Urine + Renal Function

Question 1

When do we make dilute urine?

Answer 1

When there is too much water or too little ions (concentrates the blood)

Question 2

When do we make concentrated urine?

Answer 2

When there is too little water or too many ions (dilutes the blood)

Question 3

Are the collecting ducts permeable when creating dilute urine?

Answer 3

No

Question 4

Where does most of the reabsorption occur?

Answer 4

In the PCT

Question 5

How does the osmotic gradient get set up?

Answer 5

By the thick ascending LOH pumping out ions but not water

Question 6

Why does water leave the descending LOH?

Answer 6

Because of the salty interstitial fluid - set up by the ascending limb pumping out ions

Question 7

Are the collecting ducts permeable when making concentrated urine?

Answer 7

Yes

Question 8

How do diuretics work?

Answer 8

Inhibit Na-K-Cl pumps in the ascending LOH therefore decreased water re-uptake and more dilute urine

Question 9

Hormonal regulation of tubular reabsorption (x2)

Answer 9

ADH and angiotensin

Question 10

How does ADH cause permeability in CDs?

Answer 10

Leads to the fusion of aquaporin-2 to the basolateral membrane of the collecting ducts

Question 11

Where is ADH made + stored?

Answer 11

1. Hypothalamus

2. Posterior pituitary gland

Question 12

How is high osmolarity detected?

Answer 12

Osmoreceptors in the hypothalamus detect high osmolarity in the plasma and interstitial fluid

Causes neurosecretory cells in hypothalamus to release ADH

Question 13

ADH and Na-K-Cl symporter

Answer 13

ADH increases the activity of the symporter (allows for more concentrated urine –> saltier in the medulla)

Also increases BP

Question 14

Angiotensin II and BP

Answer 14

Decrease in BP/sympathetic stimulation –> juxtaglomerular apparatus releases renin –> angiotensin II –> constriction of afferent arterioles –> increase in blood pressure and decrease in GFR

Question 15

Aldosterone and filtration

Answer 15

Aldosterone increases Na+ and Cl- reabsorption in collecting ducts (increased BP) –> increased BV –> increased blood pressure

Question 16

What does urinalysis look at?

Answer 16

Volume, colour, turbidity, odor, pH

Question 17

Ways to do blood analysis (tells you how well kidneys are working, x2)

Answer 17

1. Blood urea nitrogen: measure of urea nitrogen produced due to protein breakdown (this is filtered by the kidney)
   
   • It increases in the blood when the GFR decreases & urine production is low
2. Plasma creatinine: waste product form the breakdown of creatinine phosphate in skeletal muscle (high levels = poor kidney function)

Question 18

Renal function tests (x2)

Answer 18

1. Renal clearance

2. Glomerular filtration rate (GFR)

Question 19

What is renal clearance?

Answer 19

Determines how effectively the kidneys are removing a given substance

High plasma clearance = efficient excretion of a substance in urine (penicillin)

Glucose is the opposite

Question 20

Renal clearance formula

Answer 20

Conc. in urine x rate of urine output = conc. in plasma

Question 21

What is GFR?

Answer 21

Measure of the rate in which glomeruli filter the blood

To measure this, you need a substance that is not reabsorbed or secreted by tubules (e.g. creatinine or inulin)