Respiratory System in Humans

Respiratory System in Humans

Table of Contents

The Respiratory System

Respiratory System: Our Internal Air Traffic Controller

Imagine your body as a bustling city. Every cell needs a constant supply of oxygen, just like vehicles need fuel. The respiratory system acts like an air traffic controller, ensuring a smooth flow of oxygen in and waste removal out.

Detailed human respiratory system anatomy illustration with lungs

Why is it Vital?

Without the respiratory system, our cells wouldn’t get the oxygen needed to function. This vital gas fuels our body’s processes, keeping us alive and energized.

Breathing In and Out

  • Inhaling (Taking a breath in): We use our diaphragm, a muscle below the lungs, to expand our chest cavity. This creates a vacuum, drawing air in through the nose or mouth.
  • Exhaling (Letting out a breath): The diaphragm relaxes, pushing air back out.

Gas Exchange

As air travels through the lungs, a vital swap happens:

Infographics of breathing cycle, inspiration and expiration, gas exchange, visualisation of lung voulme during inhale and exhale, work of diaphragm

  • Oxygen enters the bloodstream: Tiny air sacs in the lungs, called alveoli, have thin walls that allow oxygen to easily pass into the blood.
  • Carbon dioxide exits: This waste product from cellular processes is carried by the blood to the lungs and released back into the air we exhale.

Simple as taking a breath, this continuous gas exchange is essential for our survival.

Components of the Respiratory System

Upper Respiratory Tract

It is the first leg of your breathing journey. Here’s a breakdown of its key parts:


  • Think of it as an air filter: Tiny hairs trap dust and dirt, while mucus catches larger particles.
Blood and the respiratory system: 1.1.1 Upper respiratory tract | OpenLearn - Open University
  • Air conditioner: It warms and humidifies cool, dry air for your lungs.
  • Smell Station (Olfactory Receptors):
  • Special cells in your nose detect odor molecules, allowing you to smell the world around you.

Pharynx (Throat)

  • Double duty: A shared passage for both air and food.
  • Swallowing Champ: Muscles in the pharynx help push food down the esophagus.
 SEER Training: Pharynx
  • Gag Reflex Protector: When you swallow the wrong thing, the pharynx triggers the gag reflex to keep it out of your airway.

Larynx (Voice Box)

  • Voice Box: Two folds of muscle called vocal cords vibrate to produce sound as you speak.
How does the larynx work? |
  • Food Blocker (Epiglottis): A tiny flap that covers the windpipe during swallowing to prevent food from entering.

Trachea (Windpipe)

  • Air Highway: A tube made of cartilage rings that carries air down to the lungs.
Vector medical educational biological chart for trachea diagram. Anatomy illustration isolated white background
  • Keeps it Open: The cartilage rings prevent the windpipe from collapsing and ensure smooth air passage.

Lower Respiratory Tract

The lower respiratory tract, also known as the respiratory tree or tracheobronchial tree, is responsible for moving air in and out of the lungs. These are the following components:

Trachea (Windpipe):

  • A tube-like structure that starts at the larynx (voice box) and branches into the two primary bronchi.
  • Cartilaginous rings help maintain its shape and prevent collapsing during inhalation.
human bronchi 3d renderings of human bronchi Trachea stock pictures, royalty-free photos & images


  • The trachea splits into two main branches called the primary bronchi.
  • Each primary bronchus further divides into secondary and tertiary bronchi within the lungs.
  • Their main function is to conduct air towards the alveoli.

Bronchi | Anatomy, Function & Location - Lesson |


inflamation of the bronchus causing asthma Asthma is a chronic inflammatory disease of the airways that is characterized by narrowing of the airways and dyspnea, wheezing, and coughing. Bronchioles stock illustrations

  • Even smaller tubes branching off from the bronchi.
  • They contain smooth muscle that helps regulate airflow.
  • As they branch further, they become smaller and are called terminal bronchioles.


