Hormones & receptor mediated regulation

 

Introduction

•    Word Hormone is derived from the Greek word hormon meaning urging on or to arouse to activity

•    Hormone can be defined as:

•    A chemical substance synthesized in an organ, gland, or body part and transported through the blood to another body part, chemically stimulating that part 

–  to increase or decrease functional activity or 

–  to increase or decrease secretion of another hormone

 

•    Body secretions are secreted by specialized tissue in different organs called gland to carryout normal body functions

•    Some gland secrete their secretions through ducts at the site of action

–  Such glands are called exocrine glands

–  E.g. Salivary glands secrete saliva

•    Other glands secrete their secretions directly into the blood stream

–  Endocrine glands or ductless glands

–  The secretions of endocrine glands are called hormones

•    Hormones are secreted by special system of ductless glands distributed throughout the body called endocrine gland system

–  Endocrine system is extremely diverse system

 

•    Major glands in endocrine system are:

–  Pituitary

–  Thyroid

–  Parathyroid

–  Adrenal

–  Pancreas – Gonades

•    Ovaries (in female only)

•    Testes (in male only)

•    Other glandular tissues also considered to secrete hormones are:

–  Kidneys

•    Angiotensis II is involved in vasodilation & BP regulation

•    Erythropoietin is secreted by JG cells of kidneys and regulates erythropoiesis (RBC maturation)

–  Thymus Gland:

•     Produce hormones that affect the formation of lymphocyte – Pineal Gland:

•     Produce hormones that antagonizes ACTH

•     Also produces glomerulptrophins that regulates the aldosterone secretion from adrenal gland – GI tract:

•     Glucagon-like peptide from small intestine

•     GI hormones regulates the gastric secretions and proper digestive function of alimentary canal

•     Some hormones are prepared in more than one tissue

–  E.g. skin, liver and kidneys are involved in calcitriol

• Hormones act on their target cells only

– Have particular receptors for that hormone