Select your language

Suggested languages for you:
Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

All-in-one learning app

  • Flashcards
  • NotesNotes
  • ExplanationsExplanations
  • Study Planner
  • Textbook solutions
Start studying

Human Gas Exchange

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now
Biology

Humans and most animals constantly need to breathe to survive. This article discusses how humans breathe and exchange gases with the environment. It also elaborates on some diseases of the respiratory system.

The arrangement of the human gas exchange system

Oxygen generates ATP in aerobic respiration and produces carbon dioxide as a by-product. Carbon dioxide needs to be removed as its buildup is toxic to cells. To function optimally, humans need to absorb large volumes of oxygen while removing large amounts of carbon dioxide from their blood.

Human gas exchange is exchanging carbon dioxide from the blood for oxygen in the air.

Gas exchange is required because:

  • The human body is composed of many living cells that undergo aerobic respiration.
  • Humans are endothermic organisms, meaning they need to maintain a constant body temperature and have a high metabolic rate.

As a result, humans need a system capable of efficiently delivering oxygen to the body while removing carbon dioxide.

The human gas-exchange system consists of various organs and structures located in the chest cavity and is protected by the ribcage. They include:

  • Trachea: The trachea is the primary airway that connects the mouth and the nasal cavity to the bronchi. C shaped cartilage rings that prevent the trachea from collapsing. Ciliated and mucus-producing epithelium line the trachea, sweeping microorganisms and dust particles away from the lungs.

  • Lungs: Humans have two lungs. They are multi-lobed organs that form the centre of the respiratory system.

  • Bronchi: Bronchi (singular: bronchus) are the two branches of the trachea to each lung. They have a similar structure to the trachea and are lined with ciliated mucosal epithelium. They become narrower and eventually connect to bronchioles.

  • Bronchioles: Bronchioles are subdivisions of the bronchi that are lined with muscles. These muscles allow them to control the flow of air into the alveoli.

  • Alveoli: Alveoli are the primary site of gas exchange. They are tiny air-sacs at the end of the bronchioles.

The mechanism of ventilation in gas exchange

For gas exchange to occur efficiently, the air is continuously moved in and out of the lung in a process called ventilation or breathing. The air movement is caused by the change of pressure inside the lungs created by the movement of the diaphragm and the intercostal muscles (located between the ribs).

Figure 1. The overall arrangement of the structures and organs in the respiratory system.

Ventilation can be broken down into two phases: Inspiration (breathing in) and expiration (breathing out).

Inspiration

Inspiration is an active process that lowers the pressure inside the lung, causing the air to flow in. Here are the main events that occur during inspiration:

  • The internal intercostal muscles relax.

  • The external intercostal muscles contract to move the ribs upward and outwards.

  • The diaphragm contracts and flattens.

Internal and external intercostal muscles act to increase the volume inside the thorax. Boyle’s law states that at a fixed temperature, the volume of gas is inversely proportional to the pressure exerted by the gas. Therefore, the increase in the volume of the thorax results in a drop in the pressure inside the lungs. Since the atmospheric pressure is higher than the pulmonary pressure, air enters the lungs.

Expiration

Quiet expiration is a passive process. The lungs and the thorax passively return to their original position after inspiration due to their natural elastic recoil. Expiration becomes active only when the demand for gas exchange is high, for example, during exercise or physical activities. The main events that occur during expiration are as follows:

  • The external intercostal muscles relax.

  • The internal intercostal muscles contract, moving the ribs downwards and inwards. (Only during active expiration)

  • The diaphragm relaxes and so returns to its dome shape.

As a result, the lung volume decreases during expiration which causes the pulmonary pressure to exceed the atmospheric pressure, pushing the air out of the lungs.

Human Gas Exchange [+] the mechanism of muscle contractions during inspiration and expiration {+]StudySmarterFigure 2. The mechanism of muscle contractions during inspiration and expiration. Source: OpenStax College, CC BY-SA 4.0, via Wikimedia Commons.

Measuring pulmonary ventilation rate

The pulmonary ventilation rate can be measured by multiplying the tidal volume by the respiratory rate. Tidal volume and the respiratory rate are measured separately.

