respiratory

Human Anatomy and Physiology, Chapter 21: The Respiratory System

21.1 Respiratory System: An Overview

  • Major Components:
    • Left lung
    • Right lung
    • Thoracic cage (cut)
    • Thoracic cavity
    • Diaphragm
    • Nose
    • Nasal cavity
    • Pharynx
    • Upper respiratory tract
    • Larynx
    • Trachea
    • Bronchi
    • Bronchiole
    • Alveoli
    • Lower respiratory tract

21.1 Basic Functions of the Respiratory System

  • Primary Function - Respiration:
    • Definition: The process that provides the body’s cells with oxygen and removes the waste product carbon dioxide.
    • Four Separate Processes:
    • Pulmonary Ventilation (Ventilation): Movement of air in and out of the lungs.
    • Pulmonary Gas Exchange: Movement of gases between the lungs and blood.
    • Gas Transport in the Blood: Movement of gases through the blood.
    • Tissue Gas Exchange: Movement of gases between the blood and tissues.
  • Other Functions of the Respiratory System:
    • Producing Speech: Facilitating vocalizations through the larynx (voice box).
    • Detecting Odors: The nasal cavity housing olfactory receptors.
    • Expelling Contents: Assisting in activities like urination, defecation, and childbirth through increased thoracic pressure.
    • Venous Blood and Lymph Flow: Aiding in the return of blood and lymph through pressure changes during respiration.
    • Maintaining Acid-Base Homeostasis: Regulating body pH through CO₂ exchange.
    • Angiotensin Production: Assisting in the production of angiotensin II, which regulates blood pressure and fluid balance.

21.2 The Nose and Nasal Cavity

  • Internal Nasal Anatomy:
    • The nasal cavity is divided into left and right portions by the Nasal Septum.
    • Nasal Conchae: Three sets of bony projections:
    • Superior and Middle Nasal Conchae: Part of the Ethmoid Bone.
    • Inferior Nasal Conchae: Independent bones.
    • Nasal Meatuses: Turbulent airflow through the Superior, Middle, and Inferior nasal meatuses helps trap debris in the mucus lining.
    • Paranasal Sinuses: Hollow cavities connected to the nasal cavity that warm, humidify, filter air, lighten skull weight, and enhance voice resonance. Named as:
    • Frontal Sinus
    • Ethmoid Sinus
    • Sphenoid Sinus
    • Maxillary Sinus

21.2 Histology

  • Olfactory Mucosa: Located on the roof of the nasal cavity housing olfactory receptors, connecting through the olfactory foramina of the cribriform plate.
  • Respiratory Mucosa: Lined with pseudostratified ciliated columnar epithelium with goblet cells for mucus secretion; foreign particles are either expelled or swallowed after passing to the pharynx.

21.2 The Pharynx

  • Three Divisions of the Pharynx:
    • Nasopharynx: Posterior to the nasal cavity, lined with pseudostratified ciliated columnar epithelium.
    • Oropharynx: Posterior to the oral cavity; lined with nonkeratinized stratified squamous epithelium suitable for food and air passage; extends from the uvula to the epiglottis.
    • Laryngopharynx: Extends from the hyoid bone to the esophagus; also lined with nonkeratinized stratified squamous epithelium.

21.2 The Larynx

  • Larynx Functions:
    • Prevents food/liquids from entering the lower respiratory tract, houses vocal cords for sound production.
    • Epithelium: Lined with pseudostratified ciliated columnar epithelium to clear mucus.
  • Cartilage Framework:
    • Made of Nine Pieces of Cartilage (3 unpaired and 6 paired):
    • Unpaired: Thyroid cartilages ("Adam’s Apple"), cricoid cartilage, and cricothyroid.
    • Paired: Arytenoid, corniculate, and cuneiform.

21.2 Mucosal Folds and Sound Production

  • Vestibular Folds (False Vocal Cords): Superior mucosal folds that close the glottis during swallowing.
  • Vocal Folds (True Vocal Cords): Inferior mucosal folds involved in voice production.

