<< Chapter < Page Chapter >> Page >

Dissolved carbon dioxide

Although carbon dioxide is not considered to be highly soluble in blood, a small fraction—about 7 to 10 percent—of the carbon dioxide that diffuses into the blood from the tissues dissolves in plasma. The dissolved carbon dioxide then travels in the bloodstream and when the blood reaches the pulmonary capillaries, the dissolved carbon dioxide diffuses across the respiratory membrane into the alveoli, where it is then exhaled during pulmonary ventilation.

Bicarbonate buffer

A large fraction—about 70 percent—of the carbon dioxide molecules that diffuse into the blood is transported to the lungs as bicarbonate. Most bicarbonate is produced in erythrocytes after carbon dioxide diffuses into the capillaries, and subsequently into red blood cells. Carbonic anhydrase (CA) causes carbon dioxide and water to form carbonic acid (H 2 CO 3 ), which dissociates into two ions: bicarbonate (HCO 3 ) and hydrogen (H + ). The following formula depicts this reaction:

CO 2  + H 2 CA  H 2 CO 3 H +  + HCO 3 MathType@MTEF@5@5@+=feaagyart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4qaiaab+eadaWgaaWcbaGaaeOmaaqabaGccaqGGaGaae4kaiaabccacaqGibWaaSbaaSqaaiaabkdaaeqaaOGaae4taiaabccajaaOdaahaaqcbaCabKazbakabaqcba6aa8XbaKazbakabaGaae4qaiaabgeaaiaawgoiaaaakiaabccacaqGibWaaSbaaSqaaiaabkdaaeqaaOGaae4qaiaab+eadaWgaaWcbaGaae4maaqabaGccqGHugYQcaqGibWaaWbaaSqabeaacaqGRaaaaOGaaeiiaiaabUcacaqGGaGaaeisaiaaboeacaqGpbWaaSbaaSqaaiaaiodacqGHsislaeqaaaaa@53ED@

Bicarbonate tends to build up in the erythrocytes, so that there is a greater concentration of bicarbonate in the erythrocytes than in the surrounding blood plasma. As a result, some of the bicarbonate will leave the erythrocytes and move down its concentration gradient into the plasma in exchange for chloride (Cl ) ions. This phenomenon is referred to as the chloride shift    and occurs because by exchanging one negative ion for another negative ion, neither the electrical charge of the erythrocytes nor that of the blood is altered.

At the pulmonary capillaries, the chemical reaction that produced bicarbonate (shown above) is reversed, and carbon dioxide and water are the products. Much of the bicarbonate in the plasma re-enters the erythrocytes in exchange for chloride ions. Hydrogen ions and bicarbonate ions join to form carbonic acid, which is converted into carbon dioxide and water by carbonic anhydrase. Carbon dioxide diffuses out of the erythrocytes and into the plasma, where it can further diffuse across the respiratory membrane into the alveoli to be exhaled during pulmonary ventilation.


About 20 percent of carbon dioxide is bound by hemoglobin and is transported to the lungs. Carbon dioxide does not bind to iron as oxygen does; instead, carbon dioxide binds amino acid moieties on the globin portions of hemoglobin to form carbaminohemoglobin    , which forms when hemoglobin and carbon dioxide bind. When hemoglobin is not transporting oxygen, it tends to have a bluish-purple tone to it, creating the darker maroon color typical of deoxygenated blood. The following formula depicts this reversible reaction:

CO 2  + Hb HbCO 2 MathType@MTEF@5@5@+=feaagyart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4qaiaab+eadaWgaaWcbaGaaeOmaaqabaGccaqGGaGaae4kaiaabccacaqGibGaaeOyaiabgsziRkaabIeacaqGIbGaae4qaiaab+eadaWgaaWcbaGaaeOmaaqabaaaaa@422F@

Similar to the transport of oxygen by heme, the binding and dissociation of carbon dioxide to and from hemoglobin is dependent on the partial pressure of carbon dioxide. Because carbon dioxide is released from the lungs, blood that leaves the lungs and reaches body tissues has a lower partial pressure of carbon dioxide than is found in the tissues. As a result, carbon dioxide leaves the tissues because of its higher partial pressure, enters the blood, and then moves into red blood cells, binding to hemoglobin. In contrast, in the pulmonary capillaries, the partial pressure of carbon dioxide is high compared to within the alveoli. As a result, carbon dioxide dissociates readily from hemoglobin and diffuses across the respiratory membrane into the air.

Questions & Answers

What is the skin
Astony Reply
What is physiology?
Njaleny Reply
it is the study of the structure of the human body and its reationship
Physiology is the function of a living organism.
It is the study of human body and how it works.
It is d entrance to the uterus
Umunna Reply
It is a small sensitive part of female sex organ which is found above d entrance to the vagina
A small hole in d skin which contains d root of a hair
A thin membrane which covers d entrance to the vagina in young girls
Is a gland that produces milk in women and other female mammals
A repeated process in which a woman's uterus gets ready for pregnancy which ends in a period if she does not get pregnant
hi sir
so in summary describe the level of structural complexity within the body
Freda Reply
how can we describe briefly the levels of organization
what is blood clotting
Yahya Reply
Tiny bits in your blood called platelets get "turned on" by triggers released when a blood vessel is damaged. They stick to the walls in the area and each other, changing shape to form a plug that fills in the broken part to stop blood from leaking out. When activated, platelets also release chemic
what is a cell membrane?
lameck Reply
the cell membrane also called the plasma membrane regulates the transport materials entering and existing the cell.
what's gonna happen if your body doesn't produce enough white blood cells?
how is speech controlled by the nervous system?
Joseph Reply
The broca's area
what does the HCG
chemical level cellular level tissue level organ level organ system level organism
Chidera Reply
Yes Yes because they can perform more than one activity in the body
the functional and structural unit of the body
A group of 2 or more tissue that come together to perform a specific function
A group of organs that work together to perform a specific function or meet the physiological needs of the body
It's the highest level of organization
2 or more cells coming together to perform a specific function
Skeletal muscles can be tetanized but not cardiac muscle.Discuss
Okeke Reply
what is regional anatomy?
Grace Reply
study of structures that contribute to specific body region
what is human anatomy?
It's the study of the interrelationships of body structures in a specific region
is the study of the structure of the body and the relationship between body systems
what is grey matter
OJO Reply
it is the major component of the central nervous system consisting of the neuronal cell bodies,neuropil,glial cells,capillaries and synapses
What is neuron cell
Dev Reply
neuron cell are the fundamental units of the brain and nervous system responsible for receiving sensory input from the external world, for sending motor commands to muscles and for transforming and relaying the electrical signals at every step in between
What is the perfect defination of Life
What does a word muscles means ?
the perfect destination of life is to have life without flaws and defects.Alife where nothing can go wrong.
what is Anatomy
Hannah Reply
because she's not yet at term
Nansi Reply
what is physiology?
Grace Reply
what is physiology
Physiology is the study of the functions of the human body
am a new one!!
what is Homeopathy

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play

Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Anatomy & Physiology' conversation and receive update notifications?