Urenal System Flashcards
What is the functional unit of kidney?
nephron
What do the kidneys do?
1) maintain blood plasma volume therefore influencing the bp (MAP)
2) regulates ions and H2O
3) regulate acid-base balance
4) eliminates wastes, drugs, hormones
5) work with the endocrine system to release renin (for BP) and erythropoietin (rbc production)
What does the nephron contain?
renal corpuscle and tubule
What are the processes that happen in the nephron that lead to urine formation?
1) Glomerular Filtration
2) Tubular Resorption
3) Tubular Secretion
What percentage of plasma is filtered in the bowman’s capsule
20%
Filtration in the filtration membrane occurs via bulk flow due pressure. True or False
True
What does the filtration membrane consist of?
1) fenestrated endothelium aka glomerulus capillaries
2) podocytes with filtration slits in between
3) fused basement membranes
Describe the glomerulus filtrate
- it is similar to plasma but without the large proteins
- contains h2o, glucose, amino acids, vitamins, ions and urea and some SMALL proteins
- pH level is around 7.45
What does glomerulus filtrate contain?
glucose, amino acids, water, vitamins, urea, ions, and small proteins
What is the pH level of glomerulus filtrate?
about 7.45
What are the different pressures influencing the net filtration pressure in the glomerulus?
1) Glomerular Hydrostatic Pressure
2) Blood Osmotic Pressure
3) Capsular Hydrostatic Pressure
4) Capsular Osmotic Pressure
What pressure promotes filtration?
glomerular hydrostatic pressure and capsular osmotic pressure
What pressure(s) opposes filtration in the glomerulus?
Blood osmotic pressure and capsular hydrostatic pressure
How do you calculate net filtration pressure
NFP = (GHP + COP) - (BOP + CHP)
The normal GHP is? (mmHg)
55 mmHg
The normal BOP is>
30 mmHg
The normal CHP is?
15 mmHg
The normal COP is?
0 mmHg
What is the normal NFP?
10 mmHg
The kidneys produce how much filtrate a day? what does this this mean about plasma volume
about 180 L/day meaning entire plasma volume is filtered about 65x in a day
How much filtrate is being produced by the kidneys in a minute
125 mL/min
What percentage of filtrate volume remains at the collecting duct for reabsorption?
less than 1%
why is it important to regulate GFR?
to keep GFR from changing when blood pressure changes
without GFR regulation, what happens to it when MAP increases
It increases as well
What are the intrinsic control to GFR?
- myogenic mechanism
- juxtaglomerular apparatus
How does myogenic mechanism regulate GFR when MAP increases and decreases?
- when MAP increases, the smooth muscle stretches which causes the afferent arteriole smooth muscle to contract which prevents glomerular blood pressure from increasing to
- when MAP decreases, the afferent arteriole smooth muscle dilates and raises glomerular blood pressure
how does the juxtaglomerular apparatus regulate GFR when blood pressure decreases?
- when blood pressure decreases, this causes the GFR to decrease which leads to low flow of filtrate past the macula densa
- as a result, the macula densa releases local factors which dilates the afferent arterioles which increases GFR back to its resting rate
In terms of extrinsic control, how does the SNS regulate GFR?
- it promotes vasoconstriction which causes decreases blood flow into the glomerulus via afferent arterioles and backs up blood in the glomerulus via efferent arterioles
in moderate SNS activation, does the GFR change?
not that much
In terms of extreme stress like heavy exercise and hemorrhage, what happens to GFR?
decreases
How does dehydration affect GFR?
it increases Blood Osmotic Pressure which decreases GFR
How do burns affect GFR?
- it increases BOP which decreases GFR
How does urinary tract obstruction (eg. kidney stones) affect GFR?
it increases Capsular Hydrostatic Pressure which decreases GFR
How much of the filtrate is reabsorbed back to the blood
99%
During tubular reabsorption, filtrate travel from the tubule to ______ + _______
peritubular capillaries and vasa recta capillaries
Is tubular reabsorption passive or active?
both
When does an active process occur in tubular reabsorption?
when reabsorbing Na+, other ions, glucose and amino acids
When does passive process occur in tubular reabsorption?
when reabsorbing Cl-, urea and water
Is the proximal tubule regulated or not?
unregulated
What substances are 100% reabsorbed in the proximal convoluted tubule? Active or passive transport?
glucose and amino acids
- active
66% of this substance is reabsorbed in the proximal convoluted tubule via __________ transport.