21.2 The Trachea

  • Trachea Description:
    • Delivers air to lower respiratory structures; dimensions: about 2 cm in diameter and 10-12 cm long.
    • Covered by C-shaped Rings of Hyaline Cartilage:
    • Keeps the trachea open (patent) but allows flexibility during ventilation.
    • Carina: The point where the trachea bifurcates into right and left primary bronchi, with a cough reflex elicited here.
    • Mucosa Layer: Inner layer with pseudostratified ciliated columnar epithelium containing goblet cells.

21.2 Smoker’s Cough

  • Condition: Deep, rattling sound caused by cigarette smoke irritation; increases mucus secretion and damages cilia, leading to coughing. Cilia can regenerate after cessation of smoking.

21.2 The Bronchial Tree

  • Structure of Bronchi:
    • Right and Left Primary Bronchi arise from trachea; the right is shorter and wider, while the left is longer and more horizontal.
    • Secondary (Lobar) Bronchi: Five total (three on the right, two on the left).
    • Tertiary (Segmental) Bronchi: Approximately 10 in each lung from secondary bronchi, with continuations for roughly 26 branches.

21.2 Changes in Bronchi Structure:

  • Cartilage: Transition from C-shaped to irregular plates; epithelium decreases in height from respiratory to shorter columnar cells; increased smooth muscle content.

21.2 Bronchioles

  • Smallest Airways: Bronchioles are less than 1 mm in diameter, lacking cartilage but possessing smooth muscle.
  • Branching: They lead to approximately 65,000 terminal bronchioles, then divide into respiratory bronchioles where alveoli budding occurs.

21.2 Alveoli and the Respiratory Membrane

  • Alveoli Structure: Surrounded by elastic fibers and capillaries, consisting of three cell types:
    • Type I Alveolar Cells: Squamous cells (90% of the wall) enabling gas diffusion.
    • Type II Alveolar Cells: Cuboidal cells (10% of the wall) containing surfactant precursors.
    • Alveolar Macrophages: Phagocytes cleaning debris and moving toward bronchioles for expulsion.

21.2 Tuberculosis (TB)

  • Definition: Respiratory infection caused by Mycobacterium tuberculosis; spread mainly through coughs and sneezes.
  • Incidence: 90% latent (asymptomatic), 10% active (symptomatic). Symptoms include a persistent cough, fever, and weight loss.
  • Untreated Infections: About a 50% mortality rate for active infections.

21.2 The Lungs and Pleurae

  • Lung Anatomy:
    • Base on the diaphragm; apex above the clavicle.
    • Hilum: Entry point for primary bronchi and blood vessels.
    • Lobes: Left lung has two lobes (superior and inferior), while the right lung has three lobes (superior, middle, inferior).
    • Bronchopulmonary Segments: Each lobe contains segments, with lobules about the size of a dime.
  • Pleural Cavity: Double-layered serous membrane surrounding lung, containing pleural fluid for lubrication.

21.2 Pneumothorax

  • Definition: Collapse of the lung due to disruption of pleura, allowing air or fluid into the pleural cavity, necessitating opening the chest cavity to refill the lung with air.

21.3 The Pressure-Volume Relationship

  • Pulmonary Ventilation: Mechanism for breathing or air movement in and out of the lungs.
  • Pressure Gradients: Gas molecules travel from high-pressure to low-pressure areas.
  • Boyle’s Law: At a constant temperature and gas quantity, the volume and pressure of a gas are inversely related, meaning that as volume increases, pressure decreases and vice versa.

21.3 Muscles of Breathing

  • Muscles of Inspiration:
    • Diaphragm (Primary muscle)
    • External intercostals
    • Accessory muscles: Sternocleidomastoid and scalene muscles.
  • Muscles of Expiration:
    • Diaphragm (relaxation is primary)
    • Internal intercostals
    • Abdominal muscles: Rectus abdominus, external oblique, internal oblique, transversus abdominus.

