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 lungs for exhalation.

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

Organs of the Respiratory System

The respiratory system consists of several organs organized into upper and lower tracts.

• Upper Respiratory Tract: Nose, pharynx, larynx

• Lower Respiratory Tract: Trachea, bronchi, lungs

Nose and Nasal Cavity

Functions of the Nose

The nose is the primary entryway for air and performs several important functions.

• Provides airway for respiration

• Moistens and warms inhaled air

• Filters and cleans inhaled air

• Detects odors

• Resonating chamber for voice

Anatomy of the Nasal Region

The external nose consists of several anatomical features that support its functions.

• Anterior nares (nostrils): Entry points for air

• Nasal septum: Divides nasal cavity into right and left chambers

• Bridge and apex: Structural features

Bony and Cartilaginous Supports

The nose is supported by both bone and cartilage.

• Superior half: Nasal bones medially, maxillae laterally

• Inferior half: Cartilages (lateral, septal, alar)

• Dense connective tissue: Forms lateral wall of each nostril

Nasal Cavity Structure

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

Nasal Cavity Mucosa

The nasal cavity is lined with specialized mucosa for defense and olfaction.

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

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

• Defensive role: Mucus traps particles; lysozyme destroys bacteria

Cilia and Erectile Tissue

Cilia and erectile tissue play important roles in maintaining nasal health.

• Cilia: Sweep debris-laden mucus into pharynx for swallowing

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

• Epistaxis (nosebleed): Often results 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 level of 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 houses the vocal cords for sound production.

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

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

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

Action of Vocal Cords

Vocal cords can be adducted (tightened) for high pitch or abducted (loosened) for low pitch. Sound is produced by vibration, but speech requires additional structures.

• Adduction: Tightens vocal cords for high pitch

• Abduction: Loosens vocal cords for low pitch

• Speech: Requires pharynx, oral cavity, tongue, lips

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 esophagus

• Support: 16-20 C-shaped cartilaginous rings

• Mucociliary escalator: Moves mucus upward toward pharynx

Tracheotomy and Tracheostomy

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

• Indications: Airway obstruction, respiratory failure

• Care: Prevent infection, ensure proper humidification

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 for triggering cough reflex.

Lungs

Surface Anatomy

The lungs are paired organs with distinct lobes and surfaces. The right lung is shorter due to the liver, and the left lung is narrower due to the heart.

• Right lung: 3 lobes (superior, middle, inferior)

• Left lung: 2 lobes (superior, inferior)

• Hilum: Entry/exit point for bronchi, blood vessels, nerves

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 conducting branches

• Alveolar sacs (alveoli): Sites of gas exchange

Alveolus Structure and Function

Alveoli are tiny air sacs where gas exchange occurs. They are lined by two types of cells and contain macrophages for defense.

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

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

• Alveolar macrophages: Remove dust and pathogens

Alveolar Blood Supply

Each alveolus is surrounded by a capillary network for efficient gas exchange.

• Pulmonary arteries: Carry deoxygenated blood to alveoli

• Pulmonary veins: Return oxygenated blood to heart

Pleurae and Pleural Fluid

Structure and Function

The lungs are enclosed by pleurae, which are double-layered membranes. The pleural cavity contains lubricating fluid.

• Visceral pleura: Covers lungs

• Parietal pleura: Lines 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 pressure differences between lungs and outside body

Respiratory Muscles

Muscles involved in breathing include the diaphragm and intercostals.

• Inspiration: Diaphragm and external intercostals expand thoracic cavity, pressure drops, air moves 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.

• Medulla oblongata: Controls basic rhythm

• Pons: Modifies rhythm for smooth transitions

Summary Table: Major Structures of the Respiratory System