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Respiration is a process which involves the exchange of respiratory gases (co2 and O2) between the organism and external environment.

Follow up:

There are two types of respiration

1.    DIRECT RESPIRATION –The specialized respiratory organs are absent.

2.    INDIRECT RESPIRATION – In this type exchange of oxygen and carbon dioxide occurs through respiratory organs such as GILLS AND LUNGS.

Indirect respiration has three phases

a.    EXTERNAL RESPIRATION – It is also called as PULMONARY RESPIRATION.

b.     INTERNAL RESPIRATION – It is also known as TISSUE RESPIRATION.

c.     CELLULAR OXIDATION – Also called cellular respiration.

Human respiratory system consist of two zones

1.Respiratory zone

2.Conducting zone

1. NASAL CAVITIES

Each cavity is divided into the three parts.

a. VESTBULE

b. OLFACTORY SEGMENT.

c. RESPIRATORY SEGMENT.

There are three types of cells

a.    OLFACTORY CELLS – These are modified neurons meant to receive stimulus of smell.

b.    SUSTENTACULAR CELLS – These support olfactory cells

c.    BASAL CELL – These divide and form new olfactory cells.

Functions of nasal cavities

1.Filters air that enters respiratory system.

2.It identifies the stimulus of smell.

3.It warms and moistens the air that enters the respiratory system.

4.It acts as resonator.

2.   PHARYNX

• It is a narrow passage that connects the nasal cavities to the windpipe (TRACHEA)

• It is divisible into NASOPHARYNX., OROPHARYNX.,LARYNGOPHARYNX

3. LARYNX

• The larynx is supported by three paired and three unpaired hyaline cartilages( Nine cartilaginous plates)  .

• The three unpaired cartilaginous plates are – Epiglottis, Thyroid and Cricoid cartilage.

• The three paired catilagenous plates are – Arytenoid, Corniculate and Cueniform cartilage.

• On the inner surface of the larynx these cartilages are produced into projection called VOCAL CORDS.

4. TRACHEA

• It is about 12 cms in length and 2.5 cms in width.

• The trachea is supported by cartilaginous rings.  The rings are ‘C’ shaped.  These incomplete rings prevent the trachea wall from collapsing.  The trachea in the thoracic cavity divides and re divides into branches called BRONCHI, SECONDARY BRONCHI, and BRONCHIOLES.

• The respiratory bronchioles contain cluster of minute thin walled sacs called ALVEOLI or AIRSACS.

• The pulmonary artery brings deoxygenated blood from the heart to lungs.  After gaseous exchange in the alveolus the oxygenated blood return to the heart through pulmonary vein.

• The branches of trachea up to alveoli are called respiratory tree.

5. LUNGS

• Each lung is covered by a thin transparent (connective) membrane called PLEURA.

• The space present between the two lungs is called mediastinum. In this space heart is situated.

• The lungs are protected by a bony cage called THORACIC CAGE

• Between the ribs the muscles that are present are called INTER COSTAL MUSCLES. The muscles on the outer surface are called EXTERNAL INTERCOSTAL MUSCLE and the muscles found on the inner surface are called INTERNAL INTERCOSTAL MUSCLES)

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