Life Sciences Glossary: Endocrine System (Hormonal Co-Ordination)

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Endocrine System (Hormonal Co-Ordination)

  • There are two integrating systems in the body, nervous and endocrine. Both are interdependent. The word ‘endocrine’ derives from a Greek word meaning ‘I separate within’ . The endocrine system achieves co-ordination and integration by transmitting information՚s through chemical messenger՚s called the hormones. Huxley called hormones as ‘chemical messengers’ . Hormones are also known as ‘autacoids’ . The word ‘hormone’ was introduced by starling in 1905. First hormone discovered was secretin by Bailys and Starling in 1903. The study of endocrine glands and hormones is ‘Endocrinology’ . The father of endocrinology is Thomas Addison. The first endocrine disease reported was Addison՚s disease (1855) caused by the destruction of adrenal cortex.
  • Hormones are secreted by ductless glands, released directly into blood. They regulate metabolism, growth, secretion, digestion, excretion, reproduction, etc. The gland with duct is called exocrine gland. Ductless gland is termed as endocrine gland. Pancreas is a mixed gland (heteroclite) , with exocrine and endocrine parts. Secretions of exocrine glands are called as enzymes whereas secretions of endocrine glands are called as hormones. Hormones have many similarities with enzymes.

They are:

  • Not obtained from food but synthesized by the body.
  • Easily soluble and diffusible.
  • Require and secrete in minute quantities.
  • Not stored (except thyroxin) and have high specificity.

Hormones differ from enzymes in following:

  • All enzymes are proteins, but hormones are chemically different.
  • Enzymes are mostly used locally; hormones are circulated in blood.
  • Enzymes catalyze metabolic reactions and are reusable, but hormones are completely used up in metabolism.

The tissue on which the hormones acts is known as ‘target tissue’ . When some hormones work together to control a process, this is called synergism e. g. , FSH and LH. But when two hormones first endocrine disease reported was Addison՚s disease (1855) caused by the destruction of adrenal cortex. There are some hormones – like substances, but not the products of endocrine glands. They are par hormones e. g. , Prostaglandins and Pheromones.

Major Mammalian Endocrine Organs and Their Products

Major Mammalian Endocrine Organs and Their Products
Endocrine OrganHormoneMajor Role of hormone
Anterior PituitaryGrowth hormonePromotes Growth of the body
ThyrotrophicStimulates thyroid
AdrenocorticotropicStimulate adrenal Cortex
Follicle Stimulating Hormone (FSH)Stimulates ovarian follicle development or testis development
Inteinising Hormone (IH)Stimulates development of Corpus lutein From ovarian Follicle; also Stimulates Progesterone or Testosterone Production
ProlactinPromotes Lactation or milk Production
Posterior PituitaryAntidiuretic hormone (ADH)Osmoregulation: stimulates water reabsorption in Kidney
OxytocinStimulates Contrition of Uterus during Labour
Hypo ThalamusVarious releasing hormone (RH)Controls secretion of hormones by the anterior Pituitary
ThyroidThyroxin and Tri-toothy-Ronnie CalcitoninIncrease metabolic rate Decreases blood Calcium level
ParathyroidParathyroid Hormone (PTH)Increases blood calcium level
Adrenal CortexGlucocorticoids, e. g. Cortisone Aldosteronecontrol metabolic rate and blood glucose Stimulates sodium Reabsorption in Kidney
Adrenal MedullaAdrenaline and noradrenalinePreparation of body for activity in Emergency
PancreasInsulin GlucagonDecreases blood Glucose Concentration Increases blood Glucose Concentration
KidneyRenin ErythropoietinPart of a blood Pressure control System Stimulates RBCs Production
OvaryEstrogensStimulate growth of endometrium Development of Female sexual Characteristics
ProgesteroneStimulates Maintenance of Uterus lining Development of Female sexual Characteristics
TestisTestosteroneDevelopment of Male sexual Characteristics

Prostaglandins

Prostaglandins were discovered from human semen in 1930. The name prostaglandin was introduced by Von Euler in 1973. The seminal vesicles are the chief source of prostaglandins in semen. The commonest prostaglandins are etc. The immediate precursors of PG in the body are essential unsaturated fatty acids, e. g. linoleic and arachidonic acids.

Pheromones

Pheromones are chemical messengers produced by animals, and released outside the body, hence called ‘ectohormones’ , The term ‘pheromone’ was proposed by Karson. Pheromones are also called ‘semi chemicals’ . Bombycid, a pheromones produced by silk moth, was the pheromous studied first.

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