Unit 5 Recap: The Respiratory System

Instructions

Use this recap to review how your respiratory system works from start to finish. Look for connections between the different structures to understand how air moves through your body, how oxygen and carbon dioxide are exchanged, and how your chest muscles power your breathing.

Tracing the Respiratory Pathway

The Respiratory Tracts Outline

Upper Respiratory Tract Functions

Nasal Cavity

Air enters through nostrils (nares)
Nasal hairs (vibrissae) filter large particles
Mucous membranes warm, moisten, and filter air
Turbinates (conchae) increase surface area for air conditioning

Pharynx (Throat)

Nasopharynx: connects nasal cavity to throat
Oropharynx: shared pathway for air and food
Laryngopharynx: directs air to larynx

Larynx (Voice Box)

Houses vocal cords for speech
Epiglottis closes during swallowing to prevent aspiration

Lower Respiratory Tract Structures

Trachea (Windpipe)

C-shaped cartilage rings provide structure
Cilia move mucus upward to trap particles

Bronchi

Trachea divides at carina into right and left mainstem bronchi
Further branch into smaller bronchi for each lung lobe

Bronchioles

Smaller airways without cartilage
Terminal bronchioles lead to respiratory zone

Alveoli

Tiny air sacs where gas exchange occurs
Surrounded by capillaries forming alveolar-capillary membrane

Remember: The respiratory system's primary function is to bring oxygen into the bloodstream and remove carbon dioxide waste from the body.

Diagram of the human respiratory system with labeled parts. — solar22 / Shutterstock

The Respiratory Highway System

The Respiratory Tracts Outline

Upper Respiratory Tract Functions

Air Conditioning

Warms cold air to body temperature
Adds moisture to achieve 100% humidity
Filters particles through nasal hairs and mucus

Protective Mechanisms

Mucociliary escalator traps and removes particles
Mucus contains enzymes that destroy pathogens
Cilia beat 1,000-1,500 times per minute to move mucus

Additional Functions

Provides sense of smell (olfaction)
Enables speech production (phonation)
Houses immune tissue (adenoids and tonsils)

Lower Respiratory Tract Structures

Trachea

Main airway (about 4½ inches long)
C-shaped cartilage prevents collapse
Bifurcates at the carina into mainstem bronchi

Bronchial Tree

Right mainstem bronchus branches at less steep angle than left
Bronchi branch into lobar bronchi, then segmental bronchi
Bronchioles lack cartilage and have simpler epithelium

Conducting Zone vs. Respiratory Zone

Conducting zone: trachea through terminal bronchioles
Respiratory zone: respiratory bronchioles through alveoli

The upper respiratory tract primarily conditions and filters air, while the lower tract conducts air to the gas exchange regions. Together, they ensure clean, warm, moist air reaches the delicate alveoli where oxygen enters the bloodstream.

How Your Body Trades Gases

Respiration and Gas Exchange Outline

External Respiration

Alveolar Structure

300-600 million alveoli provide enormous surface area (80 m²)
Alveolar walls made of thin type I pneumocytes
Surfactant produced by type II cells prevents collapse
Type III cells (macrophages) remove debris

Gas Exchange Process

Oxygen diffuses from alveoli into capillary blood
Carbon dioxide diffuses from blood into alveoli
Exchange occurs across alveolar-capillary membrane (0.004 mm thick)
Driven by concentration gradients of gases

Diagram of alveoli showing gas exchange of oxygen and carbon dioxide in blood. — Ali DM / Shutterstock

Internal Respiration

Oxygen Transport

Hemoglobin in red blood cells carries oxygen
Each red blood cell contains about 280 million hemoglobin molecules
Oxygenated blood appears bright red

Carbon Dioxide Transport

CO₂ transported in three forms: dissolved, as bicarbonate, or bound to hemoglobin
Blood pH affected by CO₂ levels
Deoxygenated blood appears darker red

Pulmonary Function Testing

Lung Volumes

Tidal volume: amount of air in normal breath (500 mL)
Vital capacity: maximum amount of air that can be moved in and out
Residual volume: air remaining in lungs after maximum exhalation

Clinical Significance

FEV₁: forced expiratory volume in one second
Reduced in obstructive diseases like asthma and COPD
PEFR (peak expiratory flow rate) measures airway function

Understanding gas exchange helps explain why diseases affecting the alveoli or blood cells can severely impact oxygen delivery to tissues and carbon dioxide removal from the body.

How Your Body Powers Respiration

Breathing Mechanics Outline

Protective Structures

Thoracic Cage

Ribs (12 pairs) protect lungs and heart
True ribs (1-7) connect directly to sternum
False ribs (8-10) connect to cartilage of ribs above
Floating ribs (11-12) attach only to spine

Pleural Membranes

Visceral pleura covers lung surface
Parietal pleura lines thoracic cavity
Pleural fluid reduces friction during breathing
Pleural space maintains negative pressure

Ventilation Process

Inspiration (Active Process)

Diaphragm contracts and flattens
External intercostal muscles lift ribs up and out
Thoracic volume increases, pressure decreases
Air flows into lungs due to pressure gradient

Expiration (Passive Process)

Diaphragm relaxes, returns to dome shape
Elastic recoil of lungs pushes air out
Thoracic volume decreases, pressure increases
During exercise, abdominal muscles assist expiration

Control of Breathing

Nervous System Control

Medulla oblongata contains respiratory center
Phrenic nerve stimulates diaphragm
Breathing rate adjusted based on CO₂ levels
Accessory muscles recruited during exercise or disease

The thoracic structures provide protection while allowing the flexibility needed for breathing. The diaphragm is the primary muscle of respiration, creating the pressure changes that drive air movement into and out of the lungs.

Diagram showing breathing mechanics: diaphragm contracts for inhalation, relaxes for exhalation.

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