Physiology of respiration, Biology



  • It is Haemotasis. It takes place in Alveoli between alveolar air and arterial cappilary by diffusion i.e., from high partial pressure to low partial pressure.
  • O2   104 →  40 mmHg
  • CO2  46 → 40 mmHg


  • O2 is less soluble so 3% O2 is transported by plasma. 97% O2 is transported by Hb.
  • 1 Hb can carry 4 O2 .
  • If Hb reacts with O3   or any other oxydising agent Methemoglobin is formed. Now it cannot carry O2 .
  • Reaction of Hb with O  is oxygenation not oxidation. Because e- are not given out.
  • Hb4  + 4O2  → Hb4 O8
  • O2   reaches to every cell in the form of oxyhaemoglobine. In cell dissociation of Hb.O2   occur.
  • Hb.O2 →  Hb + O2

2462_transportation of oxyen.png   1759_transportation of oxygen.png

  • Partial pressure of Ois less in cell.
  • If CO2   concentration is more, then dissociation curve bends to right. It is Kristan's Bohr effect.
  • This curve is Sigmoid not similar in all animals. It is normal at 40 mm Hg CO2 . Shown by winton & Begllis.


Internal respiration occur in cell. It includes glycolysis and Kreb's cycle


  • CO2   is more soluble than O2. So from cell it comes in extra cellular fluid and then in blood.
  • CO2   is transported in 3 forms.

(a)           In the form of physical solution: 7%

H2O +CO2 → H2CO3

If complete CO2   is transported in this form pH of blood will come to 4.5.

(b)            As chemical compound: 23%

CO2  +Hb.NH2  → Hb.NH.COOH

Carbomino haemoglobine

(c)           As bicarbonates - 70%

998_transportation of carbon dioxide.png

  • Mostly CO2   is diffused from plasma to RBC.
  • Here H2CO3  is formed 5000 times faster in the presence of carbonic anhydrase enzyme.
  • H2CO3 is broken into H+ and HCO- .
  • H+ combine with Hb to from HbH+ (strong buffer).
  • HCO3-  is diffused out in plasma balanced by Cl ion i.e., chloride shifting or Hemberger phenomenon.
  • In plasma HCO- reacts with Naor K+ to form their bicarbonates.
  • 4 ml CO2   is transported by 100 ml blood.
  • According to Henderson Hesselwalch at 7.4 pH ratio betwen H2CO3  and bicarbonate is 1 : 20.


As more and more oxyhaemoglobine is formed more COis released. So reaction against oxygenation is Haldane effect.

HbH+ →Hb + H+

Hb +O2 →Hb.O2

H+ +HCO→ H2CO3

H2CO3  → H2O +CO2


  1. It is automatic involuntary process negligible voluntary too.
  2. Medulla oblongeta is respiratory centre. Effected by chemicals in blood.
  3. It is bilateral. Half part is inspiratory and half part is expiratory.
  4. ICM nerve (ICM) and phrenic nerve (Diaphragm) stimulate inspiration.
  5. Streach receptors in Bronchi & Bronchioles are stimulated. It is conveyed to brain by vagus nerve.
  6. Inspiration is stoped. Expiration is started. This feed-back control is Hering Breuer Reflex.
  7. More CO2  increases rate of respiration.
  8. CO poisoning: Hb combines with CO 250 times faster. So carboxyhaemoglobine is formed.
Posted Date: 10/1/2012 9:14:31 AM | Location : United States

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