HL Kidney nephron structure and ultrafiltration IB biology HL Study online at quizlet.com/_ba61d 1.
Two Kidney functions
Excretion and Osmoregulation.
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Excretion
The removal from the body of the waste products of metabolic pathways.
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Osmoregulation
The control of the water balance of the blood, tissue, or cytoplasm of a living organism.
Name seven parts of the kidney
Cortex, Medulla, Renal artery, Renal vein, Pelvis of the kidney, and Ureter (carries urine to the bladder). The cortex and medulla contain many nephrons.
What is the structure of the glomerulus?
Basement membrane (the filter), Podocytes, fenestrated wall of capillary, arteriole, blood plasma, and red blood cells.
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What are Podocytes?
Cells with finger-like projections which wrap around capillaries in the glomerulus.
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What is Ultrafiltration?
The method used by the glomerulus to filter out solutes from the blood plasma, while retaining proteins.
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Explain Ultrafiltration
1. Small molecules, including glucose can pass through the fenestrated membranes of the capillaries, the basement membrane, and podocytes into the nephron. 2. The relatively high blood pressure in the glomerulus creates an environment in which solutes are easily lost from the blood.
Three parts of the glomerulus that allow for Ultrafiltration.
1. Pores between the cells in the walls of the capillaries are small enough to keep blood cells in but let fluid out. 2. The basement membrane covers and supports the capillaries and prevents plasma proteins from being filtered out. 3. Podocytes form the inner wall of the Bowman's capsule, provide narrow gaps through which small molecules pass easily.
Selective re-absorption
Glomerular filtrate contains not only waste products, but substances that the body may need as well (eg glucose). These substances must be re-absorbed back into the blood and this happens through selective re-absorption in the proximal convoluted tubule.
How is selective reabsorption done?
1. The wall of a nephron consists of a single layer of cells. In the proximal convoluted tubule the cells have microvilli projecting into the lumen, giving a large surface area for absorption. 2. Protein pumps in the membrane re-absorb useful substances by ACTIVE TRANSPORT, using ATP produced by mitochondria in the cells. 3. All of the glucose in the filtrate is re-absorbed. About 80% of the mineral ions, including sodium is re-absorbed. 4. Active transport of solutes makes the total solute concentration higher in the cells of the wall than in the filtrate in the tubule. 5. Water therefore moves from the filtrate to the cells and on into the adjacent blood capillary by osmosis. About 80% of the water in the filtrate is re-absorbed, leaving 20% of the original volume to flow on into the loop of Henle.
The function of the loop of Henle
The loop of Henle increases the solute concentration of the medulla. An osmotic concentration gradient allows more reabsorption of water into the blood and produces more concentrated urine than would otherwise be possible.
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Descending limbs of Loop
are permeable to water but not to sodium ions.
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Ascending limbs of Loop
are permeable to sodium ions but not to water. they pump sodium ions from the filtrate into the medulla by active transport, creating a high solute concentration in the medulla.
Osmoregulation in the collecting duct ( if water conc. in blood is too low)
If the water content of the blood is too low: 1. The pituitary gland secretes ADH. 2. This hormone makes the cells of the collecting duct put more protein channels (called aquaporins) in their membrane, which makes the collecting duct more permeable to water. 3. As the filtrate passes down the collecting duct through the high solute concentration of the medulla, most of the water in the filtrate is reabsorbed by osmosis. 4. A small volume of concentrated urine is produced.
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Osmoregulation in the collecting duct ( If water content of the blood is too high)
If the water content of the blood is too high: 1. ADH is not secreted. 2. Aquaporins are removed from the membranes of epithelial cells in the collecting duct which become less permeable to water. 3. Little water is reabsorbed as the filtrate passes down the collecting duct. 4. And a large volume of dilute urine is produced.
Explain reasons why glucose is found in the urine of untreated diabetes patients.
1. Blood glucose concentrations are high in diabetic patients. 2. There is so much glucose in the ultrafiltrate that not all of it can be reabsorbed in the proximal convoluted tubule. 3. Some glucose stays in the filtrate as it passes through the nephron. 4. This glucose gets passed into urine.
Explain the differences in the concentration of proteins, glucose and urea between blood plasma, glomerular filtrate and urine.
1. Proteins remain in the blood as protein molecules are too large to pass throuth the basement membrane into the glomerulus. 2. Urea passes easily into the glomerulus and is not reabsorbed into blood. Concentration of urea in filtrate increases as glucose, water and salts are reabsorbed into the blood 3. Glucose passes easily into glomerular filtrate but is quickly reabsorbed into the blood by active transport in proximal convoluted tubule. Concentration is highest in blood, and very low in urine. (except in diabetics)