- NaCl
- active
are small proteins reabsorbed in the PCT? How?
yes through endocytosis small proteins become amino acids and travel to the blood
are vitamins reabsorbed in the PCT?
yes
Water is obligated to be reabsorbed in the PCT. True of False
True
If water is reabsorbed in the PCT obligatory, what does this mean?
it means that large amount of solute is removed and filtrate volume decreases
is filtrate isotonic, hypotonic or hypertonic to plasma?
isotonic
what is the unit of OP/L of filtrate to plasma?
300 mOsmoles/L
Overall, what is being reabsorbed in the proximal convoluted tubule?
glucose, amino acids, vitamins, water, NaCl, small proteins
In the loop of henle, the filtrate being reabsorbed goes to where?
vasa recta
In the loop of henle, what is being reabsorbed?
NaCl and water
Which limb facilitates water reabsorption?
descending limb
Which limb facilitates NaCl reabsorption?
ascending limb
Can water pass through the ascending limb?
no
Can NaCl pass through the descending limb?
no
Where is AT present, in the ascending or descending limbs of the loop of henle?
ascending
The descending and ascending limbs are part of what?
loop of henle
What is being reabsorbed in the distal convoluted tube?
Na, Cl-, Ca2+
Is water permeable in the early part of DCT?
- no because of the absence of ADH
In the late DCT and collecting duct, what is being reabsorbed?
Na+ and water
Reabsorption of Na+ in the late DCT and collecting duct are facilitated by?
aldosterone
Is ANP (inhibits Na+ and water reabsorption) low or high?
low
What makes reabsorption of Na+ in the late DCT and collecting duct possible?
the low levels of ANP
Is water reabsorption in the late DCT and collecting duct regulated or unregulated?
regulated therefore it is facultative reabsorption
What makes water reabsorption possible in the late DCT and collecting duct?
increased ADH
nephrons usually reabsorb _______% of filtered H2O
99%
nephrons usually reabsorb _______% of filtered NaCl
99.5%
nephrons usually reabsorb _______% of filtered glucose
100%
nephrons usually reabsorb _______% of filtered urea?
50%
Will filtrate contain glucose or blood
no
traces of _______ and ______ can possibly be seen in the filtrate.
amino acids and proteins
Tubular secretion starts from _______ to the filtrate aka reverses of tubular reabsorption?
peritibular blood
what substances are being secreted?
urea, K+, uric acid, some hormones, H+ and NH4+
What makes secretion of K+ possible?
increased aldosterone levels
Secretion of H+ and NH4+ maintain what?
blood plasma pH
Countercurrent multiplication is for?
- permitting excretion of urine that could be diluted or concentrated
- producing and maintaining vertical osmotic gradient meaning there’s an increase of solutes as you move deeper into the medulla
In terms of osmolarity urine ranges from?
100 mosmol/L (diluted) to 1200 mosmol/L
In the countercurrent multiplication mechanism, what produces the vertical osmotic pressure?
the juxtamedullary nephrons
Countercurrent mechanism happens because?
1) the descending limb of the loop of henle is permeable to water but impermeable to NaCl
2) the ascending limb of the loop of henle is permeable to NaCl but impermeable to water
What pump exists in the ascending limb of loop of henle? What’s this for?
NaCl pump to pump out NaCl from the filtrate to the ISF
Explain the process of countercurrent multiplication
- as filtrate moves down the descending limb water moves to the ISF via osmosis since water is permeable here
- this causes the filtrate to be more concentrated, and as it reaches the the ascending limb, the NaCl pumps out the solutes which are NaCl into to the ISF
- The NaCl pump pumps solute against its concentration gradient with an osmolarity of 200 mosm/L` (low to high)
- as filtrate moves up the early DCT, more NaCl are removed and water stays in the filtrate which causes an osmolarity of 100 mosm/L when it enters the late DCT
What is the osmolarity of salt being pumped out by the NaCl pump?
200 mosmol/L
What is the osmolarity of the filtrate leaving the ascending limb?
