NU551 Seminar 7 Pulmonary System Structures and Functions

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Purdue University Globle 

NU551 Advanced Physiology and Pathophysiology Across the Lifespan

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Pulmonary System Overview

The pulmonary system is responsible for supplying oxygen to the body and removing carbon dioxide. This process supports cellular metabolism, maintains acid-base balance, and protects the body through specialized immune defenses within the lungs. Proper respiratory function depends on healthy airways, efficient gas exchange, normal ventilation, and adequate blood perfusion.

Healthcare professionals must understand pulmonary anatomy and physiology because alterations in these processes contribute to many common respiratory diseases, including asthma, chronic obstructive pulmonary disease (COPD), pneumonia, pulmonary edema, and respiratory failure.

Conducting Airways of the Respiratory System

The respiratory tract consists of conducting airways that transport air into the lungs and respiratory airways where gas exchange occurs.

Upper Airways

The upper airway filters, warms, and humidifies inhaled air before it reaches the lungs.

Key structures include:

• Nasopharynx

• Oropharynx

Larynx

The larynx serves as the connection between the upper and lower respiratory tract. Besides allowing airflow, it protects the airway during swallowing and houses the vocal cords.

Lower Conducting Airways

The lower conducting airways distribute air throughout the lungs.

These structures include:

• Trachea

• Main bronchi

• Terminal bronchioles

Gas Exchange Airways

Gas exchange occurs within the respiratory portion of the lungs.

The primary structures involved include:

• Respiratory bronchioles

• Alveolar ducts

• Alveoli

These microscopic air sacs provide an enormous surface area that allows oxygen to diffuse into pulmonary capillaries while carbon dioxide diffuses out for exhalation.

Alveolar Cells and Their Functions

The alveoli contain specialized epithelial cells that perform distinct functions.

Type I Alveolar Cells

Type I pneumocytes form most of the alveolar surface and provide an extremely thin membrane that allows efficient oxygen and carbon dioxide diffusion.

Type II Alveolar Cells

Type II pneumocytes produce pulmonary surfactant, which reduces surface tension inside the alveoli.

Their functions include:

• Producing surfactant

• Supporting alveolar repair

• Maintaining lung compliance

Alveolar Macrophages

Alveolar macrophages are immune cells that engulf bacteria, debris, and inhaled particles, helping protect the lungs from infection.

What Is Pulmonary Surfactant?

Pulmonary surfactant is a phospholipid-rich substance secreted by Type II alveolar cells. It coats the inner surface of the alveoli and prevents their collapse during exhalation.

Its major functions include:

• Reducing alveolar surface tension

• Preventing alveolar collapse (atelectasis)

• Improving lung compliance

• Supporting innate immune defense

Without adequate surfactant, breathing becomes significantly more difficult because collapsed alveoli require greater pressure to reopen.

Differences Between the Right and Left Bronchi

Although both bronchi conduct air into the lungs, important anatomical differences have significant clinical implications.

Because the right main bronchus is wider, shorter, and more vertical, aspirated food, foreign objects, and misplaced endotracheal tubes are more likely to enter the right lung. This anatomy also contributes to a higher incidence of aspiration pneumonia affecting the right lung.

Differences Between the Right and Left Lungs

The lungs are asymmetrical due to the position of the heart.

Pulmonary Circulation and Lung Function

The lungs perform several vital physiological functions beyond gas exchange.

Major pulmonary functions include:

• Oxygenating blood

• Removing carbon dioxide

• Delivering nutrients to lung tissue

• Acting as a blood reservoir for the left ventricle

• Filtering small blood clots, air bubbles, and debris

The pulmonary artery enters each lung through the hilum, where it branches alongside the bronchial tree into progressively smaller arteries and arterioles.

Chest Wall and Pleura

The respiratory system relies on both the chest wall and pleural membranes to facilitate breathing.

Chest Wall Components

The chest wall consists of:

• Skin

• Ribs

• Intercostal muscles

• Thoracic cavity

Pleura

The pleura is a double-layered serous membrane composed of:

• Parietal pleura

• Visceral pleura

Between these layers lies the pleural space, which contains a small amount of lubricating fluid that reduces friction during breathing.

Ventilation and Respiratory Control

Ventilation is the mechanical movement of air into and out of the lungs. It is regulated by receptors and neural control centers.

