The Endocrine System

• Exocrine Glands produce secretions that are transported via ducts. Endocrine Glands produce secretions that are transported via the blood
• The pancrease is part of both the endocrine and exocrine system.

  It produces Insulin which is transport long distances via the blood (therfore endocrine)

  It produces bile which is transported short distances via the pancreatic duct (therefore exocrine)
• Hormones are Organic Chemical Messengers

  Hormones have the following 3 properties:

  1. They do not act independently but form an integrated system.
  2. They bring about coordination and homeostasis through their effect on specific organs in the body.
  3. Each hormone affects its own specific organs in the body.
• How do hormones bring about coordination and homeostasis?

  By their effects on other specific organs functions
• The nervous system and endocrine system work together to maintain equilibrium in the body. A "need" will be picked up either by a sensory receptor in the nervous system or a chemoreceptor in the endocrine system. This information is interpreted by the brain and sends signals to the applicable glands part of the endocrine system to start/stop producing and releasing a specific hormone.
• The Hypothalamus produces the anti-diuretic hormone.
• The anti-diuretic hormone is produced in the hypothalamus but stored and released by the pituitary gland.
• The hypothalamus links the nervous system and endocrine system as it is the only structure in the brain with no blood-brain barrier and contains many chemoreceptors that rapidly read and relay information about the blood to the brain.
• ADH controls the permeability of the collecting duct and distal convoluted tubules of the nephron, allowing either the reabsorption or expulsion of water from the tubules to maintain a water equilibrium in the bloodstream.
• Why is the hypothalamus an important structure in the brain?

  It links the nervous and endocrine system it has no brain-blood barrier + chemoreceptors
• The pituitary gland is situated in a bony cavity at the base of the brain. It is made of the anterior (front) lobe and posterior (back) lobe.

  The pituitary gland produces 5 important hormones:

  1. Growth Hormone (GH)
  2. Thyroid Stimulating Hormone (TSH)
  3. Follicle Stimulating Hormone (FSH)
  4. Luteinising Hormone (LH)
  5. Prolactin (P)
• The Growth Hormone stimulates the development and growth of the skeleton and muscles in the body.
• The term for too much production of the GH is Gigantism
• The term for too little production of the GH is Dwarfism
• Over-secretion of GH in adulthood is called Acromegaly. This causes abnormal growth of the hands, feet and facial features
• Follicle Stimulating Hormone controls the production of ova in the Graafian follicle.
• FSH is highest during ovulation
• FSH in men controls the production of sperm
• Luteinising Hormone has three main functions.

  1. The release of the egg from the follicle during ovulation
  2. Causes graafian follicle to become the corpus luteum if no fertilization takes place
  3. Causes the graafian follicle to produce oestrogen if fertilization takes place
• Prolactin stimulates the production of milk. The process is called lactation.
• The thyroid gland secretes thyroxin
• Thyroxin has 2 main functions

  1. Regulates metabolic rate
  2. Affects the growth and functioning of the heart and nervous system
• Iodine is essential for the production of thyroxin. One gets iodine from shellfish and leafy greens.
• If not enough iodine is present in the body the thyroid gland enlarges causing a goitre.
• If too little thyroxin is produced (in a child) their is slow skeletal growth and the tongue enlarges (known as cretinism)
• If too little thyroxin is produced (in adults) memory loss can occur and increase in mass (known as myxoedema)
• If too much thyroxin is produced there is an increase in metabolic rate and a goitre in the eyes can form (protrusion of the eyes)
• The adrenal glands are made of two layers the adrenal cortex and adrenal medulla
• The adrenal cortex secretes aldosterone
• The adrenal medulla secretes adrenalin