F214.2 Excretion Biology Revision Cards

Laura Perry
Flashcards by Laura Perry, updated more than 1 year ago


A Levels Biology (A2 Biology) Flashcards on F214.2 Excretion Biology Revision Cards, created by Laura Perry on 02/28/2016.

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Question Answer
Excretion The removal of metabolic waste from the body
Why must carbon dioxide be removed from the body? Carbon dioxide can cause respiratory acidosis- where hydrogen ions produced by the dissociation of carbonic acid cause the blood to become more acidic, lowering the pH. A large change in pH causes difficulty breathing, headaches etc. The hydrogen ions also displace oxygen in haemoglobin, lowering the amount of oxygen carried in the blood. Carbon dioxide will also displace oxygen on haemoglobin, which has a lower affinity for oxygen.
Why must nitrogenous compounds be removed from the body? When amino acids are broken down (deamination) it produces a toxic amine group and ammonia. This ammonia is then turned into urea and a keto acid. The keto acid is then used for energy for respiration or stored. Amino acids cannot be stored in the body but they have a lot of energy so it would be wasteful just to remove them from the body.
What two vessels carry blood to the liver? Hepatic Artery- carries oxygenated blood, which is needed for aerobic respiration from the aorta. Hepatic Portal Vein- carries deoxygenated blood from the digestive system to the liver.
What is the sinusoid and where is it? The sinusoid is where the hepatic artery and hepatic portal vein meet in the lobule of the liver. It is lined with hepatocytes allowing close contact to the blood. Here the oxygenated and deoxygenated blood is mixed.
What two vessels carry blood away from the liver? Hepatic Vein- carries blood away from the liver and joins the vena cava. Bile Duct- carries bile from the liver to the gall bladder.
What is the name of a liver cell and what is its ultrastructure? Hepatocytes- they have many microvilli. They have a dense cytoplasm as it contains many organelles, needed for the metabolic processes.
How the cells arranged within the liver? 740bf119-5d94-4ff7-b3b9-d2704dbbc214.jpg (image/jpg)
What is a kupfer cell? A specialised macrophage found in the sinusoid. They break down and recycle old red blood cells. This produces bilirubin.
How is urea formed within the liver? Amino acids go through deamination producing ammonia and a keto acid. Ammonia then goes through the ornithine cycle. The ammonia combines with carbon dioxide forming urea. This reenters the blood and is transported to the kidneys where it is turned back into urine.
What are the two vessels of the kidney and what are their functions? Renal artery- supplies the kidney with blood. Renal vein- removes blood from the kidney.
What's the structure of the kidney? 371050e3-335b-44e2-b395-5cdd737ee020.jpg (image/jpg)
What are the vessels associated with the Bowman's capsule? Afferent Arteriole- carries blood to the glomerulus. It has a fairly wide lumen and there is fairly low pressure. Efferent Arteriole- carries fluid away from the glomerulus. It has a more constricted lumen and pressure is higher, causing fluid from the blood to enter the Bowman's capsule
What are the five major parts of the nephron? Proximal Convoluted Tubule Descending Limb Ascending Limb Distal Convoluted Tubule Collecting Duct
What substances are moved into the Bowman's capsule during ultrafiltration? Water, small inorganic ions, glucose, amino acids, urea.
What substances are left in the capillaries after ultrafiltration? Large proteins with a high RAM and blood cells, leading to a very low water potential.
How does the water potential decrease in the descending limb of the loop of henle? Water molecules move out of the limb by osmosis. Sodium and chlorine ions are also moved into the limb from the tissue fluid.
How does water potential increase in the ascending limb of the loop of henle? Sodium and Chlorine molecules are actively transported (pumped) out of the ascending limb at the top and diffuse out near the base. It is also impermeable to water so water cannot leave the limb.
How is the salt concentration increased in the medulla? When sodium and chlorine ions leave the ascending limb and move to the descending limb, the tissue increases in slat concentration, lowering water potential.
What is the concentration of the urine found at the top of the ascending limb? The urine at the top of the descending limb is very dilute as all sodium and chlorine ions have been actively removed from the limb and water has not been able to move out the limb by osmosis due to it being impermeable.
What happens to the urine in the distal convoluted tubule? The concentration of the salt in the urine is adjusted but the water potential is still high.
What happens when the urine travels down the collecting duct? Water leaves the tubule by osmosis and enters the tissue fluid. This happens because the medulla has low water potential as there are many sodium and chlorine ions within it. This water then enter the capillaries by osmosis.
Osmoregulation The maintenance of water and salt levels in the body.
What would happen on a cold day if a lot of fluid was drunk, in terms of osmoregulation? Less water would need to be conserved by the body so the walls of the collecting duct are less permeable to water, so less water is reabsorbed by the capillaries. This means more dilute urine will be created.
What would happen on a hot day if very little was drunk, in terms of osmoregulation? The walls of the collecting duct would be very permeable to water as more water must be conserved by the body. The capillaries would reabsorb more water so less concentrated urine would be produced.
What layer are between the blood in the capillary and the lumen of the Bowman's capsule? Endothelium of the Capillary- narrow gaps between the cells allow blood plasma and dissolved substances through. Basement Membrane- fine mesh of collagen fibres and glycoproteins prevent protein and blood cells through. Epithelial cells of the Bowman's capsule- allow gaps between the cells.
What happens when filtrate moves along the nephron and where is most of the filtrate reabsorbed? When the filtrate moves along the PCT, 85% is moved back into the capillaries. All glucose and amino acids are reabsorbed and some salts and water are reabsorbed.
How does reabsorption occur in the proximal convoluted tubule? Sodium ions are removed from the cells lining the PCT, reducing the concentration in the cell cytoplasm. Sodium ions are then moved into the cell with glucose and amino acids (facilitated diffusion). The concentration of these rises inside the cell so they diffuse out the other side of the cell into the tissue fluid and then into the blood.
How does water reabsorption happen inside the PCT? Reabsorbing salt/ glucose/ amino acids reduces the water potential in the cells and increases it in the tubule fluid. Water enters the cells and reabsorbs into the blood by osmosis.
What is the term that describes the arrangement of the loop of henle? Hairpin Counter-current Multiplier- it increases the efficiency of salt transfer from the ascending limb to the descending limb, increasing the salt concentration of the tissue fluid.
What is the name of the hormone that affects the collecting duct? How does it work? ADH (Anti-Diuretic Hormone)- It binds to the receptors in the membranes of the cells that make up the wall of the collecting duct. This causes aquaporins to be inserted in the cell surface membrane. These make the walls become more permeable to water.
How is the concentration of the hormone associated with osmoregulation affected/ controlled? Osmoreceptors in the hypothalamus monitor the water potential of the blood. When the potential is low the osmoreceptors lose water stimulating neurosecretory cells. An action potential causes the ADH to be released. This enters the blood capillaries and travels to the ducts. After 20 minutes the ADH breaks down.
How does dialysis work? Blood is passed over the dialysis membrane which is partially permeable. It allows exchange between the blood and the dialysis fluid. Substances in excess flow into the dialysis fluid whilst substances in low concentration diffuse into the blood from the dialysis fluid.
How is the liver involved in detoxification? Ethanol to Ethanal to Ethanoic Acid to Acetyl Coenzyme A. It reduces NAD when it is dehydrogenated. NAD is also needed to break down fatty acids for use in respiration.
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