This document summarizes the mechanisms of breathing and respiration. It describes that breathing occurs through the cyclical processes of inhalation and exhalation. Inhalation is caused by the downward movement of the diaphragm and contraction of intercostal muscles, decreasing intrathoracic pressure. Exhalation is caused by opposing muscle actions, increasing intrathoracic pressure. Oxygen is transported from the alveoli to tissues by diffusion and binding to hemoglobin, while carbon dioxide moves in the opposite direction and is transported in both dissolved and compound forms in the blood. Respiration is controlled both chemically through chemoreceptors sensing gas levels, and mechanically through stretch receptors in the lungs.

1. Saptarshi Samajdar
3rd Semester
NSHM COLLEGE OF PHARMACEUTICAL TECHNOLOGY

2. MECHANISM OF BREATHING(internal respiration)
Breathing occurs in two alternate & cyclical process – 1.Inhalation 2. Exhalation
INHALATION
 Increase volume of thoracic cavity.
-Downward movement of diaphragm.
-Contraction of intercostal muscle.
. Fall in intrathoracic pressure.
. Fall in intrapulmonary pressure.

3. EXHALATION
.Decrease in thoracic cavity
- Upward movement of diaphragm.
- Relaxation of external intercostal muscle.
- Downward and inward movement of ribs.
- Contraction of internal intercostal muscle and abdominal
muscle.
.Increase in intrathoracic pressure.
.Increase in pulmonary pressure.

4. MECHANISM OF REPIRATION (external)
Broadly divided in two parts: 1.Exchange of gases 2. Control of respiration.
EXCHANGE OF GASES
TRANSPORT TRANSPORT
OF
OF OXYGEN
CARBONDIOXIDE

5. TRANSPORT OF OXYGEN
O2 through respiratory Alveoli diffusion O2 enters
organs through
capillaries
3% of O2 dissolved in blood plasma and alveoli directly enters the tissue.
97% of O2 unites with Hb of RBC forming oxyhaemoglobin (Hb+O2 HbO2)
O2 becomes free nearer to the tissue through diffusion.
Bohr’s effect : The relation between PO2 & % saturation of Hb when
presented on a graph known as Hb-O2 dissociation curve which is sigmoid in
shape. A rise in PCO2 or fall in pH decrease O2 affinity of haemoglobin raising
P50 value.

6. TRANSPORT OF CARBONDIOXIDE
CO2 evolves during metabolism within tissue.
Tissue CO2 Tissue fluid CO2 Blood
capillaries
7% of CO2 transports as dissolve state in blood plasma .
93% of CO2 forms different compounds like H2CO3 ,HbCO2,
NaHCO3, KHCO3. The compounds release CO2 at Blood
capillaries of alveoli and enters the capillaries through
diffusion.

7. CONTROL OF RESPIRATION
HERING – BREUER REFLEX: In walls of bronchi and
bronchioles stretch receptors are located and are stimulated by
overstretching of lungs, nerve impulses are sent along the vagus nerve
to inhibit the inspiratory area. The result is expiration begins. Therefore
it is mainly a protective mechanism for preventing excess inflation of
lungs.
CHEMICAL CONTROL: Central chemo receptors are present in
medulla oblongata whereas the peripheral chemoreceptors are located
in in the walls of systemic arteries relay impulses to respiratory centre
over cranial nerves of PNS. Increase pCO2 , increased H+ concentration
and decreased pO2 input from central and peripheral

8. chemoreceptors causes causes the inspiratory area to become highly
active and rate and depth of breathing increases.
RESPIRATORY CENTRE: Normal respiratory
rhythm(12-14/min)is controlled by nervous system .That involves 1.
Dorsal respiratory system that transmits signal to
diaphragm for normal breathing 2. Ventral respiratory
group that regulates both inspiration as well as expiration 3.
Pneumotaxic centre that control switch off point of
inspiration.
THUS WE CAN SAY THAT RESPIRATIN HAPPENS
IN OUR BODY IN THESE MECHANISM AND
WE DERIVE ENERGY FROM THESE
MECHANISM.

9. THANK YOU.