Anatomy for Medical Coder- Respiratory System

Respiratory System for CPC Fresher

Respiratory System in human

Respiration is a procedure in which atmospheric air is exchanged with carbon dioxide at the respiratory surface (Lungs).

What is External respiration and Internal respiration ?

Exchange of gases between the blood and the lungs is called external respiration and that between the blood and the cells is called internal respiration.

The respiratory system begins with the external nostrils (nose), which allow air to enter the nasal cavity.

External Nose

Functions of the External Nose

The external nose is the first part of the respiratory system and performs three important functions:

• Warms, moistens, and filters inhaled air before it reaches the lungs.

• Detects smell (olfaction) through olfactory receptors in the nasal cavity.

• Acts as a resonating chamber, helping modify and enhance the quality of speech and voice.

Nasal Cavity

The nasal cavity is a large hollow chamber located behind the nose. It is divided into right and left chambers by the nasal septum and is lined with a mucous membrane (mucous-secreting epithelium). The mucus traps dust, microorganisms, and other foreign particles while also warming and humidifying the inhaled air before it reaches the lungs.

Pharynx

The nasal cavity opens into the pharynx, a common passage for both air and food.

The pharynx (throat) is a 12–14 cm long muscular tube located behind the nasal cavity, oral cavity, and larynx. It is a common passage for both air and food, making it part of both the respiratory system and the digestive system. Air passes into the larynx, while food enters the esophagus. During swallowing, the epiglottis closes the laryngeal opening to prevent food from entering the airway.

The pharynx is divided into three parts:

• Nasopharynx: Upper part of the pharynx located behind the nasal cavity; receives air through the internal nares (choanae).

• Oropharynx: Middle part located behind the oral cavity; serves as a passage for both air and food.

• Laryngopharynx (Hypopharynx): Lower part that connects to the larynx (airway) anteriorly and the esophagus (food pipe) posteriorly.

Larynx

From the pharynx, air passes through the larynx (voice box), which contains the vocal cords and helps in sound production. During swallowing, the epiglottis closes over the larynx to prevent food from entering the airway.

The larynx, commonly called the voice box, is a cartilaginous structure located in the anterior neck, between the pharynx and trachea, and in front of the esophagus. It contains the vocal cords, which are responsible for sound production, and also helps protect the lower airway during swallowing.

The larynx is mainly supported by three important cartilages:

• Thyroid cartilage – Largest cartilage; forms the Adam's apple.

• Cricoid cartilage – Ring-shaped cartilage located below the thyroid cartilage; provides structural support to the airway.

• Arytenoid cartilages – Paired cartilages that control the movement and tension of the vocal cords during speech.

Flow: External Nostrils → Nasal Cavity → Pharynx → Larynx

Trachea

The trachea (windpipe) extends from the larynx into the chest and divides at the level of the 5th thoracic vertebra (T5) into the right and left primary bronchi.

These further divide into secondary bronchi, tertiary bronchi, bronchioles, and finally terminal bronchioles, which end in tiny air sacs called alveoli.

The trachea (windpipe) is a 10–12 cm long tube that extends from the larynx to the bronchi. It is located anterior to the esophagus and begins at the level of the 6th cervical vertebra (C6). The trachea is supported by C-shaped hyaline cartilaginous rings, which keep the airway open and prevent it from collapsing during breathing.

Bronchi & Bronchioles

The trachea divides into the right and left primary (main) bronchi, each entering its respective lung. Inside the lungs, the bronchi continue to branch into secondary (lobar) bronchi, tertiary (segmental) bronchi, and finally into smaller bronchioles. Each bronchiole is approximately 1 mm in diameter and further divides into alveolar ducts (about 0.2 mm in diameter). These alveolar ducts open into alveolar sacs, which contain numerous alveoli, the tiny air sacs where the exchange of oxygen (O₂) and carbon dioxide (CO₂) occurs. The total surface area of the alveoli in an adult is approximately 70–100 m², providing a large area for efficient gas exchange.

In the thoracic cavity, the trachea divides into the right and left primary (main) bronchi, which enter their respective lungs. The branching network of the trachea, bronchi, and bronchioles is collectively known as the tracheobronchial tree.

Nose → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli

Alveoli are the functional units of the lungs where oxygen and carbon dioxide are exchanged with the blood.

Humans have two lungs, each covered by a double-layered pleura. The space between these layers contains pleural fluid, which reduces friction during breathing and allows smooth movement of the lungs.

The lungs are covered by a double-layered membrane called the pleura. The outer layer (parietal pleura) is attached to the inner wall of the thoracic cavity, while the inner layer (visceral pleura) covers the surface of the lungs. The space between these layers contains pleural fluid, which reduces friction and allows smooth lung movement during breathing.

The respiratory system is divided into two parts:

• The Conducting Part extends from the external nostrils to the terminal bronchioles. Its functions are to conduct air, filter dust and foreign particles, warm, and humidify the inspired air.

• The Respiratory (Exchange) Part consists of the alveoli and alveolar ducts, where oxygen (O₂) enters the blood and carbon dioxide (CO₂) leaves the blood.

  
  

The thoracic cavity is an airtight chamber formed by the vertebral column (back), sternum (front), ribs (sides), and diaphragm (bottom).

During breathing, contraction and relaxation of the diaphragm and intercostal muscles change the volume of the thoracic cavity. These volume changes cause the lungs to expand and contract, allowing inhalation and exhalation.