would cause swelling, known as oedema. This is prevented by the drainage of tissue fluid into vessels of the lymphatic system. In all tissues, there are narrow, blind-ended lymphatic vessels with permeable walls through which tissue fluid can pass. Once inside the lymphatic vessels, the fluid is referred to as lymph rather than tissue fluid. These narrow vessels join up repeatedly to form wider lymphatic vessels. Valves: Lymphatic vessels contain valves that prevent the backflow of lymph, ensuring it flows in one direction towards the lymphatic ducts. Thin Walls with Gaps: The walls of the lymphatic vessels are thin and have gaps that allow tissue fluid to enter. At the end of this system of vessels, there are just two main ducts—the left and right lymphatic ducts. These ducts merge with the subclavian veins. Thus, lymph is drained from all tissues of the body and returned to the blood circulation. Blood in the subclavian veins flows into the vena cava and on to the right side of the heart. B3.2.14 Single vs. Double Circulation Differences Between the Single Circulation of Bony Fish and the Double Circulation of Mammals: In mammals, blood circulates through arteries, capillaries, and veins, facilitated by valves in the veins and heart that ensure a one-way flow. Mammals pump blood to the lungs to be oxygenated. The blood must be at relatively low pressure to prevent capillaries in the alveoli from bursting. After flowing through the alveolar capillaries, the residual pressure is too low for the blood to flow on to other organs, so it returns to the heart to be re-pumped. Oxygenated blood returning from the lungs must not mix with deoxygenated blood being pumped to the lungs, so the heart has separate left and right sides. The left side of the heart receives oxygenated blood and pumps it to all organs of the body except the lungs, requiring relatively high blood pressure. The kidneys, in particular, carry out pressure filtration of blood, so they need much higher blood pressure than the lungs. With a few exceptions, oxygenated blood pumped by the left side of the heart flows through capillaries in only one organ and then returns to the heart deoxygenated and at much lower pressure. It returns to the right side of the heart, which pumps blood to the lungs. Double Circulation in Mammals: Mammals have a double circulation, with blood passing twice through the heart to make a full circuit. The heart acts as a double pump, delivering blood under different pressures to various organs. The two circulations are known as the pulmonary and systemic circulations. Pulmonary Circulation: Receives deoxygenated blood from the systemic circulation and sends it to the lungs. Systemic Circulation: Receives oxygenated blood from the pulmonary circulation and sends it to the rest of the body. Single Circulation in Fish: Fish pump blood to their gills to be oxygenated. The blood flows through capillaries in narrow gill filaments. Water is pumped over the gill filaments, and oxygen diffuses from the water into the blood, while carbon dioxide moves in the opposite direction. The blood can be pumped at high pressure to the gills because the surrounding water provides support and reduces the risk of capillaries bursting. After flowing through the gills, the blood is oxygenated and still has enough pressure to flow directly to another organ of the body. While passing through capillaries in one organ, the blood becomes deoxygenated and its pressure falls, so it must return to the heart for re-pumping to the gills. Fish, therefore, have a single circulation. Comparison: Mammals: Double circulation with separate pulmonary and systemic circuits, requiring two passes through the heart to complete one full body circuit. Fish: Single circulation with blood flowing from the heart to the gills and then directly to the rest of the body before returning to the heart. B3.2.15 Adaptations of the Mammalian Heart Adaptations of the Mammalian Heart for Delivering Pressurized Blood to the Arteries: The mammalian heart has evolved to pump pressurized blood to the organs of the body continuously throughout our lives. It is well adapted through its form to carry out this function. Ventricles: Chambers with a strong muscular wall that can generate high blood pressure when they contract, pumping blood out into the arteries. Atria: Chambers with a thinner muscular wall that collect blood from the veins and pump it to the ventricles. This ensures the ventricles are full when they contract and the atria are empty to collect more blood from the veins. Atrioventricular Valves: These valves are located between the atria and the ventricles. They close to prevent backflow of blood to the atria when the ventricles contract and open to allow blood to flow from the atria to the ventricles when the ventricles relax. Semilunar