Respiratory System

Respiratory System

Lecture Information

• Lecture 12
• Date: 06/11/25
• Instructor: Dr. Shaak

Overview of Topics

• Finishing up Blood lecture
• Cardiovascular system & heart
• Heart anatomy:
  • Pericardium, heart wall, chambers, & valves.
• Blood flow through heart
• Heart blood supply
• A few more heart-related things
• Blood vessels
  • Arterial system, capillaries, & venous system.
• Pulmonary circulation
• Systemic circulation
  • Arteries
  • Veins

Important Dates and Reminders

• Last day to withdraw from the course with a "W" grade is 6/12.
  • Consider this if averaging below a 70%.
• Exam 2 & practical 2 are on 6/16.
  • Study guide was posted on 6/8.

Respiratory System Overview

• Upper respiratory tract
• Lower respiratory tract
• Lungs
• Pulmonary ventilation
• Mechanics of breathing

Major Functions of the Respiratory System

• Supply body with O2 and dispose of CO2.
• Respiration – collective definition:
  1. Pulmonary ventilation (breathing): moving air in and out of lungs to replace gases in alveoli.
  2. External respiration: gas exchange between blood & air at alveoli (between atmosphere & blood).
  3. Respiratory gas transport: blood transporting gases between lungs & cells.
  4. Internal respiration: gas exchange at systemic capillaries.
  5. Cellular respiration: O2 used by cell to convert glucose to ATP…and CO2 is a waste product.

Additional Functions

• Gas conditioning: Inhaled gases are warmed, humidified, & cleansed.
• Sound production: As air moves out of lungs & through the larynx, speech/singing can be produced.
• Olfaction: Stimulation of smell receptors by airborne molecules.
• Defense: Coarse hairs at entrances; twisted passageways; goblet cells & mucous glands.

Organs of the Respiratory System

1. Nose
2. Nasal Cavities
3. Paranasal sinuses
4. Pharynx
5. Larynx
6. Trachea
7. Bronchi
8. Lungs
9. Alveoli

Functional Divisions

• Conducting zone (1-7):
  • Respiratory pathways that carry air to sites of gas exchange.
• Respiratory zone (8-9):
  • Site of gas exchange.

Upper Respiratory Tract

• Composed of:
  • Nose
  • Nasal cavity
  • Paranasal sinuses
  • Pharynx
  • & associated structures

Nose

• Main conducting airway for inhaled air.
• Nasal bones
• Septal cartilage
• Lateral cartilage
• Greater (major) alar cartilage
• Lesser (minor) alar cartilage

Nasal Cavity Boundaries

• Roof: ethmoid & sphenoid.
• Floor: hard & soft palates.
• Air enters external nares (nostrils).
• Cavity is divided by the nasal septum formed from ethmoid bone, vomer & septal cartilage.
• Internal nares (posterior nasal apertures or choanae).
• Continuous with the nasal part of the pharynx (nasopharynx).
• Superior to nares is the vestibule (“entranceway”): flared wings.
  • Nose hairs (vibrissae) act as filters.

Nasal Conchae

• Superior, middle, & inferior.
• Subdivide nasal cavity into air passages (each 1 a nasal meatus).
• Helps increase turbulence which helps with warming & humidifying air.

Mucosal Linings

• Olfactory mucosa near the roof of the cavity; houses receptors.
• Respiratory mucosa traps fine particles; ciliated cells move debris to pharynx where swallowed.

Paranasal Sinuses

• Functions:
  • Humidify & warm inhaled air
  • Decrease skull weight
  • Voice resonance
• Air-filled chambers
• Open into the nasal cavity

Pharynx

• Passageway that connects the mouth & nasal cavity (superior) to the larynx & esophagus (inferior).
• Nasopharynx: Serves only as an air passageway.
  • Uvula “little grape” closes off nasopharynx preventing food from entering the nasal cavity.
  • Lined w/ pseudostratified columnar epithelium.
• Oropharynx: Food & air passageway.
  • Posterior to mouth (oral cavity).
  • Lined with stratified squamous epithelium.
• Laryngopharynx: Continuous with the esophagus & larynx to conduct food & air.

Lower Respiratory Tract

• Composed of:
  • Larynx
  • Trachea
  • Bronchi
  • Bronchioles
  • Alveolar ducts
  • Alveoli
  • & associated structures

Larynx

• The voice box.
• Roughly cylindrical & ~4 cm in length.
• Lies between laryngopharynx & trachea.
• Functions:
  • Air passageway.
  • Blocks ingested materials.
  • Produces sound for speech.
  • Helps increase abdominal cavity pressure.
  • Involved in sneeze & cough reflex.

Larynx Framework

• 9 Cartilages & ligaments…
  • Thyroid cartilage – large shield-like cartilage
  • Laryngeal prominence is the anterior projection of the thyroid cartilage.
  • Cricoid cartilage, “Circle” – forms a complete ring.
  • Arytenoid cartilages, "Ladle-like” – paired
    • Anchor vocal ligaments (cords).
  • Corniculate cartilages “Little horn” – paired
  • Cuneiform cartilages “Wedge shaped” – paired
  • Epiglottis “Upon the tongue” – guardian of the airway.
    • Attaches to the posterior aspect of the tongue & internally to the thyroid cartilage.
    • During swallowing, the larynx is pulled superiorly & epiglottis inferiorly to seal the larynx opening.

