Regulation Of Body Fluid Osmolality Lecture

Question 1

Is the renal medulla hypertonic, hypotonic, or isotonic?

Answer 1

Hypertonic

Question 2

What is the maximum osmolality of the interstitium at the tip of the loop of Henle?

Answer 2

1200-1400 mOsmol/kg

Question 3

What is the osmolality of the fluid leaving the loop of Henle and is it hypertonic, isotonic, or hypotonic?

Answer 3

100 mOsmol/kg H20

Hypotonic

Question 4

What is the difference that the TAL maintains between the tubular fluid and the interstitium at any point along its length?

Answer 4

200 mOsmol/kg H20

Question 5

What is the descending limb of the loop of Henle highly permeable to?

Answer 5

H20

Question 6

What is the purpose of the vasa recta?

Answer 6

It supplies blood to the medulla and removes the water and solutes that are continuously added to the medullary interstitium

Question 7

What occurs if there is increased blood flow in the vasa recta?

Answer 7

It decreases the salt and solute transport by nephron segments in the medulla reducing its ability to concentrate the urine, since it dissipates the medullary gradient

Question 8

What areas are relatively impermeable to urea?

Answer 8

Thick ascending limb of the loop of Henle, the distal tubule, and the cortical collecting tubule

Question 9

Where is ADH synthesized?

Answer 9

Supraoptic and Paraventricular Nuclei in the hypothalamus

Question 10

From where is ADH secreted?

Answer 10

Posterior pituitary gland

Question 11

What do principal cells reabsorb and secrete?

Answer 11

Reabsorbs Na+, Cl-, and H20

Secretes K+

Question 12

What do intercalated cells reabsorb and secrete?

Answer 12

Reabsorb K+

Secretes H+

Question 13

In the absence of ADH, are the principal cells permeable or impermeable to water?

Answer 13

IMpermeable

Question 14

What is the mechanism of ADH on the principal cells?

Answer 14

Directs insertion of AQP-2 channels into the apical membrane allowing H20 permeability

Question 15

What is the effect of aldosterone?

Answer 15

It is able to increase ENaC channels which increases the amount of sodium being reabsorbed from the tubular fluid in exchange for secretion of K+

Question 16

What activates aldosterone?

Answer 16

High plasma K+ concentration or decrease in plasma Na+ concentration through the RAAS pathway

Question 17

What is the effect of hypothalamic osmoreceptors when the plasma is hypoosmotic?

Answer 17

It “turns” ADH off which leads to dilution of the urine

Question 18

What is the effect of Hypothalamic osmoreceptors when the plasma is hyperosmotic?

Answer 18

It “turns” ADH on and initiates the thirst response

Leading to concentrating urine and trying to get greater intake of fluids

Question 19

What are the values for plasma osmolality in an adequately hydrated person?

Answer 19

275-295 mOsm

Question 20

What are the values for a dehydrated person in plasma osmolality?

Answer 20

> 300 mOsm

Question 21

What is the cause of central/neurogenic diabetes insipidus?

Answer 21

An ability to produce or release ADH from the posterior pituitary can be caused by head injuries, infections, or can be congenital

Question 22

What is the treatment for central diabetes insipidus?

Answer 22

Desmopressin, a synthetic analog of ADH, which acts selectively on V2 receptors to increase water permeability in the late distal and collecting tubules

Question 23

What can lead to nephrogenic diabetes insipidus?

Answer 23

Loop diuretics that inhibit electrolyte reabsorption in the loop of Henle

Lithium and tetracyclines can impair the ability of the distal nephron segments to respond to ADH

Question 24

How do you distinguish between central and nephrogenic diabetes insipidus?

Answer 24

If you administer desmopressin and there is a response then it is central. If no response within 2 hours, then it is nephrogenic

Question 25

What is SIADH?

Answer 25

An excessive release of ADH, which causes inappropriate and excessive water retention

Question 26

What results due to SIADH/water retention?

Answer 26

Reduced plasma osmolality, dilutional hyponatremia, diminished aldosterone secretion, and elevated glomerular filtration rate

Question 27

What are the sx associated with diabetes insipidus?

Answer 27

High UO, low levels of ADH, HYPERnatremia, dehydrated, lose too much fluid, excessive thirst

Question 28

What are the sx for SIADH?

Answer 28

Low UO, high levels of ADH, HYPOnatremia, overhydrated, retain too much fluid, excessive thirst

Question 29

What are the causes and characteristics of hyponatremia?

Answer 29

Causes: drugs, pain, nausea, decreased effective arterial volume, strenuous exercise

Traits: high urine osmolality (>300)

Question 30

What are the causes and characteristics of hypernatremia?

Answer 30

Inadequate free water intake because of impaired access or impaired thirst

Traits: >600-800 urine osmolality

Question 31

What are the four mechanisms that can cause polyuria?

Answer 31

1. Increased intake of fluids with psychogenic causes
2. Increased GFR with hyperthyroidism, fever, and hypermetabolic states
3. Increased output of solutes as occurs in DM, hyperthyroidism, hyperparathyroidism, and use of diuretics
4. Inability of the kidney to reabsorb water in the DCT due to drugs or renal failure

Question 32

What is free water clearance?

Answer 32

The rate of free-water clearance represents the rate at which solute-free water is excreted by the kidneys

If + = h20 is excreted
If - = h20 is conserved

Question 33

What is the ratio of urine osmolality and what does it indicate?

Answer 33

It is urine osmolality to plasma osmolality which determines the ability of the kidneys to concentrate or dilute urine

Uosm: Posm >1 indicates kidneys are able to concentrate urine

Uosm: Posm =1 urine is iso-osmotic with plasma

Uosm: Posm <1 indicates the kidneys are able to dilute urine

Question 34

Where does ADH bind to?

Answer 34

It binds to the V2 receptor (a Gs GPCR) on the basolateral membrane of the collecting duct