Human Respiratory System: Function and Gas Exchange
Respiratory System
Humans obtain oxygen from the surrounding air and expel carbon dioxide. The respiratory system is responsible for circulating air between the body and the external environment. The channels through which air circulates are called airways:
- The upper respiratory tract includes the nose, pharynx, and larynx.
- Lower airways include the trachea, bronchi, and bronchioles, which end in blind sacs called alveoli.
All of the bronchioles, the alveoli, and the network of capillaries that surround them constitute the lungs. The respiratory system consists of the airways and lungs, which are housed in the chest cavity.
Air Travel in the Respiratory System
- Nose and mouth are the entry routes for air.
- From there, the air passes into the pharynx.
- Larynx – Inside it houses the vocal cords, which vibrate with the airflow and produce sounds.
- Trachea – A flexible tube that always remains open to allow air passage.
- Lungs – Two organs located in the thoracic cavity and protected by the ribs. Their base rests on the diaphragm, which separates the chest cavity from the abdomen.
- Bronchi and bronchioles – Similar to the trachea, these tubes branch like a tree. Initially, there are two, called bronchi. As they subdivide, they become thinner and are called bronchioles.
- Pulmonary alveoli – Small sacs at the end of the finest bronchioles. They are surrounded by numerous fine capillaries.
Gas Exchange
The air that enters and leaves the respiratory system contains oxygen and carbon dioxide, but in different proportions. However, the amount of nitrogen is the same in both. Unlike air, the blood that reaches the lungs is poorer in oxygen and richer in carbon dioxide than the blood that leaves, but both the entering and exiting blood contain the same amount of nitrogen.
The changes observed in the composition of air and blood in the lungs are due to the gas exchange that has occurred between them.
Gas exchange between air and blood takes place in the alveoli. Special features that facilitate the passage of gases are:
- The total surface area of all alveoli in the lungs is enormous.
- The alveoli are surrounded by many blood capillaries that circulate blood.
Nutrients: Source of Material and Energy
Nutrients are the raw material from which cells produce their own components. With them, cells replace those that are lost, grow, and produce new cells.
Nutrients are Cell Fuel
Other nutrients that reach the cells are used as fuel for cellular respiration. Glucose is the nutrient most used as fuel by cells. During cellular respiration, the following events occur:
- Oxygen consumption.
- Release of energy usable by cells.
- Production of carbon dioxide and water.
Lipids and proteins can also be used as fuel. Nutrients provide the fuel cells need for energy. Cells use this energy to carry out their functions.
Useful Energy for the Body
Our body needs the energy contained in nutrients to function; this energy is called chemical energy. Cellular respiration releases the chemical energy contained in nutrients, and this is transformed in the cells into three forms of energy:
- Chemical energy for muscle contraction, to produce new molecules.
- Thermal energy or heat to maintain body temperature.
Through cellular respiration, each type of organic nutrient provides the body with a certain amount of useful energy. In a balanced diet, carbohydrates should provide 55% of the energy, lipids 30%, and proteins the remaining 15%.