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Human Respiratory System

 RESPIRATORY SYSTEM

Respiration

Respiration can be defined as exchange of gases i.e. oxygen and carbon dioxide between the atmosphere and tissues. 

✦ Organs of respiratory system

  1. Nose
  2. Pharynx
  3. Larynx
  4. Trachea
  5. Brochi - 2
  6. Bronchioles
  7. Alveoli
  8. Lungs - 2
  9. Muscles of respiration : Intercoastal muscles and Diaphragm


✦ Mechanism of respiration :-

The normal human has 12-15 breath per min.

Each breath consists of inspiration, expiration and pause.

1) Inspiration :

  • The simultaneous contraction of intercoastal muscles and diaphragm increases the capacity of thoracic cavity. This reduces the pressure in the lungs. To equalize the pressure the air from atmosphere enters the lungs. The process of inspiration is active as it needs energy for muscle contraction. The inspiration lasts for 2 sec.


2) Expiration :

  • Relaxation of intercostal muscles and diaphragm results in decrease in the space in the lungs. As a result, the pressure inside the lungs increases as compared to atmospheric pressure. The air from the lungs is expelled from the lungs. This process is passive as does not require energy. The expiration lasts for 3 sec.


3) Pause :

  • After expiration there is pause and then the next cycle begins.


✦ Structure of lungs :-

  • There are two lungs, one lying on each side of the midline in the thoracic cavity. They are cone-shaped and have an apex, a base, costal surface and medial surface.
  • The right lung is divided into three distinct lobes : superior, middle and inferior. The lefat lung is smaller and is divided into only two lobes : superior and inferior. The division between the lobes is called fissures. Each lobe is composed of lobules. Each lobe contains small bronchial tubes.
  • These tubes divide, sub-divide and ends finally in air sacs i.e. alveoli. Each lung is surrounded by a double serous membrane called pleura composed of outer parietal and inner visceral layers. Between the pleural layers, there is pleural (serous) fluid.

✦ Functions of lungs :-

  1. Breathing (pulmonary ventilation)/ Exchange of gases oxygen and carbon dioxide.
  2. Water regulation : Water vapour is partly excreted thus heat is lost during expiration.
  3. Volatile substances like ammonia, alcohol, etc is excreted by lungs.


✦ Functions of respiratory system =

Nose :

  • Nose is involved in filtering and cleaning of air.
  • Nose is an organ of sense of smell.


Pharynx :

  • Pharynx is involved in both respiratory and digestive system i.e. it is a passage way for air and food.
  • The auditory tubes extending from the naso-pharynx to each middle ear, allows air to enter the middle ear.
  • The pharynx functions in speech by acting as a resonating chamber for sound ascending from the larynx.


Larynx : 

  • Larynx is involved in production of sound.
  • During swallowing of food larynx moves upwards, blocking the opening into it from the pharynx. In addition the epiglottis closes over the larynx. This ensures that food passes into oesophagus and not in trachea.

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