Q1

What is normal GFR?

  • 125ml/min in 70kg male, 10% less in female

What factors affect GFR?

  • Net filtration pressure
    • = hydrostatic pressure in capillaries and bowmans capsule AND colloid osmotic  pressure
    • Afferent – efferent pressure- under control of – autoregulation, sympathetic, AgtII, dobutamine, PGs, serum Na – renin
    • Pressure in bowmans capsule – renal obstruction
  • Capillary filtration coefficient
    • Relates to surface area and permeability of capillaries
    • Surface area controlled by mesagial cells under control of AgtII, ADH, NA, PGs ( constrict)
    • ANP, dopamine, cAMP, PGE2(relax)

Pass criteria

  • 3 to pass

As well as filtration, by what other means does the kidney regulate the composition of urine?

  • Secretion and resorption

Pass criteria:

  • 1 out of 2

Q2

Can you draw a nephron and describe the functions of each part.

  • Glomerulus – filtration
  • Afferent arteriole(contain juxtaglomerular cells – secrete renin) then capillary tuft then efferent arteriole encapsulate in bowmans capsule
  • PCT- resorption of most solute – Na, glucose, aa, reclaim HCO3
  • Desc limb of LOH – thin, water permeable
  • Thick Asc LOH – site of Na K 2 Cl – generates concentration gradient
  • DCT – site of Na K Cl pump
  • Proximal part is the macula densa forms juxtaglomerular apparatus –
  • CD- p cells – under control of ADH and aldosterone(water and Na resorption)
  • I cells – involved in H+ excretion

renal 1

How does vasopressin cause retention of water?

  • Increases permeability of CD, acting on V2 receptors
  • Insertion of protein water channels (aquaporin 2) in uminal membranes.
  • Water enters hypertonic interstitium
  • Urine becomes concentrated and volume decreases
  • Retention of water in excess of solute

What stimuli affect vasopressin secretion?

  • Factors increasing vasopressin secretion
    • Increased effective osmotic pressure of plasma
    • Decreased ECF volume
    • Pain, emotion, “stress”, exercise, standing
    • Nausea and vomiting
    • Clofibrate, carbamezepine, angiotensin 2
  • Factors decreasing vasopressin secretion
    • decreased effective osmotic pressure of plasma
    • increased ECF volume

Q3

How does the kidney handle potassium?

  • K+ filtered ~600meq/24hrs
  • Active K+ reabsorption in prox tubules ~560meq/24hrs
  • K+ secretion ~502meq/24hrs at distal tubule – amount proportionate to flow rate through distal tubules
  • Secretion – Electrical coupling to Na+ reab, thus H+ also

How do other ions affect potassium transport across the membranes in the nephron?
Prompt: How is potassium transported into and out of the tubules?

  • Collecting tubules Na reab’d, K excreted, electrical coupling  and passive K movement
  • Na reabsorbed in association with H secretion, K excretion decreased if Na low in distal tubule
  • Na/K 2Cl apical transporter/transport protein
  • 3Na/2K ATPase

Q4

What is a typical value for renal blood flow in an adult at rest?

  • ~25% of cardiac output or 1250 ml/min

What factors regulate renal blood flow?

  • Chemical:
    • Noradrenaline constricts interlobular and afferent arterioles.
    • Dopamine causes renal vasodilation.
    • Angiotensin II constricts efferent arterioles to a greater extent than the afferent arterioles.
    • Prostaglandins increase blood flow in the cortex and decrease blood flow in the medulla.
    • Acetylcholine produces renal vasodilation.
  • Neural:
    • Strong stimulation of the sympathetic nervous system produces renal vasoconstriction.
  • Autoregulation:
    • Direct contractile response of smooth muscle of afferent arteriole to stretch.
    • NO may be involved.
  • At low perfusion pressures angiotensin II plays a role in constricting efferent arterioles.

Q5

Please outline the structure of the Loop of Henle?

  • Thin/descending, Thick/ascending. Situated mostly in the renal medulla
  • Origin from PCT
  • Short (cortical) and long (juxta med.)loops
  • Macula densa at distal end, where joins DCT

Pass Criteria:

  • Must list 3 properties

What happens to electrolytes in the loop?

  • (Thin) Descending limb water permeable
  • Fluid becomes hypertonic as descends loop
  • (Thick) Asc limb impermeable to water, NaK Cl transported out, hypotonic at end, so K+ diffuses back
  • Active trans. ATPase

Explain the counter-current concentrating mechanism.

  • Gradient
  • Exchange (vasa recta)

Q6

What is a normal Glomerular Filtration Rate in humans?

  • 125 ml/min

What factors would cause a decrease in GFR?

  • Hydrostatic pressure
  • Renal blood flow
  • Capillary permeability
  • Plasma protein osmotic pressure
  • Size of capillary beds

Pass criteria:

  • 3 out of 5 to pass

Q7

What is the renal response to acidaemia?

  • Hydrogen ions actively secreted into the proximal tubule, thick ascending loop of Henle and distal tubules, facilitated the reabsorption of bicarbonate ions by forming the carbonic acid, which dissociates to form CO2 and water

Describe the buffer systems involved.

  • Bicarbonate
  • Phosphate
  • Ammonia

Q8

What stimuli influence vasopressin (ADH) secretion?

Increased by

  • decreased ECF volume
  • increased effective plasma osmotic pressure
  • angiotensin II
  • nausea & vomiting; stress, exercise, clofibrate, carbamazepine;

Decreased by

  • increased ECF volume
  • decreased effective plasma osmotic pressure
  • alcohol

How does vasopressin exert its anti-diuretic effect?

  • It increases permeability of the collecting ducts to water resulting in renal retention of water.
  • Activation of V2 receptors, causing insertion of proteins called water channels (aquaporins) into apical (luminal) membranes of the principal cells of the collecting ducts

Q9

What is the normal renal blood flow?

  • 1250ml/min, 25% CO

How is renal blood flow regulated?

  • Neuroendocrine; NA constrictor, DA dilator, Angio2 constrictor, PG’s (incr cortical decrease medulla), ACH dilates
  • Autoregulation, probably vessel wall stretch reflex as occurs in denervated isolated vessels
  • Renal nerves

Q10

Describe the Physiological process of Micturition.
Prompt: What muscles and nerves are involved?

  • Spinal reflex facilitated and inhibited by higher centres
  • First urge to void at 150ml
  • Marked fullness at 400ml
  • During micturition, the Detruser muscle contracts and perineal muscles/external urethral sphincter relax
  • Parasympathetic( S2,3,4) afferents respond to stretch receptors in  bladder wall to initiate reflex contraction via parasympathetic efferents.
  • Pudendal nerve to External Urethral Sphicter causes relaxation.
  • Spinal reflex integrated in sacral portion of spinal cord
  • Sympathetic (L1,2,3) play no role in micturition but only in prevention. EUS and perineal muscles can be controlled voluntary for a period of time but eventually void reflex overcomes voluntary control

Pass criteria:

Spinal Reflex
Parasympathetic control
Voluntary Control