Renal 3 Urine and renal function Flashcards
normal blood osmolarity
300 mOsm/L
what type of nephron is responsible for making dilute urine?
short loop nephron
what type of nephron is responsible for making concentrated urine?
long loop nephron
how is dilute urine made?
- solutes + water reabsorbed in PCT
- filtrate enters LOH and equilibirates; loss of water only makes filtrate more concentrated and osmolarity rises
- filtrate enters thick ascending limb of LOH; solutes are transported out by symporters (Na+-K+-2Cl-) and water cannot follow (filtrate loses solute and osmolarity decreases)
- filtrate flows to DCT and loses more solute
- filtrate enters collecting ducts and more solute is pumped out to be most dilute (NO ADH, impermeable to H2O)
how is the osmotic gradient in the interstitial space set up?
by the thick ascending limb of the LOH pumping out ions but not water; the descending limb loses water but not ions, so much water is removed by the descending limb of the LOH
why do we make concentrated urine?
if there is too little water/too many ions in the body, urine must be made which reestablishes ionic balance
- needs to be more concentrated in ions than the blood to get rid of excess ions therefore has to be greater than blood osmolarity
how is concentrated urine made?
- solutes and waters reabsorbed in PCT
- filtrate enters LOH and equilibriates; filtrate highly concentrated and osmolarity rises
- filtrate enters thick ascending limb of LOH and solutes are transported out by symporters (water does not follow) - osmolarity decreases
- filtrate flows to DCT and loses more solute; osmolarity further decreased
- filtrate enters collecting duct which is permeable to H2O in presence of ADH; water flows out to match high osm. of interstitial fluid
the longer the loop of Henle:
the greater the time for the ascending limb to pump out solutes
how do diuretics work?
they inhibit the Na+-K+2Cl- symporter in the ascending limb so there is decreased water reuptake and more urine
ADH in urine production
- ADH tastes the blood and if its too salty it wont make urine
- released into the blood stream, goes to kidneys and puts holes in the collecting ducts (allows for concentration)
ADH and aquaporins
ADH leaves the blood and leads to synthesis of water pores (aquaporin 2) in nephron collecting ducts, allowing water to easily leave tubular fluid
- the water then dilutes the blood and brings the osmolarity down to normal
- ADH also increases Na+-K+-2Cl- symporter activity
angiotensin II and blood pressure
constriction of afferent arteriole meaning little blood going to glomerulus and little filtrate made (can lead to waste accum. in blood)
angiotensin, aldosterone and filtration
AII also increases Na+ reabsorption by Na+/H+ antiporters to maintain pH balance in blood
- also causes aldosterone release from adrenal cortex, which increases Na+ and Cl- reabsorption by collecting ducts (H2O follows if ADH present)
urinalysis
anaylzing the volume, physical, chemical and microscopic properties of urine
blood analysis
involves looking a the level of waste products in the blood
blood urea nitrogen (BUN)
a measure of urea nitrogen which is produces due to protein breakdown and usually filtered by kidneys; increases in blood when GFR decreases sharply an durine production is low such as w/ dehydration
plasma creatinine
waste product from creatine phosphate breakdown in muscle; normally, the levels remain steady in blood since urine excretion = its discharge from muscle
- creatinine at levels above 110 μmols/L can indicate poor kidney function
what are the renal function tests?
renal plasma clearance and GFR
renal plasma clearance
volume of plasma that is cleared of a substance per unit of time (mL/min)
why may a substance have a high clearance rate?
it is not reabsorbed back into the capillaries and it may also be actively secreted into the tubules
why do many substances have a clearance rate of 0mL/min?
they are completely reabsorbed e.g. glucose, amino acids
what does renal plasma clearance depend on?
GFR, reabsorption and secretion
renal plasma clearance formula
urine concentration x urine flow/plasma concentration
what is the significance of the renal plasma clearance formula?
high urine levels along w/ low plasma levels indicate a substance is being cleared from a lot of plasma in a short time period; it also suggests that if rate of urine flow (production) is high, then the substance will be cleared at a particularly high rate
why is renal clearance of drugs important?
if urine production goes down and therefore renal plasma clearance, the drugs are kept in circulation a very long time and can build up to toxic levels
measuring GFR
rate at which glomeruli prod. filtrate and for substances, is equal to renal plasma clearance rate
- only true if substance is filtered by glomerulus but not reabsorbed/secreted by tubules (e.g. creatinine, inulin)
what is the normal range for GFR?
120-140 mL/min
what must happen to substances w/ renal plasma clearance in excess of the normal range?
must be secreted from blood into the tubules
what is the renal plasma clearance of urea?
less than the GFR; it is filtered and partly reabsorbed (freely moving)
what is the renal plasma clearance of penicillin?
greater than the GFR; filtered and secreted (gets into filtrate but tubule cells can actively pump it into filtrate
Dilute Urine is made
too much water or too few ions in blood
- made to concentrate blood
Fatal Water intoxication
result of blood which is too dilute
Fatal water intoxication numbers
6L in less than 3 hours
Hyponatremia
dilute all the sodium chloride in your blood and neurons do not function
Tubulues are … to water
impermeable to water
Collecting ducts are … to water
largely permeable to water in the presence of ADH
The fluid outside the tubules outside the kidney itself is
not salty at cortex but salty at tip of medulla
Descending limb will
lose water but not ions and remove a lot of water
Kindey failure
stop making urine
Are long loop nephrons juxtamedullary?
yes they are next to medulla
Blood that does not have enough water=
concentrated urine
How do we fine tune the system for each ion?
hormones are normally involved
T/F collecting ducts are selectively permeable to water?
True
Collecting duct with holes?
concentrated
Collecting duct with no holes?
dilute
What does ADH make?
aquaporin to make holes in collecting ducts for water
Obligatory reabsorption
water has to follow ions
hormones involved in regulation
ADH and RAAA system
Where does ADH act?
only where ADH receptors are
What stimulates the release of ADH?
high osmolality
Where is ADH made?
posterior pituitary
Where is the Na+K+2Cl symporter located?
in the thick ascending limb of the loop of henley
Dilute urine and ADH
no ADH
Concentrated urine and ADH
yes ADH
Urine Volume values
consistently less than 1L of urine= dehydration
consistently more than 1L of urine= diabetic or kidney malfunction
Urine colour
- vitamin c can make urine yellow
- dark red means hemolysis of RBC
- dark in babies means problems with liver
- milky means theres bacteria
Urine turbidity
cloudy means infection
transparent is normal
Urine odour
fruity means the person is diabetic
foul means there is bacteria
pH
- normal is 6
- abnormal is below 4.5 and above 8
constantly low means metabolic acidosis
High Plasma clearance indicates
efficient excretion of a substance in urine
Low plasma clearance indicates
inefficient excretion
Glucose clearance rate
0= filtered than all absorbed
Inulin clearance rate
Clearance=GFR (filtered and never reabsorbed)
Penicillin clearance rate
Clearance is greater than GFR (filtered and also secreted)
