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Week 6: Endocrine/Reproductive

Endocrinology

Updated by Tracey 16 August 02

The endocrine/hormonal system controls metabolic functions such as chemical reactions, substance trasport, growth and secreation. Hormones are chemicals secreted into the internal body fluids that exert control on cells in the body.

Two Basic Hormone Classifications:

Local: have specific local effects. ex: ACH.
General: secreted by endocrine glands into the blood to reach distant target tissues, or, in the case of a few such as GH and TH, many or all cells.

Endocrine Glands and their secretions include...

Anterior Pituitary: growth hormone; adrenocorticotropin; thyroid-stimulating hormone; follicle-stimulating hormone; luteinizing hormone; prolactin.
Poterior Pituitary: antidiuretic hormone/vasopressin; oxytocin.
Adrenal Cortex: cortisol; aldosterone.
Thyroid Gland: thyroxine; triiodothyronine; calcitonin.
Pancreas (Islets of Langerhans): insulin; glucagon.
Ovaries: estrogens; progesterone.
Testes: testosterone.
Parathyroid: parathormone.
Placenta: human chorionic gonadotropin; estrogens; progesterone; human somatomammotropin.

Hormonal Action

Endocrine hormones typically first combine with hormone receptors, usually to activate, but sometimes to inactivate it. Activation can alter membrane permeability as with muscle fibers, or activate...

Cyclic AMP: hormone's receptor protrudes into cell's cytoplasm, changing cytoplasmic ATP into cyclic 3',5'-adenosine monophosphate (cyclic AMP), which activates other enzymes, typically in cascade fashion, so very little hormone stimulates more enzymes. Depending on the target cell, cyclic AMP can, among other things...
- initiate synthesis of specific intracellular chemicals
- cause a muscle to contract or relax
- initiate cell secretion
- alter cell permeability
Calmodulin response to hormones opening CA²⁺ channels is similar. CA²⁺ binds with calmodulin protein, which also effects many enzymes. Calmodulin acts with myosin in smooth muscle to cause its contraction.
Protein Synthesis: steroid hormones bind with receptors in the cytoplasm, and are transported into the nucleus, where they activates genes to create mRNA.