Control Abnormalities Body Water

Question 1

What happens if you add more water to a Na+ solution?

Answer 1

→ Hyponatremia

→ Concentration decreases

Question 2

What happens if you remove water from a Na+ solution?

Answer 2

→ Hypernatremia

→ Concentration increases

Question 3

What does osmolarity relate to?

Answer 3

→ Number of particles per unit volume of fluid

Question 4

What does osmolality relate to?

Answer 4

→ Number of particles per unit weight of fluid

Question 5

What is the equation for estimating plasma osmolarity?

Answer 5

→ 2[Na+] + 2[K+] + [glucose] + [urea]

Question 6

What is normal plasma osmolality?

Answer 6

→ 275-295 mOsm kg-1

Question 7

What does hypernatremia mean?

Answer 7

→ hyper osmolality

→ too little water

Question 8

What does hyponatremia mean?

Answer 8

→ hypo-osmolality

→ too much water

Question 9

What happens during diabetes mellitus?

Answer 9

→ Diabetes mellitus the glucose concentration rises
→ It contributes to the osmolality
→ high glucose concentration is filtered into the kidney tubule

Question 10

What are osmoreceptors?

Answer 10

→ Sensory receptors located in the hypothalamus sense changes in osmolality of ECFV

Question 11

What does an increase in osmolality stimulate?

Answer 11

→ Thirst

→ Secretion of vasopressin

Question 12

How does ADH regulate plasma osmolality?

Answer 12

→Controlling water excretion and reabsorption

Question 13

What does concentrated urine tell you about ADH levels?

Answer 13

→ ADH relatively high

Question 14

Describe the loop of henle

Answer 14

→ Tubular fluid is iso-osmotic in the PCT
→ along the descending limb there is active reabsorption of Na+
→ Water moves out passively
→The loop has very concentrated interstitial fluid
→ in the ascending loop there is dilution of the tubular fluid as there is reabsorption of NaCl
→ at the DCT the tubular fluid is the most dilute

Question 15

What is the effect of ADH on the collecting duct?

Answer 15

→ ADH binds to basolateral receptors

→ more water channels inserted in the luminal membrane

Question 16

What is the mechanism ADH uses?

Answer 16

1) ADH binds to the receptor V2 on principal cells
2) Receptor activates cAMP
3) inserts AQP2 into apical membrane
4) V1 receptors on vascular smooth muscle - vasoconstriction but only significant with very high ADH levels- increases systemic BP

Question 17

What is the function of ADH under normal conditions?

Answer 17

→ Osmoregulation

Question 18

What does a large drop in arterial pressure cause?

Answer 18

→ release of ADH

Question 19

Why is ADH secreted during hypovolaemia?

Answer 19

→ retention of water to increase blood volume

Question 20

What happens to plasma osmolality during severe haemorrhage?

Answer 20

→ Loss of BP is sufficient to stimulate ADH
→ decrease in plasma osmolality
→ ADH effect is always dilutional (adds pure water)

Question 21

What are the two systems activated during hypovolaemia?

Answer 21

→ RAAS occurs first

→ ADH secretion happens later

Question 22

What is the first line of defense against dehydration?

Answer 22

→ Thirst

Question 23

What kind of thirsts are there?

Answer 23

→ hyperosmotic

→ hypovolemic

Question 24

What is hyperosmotic thirst?

Answer 24

→ after eating a lot of salt

Question 25

What is hypovolemic thirst?

Answer 25

→ After losing a lot of blood

Question 26

What is the metabolic waste product in the kidney excreted as?

Answer 26

→ in a solute form | → called the solute load

Question 27

How do you estimate the solute load?

Answer 27

→ body weight x 10

Question 28

How do you work out how much water is needed to excrete the solute load?

Answer 28

→ divide the urine concentration by the solute load

Question 29

What is water excess (hyponatremia)?

Answer 29

→ excessive water intake | → impairment in renal water excretion

Question 30

What is water depletion (hypernatremia) ?

Answer 30

→ Insufficient water intake | → Impairment in renal water reabsorption

Question 31

What are situations where water intake is continued but ADH is suppressed?

