Metabolism

• Metabolism: fate of digested and absorbed nutrients
• Metabolism is the sequence, or succession, of chemical reactions taking place in living organisms.
• Both catabolic and anabolic reactions are almost always occurring simultaneously. The rates of the reactions differ. E.g. growing animals are in an anabolic state.
• Hormonal regulation of the metabolic state:

  • Blood glucose control instructs the secretion of insulin or the release of glycogen
  • Maintenance of a minimal and constant source of glucose for energy is necessary
• Glucose is used for energy throughout the animal body and tissues. A drop in blood glucose happens naturally and will trigger changes in the endocrine secretions that drive postabsorptive metabolism.
• Metabolic balance from anabolism to catabolism is done through blood glucose control.
• During the postabsorptive state glucagon can stimulate glycogenolysis and gluconeogenesis which will either increase or decrease blood glucose levels.
• Maintenance of blood glucose level is important to neuronal function. Neurons cannot use fatty acids for energy so they rely on glucose.
• Between meals and during fasting, adipose tissues release fatty acids and glycerol.
• Circulating fatty acids are taken to the liver and transformed into ketones, another cellular energy substrate.
• Elevated liver ketones are markers for energy malnutrition.
• Glucocorticoids have an impact on gluconeogenesis in the liver and lipolysis of fatty acids.
• Growth hormone release is stimulated by decreases in blood glucose and has an impact on lipolysis.
• There is less glucose-yielding carbohydrate digestion in the ruminant small intestine. Most carbs are fermented in the rumen into short-chain volatile fatty acids. Most VFAs are directly absorbed through the rumen wall.
• Ruminants combat their low glucose levels by consistently undergoing gluconeogenesis.