Respiratory System Vocabulary

Objectives

• Identify important anatomy of the conducting zone, including the trachea and bronchi.
• Identify the microanatomy of the respiratory zone, including the respiratory bronchioles and alveolar components.
• Describe the gross anatomy of the lungs, including lobes, fissures, and other key features.
• Differentiate respiratory tissues based on key cellular features.
• Understand how to measure and interpret lung volumes using spirometry.
• Compare feline respiratory anatomy with that of H. sapiens.

Introduction

• The lungs have received much attention during the pandemic as the principal sites of COVID-19 infection.
• Epithelial cells of pulmonary capillaries express the ACE2 protein receptor, which the COVID-19 virus uses to attach and infect respiratory cells.
• This leads to severe inflammation and eventual pulmonary failure in susceptible individuals.
• The lab activities include exploring human and cat respiratory systems, conducting a pulmonary function test, and investigating the histology of respiratory system tissues.
• Anatomically, the lungs are divided into two main areas:
  • Conducting zone
  • Respiratory zone

Conducting Zone

• The conducting zone is a system of tubes that allows air to move from the environment to the site of gas exchange.
• It includes:
  • Nasal cavity
  • Pharynx (naso-, oro- and laryngo-)
  • Trachea (aka, windpipe)
  • Bronchi
  • Bronchioles

Respiratory Zone

• In the deeper reaches of the lung, inhaled air (approximately 21% oxygen O2) is exchanged with carbon dioxide (CO2)-rich gases from the bloodstream in the respiratory zone.
• This portion includes:
  • Respiratory bronchioles
  • Alveolar ducts
  • Alveoli (the functional site of gas exchange)

Alveoli

• The alveoli of the average adult correspond to a total surface area of more than 1000 ft^2 (> 100 m^2), which is bigger than a standard racquetball court.

Nasal Cavity

• The nasal cavity has key features to ensure the air received by the lung is at the appropriate temperature and humidity.
• Air inhaled via the external nares is humidified by mucosal secretions within the nasal cavity.
• This is important during winters in northern climates where the cold temperature creates exceptionally dry air.
• The nasal cavity also features conchae (superior, middle, and inferior) which induce turbulence within the flow of inhaled air.
• This increases the amount of time that air spends in the nasal passage and enhances the contact that inhaled air makes with the moist, warm nasal walls.

Pharynx and Larynx

• Air enters the nasopharynx via the internal nares.
• Air then transfers along the conducting zone into the oropharynx, followed by the laryngopharynx.
• At this point, the inhaled breath enters the trachea, passing through the glottis.
• The glottis is part of the larynx, which provides a portal into the lungs.

Epiglottis

• Materials other than air (such as food or water) are prevented from entering the glottis by the epiglottis, a cartilaginous structure that closes when food is swallowed.

Larynx

• The larynx features several cartilaginous structures which serve to reinforce this critical wind passage.
• Key features include:
  • Thyroid cartilage (Adam’s apple): particularly noticeable in males
  • Cricoid cartilage: located immediately inferior to the thyroid cartilage
  • Cricothyroid ligament: the space between the thyroid and cricoid cartilages, the typical site for an emergency tracheotomy
  • Arytenoid cartilage: located on the posterior portion of the thyroid cartilage, superior to the cricoid cartilage
  • Corniculate cartilage: located on the posterior portion of the thyroid cartilage, articulating with the superior margin of the arytenoid cartilage
• Together, the arytenoid and corniculate cartilages control the opening and closing of the glottis, including vocalization.

Trachea

• Past the larynx, air moves into the trachea, which is uniformly reinforced with cartilaginous rings to prevent collapse during negative pressure.
• Tracheal tissue consists of ciliated pseudostratified columnar epithelium, which facilitates the movement of dust particles and bacteria away from the deeper reaches of the lungs.
• Goblet cells scattered throughout the tracheal epithelium produce a sticky mucus which further prevents the lungs from becoming compromised.

Bronchi

• The trachea branches into left and right primary (1°) bronchi.
• The trachea further branches into secondary (2°) bronchi, also known as lobar bronchi, each serving a particular lobe of the lung.
• The left lung has two lobes: superior and inferior.
• The right lung has three lobes, including a middle lobe.
• Both lungs feature an oblique fissure separating lobar segments.
• The right lung also features a horizontal fissure.
• The right lung does not reach as deep into the abdomen due to encroachment by the liver.
• The left lung features the cardiac notch, creating additional space for the heart.
• The secondary bronchi give rise to many branches referred to as the tertiary (3°) bronchi within each lobe.

Bronchioles

• The bronchi then narrow to form the bronchioles, which feature progressively less cartilage that is ultimately replaced with smooth muscle.
• The dividing line between the conducting and respiratory zones occurs when the terminal bronchiole transitions to become the respiratory bronchiole.

Alveolar Sacs and Alveoli

• Respiratory bronchioles branch to form alveolar sacs, with each sac-like structure containing 20 – 30 alveoli.
• The simple squamous epithelium of the alveolus is intimately associated with pulmonary capillaries, facilitating gas transfer across the respiratory membrane.

Spirometry

• Part of the lab exercise analyzes pulmonary function during normal breathing, forced breathing, and coughing.
• This activity acquaints you with spirometry techniques, including interpreting lung volume data.

Procedures

• Part A: Upper Respiratory System: Review pages 835 – 839 of the textbook regarding important structures and regions.
• Part B: Lower Respiratory System: Review pages 839 – 843 of the textbook regarding important structures and regions.
• Part C: Pulmonary Histology: Review pages 843 – 846 of the textbook regarding important features of lung histology. Review Figure 23.10 as a reference for lung histology.
• iWorx Experiment (Part E): Factors That Affect Breathing Patterns

iWorx Experiment Setup

• Connect the iWorx unit to the wall via power cord and to a computer via USB cable.
• Locate the LabScribe program, typically found under Local Disk (C:) -> Program Files -> iWorx -> LabScribe.
• Load the pre-loaded settings by clicking on Settings -> Load Group, and select the IPLMv6Complete.iwxgrp dataset.
• Then, click on Settings -> Human Spirometry -> [Breathing- OtherFactors].

Spirometer Setup

• Locate the spirometer; ensure tubing is firmly connected.
• Plug in the spirometer cable to Channel 4 input port.
• Enter the calibration voltage of the spirometer into the Spirometry computed function used on the Lung Volumes channel.
• Click on STPD Vol.Human (Air Flow) next to the Lung Volumes channel title, then select Setup Function.
• Enter the calibration voltage (listed on the label) into the equation that sets the calibration voltage equal to one liter of lung volume.
• Ensure that the reset time is set to “No Reset,” and the first 10 seconds are used to zero the baseline of the Lung Volumes channel.
• Enter room temperature, barometric pressure, and expired air temperature.
• Allow the spirometer unit to warm up for 10 minutes before starting data collection.

Coughing Experiment

• Position the flow head so that outlets are pointing up.
• Have the test subject become used to breathing through the spirometer.
• Remove the flow head from the subject’s mouth and hold it at mouth level.
• Type the subject’s name in the Mark box, click the record button, and wait 10 seconds for the Lung Volumes channel to zero.
• Place the flow head to the subject’s mouth and instruct them to begin breathing; press enter to mark the recording.
• Click the Autoscale buttons for both the Air Flow and Lung Volume channels.
• Record five breaths for this portion of the activity.
• Type