Renal

Question 1

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

Answer 1

Leukocytes, red cells, casts, proteinuria.

Question 2

What are urinary casts?

Answer 2

Proteinaceous material that is precipitated in renal tubules and then washed into the bladder.

Question 3

Describe the way the kidney handles glucose. (This is a VIVA about diabetes)

Answer 3

1. Freely filtered at the glomerulus
2. Reasbsorbed in the PCT by secondary active transport
3. Sodium dependent co-transportation (SGLT2)
4. Excreted in the urine if renal threshold is exceeded.

Question 4

What are the potential consequences of glycosuria?

Answer 4

Osmotic diuresis - dehydration, electrolyte loss (Na, K)

Question 5

How does the kidney handle sodium?

Answer 5

• Filtered at the glomerulus
• 60% is reabsorbed in the PCT, primarily by Na+/H+ exchange
• 30% is reabsorbed in the thick ascending limb of the Loop of Henle
• 7% is reabsorbed in the DCT by the Na-Cl co-transporter
• 3% is reabsorbed by ENaC channels in the collecting duct (regulated by aldosterone)

Sodium is actively pumped out of the basolateral membrane via the Na/K/ATPase

Question 6

What factors affect the GFR?

Answer 6

• Size of capillary bed
• Permeability of capillary bed
• Hydrostatic pressure gradient
• Osmotic / Oncotic pressure gradient

Question 7

List some clinical conditions that will lower the GFR

Answer 7

• Reduced renal blood flow (e.g. hypotension)
• Afferent arteriolar constriction
• Ureteral obstruction (e.g. calculus)
• Lowered effective filtration surface area (kidney diseases)

Question 8

How does the kidney handle potassium?

Answer 8

• Freely filtered at the glomerulus
• Reabsorbed ACTIVELY in the PCT
• Reabsorbed in the thick ascending limb of Loop of Henle via Na-K-cotransporter
• SECRETED into the tubular lumen in the DCT and collecting ducts
• Excretion of K⁺ in urine will be reduced if there is increased excretion of H⁺ because of the H/K/ATPase

Question 9

Describe the renal response to acidosis.

Answer 9

H⁺ secreted into the tubular lumen in the PCT via the Na⁺/H⁺ exchanger.

Renal buffering systems:

Bicarbonate, Phoshate, Ammonia.

Retention of bicarbonate, in exchange for greater H⁺ secretion

Question 10

Describe the mechanisms which determine renal blood flow.

Answer 10

Systemic:

• Systemic MAP / Volume status

Local:

• Autoregulation (stretch response)
• Neurohumeral systems (RAAS)
• Dopamine + Prostaglandins + ACh (afferent arteriole dilators)
• Sympathetic nervous stimluation (afferent arteriole constrictor)
• Regional: Cortex receives greater blood flow than Medulla

(3 to pass)