Transport of Carbon Dioxide in the Blood

Respiration is a biological process. It involves the activity of interchanging oxygen and carbon dioxide via a liquid medium to use the oxygen for the oxidation of glucose inside the mitochondria (the powerhouse of cells) which produces energy, some energy is stored in the high energy bonds of ATP molecules as biological useful energy. So, respiration is a physico-chemical process.

Mechanism of transport of gases

• We breathe with the help of the mouth and nose and air reaches the larynx or voice box, and then the trachea.
• The trachea is a tube-like structure containing a cartilage ring to prevent it from collapsing.
• Branches of the trachea are divided into two bronchi, i.e., left and right bronchus. Bronchus divides continuously into smaller and smaller bronchioles.
• Air sacs are obtained by further division of bronchioles. It is called alveoli. It expands when a person inhales and collapses when a person exhales.
• While interchanging gases, oxygen from the lungs to the blood whereas carbon dioxide moves from blood to the lungs. The process is done between the alveoli and blood capillaries, located at the walls of the alveoli.
• Red blood cells move through capillaries. The wall of alveoli contains a membrane with capillaries. So, they are too close. This helps oxygen and carbon dioxide to move freely between the respiratory tract and blood.
• Oxygen fixes with red blood cells and then again moves back towards the heart. Whereas, carbon dioxide moves out from the body when another time a person exhales.
• Blood carries oxygen from the respiratory organs to the tissue cells, and also carries carbon dioxide from the tissue cells to the respiratory membrane.

Transport of Carbon Dioxide

When the process of cell—respiration is completed, tissues produced carbon—dioxide as an end product. After that, carbon dioxide from the cells disperses into blood and interchange with the oxygen present in blood under normal resting conditions. About 3.7 ml of carbon dioxide reaches 100 ml of blood. It is carried by both plasma and hemoglobin of blood.

Blood transport carbon dioxide in three ways

As Carbonic Acid

Approximately 7% of carbon dioxide (i.e., roughly 2.4ml per deciliter in arterial blood and about 2.7ml per deciliter in venous blood) is transferred by blood in the form of carbonic acid, which is prepared by the dissolution of CO₂ in water. One and all deciliters of blood transmit about 0.3ml of CO₂ in the dissolved form. This division of CO₂ is responsible to form. This division of CO₂ is responsible for the CO₂ tension in the blood.

CO₂ + H₂O——————–> H₂CO₃

This reaction mostly takes place in RBCs because it is catalyzed by a zinc-activated enzyme, carbonic anhydrase, and that is stimulated by low PO2 at the cellular level.

As bicarbonates of sodium and potassium

Approximately 70% of carbon dioxide is carried among the body tissues to the lungs as sodium and potassium bicarbonates. Inside the erythrocytes mostly carbonic acid formed which separates into hydrogen (H⁺) and bicarbonate HCO_3^– ions. Mostly bicarbonate ions break into the plasma. Equal amounts of chloride Cl ^– are scattered inside RBC’s from the plasma membrane to continue electroneutrality. This interchange of HCO_3^– of red blood cells (RBC’s) and Cl^– of plasma is known as chloride shift or Hamburger shift, given by Hamburger (1918). This process takes place in the presence of bicarbonate- chloride carrier protein in RBCs which commute (come and go) these two ions in reverse directions.

H₂CO₃ ———————> H⁺ + HCO₃^–

K. Hb ————————> K⁺ + Hb^–

(In RBC) K⁺ + HCO_3^– ————-> KHCO₃

(In plasma) Na⁺ + HCO₃ ————> NaHCO₃

As carbaminohaemoglobin

About 23% of CO₂ is transferred as carbaminohaemoglobin which is made by a reversible combo of CO₂ with amino groups (globin part) of hemoglobin. Its emergence is leaned by high PCO₂ and low PO₂ at the level of body tissues.

Hb^– + H+ ————> H -Hb (Haemoglobin acidic)

H. Hb + CO_² ————–> CO_{2 .} H Jb (Carbaminohaemoglobin)

Reversible compounds are bicarbonates, carbonic acid, and Carbaminohaemoglobin and which are formed in the presence of low PO₂ ad low acidic hemoglobin at a cellular level. Such compounds detached at the lung level, where high PO₂ prefers dissociation of carbonic acid and acidic oxyhemoglobin by carbonic anhydrase enzyme. Now, carbon dioxide becomes free to be interchanged with oxygen during external respiration.

Frequently Asked Questions

Question 1:Name three forms by which CO₂ is transported by the blood from body tissues to the lungs.

Answer:

As carbonic acid, bicarbonates of Na⁺ and K ⁺, and Carbamino hemoglobin.

Question 2. What is the main form in which CO₂ is transported by blood?

Answer:

Sodium and potassium bicarbonates.

Question 3. What is the significance of chloride shift?

Answer:

The main significance of chloride shift is to maintain an acid-base equilibrium of pH 7.4 for blood and electrical balance between erythrocytes and blood plasma.

Question 4: Where is carbonic anhydrase located? What is its function?

Answer:

It is located in the red blood cells. It facilitates the dissolution of CO₂ to form carbonic acid in water.

Question 5: What is the role of carbonic anhydrase in the transport of gases?

Answer:

It catalyzes the dissolution of CO₂ in water to form carbonic acid into RBCs.