Human Respiratory system and mechanism of respiration, Inspiration and Expiration


Respiration is defined as the exchange of gases between body tissue and environment.

Function of respiration-

- Supply of oxygen to the tissue and elimination of carbon dioxide from the body tissue.
- It helps in blood circulation.
- It regulates the acid-base balance.
- It helps in excretion of volatile substance,water,vapor and ketone.

Differnt parts of respiratory system-

(1) Nose                        (2) Pharynx
(3) Larynx                    (4) Trachea
(5) Bronchi                   (6) Lungs
Human Respiratory System, Respiration, expiration

(1) Nose :

Nose is divided in to two portion internal and external portion. 

External portion :

It consists of framework of bones ( frontal, nasal and maxillae bone) hyaline cartilage covered with muscle, skin and muscle membrane.

Internal portion :

The internal nose is a large cavity. The space within the nose is called nasal cavity.

Function of nose :

-  Warming : due to high vasculoraty in mucosa.
-  House of olfactory receptor are present for smelling.
-  It helps for filtering and cleaning due to the presence of hair .

(2) Pharynx :

- The pharynx extends from the base of skull to the upper end of the esophagus .
- It is 13 cm length.
Pharynx is divided in to 3 parts.
1. Naso pharynx
2. Oro pharynx
3. Laryngo pharynx

Function :

-  It involved both digestive and respiratory system.
-  It also helps in taste, protections and speech.

(3) Larynx :

It is a short passage way that connect the laryngopharynx to trachea. At puberty the size of larynx becomes large in male.
The wall of larynx is composed of 9 cartilage. Two important cartilage are -

Thyroid cartilage :

It consists of two fused plates of hyline cartilage in the anterior of the larynx. It presents in both male and female.

The epiglottis :

It is a leaf shaped fibro elastic cartilage. The stem of the epiglotis is attached to the anterior of the thyroid cartilage and hyoid bone. It helps to close off the larynx during swallowing and protects the lungs from accidental inhalation of foreign objects.

Function :

- It help for production of sound.
- It protect lower respiratory tract.
- It is the passage way of air.

(4) Trachea :

The trachea is a rigid fibro elastic structure. The trachea is lined up internally with ciliated columner epitheleum. It measures about 11 cm length and diameter is 2 to 2.5 cm.

Function :

- It helps to cough reflex and to expel foreign materials from mouth.
- As reaching air in to trachea the air gets filtereted, warm and humidify in trachea.

(5) Bronchi and bronchiolrs :

The trachea divided in to left bronchus and right brounches. Primarily brunches contains incomplete cartilage rings and is lined up with pseudo stratified columnar epithelium.

Function :

-  It control the air entry.
-  It helps for cough reflex.
-  Warming and humidification.

Lungs :

- Lungs are paired, cone shaped and lying on each side of the thoracic cavity.
- Due to the spaced occupied by heart the left lung is smaller than the right lung.
- The lung extends from the diaphragm slightly to the clavicles and lies against the ribs in posterior and anterior.

Function :

- It helps to make airway warm when it reaches in lung.
- It maintains the pulmonary circulation.

Physiology of respiration :


Inspiration is the process of entry of air to the lungs.The following change occur during inspiration.
(1) Chest expands during inspiration.
(2) The diaphargm moves downwards,so vertical diameter of the thorax is increased.
(3) Inter costal muscles act on the the ribs turned out and elevated.
This causes the enlargement of chest cavity.The enlargement of chest cavity permits the enlargement of lungs.
(4) When the lung is enlarged pressure inside the lung decrease.This leads to the entry of air in to the lungs.


This process is the expulsion of air in to the lungs.The following change occur during Expiration.
(1) The diaphargm is relaxed and moves upwards.
(2) Intercostal muscles are relaxed so the ribs move inwards.As the result the thoracic cavity is reduced and so the air is gradually expelled out.
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