Glomerular Filtration, Tubular (Renal) Function

Question 1

What is the glomerular filtration rate?

Answer 1

It is the volume of plasma filtered per minute

Question 2

With advancing age, how does the glomerular filtration rate change?

Answer 2

In a healthy young adult, the glomerular filtration rate is maintained constant over the pressure range 90mmHg to 180 mmHg b/c renal blood flow is constant

however, with age the renal blood flow decreases and thus, the glomerular filtration rate also decreases.

*in a neonate, the RBF and GFR are lower than adult as well.

Question 3

Does the glomerular capillary blood pressure favor or oppose filtration?

Answer 3

It favors filtration

Question 4

Does the plasma-colloid osmotic pressure favor or oppose filtration?

Answer 4

opposes filtration - this is the pressure exerted by big bulky poteins in the plasma and has a suctioning effect so it opposes by hindering stuff from moving through the filter

Question 5

Does the Bowman’s capsule hydrostatis pressure oppose or favor filtration?

Answer 5

It opposes filtration

Question 6

does the net filtration pressure of the glomerulus favor or oppose filtration?

Answer 6

it favors filtration ultimately

Question 7

When the bowman’s capsule fails, what results?

Answer 7

the bowman’s capsule is the filter of your blood. If it fails you are allowing large proteins to enter your urine through the filter causing protein urea. This ultimately causes edema or fluid buildup in the extracellular spaces

Question 8

What is the glomerular filtration barrier?

Answer 8

this barrier determines the composition of the tubular filtrate -

Question 9

What are the three layers of the glomerular filtration barrier?

Answer 9

1. endothelium of glomerular capillaries (which is fenestrated)
2. basement membrane
3. foot processes of epithelial cells (podocytes)

Question 10

The three layers of the glomerular filtration barrier contain what?

Answer 10

they contain negatively charged glycoproteins -

*proteins are negatively charged and they therefore are repulsed by the negative glycoproteins*

Question 11

What passes through the glomerular filtration barrier?

Answer 11

all components of plasma except cells and proteins

*a small amount of protein does pass through it but it is immediately reabsorbed in the distal tubule

Question 12

How do we measure glomerular filtration rate?

Answer 12

Creatinine Clearance Test - used to estimate GFR

this requires an accurate 24hr. urine collection and blood sample from the subject. it measures the creatinine conc. in both blood and urine samples.

*if we are trying to measure GFR we need something that is freely filtered and not reabsorbed or secreted by tubules - Creatinine isn’t perfect, (it is slightly secreted in the tubules), but it is only about 10% inaccurate. If we need a perfect measurement, we can inject inuline

Question 13

What is nephrotic syndrome?

Answer 13

it is a nonspecific disorder in which the kidneys are damaged, causing leakage of large amounts of protein from the blood into the urine- this causes edema

*small pores present in podocytes allowing leakage of the proteins *

Question 14

how much of our blood glucose concentration is reabsorbed in the tubules?

Answer 14

100% - none is excreted

Question 15

what percent of water is reabsorbed in our tubules after filtration?

Answer 15

99.2% of water is reabsorbed

Question 16

What does BLOOD SOKI refer to?

Answer 16

the basolateral Na/K pump - sodium out, potassium in

Question 17

how is sodium reabsorbed in the proximal tubule?

Answer 17

1. first half of the proximal tubule - sodium is exchanged for hydrogen ion on the tubular side, then the sodium is exchanged for potassium on the blood side of the cell using the sodium potassium pump. (70% of sodium reabsorbed in the proximal tubule)
2. second half of proximal tubule- sodium exchanged for hydrogen ion, this also draws a chlorine atom into the cell. The sodium is then moved to the blood in exhange for a potassium, and the potassium (now inside of the cell) moves with the chloride ion back into the blood

*Generally : Na+ reabsorbed in first half of proximal tubule coupled to H+ or organic solutes.

Na+ reabsorbed in second half of proximal tubule coupled to Cl- across the transcellular and paracellular pathway

Question 18

What drives the 70% of water to be reabsorbed in the proximal tubule?

Answer 18

the driving force is transtubular osmotic gradient established by absorption of solute.

Question 20

describe how the loop of Henle allows for the dilution/concentration of urine

Answer 20

1. descending thin limb does not reabsorb NaCl but it does reabsorb water through aquaporin 1 channels
2. ascending limb impermeable to water
3. reabsorption occurs in thin and thick ascending limbs
4. NaCl reabsorption occurs by passive diffusion in thin ascending limb.

Question 22

Describe how sodium is transported in the early distal tubule

Answer 22

on tubular side - Na+ and Cl- are cotransported into the cell, on the basolateral side, the Na+ and K+ are exchanged via the sodium potassium pump

Question 23

Where is aldosterone produced?

Answer 23

produced in the adrenal cortex

Question 24

What is the effect of aldosterone?

Answer 24

it increases the Na/Cl- symptorter in the early distal tubule. it also has multiple effects on transporters in the collecting duct

Question 25

Decrease in extracellular fluid volume activates which system?

Answer 25

the renin, angiotensin aldosterone system - which increases angiotensin 2

Question 26

Where are catecholamines released from?

Answer 26

They are released from sympathetic nerves and adrenal medulla to stimulate reabsorption of NaCl from proximal tubule, TAL, and Distal tubule and CD