Respiratory System in Pharmacy

Respiratory System

• The respiratory system is a complex of organs and tissues that exchange blood carbon dioxide (CO2) with air oxygen (O2).
• Function: Act of breathing, which includes inhaling and exhaling air in the body; the absorption of oxygen from the air to produce energy; the discharge of carbon dioxide, which is the byproduct of the process.

Divisions of the Respiratory System

• The conducting airways: serve to conduct, clean, warm, and moisten the air; composed of the nose, pharynx, larynx, trachea, bronchi, and bronchioles.
• The respiratory airways: facilitate gas exchange; located entirely within the lung and are represented by respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

Cell Types in the Respiratory System

• Goblet (Mucous) Cells: present in the trachea and bronchi; contribute to mucous secretion lining the airways.
• Basal (Short) Cells: found in the trachea and bronchi; do not reach the airway lumen and have nuclei close to the basal lamina, giving the epithelium a pseudostratified appearance.
• Clara Cells (Bronchiolar Epithelial Cell): non-ciliated columnar epithelial cells found in bronchioles; play a major role in the metabolism of exogenous agents and act as progenitor cells for bronchiolar epithelium following lung injury.
• Brush Cells: non-ciliated columnar cells found in trachea and bronchi; have a dense population of long, straight, blunt microvilli on the luminal surface and epithelioidendritic (afferent) synapses near the cell base; function is unknown, but suspected to be chemoreceptor and sensory.
• Dense Core Granule Cells (Small Granule Cell, Neuroendocrine Cell): found throughout the airways; resemble endocrine cells; secrete a variety of amine and peptide products; role in regulating lung function is incompletely understood.
• Serous Cells: non-ciliated secretory cells found predominantly in the trachea and bronchi; secrete glycoproteins and lysozymes; contribute to the low viscosity periciliary fluid covering the bronchial epithelium.
• Intermediate Cells: non-ciliated columnar cells that are immature and replace cells cast off from the epithelium; may differentiate into mucous secreting Goblet cells or ciliated cells.

Larynx

• Functions: phonation (creation of sounds for speech) and control of the air pathway so that only air reaches the lower respiratory passages.
• During swallowing, the larynx moves upwards and directs the food to the oesophagus.
• If anything other than air enters the larynx, there is a cough reflex to prevent fluids or food entering the trachea.

Histology of the Alveolar Region

• Five major cell types are present in the alveolar region of the lung:
  • Alveolar Type I Cell (Squamous alveolar epithelial cell): lines the alveoli and covers a large surface area; permeable to gases and is the major location of gas exchange.
  • Alveolar Type II Cell (Great alveolar cell, granular pneumocyte): forms tight junctions with Type I cells; secretory cells that protrude into the alveolar lumen.
  • Capillary Endothelial cell: specialized for gas exchange; receives the entire cardiac output.
  • Alveolar macrophages: large cells that wander freely in the alveoli; ingest microorganisms and inhaled particulate matter.
  • Interstitial cells: primarily fibroblasts with ramified cytoplasmic extensions; progenitor cell is capable of differentiation into fibroblasts or smooth muscle cells.

Mucociliary Apparatus

• Consists of ciliated epithelium, submucosal glands, and goblet cells that secrete serous and mucinous secretions.
• Function: trap and expel debris that has been inhaled.
• Particles above 10 microns in size do not get past the nasopharynx; particles averaging 5 to 10 microns are trapped by the mucociliary apparatus; particles 1 to 5 microns in size must be phagocytosed by macrophages in the alveoli; particles less than 1 micron remain suspended and are exhaled.

Pleura

• The lungs are covered by a thin tissue layer called the pleura.
• The same kind of thin tissue lines the inside of the chest cavity.
• A thin layer of fluid acts as a lubricant, allowing the lungs to slip smoothly as they expand and contract with each breath.