  • Microscopic air sacs at the end of the bronchioles.
  • These tiny sacs have a large surface area due to their thin, balloon-like structure.
  • Gas exchange (oxygen entering and carbon dioxide leaving) happens here between the air and the blood.
Respiratory system of human Respiratory system of human. This illustration about anatomy and physiology. Alveoli stock illustrations


Human Respiratory System Anatomy

  • Spongy organs located in the chest cavity.
  • Each lung is divided into lobes (three in the right lung and two in the left).
  • The lungs are covered by a membrane called the pleura, which helps them inflate and deflate smoothly during breathing.
Mechanism of Breathing


  • A dome-shaped muscle located below the lungs.
  • When the diaphragm contracts, it pulls down, increasing the space in the chest cavity.
  • This creates a low-pressure area in the lungs, drawing air in.
The diaphragm functions in breathing
Intercostal muscles

CrossFit | Thoracic Muscles, Part 1

  • Muscles located between the ribs.
  • They help expand and contract the chest cavity during inhalation and exhalation.

Respiration Physiology

Our body’s breathing involves a fascinating dance of gas exchange and regulation. Here’s a breakdown of the key points:

Gas Exchange

Infographics of breathing cycle, inspiration and expiration, gas exchange, visualisation of lung voulme during inhale and exhale, work of diaphragm

  • Imagine tiny air sacs in your lungs called alveoli. These have a super thin membrane.
  • Oxygen (O2) from the air you breathe diffuses across this membrane, slipping into the bloodstream.
  • At the same time, carbon dioxide (CO2), a waste product from your cells, travels out of the blood and diffuses back into the air you exhale.


Hemoglobin: Structure, Types, Functions, Diseases

  • Red blood cells carry a special protein named hemoglobin. Think of it as a tiny taxi.
  • Hemoglobin picks up oxygen from the lungs and transports it throughout your body.
  • When it reaches your tissues, the oxygen detaches from hemoglobin and is used by your cells for energy.


Brainstem Diagram | Quizlet

  • A part of your brain called the brainstem acts like a control center for breathing.
  • It constantly monitors the levels of oxygen (O2) and carbon dioxide (CO2) in your blood.


  • Special sensors in your body called chemoreceptors are like tiny spies, constantly checking the O2 and CO2 levels.
  • When CO2 levels rise (indicating the body needs to breathe out more), or O2 levels fall (signaling a need for more oxygen), these chemoreceptors send signals to the brainstem.

Adjusting the Breath

  • Based on the signals from chemoreceptors, the brainstem increases or decreases the rate and depth of your breathing.
  • This ensures a constant balance of O2 and CO2 in your body, vital for maintaining healthy function.

Disorders of the Respiratory System

The respiratory disorders you mentioned in a simple and easy-to-understand manner:

Common Colds and Flu

Facts About Common Cold & Find Best Treatment At Medicover

  • Cause: Caused by viruses.
  • Symptoms: Runny or stuffy nose, sore throat, cough, congestion, fever, chills, fatigue, body aches, headache.
  • Prevention: Frequent handwashing, avoiding close contact with sick people, getting enough sleep, and managing stress can help reduce the risk of catching a cold or flu. Vaccines are also available to help prevent the flu.


610+ Asthma Diagram Stock Photos, Pictures & Royalty-Free Images - iStock

  • Characteristics: A chronic inflammatory disease of the airways that causes recurring episodes of wheezing, breathlessness, chest tightness, and coughing.
  • Symptoms: Symptoms may vary from person to person and can be triggered by allergens, irritants, exercise, or even cold air.
  • Treatment approaches: There is no cure for asthma, but there are effective medications that can help control symptoms and improve quality of life. Inhalers are commonly used to deliver medication directly to the lungs.

Chronic Obstructive Pulmonary Disease (COPD)

  • Types:
    • Emphysema: A condition where the air sacs in the lungs are damaged, leading to shortness of breath.
    • Chronic Bronchitis: Long-term inflammation of the lining of the bronchial tubes, causing excessive mucus production and coughing

What are the symptoms of chronic obstructive pulmonary disease (COPD)? -  FITPAA

  • Causes: The main cause of COPD is smoking, but long-term exposure to air pollution and occupational dusts can also contribute.
  • Symptoms: Shortness of breath, especially during activity, wheezing, chest tightness, and a persistent cough that produces mucus.

