Respiratory System – Anatomy and Physiology
Introduction
The respiratory system is responsible for the exchange of gases — oxygen (O₂) and carbon dioxide (CO₂) — between the body and the environment. It provides oxygen for energy production and removes waste gases from the body.
This system includes organs that help in breathing, air filtration, and maintaining acid-base balance in the blood.
Definition
The respiratory system is the biological system that enables breathing. It includes all organs and structures involved in taking in oxygen and expelling carbon dioxide.
Original Notes:
Organs of the Respiratory System
The respiratory system is divided into two parts:
1. Upper Respiratory Tract
- Nose and Nasal Cavity: The entry point for air; filters, warms, and moistens incoming air.
- Pharynx (Throat): Common passage for air and food. It connects the nasal cavity to the larynx.
- Larynx (Voice Box): Contains the vocal cords and ensures air passes into the trachea.
2. Lower Respiratory Tract
- Trachea (Windpipe): A tube that carries air from the larynx to the lungs. It has C-shaped cartilage rings that keep it open.
- Bronchi: Two main branches of the trachea that lead into each lung. They further divide into smaller bronchioles.
- Bronchioles: Smaller airways that lead air to the alveoli.
- Alveoli: Tiny air sacs where the exchange of gases takes place. They are surrounded by capillaries for efficient gas exchange.
- Lungs: Two spongy organs (right lung has three lobes, left has two) that house the bronchi, bronchioles, and alveoli.
Structure of the Lungs
The lungs are soft, elastic organs located in the thoracic cavity. Each lung is covered by a double-layered membrane called the pleura:
- Visceral Pleura: Covers the lung surface.
- Parietal Pleura: Lines the chest cavity.
Between these layers is pleural fluid, which reduces friction during breathing movements.
Physiology of Respiration
Respiration involves the process of gas exchange and utilization by the body. It includes the following steps:
1. Pulmonary Ventilation (Breathing):
The process of moving air in and out of the lungs.
- Inspiration (Inhalation):
- Diaphragm contracts and moves downward.
- Intercostal muscles lift the ribs, increasing chest volume.
- Air enters the lungs as pressure decreases inside.
- Expiration (Exhalation):
- Diaphragm relaxes and moves upward.
- Rib cage returns to normal position.
- Air is pushed out as pressure inside the lungs increases.
2. External Respiration:
Exchange of gases between alveoli and blood in the capillaries.
- Oxygen moves from alveoli into blood.
- Carbon dioxide moves from blood into alveoli to be exhaled.
3. Internal Respiration:
Exchange of gases between blood and body tissues.
- Oxygen moves from blood to tissues.
- Carbon dioxide moves from tissues to blood.
4. Cellular Respiration:
The process where cells use oxygen to produce energy (ATP) from glucose and release carbon dioxide as a waste product.
Control of Respiration
The respiratory center in the medulla oblongata of the brain controls the rate and depth of breathing.
Chemoreceptors in the blood detect CO₂ levels — high CO₂ increases breathing rate.
Functions of the Respiratory System
- Exchange of oxygen and carbon dioxide.
- Regulation of blood pH.
- Filtration and humidification of inhaled air.
- Sound production through the larynx.
- Sense of smell (olfaction).
- Protection from dust and microbes through nasal hairs and mucus.
Common Disorders of the Respiratory System
- Asthma: Narrowing of airways causing breathing difficulty.
- Bronchitis: Inflammation of bronchi leading to cough and mucus production.
- Pneumonia: Infection of the lungs causing inflammation and fluid accumulation.
- Emphysema: Damage to alveoli leading to shortness of breath.
- Tuberculosis (TB): Bacterial infection caused by Mycobacterium tuberculosis.
- Chronic Obstructive Pulmonary Disease (COPD): Long-term obstruction of airflow causing breathing issues.