  • Tidal volume: measured using a respirometer.
  • Respiratory rate: number of breaths per minute counted.

The pulmonary ventilation rate measures how much air moves into the lungs per minute.

The tidal volume is the amount of air taken into the lungs with each breath during normal breathing. Tidal volume is usually measured by a device called a respirometer.

The respiratory (breathing) rate is simply the number of breaths taken per minute.

Gas exchange in the alveoli

The alveoli are tiny sacs in the lung that are in close contact with the blood. Collagenic and elastin fibres which allow the air-sacs to stretch and expand during breathing, surround the alveoli. They are lined with a single cell layer epithelium (simple squamous epithelium) that allows fast exchange of gases between the air and the blood. The alveoli are surrounded by dense capillaries that are very narrow and lined with a single layer of endothelial cells.

Gas exchange in humans occurs at the epithelium of the lung alveoli. Exchange surfaces require specific features to allow efficient transfer of materials between organisms and the environments, and the alveoli are no exception. These features include:

  1. Short diffusion distance

  2. Large surface area

  3. Partially permeable membrane

  4. A maintained diffusion gradient

Features of alveoli for an efficient gas exchange

Oxygen and carbon dioxide need to diffuse through the alveolar and capillary walls in opposite directions during the gas exchange.

The alveoli have very thin walls. They are lined with simple squamous epithelium that is only one cell thick. The blood capillaries surrounding the alveoli are also very thin, and their endothelium is one cell thick. Therefore, the gases have to diffuse over a short distance, increasing the rate and efficiency of gas exchange.

A single alveolus is quite small and has a small surface area on its own. But multiple alveoli collectively have a much larger surface area. There are approximately 300 million alveoli in each human lung with a collective surface area of 70, about half the size of a tennis court! The alveoli are surrounded by networks of fine blood capillaries that collectively have a large surface area. This extensive surface area allows the gas exchange to occur rapidly.

The constant flow of blood through the alveolar capillaries and continuous air ventilation in and out of the lungs create and maintain a steep concentration gradient for gas exchange. This gradient for oxygen is from the alveoli to the blood while the gradient for carbon dioxide is from the blood to the alveoli.

These features allow for rapid and efficient gas exchange to occur in the lungs.

Figure 3. Exchange of oxygen and carbon dioxide between an alveolus and a capillary.

The main lung diseases that impair the human gas exchange

Various disorders can affect the alveolar wall or obstruct the airways and impair the function of the lungs. These diseases include lung cancer, COPD, asthma and others.

Lung cancer

Cancer develops when mutations disrupt the control of cell replication leading to unregulated cell divisions. Tumours in the lung form when oncogenes or tumour-suppressor genes in the bronchial epithelial cells mutate. As a result, these cells undergo rapid and unregulated cell replication and create a mass of abnormal and irregular cells.

A tumour is a swelling in the body caused by abnormal tissue growth. Tumours are either benign (non-cancerous) or malignant (cancerous).

The tumour eventually begins to disrupt the normal functioning of the lungs, such as by constricting the pulmonary arteries and veins. Malignant cancer cells also infiltrate the lymphatic system. They can then travel within the lymphatics and establish another tumour at another part of the body.

You can learn more about tumours in our articles on cancer and tumours!

Patients with lung cancer often have symptoms such as a persistent cough, coughing up blood or increased mucus, sudden weight loss, and breathing difficulties.

COPD

Chronic obstructive pulmonary disease (COPD) refers to lung illnesses that include emphysema (shortness of breath) and chronic bronchitis.

COPD symptoms are shortness of breath, chest tightness, a persistent cough, wheezing when exercising or participating in any physical activity.

The ciliated epithelium of the trachea and bronchi of the lungs contain goblet cells that produce mucus. The cilia sweep up the dust and microorganisms trapped inside the mucus towards the throat and away from the lungs in healthy individuals. When these cilia become damaged or stop working, the mucus builds and causes narrowing of the airways.

Human Gas Exchange healthy and diseased alveoli in the lungs copd StudySmarterFigure 4. Healthy and diseased alveoli in the lungs. Source: NIH, Public Domain, via Wikimedia Commons.

Risk factors

Several specific risk factors increase the risk of developing COPD. These include:

  • Smoking - Smoking is also known to increase the risk of developing lung cancer.

