The Endocrine System

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The Endocrine System
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Defined

• Homeostatic system that responds to stimuli over
  time through the action of hormones secreted by
  glands throughout the body

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Endocrine System

• Hypothalamus
• Pituitary Gland
• Adrenal Glands
• Pineal Gland
• Thyroid Gland
• Parathyroid Gland
• Thymus Gland

• Pancreatic Islets
• Ovaries and Testes
• Stomach Small Intestine
• Liver
• Kidneys
• Heart

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Steroid Hormones

• Lipid soluble molecules that travel through the
  cell membrane
• Direct Mechanism - hormone binds with a receptor
  protein and together they interact with DNA
  turning on protein synthesis

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Peptide Hormones

• Water soluble molecules that cant travel through
  the cell membrane
• Second Messenger Mechanism hormone binds with a
  membrane receptor and activates internal cascade
  of events

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Second Messenger

• Specifically, the membrane complex activates a
  G-protein then adenylyl cyclase which converts
  ATP into cAMP
• cAMP activates kinases which define the specific
  response

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Control of theEndocrine System

• The endocrine system generally functions through
  a negative feedback system involving the
  Hypothalamus and Pituitary Gland
• The Hypothalamus and Pituitary Gland reside deep
  inside the forebrain

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The Posterior Pituitary

• In this relationship, neurons in the Hypothalamus
  produce and store hormones in their axon endings
  which reside in the pituitary.
• Stimuli cause the release of these hormones into
  the capillaries in the posterior pituitary

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Posterior Pituitary Hormones

1. Antidiuretic Hormone (ADH) involved in kidney
   function (more later)
2. Oxytocin (OCT) involved in birth and offspring
   nutrition (more later).

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Hypothalmic Hormones

• Hypothalmic hormones that arent stored in the
  posterior pituitary are releasers that stimulate
  the anterior pituitary.
• Gonadotropic Releasing Hormone (GnRH) involved
  in stimulating the reproductive hormones (more
  later)
• Thyroid Releasing Hormone (TRH) stimulates the
  release of thyrotropin
• Somatostatin stimulates the release of
  somatotropin or growth hormone (GH)

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Anterior Pituitary

• In this relationship, neurons in the Hypothalamus
  secrete hormones into Hypothalamic capillaries
  that travel to the pituitary

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Anterior Pituitary Hormones

• Corticotropin (ACTH) stimulates the release of
  adrenal steroid hormones from the adrenal cortex
• Thyrotropin (TSH) stimulates the release of
  thyroid hormones from the thyroid gland
• Somatotropin or Growth Hormone (GH) stimulates
  most cells in promoting cellular and molecular
  growth and metabolism
• Other anterior pituitary hormones include
  Follicle Stimulating Hormone FSH), Luteinizing
  Hormone (LH), and Prolactin involved in sexual
  maturity (more later)

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Endocrine System

• Hypothalamus
• Pituitary Gland
• Adrenal Glands
• Pineal Gland
• Thyroid Gland
• Parathyroid Gland
• Thymus Gland

• Pancreatic Islets
• Ovaries and Testes
• Stomach Small Intestine
• Liver
• Kidneys
• Heart

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Adrenal Glands

• The adrenal gland contain both the adrenal cortex
  and the adrenal medulla.
• Adrenal Cortex
• Glucocorticoids (later)
• Mineralcorticoids (later)
• Adrenal Medulla
• Epinephrine (adrenaline) Raises blood
  metabolites, and heart rate and force of
  contraction (liver, adipose, muscle). Also
  release by sympathetic nerves in the fight or
  flight response.
• Norepinephrine (noradrenaline) Promotes
  constriction or dilation of blood vessels (muscle)

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Thyroid Gland

• The thyroid gland secretes multiple hormones
• Triiodothyronine and Thyroxine target most
  cells in regulating metabolism, growth, and
  development
• Calcitonin targets the bone and causes a
  decrease in blood calcium (more bone).
• If iodine is lacking in the diet, over
  stimulating of the thyroid by the anterior
  pituitary can cause enlargement of the thyroid
  (goiter). Iodized salt has lessened this effect.

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Parathyroid

1. Parathyroid Hormone targets the bone and kidney
   in causing an increase in blood calcium (less
   bone)

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Pineal Gland

• The pineal gland produces the hormone melatonin
  which influences daily and seasonal biorhythms
  and sexual activity (in those species that are
  inhibited by the season)
• In humans melatonin levels are low during the day
  and high at night, and are involved in sleep and
  controlling temperature

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Other Endocrine Glands

• The gonads, pancreatic islets, tymus, stomach,
  small intestine, liver, kidneys, and heart also
  secrete hormones.
• Like androgens, estrogens, progesterone, insulin,
  glucagon, tymosins, gastrin, secretin,
  somatomedins, erythropoietin, and angiotensin
  (more later)