5. DSA Introduction to RBF/GFR

Question 1

What are the three layers of the glomerular filtration barrier?

Answer 1

1. capillary endothelium with fenestrae
2. glomerular basement membrane
3. podocyte epithelium (goes to bowmans capusle)

Question 2

Along with the fenestrae in the endothelium and the slits in the podocytes which monitor and filter certain sized cells, there is also a layer of biogel. What makes this in the endothelium?

Answer 2

glycocalyx forms a biogel in the endothelial lumen… when there is heparinase (breaks down heparin) glycocalyx will not form and damage will be done to the kidney

Question 3

it is important to realize that along with the podocyte slits, there is a mesh layer/’biogel’ covering the slit as well, minimizing the size of cell allowed through. What is the main component of the biogel ?

Answer 3

nephrin (CAM in glomerulus only) and cadherins

if there is a mutation in nephrin, then larger proteins will pass and can lead to kidney disease

Question 4

What size molecules are filtered freely and what size molecules are not filtered?

Answer 4

small than 20 A filtered freely while larger than 42A are not filtered

Question 5

Some freely filtered things are water, small solutes like glucose and AAs, while not freely filtered consist of?

Answer 5

large molecules and formed elements (cells)

Question 6

What are Tamm-Horsfall proteins and why are they in a high concentration in the blood?

Answer 6

The appear in the blood but are not filtered, they are produce by the renal tubular cells of the distal loop of henle and are thought to have antimicrobial characteristics to combat UTIs

Question 7

the smaller the radius and the more positive the charge of a molecule will lead to an increased clearance rate while if the radius is large and the charge is negative what will happen?

Answer 7

most likely will not get filtered through. remember there is a glycocalyx biogel that is negatively charged so it will prevent like charges from going through

Question 8

A damaged filtration barrier could lead to hematuria/proteinuria and other clincal diseases. if the negative charge of the barrier is removed (or via a mutation in glycocalyx) more negative charged anions cross leading to?

Answer 8

proteinuria…

if albumin was allowed to be filtered, then there would be a decrease in the protein plasma concentration and causing capillary oncotic pressure to decrease

Question 9

What is the difference in arrangement of tubules and vessels in the cortex compared to the medulla?

Answer 9

in the cortex they are organized into spaghetti and sprials while in medulla they are straight like pencils

Question 10

The filtered load is = to?

Answer 10

plasma concentration * GFR (glomerular filtration rate)

Question 11

what is equal to amount filtered - amount absorbed + amount secreted?

Answer 11

urinary excretion

if excretion is greater than filtration then tubular secretion must have occured

Question 12

what is equal to glomerular filtration - urinary excretion + amount secreted?

Answer 12

tubular reabsorption

above equation rewritten

Question 13

urine excretion rate is = to what?

Answer 13

U urine concentration (concentration/volume ) * V urine flow rate (urine volume/time)

Question 14

Clearance, C is flow rate at which substances are removed or cleared from plasma. What is the equation?

Answer 14

C= U * V/ P (plasma concentration)

Question 15

glomerular filtrate is the volume of plasma filtered into the combined nephrons of both kidneys per unit time. what percent of the RBF becomes glomerular filtrate?

Answer 15

it is cell and protein free and about 20% of renal blood flow becomes glomerular filtrate

Question 16

How would you calculate the filtration fraction (FF) which is the fraction of rbf that is filtered across the glomerulus?

Answer 16

FF= GFR/RPF (renal plasma flow)

otherwise know FF is usually 20%

Question 17

the capillary filtration coefficient (kf) is found using what two variables?

Answer 17

permeability * surface area

Question 18

as filteration factor increases so does the oncotic pressure of the efferent arteriole, why?

Answer 18

because there is an excessive loss of blood via filtration so there will be an increase in plasma protein concentration leading to an increase in reabsorption via oncotic capillary pressure

Question 19

the filtered load or ultrafiltrate (usually lacks large proteins) will become the urine. how do you determine what percentage of filtered load of sodium is reabsorbed per day? ***important

Answer 19

taking the amount reabsorbed / filtered load of Na

the amount reabsorbed is filtered load- excretion (V*U)
filtered load is GFR * Plasma [Na]

Question 20

What are the four rules that must be met in order to use GFR as clearance, C?

Answer 20

1. substance must be free filterable
2. substance must be neither reabsorbed nor secreted
3. substance must not be accumulated/broken down by kideny
4. substance must be physiologically inert (not toxic)

Question 21

What is equal to saying C=UV/P if the substance follows the 4 rules?

Answer 21

GFR=UV/P

GFR is usually equal to 125mL/min

Question 22

What are some examples where GFR = Clearance (c)?

Answer 22

inulin, creatinine, and para-aminohippuric acid (PAH)

Question 23

While creatinine is not an ideal marker for GFR, it is still used becuase it is produced endogenously by skeletal muscle and?

Answer 23

does not require an infusion, therefore it is very easy for a patient to measure creatintine clearance

Question 24

There are three ways the sympathetic nervous system stimulates things to increase blood pressure. What are they and what receptors do they use?

Answer 24

1. alpa1 to vasoconstrict = afferent arteriole resistance inc.
2. JG cells via Beta1 releases renin
3. Tubular epithelial cells via alpha1 activate NaKATPase to increase Na+ reabsorption

Question 25

When renal blood flow or BP is low, the sympathetic stimulation will kick in to counter this. It does so by stimulating renin production, making angiotensinII which does what 3 things?

Answer 25

thirst, restores BP via vasconstriction preferentially acting on the efferent arteriole to increase GFR

Question 26

What are the three chronic effects of consistent sympathetic stimulation?

Answer 26

decreased urinary output
decreased urinary Na excretion
increased water intake

Question 27

What is important to remember about plasma creatinine concentration and GFR?
Remember GFR and creatinine clearance are directly proportional

Answer 27

if plasma creatinine is high, GFR is low

inversely proportional

Question 28

When the BUN to creatinine ratio is high (>20:1) there is a pre-renal problem via BUN reabsorption is increased and disproportionally elevated relative to serum creatinine. What diseases can this be associated with? (4)

Answer 28

Hypovolemia
Dehydration
Reduce renal perfusion
high protein diet (high consumption of urea)

Question 29

When the BUN to creatinine ratio is normal (10-20:1) there is no problem or a post-renal problem, which could be cause by?

Answer 29

an obstruction in the ureter

Question 30

When the BUN to creatinine ratio is low (<10:1) there is an intrarenal problem via renal diseases in which BUN reabsorption is reduced, decreasing plasma levels and lowering the ratio. What diseases are associated with this? (2)

Answer 30

liver diesase

low protein diet (low consumption of urea)

Question 31

PAH is freely filtered and the amount of PAH in the renal artery is equal to the PAH in the excreted urine. Therefore what can be calculated using clearance of PAH?

Answer 31

renal blood flow (RBF)