Respiratory System: review, organs, and histology (lecture 13)

Respiratory System Overview

• Functions include gas exchange involving oxygen (O2) and carbon dioxide (CO2) between blood and air.
• The system enables communication through speech and other vocalizations.
• Olfaction, or the sense of smell, is facilitated through this system.
• Platelet production occurs, with the lungs generating over 50% of platelets via megakaryocytes, not bone marrow.
• The respiratory system filters small blood clots from the bloodstream and dissolves them, preventing clots from obstructing vital pathways.
• Holding breath assists in expelling abdominal contents through urination, defecation, and childbirth.

Divisions of the Respiratory System

• The conducting zone includes passages from the nostrils to the major bronchioles and serves primarily for airflow.
• Gas exchange is mainly facilitated through the alveoli and neighboring structures in the respiratory zone.
• The upper system extends from the nose through the larynx, including organs in the head and neck.
• The lower system runs from the trachea through the lungs, including organs of the thorax.

Nose Anatomy and Function

• The nose extends from the nostrils to the posterior nasal apertures (choanae) within the nasal cavities.
• The vestibule contains guard hairs that block debris from entering.
• Meatuses facilitate mucus covering to collect dust.
• Functions include cleansing, warming, and humidifying air.
• The nose also detects odors.

Nose Histology

• Both the olfactory and respiratory epithelium are pseudostratified.
• The olfactory epithelium contains non-motile cilia that bind to odor molecules, with olfactory glands secreting serous fluid to aid in dissolving these odor molecules.
• The respiratory epithelium contains motile cilia and utilizes goblet cells and mucous glands, which secrete mucus to trap particles.

Pharynx

• The pharynx is a muscular funnel from the nasal system to the larynx, essential for breathing, swallowing, and speech.
• It also filters air and prevents food from entering the airway.
• Eustachian tubes balance middle ear pressure.
• The nasopharynx only passes air, positioned behind the nasal apertures and above the soft palate.
• The pseudostratified columnar epithelium helps trap large particles in mucus.
• The oropharynx, behind the oral cavity from the soft palate to the epiglottis, allows passage of air, food, and drink.
• The laryngopharynx, at the tip of the epiglottis behind the larynx, allows passage of air, food, and drink.
• Stratified squamous epithelium in the oropharynx and laryngopharynx is resistant to abrasion.

Larynx

• Its primary function is to prevent food and drink from entering the airway during swallowing.
• The larynx ("voice box") is a cartilaginous chamber producing sound and preventing choking.
• The epiglottic cartilage is a spoon-shaped supportive plate in the epiglottis.
• The thyroid cartilage ("Adam's apple") is shield-shaped and the largest, providing structure and protection to the vocal cords.
• The cricoid cartilage is ring-shaped, connecting the larynx to the trachea for support.
• The epiglottis covers the larynx opening during swallowing.
• Extrinsic muscles move the larynx upwards during swallowing, the tongue moves the epiglottis downward, and the vestibular folds close the larynx.
• Vocal cords vibrate to produce sound. Intrinsic muscles control vocal cord tension and position.

Trachea

• The trachea, or "windpipe," connects the larynx to the bronchi.

Trachea Histology

• The trachea has a pseudostratified columnar lining with goblet cells.
• It utilizes the mucociliary escalator for debris removal.

Lungs

• The right lung has three lobes, while the left has two.
• Asymmetry is due to the heart, diaphragm, and liver.
• The right lung is shorter because the liver rises higher.
• The left lung is narrower due to the heart's position, creating the cardiac impression.

Bronchial Tree

• Definition: branching system of air tubes in each lung.
• Primary bronchi branch into 65,000 terminal bronchioles.
• The tree is lined with pseudostratified columnar epithelium, which gets thinner further from the trachea.
• Bronchioles branch into terminal bronchioles (the final branches of the conducting zone).
• Elastic connective tissue facilitates recoiling to expel air.
• Bronchioles lack cartilage, allowing greater flexibility, constriction, and dilation.
• Terminal bronchioles branch into respiratory bronchioles, leading to alveolar ducts.
• Alveoli are clustered into alveolar sacs.

Alveoli

• Definition: microscopic air pouches, with approximately 40 million per lung.
• Large Surface Area: Providing a surface area of 70 square meters for gas exchange.
• Type I cells are simple squamous cells covering 95% of surface area, allowing for rapid gas exchange.
• Type II cells cover 5% of surface area, are cuboidal, thicker, and repair damaged epithelium.
• Dust cells (alveolar macrophages) remove dust and debris.

Inspiratory Pathway

• The pathway includes the nasal cavity/mouth, pharynx, larynx, trachea, primary bronchus, bronchioles, terminal bronchiole, respiratory bronchiole, alveolar duct, and alveoli.
• The conducting zone includes the nasal cavity/mouth, pharynx, larynx, trachea, primary bronchus, bronchioles, and terminal bronchiole.
• The respiratory zone includes the respiratory bronchiole, alveolar duct, and alveoli.