Hormone (amines and peptide or protein hormones) are water-soluble and act on the surface of target cells via second messengers; steroid hormones, being lipid-soluble, move through the plasma membranes of target cells (both cytoplasmic and nuclear) to act within their nuclei. Hormone secretion may occur in many tissues. Endocrine glands are the cardinal example, but specialized cells in various other organs also secrete hormones. Hormone secretion occurs in response to specific biochemical signals from a wide range of regulatory systems. For instance, serum calcium concentration affects parathyroid hormone synthesis; blood sugar (serum glucose concentration) affects insulin synthesis; and because the outputs
Glucose paradox small absorption of glucose. After the body's digestion of carbohydrates and the entering the circulatory system in the form of glucose, some will be absorbed directly into the muscle tissue and will be converted into lactic acid throughout the anaerobic energy system, rather than going directly to the liver and being converted into glycogen. The lactic acid is then taken and converted by the liver, forming the material for liver glycogen. The majority of the body's liver glycogen is produced indirectly, rather than directly from glucose in the blood. Under normal physiological conditions, glucose is a poor precursor compound and