RENAL PHYSIOLOGY II

Question 1

how is the filtration happen in glomerulus?

Answer 1

freely-filtered –> not very selective and creates a plasma-like filtrate of the blood

Question 2

what determines glomerular filtration?

Answer 2

• filtration barrier
• renal blood flow
• driving forces

Question 3

how selective is the filtration barrier?

Answer 3

• small substances and glucose are freely-filtered
• large substances (haemoglobin and albumin) are not filtered

Question 4

what is the stats of renal blood flow and how does that affect the glomerulus filtration?

Answer 4

• 20% CO —> RBF approximately 1100-1200mL/min
  —> high flow for filtration rather than metabolism

Question 5

what are the 2 driving forces within glomerular filtration and what does each do?

Answer 5

hydrostatic pressure
- due to volume of fluid
- ‘pushes’ fluid away

colloid osmotic pressure
- osmotic pressure due to protein
- ‘pulls’ fluid towards

Question 6

which pressure favour and oppose filtration?

Answer 6

• positive pressure favour filtration
• negative pressure oppose filtration

Question 7

what are the 4 forces that drives the filtration?

Answer 7

• glomerular hydrostatic pressure (+50)
• blood colloid osmotic pressure (-25)
• capsular hydrostatic pressure (-15)
• capsular colloid osmotic pressure = 0

Question 8

which is the major force that favours filtration in glomerulus?

Answer 8

glomerular hydrostatic pressure (GHP)

Question 9

what is the filtration fraction and what is the number for that?

Answer 9

filtration fraction = glomerular filtration rate / renal plasma flow

GFR = 125mL/min
RPF = 625mL/min

—> 20% of the RPF is filtered and 80% remains in the glomerular capillaries (to travel to efferent aterioles and then peritubular capillaries)

Question 10

how much is the amount of plasma filtered per day by kidneys?

Answer 10

180L

Question 11

even though 180L of plasma is filtered per day, the urine excreted per day is only ______1______, therefore the process needs to be _____2______ and it is _______3_______ with the ability declines slowly from age 30

Answer 11

1: 1.5L
2: tightly regulated
3: varies from person to person

Question 12

what is renal filtered load?

Answer 12

• filtered load = amount of a particular substance filtered per unit of time
• filtered load of renal = GFR s solute plasma concentration

Question 13

what is renal clearance?

Answer 13

the volume of plasma that is cleared of a substance by the kidneys per unit time

Question 14

what is the renal clearance indicate?

Answer 14

• quantify how much a substance is handled by the kidneys
• estimate glomerular filtration rate (GFR)

Question 15

what is the clearance of creatinine?

Answer 15

clearance of creatinine = volume of plasma filtered per min = GFR

Question 16

what is the clearance of medication and toxins?

Answer 16

clearance of medication and toxins = volume of plasma flow through the kidneys per min = RPF

Question 17

what is the clearance of creatinine?

Answer 17

clearance of sodium = very small

Question 17

what is the clearance of glucose?

Answer 17

clearance of glucose = 0 (all is reabsorbed —> no plasma has been “cleared” of glucose)

Question 18

what is the equation of clearance

Answer 18

Cx = (Ux x V) / Px

Question 19

how do we estimate the GFR using the clearance

Answer 19

because we have creatinine and inulin, which is freely- filtered but not reabsorbed or secreted –> use there stats to estimate the GFR

Question 20

what is creatinine and what is inulin?

Answer 20

creatinin:
- waste product of muscles
- already in body so most commonly used clinically

inulin
- polysaccharide which is not metabolised by body
- not found in body and must be injected
- food high in inulin: wheat, shalots and red onions, bulb of leeks

Question 21

what is the relationship between GFR and plasma creatinine indicate?

Answer 21

• low plasma creatinine <—> GFR high => normal kidney function of both kidneys
• fairly normal plasma creatinine <—> one kidney working with GFR 60mL/min
• high plasma creatinine <—> kidneys ability to clear waste is reduced