Схема. Пять фаз гомеостаза глюкозы. Перевести на русский язык = Translate into Russian . Модификация: Goodman H.M., Ed. Basic Medical Endocrinology, 4th ed., Acad. Press, 2009, 344 p., см.: Физиология человека: Литература. Иллюстрации.

Примечание:

Five phases of glucose homeostasis. The graph, based on observations of a number of individuals, illustrates glucose utilization in a 70 kg man who consumed 100 g of glucose and then fasted for 40 days. The complexity of carbohydrate metabolism in mammals is evident from the changes that occur on feeding and starvation. In the 1960s, George Cahill examined the glucose utilization of obese patients as they underwent therapeutic starvation. After an initial feeding of glucose, the subjects received only water, vitamins, and minerals. Cahill noted that glucose homeostasis (maintenance of constant levels in the circulation) proceeds through five phases. Figure 12.29, based on Cahill’s observations, summarizes the metabolic changes in the five phases. 1. During the initial absorptive phase (the first four hours), dietary glucose enters the liver via the portal vein and most tissues use glucose as the primary fuel. Under these conditions, the pancreas secretes insulin, which stimulates glucose uptake by muscle and adipose tissue via GLUT4. The glucose taken up by these tissues is phosphorylated to glucose 6-phosphate, which cannot diffuse out of the cells. Liver cells also absorb glucose and convert it to glucose 6-phosphate. Excess glucose is stored as glycogen in liver and muscle cells. 2. When the dietary glucose is consumed, the body mobilizes liver glycogen to maintain circulating glucose levels. In the liver, glucose 6-phosphatase catalyzes the hydrolysis of glucose 6-phosphate to glucose, which exits the liver via glucose transporters. Glycogen in muscle (which lacks glucose 6-phosphatase) is metabolized to lactate to produce ATP for contraction; the lactate is used by other tissues as a fuel or by the liver for gluconeogenesis. 3. After about 24 hours, liver glycogen is depleted, and the only source of circulating glucose is gluconeogenesis in the liver, using lactate, glycerol, and alanine as precursors. Fatty acids mobilized from adipose tissue become an alternate fuel for most tissues. The obligatory glycolytic tissues continue to use glucose and produce lactate, which is converted to glucose in the liver by the Cori cycle; this cycle makes energy, not carbon, from fatty acid oxidation in the liver available to other tissues. 4. Gluconeogenesis in the liver continues at a high rate for a few days, then decreases. As starvation progresses, gluconeogenesis in the kidney becomes proportionately more significant. Proteins in peripheral tissues are broken down to provide gluconeogenic precursors. In this phase, the body adapts to several alternate fuels. 5. In prolonged starvation, there is less gluconeogenesis and lipid stores are depleted. If refeeding does not occur, death will follow. On refeeding, metabolism is quickly restored to the conditions of the fed state. p. 380