Endocrine system

• The endocrine system

  A set of hormone secreting glands within the body of an animal
• Endocrine gland

  A ductless organ that makes and secretes specific chemical messengers (hormones) into the blood
• Exocrine gland

  Has a duct that is used to carry the exocrine gland's section to the outside of the body e.g sweat gland
• Hormone

  Chemical messenger produced by an endocrine gland and carried by the blood to another part of the body where it has a specific effect
• Chemical nature of hormones

  Protein
• Some hormones are lipid based
• Hormones are slow to act and remain active for long periods of time
• Gland

  • Pituitary

  Location

  • Below the brain

  Hormone

  • Growth hormone

  Function

  • Causes formation of proteins - growth of bones
• Gland

  • Thyroid

  Location

  • Neck

  Hormone

  • Thyroxine

  Function

  • Stimulates metabolism
• Gland

  • Parathyroid

  Location

  • Embedded within thyroid

  Hormone

  • Parathyroid hormone

  Function

  • Increase blood calcium levels
• Gland

  • Pancreas (islets of Langerhans)

  Location

  • Under the stomach

  Hormone

  • Insulin

  Function

  • Controls blood sugar levels
• Gland

  • Adrenal

  Location

  • Over the kidneys

  Hormone

  • Adrenaline

  Function

  • Fight or flight response
• Gland

  • Ovary

  Location

  • Lower abdomen

  Hormone

  • Oestrogen + progesterone

  Function

  • Controls menstrual cycle
• Gland

  • Testes

  Location

  • Scrotum

  Hormone

  • Testosterone

  Function

  • Triggers sperm production
• Gland

  • Hypothalamus

  Location

  • Brain

  Hormone

  • ADH (anti diuretic hormone - cause the collecting duct to become more permeable to water)

  Hormone

  • Causes water to be reabsorbed in the kidneys (controls osmoregulation)
• Gland that is both endocrine and exocrine

  Pancreas
• Pancreas- exocrine function

  Production of enzymes (eg amylase)

  These pass to the duodenum (small intestine digestion) through ducts
• Pancreas endocrine function

  • Islets of Langerhans (cells) produce insulin, which is carried away by the bloodstream
  • Insulin regulates blood glucose levels - causes cells to absorb glucose from the blood
• Thyroxine deficiency

  Symptoms

  • Cretinism (childhood) - poor growth and brain development
  • Myxoedema (adults) - fatigue, reduced resistance to disease, weight gain, dry skin
  • A severe lack of iodine in the diet can cause hypothyroidism

  Corrective measures

  • Thyroxine tablets or iodine -rich diet (iodine is needed for thyroxine to work properly)
• Thyroxine excess

  Symptoms

  • Graves disease - increased metabolism and appetite, weight loss, general restlessness

  Corrective measures

  • Surgically remove part of the gland, use radioactive iodine to destroy some of the gland
• Hormone supplement examples

  1. Insulin for the treatment of diabetes mellitus
  2. HRT (oestrogen) to reduce the severity of menopause symptoms
• Feedback mechanism of thyroxine

  The concentration of thyroxine (one hormone) inhibits or stimulates the concentration of TSH (another hormone)
• Thyroxine is controlled by negative feedback, ie the correct level of one item has a negative effect on a previous step in the cycle

  Normal concentrations of thyroxine

  • If levels are normal, the pituitary is inhibited from releasing thyroid stimulating hormone (TSH)

  Low concentrations of thyroxine

  • Pituitary gland produces TSH. This causes thyroxine to be made and released by the thyroid gland until concentrations are back to normal
• Goitre

  • Enlargement of the thyroid gland - Indicates the underproduction of thyroxine
  • Usual cause: lack of iodine in the diet
  • Low concentration of thyroxine in the blood causes an increase in the TSH. This is carried to the thyroid
  • TSH normally combines with iodine to produce thyroxine, however if this cannot happen TSH is stored in the thyroid and it swells
  • Treatment: intake of iodine (seafood)
• Thyroxine feedback mechanism

  The concentration of one hormone (thyroxine) inhibits or stimulates the concentration of another hormone (TSH)