The Chloride Shift

As a result of catalysis by carbonic anhydrase within the red blood cells, large amounts of carbonic acid are produced as blood passes through the systemic capillaries. The buildup of carbonic acid concentrations within the red blood cells favors the dissociation of these molecules into hydrogen ions (protons, which contribute to the acidity of a solution) and HCO3- (bicarbonate), as shown by this equation:

The hydrogen ions (H+) released by the dissociation of carbonic acid are largely buffered by their combination with de-oxyhemoglobin within the red blood cells. Although the unbuffered hydrogen ions are free to diffuse out of the red blood cells, more bicarbonate diffuses outward into the plasma than does H+. As a result of the "trapping" of hydrogen ions within the red blood cells by their attachment to hemoglobin and the outward diffusion of bicarbonate, the inside of the red blood cell gains a net positive charge. This attracts chloride ions (Cl-), which move into the red blood cells as HCO3- moves out. This exchange of anions as blood travels through the tissue capillaries is called the chloride shift (fig. 16.38).

The unloading of oxygen is increased by the bonding of H+ (released from carbonic acid) to oxyhemoglobin. This is the Bohr effect, and results in increased conversion of oxyhemoglo-bin to deoxyhemoglobin. Now, deoxyhemoglobin bonds H+ more strongly than does oxyhemoglobin, so the act of unloading its oxygen improves the ability of hemoglobin to buffer the H+ released by carbonic acid. Removal of H+ from solution by combining with hemoglobin (through the law of mass action), in turn, favors the continued production of carbonic acid and thereby improves the ability of the blood to transport carbon dioxide. Thus, carbon dioxide increases oxygen unloading, and oxygen unloading increases carbon dioxide transport.

When blood reaches the pulmonary capillaries (fig. 16.39), deoxyhemoglobin is converted to oxyhemoglobin. Since oxyhe-moglobin has a weaker affinity for H+ than does deoxyhemoglo-bin, hydrogen ions are released within the red blood cells. This attracts HCO3- from the plasma, which combines with H+ to form carbonic acid:

Under conditions of lower PCO2, as occurs in the pulmonary capillaries, carbonic anhydrase catalyzes the conversion of carbonic acid to carbon dioxide and water:

carbonic anhydrase h2co3->- CO2 + h2o low P

Tissue cells

Tissue cells

Physiologic Chloride Shift

Red blood cells

Plasma

HCO3

(Chloride shift)

Red blood cells

Plasma

HCO3

(Chloride shift)

■ Figure 16.38 Carbon dioxide transport and the chloride shift.

Carbon dioxide is transported in three forms: as dissolved CO2 gas, attached to hemoglobin as carbaminohemoglobin, and as carbonic acid and bicarbonate. Percentages indicate the proportion of CO2 in each of the forms. Notice that when bicarbonate (HCO3-) diffuses out of the red blood cells, Cl-diffuses in to retain electrical neutrality. This exchange is the chloride shift.

In summary, the carbon dioxide produced by the cells is converted within the systemic capillaries, mostly through the action of carbonic anhydrase in the red blood cells, to carbonic acid. With the buildup of carbonic acid concentrations in the red blood cells, the carbonic acid dissociates into bicarbonate and H+, which results in the chloride shift. A reverse chloride shift operates in the pulmonary capillaries to convert carbonic acid to H2O and CO2 gas, which is eliminated in the expired breath (fig. 16.39). The PCo2, carbonic acid, H+, and bicarbonate concentrations in the systemic arteries are thus maintained relatively constant by normal ventilation. This is required to maintain the acid-base balance of the blood (fig. 16.40), as discussed in chapter 13 and in the next section.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Responses

