Lecture 14: 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.

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

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 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.

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 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 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 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 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 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).

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 extends from the nasal cavity to the terminal bronchioles and conducts air from the environment to 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 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.

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.

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.

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.

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.