Renal 5 Flashcards
Explain the importance of urea recirculation in the medulla of the kidney. Where is urea reabsorbed and where is it secreted?
100% filtered at Bowman’s capsule
50% reabsorbed through isosmotic reabsorption with water at proximal tubule
An amount equal to that reabsorbed in the proximal tubule is secreted back into the medullary thin loop of Henle
At end of loop of Henle 100% of total filtered urea is in the tubule
Distal convoluted tubule and cortical collecting ducts impermeable to urea
About 60% of original amount of urea is reabsorbed in medullary collecting ducts (dependent on ADH)
All movements are passive
Explain why a high-protein diet can enable people to concentrate their urine better than people with low protein intake.
In order to create a concentrated urine, you would want to have ADH and hyperosmotic renal medulla. 50% of the concentraion comes from urea (other is NaCl)…so the higher intake of protein higher amount of urea more concentrated urine
malnutrition can thus cause impairment of urine concentrating ability
Identify the portions of the loop of Henle that
- reabsorb sodium and chloride
- permeable to water
- impermeable to water
- thin ascending limb is passive. thick limb uses secondary transport with Cl via NaKCl cotransporter at apical and NaK ATPase pump at basolateral
- thin descending limb
- thin/thick ascending limb
State which part of the nephron is responsible for countercurrent multiplication. Be able to recognize a correct description of this process.
Loop of Henle descending thin limb runs parallel and close to the ascending limb. Countercurrent is created to maintain a gradient of increasing osmolality from the cortex to the inner medulla (which helps for the reabsorption of water as needed). Descending water goes out. Ascending NaCl goes out.
Identify the kidney structure that performs countercurrent exchange.
Vasa Recta
State if countercurrent exchange involves essentially passive or active transport. How does the process of countercurrent exchange allow medullary blood flow and removal of some medullary interstitial fluid without causing the washout of the concentration gradients in the renal medullary interstitium?
The countercurrent exchange is done by the vasa recta. Passive transport allows NaCl and Urea into the vasa recta near the tip (bottom) of the loop. Water is forced out into the interstitium. As the tube comes back up, interstitial osmolality decreases and NaCl and Urea passively move out and water passively moves in. The blood entering venous circ. has a higher (slightly) osmolarity than the blood entering the vasa recta. (meaning more water will leave and avoiding washout)
Describe the effect of ADH (vasopressin) concentration on the cortical collecting ducts and the medullary collecting ducts. Which area of the nephron can develop the highest osmolarity in the presence of ADH?
Osmolarity of fluid in coritcal and medullary collecting ducts dependent on ADH. More ADH = more aquaporins = more water leaves = tubule fluid has higher osmolarity. The medullary collecting duct can have higher osmolarity bc of the surrounding interstitium.
Describe the compensatory responses to dehydration or overhydration. (Include changes in plasma osmolarity, brain osmoreceptors, atrial stretch receptors, ADH secretion, water excretion and thirst.)
- Dehydration: causes decreased blood volume but increased blood osmolarity. Tend to increase release of ADH (more bc of osmolarity). Brain osmoreceptors will shrink. Less firing by baroreceptors causes increased ADH release and sympathetic activity. Atria release less ANP in response to low BP. Increase in sympathetic activity increase release of renin and Ang II, which increases release of ADH.
- Overhydration: Opposite affects from above. Artia release more ANP. Decrease in sympathetic activity, renin, Ang II. Decrease in osmolarity of blood and release of ADH from posterior pituitary.
Explain how/why diabetes insipidus can cause the excretion of large amounts of dilute urine. Distinguish between central and nephrogenic diabetes insipidus.
- Central diabetes insipidus: do not make ADH
- Nephrogenis diabetes insipidus: lack either ADH receptors or the needed aquaporin
Without ADH, less water is reabsorbed and urine is more dilute
- Nephrogenis diabetes insipidus: lack either ADH receptors or the needed aquaporin
Briefly explain why some lung cancers are associated with changes in ADH level and water balance. What is SIADH?
SIADH = syndrome of inappropriate antidiuretic hormone secretion. Excessive release of ADH, results in hyponatremia (plasma Na lowered). Associated with small cell carcinoma of lung (tumor secretes ADH?)
Be able to give the effect of ethanol and morphine on the release of ADH.
- Ethanol: Decrease release of ADH
- Morphine: Increase release of ADH
