B3.2 Transport Flashcards
[B3.2.1/ B3.2.11./ B3.2.12/ B3.2.13] Describe the adaptation of capillaries for exchange of materials
- Narrow diameter of about 10μm
- Branch and re-join repeatedly to form a capillary network, resulting in a large total surface area
- One thin layer of endothelium with pores that allow small particles to pass through but not macromolecules
[B3.2.1/ B3.2.11./ B3.2.12/ B3.2.13] Discuss what tissue fluid consists of, including how these substances are absorbed and excreted
Tissue fluid consists of oxygen, glucose and other substances in the blood plasma (except large protein molecules that cannot pass through capillary wall) and surrounds the capillary network. It flows between the cells of a tissue to absorb useful substances and excrete waste products. Oxygen and glucose is absorbed from the tissue fluid by diffusion and sodium-glucose cotransporters respectively. Growing cells absorb amino acids by active transport. In contrast, carbon dioxide diffuses out of cells, and into the tissue fluid.
[B3.2.1/ B3.2.11./ B3.2.12/ B3.2.13] Describe how tissue fluid forms and how this is different in other types of capillaries
Tissue fluid is formed by pressure filtration of plasma in capillaries. This is promoted by the continuous release and reuptake of tissue fluid - capillaries near arterioles with high pressured blood release tissue fluid, while capillaries near venules with low pressured blood reuptake tissue fluid. In fenestrated capillaries, larger volumes of tissue fluid is produced, speeding up the exchange between tissue cells and the blood.
[B3.2.1/ B3.2.11./ B3.2.12/ B3.2.13] Discuss the cosequences of tisssue fluid not being reuptaken and describe how it can be prevented
Although most of the tissue fluid released by capillaries returns to them, some does not as it stays in the tissues. This causes swelling, called oedema, and it can be prevented by the drainage of tissue fluid into vessels of the lymphatic system. In all tissues, there are lymphatic vessels with permeable, thin walls with valves and gaps which tissue fluid can pass. After entering the lymphatic vessels, the fluid is known as lymph, rather than tissue fluid. At the end of the system of vessels, there are just 2 - left and right lymphatic ducts - that merge with subclavian veins to drain the lymph and return them all to the blood system.
[B3.2.2] Distinguish between the stuctures of arteries and veins
Artery has thicker wall whereas vein have thinner walls
Artery has narrower lumen whereas vein have wider lumen
Artery has inner surface that is corrugated where as vein has no inner surface corrugation
Artery has fibers visible in the wall whereas vein has few or no fibers visible in the wall
[B3.2.3] Explain how the structure of arties is adapted to transport blood under high pressure
Artery walls are relatively thick and contain elastic fibers and collagen fibers. Since elastic fibers are proteins that can stretch, and collagen fibers are proteins that has high tensile strength, arteries are strong enough to withstand high blood pressures without bulging outwards or bursting.
At peak pressure, the elastic fibres allow the walls to be pushed outwards, widening the lumen. At the end of each heart beat, pressure in arteries fall, allowing stretched elastic fibres to return, squeezing the blood in the lumen for transporting to the organs. When elastic fibres recoil, the semilunar valves at the exit of the ventricles are closed to prevent the blood flowing backwards.
[B3.2.4] Describe the ways to measure pulse rate/ heart rate
To measure pulse rate/ heart rate:
- Traditional: placing fingertips on wrist or neck, where carotid and radial arteries are respectively, to count the number of pulses for 1 minute
- Digital: pulse oximeter clipped to a fingertip that shines red and IR light. The device measures how much light passes through the tissue of the finger, detecting how much blood is in the tissue every time heart beats, and from this, the heart rate is calculated
[B3.2.5] Describe the adaptations of veins
Since veins collect blood from all organs through capillaries continuously, there is no pulse. Therefore, the wall of a vein are thin, has fewer elastic fibres and smooth muscles because blood is at low pressure. As the pressure is low, veins contain valves to prevent the blood from flowing backwards. Blood flow in veins are assisted by pressures exerted by adjacent tissues like skeletal muscles. Due to the flexibility of the vein walls, contraction in the muscle squeezes the vein like a pump.
[B3.2.6] Describe the functions of coronary veins and arteries, and the consequences of the blockage of the coronary arteries
Coronary veins collect deoxygenated blood from the heart wall and return it to the right atrium. Coronary arteries branch off from the aorta and repeatedly supply oxygenated blood and glucose to parts of the muscular wall of the heart. The coronary arteries can become narrowed or completely blocked (called occlusion) by fatty deposits like cholesterol (called atheroma). When atheroma impregnated with calcium salts, it hardens the artery, restricting blood flow to the downstream region of the heart wall, often causing chest pain, shortness of breath, blood clots and heart attack as oxygen is deprived. If a blockage persists, there will be tissue death and therefore a permanent damage to the heart. The conditions associated with narrowed or blocked coronary arteries are collective known as Coronary Heart Disease (CHD).
[B3.2.6] Describe the risk factors of CHD
Risk factors that can cause CHD include:
- Hypertension (high blood pressure): raised blood pressure increases the chance of blood clot formation
- Smoking/ high salt intake/ drinking excessive amounts of alcohol: raises blood pressure
- Eating too much saturated fat and cholesterol: promotes atheroma formation
[B3.2.14] Distinguish between the circulation of blood in mammals and fish
Mammals have blood flow starting at the left-side of the heart, through arteries, capillaries where the oxygen is delivered to the organs (except lungs), veins, back to the right-side of the heart to be re-pumped to the lungs. The oxygenated blood then returns to the left-side of the heart for the circulation to begin again. Therefore, mammals have a double circulation, which the blood passing twice through the heart via pulmonary circulation and systematic circulation.
In contrast, fish pump blood to their gills to be oxygenated. The blood flows through capillaries in narrow gill filaments and water is pumped over the filaments, allowing oxygen from water to diffuse into the blood and carbon dioxide out. The oxygenated blood is then delivered to other organs, returns to the heart to re-pump the deoxygenated blood to the gills. Therefore, fish have a single circulation.
