Functional anatomy of urine production by the kidneys

Question 1

What are the 7 main regulatory functions of the kidneys?

Answer 1

1. excretion of metabolic waste, drugs, hormone metabolites
2. water and electrolyte balance
3. arterial pressure: renin/ angiotensin II
4. acid/base balance: excretion of acids
5. erythrocyte production: erythropoietin
6. 1,25-dihydroxyvitamin D3 (calcitriol) production
7. gluconeogenesis

Question 2

What are the 2 distinguishing features of renal blood flow?

Answer 2

1. high rate of blood flow
2. Two capillary beds: glomerular and peritubular, connected in series, separated by efferent arterioles. Glomerular capillaries filter, and peritubular capillaries reabsorb

Question 3

Describe the renal tubular system.

Answer 3

Question 4

What’s the difference between cortical and juxtamedullary nephrone?

Answer 4

Cortical: located mostly in the cortex, short Loop of Henele

Juxtamedullary: mostly in the medulla, long Loop of Henele, has Vasa recta

Question 5

What are the 2 main steps of micturition?

Answer 5

1. progressive urine filling leading to wall pressure reaching a threshold, then
2. activation of micturition reflex

Question 6

Describe the innervation of the urinary bladder.

Answer 6

• pelvic nerve = principle nervous supply of the bladder
• sacral plexus = sensory and motor fibers
• the sensory nerve detect bladder wall stretch –> initiates stretch
• the motor nerves = parasympathetic nerves

Question 7

Describe the micturition reflex.

Answer 7

1. progressive/ rapid increase in bladder pressure
2. sustain increase in bladder pressure
3. return of the bladder to basal tone:
   - sensory signals from bladder wall stretching –> sacral segments of the spinal cord through the pelvic nerves –> back down to the bladder via parasympathetic nerves
   - elicit another reflex –> pudendal nerve —> inhibits the external sphincter

• though micturition is an autonomic spinal cord reflex, it can be inhibited by the brainstem and cerebral cortex (mainly inhibitory but can also become excitatory)

Question 8

What factors determine the composition of urine?

Answer 8

1. glomerular filtration of substance from the blood
2. reabsorption of substance from renal tubules into blood
3. secretion of substance from the blood into the renal tubules