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A2 Biology 4.2.2
OCR biology - excretion
| Question | Answer |
|---|---|
| Where are the kidneys located + what is their blood supply? | Kidneys are located on either side of the spine, just below the lowest ribs. Renal artery carries oxygenated blood from liver to kidneys, renal vein carries deoxygenated (clean) blood away from kidneys |
| What is a nephron? What are the stages of a nephron? | A microscopic tubule that produces urine, around 1 million in each nephron. Glomerulus + Bowman's capsule = ultrafiltration. Proximal CT = selective reabsorption. Loop of Henle = water reabsorption. Distal CT = finalise ion conc. CD = osmoregulation |
| What is the first stage of the nephron? | Renal artery carries oxygenated blood to kidney, splits into afferent arterioles. Efferent is narrower, pressure difference puts blood in glomerulus under high pressure. RMM<69000 forced into BC, RMM>69000 stays in blood |
| Give examples of substances that stay in / go out of blood | Stay in : cells, plasma proteins, some water. Go out: glucose, amino acids, water, ions, urea |
| What is the blood-capsule 3 layer barrier? | 1) capillary endothelium - filtrate diffuses through pores. 2) basement membrane - glycoproteins, collagen - filters filtrate according to RMM 3) bowmans capsule endothelial cells - podocytes - major processes - filtrate diffuses through gaps |
| What occurs in the proximal convoluted tubule? | Selective reabsorption-85%. Na/K pumps actively transport Na+ out, cotransport ions carry Na+ and glucose/amino acids into cells, glucose/amino acids diffuse into capillary, water diffuses into blood osmosis, small proteins, urea |
| What are some features of the cells lining the proximal convoluted tubule? | Tight junctions between cells to prevent substances diffusing freely between them, many ribosomes, mithconidra, Na/K pumps, cotransporter proteins, many microvilli as a brush border to increase SA |
| What is a cotransporter protein? | Membrane protein that allows facilitated diffusion of small ions to be accompanied by larger molecules |
| What is a Na/K pump? | Membrane proteins that actively transport sodium and potassium ions against their concentration gradients |
| What is the aim of the loop of henle? | to make the medullary interstitial fluid as hypertonic as possible so that water can be reabsorbed from the filtrate in the descending limb and the collecting duct |
| how does the loop of henle work? | Descending limb - WP decreases, CONC. - Na+ Cl- ions diffuse into filtrate, H2O diffuses out. Ascending limb - Na+ Cl- ions diffuse out, wall is impermeable to H2O. Hairpin countercurrent MM makes ion transfer efficient. Vasa recta preserves WP gradient |
| What is the effect of a longer loop of henle? | Medulla interstitial fluid becomes more hypertonic, more water reabsorbed, less urine produced. |
| What occurs in the distal convoluted tubule? | Alters concentration of certain ions in blood (absorbing ions from filtrate, secreting ions into filtrate) to keep blood pH at 7.4! |
| WHat occurs in the collecting duct? | Filtrate is transported from cortex to pelvis, osmoregulation |
| What is osmoregulation? | The maintenance of an organism's water potential in the blood, prevents crenation and haemolysis, negative feedback |
| How is ADH produces/secreted? | Produced and secreted by neurosecretory cells. Cell body in hypothalamus produces ADH, travels along axon, terminal bulb in posterior pituitary gland stores and secretes ADH. |
| What happens when water potential of blood is too low? | Osmoreceptors (H) shrink, stimulate neurosecretory cells, action potentials, secrete ADH, bind to complementary receptors, aquaporins transported in vesicles + exocytosis, more water reabsorbed, blood WP increases, urine concentrated |
| WHat happens when the water potential of the blood is too high? | Osmoreceptors aren't stimulated, neurosecretory cells don't secrete ADH, remaining ADH in blood quicjkly become inactive, some aquaproins are removed (plasma membrane folds inwards -> vesicle), less water reabsorbed, urine dilute |
