The Kidney and the Nephron Flashcards
osmoregulation, ultrafiltration, selective reabsorption and the counter current multiplier
describe the renal cortex and medulla
Renal cortex - lighter coloured outer region consisting of Bowman’s capsules, D/PCTs and blood vessels
Renal medulla - darker coloured inner region consisting of loops of Henle, collecting ducts and blood vessels
role of the renal artery and renal vein
Renal artery - branches off the descending aorta and into afferent arterioles to supply glomerulus with oxygenated blood
Renal vein - efferent arterioles return deoxygenated blood to the heart from glomeruli
bowman’s capsule
closed end at the start of the nephron which surrounds a mass of capillaries (glomerulus), the inner layer consists of podocytes
podocytes
form projections which wrap around blood capillaries to form filtration slits so only molecule with a relative molecular mass below 69000 can pass
describe the proximal convoluted tubule
a series of loops surrounded by capillaries, walls consist of epithelial cells with microvilli
describe the structure of the loop of henle
a long, hairpin loop from the cortex into the medulla and back again, surrounded by capillaries
describe the distal convoluted tubule
a series of loops surrounded by capillaries, walls of epithelial cells, surrounded by fewer capillaries than the PCT
describe the collecting duct
the tube into which DCTs empty, lined by epithelial cells and becomes increasingly wide as it empties into the pelvis of the kidney
describe and explain the vessels of the nephron
Afferent arteriole - branched off the renal artery, it supplies the nephron with oxygenated blood, enters the renal Bowman’s capsule where it forms the glomerulus
Glomerulus - branched knot of capillaries from which fluid is forced out into the blood, glomeruli recombine to form the efferent arteriole
Efferent arteriole - carries blood away from the renal capsule and later branches to form the blood capillaries, has a smaller diameter than the afferent arteriole so it is harder for blood to flow away from the glomerulus which results in a high hydrostatic/blood pressure of the glomerulus
describe the stages of osmoregulation
Formation of glomerular filtrate by ultrafiltration
Reabsorption of glucose and water by the proximal convoluted tubule
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
explain how the glomerular filtrate is formed in the nephron (5 marks)
Blood enters the kidney via the renal artery which branches into afferent arterioles, each of which enter a Bowman’s capsule and divide to form glomerulus
The diameter of the afferent arteriole is greater than the efferent arteriole causing a build of hydrostatic pressure so water, glucose, amino acids, urea, some small peptide hormones and mineral ions are squeezed out the glomerulus to form the glomerular filtrate
Podocytes have spaces between them so act as filtration slits and filtrate can pass through gaps in between their branches and beneath them
Endothelium of glomerular capillaries have spaces up to 100 nm wide between cells so fluid can pass between these cells
As a result, HSP of blood in the glomerulus overcomes any resistances and passes into the renal capsule
describe the features which cause resistance to the filtering mechanism
Capillary epithelial cells
Connective tissue and epithelial cells of the capillary
Epithelials of Bowman’s capsule
Hydrostatic pressure of the fluid in Bowman’s capsule
Low water potential of glomerular blood
what should be missing from the filtrate in a healthy, functioning kidney
cells (RBC) or plasma proteins as they are too large to pass between the connective tissue so remain in the blood
suggest and explain a possible cause for presence of erythrocytes in urine
Erythrocytes are too large to move through the filter in the nephron, however hypertension would cause a high hydrostatic glomerular pressure so they would be forced out the podocytes/endothelial gaps into the Bowman’s capsule
describe and explain how the PCT is adapted to its function
Microvilli - large surface area to increase surface for reabsorption of substances from the filtrate
Infoldings at their bases - large surface area to transfer reabsorbed substances into blood capillaries
High density of mitochondria - provide ATP for active transport
explain how glucose and water are selectively reabsorbed in the proximal convoluted tubule
Sodium ions are actively transported out the epithelial cells of the proximal convoluted tubule into efferent blood capillaries, therefore lowering the sodium ion concentration of these cells
Sodium ions now diffuse down a concentration gradient from the lumen of the PCT into the epithelial lining cells by use of a cotransporter protein in facilitated diffusion
Through co transport, glucose molecules also move from the lumen of the PCT into the epithelial lining cells on the cotransporter protein with sodium
Water potential of the epithelial cells then decreases so water moves into them from the filtrate in the PCT lumen by osmosis
Glucose then diffuses from the epithelial cells into the blood, water then follows by osmosis because glucose decreases water potential of the blood
what is the effect on the concentration of urea as one moves along the PCT
concentration of urea increases because most of the ions and some of the water is reabsorbed. Urea is the waste product of metabolic reactions and is toxic so needs to be excreted as part of urine, meaning it needs to be removed from the filtrate later.
compare the structure of the descending limb to the ascending limb in the loop of Henle
Descending limb is narrow with thin walls which are highly permeable to water
Ascending limb is wider with thick walls that are impermeable to water
explain how a sodium ion gradient is maintained in the loop of Henle (5 marks)
Sodium ions are actively transported out of the ascending limb using ATP provided by mitochondria
This creates a lower water potential in the interstitial fluid but water is prevented from escaping the limb due to its impermeability
The filtrate reaches the descending limb where water passes out of the filtrate by osmosis because the limb is highly permeable, into the interstitial fluid. The water enters the blood capillaries in the region by osmosis and is carried away
The filtrate progressively loses water as it moves down the descending limb, lowering its water potential until it reaches its lowest water potential at the tip of the hairpin
At the base of the ascending limb, sodium ions diffuse out the filtrate and are also actively pumped out as it moves up the ascending limb, developing a progressively higher water potential
In the interstitial fluid between the ascending limb and collecting duct, there is a water potential gradient where the highest is in the cortex and there is an increasingly lowering potential as you progress further into the medulla
The collecting duct is permeable to water so water passes out of the filtrate as it moves down the duct via osmosis, passing into the blood vessels nearby to be carried away
This lowers water potential of the filtrate but water potential is also lowered in the interstitial space so water continues to move out by osmosis down the whole length of the collecting duct through aquaporins
define osmoregulation
the control of water potential in the body
describe the role of the DCT in ultrafiltration
From the top of the ascending limb, tubule fluid passes through the DCT
Active transport due to many microvilli and mitochondria allows it to reabsorb material from filtrate
Makes final adjustments to water and salts that are reabsorbed and to control pH of the blood by selecting which ions to reabsorb
describe and explain the importance of the counter current multiplier
Filtrate in the collecting duct with a lower water potential meets interstitial fluid with an even lower water potential so the gradient can exist for the whole length of the collecting duct
This allows for a steady flow of water into the interstitial fluid so around 80% of the water in the filtrate enters the interstitial space and hence the blood
If the two flows were in the same direction, less of the water would enter the blood
how may length of the loop of Henle differ in animals in different environments
Animals in dry environments would have longer loops of Henle in order to provide a longer counter current multiplier so more absorption of water by the collecting duct
why does a thicker medulla cause a higher concentration of urine
there is a longer loop of Henle so the sodium ion gradient in the medulla is therefore maintained for longer so more water is reabsorbed from the collecting duct by osmosis
