We know that systemic arteries carry oxygenated blood away from the heart and that these vessels pass through tissues, allowing oxygen to diffuse into the tissues and carbon dioxide to diffuse out into the bloodstream. We also know that veins carry blood back to the heart, which by this time is oxygen-poor due to its gas exchange with the tissues of the body. The partial pressure of oxygen in veins must be lower than it is in arteries, since the veins carry deoxygenated blood.

The remaining statements regarding gas exchange are true.

Hemoglobin is the main oxygen carrier in the human body. Each hemoglobin protein is able to carry four oxygen molecules. As the hemoglobin travels through the blood vessels of the body, the oxygen is released to tissues and used in the electron transport chain.

If oxygen is unable to bind to hemoglobin, our bodies cannot carry the needed oxygen to the tissues of the body. This can occur when carbon monoxide displaces oxygen from hemoglobin.

Oxygen is taken up from the blood by all cells to be used in ATP production. The process of cellular respiration (energy production) creates carbon dioxide as a waste product, which, if accumulated, can cause the blood to become dangerously acidic. Gases in the lungs diffuse passively into or out of the air entirely based on where the concentration is lowest. Thus, oxygen levels in the blood must be lower in concentration than those in the lungs in order for oxygen to enter the blood, and carbon dioxide levels in the blood must be higher than those in the lungs order for carbon dioxide to exit.

Hyperventilation will result in the expiration of more . It can be deduced that a greater amount of expired  will cause the above equation to shift to the left. The shifting of the equation to the left will further promote the conversion of  and  to  and .  Since the body uses  as a buffer, there will be a greater quantity of the bicarbonate in the body than . When the equation shifts to the left, the  will deplete at a faster rate and result in a higher  to  ratio. A higher  to  ratio will cause the body's blood to become more basic (increase in pH); therefore, hyperventilation increases blood bascicity.

During inspiration, the lungs expand as the diaphragm contracts and internal intercostal muscles relax. As the volume of the thoracic cavity increases, its pressure decreases. This creates a pressure gradient, driving air from an area of high pressure (the environment) into the area of low pressure (the lungs).

When you are not breathing, your respiratory system cannot perform its function. Unwanted gases, such as carbon dioxide, cannot be removed from the system and necessary gases, such as oxygen, cannot enter the system. This causes a buildup of carbon dioxide in the body, which leads to acidosis. Carbon dioxide is converted to carbonic acid via carbonic anhydrase. This carbonic acid builds in the blood, lowering its pH.

Air enters the body of most terrestrial vertebrates through the nose or the mouth; the air then passes through the trachea to narrower tubes called the bronchi, to still narrower tubes called the bronchioles. The bronchioles "dead end" into structures called alveoli, which is where gas exchange of oxygen and carbon dioxide takes place with the blood in adjacent capillaries.

The lungs contain the bronchioles, the alveoli, and part of the bronchi. The trachea carries inhaled air into the bronchi, but it is not actually enclosed by the bronchi— the lungs only enclose structures that arise after the bronchi branch away from the trachea.

By folding the respiratory surface into the body, terrestrial animals increase the humidity of the environment of the respiratory surface, which will minimize evaporation and maintain moisture. Note that water loss via evaporation and perspiration accounts for the majority of water loss in terrestrial mammals.

Smooth muscle is typically innervated by the sympathetic nervous system. Because arterioles have more smooth muscle per volume, they are able to respond to sympathetic innervation more efficiently than larger arteries. As a result, the smaller arteries are used to regulate blood pressure as well as reroute blood direction by adjusting arteriole diameter accordingly.