150 mosm/L
Why is the osmolarity of filtrate leaving the ascending limb (150 mosm/L) lower than plasma?
because of the Ascending limb is impermeable to water and the existence of NaCl pump there
what is the osmolarity of the filtrate as it moves to late DCT?
100 mosm/L
why can urine be concentrated?
due to aldosterone which increases Na+ reabsorption
and ADH is increased which facilitates facultative water reabsorption in the late DCT and CD
Concentrated urine can have an osmolarity as high as?
1200 mosm/L
What causes diluted urine?
presence of ANP which inhibits ADP as a result, water reabsorption does not occur as well as NaCl
When does concentrated urine occur?
dehydration and low blood pressure
When does diluted urine occur?
when there is excess blood plasma and high blood pressure
On average, how much urine is produced?
1 - 1.5 L/day
What regulates urine?
1) Renin-angiotensin system
2) ADH
3) Aldosterone
4) SNS
where does renin come from?
juxtaglomerular cells
An increase in renin occurs when?
there’s a decrease in blood pressure or blood volume, a decrease in NaCl in the filtrate and an increase in SNS actvity
the decrease of NaCl in the filtrate is detected by?
the macula densa
A decrease in renin occurs when?
- there’s an increase in blood pressure or volume, increase in ADH and angiotensin, and increase of NaCl in the filtrate.
in details, explain the effect of increased renin
produces more angiotensin I that eventually becomes angiotensin II which stimulates 3 things:
1) the adrenal cortex which increases production of aldosterone which increases Na+ reabsorption and K+ secretion in the kidney which causes water to follow = concentrated urine
2) increased arteriolar vasonsontriction which causes increase systemic bp (MAP) and decreased GFR IF there’s a large decrease in blood pressure
3) the brain increases signals of thirst and and increases ADH which increases facultative reabsorption of water = concentrated urine
Will an increase in renin causes concentrated urine or diluted urine?
concentrated
Will a decline in renin cause concentrated urine or diluted urine?
diluted
What does the hormone ADH do?/
increases facultative reabsorption of water in the late DCT and collecting duct
An increase in ADH occurs when?
1) low blood pressure or volume
2) increased plasma osmolarity (because there’s low H2O)
3) increased angiotensin II
4) nicotine and nausea
a decrease in ADH occurs when?
- high blood pressure or volume
- decreased plasma osmolarity
- decreased angiotensin II
- increased ANP
- alcohol
When does an increase of aldosterone occur?
increase in angiotensin II and K+ plasma concentraton
What does the steroid hormone, aldosterone do?
it turns on the genes that increase number of Na+/K+ ATPase in DCT and CD which increases Na+ reabsorption followed by water via osmosis and then Cl-
and it also increases K+ secretion
when does an increase in ANP occur?
an increase in blood pressure
what does an increase in ANP do?
decreases renin which decreases angiotensin II which decreases aldosterone, ADH and decreases vasoconstriction which increases urine volume
an increase in SNS causes what,
afferent and efferent arteriole vasoconstriction
a decrease in SNS causes what?
technically it causes a decrease in vasoconstriction BUT myogenic response in the kidney is way more powerful thus overriding the effects of a decreased SNS impulse
So when a decrease in SNS takes place, what happens?
MAP will still increase thus increasing blood flow to kidney which causes vasoconstriction inspite of the technical response of a decreased SNS impulse which is to decrease vasoconstriction (which is result of low SNS, low renin, angiotensin and increased ANP) and GFR returns to normal.
- and because theres lack of ADH and aldosterone (since theres low renin) diluted urine will be produced which decreases blood volume (cause we will pee the urine out) which decreases MAP. Hormones corrects blood pressure which keeps GFR constant
So when can the SNS really affect urine regulation?
when it causes a LARGE decrease in bp or volume
Normal urine contains what?
1) water
2) nitrogenous wastes (eg. urea, uric acid, creatine)
3) regulated substances (eg. ions)
What is the pH range of normal urine?
4.5 to 8
what is the average pH level of urine?
6
the presence of urea in urine is due to?
aa metabolism
the presence of uric acid in the urine is due to?
nucleic acid breakdown
creatinine in the urine is from?
break down of creatinine in skel. muscle
what percentage of urea is taken away from the urine due to reabsorption?
