Respiratory System for Medical Assistants

The Respiratory System

The respiratory system does one job above all others: get oxygen into the bloodstream and get carbon dioxide out. That gas exchange happens continuously, every breath, all day. As a medical assistant, you will assess respiratory function through pulse oximetry, peak flow testing, and patient observation. Understanding the anatomy helps you document accurately and recognize when something is wrong.

Upper Respiratory Tract

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

• Nose and nasal cavity: Entry point for air. Mucous membranes trap particles; cilia sweep debris toward the throat. The nasal cavity connects to sinuses (frontal, maxillary, ethmoid, sphenoid).
• Pharynx (throat): Common passageway for air and food. Divided into nasopharynx (behind nose), oropharynx (behind mouth), and laryngopharynx (connects to larynx and esophagus).
• Larynx (voice box): Houses the vocal cords. The epiglottis is a flap of cartilage that covers the trachea during swallowing to prevent aspiration.

Lower Respiratory Tract

The lower tract conducts air to the alveoli where gas exchange occurs.

• Trachea (windpipe): Rigid tube reinforced by C-shaped cartilage rings. About 4 to 5 inches long. Divides into two bronchi at the carina.
• Primary bronchi: Left and right. The right bronchus is shorter, wider, and more vertical than the left. Foreign objects and aspirated material are more likely to enter the right bronchus.
• Bronchioles: Smaller branches of the bronchi. No cartilage. Contain smooth muscle that can constrict (bronchospasm in asthma) or dilate.
• Alveoli: Tiny air sacs at the end of bronchioles. Surrounded by capillaries. Walls are one cell thick for efficient gas exchange. Adults have approximately 300 million alveoli.
• Lungs: Right lung has 3 lobes (upper, middle, lower). Left lung has 2 lobes (upper, lower) to accommodate the heart. Each lung is covered by a pleural membrane.

Gas Exchange (External Respiration)

At the alveoli, oxygen diffuses from the air into pulmonary capillaries and binds to hemoglobin in red blood cells. Carbon dioxide diffuses from the capillaries into the alveoli and is exhaled. This process depends on a concentration gradient: oxygen is more concentrated in inhaled air than in venous blood; CO2 is more concentrated in venous blood than in alveolar air.

Oxygen saturation (SpO2) measures what percentage of hemoglobin is carrying oxygen. Normal SpO2 is 95% to 100%. Below 90% is hypoxia and requires immediate attention.

Breathing Mechanics

Inhalation is active: the diaphragm and intercostal muscles contract, expanding the chest cavity, dropping pressure in the lungs, and drawing air in. Exhalation is normally passive: muscles relax, the chest recoils, and air flows out. The respiratory rate is controlled by the medulla oblongata in the brain, responding mainly to CO2 levels in the blood.

Common Respiratory Conditions

Asthma

Chronic inflammatory condition causing bronchospasm and airway narrowing. Triggers include allergens, exercise, cold air, and respiratory infections. Symptoms: wheezing, shortness of breath, chest tightness, cough. MAs assist with nebulizer treatments and peak flow meter testing. Peak flow below 50% of personal best is a severe attack requiring emergency care.

COPD (Chronic Obstructive Pulmonary Disease)

Umbrella term for chronic bronchitis and emphysema. Primarily caused by smoking. Emphysema destroys alveolar walls, reducing gas exchange surface area. Chronic bronchitis causes excessive mucus and airway inflammation. Symptoms: productive cough, dyspnea, barrel chest (in emphysema). Spirometry confirms the diagnosis.

Pneumonia

Infection of lung tissue causing alveoli to fill with fluid or pus. Can be bacterial (most commonly Streptococcus pneumoniae), viral, or fungal. Symptoms: productive cough, fever, chills, pleuritic chest pain, crackles on auscultation. MAs may assist with chest X-ray setup and specimen collection.

Bronchitis

Inflammation of the bronchial tubes. Acute bronchitis is usually viral and self-limiting. Chronic bronchitis (part of COPD) involves a productive cough for at least 3 months in 2 consecutive years. Treatment is supportive: rest, hydration, humidified air, and bronchodilators if bronchospasm is present.

Peak Flow Meters and Nebulizers

A peak flow meter measures the maximum speed at which a patient can exhale. It helps asthma patients monitor their disease at home. Values are compared to the patient personal best. Green zone (80 to 100%) means good control; yellow (50 to 79%) means caution; red (below 50%) means medical attention needed.

Nebulizers convert liquid bronchodilator medications (such as albuterol) into a fine mist for inhalation. MAs set up the equipment, instruct the patient on proper technique, and document response to treatment. Watch for adverse effects including tachycardia and tremors with albuterol.

Practice Questions