Anatomy of the Airways & Alveoli - Vocabulary

Comprehensive vocabulary flashcards generated from lecture notes on the anatomy and histology of the human airways and alveoli.

Ventilation

The process of moving gas in and out of the lungs.

Respiration

The swapping of $O_2$ and $CO_2$, categorized as External (lungs to blood) or Internal (capillaries to tissues).

Conducting Airways

Structures that connect outside air to the gas-exchange membrane where no gas exchange occurs, also known as anatomical deadspace.

Nares

The external openings of the nose.

Nasal Septum

A cartilaginous structure anteriorly dividing the nose into two nasal fossae, formed posteriorly by the vomer and ethmoid bones.

Conchae (Turbinates)

Three downward sloping, scroll-shaped bones (superior, middle, inferior) projecting from the lateral wall of the nasal cavity that increase surface area, airflow resistance, and turbulence.

Intubation

The procedure of inserting an artificial airway through the nose or mouth into the trachea, bypassing the upper airway.

Pharynx

A muscular tube posterior to the nasal and oral cavities that serves as a common passageway for air and food to the larynx and esophagus.

Nasopharynx

The upper portion of the pharynx located behind the nasal cavity, extending from the base of the skull to the soft palate.

Oropharynx

The middle portion of the pharynx located behind the oral cavity, extending from the soft palate to the base of the tongue (hyoid bone).

Laryngopharynx

The lower portion of the pharynx located behind the larynx, extending from the base of the tongue (hyoid bone) to the cricoid cartilage.

Glossopharyngeal Nerve (9th Cranial Nerve)

The sensory component of the pharyngeal musculature involved in defensive reflexes to prevent aspiration.

Vagus Nerve (10th Cranial Nerve)

The motor component of the pharyngeal musculature involved in preventing aspiration, which also mediates the laryngeal reflex causing laryngospasm.

Larynx

A cylindrical cartilaginous structure lying at the level of $\text{C4--C6}$ vertebrae that serves as a valve on top of the trachea, housing vocal cords and marking the division between upper and lower airways.

Thyroid Cartilage

The largest of the laryngeal cartilages.

Cricoid Cartilage

The only laryngeal structure forming a complete ring of cartilage around the airway, representing the narrowest region of the upper airway in infants.

Epiglottis

A thin, flat, leaf-shaped cartilage attached to the thyroid cartilage that rises above the glottis and slants upward and posteriorly toward the base of the tongue.

Vallecula

A small pocket located between the epiglottis and the base of the tongue.

Glottis

The triangular opening formed by the vocal cords that leads to the trachea, representing the narrowest part of the adult larynx.

Laryngospasm

A laryngeal reflex mediated by the vagus nerve ($10\text{th}$ cranial nerve) causing the vocal cords inside the larynx to close the tracheal opening.

Dichotomous Branching

A pattern of airway division where each individual airway divides into two smaller daughter airways.

Isothermic Saturation Boundary (ISB)

The depth in the airways below which gas temperature remains constant at body temperature ($37^\circ\text{C}$) and humidity is $100\%$ saturated with water vapor.

Parenchyma

The supportive tissue composing the lung beyond the $3\text{rd}$ generation, consisting of elastic fibers that surround and tether small non-cartilaginous airways to keep them open during forceful exhalation.

Bronchioles

Airways measuring less than $1\,\text{mm}$ in diameter that contain no cartilage in their walls.

Acinus

The functional respiratory unit/zone of the lung consisting of all airways beyond the terminal bronchioles (respiratory bronchioles to alveolar sacs), housing approximately $3000\,\text{mL}$ of air at rest.

Alveoli

Tiny gas-filled sacs (numbering around $300\text{ million}$ in adult lungs) that serve as the primary site of external respiration.

Metachronal Wave

A continuous propulsive wave created by ciliated airway cells (beating up to 1300 times per minute) to move mucus toward the pharynx.

Inspissated Mucus

Airway mucus that has become dehydrated, thick, and immobile due to a lack of humidity.

Serous Cells

Epithelial cells in the airways that can transform into goblet cells under chronic exposure to air pollutants like cigarette smoke.

Kulchitsky Cells

Endocrine cells in the airway epithelium, prominent in newborns, that act as precursors to carcinoids and small cell bronchogenic carcinomas.

Respiratory Airway Secretory Cells (RASCs)

A recently discovered population of epithelial cells lining distal airways near the alveoli.

Clara Cells

Non-ciliated secretory cells in the terminal and respiratory bronchioles that serve as a key source of mucus secretion at that level.

Mast Cells

Non-epithelial connective tissue cells in airway walls near smooth muscle that release inflammatory mediators such as histamine, prostaglandins, leukotrienes, and platelet activating factor.

Type I Cells

Flat squamous epithelial cells that make up approximately $95\%$ of the alveolar walls.

Type II Cells

Cuboidal-shaped alveolar cells containing lamellar bodies that secrete surfactant to reduce alveolar surface tension.

Surfactant

A fluid substance secreted by Type II pneumocytes from internal lamellar bodies that coats alveolar surfaces to reduce surface tension and prevent collapse.

Interstitium

The space between the basement membranes of the alveolar epithelium and capillary endothelium forming a thin blood-air barrier.

Pores of Kohn

Small openings that connect adjacent alveoli directly with one another.

Canals of Lambert

Anatomical connections between terminal bronchioles and nearby adjacent alveoli.

Alveolar Macrophages

Phagocytic cells that crawl along alveolar structures to engulf foreign material, digest microorganisms, and keep the alveoli sterile.