The endocrine system is a chemical messenger system. In humans, the main endocrine glands are the thyroid gland and the adrenal glands.

Endocrine glands

These are the glands of the endocrine system that secrete their products in which hormones move directly into spaces and then absorbed into the blood rather than a duct. The major glands of the endocrine system include the pineal gland, the pituitary gland, pancreas, testes, ovaries, thyroid gland, parathyroid gland, hypothalamus and adrenal glands.

Cells

cells make up the endocrine system are those cells that make up larger tissues and organs that function within and outside of the endocrine system.

Thyroid gland

Thyroid gland produces secrete T3 and T4 in response to elevated levels of TRH, which is produced by the hypothalamus, which further regulates the metabolic activity and rate of all cells, including cell growth and tissue differentiation.

Parathyroid gland

Epithelial cells of the parathyroid glands are richly supplied with blood and secrete parathyroid hormone (PTH). Parathyroid hormone acts on the kidney, bone, and the GI tract to increase calcium reabsorption and excretion of phosphate. Moreover, Parathyroid hormones convert Vitamin D to 1,25-dihydroxy, vitamin D3, which further stimulates calcium absorption in the GI tract.

Same as Adrenal glands, Pancreas, Gonads, Pituitary glands are discussed topics in the endocrine system.