Lung Receptors

Several receptors help regulate breathing.

Irritant receptors

Located within the airways, these receptors trigger protective reflexes such as coughing when exposed to smoke, dust, or chemical irritants.

Stretch receptors

Stretch receptors are located within airway smooth muscle and respond to lung inflation, preventing over-expansion through protective reflexes.

Central chemoreceptors

Located on the medulla, central chemoreceptors monitor cerebrospinal fluid pH and indirectly detect increases in arterial carbon dioxide (PaCO₂), making carbon dioxide the primary driver of normal breathing.

Brain Centers That Control Respiration

Normal breathing is regulated by respiratory centers located within the brainstem.

These include:

• Medulla oblongata

• Pons

Together, these structures coordinate respiratory rate, rhythm, and depth.

Muscles and Nerves Involved in Breathing

Breathing depends on coordinated muscle contraction.

Primary respiratory muscles include:

• Diaphragm

• Intercostal muscles

• Abdominal muscles (during forced expiration)

Phrenic Nerve

The phrenic nerve provides motor innervation to the diaphragm and is essential for normal inspiration.

Vagus Nerve

The vagus nerve supplies parasympathetic innervation to the lungs, influencing airway diameter, mucus secretion, and several protective respiratory reflexes.

Gas Transport Process

Oxygen delivery involves several sequential physiological steps.

The process includes:

1. Ventilation of the lungs.

2. Diffusion of oxygen from alveoli into pulmonary capillaries.

3. Perfusion of tissues with oxygen-rich blood.

4. Diffusion of oxygen into body cells.

Carbon dioxide follows the opposite pathway and is transported back to the lungs for exhalation.

Carbon Dioxide: The Primary Stimulus for Breathing

In healthy individuals, increasing carbon dioxide levels provide the strongest stimulus for respiration. As arterial CO₂ rises, central chemoreceptors stimulate the respiratory center to increase both breathing rate and depth.

Laplace’s Law and Alveolar Stability

Laplace’s Law states that the pressure required to inflate an alveolus is inversely proportional to its radius.

Smaller alveoli naturally require greater pressure to remain open. Pulmonary surfactant lowers surface tension, reducing this pressure requirement and preventing alveolar collapse.

Functional Residual Capacity (FRC)

Functional Residual Capacity (FRC) is the volume of air remaining in the lungs after a normal passive exhalation.

FRC represents the equilibrium point where:

• Lung elastic recoil inward

• Chest wall expansion outward

are balanced.

Vital Capacity

Vital capacity is the maximum volume of air that can be exhaled after taking the deepest possible breath.

Spirometry commonly measures vital capacity to evaluate pulmonary diseases such as:

• Asthma

• COPD

• Restrictive lung disease

Abnormal Breathing Patterns

Several characteristic breathing patterns indicate underlying disease.

Kussmaul Respiration

Kussmaul breathing is characterized by deep, rapid, labored respirations and commonly occurs in diabetic ketoacidosis (DKA) as the body attempts to eliminate excess carbon dioxide.

Cheyne-Stokes Respiration

Cheyne-Stokes respiration consists of alternating periods of progressively deeper breathing followed by apnea.

It may occur in:

• Heart failure

• Stroke

• Severe neurological injury

• End-of-life conditions

Common Signs and Symptoms of Pulmonary Disease

Respiratory disorders frequently present with characteristic clinical findings.

Dyspnea

Dyspnea is the subjective sensation of difficult or uncomfortable breathing.

Types include:

• Orthopnea (difficulty breathing while lying flat)

• Paroxysmal nocturnal dyspnea (awakening suddenly at night gasping for air)

Cough

Cough may be:

• Acute

• Chronic

Persistent cough often warrants further evaluation for respiratory disease.

Additional Respiratory Symptoms

Other important findings include:

• Abnormal sputum production

• Hemoptysis (coughing blood)

• Cyanosis

• Digital clubbing

• Chest pain

Hypoventilation

Hypoventilation occurs when ventilation is inadequate to eliminate carbon dioxide, leading to hypercapnia.

