PHYS Structure & Functions of the Kidneys - Week 7

Question 1

Functions of the kidneys.

Answer 1

• Regulate water volume , osmolarity & electrolyte balance
• Regulation of acid-base balance
• Excretion of metabolic waste products & foreign chemicals
• Release of endocrine hormones (e.g., renin, erythropoietin , 1, 25-dihydroxy vit D3)
• Gluconeogenesis
• Regulation of BP via Na+ regulation.

Question 2

Pathway of urine from renal papilla…

Answer 2

Renal papilla -> pelvis -> ureters.

Question 3

Nephron is composed of:

Answer 3

1. Renal corpuscle (filtration unit)
   a. Glomerulus capillaries/loops – more efficient filters than other capillaries .
   i. Afferent renal arteriole enters & efferent renal arteriole exits
   b. Bowman’s capsule (fluid-filled cavity)
2. Renal tubules

Question 4

3 x layers of the glomerular filtration barrier.

Answer 4

1. Single-celled capillary endothelium (w fenestrations/pores).
2. Non-cellular BM.
3. Single-celled epithelial lining/podocytes of Bowman’s capsule.

Question 5

3 x processes involved in the formation of urine. Include details of location. Typical substances absorbed or excreted…

Answer 5

1. Glomerular filtration – movement of fluid and solutes from glomerular capillaries -> Bowman’s capsule
   a. Passive, non-selective process
   i. Small molecules filter freely (e.g., H2O, glucose, a. acids) -> enter proximal tubular fluid.
   ii. Larger molecules cannot freely cross barrier (e.g., plasma proteins ) [thus, should not enter proximal tubular fluid].
2. Tubular reabsorption – movement of materials from the filtrate in the tubules -> peritubular capillaries (e.g., Na+, Cl-, a. acids, glucose , water).
   NB: Filtrate -> renal tubular epithelial luminal membrane -> cytoplasm -> renal tubular epithelial basolateral membrane -> interstitial fluid -> endothelium -> plasma.
3. Tubular secretion – movement of solutes from peritubular capillaries -> tubules (e.g., exogenous substances – drugs, metabolic substances – ammonium, H ions…).
   NB: Plasma -> endothelium -> interstitial fluid -> renal tubular epithelial basolateral membrane -> cytoplasm -> renal tubular epithelial luminal membrane -> filtrate.

Question 6

Describe path of blood flow through the nephron.

Answer 6

Afferent arteriole -> glomerulus -> efferent arteriole -> peritubular capillaries -> vasa recta.

Question 7

What substance is found within Bowman’s capsule?

Answer 7

Filtrate = plasma - proteins.

Question 8

What forces drive & oppose filtration of fluids & solutes and at what pressures?

Answer 8

• Glomerular (blood) hydrostatic pressure @ 55mmHg – favours filtration.
• Blood colloid osmotic pressure @ 30mmHg – opposes filtration via dilution of proteins present in blood w water from glomerular capsule.
• Capsular hydrostatic pressure @ 15mmHg – opposes filtration.

Question 9

Pathway of urine from renal papilla…

Answer 9

Renal papilla -> pelvis -> ureter.

Question 10

PNet Glomerular Filtration =

Answer 10

P GC - (P BC + pi GC)
Glomerular pressure - (Blood Colloidal + Capsular).

Question 11

What 2 x renal related measures are the most important determinants of glomerular filtration rate?

Answer 11

Renal blood flow & glomerular capillary pressure.

Question 12

GFR =

Answer 12

Volume of filtrate formed via kidneys/min.

Question 13

How is GFR usually estimated?

Answer 13

Via measurement of creatinine.

Question 14

Ideal marker for measuring GFR is a substance that is:

Answer 14

• Freely filtered by glomerulus
• Not secreted/absorbed via tubules
• Not synthesised/metabolised via kidneys.

Question 15

What is renal clearance?

Answer 15

Volume of plasma that is completely cleared of a particular substance by the kidney per unit of time.