Lecture 65 - Urine Concentration

Question 0

What is the purpose of the LOH?

Answer 0

To set up a high osmotic force in the medulla

By secreting stuff into the medulla

Question 1

Why can ACE inhibitor drugs be dangerous

Answer 1

Can lead to renal failure

If a person has an underlying problem with glomerular function, giving an ACE inhibitor can lead to a big decrease in GFR

Question 2

What determines how much water leaves the collecting duct to be reabsorbed?

Answer 2

Vasopressin

Question 3

What are the fluid inputs into the body?

Answer 3

Food & Drink

Metabolism

Question 4

What is average water input daily?

Answer 4

2.5 litres

Question 5

What are the fluid outputs?

Answer 5

Urine
Lungs
Skin
Faeces

Question 6

What is average fluid output per day?

Answer 6

2.5 litres

Question 7

What is a negative water balance in the body most obvious as?

Answer 7

Increased ECF osmolarity

Question 8

Which cells detect changes in osmolarity?

Where are these cells?

Answer 8

Osmoreceptor cells in the anterior hypothalamus

Question 9

Describe the function of the osmoreceptor cells

Answer 9

1. Increased osmolarity of ECF
2. Fluid leaves osmoreceptor cells
3. Cells shrivel
4. Release of ADH from posterior pituitary
5. Increased fluid reabsorption

Question 10

What is the osmolarity of the body?

Answer 10

300 mmol

Question 11

What is the concentration of vasopressin at the set point?

Answer 11

Certain level, not zero

This allows us to go higher as well as lower

Question 12

What is the relationship between vasopressin and osmolarity?

Answer 12

Directly proportional

The higher the body’s osmolarity, the greater the release of vasopressin

Question 13

What is the difference between diabetes mellitus and diabetes insipidus?

Answer 13

Mellitus: urine is sweet

Insipidus: urine isn’t sweet

Question 14

What is the relationship of ECF volume and vasopressin release?

Answer 14

Inversely proportional

However, ECF volume has to be very low for vasopressin levels to increase very much

Question 15

Where are aquaporins found on the loop of Henle?

Where aren’t they?

Answer 15

Thick ascending: never any aquaporins

Question 16

What is the range of urine osmolarity?

Answer 16

3-1200 mOsm

Question 17

How much solute must be excreted per day?

Answer 17

600 mOsm

Question 18

How much water must be excreted per day?

When does this change?

Answer 18

500 mL

Less than 500 ml indicates kidney failure

Question 19

Describe the relative concentration of water leaving the loop of Henle

Answer 19

Dilute

100 mOsm

Question 20

Describe the relative concentration of fluid leaving the PCT

Answer 20

Isosmotic

300 mOsm

Question 21

Describe the relative concentration of urine at the deepest point on the loop of Henle

Answer 21

Concentrated

1200 mOsm

Question 22

What is being reabsorbed from the descending loop of Henle?

Answer 22

Lots of water

Because the medulla is so concentrated

Question 23

What is being reabsorbed from the thick ascending loop of Henle?

Where does this go, and what is the result of this?

Answer 23

Solute is being reabsorbed

Goes into the medulla, making it very hyperosmolar

Question 24

The fluid leaving the ascending loop of Henle is very hyposmolar. How do we make concentrated urine?

Answer 24

Open up the aquaporins in the DCT and the collecting duct

Question 25

What is the concentration of the medulla due to?

Answer 25

Sodium | Urea

Question 26

Why is some urea reabsorbed?

Answer 26

Stays in the medulla, creating the high concentration

Question 27

Describe absorption of solutes in the thick ascending limb

Answer 27

Na/K ATPase on basolateral membrane - salt pumped into medulla Na/K/2 Cl cotransporter on the apical membrane - all these ions pumped into the tubule cell

Question 28

What is the osmolarity of the medulla interstitial fluid?

Answer 28

300 - 1200 mOsm

Question 29

Describe the action of vasopressin

Answer 29

1. ADH binds to V2 receptor 2. G protein activated 3. Activation of adenylate cyclase 4. cAMP 5. AQP2 inserted into the membrane

Question 30

Describe the osmolarity of the vasa recta

Answer 30

Follows the osmolarity of the region it is in Near cortex: 300 Deep in medulla: 1200

Question 31

Where is the collecting duct? | Why is this important?

Answer 31

It drops down into the medulla This means that if there are aquaporins present, water will move out of the collecting duct