Lung Cancer

  • Risk factors: Smoking is the leading risk factor for lung cancer. Other risk factors include exposure to secondhand smoke, radon gas, and air pollution. People with a family history of lung cancer are also at an increased risk.

What Are The Stages Of Lung Cancer? | SERO

  • Types: There are different types of lung cancer, the most common being non-small cell lung cancer and small cell lung cancer.
  • Early detection methods: Screening with low-dose CT scans can help detect lung cancer early when it is most treatable. Symptoms like coughing up blood, persistent chest pain, and unexplained weight loss can also be signs of lung cancer and should be evaluated by a doctor.


The respiratory system’s conclusion lies in its vital role of sustaining life. Here’s a summary:

  • Gas exchange: The primary function is to bring in oxygen (O2), essential for cellular processes, and remove carbon dioxide (CO2), a waste product.
  • Maintaining balance: It ensures a constant supply of O2 and efficiently eliminates CO2, keeping the body’s internal environment (pH and chemical balance) stable.
  • Supporting other systems: The respiratory system works alongside the circulatory system to deliver O2 throughout the body and remove CO2 for exhalation.


Respiration is the process by which organisms exchange gases with their environment, taking in oxygen and releasing carbon dioxide. In humans, respiration involves several parts:

  • Nasal Cavity: Filters, warms, and humidifies incoming air.
  • Trachea (Windpipe): Conducts air to and from the lungs.
  • Bronchi: Further divides into smaller tubes called bronchioles.
  • Lungs: Main organs where gas exchange occurs.
  • Alveoli: Tiny air sacs in the lungs where oxygen and carbon dioxide exchange takes place.
  • Diaphragm and Intercostal Muscles: Muscles involved in the process of breathing, aiding in inhalation and exhalation.

The respiratory system involves several steps:

  • Breathing (Ventilation): Involves inhaling and exhaling air.
  • Gas Exchange: Oxygen from the air is taken up by blood in the lungs, while carbon dioxide is released from the blood into the air.
  • Transport: Oxygen is transported through the bloodstream to cells in the body, while carbon dioxide is transported back to the lungs.
  • Cellular Respiration: Oxygen is used by cells to produce energy through the process of cellular respiration, releasing carbon dioxide as a byproduct.

The steps of respiration can be summarized as follows:

  1. Breathing In (Inhalation): Air is taken into the lungs.
  2. Gas Exchange in the Lungs: Oxygen from the air diffuses into the blood, while carbon dioxide from the blood diffuses into the air.
  3. Transport of Gases: Oxygen is transported by the bloodstream to cells throughout the body, while carbon dioxide is carried back to the lungs.
  4. Cellular Respiration: Oxygen is used by cells to produce energy through cellular respiration, generating carbon dioxide as a byproduct.
  5. Gas Exchange at the Tissues: Oxygen is released from the blood into the cells, while carbon dioxide produced by cellular respiration moves into the bloodstream.
  6. Transport of Gases in the Blood: Oxygen-rich blood is carried back to the heart and pumped to the rest of the body, while carbon dioxide-rich blood returns to the lungs.
  7. Breathing Out (Exhalation): Carbon dioxide is expelled from the lungs as waste.

Respiration can be understood at various levels:

  • Cellular Respiration: Occurs within individual cells to produce ATP.
  • Tissue Respiration: Refers to the exchange of gases at the level of tissues in the body.
  • Pulmonary Respiration: Involves the exchange of gases in the lungs.
  • External Respiration: The exchange of gases between the external environment and the body’s internal environment, primarily occurring in the lungs.


