Physiology - Endocrine Control of Body Fluid Volume and Composition

Question 1

The tubular fluid leaving the ascending loop of henle is ____________

Answer 1

The tubular fluid leaving the asceneding loop of henle is hypo-osmotic

Question 2

Where does the collecting duct originate?

Answer 2

Cortex

(then descends into the medulla)

Question 3

Hormones such as vasopressin affect which cells in the nephron?

Answer 3

Those of the distal tubule and collecting duct

Question 4

What are the key hormones which regulate fluid and salt regulation the the distal tubule and collecting duct?

Answer 4

Antidiuretic hormone

Aldosterone

Atrial natriuretic hormone

Parathyroid hormone

Question 5

What affect does ADH have?

Answer 5

Increases water reabsorption

Question 6

What affect does parathyroid hormone have?

Answer 6

Calcium reabsorption and phosphate excretion

Question 7

What effect does atrial natriuretic hormone have?

Answer 7

Reduces sodium reabsorption

Question 8

What effect does parathyroid hormone have?

Answer 8

Increases Calcium reabsorption

Decreases phosphate reabsorption

Question 9

The corticomedullary gradient is set up by which two things?

Answer 9

Salt and urea

Question 10

The distal tubule has what type of permeability to water and urea?

Answer 10

Low

Question 11

The distal tubule has two segments, which is each responsible fore reabsorbing?

Answer 11

Early distal tubule: Na+/K+/2Cl- = NaCl

Late distal tubule: Ca2+, Na+, K+ (K+ is secreted under influence of aldosterone, but in the basal state, reabsorbed)

Question 12

What are the two key properties of the late collecting duct?

Answer 12

Low ion permeability

Permeability to water and urea (influenced by ADH)

Question 13

Where is ADH synthesised?

Answer 13

Supraoptic and paraventricular nuclei in hypothalamus

Transported down nerves to terminals where it is stored and then secreted from granules in posterior pituitary

Question 14

How does vasopressin (ADH) affect the distal tubule and late collecting duct

Answer 14

Type 2 vasopressin receptor on basolateral membrane

Cell signalling response

Increase in cAMP

Insertion of aquaporins at apical membrane

Increases reabsorptive capability of cells to water

Question 15

What happens to the aquaporins on the apical membrane of the collecting duct cells when there is no vasopressin?

Answer 15

They are internalised

Question 16

High concentrations of ADH results in what?

Answer 16

Hypertonic urine

(concentrated urine, low volume)

Question 17

Why does water leave the distal tubule and collecting duct?

Answer 17

Osmosis

In order to match the high osmolarity created by the corticomedullary gradient

(this occurs to different degrees depending on the conc of ADH)

Question 18

Without ADH, the distal tubule and collecting duct are essentially ___________ to water reabsorption

Answer 18

Without ADH, the distal tubule and collecting duct are essentially impermeable to water reabsorption

Question 19

Why can ADH only affect water reabsorption and not solute reabsorption?

Answer 19

Due to ADH only affecting aquaporin channel insertion into apical membranes

Question 20

If there is a severe decrease in ECF (e.g. haemorrhage) which receptors can detect this?

Answer 20

Stretch receptors in left artria

(then increase secretion of ADH)

Question 21

What is the second effect of ADH which acts only in severe decreases in ECF?

Answer 21

Arteriolar vasoconstriction

Question 22

What are the two types of diabetes insipidus?

Answer 22

Central DI

Nephrogenic DI

Question 23

What is the cause of central DI?

Answer 23

Unable to produce or secrete ADH

Question 24

What is the cause of nephrogenic DI?

Answer 24

Failure of ADH produced to have an impact on target cells

Question 25

What is the treatment for a) Central DI b) Nephrogenic

Answer 25

a) ADH replacement b) Drugs to reduce urine output

Question 26

Which drug can induce nephrogenic DI?

Answer 26

Lithium | (around 20% of long term users)

Question 27

Nicotine will _________ ADH release and alcohol will _________ it

Answer 27

Nicotine will **stimulate** ADH release and alcohol will **reduce** it

Question 28

When will aldosterone be secreted?

Answer 28

1. Rising potassium or falling sodium in the blood 2. Activation of RAAS system

Question 29

What is the action of aldosterone?

Answer 29

Stimulates sodium reabsorption and potassium secretion This raises blood pressure and blood volume as water follows sodium

Question 30

An increase which ion will stimulate the adrenal cortex?

Answer 30

Potassium

Question 31

A decrease in which ion promotes the indirect secretion of aldosterone and by which means?

Answer 31

Sodium Juxtaglomerular apparatus detects low sodium levels (at macula densa)

Question 32

What are the actions of angiotensin II?

Answer 32

Increases ADH secretion Thirst Arteriolar constriction

Question 33

In which 3 ways is renin release controlled from granular cells in juxtaglomerular apparatus?

Answer 33

Reduced pressure in afferent arteriole Macular densa cells sense amount of NaCl in distal tubule Increase sympathetic activity as a result of reduced BP (all of these function to increase renin secretion and increase blood pressure)

Question 34

How does aldosterone impact the cells in the distal and collecting tubules?

Answer 34

Increases Na+/K+ATPases on basolateral membrane Increases sodium channels on apical membrane (this allows for a sodium gradient to be set up into the blood)

Question 35

How is fluid retention related to the RAAS?

Answer 35

Heart failure → Decreased BP → RAAS stimulated → Salt and water retention → More pressure on failing heart

Question 36

How can the issue of a failing heart and increasing RAAS activity problem be treated?

Answer 36

Low salt diet Loop diuretics ACEI

Question 37

Where is atrial natriuretic peptide produced?

Answer 37

Heart | (stored in atrial muscle cells)

Question 38

When is ANP released?

Answer 38

Atrial cells stretched | (due to increased circulatory volume)

Question 39

What is the effect of ANP?

Answer 39

Increases sodium (and water) excretion

Question 40

What are the four effects of ANP?

Answer 40

Minimises Na+ reabsorption Decreases RAAS system activity Decreases smooth muscle constricion of afferent arterioles (which increases GFR) Decreases effects of sympathetic system reducing TPR

Question 41

Which two mechanism govern the process of bladder emptying?

Answer 41

1. Micturation reflex 2. Voluntary control

Question 42

How much fluid can the bladder hold before stretch receptors become activated?

Answer 42

250-400ml | (micturation reflex is then activated)