Respiratory System – Air Passage Ways, Pharynx and Larynx, Lung Capacities

Respiratory System- The place of Gas Exchange

The respiratory system or ventilation apparatus is the network of organs and tissues that assist the organism to breathe. This system assists the living body to take in oxygen from the air so the organs can work. It likewise cleans up waste gases, such as carbon dioxide, from the blood.

Requirement of Respiratory Gas Exchange

At all levels of activities in living organisms, a continuous supply of energy is required. Respiration is among the most essential metabolic activities of all organisms. Respiration happens at two levels, i.e., organismic and cellular level. Organismic respiration is also called breathing or ventilation.

The cellular respiration is directly associated with the production of energy, needed for all living activities. Cellular respiration is the process by which cell uses oxygen, produces carbon dioxide, extracts and saves the energy from food molecules in biologically beneficial type, such as, ATP.

Respiration in Human beings

In man breathing system consists of lungs and airway which are responsible for bringing fresh air to the respiratory sites.

Parts of Respiratory System
Air Passage Ways

Air Passage Ways consist of nostrils, nasal cavities, pharynx, throat, trachea, bronchi, bronchioles and alveolar ducts which eventually lead into the alveolar sac. Nasal cavities are lined with the mucous membrane of ciliated epithelium. Each nasal cavity is partitioned into three passage ways by the projection of bones from the walls of the internal nose. Air enters the nasal cavity through the nostril and the bigger dust particles are caught by the hair and mucus in the nostrils.

Air, while passing through the nasal cavity, becomes moist, warm and filtered of smaller foreign particles by mucous membrane.

Pharynx and Larynx

The nasal cavity leads into the throat or pharynx by two internal openings. The pharynx is a muscular passage lined with mucous membrane. The air is channelized from the pharynx into the larynx. The throat or voice box is an intricate cartilaginous structure surrounding the upper end of the trachea.

One of the cartilages, the epiglottis has a muscularly controlled, hinge-like action and acts as a lid which automatically covers the opening of the throat during the act of swallowing so as to prevent the entry of food or liquids into the larynx. The opening of larynx is called glottis and is likewise lined with mucous membrane. In the glottis, the mucous membrane is stretched across into two thin edged fibrous bands called vocal cords, which assist in voice production, when vibrated by air.


Trachea or Windpipe

The trachea or windpipe is a tubular structure lying forward to the oesophagus and encompasses the chest cavity or thorax where it is divided into right and left bronchi. In the wall of the trachea, there are a series of C shaped cartilage rings which prevent the trachea from collapsing and keep the passage of air open. Each bronchus on getting in the lung divides and subdivides progressively into smaller and smaller sized bronchi.

When the smaller bronchi attain a diameter of one mm or less, then they are called bronchioles. Bronchi have the same cartilage rings as the trachea, but the rings are progressively replaced by irregularly dispersed cartilage plates and the bronchioles totally lack cartilages. Bronchioles are comprised of primarily circular smooth muscles.


The bronchioles continue to divide and partition deep into the lungs and finally open into a large number of air-sacs. Air sac is the functional system of the lungs. Each air-sac consists of several tiny single layered structures called alveoli. Overlying the alveoli there is a rich network of blood capillaries to produce an excellent site for the exchange of gases.


The lungs are closed sacs that are linked to the outside by way of the trachea and the nostrils or mouth. Lungs are spongy because of the presence of countless alveoli. Lungs are present in the chest cavity. The chest cavity is bounded by ribs and muscles on the sides. The flooring of the chest is called the diaphragm. The diaphragm is a sheet of skeletal muscles. Lungs are covered with double layered thin membranous sacs called pleura.


A person’s lungs are not of the exact same size. The right lung is a little broader than the left lung, however, it is also shorter. The right lung is much shorter because it needs to make space for the liver, which is right below it. The left lung is narrower because it must make space for the heart.


The lungs’ primary function is to help oxygen from the air we breathe enter the red cells in the blood. Red blood cells then bring oxygen around the body to be utilized in the cells present in our body. The lungs likewise help the body to get rid of CO2 gas when we breathe out. There are a variety of other tasks performed by the lungs that include:

  • Altering the pH of blood whether the blood is more acid or alkali) by increasing or decreasing the amount of CO2 in the body.
  • Removing little gas bubbles that may take place in the bloodstream.
  • Converting a chemical in the blood called angiotensin I to angiotensin II. These chemicals are very important in the control of blood pressure.
Lung Capacities

In an adult human being when the lungs are fully inflated the overall capability of lungs is 5 litres. Generally, when we are at rest or asleep the exchange is only about half a litre. The volume of air taken inside the lungs and expelled during exercise is almost 3.5 litres.

To put it simply, there is a recurring volume of 1.5 litres even during the workout which can not be expelled. Generally, at rest, we inhale and breathe out 15-20 times per minute. Throughout the workout, the breathing rate may rise to 30 times per minute. The increased rate and depth of breathing during a workout allows more oxygen to dissolve in blood and provided to the active muscles.

The additional carbon dioxide which the muscle takes into the blood is removed or eliminated by deep and quick breathing. There is a little change in the composition of inhaled and exhaled air during rest or exercise in most of the constituents of the air.

The inhaled and exhaled air constituents are as follows: