Anatomy and Physiology of Respiratory System

Epiglottis – this is a flap of tissue that serves as a guardian of the airways as it protects the superior portion of the larynx. The epiglottis does not restrict passage of air into the lower respiratory passages when a person is not swallowing. However, when a person swallows food, the epiglottis tips and forms a lid or blocks the opening of the larynx so that food will not be directed to the lower respiratory passages. The food will be then routed to the esophagus and in cases where it enters the larynx, a cough reflex is triggered to expel the substance and prevent it from continuing into the lungs. This protective reflex does not work when a person is unconscious that is why it is not allowed to offer or administer fluids to an unconscious client.

Vocal folds – a pair of folds which is also called the true vocal cords that vibrate when air is expelled.

Glottis – the slit-like passageway between the vocal folds.


Also called the windpipe, the trachea is about 10 to 12 cm long or about 4 incheas and travels dwon from the larynx to the fifth thoracic vertebra. This structure is reinforced with C-shaped rings of hyaline cartilage and these rings are very important for the following purposes:

  1. The open parts of the rings abut the esophagus that allows the structure to expand anteriorly when a person swallows a large size of food.
  2. The solid portions of the C-rings are supporting the walls of the trachea to keep it patent or open even though pressure changes during breathing.

The trachea is lined with ciliated mucosa that primarily serves for this purpose: To propel mucus loaded with dust particles and other debris away from the lungs towards the throat where it can either be swallowed or spat out.

Main Bronchi

The main bronchi, both the right and the left, are both formed by tracheal divisions. There is a slight difference between the right and left main bronchi. The right one is wider, shorter and straighter than the left. This is the most common site for an inhaled foreign object to become lodged. When air reaches the bronchi, it is already warmed, cleansed of most impurities and well humidified.


The lungs are fairly large organs that occupy the most of the thoracic cavity. The most central part of the thoracic cavity, the mediastinum, is not occupied by the lungs as this area houses the heart.

Apex – the narrow superior portion of each lung and is located just below the clavicle

Base – the resting area of the lung. This is a broad lung area that rests on the diaphragm.

Divisions of the Lungs

The lungs are divided into lobes by the presence of fissures. The left lung has two lobes while the right lung has three.

Pleural Layers

Visceral pleura – also termed as the pulmonary pleura and covers each surface of the lings.

Parietal pleura – covers the walls of the thoracic cavity.

Pleural fluid – a slippery serous secretion that allows the lungs to slide along over the thorax wall during breathing movements and causes the two pleural layers to cling together.

Bronchioles – smallest air-conducting passageways.

Bronchial tree or respiratory tree – a network formed due to the branching and rebranching of the respiratory passageways within the lungs.

Alveoli – air sacs. This is the only area where exchange of gases takes place. Millions of clustered alveoli resembles bunches of grapes and these structures make up the bulk of the lungs.

Respiratory Zone – this part includes the respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli.

Daisy Jane Antipuesto RN MN

Currently a Nursing Local Board Examination Reviewer. Subjects handled are Pediatric, Obstetric and Psychiatric Nursing. Previous work experiences include: Clinical instructor/lecturer, clinical coordinator (Level II), caregiver instructor/lecturer, NC2 examination reviewer and staff/clinic nurse. Areas of specialization: Emergency room, Orthopedic Ward and Delivery Room. Also an IELTS passer.

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