Session 5

Question 1

What does an issue with Na+ balance effect?

Answer 1

The volume

Question 2

What does an issue with water balance effect?

Answer 2

Osmolarity

Question 3

What causes plasma osmolarity to increase?

Answer 3

When water intake is less than water excretion

Question 4

What causes plasma osmolarity to decrease?

Answer 4

When water intake is more than water excretion

Question 5

What detects changes in plasma osmolarity?

Answer 5

Hypothalamic Osmoreceptors

Question 6

What are the 2 efferent pathways for plasma osmolarity?

Answer 6

ADH

Thirst sensation

Question 7

What is the effector for when ADH pathway is activated?

Answer 7

The kidney. Water excretion is effected

Question 8

What is the effector for when thirst is activated?

Answer 8

Brain. Water intake is effected

Question 9

Where, specifically, are osmoreceptors?

Answer 9

In the OVLT of the Hypothalamus

Question 10

When is ADH activated?

Answer 10

When there is water loss

Question 11

When is thirst activated?

Answer 11

When the person is already at least 10% dehydrated

Question 12

Where is ADH released from?

Answer 12

The posterior pituitary gland

Question 13

Where is ADH made?

Answer 13

In the Hypothalamus

Question 14

What stimulates ADH?

Answer 14

Increase is osmolarity (i.e loss of water)

Question 15

What inhibits ADH?

Answer 15

Decreased osmolarity (i.e lots of water)

Question 16

What stimulates osmoreceptors?

Answer 16

Increased osmolarity

Question 17

What is important to remember about the thirst reflex?

Answer 17

The water does not correct osmolarity immediately, but the brain recognises that it will be fixed so reduces the thirst sensation

Question 18

When does the body stop trying to correct osmolarity?

Answer 18

When there is severe fluid loss (i.e drop in blood volume) the body will compromise and have dilute plasma to keep the volume correct

Question 19

What are the effects of ADH on the kidney?

Answer 19

Causes vasoconstriction in the Glomerulus
Increases Na+, Cl- and K+ reabsorption in ascending limb
Water reabsorption in the the DCT and CD (by causing Aquaporin 2 to insert into the apical membrane of cells - allows for subtle changes)

Question 20

How does osmolarity effect renal water excretion?

Answer 20

Decreased osmolarity = Increased excretion

Increased osmolarity = Decreased excretion

Question 21

How much urine is excreted when it is Hypo-osmotic?

Answer 21

Large amounts of dilute urine (diuresis)

Question 22

What does hyper-osmotic urine cause?

Answer 22

The kidney to reabsorb as much water as possible, but this requires a hyper-osmotic intersitium (Achieved by counter current multiplier by Loop of Henle and vasa recta acting as counter current exchanger)

Question 23

What is the arrangement of Peritubular capillaries around Juxtamedullary nephrons?

Answer 23

Vasa recta. (Hair pin shape) Blood runs in an opposite direction to the filtrate

Question 24

What does the Vasa recta maintain? (It is needed for reabsorption)

Answer 24

The Corticopapillary Osmotic gradient (Gradient of increasing osmolarity)

Question 25

What is the Descending limb of the Loop of Henle permeable to?

Answer 25

Water

Question 26

What is the Ascending limb of the Loop of Henle permeable to?

Answer 26

Solutes