BIOLOGY: CHAPTER 7(a) - GASEOUS EXCHANGE

RESPIRATORY SURFACE-ALVEOLUS

1. LARGE SURFACE AREA-human lungs consists of million of alveolus.
2. THIN-wall of alveolus consists of one layer of thin squamous epithelial cells to facilitate diffusion of gaseous such as o2 and co2.
3. MOIST-inner surface of alveolus is lined with fluid and its surface tension is lowered by secretion of surfactant from special septal cells in the alveolus . This fluid dissolve respiratory gaseous for diffusion and speed up gas exchange.
4. Each alveolus is covered by a dense of network capillaries which carries away the oxygen and keep the partial pressure low.

THE RESPIRATORY PIGMENT- HAEMOGLOBIN

-The haemoglobin in red blood cells is responsible in transporting oxygen and carbon dioxide.
-Breathing allows the inspired air to come in contact with the blood vessel that cover the alveoli.

HAEMOGLOBIN

-Haemoglobin is a complex conjugated protein
-Quaternary in nature
-Protein consists of four polypeptide chains , two alpha and two beta
-These polypeptide chains are globular in nature and called globin
-Each haem group can associate with one molecule of oxygen that gives blood its bright red colour
-Process of associating oxygen with the haem group is called oxygenation
-Its a loose combination which allows dissociation occurs easily

TRANSPORT OF OXYGEN AND CARBON DIOXIDE IN BLOOD

-RBC are round disc , concave on each side(biconcave) and do not contain nucleus. Gives it an extremely high surface area to volume ratio for more efficient gaseous exchange.
-In the blood , only small portion of oxygen can dissolve in plasma as the solubility of o2 to plasma is very low.
-Haemoglobin in RBC increase the ability of blood to transport o2 by about 65 to 70 times.
-The main function of haemoglobin is to carry oxygen but it can help to transport c02.
-It can do so efficiently because it can bind with oxygen at very low partial pressure of oxygen.
-COOPERATIVITY@When the first o2 bind with the first haem group, the haemoglobin molecule changes shape slightly. This facilitates the binding of the next oxygen.
-When there is a drop in partial pressure of oxygen, haemoglobin will release oxygen.
-In the tissue, the partial pressure of oxygen is lower that at the alveoli , the tissues are continuously supplied with oxygen.
-CARBON DIOXIDE is more soluble in blood than oxygen.

SIMPLE ILLUSTRATION

TRANSPORTATION OF CO2 BY BLOOD TO LUNGS

-Either in RBC or BLOOD PLASMA

-Can be done in three different ways

1. Transport by RBC in the form of HYDROGEN CARBONATE IONS(HCO3) 85%

-About 85% of the CO2 produced during respiration diffuse into RBC and combine with water to form carbonic acid (H2CO3) catalysed by carbonic anhydrase.

H20 + CO2 = H2CO3

-The carbonic acid the dissociate to HCO3 and H+ with the presence of same enzyme carbonic anhydrase

H2CO3 = HCO3 + H+

-Then , the HCO3 diffuse out from the RBC into the plasma.

-This occur because RBC is very permeable to HCO3

-Later on, CL(CHLORIDE IONS) diffuse into the RBC to maintain electrical neutrality. This process is called chloride shift.

-The hydrogen carbonate ions are then carried to lungs and converted to CO2.

-Dont forget that the H+ is still in the RBC ,

-The presence of H+ ions in the RBC decrease the pH of the blood.

-This proton are quickly mopped by free haemoglobin to form HAEMOGLOBINIC ACID (HHb)

-The free haemogloobin which acts as a pH buffer is made available from the forced dissociation of oxyhaemoglobin.

-And oxygen is released to the cell , this phenomenon is called BOHR SHIFT.

-When blood reaches the lungs , the whole process is repeated.

2. CO2 combines with haemoglobin in the RBC to form CARBAMINO COMPOUND 10%

R as Hb(haemoglobin)

-CO2 produced combine in a reversible reaction with the amino group of haemoglobin and form carbaminohaemoglobin.
-The carbaminohaemoglobin then transported to the lung where it dissociates to CO2.
-The binding of CO2 to haemoglobin lowers the affinity of haemoglobin for oxygen.
-Which forces to haemoglobin to release its oxygen load.

3. CO2 dissolve in blood plasma 5%

-About 5% of CO2 dissolve in blood plasma to form carbonic acid ( H2CO3)
-But at a slower rate compared to in RBC due to lack of enzyme.
-The carbonic acid the ionises to H+ and hydrogen carbonate(HCO3)
-The presence of H+ ions causes in increase in its acidity
-Quickly buffered by plama proteins to form proteinic acid.

PICTURE REFERENCE