Renal 2: Production of dilute urine

Question 1

What is totally reabsorped from initial filtration and what is totally excreted

Answer 1

Glucose is totally reabsorbed and creatinine is totally excreted

Question 2

Describe the order of the 5 parts of the nephron tubules that forms the urine and the process happening there

Answer 2

1. Glomerulus for filtration
Tubular reabsorption in the 
2.proximal tubule, 
3.Loop of Henle (descending and ascending) 
4.Distal tubule 
5. Collecting duct

Question 3

What determines the Net Filtration pressure of glomerular filtration that determines how much water and solutes leave the blood

Answer 3

Pressure pushing fluid out is Glomerular Blood hydrostatic pressure (55)

Pressures pushing back in is
-Capsular hydrostatic pressure (exerted from elastic recoil of capsule on plasma) (15)

-Blood colloid osmotic pressure (osmotic force of proteins left in plasma) (30)

Therefore NFP = GBP- (CHP +BCOP)

Question 4

How is glomerular filtration rate regulated by myogenic autoregulation mechanisms to increase GFR
and decrease GFR

Answer 4

Myogenic:
If BP drops, there is constriction of efferent arteriole which increases BP in glomerulus-> increase of GFR

If BP increases, increased stretching of smooth muscle in afferent arteriole triggers constriction which makes pressure fall across the glomerulus-> decrease GFR

Question 5

What is the output of urine (Glomerular filtration rate) directly proportional to

Answer 5

Renal blood pressure

Question 6

How is increased glomerular filtration rate regulated by Tubuloglomerular feedback

Answer 6

1. higher GFR -> higher flow rate
2. Macular densa cells in the tubule distal tubule sense increase in Na+ and Cl- due to high flow rate.
3. Release of NO from Juxtaglomerular apparatus is decreased
4. Vasoconstriction of afferent arteriole to lower BP->thus GFR

Question 7

What is the normal pressure of the Afferent arteriole, Glomerular and the Efferent arteriole BP

Answer 7

60, 55, 50

Question 8

What two factors do regulators of glomerular filtration work on

Answer 8

The Glomerular hydrostatic pressure and the Surface area available for filtration

Question 9

How is GFR regulated by Neurons

Answer 9

The GFR can be decreased by constriction of afferent arterioles due to norepinephrine from sympathetic nerve activation

Question 10

Compare how GFR regulated by two hormones

Answer 10

Angiotensin II (produced by decreased blood vol or BP) decreases GFR by causing vasoconstriction of both efferent and afferent arterioles

whereas ANP (produced in response to stretching of atria)increases GFR by relaxing mesangial cells in glomerulus to increase SA for filtration.

Question 11

Describe the movement of Na+, Cl- and water in the Proximal tubule

Answer 11

1. Na+ is pumped out of the cell into the interstitial space by Na/KATPase to create a conc gradient for
2. 2Na+/Glucose to enter the cell via symporter (down conc gradient) and H+ to be secreted via Na+/H+ antiporter
3. Cl- follows and water follows by osmosis

Question 12

What is the difference between the cortical nephrons and juxtamedullary nephron

Answer 12

Cortical nephrons make dilute urine

and juxtamedullary nephron make concentrated urine

Question 13

What is amount of solute and water reabsorption in Proximal tubule and what is the osmolarity

Answer 13

Largest reaborption here
-60% of glomerular filtrate
-60% of NaCl and water
100% Glucose

Osmolarity similar to plasma (300mOsm)

Question 14

What part of the nephron has brush border of microvili and why

Answer 14

Proximal convoluted tubule for increased SA for membrane transport processes

Question 15

Describe the movement of Na+, Cl- and water in the Descending loop of Henle

Answer 15

There is no movement of ions Na+/K+ as it has low permeability to ions and urea.
However it is highly permeable to water so water moves out obligatory of tubule to interstitial fluid in the renal medulla because it is more concentrated than tubule.

Question 16

What is the osmolarity of the Descending loop of Henle and why

Answer 16

1200 mOsmol/L because lots of water left

Question 17

Describe the movement of Na+, Cl- and water in the Ascending loop of Henle

Answer 17

Thick cuboidal cells of tubule impermeable to water but Na+, K+ and 2Cl- absorbed through symporter powered by Na+ gradient made by NaKATPase in basolateral membrane.

Question 18

What is the osmolarity of the Ascending loop of Henle and why

Answer 18

Very dilute (100 mOsmol/L) as ions are moving out but water can’t

Question 19

What is the counter current mechanism

Answer 19

The gradient for water to leave the descending limb is set up by ions leaving the descending limb making the tip of ECF of medulla higher concentrated. This is supported by blood flow of the efferent vasa recta which takes the water away.

Question 20

Describe the movement of Na+, Cl- and water in the distal tubule and collecting duct

Answer 20

Additional Na, and Cl- is absorbed through diffusion channels because of gradient set up by NaKATPase. K+ is also secreted by these principal cells.
This section is also impermeable to water in the Absence of ADH, which makes a dilute urine.

Question 21

What is the osmolarity of the distal tubule and collecting duct and why

Answer 21

The final osm of the urine is 100mosmol/L - a large volume of dilute volume.