1. Which organ is primarily responsible for the exchange of gases in the respiratory system?

  • A) Lungs
  • B) Liver
  • C) Heart
  • D) Kidneys

Answer: A) Lungs

2. What is the function of the trachea in the respiratory system?

  • A) Pump blood to the lungs
  • B) Transport oxygen to the cells
  • C) Filter out dust and particles
  • D) Carry air to and from the lungs

Answer: D) Carry air to and from the lungs

3. Which of the following is NOT a part of the respiratory system?

  • A) Bronchi
  • B) Alveoli
  • C) Liver
  • D) Diaphragm

Answer: C) Liver

4. What is the primary gas exchanged during respiration?

  • A) Nitrogen
  • B) Carbon dioxide
  • C) Oxygen
  • D) Hydrogen

Answer: C) Oxygen

5. Which muscle helps in the process of breathing by expanding the chest cavity?

  • A) Biceps
  • B) Abdominals
  • C) Diaphragm
  • D) Quadriceps

Answer: C) Diaphragm

6. Where does the process of gas exchange occur in the lungs?

  • A) Bronchioles
  • B) Trachea
  • C) Alveoli
  • D) Bronchi

Answer: C) Alveoli

7. Which of the following is NOT a function of the nasal cavity?

  • A) Warming and humidifying air
  • B) Filtering out dust and particles
  • C) Exchanging gases
  • D) Detecting smells

Answer: C) Exchanging gases

8. What is the role of mucus in the respiratory system?

  • A) Providing oxygen to cells
  • B) Lubricating airways and trapping dust
  • C) Absorbing carbon dioxide
  • D) Regulating blood pH

Answer: B) Lubricating airways and trapping dust

9. What is the function of the epiglottis during swallowing?

  • A) Allows air to enter the lungs
  • B) Prevents food from entering the trachea
  • C) Filters out dust particles
  • D) Regulates blood pressure

Answer: B) Prevents food from entering the trachea

10. What is the term for the process of inhaling and exhaling air?

  • A) Circulation
  • B) Digestion
  • C) Respiration
  • D) Secretion

Answer: C) Respiration

11. What gas do humans exhale as a waste product of respiration?

  • A) Oxygen
  • B) Nitrogen
  • C) Carbon dioxide
  • D) Hydrogen

Answer: C) Carbon dioxide

12. Which part of the brain controls involuntary breathing?

  • A) Cerebrum
  • B) Cerebellum
  • C) Brainstem
  • D) Hypothalamus

Answer: C) Brainstem

13. What is the purpose of the bronchial tubes in the respiratory system?

  • A) To produce mucus
  • B) To warm and humidify air
  • C) To carry air to the lungs
  • D) To transport oxygen to cells

Answer: C) To carry air to the lungs

14. How many lobes does the right lung have?

  • A) One
  • B) Two
  • C) Three
  • D) Four

Answer: C) Three

15. Which gas is transported in the blood by hemoglobin?

  • A) Oxygen
  • B) Nitrogen
  • C) Carbon dioxide
  • D) Hydrogen

Answer: A) Oxygen

16. What is the medical term for difficulty breathing?

  • A) Asthma
  • B) Hypoxia
  • C) Dyspnea
  • D) Emphysema

Answer: C) Dyspnea

17. Which of the following is NOT a risk factor for respiratory diseases?

  • A) Smoking
  • B) Exercise
  • C) Air pollution
  • D) Allergies

Answer: B) Exercise

18. What is the purpose of the pleura in the respiratory system?

  • A) To produce mucus
  • B) To warm and humidify air
  • C) To protect the lungs
  • D) To carry oxygen to cells

Answer: C) To protect the lungs

19. What is the term for the tiny hair-like structures in the respiratory tract that sweep mucus and debris away from the lungs?

  • A) Alveoli
  • B) Cilia
  • C) Bronchi
  • D) Pharynx

Answer: B) Cilia

20. Which respiratory disorder is characterized by inflammation and narrowing of the airways, leading to wheezing and shortness of breath?

  • A) Pneumonia
  • B) Bronchitis
  • C) Asthma
  • D) Tuberculosis

Answer: C) Asthma

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