3.4.1 Mass transport in animals Flashcards
What are the haemoglobins?
The haemoglobins are a group of chemically similar molecules found in many different organisms. Haemoglobin is a globular protein with a quaternary structure - in most organisms (including humans) there are 4 polypeptide chains. Haemoglobins are associated with haem groups - prosthetic (ie non-protein) groups which contain an Fe ion.
Because haemoglobins are proteins found across nearly all vertebrates (ie animals with bones: fish, amphibians, reptiles, birds & mammals) the base sequences of their genes can be compared in phylogenetic studies.
Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind. Explain why.
Binding of the first oxygen causes a change in the tertiary structure of the haemoglobin. This conformational shift uncovers another haem group, allowing a second oxygen molecule to bind. This process is called ‘positive cooperativity’.
This can be seen on a graph showing the percentage saturation of haemoglobin with oxygen at different partial pressures. At a very low partial pressure of oxygen, increasing the partial pressure of oxygen correlates with little increase in saturation, but at higher partial pressures of oxygen increasing the partial pressure of oxygen correlates with a steeper rise as it gets easier for oxygen to bind.
The cooperative nature of oxygen binding means that haemoglobin readily loads oxygen in the lungs / gills.
Describe the role of haemoglobin in supplying oxygen to the tissues of the body.
Haemoglobin is found inside erythrocytes (red blood cells).
Haemoglobin associates with oxygen to form oxyhaemoglobin in blood with higher partial pressures of oxygen, such as that passing though the lungs or gills.
Oxyhaemoglobin dissociates, unloading oxygen, in blood with lower partial pressures of oxygen, such as the in capillaries passing through aerobically respiring tissue.
Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin.
increasing carbon dioxide concentration causes more unloading of oxygen by deceasing haemoglobin’s affinity for oxygen, which causes oxyhaemoglobin to dissassociate.
As carbon dioxide dissolves into the blood plasma it reacts with water to form carbonic acid, decreasing blood pH and so increasing acidity. This changes the tertiary structure of oxyhaemoglobin, making it unload oxygen more readily.
Describe the general pattern of blood circulation in a mammal.
The mammalian circulatory system is a double circulatory system (meaning pulmonary circulation is separate to systemic circulation, blood flows through heart twice during one complete circulation. This is unlike many of the non-mammalian vertebrates) and a closed circulatory system (blood is contained within vessels (this is true for all vertebrates, but not true for invertebrates).
Names the blood vessels entering and leaving the heart, lungs and kidneys.
The vena cava (from systemic circulation) and pulmonary vein (from the lungs) enter the heart. The aorta and pulmonary artery leave the heart. In addition, the coronary arteries leave the left side of the heart more or less where the left ventricle meets the aorta, carry oxygenated blood through the heart walls, and empty into the right atrium. The kidneys are served by the renal artery, while the renal vein carries blood away.
Explain how the pressure and volume changes and associated valve movements during the cardiac cycle maintain a unidirectional flow of blood.
The muscles in the atrial walls contract, decreasing the volume of the atria and so increasing the hydrostatic pressure. When the pressure in an atrium is higher than that in a ventricle the atrioventricular valve between them will open.
When the muscles in the ventricular walls contract, decreasing the volume of the ventricles and so increasing the hydrostatic pressure, the pressure in a ventricle rises higher than that in an atrium, and so the atrioventricular valve will close, preventing backflow. Tendons prevent the valve turning inside out.
When the hydrostatic pressure in a ventricle rises higher than that in the aorta/pulmonary artery the semi-lunar valve will open, allowing blood to leave the heart.
When the muscles in the atrial walls relax, the volume of the atria increase, and so the pressure falls below that of the vena cava/pulmonary vein, drawing blood down the pressure gradient into the atria.
When the hydrostatic pressure in a relaxing ventricle falls lower than that in the aorta/pulmonary artery, the semi-lunar valve will close, preventing backflow.
Explain how the structures of the walls of arteries and arterioles are related to their functions.
Artery and arteriole walls contain elastic tissue. Elastic tissue stretches under pressure (when the heart beats), then recoils, springing back and evening out blood pressure (which keeps flow at a steady rate).
Artery and arteriole walls contain muscle. Muscle contracts to reduce diameter of lumen (vasoconstriction) and relaxes to widen it (vasodilation). By coordinating vasoconstriction and vasodilation, blood flow to different organs can be increased or decreased.
Artery and arteriole walls are lined with a smooth epithelium which reduces friction.
Describe and explain how the structure of a capillary is adapted for the exchange of substances between blood and the surrounding tissue.
Capillaries are composed of a single layer of flattened endothelial cells, which reduces diffusion distance. The capillary lumen is narrow, which reduces flow rate giving more time for diffusion. Red blood cells pass through in single file and are in contact with the wall, giving a short diffusion distance. In places the endothelial cells have small gaps between them (fenestrations), which allows formation of tissue fluid. The outside of the capillaries is lined with a permeable basement membrane of collagen which prevent large proteins like albumin from passing through, lowering the water potential towards the venule end of the capillary.
Describe how tissue fluid is formed and how it is returned to the circulatory system.
At the arteriole end the high hydrostatic pressure of the blood forces fluid out through fenestrations in the capillary wall. Large proteins such as albumin remain in the capillary, where they lower the water potential of the remaining blood.
At the venule end water enters the capillary by osmosis down a water potential gradient, as the oncotic pressure to move in is greater than the hydrostatic pressure to move out.
The remaining tissue fluid drains into the lymphatic system, and reenters the blood at the subclavian veins (which join at the vena cava).