Valves: Located between the ventricles and the arteries. These valves close to prevent backflow of blood to the ventricles when they relax and open to allow blood to flow from the ventricles to the arteries when the ventricles contract. Cardiac Muscle: Specialized muscle tissue that forms the walls of the ventricles and atria. Cardiac muscle has branched cells and connections between the plasma membranes of adjacent cells, allowing electrical signals to propagate throughout the heart wall, enabling coordinated contractions. Cardiac muscle can contract without stimulation from motor neurons—a property called myogenic contraction. The depolarization of a heart muscle cell triggers the contraction of adjacent cells, leading to nearly simultaneous contractions at the fastest rate among them. Pacemaker (Sinoatrial Node): Located in the wall of the right atrium, this node initiates each heartbeat by sending an electrical signal to the atria. The interval between signals determines the heart rate. The sinoatrial node's cells are the first to depolarize in each cardiac cycle, setting the pace for the heartbeat. Septum: The wall separating the left and right ventricles and atria, preventing the mixing of oxygenated blood in the left side of the heart with deoxygenated blood in the right side. Coronary Vessels: The coronary arteries and veins in the heart wall. The coronary arteries carry oxygenated blood from the aorta to all parts of the heart wall, supplying oxygen and glucose, while the coronary veins collect deoxygenated blood from the heart wall and return it to the right atrium. Name of Valve Location Prevents Backflow From Where to Where? Tricuspid Valve Between the right atrium and Right ventricle to right atrium right ventricle Pulmonary Valve Between the right ventricle Pulmonary artery to right and pulmonary artery ventricle Mitral (Bicuspid) Valve Between the left atrium and Left ventricle to left atrium left ventricle Aortic Valve Between the left ventricle and Aorta to left ventricle aorta Functions: Tricuspid Valve: Ensures blood flows from the right atrium to the right ventricle without backflow. Pulmonary Valve: Prevents blood from flowing back into the right ventricle after it has entered the pulmonary artery. Mitral (Bicuspid) Valve: Ensures blood flows from the left atrium to the left ventricle without backflow. Aortic Valve: Prevents blood from flowing back into the left ventricle after it has entered the aorta. B3.2.16 Stages of the Cardiac Cycle Stages in the Cardiac Cycle: The heart follows a repeating sequence of actions, known as the cardiac cycle. The sinoatrial node initiates each turn of the cycle by sending out an electrical signal that spreads throughout the walls of the atria. It takes less than a tenth of a second for all cells in the atria to receive the signal. This propagation of the electrical signal causes both the left and right atria to contract. Sinoatrial Node: Initiates each heartbeat by sending an electrical signal into the atria. This signal spreads rapidly through the atrial walls, causing them to contract almost simultaneously. After a time-delay of about 0.1 seconds, the electrical signal is conveyed to the ventricles. The delay allows the atria to pump the blood they are holding into the ventricles, ensuring the ventricles are as full as possible when they contract. The electrical signal is then propagated throughout the walls of the ventricles, stimulating them to contract and pump blood out into the arteries.  Time-Delay: Ensures that the atria pump blood into the ventricles before the ventricles contract, maximizing the efficiency of the blood flow. Stages in the cardiac cycle can be deduced from a graph showing pressure changes during a heartbeat in the atrium, ventricle, and artery on one side of the heart. By interpreting these graphs, one can understand the systolic and diastolic blood pressure measurements. Systolic pressure represents the pressure in the arteries when the ventricles contract, while diastolic pressure is the pressure in the arteries when the ventricles relax. Stages in the cardiac cycle Stage Events Atrial Systole - Passive filling from pulmonary veins and vena cava - Atria contract, forcing blood into the ventricles - Pressure increases slowly, AV valves are open, SL valves still closed Ventricular Systole (Early) - Isovolumetric contraction of the ventricles - Pressure rises steeply, pushing the AV valves closed ("lub" sound) - Semilunar (SL) valves remain closed as pressure in the aorta and pulmonary artery is higher than in the ventricles Ventricular Systole (Late) - Ventricular contraction continues - Pressure in ventricles exceeds the pressure in the pulmonary artery and aorta - SL valves are pushed open and blood is ejected Ventricular Diastole (Early) - Ventricles relax - Pressure in the