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vanessa urinary > how does the nephron work? > Flashcards

how does the nephron work? Flashcards

1
Q

what is the first step in the nephron?

A

glomerular filtration

  • “dumping of filtrate into a waste container”
  • does not allow blood cells , protein to pass through larger than 5mm )
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2
Q

what is the second step in the nephron?

A

tubular reabsorption

  • reclaiming what the body needs
  • reclaims almost everything (all of glucose, amino acid and 99% of water, salt and other components
  • most take place in proximal tubule
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3
Q

what is the third step of tubular secretion?

A

tubular secretion

  • selectively moving substance from the blood into the filtrate
  • most in the pct and dct
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4
Q

what is the normal urine look like?

A
  1. clear and pale to deep yellow (urochrome colour)
  2. slightly aromatic ( release of ammonia due to the break down of urea)
  3. slightly acidic Ph6
  4. greater mass than distilled water
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5
Q

what is the normal composition of urine ?

A 
95% water 
5% solutes
urea from amino acids 
creratine 
contains Ca Mg Hco3-

has urea> Na> Po43-> SO42-> creatinine> uric acid

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6
Q

what are some of the causes of abnormal urine colour?

A 
food 
drugs 
vitamins 
bile pigment 
bacteria
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7
Q

what is glomerular filtration?

A

it is the hydrostatic pressure that forces fluid and solutes through a membrane
it is measured by glomerular filtration rate
only allows molecules smaller than 3mn to pass through

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8
Q

what is the corpuscle made up of?

A
  1. fenestrated endothelium of the glomerular capillaries, it is porous and allows all blood components to pass through except blood cells
  2. it has basement membrane that forms a physical barrier that blocks all but the smallest protein while still permitting other solutes to pass
  3. foot processes of podocytes of glomerular capsule, the slit diaphragm prevent almost all of the macrophages from travelling further
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9
Q

what is the reason behind preventing plasma from being filtered?

A

it is to maintain the colloid osmotic pressure preventing loss of all water into capsular space

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10
Q

what are the two pressures affecting filtration?

A 
outward pressure (glomerular hydrostatic pressure)
inward pressure (capsular hydrostatic pressure and blood colloid osmotic pressure)
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11
Q

what is the outward pressure that promotes filtration?

A

glomerular hydrostatic pressure (55mmHg)
- chief force pushing water and solutes out of the blood across the filtration membrane and is caused by the pressure from the afferent and efferent arterioles

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12
Q

what are the inward pressure of glomerular filtration?

A
  1. hydrostatic pressure in capsular space (-15mmHg)
    - pressure exerted by filtrate in glomerular capsule
  2. colloid osmotic pressure in glomerular capillaries (-30mmHg)
    - pressure exerted by the proteins in the blood that sucks water into the capillary
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13
Q

what is the net filtration pressure?

A

55-30-15 = 10

it is responsible for filtrate formation

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14
Q

what happens if the blood pressure decreases?

A

there will be no filtration and acute renal shut down will happen

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15
Q

what to do when there is no filtration?

A

administer IV fluids and insert renal catheter to monitor the renal output

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16
Q

what is glomerular filtration rate?

A

A glomerular filtration rate (GFR) is a blood test that checks how well your kidneys are working.
A GFR test estimates how much blood passes through these filters each minute.

it is the best overall index of kidney function

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17
Q

what is the glomerular filtration rate of a healthy adult?

A

125ml/min

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18
Q

what is he glomerular filtration rate directly proportional to?

A
  1. net filtration pressure , can be changed by changing the diameter of the arterioles
  2. total surface area for filtration
  3. filtration permeability, very permeable due to the fenestrations
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19
Q

what can be used to test the glomerular filtration rate?

A

inulin as it is filtered freely and is not reabsorbed by the kidney

creatinine is often used as a quick estimate as it does not need to be infused IV

20
Q

what controls the glomerular filtration rate?

A
  1. intrinsic control (renal autoregulation)

2. extrinsic control (nervous and endocrine)

21
Q

what is the intrinsic control of glomerular filtration rate?

A

it is the tubuloglomerular feedback
- mascula densa cells in dct sense the amount of Nacl in the filtrate
when there is increased blood flow, there is not enough time for reabsorption and there will be more Nacl in the DCt and is detected by macula densa cells
- it will release vasoconstriction and causes afferent arteriole to constrict decreasing blood flow

the mean arteriole pressure is between 80 and 180mmHg

22
Q

what is the hormonal extrinsic control of glomerular filtration rate?

