Renal - Lecture 2 Flashcards
What is the first step of urine formation?
glomerular filtration
What passes freely through the filtration barrier of the glomerular space?
water and low-molecular weight substances
What does not get filtered by the glomerulus?
cells
proteins
protein-bound substances
What kind of proteins are not filtered by the glomerulus?
albumins and globulins (large proteins)
Seeing proteins and blood cells in the urine is a sign of what disease?
glomerular disease
___ bound to proteins do not get filtered in the glomerulus?
fats and calcium
The composition of the glomerular filtrate is almost identical to that of ___.
plasma
What is the major force that drives the glomerular filtration?
pressure in the capillary (Pgc)
What is the glomerular capillary blood pressure in glomerular filtration?
60 mmHg
What are the 2 opposing forces in the glomerular filtration?
- pressure in the Bowman’s space
- oncotic pressure
The pressure in the Bowman’s space pushes ___ the filtration.
back
What is the protein in the oncotic pressure that pulls the water back from the Bowman’s space?
albumin
What is the pressure in the Bowman’s space equal to?
15 mmHg
What is the osmotic force (oncotic pressure) equal to?
29 mmhg
What is the net glomerular filtration pressure formula?
glomerular capillary blood pressure - Bowman’s space pressure - oncotic pressure
What is the value of net glomerular filtration pressure?
16 mmHg
Why is there no oncotic pressure from the Bowman’s space?
because there are no proteins in the Bowman’s space
What is glomerular filtration rate?
the volume of fluid filtered from the glomeruli into Bowman’s space per unit time
What 3 things regulate the GFR?
- net filtration pressure
- membrane permeability
- surface area available for filtration
What is the normal GFR of a 70 kg person?
180 L/day
What is the rate of the normal GFR in a 70 kg person?
125 mL/min
What is the NB plasma of a person who has a normal GFR of 180L/day?
3.5 L
How much plasma is filtered per day at glomeruli in someone who has a GFR of 180 L/day and a plasma volume of 3.5 L?
51
How can you decrease GFR? (2)
- constrict afferent arterioles
- dilating efferent arterioles
How can you increase GFR? (2)
- constrict efferent arterioles
- dilate afferent arterioles
What is filtered load?
total amount of any freely filtered substance per unit time
What is the formula for filtered load?
GFR x plasma concentration of the substance
Filtered load ___ amount excreted in the urine = net reabsorption
> (greater than)
Filtered load _ amount excreted in the urine = net secretion
< (less than)
Are there many GFR for many different substances?
no, it is unique to a person
What is filtered load unique to?
each substance in a person’s body
Reabsorption is the movement of substance from the ___ ___ to ___ ___.
tubular lumen
peritubular capillary
What is responsible for bringing oxygen and nutrients to the tubular epithelial cells?
peritubular capillary
Where do peritubular capillaries receive substances reabsorbed from the tubular lumen?
tubular lumen
What are the 2 membranes of the tubular epithelial cells?
- basolateral membrane
- laminal membrane
How can reabsorption happen? (2)
paracellularly and transcellular
A huge amount of water, sodium and glucose is filtered, but most of it is ___.
reabsorbed
Filtered loads are enormous, generally ___ than the amounts of the substance in the body.
greater
Reabsorption of waste products is relatively ___.
incomplete
Reabsorption of most useful plasma components is relatively ___.
incomplete
Reabsorption of some substances are not ___ while others are highly ___.
regulated
Reabsorption of what substance are not regulated?
glucose, amino acids
Reabsorption of what substance are highly regulated?
water, inorganic ions
What are the 2 mechanisms of reabsorption?
diffusion and mediated transport
Reabsorption by diffusion happens across what? What do they connect?
tight junctions
they connect the tubular epithelial cells
What is an example of diffusion of reabsorption?
urea reabsorption in the proximal tubule
Urea is ___ filtered at glomerulus.
freely
Where does water reabsorption occur?
in the proximal tubule
Urea concentration in the tubular fluid becomes ___ during reabsorption in the proximal tubule.
higher
Where does urea diffuse into?
the ISF and peritubular capillaries
Reabsorption by mediated transport occurs across which cells?
tubular cells
What does mediated transport of reabsorption require the participation of?
transport proteins
What is mediated transport usually coupled to?
the reabsorption of sodium
What moves from the tubular lumen to the tubular epithelial cells?
sodium, glucose, amino acids
What moves out of the tubular epithelial cells to the peritubular capillary?
sodium
What drives the movement of sodium, glucose and amino acids from the tubular lumen to the tubular epithelial cell?
low concentrations of sodium
What are the proteins that helps molecules travel called?
cotransporter
What is transport maximum?
when the membrane transport proteins become saturated, the tubule can not reabsorb the substance any more.
What happens to transport maximum in individuals with uncontrolled diabetes mellitus?
it is exceeded
What is the result of exceeded transport maximum in individuals with diabetes mellitus?
glucose appears in the urine (glucosuria)
Tubular secretion moves substances from ___ ___ into the ___ ___.
peritubular capillaries
tubular lumen
Tubular secretion is the opposite of ___.
reabsorption
What is tubular secretion mediated by? (2)
diffusion and transcellular mediated transport
In tubular secretion, most important substances secreted by the tubules are:
hydrogen ions and potassium
Tubular secretion is usually coupled to the reabsorption of ___.
sodium
In order to excrete waste products, the GFR must be very ___.
large
The filtered volume of water and the filtered loads of all the nonwaste plasma solutes are very ___.
large
What does the proximal tubules reabsorb?
most of the filtered water and solutes
What is the proximal tubule a major site of secretion for?
various solutes except K+
What does Henle’s loop reabsorb relatively large quantities of?
major ions (less water)
The volume of water and masses of solutes reaching the DCT and CD are relatively ___.
small
What does the DCT/CD determine?
the final amounts of water and masses in the urine
Where are most homeostatic controls exerted?
DCT/CD
How does the DCT/CD determine the final amounts of water and masses excreted in the urine?
by adjusting the rates of reabsorption and secretion
What is clearance?
the volume of plasma from which that substance is completely removed by the kidneys per unit time
What is the formula for clearance?
mass of S excreted per unit time / plasma concentration of S
What is the formula for mass of S excreted per unit time?
urine concentration os S x urine volume per unit time
What can clearance be used to measure/estimate?
glomerular filtration rate
How is inulin administered?
intravenously
Where is inulin freely filtered?
glomerulus
Is inulin reabsorbed, secreted, or metabolized by the tubule?
no
What is the clearance of inulin equal to?
the volume of plasma originally filtered
CNin=
GFR
What is the most accurate marker of GFR?
Cin
Why is inulin clearance not convinient?
because you have to infuse it
How do you calculate amount of inulin excreted in the urine?
urine volume x inulin concentration in the urine
How do you calculate Cin?
amount of inulin excreted in the urine divided by concentration of inulin in plasma
What is creatinine?
a waste product produced by muscle
Where is creatinine filtered freely?
glomerulus
Is creatinine reabsorbed?
no
Where is creatinine secreted in small amounts?
tubule
What is creatine clearance used as a clinical marker for?
GFR
What is the formula for creatinine clearance?
urine concentration of creatinine (Ucr) multiplied by urine volume divided by plasma concentration of creatinine (Pcr)
Clearance of a substance > GFR
It is ___ at the tubule
secreted
Clearance of a substance < GFR
It is ___ at the tubule
reabsorbed
What is an example of clearance > GFR (secretion)?
para-amino-hippurate marker of renal plasma flow
