Anatomy and Physiology of Respiratory System | A Complete Guide

The respiratory system is one of the 11 organ systems of the body. It is responsible for the passage of air into our body, which is the source of life energy.

We breathe in air rich in oxygen by the process called inspiration and breathe out air rich in CO2 by a process called expiration.

The respiratory system helps in the safe exchange of gases from the outer atmosphere to the inside of the body.

The physiology of the respiratory system of the human body is not a problematic one mostly, but it is a delicate one, and if neglected or hampered in early life, it can reduce the life span and quality of life drastically.

The disorders of the respiratory system are many but are not fatal on an instant basis. They can be reduced or treated by proper medical care.

See the difference between anatomy vs. physiology.

Anatomy and Physiology of Respiratory System | Main Parts

The respiratory system parts consist of

  1. Nose
  2. Pharynx
  3. Larynx
  4. Trachea
  5. Two bronchi
  6. Bronchioles
  7. Two lungs (inside them alveoli).
  8. Diaphragm and inter-coastal muscles.
Anatomy and Physiology of Respiratory System | labelled Diagram


  • This is the starting point of the pulmonary system and is exposed to the external environment.
  • It is the route of entry and exit of the air into and out of the body, respectively.
  • The nasal cavity is partly made of cartilaginous bone and skull bone. It is divided by the septum into two equal passages for air.
  • It has olfactory receptors at the roof in the nostril’s walls. Also, there is a small tuft of hair inside to entrap any dust particles passing along with air.


  • This is present immediately after the nose.
  • This is a tube approximately 14 centimeters long.
  • It starts from the base of the skull and ends at the level of the 6th cervical vertebra (neck region).
  • It is divided into three parts are nasopharynx, oropharynx, and laryngopharynx.
  • It is divided into three parts as nasopharynx, oropharynx, and also laryngopharynx.


  • This is the tract of the respiratory system in the throat.
  • It is responsible for sound and is made of cartilage.


  • This is a longer part of the track and is made of circles of cartilaginous bones with a capacity to contract and relax.
  • This trachea divides into two bronchi before entry into the lungs.


  • These are two of them as the right and left, and each enters into the respective lung.
  • Bronchi further divide into smaller branches as bronchioles, which almost extend into the alveoli of the lungs.


  • Here, the actual process of respiration occurs. They are large sac-like structures (balloon-like).
  • There are two in number, with one on the left side and others on the right of the thorax or chest.
  • They are very thin layered and a bit transparent. Their walls have many passing tiny blood vessels.
  • They are very delicate to sharp objects and get punctured easily on an injury.
  • Inside these lungs, there are small sacs called alveoli, which are involved in the exchange of gases between blood and air.


This is a skeletal muscle that separates the respiratory cavity from the abdominal cavity.

Respiratory system accessories


This tiny bristle-like structure on the surface of the respiratory tract is helping in the movement of dust and phlegm from inside to out of the track.

They move in one specific direction only.

In older people and people with inflammation, the cilia activity is low, and hence phlegm accumulates a lot in their respiratory tract.

Anatomy and Physiology of Respiratory System


  • Phlegm is a mucous secretion in the respiratory tract aimed to keep the tract moist and remove any dust particles entered into the tract by flowing towards the nose.
  • This movement of phlegm is helped by cilia on the surface of the tract. But profuse secretion and accumulation of mucus can be havoc to patients.

Functions of Respiratory organs

Nose functions

Being the first passage of the respiratory system, the nose performs vital functions.

a) Sense of smell: Olfactory function is one of the key functions of the nose. There are olfactory nerves that begin from the roof of the nose to form an olfactory bulb that carries the information of the sense of the odor into the olfactory lobe in the brain for perception.

b) Warming the passing air: When air enters the nose, the mucous wall in the nose gets in contact. Due to the high blood supply to this layer, the air gets warmed.

c) Cleaning and filtering: The air might have bacteria and dust particles. These are trapped in the nose. Hair in the nose traps large particles while the moist mucosa traps bacteria and small dust particles.

d) Moistening: When air travels over the mucous layer, the moisture present saturates the air with water vapor.

Pharynx function

1. It helps in the passage of air and food.

2. Warms and humidifies the air.

3. Protection against microbes by producing antigens from tonsils.

4. In the production of speech, it helps to resonate sound coming out from the larynx.

Physiology of respiratory system

  • Gaseous exchange: Helps in the intake of oxygen (O2) into the blood from the atmosphere and leaves out CO2.Anatomy and Physiology of Respiratory System-gaseous exchange
  • Nervous control: It is under involuntary control but partial under voluntary control.
  • Metabolism: Some drugs and substances get metabolized in the lungs due to heavy O2 content.
  • Excretory in function: Lungs help in the excretion of gaseous or volatile substances like Ammonia (NH3), Alcohol, etc. Hence, when one drinks alcohol, its odor is detected in the breath. So, breath analyzers are used to test drivers.

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