Chapter 9: Gas exchange and smoking

Mammalian Gas Exchange System

  • Gas exchange takes place in the human thorax. This is a collection of organs and tissues in the chest cavity.
  • Air enters the body through the mouth or nose and quickly moves to the pharynx, or throat. From there, it passes through the larynx, or voice box, and enters the trachea.
  • The trachea is a strong tube that contains rings of cartilage that prevent it from collapsing.
  • Within the lungs, the trachea branches into a left and right bronchus. These further divide into smaller and smaller branches called bronchioles.
  • The smallest bronchioles end in tiny air sacs. These are called alveoli. They inflate when a person inhales and deflate when a person exhales.
  • During gas exchange oxygen moves from the lungs to the bloodstream. At the same time carbon dioxide passes from the blood to the lungs. This happens in the lungs between the alveoli and a network of tiny blood vessels called capillaries, which are located in the walls of the alveoli.
  • Here you see red blood cells traveling through the capillaries. The walls of the alveoli share a membrane with the capillaries. That’s how close they are. This lets oxygen and carbon dioxide diffuse, or move freely, between the respiratory system and the bloodstream.
  • Oxygen molecules attach to red blood cells, which travel back to the heart. At the same time, the carbon dioxide molecules in the alveoli are blown out of the body the next time a person exhales.
  • Gas exchange allows the body to replenish the oxygen and eliminate the carbon dioxide. Doing both is necessary for survival.

The structure and function of gas exchange system includes following:

  • Ciliated epithelial cells, goblet cells and mucous glands play vital roles in maintaining the health of the gas exchange system
  • Cartilage, smooth muscle, elastic fibers and squamous epithelial tissue all play important structural roles in maintaining the gas exchange system.


Smoking is a practice in which a substance is burned and the resulting smoke is typically breathed in to be tasted and absorbed into the bloodstream. Most commonly, the substance used is the dried leaves of the tobacco plant, which have been rolled into a small rectangle of rolling paper to create a small, round cylinder called a “cigarette“.

Tobacco Smoke

Tobacco smoke contains many chemicals that are harmful to smokers and non-smokers. Breathing even small amounts of tobacco smoke can be harmful. Of the more than 7,000 chemicals in tobacco smoke, at least 250 are known to be harmful, including hydrogen cyanide, carbon monoxide, and ammonia.

The main components of smoke are:

  • Tar which contains carcinogens

Tar contains most of the cancer-causing and other harmful chemicals found in tobacco smoke. When tobacco smoke is inhaled, the tar can form a sticky layer on the inside of the lungs. This damages the lungs and may lead to lung cancer, emphysema, or other lung problems.

  • Carbon Monoxide

They combine irreversibly with Haemoglobin, reducing the oxygen carrying capacity of the blood.

  • Nicotine

They stimulate the nervous system, increasing heart rate and blood pressure and stimulating vasoconstriction which reduces blood flow.

Lung Diseases

The term lung disease refers to many disorders affecting the lungs, such as asthma, COPD, infections like influenza, pneumonia and tuberculosis, lung cancer, and many other breathing problems. Some lung diseases can lead to respiratory failure. COPD (long term) Obstructive Pulmonary Diseases such as asthma, chronic bronchitis and emphysema are now common.

Chronic Bronchitis

Chronic bronchitis is long-term inflammation of the bronchi. It is common among smokers. People with chronic bronchitis tend to get lung infections more easily. They also have episodes of acute bronchitis, when symptoms are worse. Some people with chronic bronchitis get frequent respiratory infections such as colds and the flu. In severe cases, chronic bronchitis can cause weight loss, weakness in your lower muscles, and swelling in your ankles, feet, or legs.


Emphysema is one of the diseases that comprise COPD (chronic obstructive pulmonary disease). Emphysema develops over time and involves the gradual damage of lung tissue, specifically the destruction of the alveoli (tiny air sacs). The main cause of emphysema is long-term exposure to airborne irritants, including: Tobacco smoke, Marijuana smoke and Air pollution.

When emphysema develops, the alveoli and lung tissue are destroyed. With this damage, the alveoli cannot support the bronchial tubes. The tubes collapse and cause an “obstruction” (a blockage), which traps air inside the lungs. Too much air trapped in the lungs can give some patients a barrel-chested appearance.