formation of urine: filtration and tubular secretion

what is the percentage of cardiac output that goes to the kidneys

25%

how much is filtered from the kidney and what does that give in urine per day

• 120ml/min

• giving 1.5L urine/day

what are the 3 fundamental processes that account for renal excretion

1. glomerular filtration

2. tubular secretion

3. reabsorption from tubule

how do you calculate urinary excretion rate 

filtration rate + secretion rate - re-absorption rate

what is an example of a substance that is filtered and secreted but not reabsorbed

penicillin 

what is an example of a substance that is filtered and some of it is reabsorbed

urea

what is an example of a substance that is filtered and completely reabsorbed

glucose 

what is an example of a substance that is filtered and none of it is reabsorbed

creatinine 

where does glomerulus filtration occur

in the glomerulus

what is the percentage of filtration in glomerulus filtration 

• 10-20%

• the rest passes into the efferent arteriole 

what lumen of arteriole is smaller

the lumen of the efferent arteriole is smaller than the afferent arteriole 

how many layers is fluid filtered through in glomerulus filtration

3 layers

what are the 3 layers the fluid is filtered through in glomerulus filtration

• the glomerular capillary wall

• the basement membrane

• the inner layer of bowman’s capsule

what is the capillary wall lined with

• endothelial cells which are leaky

• also have fenestrations

what do the capillaries and bowman’s capsule allow due to them being leaky 

allows the passage of plasma components 

what molecules can pass in glomerular filtration

all small molecules e.g. glucose, amino acids, and ions 

what drugs can pass in glomerular filtration

• unbound drugs

• protein bound drugs/compounds cant be filtered

what is the size of a molecule that moves into the filtrate easily 

• <20,000 daltons Mwt

• >50,000 are not filtered

why is glomerular filtration rate measured

to assess kidney function

what is a normal GFR

120 ml/min

when does GFR decline

with age and pathology

why can we use creatinine to measure GFR

none of it is reabsorbed so you measure how long it takes to get into urine 

what is GFR regulated by 

• the autonomic nervous system 

• constriction/dilation of the arterioles 

what is the percentage of of fluid passing to the peritubular capillaries in the proximal tubule 

80-90%

in tubular secretion where does secretion move substances

into the tubule

what are the transporters involved in tubular secretion

• OAT (organic anion transporter)

• OCT (organic cation transporter)