Question

MCAT Mini-Tutorial: Regulation of pH and Blood Pressure in the Kidneys

Answer 1

\({\bf{pH~Regulation:}}\)
- high pH conditions:
> HCO3- released into urine
- low pH conditions:
> H+ excreted into urine

enzyme is carbonic anhydrase. pathway is CO2 --> carbonic acid --> bicarbonate + H+

compared to respiratory pH regulation, renal pH regulation is slow and takes place over days

Answer 2

\({\bf{Blood~Pressure~Regulation:}}\)
- two main sites: juxtaglomerular cells in the afferent arteriole, and the macula densa in the distal tubule

- stimulus: low blood pressure
> JG cells release renin into bloodstream
- renin converst angiotensinogen to angiotensin I
- antiotensin converting enzyme (ACE) converts angiotensin I to II in lungs
- angiotensin II raises blood pressure thru vasoconstriction
- angiotensin releases aldosterone which also increases BP

- stimulus: low osmolarity
> macula densa cells: stimulate JG cells to release renin
- dilates the afferent arteriole to increase blood flow

Answer 3

Source material is Chapter 10.3 of MCAT: Biology Review, 2nd edition by Princeton Review