Respiratory System Overview

Functions of the Respiratory System

The respiratory system is essential for gas exchange, supplying oxygen to the body and removing carbon dioxide. It also plays roles in vocalization, olfaction, and maintaining homeostasis.

• Ventilation: Movement of air into and out of the lungs.

• Gas Exchange: Oxygen moves from air to blood, then to tissues; carbon dioxide moves from tissues to blood, then to air.

• Cellular Respiration: Cells use oxygen to produce ATP, the energy currency of the cell.

Anatomy of the Respiratory System

Organs and Divisions

The respiratory system consists of several organs, divided into upper and lower tracts:

• Upper respiratory tract: Nose, pharynx, larynx

• Lower respiratory tract: Trachea, bronchi, lungs

Nose and Nasal Region

The nose is the primary entryway for air and has several functions:

• Provides airway for respiration

• Moistens and warms inhaled air

• Filters and cleans inhaled air

• Detects odors via olfactory mucosa

• Resonating chamber for voice amplification

Bony and Cartilaginous Supports of the Nose

The nose is supported by both bone and cartilage:

• Superior half: Nasal bones medially, maxillae laterally

• Inferior half: Cartilages and dense connective tissue

• Flared portion: Dense connective tissue forms lateral wall of each nostril

Nasal Cavity

The nasal cavity extends from the nostrils to the posterior nares and is divided by the nasal septum:

• Vestibule: Dilated chamber inside nostrils, lined with stratified squamous epithelium and vibrissae (guard hairs)

• Nasal conchae: Superior, middle, and inferior projections that increase surface area

• Nasal fossae: Right and left chambers divided by the septum

Nasal Cavity Mucosa

The nasal cavity is lined with two types of mucosa:

• Olfactory mucosa: Detects odors, lines roof of nasal fossa

• Respiratory mucosa: Ciliated pseudostratified epithelium lines the rest of the cavity

• Defensive role: Mucus traps inhaled particles; lysozyme destroys bacteria

Cilia and Erectile Tissue

Cilia and erectile tissue play important roles in the nasal cavity:

• Cilia: Sweep debris-laden mucus into the pharynx to be swallowed

• Erectile tissue: Venous plexus in inferior concha engorges with blood, shifting airflow to prevent drying and warm air

• Epistaxis: Nosebleeds often result from trauma to lower nasal septum or erectile tissue

Pharynx

Regions of the Pharynx

The pharynx is a muscular tube that serves as a passageway for air, food, and drink. It is divided into three regions:

• Nasopharynx: Receives auditory tubes, contains pharyngeal tonsil; passage for air only

• Oropharynx: Contains palatine and lingual tonsils; passage for air, food, and drink

• Laryngopharynx: At the level of the hyoid bone; passage for air, food, and drink

Larynx (Voicebox)

Structure and Function

The larynx is a cartilaginous chamber whose primary function is to keep food and drink out of the airway. It also produces sound for speech.

• Epiglottis: Flap of tissue that guards the glottis, directing food and drink to the esophagus

• Glottis: Vocal cords and opening to the trachea; controls vocal cord movement

• Infant larynx: Higher in the throat, allows breathing while swallowing; descends by age 2

Action of Vocal Cords

Vocal cords can be adducted (tightened) or abducted (loosened) to produce different pitches. Sound is produced by vibration of the cords, but speech requires additional structures.

• Adduction: Tightens cords for high pitch

• Abduction: Loosens cords for low pitch

Trachea (Windpipe)

Structure and Function

The trachea is a rigid tube supported by C-shaped cartilaginous rings. It is lined with ciliated pseudostratified epithelium, functioning as a mucociliary escalator to move mucus and debris upward.

• Length: 4.5 inches long, 2.5 inches in diameter

• Location: Anterior to the esophagus

• Support: 16-20 C-shaped rings

Tracheotomy and Tracheostomy

A tracheotomy is a surgical procedure to create an opening in the trachea (tracheostomy) for air passage. Air must be filtered and humidified.

Carina

The carina is a median ridge at the point where the trachea forks into the right and left primary bronchi. It is a sensitive area that triggers coughing when stimulated.

Lungs

Surface Anatomy

The lungs are paired organs located in the thoracic cavity. They are not symmetrical due to the position of the heart and liver.

• Right lung: Shorter (due to liver), has three lobes

• Left lung: Narrower (due to heart), has two lobes

Bronchial Tree

The bronchial tree consists of branching airways that conduct air to the alveoli:

• Primary bronchi: Right is wider and more vertical (aspiration risk)

• Secondary bronchi: 2 in left lung, 3 in right lung

• Tertiary bronchi: 10 in right, 8 in left; each supplies a bronchopulmonary segment

• Bronchioles: Smaller branches

• Terminal bronchioles: Final branches before alveolar sacs

• Alveolar sacs (alveoli): Site of gas exchange

Alveolus Structure and Function

Alveoli are tiny air sacs where gas exchange occurs. They are lined by two types of cells:

• Type I (Squamous alveolar cells): 95% of surface area, specialized for gas exchange

• Type II (Great alveolar cells): Cuboidal, secrete surfactant to lower surface tension

• Alveolar macrophages: "Dust cells" that remove debris and pathogens

Alveolar Blood Supply

Each alveolus is surrounded by a capillary network, facilitating efficient gas exchange between air and blood.

Pleurae and Pleural Fluid

Structure and Function

The lungs are enclosed by pleurae, which are serous membranes:

• Visceral pleura: Covers the lungs

• Parietal pleura: Lines the rib cage

• Pleural cavity: Space between pleurae, lubricated with fluid

• Functions: Reduce friction, create pressure gradient for lung inflation, compartmentalize to prevent infection spread

Pulmonary Ventilation

Mechanics of Breathing

Pulmonary ventilation is the process of moving air in and out of the lungs. It consists of inspiration and expiration:

• Quiet respiration: Occurs at rest

• Forced respiration: Occurs during exercise

• Pressure difference: Air flows due to differences between lung and atmospheric pressure

Respiratory Muscles

Muscles involved in breathing include:

• Inspiration: Diaphragm and external intercostals expand thoracic cavity, lowering pressure and drawing air in

• Expiration: Elastic recoil during quiet breathing; abdominal and internal intercostal muscles intensify expiration

Neural Control of Breathing

Brain Centers

Breathing is controlled by repetitive stimuli from the brain, specifically neurons in the medulla oblongata and pons, which regulate unconscious breathing.

Summary Table: Major Structures and Functions of the Respiratory System

Key Equations

Boyle's Law: Describes the relationship between pressure and volume in the lungs:

Gas Exchange Equation: Partial pressure gradients drive diffusion:

Additional info: Expanded explanations and context were added to clarify anatomical structures and physiological functions for exam preparation.