Kidney as a producer, excreter and regulator

Question 1

Erythropoeitin

Answer 1

• Produced when fall in oxygen levels
• Secreted by peritubular cells
• Stimulates RBC production

Question 2

Vitamin D

Answer 2

• Skin + UVB = cholecalciferol
• Liver converts to calcidiol (25-hydroxycalciferol)
• Kidney: converted to 1,25-dihydryoxycalciferol
• Calcitriol increases Ca2+ by promoting GI absorption, decreasing renal excretion and stimulating bone reabsorption

Question 3

How does fluid travel in nephron

Answer 3

Blood, PCT, LOH, DCT, CD

Question 4

Tight junctions in PCT, DCT, CD

Answer 4

• Large number of proteins creates a barrier to water and dissolved particles
• Loose in PCT
• Tight in DCT
• Very tight in CD

Question 5

Journey through nephron

Answer 5

• Afferent arteriole - Bowman’s capsule - filtrate - efferent removes unfiltered
• Nephron transmits between cortex and medulla
• Glomerulus - PCT - LOH - DCT - CT

Question 6

Cortical glomeruli

Answer 6

Dilute but don’t concentrate

Question 7

Function of inter medullary glomeruli

Answer 7

Concentrate and dilute

Question 8

Podocytes

Answer 8

negatively charged, cover glomerular capillaries, have small filtration channels

Question 9

Glomerulus

Answer 9

Produces filtrate by high pressure system
Anions pass less easily than cations
Na+, HCO3-, glucose but no proteins

Question 10

What is GFR?

Answer 10

Marker of renal function

Question 11

How to calculate rate of filtration

Answer 11

Urine flow x urine concentration

Question 12

Markers of renal function

Answer 12

creatinine (product of muscle metabolism, slight overestimation), cystatin C (produced by most cells) and inulin (plant extract, infuse to steady state)

Question 13

How to calculate GFR

Answer 13

(UFR x Cu) / Cp

Cu = creatinine in urine, Cp is creatinine in plasma

Question 14

When will GFR be proportional to 1/Cp

Answer 14

Creatinine production constant

Question 15

What happens when arterial pressure falls?

Answer 15

Drop in RBF and GFR
Arteriole dilates, improving RBF
Efferent arteriole constricts, improving GFR

Question 16

Function of adenosine

Answer 16

produced in hydrated state, constricts afferent arteriole to reduce GFR and inhibit renin release, switched off with reduced filtrate flow

Question 17

Function of angiotensin ii

Answer 17

produced from renin cascade, constricts efferent arteriole to maintain GFR, leads to ATII inihibition in hypovolaemia

Question 18

Function of PGE 2

Answer 18

roduced in DCT when filtrate flow decreased, dilates afferent arteriole to maintain RBF, cytoprotective to tubule, antagonises vasopressin, beware NSAIDs in hypovolaemia

Question 19

Two types of auto regulation mechanisms

Answer 19

Myogenic and tubule-glomerular feedback

Question 20

3 types of tubule-glomerular feedback

Answer 20

Adenosine, angiotensin ii and PGE 2

Question 21

Function of PCT

Answer 21

• Conservation of majority of useful filrate components
• Reabsorbs Na+, HCO3- and glucose and water
• At the end, [Na+] same as plasma, no HCO3- and no glucose
• H2CO3 breaks down to produce the proton
• Exchanges for Na+ in antiporter
• Sodium leaves, water follows
• Transport maximum of glucose is 2mmol/min, when this is reached, glycosuria results

Question 22

Function of LOH

Answer 22

• Produced hypotonic tubular fluid and hypertonic interstitial fluid and some reabsorption of Na+, K+ and Cl-
• At the end, extremes in osmolality (medulla interstitium is very high and tubular fluid is very low)
• Mechanism: selective permeabilities to ions and water
• Ascending limb: impermeable to water but permeable to ions, causing high concentration of ions in interstitial space
• Fluid is progressively more dilute as you ascend
• Ion reabsorption in ascending limb: Na+/K+ co-transporter, K+ into blood, Na+ leaves

Question 23

How does furosemide work

Answer 23

diuretic, blocks co-transporter of Na+ and K+ so none reabsorbed

Question 24

Characteristics of descending limb

Answer 24

• Permeable to water, impermeable to ions
• Water is lost via AQP1
• Tubular fluid more concentrated coming down

Question 25

Where does water move in LOH

Answer 25

From descending LOH to ascending limb of vasa recta

Question 26

Why is water reabsorbed efficiently in CD

Answer 26

Hypertonic environment

Question 27

Function of DCT

Answer 27

Final regulation of sodium, potassium, hydrogen

Question 28

Function of principal cells

Answer 28

reabsorb sodium and secrete potassium, regulated by aldosterone

Question 29

Function of intercalated cells

Answer 29

reabsorb potassium and secrete hydrogen, driven by ATPase

Question 30

Stimuli of principal cells

Answer 30

Aldosterone, increased potassium, alkalosis, increased tubular flow

Question 31

Stimuli for intercalated cells

Answer 31

Acidosis, decreased potassium

Question 32

Function of CD

Answer 32

Final water regulation, regulated by ADH

Question 33

Aquaporins

Answer 33

- Water channels - Narrow shape and charged walls - Positive in core - Over 8 sub-types

Question 34

Site and nature of AQP 1

Answer 34

``` Site = PCT, descending LOH basal membrane Nature = continuous water reabsorption ```

Question 35

Site and nature of AQP 2

Answer 35

Site: CD Nature: response to ADH, variable water reabsorption

Question 36

Site and nature of AQP 3

Answer 36

Site: CD basal membrane Nature: continuous water reabsorption

Question 37

Site and nature of AQP 4

Answer 37

Site: CD basal membrane Nature: continuous water reabsorption

Question 38

How is water reabsorbed in CD

Answer 38

- ADH released from posterior pituitary in response to hypothalamic osmoreceptors - ADH causes AQP2 to insert - 3 receptors - all G-protein 3 receptor are V1a, 2 and 3

Question 39

Where is H+ secreted and HCO3 absorbed

Answer 39

PCT

Question 40

Which cells make final adjustments in DCT

Answer 40

Intercalated cells

Question 41

How is H= secreted and HCO3 reabsorbed

Answer 41

H2CO3 forms H+ and HCO3- H+/Na+ moves hydrogen into lumen and Na+ into tubular cells Na+/HCO3- co-transporter moves into blood

Question 42

Function of JGA

Answer 42

- Between afferent arteriole and DCT - Senses decrease in pressure (granular cells) or decreased sodium tubular flow (macula densa cells) - Triggering of this apparatus leads to dilation of afferent arteriole (decreased adenosine and PGE2) and releases renin (also triggered by B1 stimulation)

Question 43

Function of AT 1

Answer 43

Acts on aldosterone = volume retention in kidneys

Question 44

Function of angiotensin ii

Answer 44

Vasopressin - water retention (V2) and vasoconstriction (V1a)

Question 45

Function of baroreceptors

Answer 45

Increase HR and vasoconstriction