The pharynx is shared by the respiratory and digestive systems, and is separated into three sections. The nasopharynx is primarily used for respiration, while the laryngopharynx is primarily used for digestion; it is inferior to the epiglottis and connects to the esophagus. The oropharynx is shared by pathways for both respiration and digestion. 

The trachea and alveoli are exclusively used for respiration, while the esophagus and pyloric sphincter are exclusively used for digestion. Alveoli are the site of gas exchange in the lungs. The pyloric sphincter connects the stomach to the small intestine.

If the volume of the lungs increases, the air pressure inside the lungs decreases. Boyle's Law can be used to describe the process of human breathing. It states that for fixed mass, pressure and volume are inversely proportional.

If the volume increases, then pressure must decrease in order for these equations to hold true. This is responsible for the mechanics of inspiration. As the diaphragm contracts, the volume of the lungs increases and creates a negative pressure differential with the environmental atmosphere. This pressure differential draws air into the lungs through the nose and mouth.

The correct answer is a negative pressure change within the pleural space. When the diaphragm and intercostal muscles contract, they expand the chest cavity creating a higher volume of space within the pleural space. As volume within this space increased, the pressure responds by decreasing. This drop in pressure within the pleural space causes air from outside the body (high pressure) to low pressure (within the chest and the lungs).

Oxygen will attach to hemoglobin and be delivered to the body's tissues via gas exchange. In order to detach from hemoglobin, there needs to be a decrease in the partial pressure of oxygen. The oxygen pressure in the lungs is much higher than in the body. This is why oxygen attaches to hemoglobin in the lungs. As the hemoglobin goes to the body's tissues, oxygen pressure decreases. This causes the oxygen to detach and be diffused into the tissues.

There are three main ways that carbon dioxide can be carried in the blood: it can be in solution independently, it can be turned into a bicarbonate ion via the enzyme carbonic anhydrase, or it can be attached to hemoglobin and other proteins. Carbon dioxide transport as bicarbonate ions is ten times more common than any other method.

In the lungs, the bicarbonate ion will undergo the reverse reaction experienced in the tissues, and dissociate into carbon dioxide and water. This allows the carbon dioxide gas to be exhaled.

There are a few factors which can decrease the affinity of hemoglobin for oxygen: increased acidity, increased temperature, and carbon dioxide pressure. As carbon dioxide levels increase, hemoglobin's affinity for oxygen decreases. This means that it will release oxygen more readily in areas of high carbon dioxide levels, such as in the body's tissues. Since carbon dioxide is a product of cell metabolism, regions with high carbon dioxide content are likely very active in metabolism. This metabolism requires oxygen for the electron transport chain; thus, it is beneficial for hemoglobin to release oxygen in these regions in order to promote further metabolism.

Normal blood pH is about 7.4 in most tissues (it is a bit lower in veins since they carry waste products, which are acidic). To get back to the physiological set point of pH = 7.4, we want to remove the acid from the blood. The major blood buffer system is shown in the following equation: 

As we know, carbon dioxide is one of the major byproducts of respiration, and is considered waste for our bodies. Combined with water and catalyzed by carbonic anhydrase, it is converted into carbonic acid. Carbonic acid is a weak acid and will partially dissociate into hydrogen ions and bicarbonate ions. Thus, overall, carbon dioxide and water yields acid (hydrogen ions). As a result, excess carbon dioxide in the blood will lower the pH.

In order to increase the pH, we must stop this equation from proceeding in the forward direction; thus, (remember Le Chatelier's principle) we must remove carbon dioxide from the left side. This will push the reaction in the reverse direction, quenching hydrogen ions (acid) and removing them from the blood, increasing blood pH back to normal.

Since we want to get rid of excess carbon dioxide, we breathe faster. Oxygen does not have any effect on blood pH. Furthermore, the atmospheric oxygen level (21%) is plenty for our bodies to utilize, as when we exhale there is about 15% oxygen left over, meaning we only use about 25% of the oxygen we breathe (this is why CPR works!).

Surfactant coats each alveolus, and is a detergent that lowers surface tension that prevents the alveolus from collapsing on itself. Also, decreasing surface tension facilitates the diffusion of gasses across the alveolar epithelium.

Cyanosis in the body occurs due a reduced hemoglobin concentration that is at least 6-8 grams of hemoglobin per deciliter of blood lower than the normal hemoglobin range for men and women.

Hemoglobin is what carries oxygen in the blood. The blood then carries this oxygen to various tissues in the body. When hemoglobin is low, oxygen is not delivered fast and efficiently enough to the appropriate tissues of the body, thus turning them visibly blue (cyanosis). 

The man has above normal residual lung volume , as the normal residual volume (RV) for an adult male of average size is 1.2 liters. Causes for such high residual lung volumes in a man can occur from lung diseases, such as emphysema, that cause obstruction of the lungs and trapping of air.