| What is the role of the ureters and urethra? | 2 ureters carry urine from RENAL pelvis to balder. Urethra carries urine from bladder to outside of the body. |
| List the kidney functions | Formation of urine, osmoregulation, controls ion concentrations in the blood, controls production of erythrocytes, secretes hormones that control blood pressure, produces vitamin D |
| What is kidney failure and why might it occur? | When kidneys stop working properly-metabolic waste/excess water isn't removed from blood (fluid retention), disrupts homeostasis of blood [salt]/ water potential. Infection of glomeruli, diabetes mellitus, hypertension |
| What are the methods for treating kidney failure? | Dialysis (haemodialysis and peritoneal dialysis) and kidney transplant |
| How does haemodialysis work? | Blood from vein/radial artery circulates through external dialysis machine. Dialyser: fine capillaries, surfaces are dialysis membrane, substances with Mr<68,000 diffuse through until equilibrium. Dialysis fluid has optimal make-up, all urea leaves blood |
| Cont | Creates optimal concs/ WP in blood. Blood is pumped at high pressure, dialysis fluid flows in opposite direction to create a countercurrent mechanism. Heparin prevents blood clotting, air trap, 3 times a week in a clinic, diet must be controlled |
| How does peritoneal dialysis work? | Dialysis fluid with optimal concentrations of solutes enters abdominal cavity through catheter, peritoneum is the dialysis membrane, substances with low Mr diffuse between dialysis fluid inside cavity and blood on other side. All urea leaves blood |
| Cont | Creates optimal concentrations of solutes/ WP in blood. After 3 hours, dirty dialysis fluid is drained out and is replaced with fresh fluid. Every day, patients can move around, diet is less restricted |
| When is a kidney transplant used? | When kidneys are infected or cancerous |
| What are the advantages of a kidney transplant? | Better quality of life (free from burden of dialysis, able to travel), no longer chronically ill, better physical health, no longer have to control diet so much |
| What are the disadvantages of kidney transplant? | May take a long time to find a match, high risk of immune system rejecting organ, immunosuppressants increase susceptibility to infection, antirejection medicines cause fluid retention and hypertension, surgical complications (bleeding/damage/infection) |
| How does a pregnancy test work? | Dipstick dipped in urine. If pregnant, hCG binds to mobile monoclonal antibodies with coloured granule. Urine + hCG-antibodies move, capillary action. hCG-antibodies dock to immobilised antibodies in test window= coloured line. Control window=2nd line |
| Why are there 2 lines on a dipstick for a pregnant woman? | 1) test window- hCG-antibody complex docks to a line of immobilised antibodies, coloured granules form a line of colour confirming pregnancy. 2) control window - antibodies not bound to hCG dock to immobilised antibodies, shows test has run correctly |
| What is hCG? | Human chorionic gonadotrophin, a hormone secreted by human embryos once implanted in uterus lining, 6 days after conception. Mr is < 69000 (38700) so it appears in urine |
| What are anabolic steroids and how are they tested for? | Steroids mimic steroid hormones +cause protein synthesis + muscle growth. Used in sports for competitive advantage. Mass spectrometry: compare mass spectrum of urine to anabolic steroid spectra |
| What is the structure of the liver + blood supply? | 2 lobes, cylindrical lobules. Hepatic artery- oxygenated blood to liver. Hepatic portal vein- deoxygenated blood from intestines (poisons, bacteria, amino acids). Hepatic vein-deoxygenated |
| What are sinusoids? | Low pressure channels between hepatocytes where blood flows from interlobular vessels of hepatic artery and hepatic portal vein to interlobular vessels of hepatic vein. Kupffer cells are specialised, stellate macrophages found in sinusoids |
