The Role Of Nephrones Flashcards
Explain why a person with untreated diabetes would have glucose in their urine.
- they would have a high glucose con in their blood
- this means a lot of glucose would be filtered out of the blood during ultrafiltration, producing a filtrate with high glucose con
- during selective reabsorbtion in the PCT, the co-transport proteins that are responsible for reabsorbing glucose will be saturated.
- this means that not all of the glucose from the filtrate can be reabsorbed and some will remain in the urine.
what is the main role of the kidneys?
To filter blood and produce urine which:
- removes harmful waste products (urea)
- controls water potential of the blood (osmoregulation)
what do the afferent and efferent artioles do?
- Afferent arteriole supplies blood to the glomerulus
- Efferent arterioles branch into a network of capillaries that surround the nephron
-this ensures that the whole structure of the nephron has a short diffusion distance to blood.
Describe ultrafiltration
- high hydrostatic pressure in the glomerulus is created because the lumen of the efferent arterial is smaller than the afferent.
- this creates a pressure difference between the glomerulus and bowman’s capsule, causing substances in blood to move down the pressure gradient into the Bowman’s capsule.
- only glucose, ions, water and urea can pass through the pores in the endothelium, the basement membrane and the podocytes into the Bowman’s capsule. they are now called the glomerulus filtrate
- other larger molecules like proteins and red blood cells stay in the blood
describe selective reabsorption of glucose and sodium ions in the PCT.
- there are sodium ions in the PCT and the epithelial cells
-sodium ions move into the capillaries via active transport - creating a concentration gradient between PCT and capillaries.
- co-transport proteins move more sodium to the epithelial cells from PCT via transport proteins
- co-transport proteins also move glucose into epitheliul celss,
- sodium ions and glucose then move down a concentration gradient into the blood
describe the selective reabsorption of water in the PCT
- when glucose and sodium ions move out of the PCT, the water potential increases in the PCT,
-when they move into the epithelial cells the water potential decreases in the cells. - this creates a water potential gradient between the PCT and epithelial cells.
- therefore water moves from the PCT lumen into the PCT by osmosis
- then it moves into the blood by osmosis.
4 adaptations of selective reabsorption
PCT contains mitochondria
- needed to generate the ATP used in the active transport of sodium ions from epithelial cells to capillaries
Large number and variety of co-transport proteins
- allows for selective reabsorption
- increases amount of sel. rea. keeping the rate of transport high
- wide variety ensures many useful substances are reabsorbed as co transport is not limited to just glucose.
Substances only need to pass through the epithelium cell between the lumen and blood
- short diffusion distance increases rate of reabsorption.
What happens in the Loop of Henlee (ascending limb)
- ascending limb is impermeable to water
-contains enzymes that actively transport sodium ions out into the medulla - water potential of the medulla decreases, lower than the loop of Henlee
- creates a water potential gradient
What happens in the Loop of Henlee (descending limb)
- permeable to water
sodium ions enter medulla - water potential of medulla is lower that loop of henlee
- therefore water moves from descending limb into the medulla via osmosis down a conc. gradient.
describe the counter current multiplier effect
- Countercurrent flow in the loop of Henle enhances the exchange of substances compared to parallel flow.
- Filtrate in the collecting duct with a lower water potential meets interstitial fluid with an even lower water potential.
- This creates a small but continuous water potential gradient along the collecting duct, allowing water to steadily flow into the interstitial fluid.
- Around 80% of the water is reabsorbed into the interstitial fluid and then into the blood.
- In a parallel flow system, less water would enter the blood compared to the countercurrent system.
what effect does having a longer loop of henlee have ?
- more sodium ions are actively transported out of the ascending limb
- greater water potential in the medulla
- more water leaves the descending limb by osmosis
- more water reabsorbed into the blood
describe how the sodium ions and glucose are reabsorbed at the loop of henlee
- in the loop of henlee, sodium ions are actively transported out of the ascending limb and into the medulla
- this decreases the water potential in the medulla
-creating a water potential gradient - so water moves out the descending limb abd ito medula via osmosis, down a conc gradient
- this is an example of the counter current muchanisim/ multiplier effect
- in the medulla, both the sodium ions and water are reabsorbed into the blood
describe response to increase in blood water potential
- osmoreceptors detect increase in water potential so hypothalamus produces less ADH
- posterior pituitary gland secretes less ADH into the blood
- less ADH attaches to receptors on the collecting duct and DCT
- decreasing the amount of aquaporins,
- decreasing the permeability of cells to water
- less water moves into medulla
- urine is higher in volume and less concentrated
describe response to decrease in blood water potential
- osmoreceptors detect decrease in water potential so hypothalamus produces more ADH
- posterior pituitary gland secretes more ADH into the blood
- more ADH attaches to receptors on the collecting duct and DCT
- increasing the amount of aquaporins,
- increasing the permeability of cells to water
- more water moves into medulla
- urine is lower in volume and more concentrated
why is an optimum concentration of water and salts
is maintained in the blood?
to ensure a fairly constant water potential of blood
plasma and tissue fluid.
define osmoregulation
the homeostatic control of the water potential of blood
what is the structure of the mammalian kidney
-fibrous capsule
- cortex
- medulla
- renal pelvis
- ureter
- renal artery
- renal vein
what is the functional unit of the kidneys?
the nephron
fibrous capsule
- an outer membrane that protects the kidney
cortex
- a lighter coloured outer region made up of renal (Bowman’s) capsules, convoluted tubules and blood vessels
medulla
- a darker coloured inner region made up of loops of
Henle, collecting ducts and blood vessels
renal pelvis
- a funnel-shaped cavity that collects urine into the ureter
ureter
- a tube that carries urine to the bladder
renal artery
- supplies the kidney with blood from the heart via the aorta
renal vein
returns blood to the heart via the vena cava.
what effect does ADH have on the DCT and the collecting duct
- specific protein receptors on the cell- surface membrane of DCT and collecting duct bind to AH molecule
- activating an enzyme called phosphorylase within the cell
- activation of phosphorylase causes vesicles that contain aquaporin channel proteins to fuse with cell surface membrane.
this increases the number of aquaporins increasing the cells permeability to water - therefore more water can move out of the DCT and collecting duct cells into the medulla.
a fall in solute concentration of the blood can be caused by;
- large volumes of water being consumed
- salts used in metabolism or excreted not being replaced in the diet
One symptom of diabetes is dehydration. From
your knowledge of how water is reabsorbed in the
collecting ducts, explain why diabetes might cause
dehydration.
The reabsorption of water from the collecting ducts
depends on there being a large water potential
gradient between the fluid in the collecting duct and that in the blood capillaries. The presence of glucose in the fluid in the collecting duct reduces this gradient and leads to more water being lost in urine leading to dehydration.
