PHYSIOLOGY OF RESPIRATION -

1.      EXCHANGE OF GASES -

• 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

2.      TRANSPORTATION OF O₂  BY BLOOD -

• 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 O₂   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

• Partial pressure of O₂ is 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.

3.      INTERNAL RESPIRATION -

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

4.      TRANSPORTATION OF CO -

• 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%

• 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 Na⁺ or 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.

5.      RELEASE OF CO₂  AT RESPIRATORY SURFACE-

As more and more oxyhaemoglobine is formed more CO₂ is released. So reaction against oxygenation is Haldane effect.

HbH⁺ →Hb + H⁺

Hb +O₂ →Hb.O₂

H⁺ +HCO^- → H₂CO₃

H₂CO₃  → H₂O +CO₂

6.      CONTROL ON RESPIRATION-

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.