ventricles falls rapidly - SL valves close shut due to backflow of blood ("dub" sound) - Passive ventricular filling starts Atrial & Ventricular Diastole - Continued passive filling of both atria and ventricles through open AV valves due to backflow of blood from vena cava and pulmonary vein - Pressure in the aorta is much higher than in the left ventricle, causing the SL valves to be closed. Content Statements questions to be asked and answered 1. Adaptations of Capillaries for Exchange of Materials (B3.2.1) ○ What structural adaptations do capillaries have that facilitate the rapid exchange of materials? Capillaries are adapted for material exchange by having a large surface area due to extensive branching and narrow diameters. They possess thin walls (one cell thick) to allow easy diffusion of gases, nutrients, and waste products. Fenestrations (tiny pores) in some capillaries facilitate rapid exchange where needed. 2. Structure of Arteries and Veins (B3.2.2) ○ How can students distinguish between arteries and veins in micrographs based on the structure of vessel walls and the thickness relative to the diameter of the lumen? Students can distinguish arteries and veins in micrographs by examining the thickness of the vessel wall relative to the diameter of the lumen. Arteries have thicker walls with more muscle and elastic tissue to withstand higher pressure, whereas veins have thinner walls and larger lumens to accommodate the volume of blood at lower pressure. 3. Adaptations of Arteries for Blood Transport (B3.2.3) ○ How do the layers of muscle and elastic tissue in arterial walls help arteries withstand and maintain high blood pressures? The layers of muscle and elastic tissue in arterial walls help arteries withstand and maintain high blood pressures. The elastic fibers allow arteries to stretch and recoil with each heartbeat, maintaining continuous blood flow, while smooth muscle can constrict or dilate to regulate blood pressure and flow. 4. Measurement of Pulse Rates (B3.2.4) ○ How can students determine heart rate by feeling the carotid or radial pulse with fingertips? How do traditional methods compare with digital ones? Students can determine heart rate by feeling the carotid or radial pulse with their fingertips. Traditional methods involve manually counting beats per minute, while digital methods use devices like heart rate monitors to provide an accurate reading. 5. Adaptations of Veins for Blood Return (B3.2.5) ○ What adaptations do veins have to prevent backflow and allow them to be compressed by muscle action? Veins are adapted to return blood to the heart by having valves that prevent backflow and ensure unidirectional flow. The walls of veins are flexible, allowing them to be compressed by surrounding muscle action, which helps propel blood back to the heart. 6. Causes and Consequences of Occlusion of Coronary Arteries (B3.2.6) ○ What skills should students develop to evaluate epidemiological data related to coronary heart disease? What role do correlation coefficients play in understanding the incidence of coronary heart disease? Occlusion of the coronary arteries can lead to coronary heart disease. This condition restricts blood flow to the heart muscle, potentially causing angina, heart attacks, or heart failure. Epidemiological data help evaluate the incidence of this disease, while understanding correlation coefficients can quantify relationships between variables like diet and heart disease. 7. Release and Reuptake of Tissue Fluid in Capillaries (HL - B3.2.11) ○ How is tissue fluid formed by pressure filtration in capillaries, and what mechanisms allow it to drain back into capillaries? Tissue fluid is formed by pressure filtration of plasma in capillaries, driven by higher pressure from arterioles. Lower pressure in venules allows tissue fluid to drain back into capillaries. This fluid exchange ensures that nutrients and waste products are efficiently managed. 8. Exchange of Substances Between Tissue Fluid and Cells (HL - B3.2.12) ○ What is the composition of plasma and tissue fluid, and how do they facilitate the exchange of substances between cells and the bloodstream? Plasma and tissue fluid facilitate the exchange of substances between cells and the bloodstream. Plasma contains nutrients, gases, proteins, and waste products, which diffuse into the tissue fluid and are exchanged with cells in tissues. 9. Drainage of Excess Tissue Fluid into Lymph Ducts (HL - B3.2.13) ○ What role do valves and thin walls with gaps play in the drainage of excess tissue fluid into lymph ducts and its return to blood circulation? Lymph ducts have valves and thin walls with gaps that allow excess tissue fluid to drain into them. This fluid, now called lymph, is returned to the blood circulation, ensuring that tissues do not become waterlogged. 