10: Physiology 6

Question 1

The fluid which enters the Loop of Henle has a ___ osmolarity.

The fluid which leaves the Loop of Henle has a ___ osmolarity.

Answer 1

entering - low osmolarity

leaving - still a low osmolarity, but ADH sorts that in distal tubules and collecting duct

Tubular fluid becomes highly concentrated in the Loop of Henle to set up the cortico-medullary concentration gradient and then becomes less concentrated again as it leaves

Question 2

What is the osmolarity of the interstitium of the renal cortex?

Answer 2

300 mosmol/L

same as most of the body

Question 3

What is the concentration gradient going from the renal cortex to medulla?

Answer 3

Increasing

(300 - 1200 mosmol/L)

Question 4

As fluid goes down the collecting ducts, the osmolarity of the interstitium around it (increases / decreases).

Answer 4

osmolarity increases

So the water from the fluid moves to the interstitium, increasing fluid osmolarity

Leading to the production of a low volume of hypertonic urine

Question 5

Where do the distal tubules drain?

Answer 5

Collecting ducts

Question 6

What occurs in the distal tubules and collecting ducts?

Answer 6

Water balance

Ion balance

Question 7

What regulates the absorption of ions and water in the distal tubules and collecting ducts?

Answer 7

Hormones

Question 8

What hormones regulate water and ion reabsorption in the distal tubules and collecting ducts?

Answer 8

ADH

Aldosterone

ANP

PTH

Question 9

What does ADH cause?

Answer 9

Increased water reabsorption

Question 10

What does aldosterone cause?

Answer 10

Increased SODIUM REABSORPTION

Increased K+ and H+ secretion

Question 11

What does ANP cause?

Answer 11

Decreased sodium reabsorption

opposite of aldosterone

Question 12

What affects the permeability of the distal tubules to water?

Answer 12

[ADH]

Question 13

In the absence of ADH, the permeability of the distal tubules to water is ___.

Answer 13

low

Question 14

How does the early distal tubule absorb ions?

Answer 14

Triple transporter

Question 15

How does the late distal tubule reabsorb ions?

Answer 15

Action of ALDOSTERONE (Na+) and PTH (Ca²⁺)

Question 16

In the basal state, how permeable is the early collecting duct to ions?

Answer 16

Impermeable

Question 17

Which gland produces ADH?

Answer 17

Hypothalamus

stored and secreted by posterior pituitary

Question 18

Which ion triggers __cytosis of peptide hormones from cells?

Answer 18

Ca2+ dependent exocytosis

Question 19

What is the half life of ADH?

Answer 19

10 - 15 minutes

Question 20

When is ADH released by the posterior pituitary?

Answer 20

Reduced blood volume e.g dehydration, haemorrhage, sepsis

Question 21

Which vessels have ADH receptors?

Which type of receptor are they?

Answer 21

Distal tubules

Late collecting ducts

G-protein coupled receptors

Question 22

What is produced by G-protein-coupled ADH receptors when they are activated?

What does this cause in the apical membrane of the distal tubule and late collecting duct?

Answer 22

Cyclic AMP

Opening of aquaporins

Reabsorption of water

Question 23

What is ADH also known as?

Answer 23

Vasopressin

Question 24

The movement of water through ___ of the distal tubules and late collecting duct creates what between the tubules and capillaries?

Answer 24

aquaporins

osmotic gradient

Question 25

High levels of ADH lead to the production of ___ urine. Low levels of ADH lead to the production of ___ urine.

Answer 25

**hypertonic / concentrated** **hypotonic / dilute**

Question 26

As water is reabsorbed, the **osmolarity** of tubular fluid \_\_\_.

Answer 26

**increases**

Question 27

Is the ascending limb of the Loop of Henle permeable to water?

Answer 27

**No** **NaCl only**

Question 28

In high concentrations of ADH, the distal tubules and collecting ducts are ___ to water.

Answer 28

**permeable**

Question 29

In low concentrations of ADH, the distal tubule and collecting ducts are ___ to water.

Answer 29

**impermeable**

Question 30

Why does fluid leaving the Loop of Henle always have a low osmolarity?

Answer 30

Corticomedullary concentration gradient, **loses all its salt** as it travels back up, reducing its osmolarity Remember ascending limb is impermeable to water so osmosis INTO the ascending limb doesn't occur to reduce the osmolarity

Question 31

What are the Loop of Henle and ADH's roles in the production of hypertonic urine?

Answer 31

**Loop of Henle creates corticomedullary concentration gradient, but tubular fluid LEAVES loop with a low osmolarity again (because of the gradient)** **ADH then alters permeability to water to increase/decrease fluid's osmolarity as it travels back down into medulla** **Usually producing hypertonic urine**

Question 32

Does ADH affect the reabsorption of salt?

Answer 32

**No, water only**

Question 33

Which part of the brain detects the water content of the blood?

Answer 33

**Hypothalamus**

Question 34

What changes does the hypothalamus trigger in response to dehydration?

Answer 34

**Increased secretion of ADH** **Increased sensation of thirst**

Question 35

In which situations may a low blood water content cause the hypothalamus to increase ADH secretion and thirst?

Answer 35

**Inadequate fluid intake** **Haemorrhage** **Profuse vomiting** **Sepsis** (leaky vessels)

Question 36

Hypovolaemia causes a decrease in systemic ___ \_\_\_, which is detected by ___ \_\_\_ in the left atrium. What does this cause?

