renal physiology

Question 1

location of kidney

Answer 1

-11cm long x 6cm wide x 3cm thick
-posterior to abdominal wall
- inferior to diaphragm
- hilum on medial border
- renal arteries enter, veins and ureters leave

Question 2

ureter

Answer 2

• carry urine from kidney to bladder
• 25-30 cm long
• thick walled, narrow tube - 3mm in diameter
• peristaltic contractions 4-5 times a minute

Question 3

IV pyelogram then X ray

Answer 3

patient administered with radio-opaque compound that will enter the urine

follow passage of compound as it flows through the urinary system

non invasive approach helpful for physicians and good if looking for solid masses or blockages

Question 4

vascularity of the kidney

Answer 4

extremely vascular
- each kidney receives more blood than any other organ
- it receives about 20% of cardiac output at any one time

Question 5

the nephron

Answer 5

functional unit of the kidney
- each side inside each kidney We’ve got over a million nephrons.
- these are tightly packed
This is where all the action happens.

Question 6

cortical nephrons

Answer 6

• Sit right up in the cortex
• the loop of henle just sticks down into the medulla.
  85% of the nephrons are cortical nephrons

Question 7

juxtaglomerular nephrons

Answer 7

• Sit lower down
  the loop of Henle of these dips right down to the inner medulla.

Question 8

1. glomerular filtration

Answer 8

creates a plasma-like filtrate of the blood

Question 9

2. tubular reabsorption

Answer 9

removes useful solutes from the filtrate, returns them to the blood

Question 10

3. tubular secretion

Answer 10

removes additional wastes from the blood, adds them to the filtrate

Question 11

4. water conservation

Answer 11

removes water from the urine and returns it to blood, concentrates wastes

Question 12

glomerulus

Answer 12

glomerulus is a knot of capillaries, which is surrounded by the Bowman’s capsule
- blood enters the glomerulus So we have an arteriole which brings blood into this capillary Network here from the afferent arteriole.
- We have blood leaving by the efferent arteriole
- The afferent arteriole is much bigger than the efferent

Question 13

glomerular filtration

Answer 13

filtration of a protein-free plasma from the glomerulus to the Bowman’s capsule

So all the proteins need to stay in the bloodstream.

Question 14

what structures do components of the blood need to pass in order for this glomerular filtration to occur

Answer 14

• wall of the glomerular capillary
• basement membrane
• inner layer of Bowman’s capsule (podocytes, pedicels, filtration slits)

Question 15

glomerular capillary

Answer 15

• Capillary with holes in it that allow passage
• as the Blood comes through the capillary, Anything that’s small enough can pass through those holes (fenestrations)
• The podocytes are large cells that wrap around the glomerulus and they’ve got pedicels so anything small enough to get through those fenestrations has then got to pass through those pedicels which form filtration slits.

Question 16

filtration forces

Answer 16

help components to move across
-blood hydrostatic pressure is the pressure that is exerted on the blood vessels as the blood travels through it - 60 millimeters of mercury.
- because we’ve got proteins in the plasma, in the glomerulus Those proteins are going to be pulling fluids back - colloid osmotic pressure.
○ So that’s a negative pressure.
- So There is a little bit of a pullback certainly on fluids
- we’ve also got capsular pressure which is another negative pressure.

• overall there is a positive pressure moving across from the glomerulus into the PCT of 10 millimeters of mercury

Question 17

why is it important to maintain the positive filtration pressure of 10 mm of mercury

Answer 17

• We have to maintain that pressure in the glomerulus otherwise there would be no filtration.
  So if something changes in your circulatory system and that pressure isn’t maintained the kidneys start to fail.

Question 18

what passes across the glomerular membrane into the PCT

Answer 18

water, glucose, amino acids, electrolytes

Question 19

what stays in the blood

Answer 19

anything greater than 70 nm

Question 20

why are podocytes useful

Answer 20

those podocytes are quite useful as well because they carry a negative charge on the membranes
- because the podocytes are negatively charged It means positive electrolytes tend to move a lot easier across the membrane
- and the negatively charged compounds tend to be a little bit more repelled.

Question 21

glomerular filtration rate

Answer 21

the volume of plasma (per unit time) that is filtered by the glomerulus

Question 22

how can we measure GFR - what criteria does the compound used need to meet

Answer 22

• we can do Several tests, but we need to think about what sort of compound will be useful to monitor.
• First we need to think of something that can pass through from the glomerulus into Bowman’s capsule quite freely.
• We don’t want something that’s going to be reabsorbed straight away back into the bloodstream
• we don’t want something that’s going to be excreted from the blood directly into the tubules,
• we don’t want something that can be produced by the kidney or metabolized.
• We need to find something that is easy to Monitor and it doesn’t have an impact or isn’t impacted by any of these things.
• we don’t want a compound that can alter glomerular filtration rate in whatever way.

