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Adenosine is a key factor in regulating the body's sleep-wake cycle. [39] Adenosine levels rise during periods of wakefulness and lowers during sleep. Higher adenosine levels correlate with a stronger feeling of sleepiness , also known as sleep drive or sleep pressure. [ 40 ]
Adenosine diphosphate (ADP), also known as adenosine pyrophosphate (APP), is an important organic compound in metabolism and is essential to the flow of energy in living cells. ADP consists of three important structural components: a sugar backbone attached to adenine and two phosphate groups bonded to the 5 carbon atom of ribose .
Adenosine triphosphate (ATP) is a nucleoside triphosphate [2] that provides energy to drive and support many processes in living cells, such as muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all known forms of life, it is often referred to as the "molecular unit of currency" for intracellular energy transfer. [3]
Adenosine deaminase (also known as adenosine aminohydrolase, or ADA) is an enzyme (EC 3.5.4.4) involved in purine metabolism. It is needed for the breakdown of adenosine from food and for the turnover of nucleic acids in tissues. Its primary function in humans is the development and maintenance of the immune system. [5]
Caffeine keeps you awake by blocking adenosine receptors. Each type of adenosine receptor has different functions, although with some overlap. [3] For instance, both A 1 receptors and A 2A play roles in the heart, regulating myocardial oxygen consumption and coronary blood flow, while the A 2A receptor also has broader anti-inflammatory effects throughout the body. [4]
Bioenergetic systems are metabolic processes that relate to the flow of energy in living organisms. Those processes convert energy into adenosine triphosphate (ATP), which is the form suitable for muscular activity. There are two main forms of synthesis of ATP: aerobic, which uses oxygen from the bloodstream, and anaerobic, which does not.
In the peripheral nervous system, Schwann cells respond to nerve stimulation and modulate the release of neurotransmitters through mechanisms involving ATP and adenosine signalling. [37] In the retina and the olfactory bulb , ATP is released by neurons to evoke transient calcium signals in several glial cells such as Muller glia and astrocytes.
Fatigue and sedation after heavy exertion can be caused by excess adenosine in the cells which signals muscle fiber to feel fatigued. In the brain, excess adenosine decreases alertness and causes sleepiness. In this way, adenosine may play a role in fatigue from MADD. [4] Recovery from over-exertion can be hours, days or even months.