  • Air pollution.

  • Genetics (some people are genetically more likely to develop lung disease while others are less likely).

  • Infections - frequent chest infections increase the risk of developing COPD.

  • Occupation - (working with harmful chemicals and gases also increases chances of developing COPD and lung cancer).

Asthma

During an asthma attack, the muscles lining the lungs’ airways constrict in response to anxiety or foreign particles. This causes narrowing of the airways and impairs breathing. People with asthma use inhalers that contain salbutamol. Salbutamol causes these muscles to relax, resulting in the opening of the airways.

A triad of risk factors increases the risks of developing asthma in person. This triad is called the atopy triad, and it includes:

  1. Family history of asthma

  2. Allergies usch as hay fever

  3. Eczema

Human Gas Exchange [+] asthma attack [+] StudySmarterFigure 5. A: the location of the lungs and airways in the body; B: a cross-section of a normal airway; C: a cross-section of an airway during asthma symptoms. Source: United States - National Institute of Health: National Heart, Lung and Blood Institute, Public Domain, via Wikimedia Commons.

Human Gas Exchange - Key takeaways

  • The human gas-exchange system consists of various organs and structures located in the chest cavity and protected by the ribcage. They include:
    • Trachea
    • Lungs
    • Bronchi
    • Bronchioles
    • Alveoli
  • Lung ventilation is comprised of two processes:
    • Inspiration: movement of air into the lungs (active process)
      • The internal intercostal muscles relax.
      • The external intercostal muscles contract to move the ribs upward and outwards. (Just like the handle of a bucket moving upward and outward!, Figure 2)
      • The diaphragm contracts and flattens.
    • Expiration: movement of air out of the lungs (passive process at rest)
      • The external intercostal muscles relax.
      • The internal intercostal muscles contract, moving the ribs downwards and inwards. (Only during active expiration)
      • The diaphragm relaxes and so returns to its dome shape.
  • Pulmonary ventilation rate (dm^3.min^-1) = tidal volume (dm^3) x respiratory rate(min^-1).
  • Alveoli are adapted to maximise the efficiency of gas exchange. These adaptations include:
    1. Short diffusion distance
    2. Large surface area
    3. Partially permeable membrane
    4. A maintained diffusion gradient
  • There are various diseases of the lungs. Some examples are: COPD, lung cancer, and asthma.

Human Gas Exchange

Gas exchange occurs in the alveoli of the lungs.

The alveoli and their surrounding capillaries are one cell thick so the diffusion distance is short. There are over 300 million alveoli in each lung providing a large surface area for gas exchange. The continuous ventilation of air and the flow of blood maintain a steep concentration gradient for gas exchange.  

The process of moving air in (inspiration) and out (expiration) of the lungs. Inspiration is an active process that involves the contraction of the diaphragm and the external intercostal muscles. These muscles increase the volume of the thorax and lower the pulmonary pressure forcing the air to enter the lungs. Expiration is usually a passive process but it requires active muscle involvement when there is a high demand for gas exchange, for example, during exercise. During active expiration, the internal intercostal muscles contract, lowering the volume of the lungs and raising the pulmonary pressure that forces the air out.  

Ventilation, diffusion, and perfusion.

Shortness of breath, chest tightness, a persistent cough, and wheezing during physical activity. Sudden weight loss can also be a symptom of cancer.

Final Human Gas Exchange Quiz

Question

The lungs are specifically adapted for __________.

Show answer

Answer

Gas exchange

Show question

Question

Why do humans need oxygen?

Show answer

Answer

Oxygen is used in aerobic respiration to generate ATP.

Show question

Question

Why do humans need to expire carbon dioxide?


Show answer

Answer

Carbon dioxide is produced as a by-product of aerobic respiration. Carbon dioxide needs to be removed as its buildup is toxic to cells.

Show question

Question

What is the trachea?


Show answer

Answer

The trachea is the main airway of the lung. It is lined with ciliated epithelium and contains C shaped rings of cartilage that prevent it from collapsing.

Show question

Question

The trachea splits into two _________. 


Show answer

Answer

Bronchi

Show question

Question

Each bronchus branches off to _________.