Common causes include:

• Drug overdose

• Airway obstruction (choking)

• Head injury

• Seizures

• COPD

• Obstructive sleep apnea (OSA)

Medications Associated with Hypoventilation

Several substances suppress respiratory drive, including:

• Opioids

• Antiseizure medications

• Alcohol

• Illicit drugs

Hyperventilation

Hyperventilation occurs when ventilation exceeds metabolic demand, causing excessive carbon dioxide loss and hypocapnia.

Common causes include:

• Anxiety

• Emotional stress

• Panic attacks

• COPD exacerbations

• Congestive heart failure (CHF)

Medications Associated with Hyperventilation

Drugs that may contribute to hyperventilation include:

• Aspirin (salicylate toxicity)

• Stimulants

• Iron toxicity

• Beta₂-adrenergic agonists

Key Facts to Remember

• Gas exchange occurs in the alveoli.

• Type I alveolar cells perform gas diffusion.

• Type II alveolar cells produce surfactant.

• Surfactant prevents alveolar collapse.

• Carbon dioxide is the primary respiratory stimulus.

• The medulla and pons regulate breathing.

• The phrenic nerve controls the diaphragm.

• The vagus nerve provides parasympathetic innervation to the lungs.

• The right bronchus is wider, shorter, and more vertical than the left.

• Functional residual capacity is the air remaining after normal exhalation.

• Vital capacity is measured using spirometry to assess lung function.

Frequently Asked Questions

What is the primary function of the pulmonary system?

The pulmonary system exchanges oxygen and carbon dioxide between the atmosphere and bloodstream while helping regulate acid-base balance and supporting immune defense.

Which cells produce pulmonary surfactant?

Type II alveolar cells produce surfactant, which lowers surface tension and prevents alveolar collapse during exhalation.

Why is the right bronchus clinically significant?

The right main bronchus is shorter, wider, and more vertical, making it the most common location for aspirated objects and accidental endotracheal tube placement.

Which part of the brain controls breathing?

The medulla oblongata and pons within the brainstem regulate respiratory rate, rhythm, and depth.

What is functional residual capacity?

Functional residual capacity is the amount of air remaining in the lungs after a normal passive exhalation when lung recoil and chest wall expansion are balanced.

What stimulates normal breathing?

Rising arterial carbon dioxide levels are the primary physiological stimulus for normal breathing because they activate central chemoreceptors in the medulla.

Healthy lungs rely on coordinated airway anatomy, surfactant production, effective ventilation, efficient gas exchange, and proper neurological control to maintain oxygen delivery and carbon dioxide removal. Understanding these core respiratory concepts supports accurate assessment, diagnosis, and management of pulmonary disorders while providing a strong foundation for clinical nursing and medical practice.

NU551 Seminar 7 Pulmonary System Structures and Functions

Gas Exchange: Oxygen diffuses from the alveoli into pulmonary capillaries, while carbon dioxide diffuses from the blood into the alveoli for exhalation.

Surfactant Function: Type II alveolar cells produce surfactant, which reduces surface tension, improves lung compliance, and prevents alveolar collapse.

Respiratory Control: The medulla oblongata and pons regulate breathing, while elevated arterial carbon dioxide levels provide the primary stimulus for ventilation.

Clinical Anatomy: The right main bronchus is shorter, wider, and more vertical than the left, increasing the likelihood of aspiration and right-sided pneumonia.

References

Hall, J. E. (2021). Guyton and Hall textbook of medical physiology (14th ed.). Elsevier. https://www.elsevier.com/books/guyton-and-hall-textbook-of-medical-physiology/hall/978-0-323-59712-8

Huether, S. E., McCance, K. L., & Brashers, V. L. (2023). Understanding pathophysiology (8th ed.). Elsevier. https://www.elsevier.com/books/understanding-pathophysiology/huether/978-0-323-67303-7

NU551 Seminar 7 Pulmonary System Structures and Functions

Lewis, S. L., Bucher, L., Heitkemper, M. M., Harding, M., Kwong, J., & Roberts, D. (2023). Medical-surgical nursing: Assessment and management of clinical problems (12th ed.). Elsevier. https://www.elsevier.com/books/lewis-medical-surgical-nursing/lewis/978-0-323-79315-5

West, J. B., & Luks, A. M. (2021). West’s respiratory physiology: The essentials (11th ed.). Wolters Kluwer. https://shop.lww.com/West-s-Respiratory-Physiology/p/9781975150485