Urinary 2 Flashcards
(16 cards)
Urinary extraction = ?
glomerular filtration - tubular reabsorption + tubular secretion
Renal handling of substances
1) passive diffusion
transport substances across membrane along their concentration gradient without ATP
2) facilitated diffusion (carrier mediated)
transport substances across membrane using proteins, carriers along their concentration gradient
3) active transport
transport substances against their concentration gradient, using ATP
- primary active transport
ATP acquire from ATP hydrolysis, uses ATP directly to transport substance - secondary active transport
the movement of sodium molecules transported by transported by Na+/K+ ATPase generates energy. this energy is used to transport substances
1) co-transporter (transport substances in the same direction)
2) exchangers (transport substances in the opposite direction)
3) osmosis (movement of water to a region with higher solute region, water following solute)
transport maximum (Tm) & renal threshold meaning
Tm= limit at which the channels, pumps & transporters are able to transport the substances for reabsorption.
renal threshold = plasma concentration of the substance at which it is starting to be excreted in urine
renal threshold of glucose
Tm= 300 mg/dL
renal threshold = 180 mg/dL
values vary due to the fact that not every nephron has the same renal threshold, some nephron would already start to secrete glucose in the urine even before some nephron have reached their transport maximum
what happens @ PCT
NA+, calcium, K+, Cl-
water
glucose and amino acid (fully reabsorbed)
there is also H+ secretion and HCO3- reabsorption
> 60% of filtered water and electrolytes are reabsorbed at the PCT
fluid remains iso-osmotic from the start of the PCT to the end of the PCT (same concentration of solute and solvent)
the loop of henle consist of 3 parts, what are they
thin limb of descending loop (permeable to water, not permeable to solutes)
thin limb of ascending loop (not permeable to water, reabsorption of Nacl)
thick limb of ascending loop (not permeable to water, reabsorption of various electrolytes)
cells in thick limb are highly metabolic and high resorptive capacity
apical membrane: 1na, 2cl, 1k cotransporter
basolateral membrane: na+/k+ ATPase, pumps na+ out of renal cells back into blood vessels
@ early distal tubules
@ late distal tubules
@ early distal tubules
- still impermeable to water but allows for reabsorption of nacl
@ late distal tubules
- allows for water and electrolyte reabsorption
- 2 key specialised cells
1) principal cells
2) Type A intercalated cells
1) principal cells (controlled by aldosterone)
apical membrane
- ENaC channel (sodium channel)
basolateral membrane
- na+/k+ ATPase
increase aldosterone levels = increase activity of existing pumps and by incorporating more existing pumps and also incorporation of k+ channels
2) Type A intercalated cells
apical membrane
- H+ ATPase
- h+/k+ exchanger
basolateral membrane
- HCO3-/cl- exchanger
@ late distal tubules and collecting duct
only at this region where it can be controlled by ADH and aldosterone
2 key specialised cells
1) principal cells
2) Type A intercalated cells
1) principal cells (controlled by aldosterone)
regulates na+ k+
apical membrane
- ENaC channel (sodium channel)
basolateral membrane
- na+/k+ ATPase
increase aldosterone levels = increase activity of existing pumps and by incorporating more existing pumps and also incorporation of k+ channels
2) Type A intercalated cells
regulate acid base balance
apical membrane
- H+ ATPase
- h+/k+ exchanger
basolateral membrane
- HCO3-/cl- exchanger
secretion of h+ into tubules to acidify urine, reabsorption of bicarbonate to neutralize acidity
what factors regulate tubular reabsorption
1) glomerulotubular balance
2) aldosterone
3) angiotensin II
4) ADH (vasopressin)
5) ANP (atrial natriuretic peptides)
@ medullary collecting duct
- little reabsorption of water and sodium
- plays an important role in concentration and dilution of urine
- ADH controls the reuptake of water
increase ADH levels > allows for incorporation of more aquaporin 2 water channel at the late distal tubule and at the collecting duct, allowing for an increase in efficiency of water reabsorption
more channels = more enhanced ability to reabsorb water
the relationship between tubuloglomerular feedback and glomerulotubular balance
work together to buffer the effects of spontaneous changes in GFR on urine output
glomerulotubular balance
when GFR increase > more water and electrolytes get reabsorbed at the PCT and loop of henle > lessen the load of substances needed for reabsorption @ the DCT (preventing overloading)
tubuloglomerular feedback
decrease in arterial pressure > decrease in renal blood flow > decrease hydrostatic pressure > GFR decreasing > macula densa stimulated to reduce transportation of nacl into tubules and also there is increase reabsorption of nacl in the tubules > increase in renin secretion by juxtaglomerular cells > increase angiotensin II (potent vasoconstrictor) constricts blood vessels > increase blood pressure > increase resistance at the efferent arterioles >increase GFR
Glucose and amino acid reabsorption @ PCT
glucose
- apical membrane: SGLT -2 co-transporter
sodium dependent co transporter, transport sodium from tubules into cells and at the same time also transport glucose
glucose gets transported into renal cells and leaves the cells back into the blood vessels via GLUT-2
- basolateral membrane: GLUT-2 facilitated diffusion, helps transport glucose back into blood vessels
- na/k ATPase helping with reabsorption of sodium
amino acid
- na/amino acid co-transporter
for every sodium that gets transported, amino acid concurrently gets transported as well
important mechanism in concentrating urine
1) ADH levels
2) countercurrent mechanism
potassium regulation
hyper vs hypo kalemia
hyperkalemia (high blood potassium level)
stimulate the principal cells via aldosterone levels increase
aldosterone stimulate increase in activities of ENaC sodium channel, incorporation of more K+ channel and na+/k+ ATPase
hypokalemia (low blood potassium level)
stimulate type A intercalated cells, only the H+ ATPase gets influences by aldosterone, increase H+ secretion into tubules.
The h+/k+ exchanger secretes more h+ in order to reabsorb more k+
both scenario results in fatal cardiac arrythmia (abnormal heart rhythm)
in low potassium levels, it can also lead to muscle weakness
define osmolarity, osmolality and specific gravity
osmolarity = concentration of solute per litre of solvent
osmolality = concentration of solute per kg of solvent
urine osmolality vs plasma osmolality
high variation in urine as it depends on what the body requires.
If body is dehydrated, water needs to be reabsorbed, resulting in increase urine osmolarity
specific gravity = measures the weight of the solute in a given volume
can be measured from knowing the number and size of the solute
2 substances that leads to diuretic effects
1) glucose - osmotic diuresis
presence of glucose in the renal tubules can attract the water to diffuse into the tubes and get excreted (urine is low in osmolality as it is highly diluted) increase in urine output
2) alcohol intake
alcohol consumption inhibits the activity of vasopressin (ADH) leading to increase amount of water excreted can lead to dehydration in body
countercurrent mechanism
tho they travel parallel to each other but the substances travelling within them is in opposite direction
countercurrent multipliers of the loop of henle
- descending limb of loop of henle, allows for water to reabsorb into ascending limb of the vasa recta and returns back to circulation, diluting the solute concentration within the vasa recta
- ascending limb of loop of henle, allows for solute reabsorption but not water, solute reabsorb into descending limb of vasa recta, concentrating that region.
countercurrent exchanger of the vasa recta
- water exits from the descending limb of the vasa recta into the medullary interstitium while solute enters
- solute travels down the vasa recta, concentrating the fluid within
- water enters at the ascending limb of the vasa recta from the descending limb of the loop of henle, diluting the fluid within
- solute exits from the ascending limb of the vasa recta into the medullary interstitium
a constant and balanced osmolality helps with concentration and dilution of urine output