Show answer

Answer

Bronchioles

Show question

Question

The bronchioles end in ___________.


Show answer

Answer

Alveoli or air sacs

Show question

Question

What are the 3 important adaptations of the human gas-exchange surface?


Show answer

Answer

The three most important adaptations are short diffusion distance, large surface area, and a maintained steep concentration gradient.

Show question

Question

Give two examples of COPD.


Show answer

Answer

Chronic bronchitis, and emphysema.  

Show question

Question

What are the symptoms of lung cancer?


Show answer

Answer

Some symptoms of cancer include persistent cough, coughing up blood, weight loss, back pain, and difficulty breathing.

Show question

Question

Name some risk factors for COPD.


Show answer

Answer

  • Smoking (smoking is also known to increase the risk of developing lung cancer).
  • Air pollution.
  • Genetics (some people are genetically more likely to develop lung disease while some other people are less likely).
  • Infections (frequent chest infections are known to increase the risk of developing COPD).
  • Occupation (working with harmful chemicals and gases also increase the risk of COPD and lung cancer)

Show question

Question

Where does gas exchange occur in the human respiratory system?


Show answer

Answer

Gas exchange occurs in the alveoli of the lungs.

Show question

Question

What is the atopy triad? 


Show answer

Answer

It’s a triad of risk factors predisposing the development of asthma. They include a family history of asthma, allergies such as hay fever, and eczema.

Show question

Question

Is asthma a type of COPD?

Show answer

Answer

No

Show question

Question

What diseases are included in COPD?


Show answer

Answer

Emphysema and chronic bronchitis

Show question

Question

What substances can individuals smoke?

Show answer

Answer

Tobacco, cannabis, methamphetamine, heroin.

Show question

Question

Identify the 2 hormones that nicotine triggers the release of. 

Show answer

Answer

Adrenaline. Dopamine.

Show question

Question

What are the main causes of smoking?

Show answer

Answer

The main causes of smoking include anxiety, stress, depression, media influence and peer influence. 

Show question

Question

What fertility complications can tobacco smoke trigger?

Show answer

Answer

Males can have reduced sperm motility, sperm count and increase sperm DNA mutations. 


In females, tobacco smoke increases the likelihood of an ectopic pregnancy and interrupts the egg maturation process.

Show question

Question

Briefly describe ectopic pregnancies. 

Show answer

Answer

Ectopic pregnancies occur when a fertilised egg implants in tissues outside of the uterus and this includes the fallopian tubes, ovaries or the cervix.

Show question

Question

Identify the important protein needed for skin health.

Show answer

Answer

Collagen.

Show question

Question

How does smoking increase the chances of gum disease?

Show answer

Answer

Toxins in tobacco smoke damage the connective tissue in your teeth, making them prone to structural loss and deterioration.

Show question

Question

Identify three types of diseases caused by smoking.

Show answer

Answer

Any suitable answer is sufficient. Examples include atherosclerosis, COPD, emphysema, cancer, bronchitis, gum disease etc.

Show question

Question

Identify key processes in atherosclerosis pathogenesis.

Show answer

Answer

Any suitable answer is sufficient. Examples include: endothelial damage/dysfunction, increased cholesterol levels, inflammation, insulin resistance, changes in lipid metabolism etc.

Show question

Question

What are the clinical symptoms of emphysema?

Show answer

Answer

Chronic cough, excessive mucus secretion, shortness of breath.

Show question

Question

Define carcinogens. 

Show answer

Answer

Chemical agents that are capable of promoting cancer development.

Show question

Question

What are oncogenes?

Show answer

Answer

Oncogenes are genes that are involved in cell cycle and growth regulation.

Show question

Question

What would happen if significant mutations occur in oncogenes?

Show answer

Answer

The regulation of the cell cycle and growth will become uncontrollable. This contributes to cancer development.

Show question

Question

Identify the hormone involved in the fight-or-flight response. 

Show answer

Answer

Adrenaline. 

Show question

Question

Define mutations. 

Show answer

Answer

Mutations are changes in the nucleotide sequence of DNA.

Show question

More about Substance Exchange
60%

of the users don't pass the Human Gas Exchange quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Sign up to highlight and take notes. It’s 100% free.