10. Differences Between Single and Double Circulation (HL - B3.2.14) ○ What are the key differences between the single circulation of bony fish and the double circulation of mammals? How can simple circuit diagrams illustrate these differences? Single circulation, seen in bony fish, involves blood passing through the heart once per circuit (heart -> gills -> body -> heart). Double circulation, seen in mammals, involves blood passing through the heart twice per circuit (heart -> lungs -> heart -> body -> heart), ensuring efficient oxygenation and nutrient delivery. 11. Adaptations of the Mammalian Heart (HL - B3.2.15) ○ How are the structures of the mammalian heart adapted for delivering pressurized blood to the arteries? Can students identify these features on a heart diagram and trace the unidirectional flow of blood? The mammalian heart has structural adaptations like cardiac muscle, pacemaker cells, atria, ventricles, atrioventricular and semilunar valves, septum, and coronary vessels. These adaptations ensure efficient blood pumping under high pressure and unidirectional flow. 1. How are the 4 chambers of the heart called? The four chambers of the heart are called the right atrium, right ventricle, left atrium, and left ventricle. 2. Which chamber pumps deoxygenated blood into the pulmonary circuit? The right ventricle pumps deoxygenated blood into the pulmonary circuit. 3. Which blood vessel delivers deoxygenated blood from the systemic circuit back to the heart? The superior and inferior vena cava deliver deoxygenated blood from the systemic circuit back to the heart.  4. What is the name of the valve, which separates the left atrium from the left ventricle? The valve that separates the left atrium from the left ventricle is called the mitral valve (or bicuspid valve). 5. Name the valves which prevent backflow from the systemic/pulmonary circuit: The semilunar valves prevent backflow from the systemic and pulmonary circuits. These are the aortic valve and the pulmonary valve. 6. Name the blood vessel which delivers oxygenated blood into the systemic circuit: The aorta is the blood vessel that delivers oxygenated blood into the systemic circuit. 7. Name the sac of connective tissue which surrounds the heart: The sac of connective tissue that surrounds the heart is called the pericardium. 8. Name the blood vessels which supply the heart muscle with oxygen: The coronary arteries supply the heart muscle with oxygen. 9. Describe the structural differences between left and right ventricles: The left ventricle has a thicker muscular wall compared to the right ventricle. This is because the left ventricle needs to generate higher pressure to pump blood throughout the systemic circuit, whereas the right ventricle pumps blood only to the nearby lungs in the pulmonary circuit. 12. Stages in the Cardiac Cycle (HL - B3.2.16) ○ What are the sequence of events in the left side of the heart following the initiation of the heartbeat by the sinoatrial node? How can students interpret systolic and diastolic blood pressure measurements from data and graphs? The cardiac cycle involves the sequence of atrial systole, ventricular systole (early and late), and atrial and ventricular diastole. These stages ensure efficient blood pumping and circulation. Understanding systolic and diastolic blood pressure measurements from data and graphs helps interpret heart function and health. Tissue fluid formation Tissue fluid is formed when some of the contents of blood plasma is forced through the capillary walls due to high pressure and into the surrounding tissues. The diagram below is a simple diagram to show the stages of tissue fluid formation and then the drainage back into the capillaries. Number the sentences below to place these steps in the correct order. 1. Blood flows into the capillary at the arterial end under high hydrostatic pressure. 2. Molecules such as water, glucose and hormones are forced out of the blood plasma in the capillary due to the high pressure (ultrafiltration) and go into the space in between the surrounding cells. Tissue fluid is formed. 3. Molecules such as water, ions, glucose and hormones then move from the tissue fluid and into the cells in the surrounding tissue. 4. Waste products, such as carbon dioxide, move from the tissue cells into the tissue fluid. 5. These molecules then moved from the tissue fluid into the plasma in the capillary. This is due to their being a much lower hydrostatic pressure at the venule end as the plasma has lost a lot of its fluid. The substances also move from a high concentration to a lower concentration. 6. The majority of the tissue fluid is returned back into the capillary and the circulatory system. 7. 10% of the tissue fluid drains into the lymph capillaries. 8. The lymph is then taken to the lymph nodes and into the lymphatic system.