3.5 The Endocrine System

• Endocrine System
  • a series of glands that produce chemical substances known as hormones.
• Hormones
  • chemical messengers of the body.
  • like neurotransmitters, they bind to a receptor in order to send their signal
    • however, they are secreted into the bloodstream and travel throughout the body (unlike neurotransmitters that are secreted in close proximity to cells and their receptor).
    • their effects are also widespread, and tend to persist for a long time.
  • involved in regulating bodily functions in order to achieve homeostasis.
  • controlled through interactions with the hypothalamus and the pituitary gland

Major Glands

• Pituitary
  • located just below the hypothalamus
  • works closely with the hypothalamus to send messenger hormones throughout the body.
    • these messenger hormones control the other glands in the endocrine system.
    • this is why it is called the master gland.
  • it secretes hormones for stimulating growth (growth hormone), pain relief (endorphins), and hormones that regulate fluid levels in the body.
• Thyroid
  • located in the neck
  • releases hormones that regulate growth. metabolism, and appetite.
  • some disorders exist due to disorder in the normal function of the thyroid:
    • hyperthyroidism is a disorder when the thyroid releases too much of the hormone thyroxine.
      • symptoms are: agitation, bulging eyes, and weight loss.
      • causes of hyperthyroidism is Graves’ disease
    • hypothyroidism is a disorder when the thyroid releases too little of the hormone
      • symptoms are: tiredness and sensation of being cold.
    • thyroid disorders are treatable with proper medications that reestablish balance in the hormones secreted by the thyroid.
• Adrenal
  • located atop the kidneys
  • secretes hormones involved in the stress response (epinephrine and norepinephrine)
• Pancreas
  • internal organ that secretes hormones that regulate blood sugar levels
    • they secrete insulin or glucagon throughout the day which help lower or raise blood sugar levels in the body
  • people with diabetes do not produce enough insulin
    • therefore, they must take medications that simulate or replace insulin
    • they are also advised to control the sugars/carbohydrates they consume
• Gonads
  • secretes sexual hormones that are essential for reproduction and mediates sexual motivation and behavior
    • the female gonads, the ovaries, secretes estrogens and progesterone
    • the male gonads, the testes, secretes testosterone

Endocrine Gland	Associated Hormones	Function
Pituitary	Growth Hormone Releasing and Inhibiting Hormones	Regulates growth Regulates hormone release
Thyroid	Thyroxine Triiodothyronine	Regulates metabolism Regulates appetite
Pineal	Melatonin	Regulates some biological rhythms (eg. the sleep cycle)
Adrenal	Epinephrine Norepinephrine	Stress response Increases metabolic activities
Pancreas	Insulin Glucagon	Regulate blood sugar levels
Ovaries	Estrogens Progesterone	Mediate sexual motivation and behavior Reproduction
Testes	Androgens (eg. Testosterone)	Mediate sexual motivation and behavior Reproduction