Session 5 Flashcards
(10 cards)
What nephrons are responsible for water balance?
What main feature?
Juxtamedullary
Vas’s recta bed of capillaries running parallel down the LOH.
Describe two parts to LOH
Descending limb-not permeable to NA but highly permeable to h20 due to aquaporins. So osmolality is high.
Ascending- not permeable to water as no aquaporins but has a NAKCC transporter bringing them into interstitium making the lumen hypoosmotic.
How does urea get into the interstitium?
Where is urea recycled?
What happens to urea recycling under the influence of ADH?
Via a sodium dependent co-transporter.
In medullary CD cells as cortical is impermeable. So diffused back into LOH.
Urea recycling increases and fractional excretion decreases.
Role of the vasa recta?
Acts as a counter current exchanger maintaining the concentration gradient produced by the LOH.
Balance between not washing out gradient whilst supplying kidney tissues with nutrients and oxygen.
How does the Vasa recta achieve its balance?
What is the VR a branch of?
It has a low slow blood flow. So delivers nutrients whilst maintaining medullary hypertonicity.
Moreover flow direction is opposite to tubular flow.
The efferent Arterioles
How does the VR work?
Hair pin config with same exit/entry. Down ascending limb gaining osmoles then up descending drawing in the h20. As moving slowly blood can equilibriate at each stratification level minimising washout.
What senses change in plasma osmolarity?
How does a lower bp effect osmolarity response?
Osmorecptora in the hypothalamus (OVLT) with fenestrated endothelium exposed directly to systemic blood flow. Gives urine concentration (via ADH) and thirst as the two efferent pathways.
Set point is shifted to lower osmolarity values. As volume is more important than osmolarity.
What is central diabetes insipidous?
Nephrogenic diabetes insipidous?
Plasma ADH levels are too low from brain injury or tumour to pit. Large quantity of urine as not properly reabsorbed.
Acquired insensitivity of kidney to ADH. Same problem so ADH injections required.
SIADH?
Too much ADH from PP causing dilusional hyponatraemia (low NA) as total body fluid is increased.
Of the collecting duct which face needs ADH to express its aquaporins?
The apical face
