Renal structure and function 2 Flashcards
What are the different types of nephrons?
- Cortical
- Juxtamedullar
What is the difference between the 2 types of nephrons?
- Cortical have loops of Henle in renal medulla near junction with renal cortex
- Juxtamedullary have their loops of Henle deep in renal medulla (glomeruli close to medulla but still in cortex)
What is the vascular arrangement of cortical nephrons?
Peritubular capillaries
What is the vascular arrangement of the juxtamedullary nephrons?
Have the vasa recta
Which of the nephrons concentrate the urine?
Juxtamedullary nephrons
What is the function of the loop of Henle?
Confer ability to produce concentrated urine
What is the permeability of the descending limb of the Loop of Henle?
- Permeable to water
- Via aquaporin-1
What is the permeability of the ascending limb of the Loop of Henle?
- Permable to solutes
- Impermeable to water
If an animal is dehydrated but is producing iso-osmolar urine what does this suggest and why?
- Proximal tubule carries out bulk removal of volume so start of loop of iso-osmotic
- If there is no change to the urine but animal is dehydrated, suggests kidney failure
- Not concentrating the urine even though is dehydrated
Give a general overview of the movement of solutes and water through the Loop of Henle
- Descending limb pumping out water (aquaporin-1), pumping out water -> hypertonic at end of loop
- Ascending limb impermeable to water, pumping out solutes, becomes dilute again
- Generates gradient in the interstitium
What is the tonicity of the medullary interstitium and how is this acheived?
- Hypertonic
- Countercurrent multiplier and countercurrent exchange, maintained by vasa recta
Describe the countercurrent multiplier system in the Loop of Henle
- Descending loop permeable to water, not solutes
- Ascending loop permeable to solutes not water
- Interstitial osmolarity elevates as go deeper, drawing water out of descending
- Solute concentration of fluid in ascending limb higher, more ions pumped out
- Increases interstitial osmolarity more, more water drawn out of descending
- U-shaped vasa recta prevents dissipation of this gradient
Describe the countercurrent exchange in the Loop of Henle
- Descending limb of vasa recta: as descends through high osmolarity water out of capillary, NaCl in
- Ascending: up through hypotonic, solutes out, more water in
- Result is no net change in medullary gradient
What is the function of the counter current mechanism?
- Concentration then dilution as pass through loop
- Establishes vertical gradient through kidney to enable production of concentrated urine
- Provides mechanisms for producing dilute urine
Explain how urea acts to support the generation of the renal medullary concentration gradient
- Is a weak osmolite
- Requires water to be excreted
- Recycling of urea maintains medullary gradient needed for counter current multiplier
Describe the passage of urea in the collecting duct
- Nephron impermeable to urea until inner medullary portion of collecting duct
- Tubular urea more concentrated as water removed
- Lower collecting duct ura passively reabsorbed via urea transporters (ADH sensitive)
- Diffuses into interstitial fluid if necessary
What are the main water outputs in the body?
- Kidneys (main one)
- Lungs
- Faeces
- Skin
- Sweat
What are the main water inputs into the body?
- Drinking (main one)
- Metabolic water
What is body water controlled by?
- Thirst (mostly)
- ADH
- Aquaporins
What, in general, do the water control systems respond to?
Changes in ECF osmolality and changes in blood volume
What is thirst controlled by?
- Osmoreceptors in hypothalamus
- Stimulate thirst in response to concentrated ECF
- Degree of stimulus leads to modification of firing of neurons
What does urine specific gravity measure?
The weight of solids in water
What is the relationship between USG and osmolality?
- Osmolality is the number of dissolved osmoles in a kg of water
- USG and osmolality usually change in parallel
- Diverge when large and heavy molecules (e.g. glucose, proteins) are present in urine
What is hypersthenuria?
Concentrated urine - lots of solutes, not much water