Endocrinology Hormone and endocrine system Functions of hormones Functional types of hormones Chemical types of hormones Production and secretion of hormone Hormonal regulation by hypothalamus

Hormone and endocrine system The endocrine system consists of a number of ductless glands that produce highly active chemical regulators called hormone. These chemical messengers are secreted into blood stream and carried to target organs elsewhere where they act upon specific receptor cells. The protein and polypeptide hormones( from hypothalamus, anterior and posterior pituitary, pancreas, parathyroid) are soluble in plasma but steroids (from adrenal cortex, and gonads) and the iodinated thyronine derivatives (from the thyroid) are poorly soluble; they require specific plasma transport proteins.

Functions of hormones Hormones regulate metabolism and assist in continuation of the species by influencing a wide variety of biological system to perform the following functions: To maintain a constant internal environmental in the body fluids (homeostasis). To regulate the growth and development of the body as whole. To promote sexual maturation, maintain sexual rhythms, and facilitate the reproductive process. To regulate energy production, stabilize the metabolic rate. To help the body adjust to stressful or emergency situation.

Functional types of hormones There are 3 functional types of hormones: Releasing factors (RF) from the hypothalamus. Act only upon the anterior pituitary. Tropic hormones that stimulate the growth and activity of other endocrine glands. Act only upon other endocrine glands. Nontropic or effector hormones which are secreted by all endocrine glands. The target cells of the effector hormone are the tissue cells upon which these hormones exert their metabolic effects.

Chemical types of hormones Hormones are of 5 general chemical types: Glycoproteins composed of 2 dissimilar chains. (TSH, FSH, LH) Proteins or long-chain polypeptides. (GH, ACTH, insulin, glucagon) Short-chain polypeptides.(releasing factor, GHRF) Steroids. (cortisol, estrogen, progesterone) Amino acids. (epinephrine, thyroxine).

Production and secretion of hormone The production and secretion of hormone by endocrine gland may be initiated by one or more of the following: Stimulation of the cerebral cortex by: thoughts, stress, emotion, periodic rhythms that may be daily, monthly.. Change in plasma concentration of particular ions. Secretion of tropic hormones. Variation in blood osmolality. Release of hormone in gastrointestinal tract in the presence of various foods (food in stomach stimulates gastrin secretion by stomach)

Hormonal regulation by hypothalamus