Internal respiration is a biological process where the body’s cells utilize oxygen and produce carbon dioxide. This process is distinct from the act of breathing, focusing instead on the cellular level. It represents the mechanism by which the body converts chemical energy from food into a usable form for sustaining life functions. This cellular activity is constant and provides the necessary energy currency for all bodily operations.
The Cellular Site of Respiration
Internal respiration occurs within the body’s cells. Within these cells, specialized compartments called mitochondria are the main sites for this energy-releasing process. Mitochondria are often referred to as the “powerhouses” of the cell because of their central role in generating cellular energy. All cells that require oxygen for their metabolic functions perform this type of respiration, making it a universal process.
The Energy Production Process
Internal respiration involves biochemical reactions. During this process, fuel molecules, primarily glucose, are broken down in the presence of oxygen. This breakdown releases stored chemical energy, which is then captured and converted into adenosine triphosphate (ATP). ATP acts as the main energy currency that powers nearly all cellular activities, from muscle contraction to nerve impulse transmission. Carbon dioxide and water are generated as byproducts.
Transport System for Respiration
For internal respiration to occur, a transport system is necessary to deliver oxygen and fuel to the cells and remove waste products. The circulatory system is key to this exchange. Oxygen-rich blood, pumped from the heart, travels through arteries and arterioles, eventually reaching tiny blood vessels called capillaries that permeate all tissues. Oxygen diffuses from the blood into cells across capillary walls. Simultaneously, carbon dioxide, produced by the cells, moves from the cells into the capillaries to be carried away by the blood.
Internal vs. External Respiration
Internal and external respiration are distinct aspects of the respiratory process. External respiration refers to the exchange of gases between the lungs and the bloodstream. This includes the inhalation of oxygen into the lungs and its diffusion into the blood, as well as the release of carbon dioxide from the blood into the lungs for exhalation. Internal respiration, conversely, is the gas exchange and energy generation within the body’s cells and tissues. This cellular process ensures that oxygen reaches its final destination for metabolic use, while carbon dioxide is collected for elimination.