Glottis

• Vocal ligaments:
  • Anteriorly from arytenoid to thyroid cartilages.
  • Elastic fibers covered by mucous membrane to form vocal folds/true vocal cords.
  • Produces sound.
  • During puberty – male’s larynx will enlarge making vocal cords longer; vibrate slower to cause a deeper sound.
  • Rima glottidis: Medial folds forming opening.
• Vestibular folds or False vocal cords – produce no sound; protect vocal folds.

Trachea

• Location: Descends from the larynx, through the neck into mediastinum & divides mid-thorax into primary bronchi (main bronchi).
• 12-14 cm length; ~2.5 cm diameter.
• Structure:
  • 15-20 C-shaped tracheal cartilages (cartilage “rings”)
  • Annular ligaments: connective tissue sheets connecting cartilage rings.
  • Trachealis muscle: binds together open ends of cartilage rings along with a ligamentous membrane.
  • Main bronchi – separated by most inferior tracheal cartilage.

Bronchial Tree

• Branched system of air passageways that originate from left & right main bronchi; get progressively narrower as they branch/diverge throughout lungs.
• Bronchi in Conducting Zone:
  • Primary branch – Primary bronchi
  • Secondary branch – Lobar bronchi
  • Tertiary branch – Segmental bronchi
  • Bronchioles “Little bronchi” – 1mm diameter
  • Terminal bronchioles
• Composition mimics trachea.

Changes in Bronchial Tree

• As branches get smaller, changes occur:
  1. Cartilage rings are replaced with irregular plates of cartilage, & then lack cartilage (i.e., in bronchioles).
  2. Cartilage is replaced with elastin.
  3. Epithelium changes from pseudostratified columnar to simple columnar or simple cuboidal epithelium.
  4. Thicker layer of smooth muscle appears; wraps around branches to regulate the amount of air entering alveoli.

Respiratory Zone

• Respiratory zone: end of respiratory tree.
• Structures:
  • Respiratory bronchioles – branch from terminal bronchioles.
  • Alveolar ducts – lead from respiratory bronchioles to alveolar sacs.
  • Alveolar sacs – terminal clusters of alveoli.
    • Epithelium much thinner than in conducting portion.
    • Simple squamous epithelium.

Alveoli Features

• Significant features of alveoli:
  • Fine elastic fibers surrounding structures.
  • Adjacent alveoli interconnected by alveolar pores.
    • Allows for equalization of air pressure throughout lungs.
    • Provides alternate routes for air around collapsed alveoli.

Alveoli Features Continued

• Further features…
  • Alveolar surfaces provide free movement of alveolar macrophages to remove inhaled particles not trapped by mucus.
  • Alveolar wall
    • Type I cell: simple squamous epithelial cell.
    • Type II cells: scattered among type I cells; cuboidal epithelial cells that secrete a fluid – pulmonary surfactant, which helps keep alveoli from collapsing.

Air-Blood Barrier

• Thin wall between alveolar lumen & blood.
• O2 & CO2 diffuse across.
• Alveolus layers forming air-blood barrier:
  • Plasma membranes of alveolar type I cell.
  • Endothelial cell of capillary.
  • Fused basement membranes.

Lungs

• Primary organs of respiration.
• House bronchial tree & respiratory portion of the respiratory system.
• Right & left lungs are separated via the mediastinum.

Pleura

• Serous membrane sac around lungs.
• Layers:
  • Parietal pleura: Outer layer covering the internal surface of the thoracic wall & superior surface of the diaphragm; continuous w/…
  • Visceral pleura: Covers the external lung surface.
  • Pleural cavity: Filled with pleural fluid to reduce friction.

Lung Structure

• Paired & spongy; roughly conical.
• Extends from base inferiorly to apex superiorly.
• Bordered by the thoracic wall anteriorly, posteriorly, & laterally.
• Supported & protected by the rib cage.

Lung Surfaces

• Costal surface: rounded, broad surface in contact with the thoracic wall.
• Mediastinal surface: medially facing surface of lungs.
  • Hilum: indented area where bronchi, pulmonary vessels, nerves, and so on pass (Contents of hilum = lung root).
  • Cardiac impression: medial indentation of the left lung.
• Cardiac notch on the anterior surface of the left lung.

Lung Lobes and Fissures

• Right lung: (3 lobes & 2 fissures)
  • Superior, inferior, & middle lobes.
  • Horizontal & oblique fissures.
• Left lung: (2 lobes & 1 fissure)
  • Only superior & inferior lobes.
  • Lingula: on superior lobe; homologous to middle lobe.
  • Only has an oblique fissure.
• Bronchopulmonary segments:
  • 10 in the right lung & 8-10 in the left lung (same as with segmental bronchi).

Breathing / Pulmonary Ventilation

• Pulmonary ventilation (breathing): movement of air into & out of the respiratory system.
• Quiet breathing: rhythmic; occurs at rest.
• Forced breathing: vigorous; occurs during/after exercise or hard exertion.
• Boyle’s law: “Pressure of a gas decreases if the volume of the container increases, & vice versa.”
  • Air flows from a region of higher pressure into a region of lower pressure.

Integrated Aspects of Breathing

1. Actions of skeletal muscles of breathing.
2. Dimensional (volume) changes within the thoracic cavity.
3. Pressure changes resulting from volume changes (Boyle’s law).
4. Pressure gradients.
5. Volumes & pressures associated with breathing.

Next Lecture: Digestive System