Chapter 24: The Respiratory System

Overview of the Respiratory System

• The respiratory system comprises:

  • Nose

  • Nasal cavity and sinuses

  • Pharynx

  • Larynx

  • Trachea

  • Conducting passageways leading to lungs

• It is important to understand and know that the respiratory system is divided into the Upper & Lower Respiratory Tracts

Structure of the Respiratory Tract

• Upper Respiratory System:

  • Paranasal sinuses

  • Nasal conchae

  • Nose

  • Nasal cavity

  • Nasopharynx

• Lower Respiratory System:

  • Larynx

  • Trachea

  • Lungs

  • Bronchi

  • Bronchioles

  • Alveoli

• Respiratory Tract Portions:

  • Conducting Portion: The portion of the Respiratory System involved air transportation— all of the respiratory organs from the Nasal cavity to bronchioles

  • Respiratory Portion: The portion of the Respiratory System involved in gas exchange— Bronchioles and Alveoli

Functions of the Respiratory System

1. Gas exchange between air and blood

   • Cells obtain O2 and eliminate CO2

2. Moves air to/from exchange surfaces

3. Protects respiratory surfaces

4. Defends against pathogens

5. Permits vocal communication

6. Regulates blood volume, pressure, and pH

Respiratory Epithelium

• Lines conducting portions down to terminal bronchioles

• Structure: Pseudostratified, ciliated, columnar epithelium with mucous cells

  • Produces mucus to trap particles

  • Lamina propria (connective tissue layer) beneath epithelium forms a mucosa

  • Stratified squamous surrounds the pharynx

• Defense Mechanism:

  • Mucous glands

  • Alveolar macrophages

  • Hairs and cilia

Upper Respiratory System

Nose and Nasal Cavity

• Air enters via nostrils (nares)

• Nasal vestibule is guarded by hairs (screen large particles)

• Air flows through meatuses and conchal surfaces

• Hard and soft palate divide oral and nasal cavities

Pharynx

• Common chamber for digestive and respiratory systems— serves as a passageway connecting the nose to the mouth and throat

• Parts:

  • Nasopharynx— The back of the nose that extends down to the soft palate, allowing airflow from the nasal cavities to the throat.

  • Oropharynx— The back of the mouth that lies behind the oral cavity, it serves as a passageway for both air and food, facilitating respiration and digestion.

  • Laryngopharynx— The most inferior portion of the pharynx, it connects with the Layrnx (respiratory) & the Esophagus (digestive)

Lower Respiratory System

Larynx

• Protects glottis; involved in sound production

  • Epiglottis— A flap of cartilage located at the root of the tongue, it acts as a valve to cover the larynx during swallowing, preventing food or fluid from entering the airway.

• Contains vocal folds and vestibular folds

• Regulated by intrinsic and extrinsic laryngeal muscles

  • Laryngeal Muscles—

  • Laryngeal Ligaments—

Trachea

• Extends from cervical to thoracic vertebrae

• Contains C-shaped tracheal cartilages for support

• Allows for flexibility during swallowing

• Trachea Glands— produce mucus to trap foreign particles and keep the airway moist., located in the submucosa of the trachea,.

• The trachea branches at the Carina, forming the L & R Primary Bronchi—

  • The diameter of the R primary bronchi is larger than the L

  • The R Bronchi is shorter than the L

  • The R Bronchi decesnds toward the lung at a steeper angle than the L

    • If food is asperated down the trachea it will likely end up in the R lung

Lobes and Fissures of the Lungs

• Right Lung: 3 lobes (superior, middle, inferior) & 2 fissures (horizontal, oblique)

• Left Lung: 2 lobes (superior, inferior) & 1 fissure (oblique)

  • The R Lung is slightly larger than the L lung

  • Lobes separated by fissures

Main Bronchi and Lungs

• Trachea branches into left and right primary bronchi

• Each bronchus enters lung at the hilum (root includes bronchus, vessels, nerves)

  • The bronchi further divide into secondary & tertiary bronchi, which decrease in diameter and increase in the number of branches

  • Bronchopulmonary Segments— are the smallest functionally independent regions of the lungs. Consists of tertiary bronchi, bronchioles, & alveolar structures.

  • Each lung is divided into segments (10 right, 8-9 left)

• Bronchioles— Smaller branches of the bronchi that lead to the alveoli, where gas exchange occurs. They are mainly composed of smooth muscle and elastic fibers, allowing for the regulation of airflow and resistance.

  • The autonomic nervous system contorols—

    • Bronchodilation— (sympathetic) Increased airflow

    • Bronchoconstriction—(parasympathetic) Decreased airflow

Alveolar Structures

• Alveolar Ducts: Smallest airways leading to clusters of alveoli.

• Alveolar Sacs: Groups of alveoli connected to a common duct.

• Alveoli: Tiny air sacs with thin walls— simple squamous epithelium where oxygen enters the blood and CO₂ is expelled (gas exchange occurs).

  • Oxygen Diffusion into Blood—

    • Oxygen moves from the alveoli (high O₂ concentration) → through the respiratory membrane → into the capillary blood (low O₂ concentration).

    • Oxygen binds to Hb in RBCs, which is then transported to tissues.

  • Carbon Dioxide Exchange

    • Carbon dioxide (CO₂) from the tissues is carried in the blood (dissolved in plasma, bound to hemoglobin, or as bicarbonate).

    • In the capillaries, CO₂ diffuses from blood (high CO₂ concentration) → into the alveoli (low CO₂ concentration) → exhaled out through the airway.

• Blood-air barrier:

  • Type 1 Cells— Simple squamous epithelium that facilitates gas exchange due to their thin structure, allowing oxygen and carbon dioxide to diffuse easily between the alveoli and blood.

    • Has to be a thin membrane in order to facilitate quick gas exchange

  • Type II Cells— Cuboidal epithelial cells that secrete pulmonary Surfactant, which reduces surface tension in the alveoli and prevents their collapse during exhalation.

• Alveolar macrophages protect the epithelium

Pleural Cavities and Membranes

• Each lung in a separate pleural cavity lined by pleura (serous membrane)

• Two types:

  • Parietal pleura— Inner membrane (thoracic wall)

  • Visceral pleura— Outer membrane (lungs)

Respiratory Muscles and Pulmonary Ventilation

• Major Muscles:

  • Diaphragm— Inhalation & exhalation

  • External intercostals— Elevate the ribs to assist in inhalation

• Diaphragm contraction increases thoracic cavity volume

• Accessory muscles assist during heavy breathing (e.g., scalene, pectoralis minor)

Respiratory Changes at Birth

• Fetal lungs are fluid-filled; inflate upon first breath

Brain Control of Respiration

• Controlled by the Pons & Medulla Oblongata

  • Respiratory rhythmicity center: Sets pace

  • Apneustic center: Sustains inspiration

  • Pneumotaxic center: Inhibits deep breaths

• Receptors/Reflexes involved:

  1. Mechanoreceptors (lung volume changes)

  2. Chemoreceptors (CO2, pH changes)

  3. Protective reflexes (injury/irritation)

Aging and the Respiratory System

• Efficiency declines with age due to:

  1. Deterioration of elastic tissue

  2. Chest cage movement restrictions

  3. Reduced lung volume and capacity

  4. Development of emphysema in older age