Question 23

what compound is used for GFR

Answer 23

CREATININE
creatinine is a product of skeletal muscle catabolism.
were all producing it all the time and it’s proportional to our muscle mass.

CYSTATIN C
- also used clinically to monitor GFR

Question 24

glomerular filtration rate formula

Answer 24

GFR = UV/P

U = conc in urine (mg/l)
v = volume of urine produced (l) per min
P = conc in plasma (mg/l)

Question 25

normal GFR for female and male

Answer 25

female: 115 ml/min = 160 litres of plasma per day
male: 125ml/min = 180 litres of plasma per day

Question 26

negative clearance indicator

Answer 26

if something is filtered then it’s reabsorbed It’s often said to have a negative clearance indicator

Question 27

positive clearance indicator

Answer 27

If something is secreted from the plasma into the filtrate. It might have a positive clearance indicator

Question 28

what is GFR an indicator of

Answer 28

an indicator of renal function as sum filtration rate of all functioning nephrons

fall in GFR clinical sign of disease

Question 29

blood pressure and GFR relation

Answer 29

In order for glomerular filtration rate to continue We need to ensure that We’ve always got that 10 mm of mercury pressure in the glomerulus that allows that move and that filtration.
- a blood pressure can vary quite a lot
If you’ve gone standing to sitting that blood pressure can fall
- but the kidneys are very sensitive to changes in blood pressure.
there are mechanisms in place that help to maintain that filtration pressure, Even when systemically our blood pressure changes.

Question 30

how is GFR maintained despite changes in surrounding blood pressure

Answer 30

in an individual, we want to keep our GFR constant despite changes in blood pressure
- and it’s done by changing the diameter of the afferent and efferent arterioles.
- if we change the diameter of those that will change the pressure within the glomerular.

Question 31

how are the diameter of the afferent and efferent arteries changed to maintain GFR

Answer 31

If we dilate the afferent arteriole And we constrict the efferent arteriole GFR will go up.

if we constrict the afferent arteriole and we dilate the efferent arteriole GFR will go down

Question 32

3 ways to control GFR in healthy individual

Answer 32

• autoregulation
• hormonal regulation
• autonomic regulation

Question 33

autoregulation control of GFR

Answer 33

• Decreased renal blood flow -> decreased renal BP
• dilation of afferent arterioles, as supporting cells relax
• dilation increases RBF in glomerular capillaries
• causes increase in GFR
• increase in renal blood flow and renal blood pressure
• rise in pressure stretched afferent arterioles
• MYOGENIC REFLEX - recoil which will reduce blood flow
  response - decrease in GFR

Question 34

Juxtaglomerular apparatus

Answer 34

An area of the DCT where we see the distal convoluted tubule comes back and
bends around.
we term this whole Part of the Nephron the juxtaglomerular apparatus.

It’s in close anatomical proximity with the Bowman’s capsule and the glomerulus and the arterioles.

Question 35

hormonal regulation of GFR

Answer 35

We’ve got these juxtaglomerular cells that wrap around the afferent arteriole and they are stretch receptors.
if there’s a fall in renal blood flow coming through, These specialized cells can secrete an enzyme renin
- Renin can then convert angiotensinogen to Angiotensin 1
- the enzyme Ace converts angiotensin 1 to Angiotensin 2

Question 36

role of angiotensin 2 in hormonal regulation of GFR

Answer 36

• Angiotensin 2 is a powerful vasoconstrictor in normal systemic effects, but in the renal system, angiotensin 2, depending on its concentration has different effects on the afferent and efferent arteriole.
  ○ at low concentrations it constricts the efferent arteriole which will stop blood flow will try to increase GFR.
  ○ As the concentration begins to increase of angiotensin 2. It eventually will start to constrict the afferent arteriole.
  So that’s going to reduce and limit the amount of blood flow into the glomerulus.
  It’s a self-regulating process.

Question 37

autonomic regulation of GFR

Answer 37

autonomic control = sympathetic innervation
get powerful vasoconstriction of the afferent arterioles.
- so it’s trying to regulate because our blood pressure and everything else is going to go up
- the sympathetic nervous system almost tries to limit the blood flow to slow things down to ensure that we don’t get rapid changes in GFR.

Question 38

factors that cause renal BP to fall

Answer 38

• hypovalaemic shock
• haemorrhaging
• dehydration