Answer 36

**decreased systemic blood pressure** **stretch receptors** **Increased ADH production**

Question 37

What genetic disease is caused by **low ADH secretion** or **abnormal receptor response to ADH?**

Answer 37

**Diabetes inspidus** Low ADH secreiton - central DI Resistance / abnormal receptors - nephrogenic DI

Question 38

What are the symptoms of diabetes insipidus?

Answer 38

**Large volumes of dilute urine** **Extreme thirst**

Question 39

Apart from genetic causes, what may cause central diabetes insipidus?

Answer 39

**Pituitary problems** e.g tumour, haemorrhage

Question 40

How is diabetes insipidus treated?

Answer 40

**ADH replacement** Desmopressin

Question 41

What drug can cause diabetes insipidus? Which type of the disease?

Answer 41

**Lithium** **Nephrogenic diabetes insipidus**

Question 42

Which two receptors can detect the conditions which trigger ADH secretion?

Answer 42

**Osmoreceptors** in the hypothalamus - detect decreased [water]_blood **Stretch receptors** in the atria - detect decreased atrial stretch

Question 43

Which type of receptors are found in the GI tract and **inhibit** **ADH secretion** in response to ingestion of fluid? What type of mechanism is this?

Answer 43

**Stretch receptors** **Feedforward mechanism** - because the change is happening in anticipation of increased [water]_blood

Question 44

Which substance **inhibits** ADH secretion?

Answer 44

**Alcohol**

Question 45

What happens to fluid osmolarity in the a) proximal tubules b) descending Loop of Henle c) ascending Loop of Henle d) distal tubules and collecting ducts **with high ADH levels** e) "" **with low ADH levels**

Answer 45

**a) Stays the same** (water and salt reabsorption at same rate) **b) Increases** **c) Decreases back to 300 mosmol/L** **d) Increases** (as water is being reabsorbed) **e) De****creases** (as water isn't reabsorbed and some salt will be reabsorbed)

Question 46

Where is **aldosterone** secreted?

Answer 46

**Zona glomerulosa** of adrenal cortex

Question 47

In what conditions is **aldosterone** secreted?

Answer 47

**1. Decrease in [Na**+**], stimulating RAAS** **2. Increase in [K**+**], directly stimulating cells**

Question 48

What is the action of aldosterone?

Answer 48

**Increases Na**+ **reabsorption** **Increases** **K**+ **and H**+ **secretion**

Question 49

What are the effects of **aldosterone** on a) K+ b) Na+ c) H+?

Answer 49

**a) Increases K**+ **secretion** **b) Increases Na**+ **rea****bsorption** **c) Increase H**+ **secretion**

Question 50

Concentration of which ion is closely related to blood pressure?

Answer 50

**Na**+

Question 51

How does aldosterone increase blood pressure?

Answer 51

**Increases Na**+ **reabsorption** Causing an increase in BP, **because water follows sodium**

Question 52

Where is most **K**+ **reabsorbed**?

Answer 52

**Proximal tubules** 90% of potassium

Question 53

**Aldosterone** is responsible for the absorption of what proportion of potassium?

Answer 53

**10%**

Question 54

What electrolyte changes cause aldosterone secretion?

Answer 54

**Decrease in sodium** (indirectly, by RAAS) ## Footnote **Increase in potassium**

Question 55

Which substance acts on the adrenal cortex to cause the secretion of aldosterone in RAAS?

Answer 55

**Angiotensin II**

Question 56

How do a) aldosterone b) angiotensin II increase blood pressure?

Answer 56

**a) Increased Na**+ **reabsorption, vasoconstriction** ## Footnote **b) Vasoconstriction, thirst**

Question 57

Which conditions cause renin release by the granular cells of the juxtaglomerular apparatus?

Answer 57

**Renal hypoperfusion** (as in hypotension or renal artery stenosis) **Decrease in tubular NaCl concentration** **Sympathetic stimulation** three different mechanisms

Question 58

Aldosterone increases the expression of which channels in the renal tubules?

Answer 58

**Na**+ transporter on apical membrane **NaKATPase** on basolateral membrane

Question 59

Why does heart failure cause fluid retention and oedema?

Answer 59

**Reduced renal perfusion** **Increase in renin secretion** **Increased reabsorption of Na**+ and **water** **Increased blood volume** (exacerbating heart failure)

Question 60

What hormone is held in heart muscle and is secreted when stretch of muscle increases? What does it do? Why might muscle stretch increase?

Answer 60

**Atrial natriuretic peptide** **Decreases** **Na**+ **reabsorption****, increasing water loss, causing decrease in blood volume** **Hypervolaemia** (so corrects this)

Question 61

What are three effects of ANP?

Answer 61

**Decreases Na**+ **reabsorption** **VasoDILATION of afferent arterioles in glomeruli** **Decreases sympathetic input**

Question 62

What is **micturation**?

Answer 62

**Urination**

Question 63

Which reflex causes involuntary urination?

Answer 63

**Micturation reflex**

Question 64

What triggers the micturation reflex? Which autonomic nerves are involved in the contraction of the detrusor muscle?

Answer 64

**Stretch of bladder wall** **Parasympathetic**

Question 65

Can the micturation reflex be resisted?

Answer 65

**Yes**

Question 66

**Increased atrial stretch** causes the secretion of which hormone?

Answer 66

**ANP**

Question 67

**Decreased atrial stretch** causes the secretion of which hormone?

Answer 67

**ADH**