Endocrine System

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Endocrine System
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By the end of this class you should understand

• The major glands of the endocrine system
• The concept and function of a negative feedback
  loop
• The major effects of the hormones on the glands
  and the body

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Endocrine System

• The endocrine system is the other control
  system of the body
• Works closely with nervous system
• Connection is hypothalamus -gt pituitary gland
• Any organ that releases signal molecules
  (hormones) into the blood is part of the
  endocrine system
• Many organs scattered throughout the body

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Hormones

• A hormone is any signal molecule that enter the
  blood and attaches to a target cells receptors
• Two major types of hormones Steroid hormones and
  nonsteroid hormones
• Steroid hormones are made from cholesterol and
  include testosterone estrogen
• Most hormones are nonsteroid

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Steroid vs. Nonsteroid

• A steroid hormone is lipid-soluble
• Therefore can pass through cell membrane
• Binds to molecules inside cytoplasm or nucleus to
  change cell behavior
• A nonsteroid hormone must bind to receptor
  molecules on the surface of the cell membrane
• These receptors release second messengers that
  enter the nucleus and change the cell behavior

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Negative Feedback Loop

• Essential core of endocrinology is the negative
  feedback loop
• In a negative feedback loop, the product of a
  signal blocks its own signal
• A increases B, but B decreases A
• Creates an optimal amount of signal and product
• Example EPO
• Signal lack of oxygen Product more RBCs

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Endocrine Signaling

• Many organs are part of at least one signal
  pathway
• Technically the heart, liver, fat tissue, thymus,
  etc. are all part of the endocrine system
• Todays focus will be on what is sometimes called
  the HPA Axis
• Hypothalamus, Pituitary, Adrenal Glands
• Also will focus on metabolism management
  (pancreas and thyroid)

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Hypothalamus

• The hypothalamus is in the center of the brain
  and receives signals from the rest of the brain
• Hypothalamus is also outside the blood-brain
  barrier so it can monitor blood temperature,
  nutrient and ion levels, etc.
• To affect the body, the hypothalamus sends
  hormonal and nervous signals to the pituitary
  gland

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Pituitary Gland

• The pituitary gland has a front and back portion
  that are both for hormonal signals
• The anterior pituitary signals the other glands
  of the body
• The posterior pituitary handles the release of
  two other hormones ADH and oxytocin

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ADH Anti-diuretic Hormone

• A diuretic is anything that increases urination
• Alcohol, caffeine, etc
• Anti-diuretic hormone is released to conserve
  water in the body
• Changes the behavior of the kidneys
• Kidneys reabsorb more water from urine when
  signaled with ADH
• Failure to release ADH means kidneys urinate
  water even when you are dehydrated

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Oxytocin

• Oxytocin in women promotes lactation and is
  involved in childbirth
• Was thought to be only in women
• Oxytocin also has effects on the brain in both
  men and women
• Primarily promotes bonding and affection
• Is released during orgasm
• No strings attached sex? Not if your posterior
  pituitary can help it!

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Anterior Pituitary

• The anterior pituitary releases hormones that
  primarily stimulate other glands
• TSH Thyroid
• ACTH Adrenal glands
• FSH LH Gonads (will be covered in chapter 16)
• Growth Hormone (GH) long bones muscles

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Growth Hormone

• Growth hormone stimulates growth in the long
  bones at the growth plate
• Deficiency of growth hormone during youth can
  cause pituitary dwarfism
• Excess can make you very tall
• Works by stimulating bones to grow and also
  increases metabolism

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Thyroid

• The thyroid is a gland in your neck, stimulated
  by the anterior pituitary
• The thyroid releases thyroxine which stimulates
  cells to increase metabolism
• Thyroxines key ingredient is iodine, which is
  required in small doses for life
• Hypothyroidism (less thyroxine) causes exhaustion
  and weight gain
• Lack of iodine can cause hypothyroidism and a
  swelling of the thyroid (goiter)

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Adrenal Cortex

• The adrenal glands are a multi-layered gland
• Adrenal cortex releases cortisol and aldosterone
  (and similar hormones)
• Stimulated to release cortisol by ACTH
• Cortisol is a stress hormone that causes the body
  to conserve resources
• Aldosterone helps conserve sodium and potassium,
  and helps keep sodium concentration higher than
  potassium

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Adrenal Medulla

• The adrenal medulla releases epinephrine
  (adrenaline) when stimulated by the sympathetic
  nervous system
• Epinephrine increases heart rate (by stimulating
  SA node), dilates passageways of lungs, increases
  blood flow to muscles, and increases alertness by
  stimulating midbrain

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Glucose Management

• Long-term metabolism is controlled by the
  pituitary gland (GH)
• Medium-term metabolism is controlled by the
  thyroid (thyroxine)
• Short-term metabolism is controlled by the
  pancreas
• Releases hormones that manage glucose levels in
  the blood

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Why Glucose?

• Recall that glucose is the energy source for all
  cells in the body
• Neurons in particular absolutely must be
  nourished by glucose
• Also recall that glucose is a polar (hydrophilic)
  molecule and so is sticky
• No one wants to have their heart pump syrup
  through their arteries

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Insulin

• The pancreas releases insulin whenever blood
  glucose gets high
• Signals all cells to absorb additional glucose
• This helps cells use and store energy
• The liver produces more glycogen
• Fat cells convert sugar to fat
• Failure to release or receive insulin is called
  diabetes

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Glucagon

• The pancreas releases glucagon whenever blood
  sugar gets low
• Stimulates fat and liver to release glucose into
  bloodstream
• A deficiency of glucagon or excess of insulin can
  cause hypoglycemia
• Critically low blood sugar causes crankiness
  followed by coma and death

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Calcium Management

• The thyroid releases calcitonin, ostensibly to
  decrease calcium levels
• Not clear whether its action is important
• The thyroid also has small glands attached called
  the parathyroid glands
• Four or eight small dots on the back
• The parathyroid glands release parathyroid
  hormone or PTH

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PTH

• PTH is released when blood calcium is low
• Stimulates digestive system to absorb calcium
• Stimulates kidneys to reabsorb calcium from urine
• Stimulates osteoclasts to release calcium from
  bone
• This is a big part of why calcium intake should
  be ongoing and not just once a week

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Negative Feedback Loops!

• Glucose goes high insulin released, glucose goes
  down, insulin inhibited
• Glucose goes down glucagon released, glucose
  goes up, glucagon inhibited
• Metabolism goes down thyroxine released,
  metabolism goes up, but thyroxine inhibits TSH
  from pituitary
• Calcium goes down PTH released, calcium goes up,
  PTH inhibited

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See you next week!

• Monday is digestive anatomy
• Wednesday is nutrition!
• Be sure to record a full week of nutrition
  information for the nutrition lab!