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The Kidney
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- 1What are kidneys?A pair of reddish-brown organs attached to the back of the abdominal cavity. They are usually surrounded by a later of thick, protective fat and fibrous connective tissue. They are involved in excretion and osmoregulation.
- 2Blood in the kidneys?Enters via renal arteries which branch off from the aorta. Blood that has been through the kidneys goes back to the vena cava. 90-120cm3 of blood goes through the kidneys every minute.
- 3Kidney structure?There are three main sections of the kidney - the medulla, cortex and pelvis.
- 4What is the renal cortex?The renal cortex is the dark outer layer which filters the blood. It has a very dense capillary network which carries blood from the renal artery to nephrons.
- 5What is the renal medulla?The lighter inner area of the kidney. It contains the tubueles of the nephrons which form the pyramids and the collecting ducts.
- 6What is the renal pelvis?The central chamber of the kidney where urine collects before passing out the ureter
- 7What is the job of the nephron?To filter all of the blood, removing waste products and returning everything else back to the blood. Each nephron is about 3cm long and there are around 1.5 million in each kidney.
- 8What is the bowmans capsule of the kidney?The cup-shaped structure that contains the glomerus which is a tangle of capillaries. It ultrafiltrates the blood into the nephron. The afferent arteriole is wider in diameter than the efferent arteriole so blood is passed through at high pressure but slowly, enabling ultrafiltration to occur.
- 9What is the proximal convoluted tubule of the nephron?The first, coiled region of the tubule after the Bowman's capsule. It is found in the cortex and many of the substances that are needed are reabsorbed into the blood.
- 10What is the loop of Henle?The long loop of the tubule that creates a region of very high solute concentration in the tissue fluid in the medulla. There is a descending limb and an ascending limb with a bend at the bottom. The loop travels through the cortex, into the medulla and back up to the cortex again.
- 11What is the distal convoluted tubule?A second twisted tubule where fine-tuning of water balance takes place. The permeability of the walls can be altered by ADH (anti-diuretic hormone) for water uptake. It can also regulate ion balance and PH of the blood.
- 12What is the collecting duct?The urine passes down the collecting duct through the medulla into the pelvis. Further fine tuning of water balance can happen here as it is also sensitive to ADH.
- 13What surrounds the nephron?A network of capillaries that all lead into a venule then to the renal vein. The blood that leaves the kidney has a great reduction in urea and waste products but the same concentration of substances like amino acids and glucose.
- 14Where does the blood pass through in ultrafiltration?It leaves the capillary wall into the basement membrane which is made up of collagen fibres that act like a sieve. This stops any large molecules from passing into the nephron, like proteins. The blood then has to pass through podocytes on the wall of the Bowman's capsule which have extensions that form slits to stap any large proteins further.
- 15What is the blood that enters the Bowman's capsule like?It contains glucose, salt, urea and many other substances
- 16What is the glomerular filtration rate?The volume of blood that is filtered through the kidneys at any given time
- 17Why donwe need absorption in the kidney?Lots of molecules that pass into the nephron are needed, such as glucose and some water. So, the nephron (after the Bowman's capsule) needs to reabsorb these substances.
- 18How does this happen?In the PCT, all of the glucose, amino acids, vitamins and hormones from the renal filtrate are moved from the filtrate back into the blood by active transport. Around 85% of the salt and water is reabsorbed too. The PCT is adapted for this with lots of mitochondria and microvilli for a greater surface area.
- 19What are the concentrations of filtrate like opposed to the concentrations of the blood?The filtrate at first is hypotonic (less concentrated then) the blood plasma. When the filtrate reaches the Loop of Henle, it is isotonic (the same concentration as) the blood plasma.
- 20How much of the substances have been reabsorbed come the Loop of Henle?Around 80%
- 21How is the Loop of Henle adapted to produce more urea?The different sections of it have different permeability to water. It works as a countercurrent, using energy to produce a concentration gradient which results in the movement of substances such as water from one area to another. Cells use ATP to transport ions using active transport and this produces the diffusion gradient.
- 22What happens in the descending limb of the Loop of Henle?The water diffuses out down a concentration gradient. It moves out due to a high concentration of sodium and chlorine ions in the tissue fluid. The filtrate that reaches the Loop at the bottom is very concentrated and hypertonic to the blood as it's had lots of its water removed.
- 23What happens at the ascending limb of the Loop of Henle?The first section of it is very permeable to sodium and chloride ions. They move out of the ascending limb into the surrounding tissue fluid by diffusion down a concentration gradient. In the second section of the ascending limb, they are pumped out by active transport as there is already lots of Na and Cl in the tissue fluid. This produces a high concentration of Na and Cl in the tissue fluid which is what sets up the concentration gradient for water to be removed from the descending limb. The ascending limb is impermeable to water so water cannot leave.
- 24What happens at the DCT?By the time the filtrate reaches the DCT it is hypotonic to the blood again. In the DCT, the water is balanced. The permeability of the DCT is controlled by the ADH. If the body lacks salt, the DCT will pump out sodium ions and chloride ions would follow passively.
- 25What does the collecting duct do?The collecting duct is the main site for the concentration and volume of urine. Water moves out of the collecting duct by diffusion down a concentration gradient as it passes through the medulla. Hence, urine becomes concentrated. The urine produced is hypertonic when the body needs to conserve water.
- 26How does glucose get back into the blood?In the PCT, the sodium ions are actively pumped out to create a concentration gradient. Once there is this concentration gradient, sodium continues to move out but here is a cotransport mechanism that takes glucose with it too. Amino acids are pumped out the same way
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- A level (Module 5 ) Biology Fichas sobre The Kidney, creado por Emma Lloyd el 09/06/2017.
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- Emma Lloyd
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