Reg of Body Fluid Osmolality

Question 1

1st Step

Answer 1

Tubular fluid enters the descending limb from the PT, it is isotonic

Question 2

2nd Step

Answer 2

The active salt pumps in the TAL transport NaCl out of the lumen until the surrounding interstitium fluid is 200mOsm/L more concentrated than the tubular fluid

Water can not follow from the TAL

Net diffusion of water occurs int he descending limb into the interstitium

Question 3

3rd Step

Answer 3

Passive movement of water continues until the the osmolarities of the fluid in the descending limb and the interstitium are equilibrated

Question 4

4th Step

Answer 4

A mass of 200mOsm/L fluid exits the TAL and enters the DT. A new mass of 300mOsm/L, isotonic, fluid enters the descending limb.

At bottom of limb, a comparable mass of 400 moves around the bottom of the loop

Question 5

5th Step

Answer 5

Additional flow of fluid into the LoH from the PT, which causes the hyperosmotic fluid previously formed in the descending limb to flow into the ascending limb

Ions are pumped from the ascending limb until a 200 mOsm/L gradient is established. Interstitial osmolarity rising to 500mOsm/L

Question 6

7th Step

Answer 6

Steps 4-6 are repeated until max concentration is 1200-1400 mOsm/L at the bottom of the loop

Question 7

Vasa Recta

Answer 7

Blood supply to the medulla, is highly permeable to salute and water

removes water and solutes that are continuously added to the medullary interstitium by the nephron

Ability to maintain gradient is flow dependent

Increase in flow dissipates the medullary gradient, called medullary washout

Decrease in blood flow decreases salt and solute transport by nephron, reducing ability to concentrate urine

Question 8

Urea Recycling

Answer 8

Urea reabsorption occurs in medullary CD and thin descending limb

UT-A1 and UT-A3—> transporters in medullary CD
UT-A2 in thin limb

Some of the urea that moves into the medullary interstitium eventually diffuses into the thin loop and passes upward thru the TAL to the DT and eventually CD

Question 9

ADH

Answer 9

Secreted in response to osmotic stims, sensed by supraoptic and paraventricular nuclei of hypothalamus

Secreted from posterior pituitary gland

Question 10

Osmoreceptors

Answer 10

Sensitive to small changes in plasma osmolality -1-2% can cause release of ADH

Activate ADH path before thirst path

Question 11

Aldosterone

Answer 11

Release from adrenal cortex

Increase ENaC channels, which increases the amount of Na being reabsorbed

Increases reabsorption of Na and secretion of K

Question 12

Aquaporin-2 Insertion

Answer 12

Aquaporin channels are inserted into the apical membrane of principal cells

Less ADH=Less aquaporin insertion

Question 13

Central Diabetes Insipidus

Answer 13

Inability to release ADH

Tx by desmopressin

Question 14

Nephrogenic DI

Answer 14

Inability of kidneys to respond to ADH

Either failure of the countercurrent mechanism or failure of the distal and collecting tubules to respond to ADH

Question 15

SIADH

Answer 15

Excessive release of ADH, which causes excessive water retention and disrupting the electrolyte balance

Fluid shifts into the cells causing them to swell

Body holds on to electrolyte free water

Major cause of low sodium levels

Water is retained while Na is excreted

Question 16

Hyponatremia

Answer 16

Most abundant electrolyte disturbance

Represents an excess of water relative to solute in the body

Usually results from ADH in the kidney to diminish free water excretion

Question 17

Hypernatremia

Answer 17

Deficit of free water relative to solute

Most adults also have concurrent volume depletion

Question 18

Water diuresis

Answer 18

Icnerase water excretion without corresponding increase in salt ecretion

Primary cause = increased intake of water, polydipsia, DI

Question 19

Solute (osmotic) diuresis

Answer 19

Increase water excretion concurrent with increased salt excretion

Primary cause = significant increase in salt present in the tubular fluid

Question 20

Polyuria

Answer 20

Passage of excessive quantity of urine and it implies water or solute diuresis

Question 21

Mechanisms that cause polyuria

Answer 21

1) Increased intake of fluids as in psychogenic causes, stress and anxiety
2) Increased GFR as in hyperthyroidism, fever, hypermetabolic states
3) Increased output of solutes as occurs in DM, hyperthyroidism, hyperparathyroidism, use of diuretics
4) Inability of the kidney to reabsorb water in DCT as in CDI, NDI, drugs and chronic renal failure

Question 22

Free water clearance

Answer 22

Represents the rate at which solute-free water is excreted by the kidneys

When urine osmolarity is greater than plasma osmolarity, free water clearance will be negative, indicating water conservation