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Medicine LibreTexts

16.12: Summary

  • Hormones are chemicals that are released into the blood by endocrine glandsi.e. Glands with no ducts. Hormones act on specific target organs that recognize them.
  • The main endocrine glands in the body are the hypothalamus, pituitary, pineal, thyroid, parathyroid and adrenal glands, the pancreas, ovaries and testes.
  • The hypothalamus is situated under the cerebrum of the brain. It produces or controls many of the hormones released by the pituitary gland lying adjacent to it.
  • The pituitary gland is divided into two parts: the anterior pituitary and the posterior pituitary.
  • The anterior pituitary produces:
  • Growth hormone that stimulates body growth
  • Prolactin that initiates milk production
  • Follicle stimulating hormone (FSH) that stimulates the development of ova
  • Luteinising hormone (LH) that stimulates the development of the corpus luteum
  • Plus several other hormones
  • The posterior pituitary releases:
  • Antidiuretic hormone (ADH) that regulates water loss and raises blood pressure
  • Oxytocin that stimulates milk “let down”.
  • The pineal gland in the brain produces melatonin that influences sexual development and breeding cycles.
  • The thyroid gland located in the neck, produces thyroxine, which influences the rate of growth and development of young animals. Thyroxine consists of 60% iodine. Lack of iodine leads to goitre.
  • The parathyroid glands situated adjacent to the thyroid glands in the neck produce parathormone that regulates blood calcium levels and the excretion of phosphates.
  • The adrenal gland located adjacent to the kidneys is divided into the outer cortex and the inner medulla.
  • The adrenal cortex produces:
  • Aldosterone that regulates the blood concentration of sodium and potassium
  • Cortisone and hydrocortisone that affect glucose, protein and fatmetabolism
  • Male and female sex hormones
  • The adrenal medulla produces adrenalin responsible for the flight, fright, fightresponse that prepares animals for emergencies.
  • The pancreas that lies in the first bend of the small intestine produces insulinthat regulates blood glucose levels.
  • The ovaries are located in the lower abdomen produce 2 important sex hormones:
  • The follicle cells of the developing ova produce oestrogen, which controls the development of the mammary glands and prepares the uterus for pregnancy.
  • The corpus luteum that develops in the empty follicle after ovulation produces progesterone. This hormone further prepares the uterus for pregnancy and maintains the pregnancy.
  • The testes produce testosterone that stimulates the development of the male reproductive system and sexual characteristics.

Contributors

  • Ruth Lawson (Otago Polytechnic; Dunedin, New Zealand)