1. Endocrine System
  1. The nervous system and the endocrine system control internal communication in the body between specialized body parts. They work together to achieve coordination.
  2. Life is a symphony and the body is an orchestra. Each specialized part of the body, each musician must coordinate its activities with each other, in concert to create a harmony.
  3. The endocrine system conveys information between organs of the body using chemical messengers.
  4. The chemical signals move via the blood throughout the body, but only certain cells can respond to them. These chemical signals are called hormones (from Greek word hormon, which means excite).
    1. Peptide hormones -bind receptors and activate second messenger.
    2. Steroid hormones- enters the cell and bind receptors.
  1. Hormones are chemical messengers that influence the metabolism of the cell either directly or indirectly, depending on the hormone type.
  2. There are 50 known hormones in humans. Hormones are very potent and can act at low concentrations.
  3. Hormones are chemical signals that are secreted into the blood by specialized cells called endocrine cells.
    1. These cells are in organs called endocrine glands (sometimes called ductless glands, because they don't have ducts for the transport of their secretions).
  1. Control is required
    1. Usually controlled by negative feedback.
    2. Negative feedback is like a thermostat. Set the temperature at 70 degrees. The heater turns on and heats the room, then, receptor senses that the room is at 70 degrees and shuts off the heater.
    3. Examples: ADH and the amount of water in the blood. Thyroxin and the regulation of metabolism.
  1. Hypothalamus
  1. Hypothalamus is beneath the thalamus in the third ventricle of the brain. It regulates the internal environment. Controls heart rate, body temperature, water balance, and the pituitary gland.
  2. The pituitary gland is 1 cm in diameter just below the hypothalamus. Composed of posterior pituitary and anterior pituitary.
  3. The posterior pituitary is connected to the hypothalamus by means of a stalk-like structure. Neurons in the hypothalamus called neurosecretory cells respond to neurotransmitters and produce the hormones, which are stored and released from the posterior pituitary. One hormone is called antidiuretic hormone (ADH). ADH promotes the reabsorption of water from the collecting duct in the kidney.
    1. Blood osmolarity is monitored by a group of nerve cells that are osmoreceptors in the hypothalamus.
    2. When blood gets more concentrated the cells of the osmoreceptors shrink because of osmosis and send an impulse to neurosecretory cells to release ADH.
    3. ADH goes via the blood to the kidney, binds receptors, activating a second messenger system, which increases the water permeability of the epithelium. Water exits the collecting ducts and then enters the capillaries.
    4. Once the blood is more dilute, and reaches the brain, the production of ADH slows.
  1. Pituitary Gland
  2. Thyroid
  1. Increases metabolic rate helps regulate growth and development.
  2. Hormones are thyroxin and Calcitonin.
  3. Iodine is used to make thyroxin.
  4. If there is no iodine the thyroid gland enlarges producing goiter, low levels of thyroxin in the blood.
  5. Anterior pituitary makes TSH (thyroid stimulating hormone), which causes the thyroid to enlarge, so that thyroxin is produced, but if there is not enough thyroxin made the enlargement continues.
  6. Thyroxin stimulates cells to metabolize at a faster rate.
  7. Not enough thyroxin the disease is cretinism, short stocky, retarded. Or myxedema, lethargy, hair loss.
  8. Too much thyroxin causes hypergoiter, edema, eyes swell, Graves disease, hyperactive, insomnia.
  9. Hypothalamus release TRH (thyroid releasing hormone) which stimulates the anterior pituitary to release TSH, which stimulates the thyroid to secrete thyroxin. The level of thyroxin is controlled in 3 ways.
    1. TSH exerts feedback on the hypothalamus.
    2. Thyroxin exerts feedback over anterior pituitary.
    3. Thyroxin exerts feedback control over the hypothalamus.
  1. Adrenal Glands
  2. Pancreas
  3. Other endocrine glands

19. Find another example of negative feedback in the endocrine system.