Role of the nephron in osmoregulation Flashcards
What is one of the main important role of the kidney
-one of the important functions of the kidney is to maintain the water potential of plasma and hence tissue fluid (osmoregulation)
What are the stages the nephron carries out in its role of osmoregulation?
- the formation of glomerular filtrate by ultrafiltration
- re absorption of glucose and water by the proximal convoluted tubules
- maintenance of a gradient of sodium ions in the medulla by the loop of Henle
- reabsorption of water by the distal convoluted tubule and collecting ducts
What is the formation of glomerular filtrate by ultrafiltration?
- blood enters the kidney through the renal artery,
- renal artery branches to give afferent arterioles,
- afferent arterioles enter the bowman’s capsule and divide to give the glomerulus capillaries
- glomerular capillaries merge to form the efferent arterioles
- efferent arterioles sub-divides again into capillaries, which combine to form the renal vain
- the diameter of the affront arteriole is greater than the efferent arteriole so there is a build up of hydrostatic pressure within the glomerulus causing water, glucose and mineral ions to be squeezed out of a capillary to form the glomerular filtrate
what is the movement of filtrate out of the glomerulus resisted by?
- capillary epithelial cells
- connective tissue and epithelial cells of the blood capillary
- epithelial cells of the renal capsule
- the hydrostatic pressure of the fluid in the renal capsule space
- the low water potential of the blood in the glomerulus
Which modifications reduce the barrier to the flow of filtrate?
- podocytes are the inside layer of the renal capsule, these cells, have spaces between them, this allows filtrate to pass through the gaps
- the endothelium of the glomerular capillaries has spaces between its cells, so fluid can therefore pass between as a result the hydrostatic pressure of the blood in the glomerulus is sufficient to overcome their resistance and so filtrate passes from the blood into the renal capsule
How are the proximal convoluted tubules adapted to reabsorb substances into the blood by having epithelial cells?
- microvilli to provide a large surface area to reabsorb substances from the citrate
- infolding at their bases to give a large surface area to transfer reabsorbed substances into blood capillaries
- a high density of mitochondria to provide ATP for active transport
What is the process of re-absorbance of substances into the blood through proximal convoluted tumbles?
- sodium ions are actively transported out of the cells into capillaries
- the sodium ion concentration is lowered
- sodium ions now diffuse down a concentration gradient from the proximal convoluted tubule into the epithelial lining cells but only through special carrier proteins by facilitated diffusion
- the molecules which have been co-transported into the cells of the proximal convoluted tubule then diffuse into the blood, as a result all the glucose and most other valuable molecules are reabsorbed as well as water
What is the loop of Henley?
- the loop of Henle is a hairpin-shaped tubule that extends into the medulla of the kidney
- it is responsible for water being reabsorbed from the collecting duct, and concentrating the urine so that it has a lower water potential than blood
What are the regions of the loop of Henley?
- the resending limb, which is narrow, with thin walls that are highly permeable to water
- the ascending limb, which is wider, with thick walls that are impermeable to water
How does the loop of Henley maintain gradient of sodium ions by counter-current multiplier?
1-sodium Ions are actively transported out of the ascending limb of the loop of Henle using ATP provided by the many mitochondria in the cells of its wall
2-this creates a low water potential (high ion concentration) in he region of the medulla between the two limbs (called the interstitial region) in normal circumstances water would pass out of the ascending limb by osmosis, however the thick walls are almost impermeable to water and so very little, if any escapes
3-the walls of the descending limb are however very permeable to water and so passes out of the citrate by osmosis into the interstitial space, this water enters the blood capillaries in this region by osmosis and is carried away
4-the filtrate progressively loses water in this way as it moves done the descending limb lowering its water potential
-it reaches its lowest water potential at the tip of the hairpin
5-at the base of the ascending limb, sodium ions diffuse out of the filtrate and as it moves up the ascending limb these ions are also actively pumped out and therefore the citrate develops a progressively higher water potential
6-in the interstitial space between the ascending limb and the collecting duct there is a gradient of water potential with the highest water potential (lowest concentration of ions) in the cortex and an increasingly lower water potential (higher concentration of ions) the further into the medulla one goes
7-the collecting duct is permeable to water and so, as the citrate moves down it, water passes out of it by osmosis
-this water passes by osmosis into the blood vessels that occupy this space and is carried away
8-as water passes out of the filtrate its water potential is also lowered in the interstitial space and so water continues to move out by osmosis down the whole length of the collecting duct
-the counter-current multiplier ensures that there is always a water potential gradient drawing water out of the tubule
What is the antidiuretic hormone?
- the water that passes out of the collecting duct by osmosis does so through channel proteins that are specific to water (aquaporins)
- antidiuretic hormone can alter the number of these channels and so control water loss
- by the time the filtrate, now called urine, leaves the collecting duct on its way to the bladder, it has lost most of its water and so it has a lower water potential is more concentrated than the blood
What is the distal convoluted tubule?
-the cells that make up the walls of the distal convoluted tubule have microvilli and many mitochondria that allow them to reabsorb material rapidly from the filtrate, by active transport
0the main role of the distal tubule is to make final adjustments to he water and salts that are reabsorbed and to control the pH of the blood by selecting which ions to reabsorb
-to achieve this, the permeability of its walls becomes altered under the influence of various hormones
What is the counter-current multiplier?
- in the case of the loop of Henle, the counter-current flow means that the filtrate in the collecting duct with a lower water potential
- this meets interstitial fluid that has an even lower water potential
- this means that although the water potential gradient between the collecting duct and interstitial fluid is small, it exists for the whole length of the collecting duct
- there is therefore a steady flow of water into the interstitial fluid, so water enters the interstitial fluid and hence the bold
