Humans need food to produce energy. The complex process is called metabolism, which involves several stages:
-
Digestion:
- Mouth: Chewing breaks down food into smaller pieces, and enzymes in saliva begin to digest carbohydrates.
- Stomach: Gastric juices and enzymes further break down proteins and mix food into a semi-liquid form called chyme.
- Small Intestine: Enzymes from the pancreas and bile from the liver continue to digest carbohydrates, proteins, and fats. Nutrients are absorbed through the intestinal walls into the bloodstream.
-
Absorption:
- Nutrients such as glucose (from carbohydrates), amino acids (from proteins), and fatty acids and glycerol (from fats) are absorbed into the bloodstream and transported to cells.
-
Cellular Respiration:
- Inside cells, nutrients are used to produce energy through cellular respiration, which occurs in the mitochondria. This process involves three main stages:
- Glycolysis: Glucose is broken down into pyruvate, producing a small amount of ATP (adenosine triphosphate) and NADH (an electron carrier).
- Krebs Cycle (Citric Acid Cycle): Pyruvate is further broken down, producing more NADH, FADH₂ (another electron carrier), and a small amount of ATP.
- Electron Transport Chain (ETC): NADH and FADH₂ donate electrons to the ETC, creating a flow of electrons that drives the production of a large amount of ATP through oxidative phosphorylation. Oxygen is the final electron acceptor, forming water.
-
Energy Utilization:
- ATP produced during cellular respiration is used as the primary energy currency of the cell. It powers various cellular processes, including muscle contraction, cell division, and biochemical reactions.
-
Storage:
- Excess nutrients are stored for future use. Glucose can be stored as glycogen in the liver and muscles, while excess fatty acids are stored as triglycerides in adipose (fat) tissue.
This metabolic process ensures that the body has a continuous supply of energy to perform vital functions and maintain homeostasis.
[Top]