BIOL 2420 Lecture Notes - Lecture 13: Collecting Duct System, Proximal Tubule, Alkalosis

7 views3 pages
Unit 8 Lecture 13
The Distal Nephron Controls Acid Excretion
- Distal nephron plays a significant role in the fine regulation of acid-base balance
- Specialized cells called intercalated cells (I cells) interspersed among the principal cells
are primarily responsible for acid-base regulation
- Intercalated cells are characterized by high concentrations of carbonic anhydrase in their
cytoplasm
o This enzyme allows them to rapidly convert CO2 and water into H+ and HCO3-
o The H+ ions are pumped out of the intercalated cell either by the H+-ATPase or by
the H+-K+-ATPase
o Bicarbonate leaves the cell by means of the HCO3--Cl- antiport exchanger
- There are two types of intercalated cells
o Their transporters are found on different faces of the epithelial cell
o During periods of acidosis, type A intercalated cells secrete H+ and reabsorb
bicarbonate
o During periods of alkalosis, type B intercalated cells secrete HCO3- and reabsorb
H+
- Figure above on the left shows how type A intercalated cells work during acidosis
o Secreting H+ and reabsorbing HCO3-
o The process is similar to H+ secretion in the proximal tubule except for the
specific H+ transporters
o The distal nephron uses apical H+-ATPase and H+-K+-ATPase rather than the Na+-
H+ antiport protein found in the proximal tubule
- During alkalosis, when the H+ concentration of the body is too low, H+ is reabsorbed and
HCO3= buffer is excreted in the urine
o The ions are formed from H2O and CO2
o Hydrogen ions are reabsorbed by transport into the ECF on the basolateral side of
the cell, and HCO3- is secreted into the lumen
o The polarity of the two types of I cells is reversed, with the same transport
processes taking place, but on the opposite sides of the cell
- The H+-K+-ATPase of the distal nephron helps create parallel disturbances of acid-base
balance and J+ balance
o In acidosis, when plasma H+ is high, the kidney secretes H+ and reabsorbs K+
Acidosis is often accompanied by hyperkalemia
o Alkalosis, when blood H+ levels are low
Mechanism that allows the distal nephron to reabsorb H+ simultaneously
causes it to secrete K+ with the result that alkalosis goes hand in hand
with hypokalemia
Acid-Base Disturbances May Be Respiratory or Metabolic
- 3 compensatory mechanisms take care of most variations in plasma pH
o under some circumstances, the production or loss of H+ or HCO3- is so extreme
that compensatory mechanisms fail to maintain pH homeostasis
find more resources at oneclass.com
find more resources at oneclass.com
Unlock document

This preview shows page 1 of the document.
Unlock all 3 pages and 3 million more documents.

Already have an account? Log in

Get access

Grade+
$40 USD/m
Billed monthly
Grade+
Homework Help
Study Guides
Textbook Solutions
Class Notes
Textbook Notes
Booster Class
10 Verified Answers
Class+
$30 USD/m
Billed monthly
Class+
Homework Help
Study Guides
Textbook Solutions
Class Notes
Textbook Notes
Booster Class
7 Verified Answers

Related Documents

Related Questions