Urine concentration/fluid regulation Flashcards
What are the permeability characteristics of the thin descending limbs of Henle’s Loop
Concentrating segments they are permeable to water but impermeable to reabsorption of solutes. (Urea can be secreted into the tubule, further concentrating the tubular fluid.)
What are the permeability characteristics of the thick ascending limbs of Henle’s Loop?
Diluting segment. these segments are impermeable to water, but Na+-K+-2Cl- (NKCC-2) and Na/C cotransporters reabsorb electrolytes.
What is the osmolarity of the tubular fluid entering the distal tubule?
about 100 milliosmoles per liter
What stimulates the insertion of aquaporins into the membranes of the collecting ducts?
antidiuretic hormone
What makes it possible for solute free water to be reabsorbed into the UF at the descending limb on Henle and the CDs?
the osmolar concentration gradient within the medullary interstitial fluid and the presence of aquaporins
What is the osmolarity at the corticomedullary border?
at the deepest part of the medullary interstitium?
about 300 mosm/L
about 1200 mosm/L
What is the medullary countercurrent multiplier?
- As the UF goes through the descending loop of Henle, only H2O can be reabsorbed.
- When the UF gets the the ascending loop of Henle, electrolytes are actively reabsorbed, thus increasing the osmolarity of the interstitium.
- By increaseing the osmolarity of the interstitium, the water is more inclined to be reabsorbed at the descending loop of henly, so the more electrolytes that get reabsorbed, the more water does.
How is Na and fluid reabsorption regulated intrarenally?
- GFR- increased GFR=increased FL of Na, reabsorption amt throughout the tubule is about the same, thus more Na enters the loop of Henly, more Na is excreted and more H2O follows.
- Tubular fluid flow rate- too fast will disrpupt the osmolar gradient in medullary interstitium and cause higher Na and H2O excretion. too slow will cause less Na to be delivered to loop of Henly, reducing the ability to reabsorb H2O in CDs.
- baroreceptors- located in walls of afferent arterioles. When BP decreses, reduced stretch causes release of Renin.
- Medullary blood flow- Increased BF to vasa recta causes reduced concentration gradient in medullary Interstitium, leading to decreased solute and later H2O reabsorption; ability to concentrate urine is decreased
How is Na reabsorption controlled neurally?
- sympathetic nerves
- innervate afferent and efferent arterioles. During SNS stimulation, arterioles constrict, decreasing GFR and Na excretion
- RAAS
- Renin released by justaglomerular cells in response to low tubular Na concentration and low tubular flow rate.
- Aldosterone
- Aldosterone increases Na/K ATPases, allowing for more Na (and therefore H2O) reabsorption
- ANP
- Increases GR by dilating the afferent arteriole and constricting the efferent arteriole
- decreases Na reabsorption in DT
- Urodilatin
- Similar to ANP but produces in medullary DT
Who has the highest % body water?
lowest?
Infants- very littl fat
Elderly- more fat
Through what organs are fluids excreted?
Urinary tract (most)
bowels
lungs (exhalation)
skin (sweat)
What primarily controls the amount of fluid excreted in the urine?
- ADH
- Aldosterone
- ANP/BNP
Where does ADH come from?
- Made in the hypothalamus
- released from the posterior pituitary gland
What factors increase the release of ADH?
- Increased osmolality of ECF
- decreased circulating volume
- pain
- nausea
- physiologic and psychological stressors
Where does Aldosterone come from?
What stimulates its release?
Secreted by the adrenal cortex
Angiotensin II or increased concentration of potassium ions in plasma stimulates its release
