BREATHING & EXCHANGE OF GASES

Anatomy of the Respiratory System

  1. Upper Respiratory System: Nose, pharynx

  2. Lower Respiratory System: Larynx, trachea, bronchi, bronchial tree, pulmonary alveoli, lungs

i) Nose: includes nasal cavity for the passage of air. It is divided into two by a cartilaginous internasal septum .

Each half is called a nasal fossa

Anterior openings (through nostril) of the nasal cavity are lined with stratified squamous epithelium.

conchae are lined with pseusostratified cilliated columnar epithelium

Functions:

  1. Warms, moistens & cleans the inspired air. Dust and other fine particles are trapped by the hair and the moist mucous membrane lining the nasal cavity.

  2. The olfactory epithelium in the dorso-lateral part of the nasal cavity has receptors for smell.

ii) Pharynx: connects the nasal & oral cavities to the to the larynx of the respiratory system & the esophagus of the digestive system

iii) Larynx: voice box. It is positioned in the anterior midline of the neck at the level of the fourth through sixth cervical vertebrae.

Functions”

  1. Its primary function is to prevent food or fluid from entering the trachea and lungs during swallowing and to permit the passage of air while breathing.

  2. Its secondary function is sound production.

iv) Trachea: connects the larynx to primary bronchi. Internally supported by a series of 16 to 20 C shaped hyaline cartilages. These hyaline cartilages ensure that the airway will always remain open.

The mucosa consists of pseudostratofied cilliated columnar epithelium containing mucous-secreting goblet cells .

It provides protection against dust and other particles.

v) Bronchi: In the thorax, the trachea bifuricates at the level of the 5th thoraic vertebra into right and left primary bronchi. Like the trachea, the walls of the bronchi are supported by rings of hyaline cartilage.

vi) Bronchial tree:

Principal bronchus —> secondary bronchi—> tertiary bronchi—> bronchioles

terminal bronchioles—> respiratory bronchioles—>alveolar ducts—> alveolar sacs

The conduction portion of the respiratory system ends at the terminal bronchioles and the respiratory portion begins at the respiratory bronchioles.

vii) Pulmonary Alveoli: The alveolar ducts, pulmonary alveoli & alveolar sacs make up the respiratory division of the lungs.

Gas exchange occurs across the walls of the Pulmonary alveoli. Hence they are the functional units of the respiratory system

The vast number of the pulmonary alveoli (around 350 million per lung) provides very large surface area for diffusion of gases.

Walls of the alveoli (extremely thin) are made up of 2 types of cells. Type I alveolar cells permit diffusion. Type II alveolar cells secrete a substance called surfactant that reduces the tendency of the pulmonary alveoli to collapse

In people who smoke, the alveoli collapse because nicotine removes the surfactant. This reduces the surface area of the lungs, causing shortness of breath. This pathological condition is called emphysema