hoprmones

Introduction to the Human Endocrine System

This page is a basic introduction to the human endocrine system.

General Introductory Notes:

Basic summary notes about the endocrine system include:

• Hormones are 'chemical messengers'.
• Hormones have 'target organs'.
• Endocrine glands are ductless glands that secret hormones directly into the blood.

Functions of Hormones:

1. Hormones help to regulate:
   
   • Volume and chemical composition of Extra-Cellular Fluid (ECF).
   • Metabolism - see also metabolic rate
   • Biological Clock (Circadian Rhythms)
   • Glandular Secretions
   • Contraction of smooth and cardiac muscle fibres
   • Some immune system activities.
     
     
2. Hormones control growth and development.
   
   
3. Hormones govern the opertation of reproductive systems.

Hypothalamus

Releases hormones that regulate the anterior pituitary; includes hormones from the posterior pituitary (see posterior pituitary)

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Posterior pituitary gland

Oxytocin stimulates contraction of uterus and mammary gland cells; Antidiuretic hormone (ADH) promotes retention of water by kidneys

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Anterior pituitary gland

Growth hormone (GH) stimulates growth (especially bones) and metabolic functions
Prolactin (PRL) stimulates milk production and secretion
Follicle-stimulating hormone (FSH) stimulates production of ova and sperm
Luteinizing hormone (LH) stimulates ovaries and testes
Thyroid-stimulating hormone (TSH) stimulates thyroid gland
Adrenocorticotropic hormone (ACTH) stimulates adrenal cortex to secrete glucocorticoids

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Thyroid gland

Triiodothyronine (T3) and thyroxine (T4) stimulate and maintain metabolic processes
Calcitonin lowers blood calcium level

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Parathyroid glands

Parathyroid hormone (PTH) raises blood calcium level

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Pancreas

Insulin lowers blood glucose level
Glucagon raises blood glucose level

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Adrenal medulla

Epinephrine and norepinephrine raise blood glucose level; increase metabolic activities; constrict certain blood vessels

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Adrenal cortex

Glucocorticoids raise blood glucose level
Mineralocorticoids promote reabsorption of Na+ and excretion of K+ in kidneys

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Testes

Androgens support sperm formation; promote development and maintenance of male secondary sex characteristics

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Ovaries

Estrogens stimulate uterine lining growth; promote development and maintenance of female secondary sex characteristics
Progestins promote uterine lining growth

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Pineal gland

Melatonin involved in biological rhytms