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B4.2 - Excretion
Excretion - OCR A2 Biology
| Question | Answer |
|---|---|
| Define excretion: | The removal of by-products that could become toxic if allowed to build up. |
| Define egestion: | Getting rid of unused materials such as faeces. |
| What substances are found in urine? | Urea, water, salts. |
| How is Carbon Dioxide removed from the body? | Passed from respiring cells to the bloodstream. Transported to the lungs where it is breathed out. |
| How is urea removed from the body? | Excess amino acids are deaminated to form Ammonia and Keto acid. The ammonia is combined with co2 in the Ornithine cycle = Urea. This travels in the blood stream to the kidneys. The kidneys removed urea from the blood and store it in the bladder. |
| Why must Carbon Dioxide be removed? | Too much can reduce Oxygen transport. Can form carboxyhaemoglobin which has a lower affinity for Oxygen. |
| Why must Nitrogenous compounds be removed? | The body cannot store excess protein as excess amino acids can be damaging to the body. |
| What type of blood does the Hepatic artery supply, and to what organ? | Oxygenated blood to the Liver. |
| What type of blood does the hepatic portal vein supply to the Liver? | Deoxygenated blood. This is rich in nutrients. |
| What does the Bile duct do? | It carries bile from the liver to the Gall bladder. It's stored here until it is required to aid digestion. |
| What are Sinusoids? | At intervals, branches of the hepatic artery and portal vein enter liver lobules. The blood is mixed here and passes a long a SINUSOID (this is lined by liver cells). |
| What does the liver do? | Control blood glucose levels, amino acid levels and Lipid levels. |
| What happens in the Ornithine cycle? | Ammonia is combine with Carbon Dioxide to produce urea and Water. |
| What four parts make up a Kidney? | Medulla, Cortex, Capsule and the Pelvis. |
| What brings blood to the Kidneys? | The renal artery. |
| What takes blood away from the Kidneys? | The renal vein. |
| What are four functions of the Kidney? | Regulation of blood water levels, reabsorption of useful substances, adjustment of levels of salts and ions, and excretion of urea and metabolic wastes. |
| What is a nephron? | Extremely thin tubules. Start in the Cortex. Blood enters them via the renal artery. There is a knot of capillaries called a Glomerulus. This is surrounded by a Bowman's Capsule. The blood enters via the afferent arteriole, and Exits via the Efferent. |
| What does the nephron do? | Fluid from the blood is pushed into the Bowman's capsule via ultrafiltration. As it moves along, through the PCT, loop of Henle and DCT, the composition of the fluid changes. Selective reabsorption takes place. |
| How does the blood exit the capillaries and enter the Bowman's capsule? | The afferent arteriole has a larger lumen than the efferent arteriole. This means the blood in the Glomerulus is under high pressure so is forced out into the Bowman's capsule. |
| Is the water potential high or low in the Descending limb? | The water potential starts off high, then lowers as water diffuses out and is absorbed into the blood due to there being a lower water potential in the medulla than inside the Descending limb. |
| Is the water potential high or low in the Ascending limb? | The water potential starts off low, then increases as the solutes are actively removed, to provide a low water potential in the Medulla. |
| What happens to the water that is in the collecting duct? | The water diffuses out via osmosis. This is due to the water potential being lower outside the duct than inside (from the solutes being actively pumped out in the ascending loop of Henle). |
| What does the Bowman's Capsule consist of? | Capillary endothelial cells, the basement membrane and epithelial cells. |
| What do the capillary endothelial cells do? | They have narrow gaps between them to allow blood plasma to pass through. |
| What does the Basement Membrane do? | Collagen fibres and glycoproteins act as a filter to prevent large molecules getting through. |
| What do the epithelial cells do? | They have a specialised shape to ensure that there are gaps between the cells. |
| How does reabsorption occur? | Na & K pumps remove Na from cells lining the PCT. This allows glucose, amino acids and Na to enter the cell via facilitated diffusion. As concentrations rise, the substances are then able to diffuse out. This also allows water to enter via Osmosis. |
| How do Kidney infections cause kidney failure? | These can cause inflammation of the kidney, which damages cells. This interferes with filtering in the renal capsules. |
| How does high blood pressure cause kidney failure? | This can damage the capillaries in the Glomeruli. Enabling larger molecules to get through the capillary walls (e.g. proteins) |
| What issues can kidney failure cause? | Waste build-up, fluid accumulating in tissues, ion levels un-balance, anaemia (lack of Hb in blood) |
| What is renal dialysis? | A machine filters the patients blood. The blood is passed through a partially permeable membrane with dialysis fluid on the other side. Waste products diffuse across and are taken away. |
| What is a kidney transplant? | A new kidney is implanted from a person with the same blood and tissue type. |
| What is Osmoregulation? | The control of water and salt levels. |
| What do Osmoreceptors monitor and where are they located? | Water concentration in the blood. They are located in the Hypothalamus in the Brain. |
| What happens when Osmoreceptors detect a low water concentration in the blood? | They stimulate the Posterior Pituitary Gland to release ADH (anti-diuretic hormone). This makes the walls of the collecting duct more permeable by releasing vesicles that contain water-permeable channels. |
| How is urine used to test for pregnancy? | Pregnant women release the hormone hCG (Human Chorionic Gonadotropin). This is detected when they pee on a stick, that contains antibodies for this hormone attached to a blue bead. If hCG is present, the blue beads move up the stick turning it blue. |
| How is urine used to test for steroids? | Steroids are removed from the blood via urine. Their urine is tested for the substances that the body breaks steroids down into. Gas chromatography. The sample is passed through a column, it's speed is compared to a steroid. |
Created by:
Sparksy
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