Respiratory System Course Outline

Introduction to Respiratory System

• The respiratory system is a biological system consisting of specific organs and structures used for gas exchange in animals and plants.
• It includes the airways, lungs, and blood vessels, and the muscles that power the lungs.

Respiration Process

• Respiration is the process by which oxygen is taken in and carbon dioxide is given out through the placenta.
• There are two types of respiration: external respiration (exchange of gases between lungs and blood) and internal respiration (exchange of gases between blood and tissues).
• Respiration occurs in two phases: inspiration (air enters the lungs) and expiration (air leaves the lungs).

Respiratory Rate

• Respiratory rate decreases with age:
  • Newborns: 30-60/minute
  • Early childhood: 20-40/minute
  • Late childhood: 15-25/minute
  • Adult: 12-16/minute

Pleura

• The pleura is a bilayered serous membrane that encloses the lungs.
• It has two layers: visceral layer (attached to the surface of the lungs) and parietal layer (attached to the wall of the thoracic cavity).
• The intrapleural space or pleural cavity is the narrow space between the two layers of pleura.

Functions of Intrapleural Fluid

• Lubricant to prevent friction between two layers of pleura
• Creates negative pressure in the intrapleural space

Respiratory Tract

• The respiratory tract is divided into an upper and lower tract.
• The upper tract includes the nose, nasal cavities, sinuses, pharynx, and the part of the larynx above the vocal folds.
• The lower tract includes the lower part of the larynx, trachea, bronchi, bronchioles, and alveoli.

Tracheobronchial Tree

• The trachea bifurcates into two mainstem bronchi, which divide into lobar or secondary bronchi.
• Each secondary bronchus divides into tertiary or segmental bronchi.
• Tertiary bronchi divide into many generations of bronchioles.

Respiratory Unit

• The respiratory unit is the structural and functional unit of the lung.
• It starts from the respiratory bronchioles of 0.5 mm in diameter.
• Each respiratory bronchiole divides into alveolar ducts, which enter an enlarged structure called the alveolar sac.

Alveoli

• Alveoli are small pouches with a diameter of 0.2-0.5 mm.
• They are lined by epithelial cells and are the site of gas exchange between the alveolus and blood.

Non-Respiratory Functions of Respiratory Tract

• Olfaction: olfactory receptors in the mucous membrane of the nostrils are responsible for olfactory sensation.
• Vocalization: the larynx plays a major role in the process of vocalization.
• Defense mechanism: the respiratory tract is involved in the immunological defense system of the body.
• Maintenance of water balance: the respiratory tract plays a role in the water loss mechanism.
• Regulation of body temperature: the respiratory tract plays a role in the heat loss mechanism.
• Anticoagulant function: mast cells in the lungs secrete heparin, an anticoagulant.
• Regulation of acid-base balance: the respiratory tract plays a role in the maintenance of acid-base balance of the body.

Endocrine Functions of the Lung

• Synthesis of hormonal substances: prostaglandins, acetylcholine, and serotonin.
• Release of inflammatory mediators: histamine, endothelin, and eicosanoids.
• Release of nitric oxide to regulate smooth muscle tone.