The Respiratory System


The tissues of the bronchial walls resemble the tissues of the trachea. As the passages branch they become smaller. Pimary bronchi, branch to form secondary bronchi. Secondary bronchi branch to form tertiary bronchi. Smaller passages, bronchioles, lack supporting the suportive cartilages that are typical of the bronchi. Bronchioles continue to branch and form smaller passages. In the bronchioles the pseudostratified columnar epithelium is replaced by simple cuboidal cells. Submucosal glands are also absent in the smaller brochioles.



Terminal bronchioles branch to form respiratory bronchioles. Respiratory bronchioles lead into alveolar ducts. Alveolar ducts have abundant openings into the surrounding alveolar sacs and alveoli.

The abundance of alveoli, and small, thin walled passages make the tissue of the lung appear spongy. In the alveolar regions of the lung there are an abundance of small vessels and capillaries to absorb oxygen from the alveolar spaces. Lining the alveoli are simple squamous type I alveolar cells. Oxygen diffuses across the thin typeI cell and across the endothelial lining of the capillaries to enter the blood and bind to hemoglobin in the red blood cells. The type II alveolar cells form part of the alveolar wall, and produce surfactant for the moist surfaces of the alveolar regions of the lung.



Dust cells, also known as alveolar macrophage cells, help to keep the alveoli clean of bacteria and small particulates.









































Overview of Respiratory System

Human Nasal Passages

Human Pharynx Regions

Human Larynx and Trachea

Human Bronchi and Lungs

Muscles of Human Respiration

Lower Respiratory Development

Fish Lungs/Air Bladders

Tetrapod Lungs

Lung Ventilation Systems

Gills of Vertebrate Animals

Things I Should Know