Q51

What are the major physiological features of acute intrinsic renal failure?

PROMPT – What happens to urine concentration?

  • Loss of urine concentrating and diluting capacity due to loss of countercurrent mechanism and nephron number. Polyuria -> Oliguria -> Anuria
  • Uraemia due to urea and creatinine and toxins (phenol and acids) build up.
  • Acidosis
  • Anaemia
  • Sodium retention and oedema and heart failure

Pass Criteria:

  • 3/5 bold

What are common findings in urinalysis of acute intrinsic renal failure?

  • Proteinuria
  • Leucocytes
  • Red cells
  • Casts

Pass Criteria:

  • 3 bold 

What are urinary casts?

  • Proteinaceous material precipitated in tubules washed into bladder

Pass Criteria:

  • Bold to pass

Q52

Describe the way the kidney handles glucose.

  1. Freely filtered at the glomerulus
  2. Resorbed in the early part of the PCT by secondary active transport
  3. Na dependent co-transportation (SGLT2 into cells then GLUT 2 facilitated diffusion into interstitial fluid).
  4. Excreted in the urine if renal threshold is exceeded.

Pass Criteria:

  • 1 & 2, plus understanding of 3 & 4

What are the potential consequences of glycosuria?

  • Osmotic diuresis – dehydration, electrolyte loss (Na, K)

Pass Criteria:

  • Understanding

Q53

What is normal renal blood flow?

  • Renal blood flow = approx 1250 mL/min

Pass Criteria:

  • Bold (accept 1000-1500)

What substances influence renal blood flow and how?

  • Noradrenaline
    • Constriction
  • Dopamine, ACh
    • Dilatation
  • Angiotensin II
    • Constricts afferent and efferent arterioles
  • PGs
    • Increase flow in cortex and decrease in medulla

Pass Criteria:

  • 2/5 substances + correct action

How can renal blood flow be measured?
Prompt: What substance can be used to measure renal plasma flow?

  1. Fick principle
    • Amount of a substance taken up per unit time divided by arterio-venous concentration difference
  2. PAH (or any substance that is excreted, not metabolised or stored, doesn’t affect flow)is used to measure effective renal plasma flow (90% cleared)
  3. Actual renal plasma flow = ERPF/0.9 = 700 mL/min
  4. Renal blood flow = RPF x 1/1-Hct   (Hct = 0.45)

Pass Criteria:

  • Concept/principle

Q54

What is the definition of the glomerular filtration rate?

  • The amount of fluid (plasma filtrate) filtered by the glomerulus per unit time

Pass Criteria:

  • Concept of filtration and time to pass

What is the normal GFR?

  • Usually 125 mL/min
  • 180 L/day
  • 10% less in women

Pass Criteria:

  • +/- 20% to pass
  • either per min or per day

What are the mesangial cells?
Prompt: Where are mesangial cells found? What do mesangial cells do?

Prompt: If “in nephron” stated – where in nephron?

  • Contractile cells that help to regulate GFR
  • Located between the basal lamina and the endothelium, in the glomerulus
  • Common between neighbouring capillaries, and in these locations the basal membrane forms a sheath share by both capillaries
  • Also secrete the extracellular matrix, take up immune complexes, and are involved in the progression of glomerular disease

Pass Criteria:

  • Bold to pass

What factors influence GFR?

  • Age
  • Afferent arterial (renal artery) pressure (however autoregulation keeps this stable between about 90-210 mmHg)
  • Afferent arteriolar pressure
  • Efferent arteriolar pressure
  • Efferent venous pressure
  • Intra-renal (interstitial) pressure (obstruction, oedema)
  • Oncotic pressure
  • Glomerular filtration fraction

Pass Criteria:

  • Any 3 to pass

What substances act on mesangial cells to change GFR?
Prompt: What substances act on mesangial cells to alter their function?

  • Glomerular filtration fraction (mesangial cell function) – influence by:
    • Increased
      • ANP, dopamine, PGE2, cAMP
    • Decreased
      • Noradrenaline, vasopressin, AII, PGF2, endothelins, TXA2, leukotrienes

Pass Criteria:

  • BONUS

Q55

How will the kidneys respond to a metabolic acidosis?
Prompt: Describe the role of buffers in the kidney.

  • Aims to return serum pH to normal by increasing the H+ excretion.
  • Kidneys reabsorb HCO3- by actively secreting H+
  • Renal tubule cells contain carbonic anhydrase, converting CO2 to H+ and HCO3-, then PCT cells secrete H+ in exchange for Na+
  • In the DCT, H+ is secreted by a proton pump, limited by urinary pH>4.5 (limiting pH)
  • Buffering in tubular fluid pH with H2CO3, HPO4 and NH3 allows greater H+secretion

Pass Criteria:

  • Must know that H+ actively secreted into tubular fluid in exchange for Na+
  • Must know about buffering and be able to name 2 buffers.