Renal Function 1 (MET1 Revision)

Question 1

Answer 1

Question 2

Answer 2

Question 3

which arteries supply the kidneys?
from what origins?
what vertebral level found?

Answer 3

renal arteries

• L1-L2 level
• come from thoracic aorta
• lie inferior to superior mesenteric artery

Question 4

how does the main renal artery divides after entering the kidneys?

what is each glomerulus enclosed in?

Answer 4

renal artery –> interlobar vessels –> arcuate arteries (in renal cortex) -> afferent arteriole , where terminates in the cortex called a glomerulus

each glom: enclosed in Bowman’s Capsule

Question 5

:) look !

Answer 5

Question 6

describe flow of urine into / out of kidney

Answer 6

• urine drains into the calyxes –> renal pelvis –> ureter

Answer 7

• blood enters glomerulus through afferent arteriole, which has a smaller
• 20% blood plasma filtered through glomerulus –> proximal tubule

Question 8

describe the structure of capillaries found on glomerulus & how this achieves filtration

what is proteinura?

Answer 8

• fenestrated gaps
• have layer of podocytes: have slits between them
• the slits form the filtration mechanism (let ions through, but not proteins)

proteinura: increased levels of protein in the urine (whenn ^^ becomes inflammed & damaged)

Question 9

what controls the filtration of water into from glomerulus into the Bowmans capsule?
what is usual pressure of glomerular capillaries? what is normal pressure in Bowmans capsule?* how does pressure get to this BC?)

Answer 9

controlled by the constriction or relaxtion of afferent arteriole
normal pressure in capillaries: 55 mm Hg
normal pressure in Bowmans capsule: 10 mm Hg (a result of: glomerulus hydrostatic pressure (55 mm Hg) - blood colloid osmotic pressure (30 mm Hg) - capsular hydrostatic pressure (15 mm Hg) : 55-30-15 = 10 :)

Question 10

describe the anatomical pathway of kidney nephron

Answer 10

• Fluid passes from Bowman’s capsule into the proximal tubule
• Here, filtered materials can be reabsorbed into the peritubular capillaries
• Material can also be transported out of the capillaries and secreted into the tubular fluid
• The amount of a material (e.g. glucose) excreted is the amount filtered plus the amount secreted minus the amount reabsorbed

- Fluid passes out of the proximal convoluted tubule fluid and enters the ‘Loop of Henle’

- After the loop it enters the distal convoluted tubule

• The DCT returns to the junction where the afferent and efferent arterioles meet the glomerulus = juxtaglomerular apparatus.
• Finally the distal tubule enters the collecting duct.
• The collecting ducts drain into the ureter.

Question 11

explain the mechanism of when is water reabsorbed back into the capillaries from the PCT?

(when water and solutes within the PCT are transported into the bloodstream)

Answer 11

• The proximal tubule is lined with epithelial cells

- The basal membranes of the cells (i.e. the layer not in contact with filtered fluid) contain sodium pumps which pump sodium into the interstitial fluid (1)

- Sodium channels exist in the luminal (inner) membrane of the cells and so sodium passes out of the lumen into the cells down its concentration gradient. (2).This sodium influx carries glucose with it.

• Water is reabsorbed down an osmotic gradient generated by the sodium pumps from the lumen into the cells and then out into the interstitial fluid

Question 12

how much of water filtered in the glomerulus is reabsorbed in the PCT?

Answer 12

About 2/3 of all the water filtered in the glomerulus is reabsorbed in the proximal tubule

Question 13

how much fluid is filtereted through all the glomeruli in both kidneys in fit adult? - what is this aka?
which system determines glomerular filtration rate / GFR?
what type of regulation is this? - what does this mean regarding differing BPs?

Answer 13

The total amount of fluid filtered through ALL the glomeruli in BOTH kidneys in a fit adult is about 120-125 ml/min. (depending on body size). This is the Glomerular Filtration Rate (GFR).

GFR is autoregulated by tubuloglomerular feedback

Autoregulation of GFR means that renal blood flow also does not change over a wide range of blood pressures.

Question 14

how does tubuloglomerular feedback regulate GFR

what happens to GFR if affererent arterioles constrict / relax?

Answer 14

• (for ur understanding / from youtube:
• blood enters afferent arterioles at around 100 mm Hg
• afferent arteriole has less constrictor tone, , which reduces the pressure to about 50 mm Hg(otherwise would damage the glom capillaries)
• yet after been in the glomerulus capillaires, need to up pressure again
• so efferent arteriole, increases resistance, so more pressure is applied to blood*

https://www.youtube.com/watch?v=ZDvWnezLdDU

Tubuloglomerular feedback regulates the GFR by regulating the degree of constriction in the smooth muscle of the afferent arteriole

• *so:**
• if afferent arterioles contrict: lowers filtration pressure & GFR
• if afferent arterioles relax: increases filtration pressure & GFR