A

it is the MAIN mechanism to increase bp as without enough pressure, glomerular filtration is not possible
- when BP is low, granular cells of the juxtaglomerular complex releases renin and it leads to an increase in bp

23
Q

what is the mechanism of renin?

A

renin converts angiotensin into angiotensin I

ACE convert angiotensin I to angiotensin II

24
Q

what is the function of angiotensin II?

A
  1. it shrinks blood vessels and causes vasoconstriction
  2. go to kidney adrenal gland and stimulate aldosterone which increases sodium reabsorption
  3. go to pitutary glands and secrete ADH which reabsorbs water from the urine and increase blood volume and BP)
25
Q

what is the extrinsic neural control of the glomerular filtration rate?

A

when the blood pressure is very low, blood is shunt to vital organs and neural controls may override the autoregulatory mechanism

  • when blood pressure falls , norepinephrine is released by sympathetic nerve fibers and causes vascular smooth muscles to constrict increasing peripheral resistance bringing blood pressure back up to normal
  • afferent arterioles also constrict and it decreases GFR and restores blood volume and pressure to normal
26
Q

what is tubular reabsorption?

A

it is the process if reabsorbing the required substances of the body

27
Q

what are the two different routes for reabsorption?

A
  1. transcellular route

2. paracellular route

28
Q

what is transcellular route?

A
  1. transport across apical membrane
  2. diffusion through the cytosol
  3. movement through the membrane into the capillaries

active transport, requires ATP

29
Q

what is the paracellular route?

A

tubular reabsorption through the leaky tight junctions in the PCT

passive transport, diffusion

30
Q

what are the things being reabsorbed in the PCT ?

A

has microvilli to increase the surface area

sodium ions (65% is reabsorbed)
all nutrients (glucose, aminoacid, vitamins by secondary active transport w NA)
Cations (K , Mg, Ca)
anions  (Cl, HCO3)
water 
urea and lipid soluble solutes 
small proteins

nearly all uric acid and half of urea are reabsorbed in the proximal tubule and later secreted back to the filtrate

31
Q

what is reabsorbed at the descending loop of henle?

A

water only

32
Q

what is being reabsorbed at the ascending limb of loop of henle?

A

Na, Cl, K (Secondary active transport)

Ca and Mg

33
Q

what is being reabsorbed in the DCT?

A

Na (primary active transport)
Cl (secondary active transport)
Ca (passive)

34
Q

what is being reabsorbed in collecting duct?

A

Na (primary active transport and requires aldosterone)
H, K, HCO3, CL (passive)
water (osmosis and requires ADH to insert aquaporins)
urea (facilitated diffusion, increased with ADH)

35
Q

what is transport maximum?

A

maximum amount of substance which can be reabsorbed per unit time
every substance that has a transport protein will have a Tmax, it reflects the number of transport protein in the renal tubule available to ferry a particular substance

36
Q

what happens when a transport maximum is reached.

A

the excess is secreted in urine

37
Q

what us the Tmax of glucose ?

A

maximum rate is :375mg/min (max reabsorption)
body threshold is 180mg/dl
if more than that, glycosuria

38
Q

what is tubular secretion?

why is it important?

A

it is reabsorption in reverse
1, eliminating undesirable substances or end products reabsorbed by the passive process
2. disposing substances that are tightly bounded to plasma proteins
3. getting rid of K+
4. controls the blood PH

39
Q

where is the main site for secretion?

A

PCT where H+, K+ Nh4+ , creatine and other organic acids are secreted
(blood PH is reduced as H+ is secreted)

40
Q

what is the pathway of K ions ?

A

it is reabsorbed at PCT and ascending loop of henle but secreted in late DCT and collecting duct by aldosterone

41
Q

what is the pathway of urea?

A

it is secreted in the ascending loop of henle and secreted in collecting duct

42
Q

what are the total substances secreted by kidney?

A 
water 1%
sodium 0.5%
glucose 0%
urea 50%
phenol 100%
43
Q

what is the function of ADH? secreted by posterior pituitary gland

A

inhibit diuresis and urine output
- makes CD more permeable to water by causing aquaporins
- increase urea reabsorption too
DIRECTLY cause water reabsorption

44
Q

what is the function of aldosterone ? secreted by adrenal cortex

A

regulates salt and water balance of the body

  • increase the retention of sodium and water, decrease urine production
  • excretion of potassium

target collecting duct and principle DCT, directly causes sodium retention

45
Q

what is the function of ANP ?

A

reduces blood Na, decreasing the blood volume and pressure

46
Q

what is the function of parathyroid hormone ?

A

increases reabsorption of Ca and acts on DCT

vanessa urinary (3 decks)

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