Bioenergetics: Breathing Overview

Respiration is a set of metabolic reactions that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products.
The reactions involved in respiration are catabolic reactions, which break down large molecules into smaller ones, releasing energy in the process.

Aerobic Respiration

Aerobic respiration is a type of respiration that requires oxygen and is the most efficient way to produce ATP.
The overall equation for aerobic respiration in humans is: glucose + oxygen -> carbon dioxide + water + energy.
Aerobic respiration occurs in four stages: glycolysis, the link reaction, the Krebs cycle, and oxidative phosphorylation.

Anaerobic respiration does not require oxygen and happens when no oxygen is available for the cell.
The overall equation for anaerobic respiration in humans is: glucose -> lactic acid + energy.
Unlike aerobic respiration, anaerobic respiration produces lactic acid, which can lead to muscle fatigue.

The respiratory system in humans includes the airways, lungs, and respiratory muscles that mediate the movement of air into and out of the body.
Within the respiratory system, the breathing process is carried out through inhaling and exhaling.
During inhalation, the diaphragm contracts and ribcage expands, reducing pressure inside the chest and drawing in air.
During exhalation, the diaphragm relaxes and the ribcage contracts, increasing the pressure and pushing out air.

In the lungs, oxygen in the inhaled air diffuses into the bloodstream, and carbon dioxide in the blood diffuses into the air in the lungs to be exhaled.
The lungs contain millions of alveoli, tiny air sacs, which provide a large surface area for gas exchange.
The thin walls of the alveoli and surrounding capillaries, the moist lining of the alveoli, and the difference in concentration of gases in the alveoli and the blood all facilitate efficient gas exchange.

The oxygen obtained by the respiratory system is used by cells for aerobic respiration, producing energy in the form of ATP, necessary for physiological processes.
The carbon dioxide produced as a waste product of respiration is removed from the body by the respiratory system during exhalation, maintaining the balance of gases in blood and tissues.