The body tightly regulates blood glucose levels as a part of metabolic homeostasis. ILCs play an important role in maintaining dietary stress, and metabolic homeostasis. Intestinal macrophages are critical in maintaining gut homeostasis. Leptin is a peptide hormone that affects homeostasis and immune responses. Vitamin D has a significant role in calcium homeostasis and metabolism. Insulin is a peptide hormone involved in glucose homeostasis within certain organisms. Mitochondria can transiently store calcium, a contributing process for the cell's homeostasis of calcium. Adenosine receptors play a key role in the homeostasis of bone. Alternatively-activated macrophages are important to maintaining glucose homeostasis (i.e., blood sugar regulation). Butyrate is extremely essential to host immune homeostasis. Ferroportin and hepcidin are critical proteins for the regulation of systemic iron homeostasis. These glands often secrete hormones which play an important role in maintaining homeostasis. For a detailed description of magnesium homeostasis and metabolism see hypomagnesemia. Calcitonin plays a role in calcium homeostasis. In addition, glucocorticoids play important roles in fetal development and body fluid homeostasis.