Lecture 14: The Respiratory System

The Respiratory System

• The respiratory system's roles include movement of air into and out of the lungs, exchange of gases (O2/CO2) between the lungs and the blood, and regulation of blood pH, speaking, and sense of olfaction/smell.

Structure of the Respiratory System

• The respiratory system has two subdivisions: upper respiratory system (nose, nasal cavity, pharynx) and lower respiratory system (larynx, trachea, bronchial tree, lungs).
• The passageway is lined with mucosa, except in the vestibule, and is composed of ciliated pseudostratified epithelial cells (with mucous producing goblet cells) and a connective tissue layer known as the lamina propria.

The Nose

• The nose is composed of nasal bones, cartilage, and connective and adipose tissue.
• The nostrils are also known as the nares.

The Nasal Cavity

• The nasal cavity is divided into two by the nasal septum.
• The anterior region is lined with hyaline cartilage, while the posterior region is lined with different bones.
• The nasal cavity warms and moistens incoming air and is responsible for olfaction (sense of smell) and speaking (resonance chamber).
• The vestibule is lined with skin with coarse hair (stratified squamous epithelia), while the respiratory region is lined with mucosa (ciliated pseudostratified epithelial cells).
• The nasal conchae and mucus membrane-lined meatuses (grooves) increase surface area and cause incoming air to swirl, warming and moistening the air.
• Tears drain into the nasal cavity through the lacrimal duct.

The Olfactory Area

• The olfactory area is located in the roof of the nasal cavity and is involved in the sense of smell.
• It contains neurons that act as olfactory receptors.

The Paranasal Sinuses

• There are eight air-filled spaces in the skull bones (frontal, sphenoid, ethmoid, and maxillae) that open into the nasal cavity.
• They serve to warm and moisten air and lighten the skull.
• Sinusitis is the inflammation of the mucous membranes of the sinuses.

The Pharynx

• The pharynx extends from the internal nares to the top of the larynx and serves as a passageway for food and air and a resonating chamber.
• It includes the nasopharynx, oropharynx, and laryngopharynx.

The Larynx

• The larynx is a passageway for air composed of 9 pieces of cartilage (all hyaline cartilage except the epiglottis).
• The epiglottis covers the glottis during swallowing and is composed of elastic cartilage.
• The true vocal cords (produce sound) and the vestibular folds (false vocal cords) are located in the larynx.
• Inflammation of the vocal cords is known as laryngitis.

The Trachea

• The trachea connects the larynx to the main bronchi and is composed of 20 C-shaped pieces of hyaline cartilage.
• It is located anterior to the esophagus and serves as a passageway for air.

The Bronchial Tree

• The bronchial tree leads from the main bronchi to the alveolar ducts and is composed of ciliated pseudostratified epithelial cells in the upper bronchi and non-ciliated squamous epithelial cells in the lower bronchi.

The Lungs

• The right and left lungs are separated by the mediastinum (containing the heart).
• The right lung has three lobes (superior, middle, and inferior), while the left lung has two lobes (superior and inferior).

The Pleural Membrane

• Each lung is enclosed by its own double-layered pleural membrane, consisting of visceral pleural membrane (covers the surface of the lung) and parietal pleural membrane (attached to the inner thoracic wall, diaphragm, and mediastinum).
• The pleural cavity contains pleural fluid, which reduces friction and holds the lungs to the walls of the thoracic cavity.

The Conduction Zone

• The conduction zone extends from the nasal cavity to the terminal bronchioles and conducts air from the environment to the respiratory zone.

The Respiratory Zone

• The respiratory zone extends from the respiratory bronchioles to the alveoli and is responsible for the exchange of gases (O2/CO2) between the blood and the lungs.

The Respiratory Membrane

• The respiratory membrane consists of the walls of the alveoli and the blood vessels.
• Type I alveolar cells are simple squamous epithelial cells that allow for gas diffusion, while type II alveolar cells are simple cuboidal cells that secrete surfactant.
• Alveolar macrophages move across the surface of type I cells, removing foreign matter, and alveolar pores allow for air movement between the alveoli.

Blood Supply to the Lungs: Pulmonary Circulation

• Deoxygenated blood is pumped from the right ventricle to the pulmonary trunk, then to the pulmonary arteries.
• Oxygenated blood returns to the left atrium via the pulmonary veins.

Blood Supply to the Lungs: Systemic Circulation

• Oxygenated blood is pumped from the left ventricle to the bronchial arteries.
• Blood becomes deoxygenated as it passes through lung tissue, and deoxygenated blood enters the bronchial veins and returns to the right atrium via the vena cava.

Clinical Applications

• Pulmonary edema: accumulation of fluid in the lungs due to heart failure.
• Pneumonia: inflammation of alveoli due to infection.
• Tuberculosis: infection with Mycobacterium tuberculosis, resulting in the thickening of the respiratory membrane and decreased lung elasticity.
• Pulmonary embolism: blockage of pulmonary blood vessels, inhibiting oxygenation of blood.
• Pneumothorax: entry of air into the pleural cavity, causing the lung(s) to collapse.
• Emphysema: breakdown of alveolar walls due to smoking, air pollution, or inhaling chemical fumes or dust, resulting in larger alveoli, decreased elasticity, and decreased recoil.

Ventilation/Breathing

• Inspiration/inhalation: intake of air into the lungs, 75% of which is due to diaphragm contraction, and 25% of which is due to external intercostal contraction.
• Expiration/exhalation: movement of air out of the lungs, normally a passive process, but active during forceful breathing.