Respiratory System: Anatomy & Physiology Study Guide

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Respiratory System Anatomy

Respiratory Mucosa

The respiratory mucosa is a specialized lining found throughout much of the respiratory tract. It consists of an epithelial layer and an underlying connective tissue (lamina propria).

Function: Warms, moistens, and filters incoming air.
Structure: Typically pseudostratified ciliated columnar epithelium with goblet cells that secrete mucus.
Example: The nasal cavity is lined with respiratory mucosa to trap dust and pathogens.

Mucus Escalator

The mucus escalator refers to the coordinated movement of cilia in the respiratory tract that propels mucus (and trapped particles) upward toward the pharynx for swallowing or expectoration.

Importance: Protects the lungs from infection and debris.

Nasal Cavity: Warming and Moistening Air

The nose warms and moistens inspired air through its rich vascular supply and mucous secretions.

Mechanism: Blood vessels in the nasal mucosa transfer heat; mucus and serous secretions humidify air.
Example: Turbinates (conchae) increase surface area for air contact.

Pharynx Regions and Epithelium

The pharynx is divided into three regions, each with distinct epithelial linings:

Nasopharynx: Pseudostratified ciliated columnar epithelium.
Oropharynx: Stratified squamous epithelium.
Laryngopharynx: Stratified squamous epithelium.

Larynx Structure

The larynx is a cartilaginous structure that houses the vocal cords and connects the pharynx to the trachea.

Main Cartilages: Thyroid, cricoid, arytenoid, epiglottis.
Function: Air passage, voice production, and protection of the lower airway.

Tracheal Wall

The tracheal wall consists of several layers:

Mucosa: Pseudostratified ciliated columnar epithelium.
Submucosa: Contains seromucous glands.
Cartilage: C-shaped hyaline cartilage rings.
Adventitia: Outermost connective tissue.

Bronchial Tree and Air Flow

Air passes through the following structures:

Nasal cavity
Pharynx
Larynx
Trachea
Primary bronchi
Secondary (lobar) bronchi
Tertiary (segmental) bronchi
Bronchioles
Terminal bronchioles
Respiratory bronchioles
Alveolar ducts
Alveolar sacs
Alveoli

Right vs. Left Lung Anatomy

Right Lung: Three lobes (superior, middle, inferior); shorter and wider.
Left Lung: Two lobes (superior, inferior); has cardiac notch for heart.

Layers for Gas Diffusion (External Respiration)

During external respiration, an air molecule must diffuse through:

Alveolar epithelium
Fused basement membrane
Capillary endothelium

Serous Membrane of the Lungs

The pleura is the serous membrane surrounding the lungs:

Visceral pleura: Covers lung surface.
Parietal pleura: Lines thoracic cavity.
Pleural cavity: Contains lubricating fluid.

Respiratory System Physiology

Functions of the Respiratory System

Gas exchange (O2 in, CO2 out)
Regulation of blood pH
Voice production
Olfaction (smell)
Protection (filtering, warming, humidifying air)

Key Definitions

Pulmonary ventilation: Movement of air into and out of the lungs.
External respiration: Gas exchange between alveoli and blood.
Internal respiration: Gas exchange between blood and tissues.

Pressures in Respiration

Atmospheric pressure (Patm): Pressure exerted by air outside the body.
Pulmonic (intrapulmonary) pressure (Ppul): Pressure within alveoli.
Intrapleural pressure (Pip): Pressure within pleural cavity; always less than Ppul.

Boyle’s Law and Pulmonary Ventilation

Boyle’s Law: The pressure of a gas is inversely proportional to its volume at constant temperature.

Equation:

During inspiration, lung volume increases, pressure decreases, air flows in.
During expiration, lung volume decreases, pressure increases, air flows out.

Movement of Gases During Ventilation

Oxygen: Moves from alveoli (high pressure) to blood (low pressure).
Carbon dioxide: Moves from blood (high pressure) to alveoli (low pressure).

Muscles of Breathing

Inspiration: Diaphragm contracts, external intercostals elevate ribs.
Expiration: Normally passive; forced expiration uses internal intercostals and abdominal muscles.

Normal vs. Forced Exhalation

Normal (quiet) exhalation: Passive, due to elastic recoil.
Forced exhalation: Active, uses additional muscles.

Respiratory Volumes

Volume	Definition
Tidal Volume (TV)	Amount of air inhaled or exhaled in one breath (normal breathing)
Inspiratory Reserve Volume (IRV)	Additional air that can be inhaled after a normal inspiration
Expiratory Reserve Volume (ERV)	Additional air that can be exhaled after a normal expiration
Vital Capacity (VC)	Total amount of air that can be exhaled after maximum inhalation (TV + IRV + ERV)

Dalton’s Law and Partial Pressure

Dalton’s Law: The total pressure of a mixture of gases is the sum of the partial pressures of each individual gas.

Equation:

Partial pressure: Pressure exerted by a single gas in a mixture.

Gas Concentrations in Air

Gas	Approximate % in Air
Oxygen (O2)	~21%
Carbon Dioxide (CO2)	~0.04%
Nitrogen (N2)	~78%

Henry’s Law and Gas Solubility

Henry’s Law: The amount of gas that dissolves in a liquid is proportional to its partial pressure and solubility.

Equation:

Application: Explains why soda foams when opened (CO2 escapes as pressure drops).

External and Internal Respiration

External respiration: O2 diffuses from alveoli to blood; CO2 diffuses from blood to alveoli.
Internal respiration: O2 diffuses from blood to tissues; CO2 diffuses from tissues to blood.

Oxygen Transport in Blood

Most O2: Bound to hemoglobin (Hb) in red blood cells.
Small amount: Dissolved in plasma.

Hemoglobin Saturation and pH Effects

Hb saturation: Percentage of hemoglobin molecules bound to O2.
At 60 mm Hg: Lower saturation than at 100 mm Hg.
Decrease in pH: Reduces Hb affinity for O2 (Bohr effect).
Fetal vs. Adult Hb: Fetal Hb has higher affinity for O2 than adult Hb.

Carbon Dioxide Transport in Blood

Dissolved in plasma (~7%)
Bound to Hb (carbaminohemoglobin) (~23%)
As bicarbonate ions (HCO3-) (~70%)

Bicarbonate Formation in Blood

CO2 reacts with water to form carbonic acid, which dissociates into bicarbonate and hydrogen ions.

Equation:

Tracing Gas Movement by Pressure Gradients

Oxygen: Air (high PO2) → alveoli → blood → tissues (low PO2).
Carbon dioxide: Tissues (high PCO2) → blood → alveoli → air (low PCO2).

Neural Control of Respiration

Medullary respiratory centers: Control basic rhythm.
Pontine centers: Modify rhythm for speech, exercise.
Chemoreceptors: Respond to changes in CO2, O2, and pH.

Additional info: Figures 23-20 and 23-21 referenced in the questions likely show oxygen-hemoglobin dissociation curves and effects of pH on Hb saturation. The Bohr effect describes how decreased pH (increased acidity) reduces hemoglobin's affinity for oxygen, facilitating oxygen release in tissues.