50%
What percentage of uric acid is reabsorbed (not present in urine)
10%
is uric acid secreted in the nephron?
yes
Is creatinine reabsorbed in the nephron?
no
What causes creatinine to not be reabsorbed?
constant production and excretion
Creatinine which is found in the urine is used for?
estimating GFR and can indicate kidney disease before symptoms occur
How soluble is uric acid? What does this mean
very poorly soluble which means accumulation can happen which lead to gout (in joint) and kidney stones formation
What does abnormal urine contain?
1) significant amount of proteins
2) glucose
Presence of significant amount of proteins cause what?
proteinuria (aka albuminuria)
What causes proteinuria (albuminuria)
1) increased permeability of glomerulus which is due to heavy metals and glomerulonephritis
presence of glucose causes what?
1) temporary glycosuria
2) pathological glycosuria
an example of temporary glycosuria is?
IV glucose
An example of pathological glycosuria is?
diabetes mellitus which mens there’s high blood glucose (no insulin or receptors are not responding)
What is micturition?
urinating
Describe the flow of urine, in simple terms?
1) starts from the kidney which travels down the ureter
2) from there, it travels to the urinary bladder due to peristalsis and gravity
3) from there it goes to the urethra due to contraction of smooth muscle detrusor which produces pressure gradient
In details what happens when urine reaches the bladder?
- the stretch receptors send signals to:
1) sacral spinal cord micturition centre - which stimulates the PSNS which causes detrusor sm muscle to contract internal urethral sphincter which contributes to expulsion of urine
2) cortex which gives the “gotta pee feeling” and it either:- causes the external urethral sphincter to relax which contributes to urine expulsion or
- causes “gotta wait” feeling which external urethral sphincter to not relax which causes urine hold back
- BUT if bladder fills up pass 500 mL, external urethral sphincter relaxes and urine is expelled
what is renal plasma clearance?
refers to the volume of plasma cleared of a substance in one minute
What does plasma clearance estimate?
the time a substance remains in blood eg. drugs
How do you calculate plasma clearance of a substance
PC of a substance “A” = volume of urine/min x volume of “a” in urine/volume of “A” in arterial plasma
what can be used to estimate GFR in terms of plasma clearance?
inulin
Why is inulin useful in determining GFR in terms of plasma clearance
because it is filtered but not reabsorbed, secreted or metabolized therefore the amount of inulin in the urine is the filtrate amount
If PC of a substance is lower than the GFR aka plasma clearance of inulin (124 mL/min)what does this mean?
it means that the substance is reabsorbed from the filtrate
what is the PC of urea?
about 75 mL/min
what is the PC of glucose? what does this mean?
0 meaning it is 100% reabsorbed
If PC of a substance is higher than the GFR aka plasma clearance of inulin (125 mL/min) what does this mean?
it means that the substance has been secreted into the filtrate
which substance has a higher plasma clearance than GFR aka inulin plasma clearance?
penicillin and H+
what is the acid-base balance?
regulation of free H+ in ECF
H+ are normally produced by?
metabolism
what is the normal body pH?
7.35 -7.45
What does it mean when body pH is between 6.38 - 7.35?
acidosis
What does it mean when body pH is between 7.45 - 8.0?
alkalosis
What does it mean when pH is at 0 or 14?
death
What prevents body pH from changing?
H+ is buffered
buffered H+ is eliminated by?
respiratory system and renal system
Chemical buffer systems are?
pairs of chemicals that work to prevent pH changes
Describe the relationship of bases with H+?
they take up H+ meaning they remove H+ from solution
Describe the relationship between acids and H+
they give up H+ meaning they add H+ to solution
Balance of acids and bases mean?
minimized pH changes
What is the main buffer system in the body?
bicarbonate buffer system
CO2 + H2O H2CO3(carbonic acid = acid) H+ +HCO3- (base)
What are other buffers in the body?
1) Hb + H –> HbH in RBC
2) proteins in plasma and cells
what is the buffer system in cells and plasma?
proteins
What is the buffer system in the RBC?
HbH
How does the respiratory system regulate pH levels?
Expulsion of CO2 due to rapid respiration causes decreased H+
If too much H+ are removed, what happens?
hyperventilation (alkalosis)
If too much H+ are retained, what happens?
hypoventilation —> acidosis
Does the respiratory system work quickly as a buffer system?
yes
