Water Balance

Question 1

What are the 3 regulatory hormones of body fluid osmolarity?

Answer 1

1. ADH
2. RAAS
3. ANP

Question 2

What are the three man mechanisms of ADH?

Answer 2

1. Increase H20 permeability in late Distal tubule and collecting duct
2. Increase Urea permeability inner medullary collecting duct
3. Increase Na+ Reabsorption in thick ascending LOH

Question 3

What are the three key signs of severe dehydration?

Answer 3

Obtundation, sunken eyes, and poor skin turgor

Question 4

What is normal ECF/ICF fluid osmolarity?

Answer 4

280-290 mOsM

Question 5

What happens to EC/IC fluid after gaining hypotonic fluid?

Answer 5

EC: INC Volume, DEC Osmolarity

IC: INC volume, DEC Osmolarity

Question 6

What happens to EC/IC fluid after gaining hypertonic fluid?

Answer 6

EC: INC Volume, INC Osmolarity

IC: DEC Volume, INC Osmolarity

Question 7

What happens to EC/IC fluid after losing isotonic fluid?

Answer 7

EC: Loss of Volume; NO Change in Osmolarity

IC: No change

Question 8

What happens to EC/IC fluid after losing hypotonic fluid?

Answer 8

EC: DEC Volume, INC Osmolarity

IC: DEC Volume, INC Osmolarity

Question 9

What happens to EC/IC fluid after losing hypertonic fluid?

Answer 9

EC: DEC Volume + OSmolarity

IC: DEC Osmolarity + INC Volume

Question 10

What is the empirical formula for calculating plasma osmolality?

Answer 10

PO = 2(N + K) + (BUN/2.8) + (Glucose/18)

Question 11

Where is ADH produced?

Answer 11

Supraoptic nuclei of hypothalamus

Question 12

How does ADH result in Greater water permeability?

Answer 12

Activates insertion of AQP2 on apical membrane

AVP -> V2 —> INC cAMP —> INC AQP2

Question 13

Why does a solar it’s in the inner medulla increase with ADH despite increased water reabsorption?

Answer 13

Urea Recycling

• ADH H20 reabsorption —>Urea concentration builds ruses and reaches maximum at inner level of medulla
• ADH enables Urea diffusion into interstitium —> Build up of corticomedullary osmotic gradient —> INC H20 Reabsorption

Question 14

How do ascending and descending vasa Recta differ anatomically?

Answer 14

Ascending are Fenestrated and more permeable to fluids.

Question 15

What are the main regulators of ADH secretion?

Answer 15

1. Plasma Osmolarity (Most sensitive)
2. Decrease in ECF volume/pressure (Not very sensitive)
3. Other hormones (Angiotensin II or ANP)
4. Temperature and stress
5. Pain, nausea, vomiting, and ethanol

Question 16

What is characterized by diuretics, polyuria, polydypsia, hypervolemic shock, and ADH deficiency?

Answer 16

Diabetes insipidus

Question 17

What are the two types of diabetes insipidus?

Answer 17

1. Central: insufficient ADH; Head injury, CNS infections, pituitary stroke, cranipharyngioma, etc
2. Nephrogenic: Decreased renal response to ADH; Abnormal vasopressin receptors or AQP in renal tubule

Question 18

What is SIADH

Answer 18

• Excess ADH —> Water retention
• Hyponatremia Andi water intoxication
• Lung disease, CNA disease, or drugs like ecstasy

*** Paradoxical High Urine Osmolarity due to Na+ excretion