Answer 31

``` → vomiting , diarrhoea → Ecstasy → Ectopic secretion of ADH (SIADH) → Hypocortisolism → Primary adrenal insufficiency ( Addisons) ```

Question 32

What is missing in people with Addisons?

Answer 32

→ Loss of cortisol | → Loss of aldosterone

Question 33

What is the effect of Addisons?

Answer 33

→ Lack of sodium retention → Water is lost with it → hyponatremia due to water intake

Question 34

What are the major causes of SIADH(syndrome of inappropriate antidiuretic hormone secretion )?

Answer 34

→ TUMOR - ectopic production of ADH → CNS disturbance - trauma, stroke, infection → DRUGS - carbamazepine, prozac

Question 35

What are signs of SIADH?

Answer 35

Low plasma sodium → Low plasma osmolality → High urine osmolality

Question 36

How can water depletion from decreased intake of water occur?

Answer 36

→ Infants → Elderly → Individuals in a coma → Individuals with no access to water

Question 37

How can water depletion from increased loss of water through the kidney occur?

Answer 37

→ Diabetes mellitus | → Impairment in ADH release

Question 38

What are nephrogenic causes of diabetes insipidus?

Answer 38

→ Mutation of ADH receptor → Mutation of ADH dependent H2O channels → Renal disease → Lithium

Question 39

What are central causes of diabetes insipidus?

Answer 39

→ genetic mutations → head trauma → disease of the hypothalamus /pituitary region

Question 40

What is the ECF divided into?

Answer 40

the interstitial compartment and the plasma compartment. Movement between the two is controlled by starling’s forces

Question 41

What happens when pure water was added to ECF?

Answer 41

initially the concentration in ECF will be diluted but then this creates osmotic gradient between ICF and ECF resulting in movement of water into ICF.

Question 42

How is the osmolarity of the ECF adjusted?

Answer 42

adding or removing water, not solute

Question 43

What happens as a defence against dehydration with ADH?

Answer 43

→Net water loss increases ECF osmolarity →Changes detected by osmoreceptors in anterior hypothalamus →Project to magnocellular neurons of paraventricular and supraoptic nuclei of hypothalamus →PVN and SON neurons release ADH from their axon terminals in posterior pituitary

Question 44

What is the normal range for ADH?

Answer 44

Normal range 285-295 mOsm/kg Above this range small changes in osmolality produce large changes in ADH secretion

Question 45

What happens to stimulate thirst in defence against dehydration?

Answer 45

Changes detected by osmoreceptors in anterior hypothalamus →Strong desire to drink when plasma osmolality ≥295 mOsm/kg →Large (10-15%) drops in blood volume/pressure →Angiotensin 2 acting on hypothalamus in significant drop of blood volume

Question 46

What other receptors reduce thirst?

Answer 46

Oropharyngeal and upper gastrointestinal receptors reduce thirst on drinking- unless osmolarity is brought back within controlled range, thirst sensation returns

Question 47

What does principle of electroneutrality dictate?

Answer 47

dictates that a molar equivalent number of anions must be present →Mainly Cl-, significant amount HCO3-, small contribution from other inorganic and organic anions

Question 48

Causes of hypernatremia in gain of sodium...

Answer 48

→Iatrogenic- mistakes in i.v →Excess ingestion (rare) →Excess mineralocorticoid activity

Question 49

What is diabetes insipidus?

Answer 49

a condition characterized by large amounts of dilute urine and increased thirst.

Question 50

What happens in severe volume depletion?

Answer 50

the retention of water will lead to hyponatraemia

Question 51

Why is ADH less effective to retain water than RAAS?

Answer 51

ADH promotes retention of pure water which will distribute between ICF and ECF so effect is weaker

Question 52

What happens in hypervolemic hyponatremia?

Answer 52

→Can occur when total sodium is increased, but total water increased more →Example: congestive heart failure →RAAS ‘thinks’ body is hypovolemic →Na/water retention (volume expansion) Volume expansion is ineffective because perturbed Starling forces (excess capillary filtration): oedema →If low volume signals activate ADH hyponatremia will ensue →If continued intake of water then hyponatremia