Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 18

Mitochondria are small bean-/boat-shaped cellular organelles (Figure 1.1) responsible for releasing energy within cells. Each mitochondrion consists of an outer smooth membrane and a highly folded inner membrane. The prominent folds of the inner membrane are termed cristae and associated with these folds are the enzymes responsible for cellular respiration. Within the mitochondria, glucose, which is derived from carbohydrate-rich foods, is reacted with oxygen acquired by our respiratory system to release energy. This energy is then used to synthesise the energy storage molecule adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and free phosphate. This process results in the production of water and carbon dioxide as waste products. Since these biochemical reactions occur in the presence of oxygen, the process is referred to as aerobic respiration.

Glucose (C₆H₁₂O₆) + Oxygen (O₂) → Carbon dioxide (CO₂) + Water (H₂O) + Energy (38ATP)

In theory each molecule of glucose can yield 38 molecules of ATP but in reality this is never achieved, and a yield of around 30 ATPs per glucose molecule is typical. From a nursing point of view the simple equation above tells us something essential about human physiology: to generate the energy necessary to keep us alive we must eat (glucose) and breathe (oxygen). Indeed, a key role that nurses play is in ensuring that their patients receive adequate nutrition and that oxygenation of the blood is maintained.

If the supply of oxygen is significantly reduced then aerobic respiration becomes impossible and the cell is forced into anaerobic respiration. This is a far less efficient process that results in only 2 ATP molecules being produced per molecule of glucose. The incomplete breakdown of glucose also leads to the accumulation of the metabolic waste product lactic acid (lactate). Many people experience the effects of anaerobic respiration when they participate in hard manual labour or when lifting weights in a gym. When muscles are forced into anaerobic respiration the accumulation of lactic acid is usually experienced as soreness, fatigue and sometimes pain.