respiratory system

• Nose is the only external part of the respiratory tract, divided into two cavities by nasal septum.
• Nose is rich in blood vessels in mucosa and hairs in the anterior nares.
• Nose warms, moistens, humidifies, filters, and smells air.
• Nose is divided into two cavities by nasal septum.
• Nasal cavity is the superior part of the respiratory tract, containing the superior nasal concha with a superior meatus opening into the posterior ethmoidal sinus, the middle nasal concha with a middle meatus opening into the frontal, anterior, middle ethmoidal and maxillary sinus, and the inferior nasal concha with an inferior meatus opening into the nasolacrimal duct.
• Conchae are erectile tissue to help increase the surface area, facilitating contact between air and mucous blanket.
• Nasal cavity is covered in respiratory epithelium, with the vestibular area lined with thin skin containing soft, stiff hairs, sebaceous glands, and sweat glands, and the respiratory area lined with respiratory epithelium.
• Olfactory area of the nasal cavity contains the olfactory epithelium, underlying lamina propria, and is located in the superior part of the nasal cavity, covering the surface of the cribriform plate, extending to the superior nasal concha.
• Olfactory epithelium contains olfactory cells, bipolar neurons, centrally located, prominent nuclei, and basal cells, which are precursor cells to olfactory cells.
• Paranasal sinuses are air-containing cavities in bones of face and cranium, which open or drain into the nasal cavity.
• Nasopharynx is posterior to the nasal cavity, inferior to the sphenoid bone, superior to the soft palate, and contains the opening of the eustachian tube.
• Oropharynx is posterior to the oral cavity, inferior to the soft palate, superior to the epiglottis, and provides a passageway for food and air.
• The larynx is lined by stratified squamous non-keratinized epithelium.
• The lamina propria of the larynx is loose to dense irregular connective tissue with seromucous glands and pharyngeal tonsil in the posterior portion.
• The muscular layer of the larynx contains constrictor muscles found below the lamina propria.
• The functions of the larynx include passageway for air and food, warming, humidifying air as it passes through, protection from pharyngeal tonsils, taste, auditory tubes for detecting pressure on each side of the tympanic membrane for hearing, speech, and working with sinuses to give voice characteristics.
• The larynx extends for about 5cm from the 4th-6th cervical vertebrae and attaches to the hyoid bone, opening into the laryngopharynx.
• The inferior part of the larynx is continuous with the trachea.
• The trachea is a rigid fibroelastic structure descending from the larynx, consisting of 16-20 c-shaped rings, ending by dividing into two main bronchi.
• The trachea has four layers: mucosa, submucosa, cartilaginous layer, and trachealis muscle.
• The right primary bronchus is steeper and larger in diameter than the left.
• The left bronchus divides into 2 lobar bronchial branches, while the right bronchus divides into 3 lobar bronchial branches.
• The right bronchus also contains more lobar bronchial branches than the left.
• The right bronchus has more secondary bronchi than the left.
• The right bronchus has more tertiary bronchi than the left.
• The right bronchus has more extrapulmonary bronchi than the left.
• The right bronchus has more intrapulmonary bronchi than the left.
• The right bronchus has more bronchioles than the left.
• The right bronchus has more terminal bronchioles than the left.
• The right bronchus has more alveoli than the left.
• Laryngopharynx is a passageway for food and air, posterior to the upright epiglottis, extends to the larynx, and is superior to the cricoid cartilage.
• Thick layers of smooth muscle are present in the respiratory system, making it smooth muscle dominant.
• Clara cells are found in the epithelium of terminal bronchioles and are non-ciliated columnar cells with rounded or dome-shaped apical surface projection.
• Clara cells secrete surfactant, which lines alveoli and degrades toxins in the air.
• Clara cells produce glycosaminoglycans and detoxify noxious substances.
• The initial area of gas exchange, the respiratory bronchiole, is continuous with the alveolar duct and its wall is similar to that of a terminal bronchiole.
• The wall of the initial respiratory bronchiole contains simple cuboidal epithelium with ciliated cells and clara cells.
• The respiratory bronchiole gradually transforms to a low cuboid with discontinuous replacement of alveolar squamous cell type I.
• The respiratory bronchiole has an incomplete layer of smooth muscle.
• Alveoli open at the wall of respiratory bronchioles.