Mass Transport

• The dissociation curve of haemoglobin is sigmoidal
• 1. At lower oxygen partial pressures the haemoglobin does not easily bind to oxygen. This is because the haem groups are in the centre of the haemoglobin which makes it difficult for the oxygen to bind so there is low saturation levels at low oxygen partial pressures (low affinity)
• 2. As the oxygen partial pressure increases, the diffusion gradient into the haemoglobin increases so eventually an oxygen molecule will associate with one of the haem groups so there is a change in the shape of the haemoglobin molecule and more oxygen molecules can associate with other haem groups. The gradient of the curve increases as the oxygen partial pressure does.
• 3. It is difficult for all the haemoglobin molecules to become 100% saturated even at high oxygen partial pressures because it is difficult for the last oxygen to diffuse and associate with the fourth haem group.
• haemoglobin unloads oxygen more readily at a higher partial pressure of carbon dioxide, when cells respire they produce CO2 which raises pCO2 and therefore increases the rate at which oxyhaemoglobin dissociates to form oxygen and haemoglobin. the dissociation curve shifts to the right ( the Bohr effect)
• the Bohr effect results in more oxygen being released when more carbon dioxide is being produced
• in low oxygen environments e.g. lugworm haemoglobin has a higher affinity for oxygen because there isn’t much oxygen available so the haemoglobin has to be good at loading any available oxygen. the curve is to the left of a humans
• High activity levels e.g. hawk- organisms that are very active and have a high oxygen demand have haemoglobin with a lower affinity for oxygen because they need haemoglobin to easily unload oxygen so it’s available to use. The curve is to the right of a humans
• Size e.g. rat- small mammals have a higher surface area to volume ratio so lose heat quickly and have a high metabolic rate to keep them warm, therefore they have a lower affinity for oxygen because they need their haemoglobin to easily unload oxygen, the curve is to the right of a humans
• Mammals have a closed, double circulatory system: closed- blood is confined to vessels and double- blood passes twice through the heart for each complete circuit of the body
• Pulmonary circulation- to and from the lungs
• Systematic circulation- to and from the heart and body
• pulmonary artery carries blood from the heart to the lungs
• pulmonary vein carries blood from lungs to heart
• aorta carries blood from heart to body
• vena cava carries blood from the body to the heart
• renal artery carries blood from heart to the kidney
• renal vein carries blood from the kidney to the heart (vena cava)
• The right side of the heart pumps deoxygenated blood to the lungs
• the left side of the heart pumps oxygenated blood to the whole body
• the ventricles have thicker muscle walls than the atria so can push blood out of the heart whereas atria just need to push blood into the ventricles
• The left ventricle muscle is much thicker than the right ventricle so it can contract more powerfully and pump blood all around the body
• The right side of the heart is less muscular so it’s contractions are only powerful enough to pump blood to the nearby lungs
• The heart has its own blood supply- the left and right coronary arteries
• the septum separates the two sides of the heart so oxygenated and deoxygenated blood do not mix and so there can be different pressures on either side of the heart
• Arteries carry blood from the heart to the rest of the body and divide into smaller blood vessels called arterioles which form a network throughout the body. Blood is at a very high pressure due to the contraction of the left ventricle muscle.
• In arteries, the lumen is small to maintain blood pressure, the collagen fibres and fibrous proteins mean the thick wall can withstand high pressure, the elastic tissue allows the wall to stretch and recoil to maintain the diastolic blood pressure, the endothelium is smooth to reduce friction and is also folded so it can unfold when the artery stretches. Smooth muscle allows construction and vasoconstriction which narrows the lumen of the artery.
• in arterioles, the muscle enables blood to be directed to different areas of demand in the body- muscle contracts to restrict blood flow and relaxes to allow full blood flow
• Veins carry blood back to the heart, the blood is at a lower pressure than the artery, arterioles or capillaries
• Veins have a large lumen to ease the flow of blood, the walls have less collagen, smooth muscle and elastic tissue than the artery so the wall is thin but strong. the valves prevent backflow of blood. to move the blood back into the heart, pressure is exerted by the movement of muscles and there is also some residual pressure from the contraction of the left ventricle muscle wall
• Arterioles branch into capillaries which are the smallest blood vessel, the blood is at high pressure at the arteriole end due to the contraction of the left ventricle wall but the pressure falls as it goes to the venous end.
• Capillary walls are made up of a single layer of flattened endothelial cells which reduce diffusion distance, the narrow lumen ensures that cells are squeezed as they travel through again reducing diffusion distance so more oxygen can diffuse. Smooth endothelium reduces friction for blood flow, gaps between the endothelial cells allows movement of nutrients proteins cannot pass and capillaries have a large total surface area for more exchange
• molecules are exchanged between capillaries and cells
• Systole- contraction of cardiac muscle
• Diastole- relaxation of cardiac muscle
• Cardiac cycle step 1- ventricles relax, atria contract. Atria fill with blood, atria contract (atrial systole) decreasing the volume of the atria and increasing the pressure inside the chambers. blood is squeezed into the ventricle via the atrioventricular valve
• Cardiac cycle step 2- ventricles contract, atria relax. Ventricles contract (ventricular systole) decreasing their volume and increasing the pressure inside the chambers. The pressure inside the ventricle becomes greater than the pressure in the atria forcing the atrioventricular valves to shut to prevent backflow of blood. The pressure in the ventricles is also higher than that of the arteries which forces the semi lunar valves open.
• Cardiac Cycle step 3- ventricles relax, atria relax. Ventricles and atria both relax (diastole). The higher pressure in the arteries than ventricles causes the semi lunar valves to close to prevent back flow of blood into the ventricles. Atria fill with blood. Cycle repeats
• Atrioventricular valves open when the pressure in the atria is greater than the ventricles
• Semi lunar valves open when the pressure in the ventricles is greater than the arteries (pulmonary artery and aorta)