General hormones are the hormones released by the endocrine system. They are released into the body fluids, the blood, and may affect many cell types in a tissue and body fluids.
Exocrine glands include sweat, oil, mucous, and digestive glands. Endocrine glands release hormones directly into body fluids. The pancreas acts as both exocrine and endocrine gland. The effects of of the endocrine system tend to be slower, less direct, and longer lasting than those of the nervous system.
All hormones act by binding to proteins called receptors. Each receptor is highly specific for its hormone. The effects of the endocrine system are to alter metabolic activities, regulate growth and development, and guide reproduction. Many endocrine glands are stimulated by neurons to secrete their hormones.
Hormones exist in three basic chemistry types: 1) peptide hormones 2) steroid hormones 3) tyrosine derivatives
Peptide Hormones are derived from peptides. All peptide hormones are manufactured in the rough ER. Peptide hormones are water soluble, and thuse move freely through the blood, but have difficulty diffusing through the cell membrane of the effector. The effector is the target cell of the hormone; the cell the hormone is meant to affect. Instead of diffusing through the membrane, peptide hormones attach to a membrane-bound receptor. The receptor may itself act as an ion channel increasing membrane permeability to a specific ion, or the receptor may activate or deactivate other intrinsic membrane proteins also acting as ion channels.
Another effect of the hormone binding to the receptor is to activate an intracellular second mesenger such as cAMP or cGMP. The second messenger activates or deactivates enzymes and or ion channels and often creates a cascasde of chemical reactions that amplifies the effect of the hormone.
List of Peptide Hormones:
the anterior pituitary hormones: FSH, LH, ACTH, hGH, TSH, Prolactin
the posterior pituitary hormones: ADH and oxytocin
the parathyroid hormone: PTH
the pancreatic hormones: glucagon and insulin
Steroid Hormones: are often chemically similar to cholestrol. They are formed in the smooth ER and the mitochondria. Since they are lipids, steroids typically require a protein transport molecule in order to dissolve into the blood stream. Steroids diffuse through the cell membrane of their effector. Once inside the cell, they combine with a receptor in the cytosol. The receptor transports the steroid into the nucleus, and the steroid acts at the transcription level.
List of important steroid hormones:
the glucocorticoids and mineral corticoids of the adrenal cortex: cortisol and aldosterone
the gonadal hormones: estrogen, progesterone, testosterone
The tyrosine derivatives are: the thyroid hormones T3, T4 and the catecholamines formed in the adrenal medulla: epinephrine and norepinephrine. All tyrosine derivative hormones are formed by enzymes in the cytosol or on the rough ER.
Thyroid hormones are lipid soluble and must be carried in the blood by plasma protein carriers. They then bind to receptors inside the nucleus. Their high affinity to their binding proteins in the plasma and in the nucleus create a latent period in their response and increase the duration of the effect of thyroid hormones. Epinephrine and norepinephrine are water soluble.