| What is bile, how is it transported? | Bile emulsifies fats, hydrophobic part dissolves in lipid globule + hydrophilic part sticks into water so lipid globules are miscible with water. Made by hepatocytes, transported in bile canaliculi to bile duct, gall bladder, stored -> small intestine |
| What is the structure of hepatocytes? | Cuboidal epithelial cells. Dense cytoplasm: lots of mitochondria (ATP for bulk transport, ornithine cycle), lots of ribosomes (proteins +enzymes for deamination, ornithine cycle). Microvilli increase SA in contact with blood to speed up diffusion |
| What is the portal triad? | Branch of hepatic artery, branch of hepatic portal vein, branch of bile duct |
| List the functions of the liver | Deamination+formation of urea, detoxification, storage of glycogen/vitA, B12, D/iron, kupffer cells digest foreign particles, break down old erythrocytes (bilirubin), synthesis of bile, cholesterol, plasma proteins +rbcs in foetus, break down old hormones |
| Why is deamination necessary + eqn? | Body can't store protein as amine groups make amino acids toxic, but whole amino acids can't be excreted as they contain lots of energy for respiration. Amino acid + 1/2 O2 -> keto acid (used for respiration/ converted to fat) + NH3 |
| What problem is there after deamination and how is it solved? | NH3 is water soluble, reacts with water NH4OH which is corrosive. Ornithine cycle: 2NH3 + CO2 -> CO(NH2)2 + H2O. Urea is less water soluble and toxic, transported to kidneys in hepatic vein, excreted as urine |
| Define and give examples for ammonotelic, uricotelic and ureotelic organisms | Ammonotelic - organisms that excrete nitrogenous waste as NH3 e.g. fish. Uricotelic - organisms that excrete nitrogenous waste as uric acid e.g. birds. Ureotelic- organisms that excrete nitrogenous waste as urea e.g. mammals |
| What is detoxification? | The conversion of toxic substances (e.g. drugs, H2O2) into non-toxic ones via oxidation, reduction , methylation or by reacting with substances on the surface of the SER in hepatocytes |
| Describe the detoxification of H2O2 | H2O2 is produced by mitochondria, converted into H2O and O2 by catalase enzyme in hepatocytes which has a turnover rate of 5 million per minute |
| Why must ethanol be detoxified? | It contains a lot of energy that could be used in respiration and it depresses nervous activity |
| How is ethanol detoxified? | Ethanol -> ethanal - oxidation, ethanol dehydrogenase. Ethanal -> ethanoic acid - oxidation, ethanal dehydrogenase. Ethanoic acid + coenzyme A -> acetyl coenzyme A (used in respiration). H atoms reduce NAD+ to NADH. |
| Why does ethanol detoxification pose a problem? | H atoms would cause acidic cells: they reduce NAD+ to NADH. NAD+ is used in B-oxidation pathway, break down of fatty acids. If it is occupied detoxifying ethanol, smaller proportion of fatty acids are broken down, more form complex lipids = fatty liver. |
| What results from fatty liver? | Hepatitis (inflammation) then cirrhosis - progressive disease where liver tissue is replaced by scar tissue which blocks blood flow and disrupts liver function. |
| What do cytochrome p450 enzymes do/where are they found? | Some toxic drugs are broken down by cytochrome p450 enzymes, located in the endoplasmic reticulum of hepatocytes |
| What is excretion? | The removal of metabolic waste from the body. Metabolic waste is toxic or unwanted substances, produced - often in excess - by reactions inside cells, e.g. CO2 and urea |
| Why must CO2 be excreted? | Reduces oxygen-carrying capacity of the blood- carbaminohaemoglobin, haemoglobinic acid. Respiratory acidosis- excess CO2 in blood, pH<7.35, drowsiness, headache, shortness of breath, caused by asthma/emphysema/chronic bronchitis/blockage |
| How do you calculate effective filtration pressure? | Blood hydrostatic pressure - (capsular filtrate hydrostatic pressure - blood water potential) |
| What are osmoreceptors? | Sensory receptors in hypothalamus that monitor blood water potential + osmotic pressure, involved in osmoregulation |
| What is the concentration of ions measured in in the loop of henle? | milliosmoles per litre: mOsm/kg, thousandths of a mole per kg of water |
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