Renal 51 to 60
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.
- Sodium retention and oedema and heart failure
- 3/5 bold
What are common findings in urinalysis of acute intrinsic renal failure?
- Red cells
- 3 bold
What are urinary casts?
- Proteinaceous material precipitated in tubules washed into bladder
- Bold to pass
Describe the way the kidney handles glucose.
- Freely filtered at the glomerulus
- Resorbed in the early part of the PCT by secondary active transport
- Na dependent co-transportation (SGLT2 into cells then GLUT 2 facilitated diffusion into interstitial fluid).
- Excreted in the urine if renal threshold is exceeded.
- 1 & 2, plus understanding of 3 & 4
What are the potential consequences of glycosuria?
- Osmotic diuresis – dehydration, electrolyte loss (Na, K)
What is normal renal blood flow?
- Renal blood flow = approx 1250 mL/min
- Bold (accept 1000-1500)
What substances influence renal blood flow and how?
- Dopamine, ACh
- Angiotensin II
- Constricts afferent and efferent arterioles
- Increase flow in cortex and decrease in medulla
- 2/5 substances + correct action
How can renal blood flow be measured?
Prompt: What substance can be used to measure renal plasma flow?
- Fick principle
- Amount of a substance taken up per unit time divided by arterio-venous concentration difference
- 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)
- Actual renal plasma flow = ERPF/0.9 = 700 mL/min
- Renal blood flow = RPF x 1/1-Hct (Hct = 0.45)
What is the definition of the glomerular filtration rate?
- The amount of fluid (plasma filtrate) filtered by the glomerulus per unit time
- Concept of filtration and time to pass
What is the normal GFR?
- Usually 125 mL/min
- 180 L/day
- 10% less in women
- +/- 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
- Bold to pass
What factors influence GFR?
- 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
- 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:
- ANP, dopamine, PGE2, cAMP
- Noradrenaline, vasopressin, AII, PGF2, endothelins, TXA2, leukotrienes
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
- Must know that H+ actively secreted into tubular fluid in exchange for Na+
- Must know about buffering and be able to name 2 buffers.