  • Kaj
    How carbondioxide is trasported through blood?
    7 years ago
  • melanie grunwald
    Are chloride level higher in pulmonary capillaries or systemic capillaries?
    7 years ago
  • anni
    When does chloride move out of the red blood cell?
    7 years ago
  • peter
    Why does deoxyhemoblobin buffer more H than HbO2 does?
    7 years ago
  • antje
    What is chloride shift the reverse?
    7 years ago
  • gormadoc
    How does chloride shift bicarb?
    7 years ago
  • nereo
    When co2 is on hemoglobin, does chloride shift into the plasma?
    7 years ago
  • Tina
    Does cl diffuse from the plasma into the rbc?
    7 years ago
  • Ahmed Findlay
    Why does the chloride shift occur during co2 transport?
    7 years ago
  • anke hueber
    How is carbon dioxide is exchanged at tissue cells and include the chloride shift?
    7 years ago
  • DONNINO
    How carbon dioxide is exchanged with oxygen at tissue cells chloride shift?
    7 years ago
  • Efrem Fethawi
    What is the cl shift in the RBC for systemic gas exchange?
    7 years ago
  • anja
    Why is it called chloride shift?
    7 years ago
  • Haddas
    Is cell bicarbinate concentration higher than blood?
    7 years ago
  • ROMAN
    When concentration of HCO3 in red blood cell is grater than in the plasma?
    7 years ago
  • stephanie
    Does h diffuse into the capillaries?
    7 years ago
  • REZENE
    How is electrical neutrality maintained in red blood cells?
    6 years ago
  • Luca
    How does carbonic anhydrase catalyze alter H concentration in red blood cells?
    6 years ago
  • Ansegar Gammidge
    How does calcium chloride diffuse through the red blood cell?
    6 years ago
  • MIIA
    Does hco3 diffuse out the red blood cells into plasma?
    6 years ago
  • paola
    Why does CO2 form HCO3 and H in the systemic capillaries?
    6 years ago
  • licia
    Why does the chloride shift occur during co2 transport in the plasma?
    6 years ago
  • sandra
    What is the purpose of chloride shift?
    6 years ago
  • JENS
    Does chloride enter red blood cells on the chloride shift?
    6 years ago
  • Juhani
    What electrical balance does the chloride shift maintain?
    6 years ago
  • Gaudenzia
    What is the role of chloride shift?
    6 years ago
  • Kaija
    Why does HCO3 quickly diffuse from RBCs in the tissues?
    6 years ago
  • destiny
    Does the chloride shift affect blood cell volume?
    6 years ago
  • BILDAT
    How does the chloride shift work?
    6 years ago
  • felix
    What are hydrogen ions released by the dissociation of carbonic acid are buffered by their?
    6 years ago
  • Annett
    Does chloride shift change red blood cell volume?
    6 years ago
  • Sandra
    How do chloride shift works?
    6 years ago
  • SMERALDA
    How chloride work in anatomy?
    5 years ago
  • may
    How does chloride facilitate the conversion of co2 to hco3?
    5 years ago
  • jessica
    What is the chloride shift physiology?
    5 years ago
  • Dirk
    Does the chloride shift maintain electro neutrality?
    5 years ago
  • Katherine
    What is chloride shift anatomy?
    5 years ago
  • kevin law
    Why is the chloride shift required?
    4 years ago
  • Ishbel Docherty
    Why does bicarbonate diffuse out of the red blood cell?
    4 years ago
  • marley
    Does chloride affect carbonic anhydrase?
    4 years ago
  • meeri
    What is electrical neutrality by chloride shift?
    4 years ago
  • riikka
    Does Chloride shifts out of the red cell?
    4 years ago
  • pupetta
    Which of the following best describes the chloride shift as seen in the figure?
    3 years ago
  • swen
    Where does the reverse chloride shift occur?
    3 years ago
  • muhammed
    Which of the following best describe the chloride shift as seen in the figure?
    3 years ago
  • Frodo
    How does chloride affect H ions?
    3 years ago
  • carol
    What is chloride shift formula?
    3 years ago
  • Futsum
    What is the purpose of chloride bicarbonate shift?
    3 years ago
  • Charles
    What is choloride shift?
    3 years ago
  • irene
    Why chloride shift occur although H combines with Hb?
    3 years ago
  • Togo
    Which ions diffuse out of the red blood cells to maintain electrical neutrality?
    3 years ago
  • trudy
    How does co2 fixation occur in erythrocyte cells?
    3 years ago
  • tesfalem
    How does the chloride shift in systemic capillaries happen?
    3 years ago
  • michael theissen
    How does the haemoglobin acid and chloride shifts?
    3 years ago
  • Anna-Liisa
    What is called reverse of chloride shift?
    3 years ago
  • orgulas
    What happens to chloride when blood pass through capillaries?
    3 years ago
  • mikaela
    What is the significance of chloride shift?
    3 years ago
  • pamphila
    What is chloride shift in clinical chemistry?
    3 years ago
  • lacey
    How chloride shift maintains the ph of blood?
    3 years ago
  • celio
    What is the function of chloride shift?
    3 years ago
  • Max
    Does carbonic anhydrase dissociate into bicarbonate and hydrogen acid?
    3 years ago
  • dominik
    Which of the following best describes the chloride shift as seen in the figure easynotecards?
    3 years ago
  • Adonay
    When bicarbonate moves from the red blood cell with clohride into plamas what is this called?
    3 years ago
  • agata
    What is chloride shift illustrate?
    3 years ago
  • monica
    What is chloride shift in nerve physiology?
    2 years ago
  • annika
    What is the role of chloride ion in CO2 transport?
    2 years ago
  • askalu bisrat
    What is cloride shiff?
    2 years ago
  • wiseman
    How large is the chloride shift?
    2 years ago
  • hana
    Why bicarbonate diffuses out in red blood cells?
    2 years ago
  • germano
    What happen after HCO3 diffuse out from red blood cell?
    2 years ago
  • Abbey
    What is the chloride shift and why does it occur in simple way?
    2 years ago
  • catriona
    What is the magnesium and chloride shift?
    2 years ago
  • JUKKA
    Which of the following molecules acts as a buffer during the chloride shift?
    2 years ago
  • mario
    What is the benefit of chloride shift and reverse chloride shift?
    2 years ago
  • Sandy
    What is positive cl shift?
    2 years ago
  • Nina Johnstone
    Which of the following molecules act as a buffer during cholride shift?
    1 year ago
  • neftalem iggi
    How chloride shift maintain phsiological ph?
    1 year ago
  • krystian
    Why do rbc doesnt burst due to accumulation of chloride ions in them during chloride shift?
    1 year ago
  • JUHANI
    What is chloride shiff?
    1 year ago
  • mikolaj
    How cloride shift increase size of rbc?
    1 year ago
  • marina
    What is chloride shift definition?
    1 year ago
  • SILKE
    How chloride shift bicarbonate into cells?
    1 year ago
  • niina hurme
    What is chlorine shiftwhat its significance during respiration?
    1 year ago
  • matthias
    What is chloride shiftWhere and when does it take place?
    1 year ago
  • Rocio
    Why chloride is used for exchange with co2 in blood?
    10 months ago
  • Hana
    Why does increased chloride shift oxygen?
    10 months ago
  • Anu
    How does chloride ion enhances the release of oxygen to the tissues?
    9 months ago
  • Darryl
    What ion enter the cell to maintain electrical neutrality with regard to red blood cell?
    7 months ago
  • jodie
    Where chloride shif occur?
    6 months ago
  • Niklas
    How does chloride assist in the movement of co2?
    3 months ago
  • Maximilian
    Where in the body does the reverse chloride shift occur?
    1 month ago

Post a comment