Renal Physiology

Question 1

Blood supply

Answer 1

Renal artery –> interloper arteries –> arcuate arteries –> interlobular arteries –> glomerulus
20-25% cardiac output
90% cortex 10% medulla
Afferent arteriole to Bowmans capsule, efferent away
Autoregulation
- Renal blood flow maintained over wide range of MAP 75-160
- Myogenic response - vasoconstriction in response to stretch (generic smooth muscle response)
- Tubuloglomerular feedback - reduced renal blood flow in response to high tubular sodium
- AngII / NO
Massive sympathetic states e.g. shock impair auto regulation

Question 2

Filtrate mainly determined by molecular size

Answer 2

Upper limit 70kDA
Below 7kDa freely filtered

Question 3

Filtration physiology

Answer 3

In renal vascular bed, efferent arteriole is the resistance vessel
Glomerular capillary pressure opposed by hydrostatic pressure in bowman capsule and capillary oncotic pressure
Renal plasma flow = 600ml/min
GFR = 120ml/min
Filtration fraction = 20%

Question 4

Tubular transport

Answer 4

Primary active transport (H+, H+/K+ exchange, Na+/K+ exchange)
Secondary active transport - uses ionic gradient established by primary AT
Ion channels
Uniporters
Paracellular movement

Question 5

Aquaporins

Answer 5

H2O channels
- AQP1 - apical and basal membranes of proximities convuluted tubule
AQP2 - ADH control collecting duct

Question 6

Na+ reabsorption

Answer 6

Proximal tubule high Na+ permeability - electrochemical gradient
Exchanged for H+ (excreted)
Na+/K+ pump on basal membrane
Cl- absorbed in exchange for anions (HCO3)

Question 7

Glucose reabsorption

Answer 7

Normally all filtered glucose reasbored
When > 11, nephron capacity to reabsorb overwhelmed (exceed Tm)
Symbort with Na+ down Na+ concentration gradient

Question 8

Other reabsorptions

Answer 8

Amino acid - freely filtered and reabsorbed
Phosphate - excretion 20% of filtered
Urea - 50% reasbroebed
Bicarbonate - 90% reabsorbed PCT
H20 - 60-70% reabsorbed in PCT
Leads to isotonic fluid in lateral intercellular space

Question 9

Loop of Henle

Answer 9

Isotonic fluid enters, hypotonic fluid leaves
Generates hypertonic medullary interstitial - countercurrent multiplier which allows urine concentration by absorption of water at collecting ducts
- Descending - permeable to Na and Cl (in) and H2O) (out)
- Ascending - impermeable to H2O, actively exudes ions
Urea contributes to interstitial osmotic pressure

Question 10

Vasa recta

Answer 10

capillaries from efferent arteriole - nutrient and removal of waste products from renal medulla without washing away solutes
Water extracted from blood in medulla, increases viscosity and slows flow. Minimal washout but inefficient for O2 delivery

Question 11

Collecting duct

Answer 11

180L/day glomerular filtration
70% reabsorbed PCT 15% LOH
23L/day reaches distal tubule and collecting duct and under ADH controlAD

Question 12

ADH

Answer 12

SON hypothalamus, stored post.pituitary
Osmoreceptors regulate release
V2 receptors - GPCR - basal membrane, open AQP2
inc. blood osmolarity, Inc. ADH, inc. H2O reabsorption
Max ADH - 400ml/day urine
Zero ADH - 23L/day urine dilute

Question 13

Juxtagloumerular apparatus

Answer 13

Distal tubule comes into contact with own bowman capsule, afferent, efferent arterioles. Macula densa, renin.

Question 14

Renin release stimulated by…

Answer 14

• low afferent arteriole wall tension (baroreceptor)
• increased renal sympathetic flow
• reduced Na+ to macular densa

Question 15

AngII causes

Answer 15

Quick
- Vasoconstriction
- ADH release –> H2O retention
- Reduced renin
Slow
- Aldosterone release
- Na+ reabsorption (PCT and DCT)

Question 16

Aldosterone causes

Answer 16

• Increased Na+ reabsorption in DCT
• Increases H+/K+ loss
• Increased Na+ absorption from GI tract

Question 17

Buffer

Answer 17

Solution that resists change in pH when acid or alkali added
pH = aka + log [conjugate base] / [acid]

Question 18

Buffer systems

Answer 18

Bicarbonate buffer
Phospate
Haemoglobin
Proteins

Bicarb - metabolism generates H+. Reacts with HCO3-. Kidneys must conserve HCO3- to balance. Tm is close to amount filtered at normal plasma concentration
Process of HCO3- reabsorption requires H+ secretion into lumen - buffered by phosphate

Question 19

Functions of the kidneys

Answer 19

• removal of waste products, particularly nitrogenous
• Salt and water homeostasis
• Control of osmolarity
• pH homeostasis
• Endocrine - Vit. D
• Erythropoesis - EPO

Question 20

Base Excess

Answer 20

Amount of acid or base that must be added to blood to make it pH 7.4 paCO2 5.3 temp 38
corrects for respiratory component of acidosis