Different Phases of Respiration

Respiration in humans can be classified into two main phases: external respiration and internal respiration.

External Respiration

External respiration refers to the exchange of gases between the atmosphere and the blood. This process occurs in the lungs and involves several steps:

1. Ventilation: The mechanical process of inhaling (inspiration) and exhaling (expiration). During inspiration, air is drawn into the lungs, while during expiration, air is expelled from the lungs.
2. Gas Exchange: Once air reaches the alveoli (the tiny air sacs in the lungs), oxygen diffuses from the alveoli into the blood in the pulmonary capillaries, while carbon dioxide diffuses from the blood into the alveoli to be exhaled.
3. Transport of Gases: Oxygen is transported by hemoglobin in red blood cells to tissues throughout the body, while carbon dioxide produced by cellular metabolism is transported back to the lungs for exhalation.

Internal Respiration

Internal respiration refers to gas exchange at the cellular level within tissues. This phase involves:

1. Oxygen Utilization: Cells use oxygen for metabolic processes, primarily cellular respiration, which produces ATP (adenosine triphosphate) as energy.
2. Carbon Dioxide Production: As a byproduct of metabolism, carbon dioxide is produced and must be removed from cells and transported back to the lungs for exhalation.

Classification of Respiratory System According to Structure and Function

The respiratory system can be classified based on its structure and function into two main categories:

Structural Classification

1. Upper Respiratory Tract:
   • Comprises structures above the vocal cords.
   • Includes:
     • Nasal cavity
     • Pharynx
     • Larynx
2. Lower Respiratory Tract:
   • Comprises structures below the vocal cords.
   • Includes:
     • Trachea
     • Bronchi
     • Bronchioles
     • Alveoli

Functional Classification

1. Conducting Zone:
   • Responsible for transporting air to sites of gas exchange.
   • Includes:
     • Nasal cavity
     • Pharynx
     • Larynx
     • Trachea
     • Bronchi
     • Bronchioles (up to terminal bronchioles)
2. Respiratory Zone:
   • Site of gas exchange.
   • Includes:
     • Respiratory bronchioles
     • Alveolar ducts
     • Alveoli

Structure and Functions of Key Components of Respiratory System

1. Nasal Cavity

Structure:

• The nasal cavity is a hollow space located behind the nose, divided by a septum into two nostrils.
• It has a mucous membrane lining that contains cilia and goblet cells.

Functions:

• Filters, warms, and humidifies incoming air.
• Contains olfactory receptors for smell.
• Aids in resonance for speech.

2. Pharynx

Structure:

• A muscular tube that connects nasal cavity to larynx; divided into three parts: nasopharynx, oropharynx, laryngopharynx.

Functions:

• Serves as a passageway for both air and food.
• Plays a role in immune defense with tonsils located within it.

3. Larynx

Structure:

• Composed of cartilage structures including thyroid cartilage (Adam’s apple), cricoid cartilage, and epiglottis.

Functions:

• Houses vocal cords; responsible for sound production.
• Acts as a protective mechanism against aspiration during swallowing by closing off trachea.

4. Trachea

Structure:

• A tubular structure made up of C-shaped cartilaginous rings lined with ciliated epithelium.

Functions:

• Provides a clear airway for air passage from larynx to bronchi.
• Filters and traps particles through mucus secretion and ciliary action.

5. Bronchi

Structure:

• The trachea bifurcates into right and left primary bronchi which further divide into secondary (lobar) bronchi and tertiary (segmental) bronchi.

Functions:

• Conducts air from trachea to lungs; continues filtration process initiated in trachea.

6. Bronchioles

Structure:

• Smaller branches of bronchi that lack cartilage but have smooth muscle walls; further divide into terminal bronchioles leading to respiratory bronchioles.

Functions:

• Regulates airflow through constriction or dilation; conducts air towards alveoli where gas exchange occurs.

7. Alveoli

Structure:

• Tiny sac-like structures at the end of bronchioles surrounded by capillaries; composed of simple squamous epithelium for efficient gas exchange.

Functions:

• Primary site for gas exchange; oxygen diffuses into blood while carbon dioxide diffuses out due to concentration gradients across alveolar walls.

In summary, each component of the respiratory system plays a crucial role in ensuring efficient breathing and gas exchange necessary for sustaining life.