21.3 Interactive Physiology

  • Link to resource: Interactive Physiology 2.0 on Breathing Cycles and Muscles.

21.3 Physical Factors Influencing Pulmonary Ventilation

  • Three Factors:
    • Airway Resistance: Anything impeding airflow.
    • Alveolar Surface Tension: Affects the gas-water interface, which can hinder alveolar expansion.
    • Pulmonary Compliance: The elasticity of the lungs and chest wall.
  • Airway Resistance Mechanisms:
    • Bronchodilation: Increased airflow during exercise via norepinephrine release.
    • Bronchoconstriction: Reduced airflow increasing resistance.

21.3 Effects of Surfactant

  • Function of Surfactant: Produced by Type II alveolar cells to reduce surface tensions, keeping alveoli open even during expiration. Without surfactant, collapsed alveoli (atelectasis) can occur.

21.3 Infant Respiratory Distress Syndrome (RDS)

  • Issue: Many premature infants lack sufficient surfactant, risking airway collapse. Factors leading to RDS may include prematurity and maternal diabetes.
  • Treatment: Involves inhalation of natural or synthetic surfactants.

21.3 Pulmonary Volumes and Capacities

  • Spirometry: Measures air volumes exchanged during breathing. Pulmonary volumes are measured directly. Capacities are combinations of volumes.
  • Pulmonary Volumes Defined:
    • Tidal Volume (TV): 500 ml inspired or expired per breath.
    • Minute Volume: TV multiplied by breaths per minute (average 12 breaths/min = about 6 liters/min).
    • Dead Space: Air remaining in conducting airways (about 350 ml out of tidal inspiration).
    • Alveolar Ventilation Rate (AVR): Volume reaching alveoli multiplied by breaths/min (about 4.2 liters/min).

21.3 Expiratory and Inspiratory Reserve Volumes

  • Inspiratory Reserve Volume (IRV): Additional air inspired forcefully after a tidal inspiration (2100-3300 ml).
  • Expiratory Reserve Volume (ERV): Volume expelled forcefully after normal expiration (700-1200 ml).
  • Residual Volume (RV): Air in lungs due to intra-pleural pressure preventing full collapse.

21.3 Pulmonary Capacities Defined:

  • Inspiratory Capacity: Total air volume that can be inspired after tidal expiration.
  • Functional Residual Capacity: Amount of air remaining after normal expiration.
  • Vital Capacity: Total volume of air exchanged during breathing.
  • Total Lung Capacity: Total volume of exchangeable and non-exchangeable air.

21.5 Oxygen & Carbon Dioxide Transport

  • Oxygen Transport:
    • Bound to Hemoglobin (Hb): 98%
    • Dissolved in Plasma: 2%
  • Carbon Dioxide Transport:
    • Dissolved in Plasma: 7-10%
    • Bound to Hemoglobin: About 20% forms carbaminohemoglobin.
    • As Bicarbonate Ions: About 70% is converted to bicarbonate ions in the blood.

21.5 Mechanism of Bicarbonate Ion Formation

  • Process in Erythrocytes: CO₂ diffuses in, reacts with water via Carbonic Anhydrase to form carbonic acid which dissociates into bicarbonate ions ( ext{HCO}_3^-) and hydrogen ions (H+).
  • Buffering Effect: Hb binds to H+ ions, helping maintain pH balance.

21.7 Neural Control of Ventilation

  • Dyspnea: A sensation of shortness of breath.
  • Neural Control: Governed by neurons in the brainstem responding to CO₂, pH, and O₂ levels.

21.7 Groups in Ventilation Control:

  • Ventral Respiratory Group (VRG): Anterior/lateral medulla, stimulating diaphragm and intercostals for inspiration.
  • Dorsal Respiratory Group (DRG): Posterior medulla, integrating sensory data and supporting rhythmic breathing.