Study guide
4.2 The Respiratory System
ATI TEAS 7 Nursing Admission
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1 Introduction to the ATI TEAS 7
1.1 About the ATI TEAS 7 Exam 1.2 Content Area Breakdown 1.3 Scoring and Program Requirements 1.4 Building Your TEAS Study Plan
2 Reading
2.1 Identifying the Main Idea 2.2 Making Inferences and Drawing Conclusions 2.3 Summarizing and Paraphrasing 2.4 Understanding Text Structure 2.5 Author's Purpose, Tone, and Point of View 2.6 Evaluating Arguments, Evidence, and Credibility 2.7 Integrating Information and Interpreting Graphics 2.8 TEAS Reading Strategies, Pacing, and Practice
3 Mathematics
3.1 Whole Numbers and Basic Operations 3.2 Fractions 3.3 Decimals and Percentages 3.4 Ratios and Proportions 3.5 Algebra and Equations 3.6 Measurement and Unit Conversions 3.7 Statistics and Data Interpretation 3.8 Geometry Basics
4 Science
4.1 The Cardiovascular System 4.2 The Respiratory System 4.3 The Digestive System 4.4 The Nervous System 4.5 The Musculoskeletal System 4.6 The Urinary and Reproductive Systems 4.7 Cell Biology and Genetics 4.8 Chemistry Basics 4.9 Scientific Reasoning and the Scientific Method
5 English & Language Usage
5.1 Grammar and the Parts of Speech 5.2 Sentence Structure 5.3 Punctuation 5.4 Spelling and Word Usage 5.5 Vocabulary in Context and Word Parts 5.6 Paragraph Organization and the Writing Process 5.7 Formal vs. Informal Language, Audience, and Tone 5.8 TEAS English Section Strategies and Pacing
4.2 The Respiratory System
Key Takeaways Explain This Topic AI
Air pathway: nose/mouth → pharynx → larynx → trachea → bronchi → bronchioles → alveoli
Gas exchange occurs across the thin walls of the alveoli (about 480 million of them) by simple diffusion
Inhalation is active: the diaphragm contracts and moves down, the chest expands, and pressure drops to pull air in
About 98.5% of oxygen travels bound to hemoglobin in red blood cells; most CO₂ travels as bicarbonate ions
- Rising blood CO₂ (sensed in the medulla) is the strongest stimulus that increases breathing rate
- Last updated: October 2026
The respiratory system delivers oxygen to the blood and removes carbon dioxide, working hand-in-hand with the cardiovascular system you just studied. Expect questions that pair these two systems, because gas exchange is meaningless without a pump to carry the gases. Your job on the exam is to trace the path of air, explain where and how gas exchange happens, describe the mechanics of a single breath, and reason about what controls breathing rate. The recurring theme is diffusion : gases always move from areas of higher concentration to areas of lower concentration, and no energy is required to make that happen.
Anatomy: Upper and Lower Airways
Anatomists split the respiratory tract into an upper portion (in the head and neck) and a lower portion (in the chest).
- Tract Structure Function
- Upper Nose / nasal cavity Filters, warms, and humidifies incoming air
- Upper Pharynx (throat) Shared passageway for air and food
- Upper Larynx (voice box) Houses the vocal cords; routes air to the trachea
- Upper Epiglottis Flap that covers the trachea during swallowing
- Lower Trachea (windpipe) Main airway, reinforced by C-shaped cartilage rings
- Lower Bronchi Two branches, one into each lung
- Lower Bronchioles Progressively smaller branching airways
- Lower Alveoli Microscopic air sacs where gas exchange occurs
The epiglottis is worth knowing: this small flap closes over the larynx when you swallow so that food enters the esophagus, not the airway. When it fails, you choke.
The Pathway of Air
Trace a single breath of air from outside to the exchange surface:
Air enters through the nose or mouth .
It passes through the pharynx (throat).
It moves through the larynx (voice box).
It travels down the trachea (windpipe).
The trachea splits into the left and right bronchi .
Each bronchus branches into smaller and smaller bronchioles .
Air finally reaches the alveoli , where gas exchange occurs.
Gas Exchange in the Alveoli
The alveoli are roughly 480 million tiny sacs wrapped in capillaries, giving the lungs a gas-exchange surface area of about 70 square meters — close to the size of a tennis court. Their walls are a single cell thick, so the diffusion distance is about one micrometer. This is the whole design goal: huge area, tiny distance, maximum diffusion.
External respiration (in the lungs): oxygen diffuses from the alveoli into the blood; carbon dioxide diffuses from the blood into the alveoli to be exhaled.
Internal respiration (at the tissues): oxygen diffuses from the blood into body cells; carbon dioxide diffuses from cells into the blood.
The Mechanics of Breathing
Breathing is driven by pressure differences created when the diaphragm — the dome-shaped muscle beneath the lungs — changes shape. Remember: when the diaphragm contracts , it flattens and moves down .
- Phase Diaphragm Chest Volume Lung Pressure Air Movement
- Inhalation Contracts, moves down Increases Decreases Air rushes in
- Exhalation Relaxes, moves up Decreases Increases Air pushed out
The key principle is Boyle's law : when the chest cavity gets bigger, the pressure inside drops below atmospheric pressure, so air flows in to equalize. The intercostal muscles between the ribs assist by lifting the rib cage. Quiet inhalation is active (it requires muscle work), while quiet exhalation is mostly passive (the tissues simply recoil).
Oxygen and Carbon Dioxide Transport
Gases do not just float in the blood — they are carried in specific ways the TEAS expects you to know.
Oxygen transport:
About 98.5% binds to hemoglobin , the iron-containing protein inside red blood cells; each hemoglobin molecule carries up to four oxygen molecules
About 1.5% dissolves directly in the plasma
Carbon dioxide transport:
- Method Approximate Share
- Converted to bicarbonate ions (HCO₃⁻) in plasma ~70%
- Bound to hemoglobin ~23%
- Dissolved in plasma ~7%
- Respiratory Volumes
Clinicians measure how much air the lungs move using standard volumes:
- Term Definition
- Tidal volume Air in one normal breath (~500 mL)
- Inspiratory reserve Extra air you can forcibly inhale
- Expiratory reserve Extra air you can forcibly exhale
- Residual volume Air that always remains after a full exhale
- Vital capacity Maximum air exhaled after a maximum inhale
- Total lung capacity Vital capacity + residual volume
- Control of Breathing
The medulla oblongata in the brainstem is the primary respiratory control center, with the pons fine-tuning rhythm. Chemoreceptors monitor the blood, and the dominant signal may surprise you: it is not low oxygen but rising carbon dioxide (and the falling pH it causes) that most strongly drives you to breathe faster.
Worked Example: A patient holds their breath. Within seconds they feel an overwhelming urge to breathe. Is this because oxygen has run low, or because carbon dioxide has built up? The urge is driven mainly by rising CO₂ . As CO₂ accumulates, it forms carbonic acid, lowering blood pH; chemoreceptors in the medulla detect this and force the breathing reflex — well before oxygen reaches a dangerous low. That is why CO₂, not O₂, is the primary respiratory stimulus.