tructure and function of the human kidney. Flashcards
Describe the formation of glomerular filtrate
- High hydrostatic pressure in glomerulus
○ As diameter of afferent arteriole (in) is wider than efferent arteriole (out) - Small substances eg. water, glucose, ions, urea forced into glomerular filtrate, filtered by:
a. Pores / fenestrations between capillary endothelial cells
b. Capillary basement membrane
c. Podocytes - Large proteins / blood cells remain in blood
Describe the reabsorption of glucose
by the proximal convoluted tubule
- Na+ actively transported out of epithelial cells to capillary
- Na+ moves by facilitated diffusion into epithelial cells down a concentration gradient, bringing
glucose against its concentration gradient - Glucose moves into capillary by facilitated
diffusion down its concentration gradient
water reabsorp by pct
● Glucose etc. in capillaries lower water potential
● Water moves by osmosis down a water potential
gradient
Describe and explain how features of the cells in the PCT allow the rapid reabsorption of glucose into the blood
● Microvilli / folded cell-surface membrane → provides a large surface area
● Many channel / carrier proteins → for facilitated diffusion / co-transport
● Many carrier proteins → for active transport
● Many mitochondria → produce ATP for active transport
● Many ribosomes → produce carrier / channel proteins
Suggest why glucose is found in the urine of an untreated diabetic person
Blood glucose concentration is too high so not all glucose is reabsorbed at the PCT
● As glucose carrier / cotransporter proteins are saturated / working at maximum rate
Explain the importance of maintaining a gradient of sodium ions in the medulla (concentration increases further down)
● So water potential decreases down the medulla (compared to filtrate in collecting duct)
● So a water potential gradient is maintained between the collecting duct and medulla
● To maximise reabsorption of water by osmosis from filtrate
Describe the role of the loop of Henle in maintaining a gradient of sodium ions in the medulla
In the ascending limb:
○ Na+ actively transported out (so filtrate concentration decreases)
○ Water remains as ascending limb is impermeable to water
○ This increases concentration of Na+ in the medulla, lowering water potential
2. In the descending limb:
○ Water moves out by osmosis then reabsorbed by capillaries (so filtrate concentration increases)
○ Na+ ‘recycled’ → diffuses back in
Suggest why animals needing to conserve water have long loops of Henl
● More Na+ moved out → Na+ gradient is maintained for longer in medulla / higher Na+ concentration
● So water potential gradient is maintained for longer
● So more water can be reabsorbed from collecting duct by osmosis
Describe the reabsorption of water by the distal convoluted tubule and collecting ducts
● Water moves out of distal convoluted tubule & collecting duct by osmosis down a water potential gradient
● Controlled by ADH which increases their permeability
Osmoregulation
Control of water potential of the blood (by negative feedback)
Describe the role of the hypothalamus in osmoregulation
- Contains osmoreceptors which detect increase OR decrease in blood water potential
- Produces more ADH when water potential is low OR less ADH when water potential is high
Describe the role of the posterior pituitary gland in osmoregulation
Secretes (more / less) ADH into blood due to signals from the hypothalamus
Role of adh in osmoreg
- Attaches to receptors on collecting duct (and distal convoluted tubule)
- Stimulating addition of channel proteins (aquaporins) into cell-surface membranes
- So increases permeability of cells of collecting duct and DCT to water
- So increases water reabsorption from collecting duct / DCT (back into blood) by osmosis
- So decreases volume and increases concentration of urine produced