Question 15

Answer 15

Question 16

explain the mechanism that occurs if GFR is too low

and high :)

whole process = autoregulation

Answer 16

• *GFR too low**
• Cells in the macula densa of the JGA detect the concentration of sodium in the distal tubular fluid
• If Na+ levels are low, shows that GFR is too low
• The macula densa releases local chemical factors which relax the smooth muscle in the proximal tubule
• this increases the filtration pressure and GFR.
• *GFR too high**
• Cells in the macula densa of the JGA detect the concentration of sodium in the distal tubular fluid
• If Na+ levels are high, shows that GFR is too high
• The macula densa releases local chemical factors which constrict the smooth muscle in the proximal tubule
• decreases filtration pressure and GFR

Question 17

what other function do macula dense cells do ? / what do they produce?

Answer 17

The macula densa cells also tonically produce prostaglandin PGE2
which acts on juxtaglomerular cells to stimulate renin release

low sodium levels = More prostaglandin = more renin

Question 18

How do u measure GFR?

Answer 18

GFR is measured by the CLEARANCE of a selected material.
It is the effective volume of plasma completely ‘cleared’ of a substance per minute
​Clearance is measured in units of litres/minute

e.g.

if 100% of a blood component is filtered through the glomerulus. This means that the material goes into the proximal tubule at exactly the same rate as the water in the plasma. if all of this filtered material appears in the urine (none is reabsorbed). Then the clearance of this substance will be the same as the glomerular filtration rate (125 ml/min).

OR

Suppose that 100% of a blood component is filtered through the glomerulus. And that all of this filtered material is reabsorbed. Then no blood will be ‘cleared’ of the material as it is all reabsorbed. The clearance of this substance will be ZERO

OR

if 100 % of the material is filtered and in addition all of the material in the efferent arteriolar blood is secreted into the urine.

The renal venous blood will have NO material in it. All the blood passing through the kidney will have been cleared of the material. The clearance will then equal the renal plasma flow. So the clearance of a material can be anything from zero to the renal plasma flow.

Question 19

when does:

a) Clearance = zero?
b) Clearance = GFR?
c) Clearance = RPF (renal plasma flow)?

Answer 19

Substance in blood

1. Not removed at all by kidney: Clearance = zero

2. Removed at same rate as water passes through glomeruli: Clearance = GFR

3. Completely removed from blood passing through kidney: Clearance = RPF

Question 20

why is some material still present in renal venous blood?

Answer 20

due to the proportion of the plasma which is not filtered (that which enters the efferent arteriole) will still contain the normal concentration of the material. Some material will be present in the renal venous blood.

Question 21

what happens to GFR value if kidneys are damaged?

Answer 21

Generally GFR will decrease although RPF may be normal. Measurement of GFR is an essential test of kidney health.

Question 22

how do u measure clearance of a substance?

what three steps do u need to do?

Answer 22

Question 23

which substance do u measure GFR:

i) in specialised kidney research units
ii) clinical practice

Answer 23

i) specialised kidney research units
INULIN - BUT inulin does not occur naturally in plasma!

to measure inulin clearance you have to infuse inulin i.v. over a period of hours, to reach a steady plasma concentration

• *ii) clinical practise:**
• creatinine clearance is used to measure GFR
• freely filtered across the glom and neither reabsorbed nor metabolised
• creatinine clearance overestimates actual **GFR by 10-20%
• ** a 24 hour urine collection is undertaken, from empty-bladder one morning to the contents of the bladder the following morning, with a blood test for creatinine then taken

Question 24

what happens to i) serum creatinine & ii) creatinine clearance when have:

• bilateral renal damage?
• one kidney damage?

Answer 24

bilateral renal damage:

• **serum creatinine goes up
• creatinine clearance goes down**

one kidney damage:
- serum creatinine & creatinine clearance stays normal

Question 25

when does clearance equal the renal plasma flow?

Answer 25

If all of a particular substance & warter is filtered
AND
all of the material in the efferent arteriolar blood is secreted into the urine

= the renal venous blood will have NO material in it. i.e. All the blood passing through the kidney will have been cleared of the material.

Question 26

what does clearance of PAH (para-amin-hippuric acid) measure?

Answer 26

Clearance of PAH (para-amin-hippuric acid) measures renal plasma flow (RPF) because all PAH is secreted into blood, therefore all blood passing through kidney is ‘cleared’ of PAH.

Question 27

what are normal creatinine clearances for men & women?

what is normal RPF for both kidneys?

Answer 27

Normal creatinine clearances:

women 88-128 mL/min.

men 97 to 137* mL/min (*equals about 90ml/min/1.73 m2 ).

_Normal RPF (both kidneys)_
**600-700 ml/min**

Question 28

* what is relationship between GFR and serum creatinine *

Answer 28

serum creatinine is inversely proportional to GFR: high serum creatinine = low GFR

BUT

this also means that monitoring serum creatinine level does not detect early changes in GFR