Monday, April 23, 2012

Endocrinology - Hormones

Posterior Lobe of the Pituitary Gland
Hormones released here are made in the hypothalamus.  There are 2:
  • ADH - anti-diuretic hormone - increases permeability of the collecting ducts in the kidney so they absorb more water back out of the filtrate and into the blood.
  • Oxytocin - stimulates contractions of vans deferens and uterus during intercourse.  Also stimulates uterine contraction during labor (a synthetic form "pitocin" is sometimes given to induce labor), and milk let-down during lactation.  According to this site I found, this hormone is also responsible for bonding feelings between males and females after mating, for mother-newborn bonding, and it also increases levels of trust in people.  Cool.

Anterior Lobe of the Pituitary Gland
  • TSH - Thyroid Stimulating Hormone.
    • The release of this hormone is stimulated by thyrotropin releasing hormone (TRH) from the hypothalamus.
    • TSH acts on the thyroid to release T3 and T4.
    • T3 and T4 - stimulate protein synthesis and growth, promotes normal growth of the nervous system and myelin sheaths, controls basal metabolic rate.
    • Negative feedback loop - presence of T3 and T4 inhibit release of TSH (as does stress)
  • GH - Growth Hormone.
    • Release is stimulated by GHRH from the hypothalamus.
    • Sleep, exercise, fasting, and hypoglycemia increase GHRH which increases GH
    • Stimulates release of somatomedins from liver and other tissues
      • promote growth of long bones at ephiphyseal plates (growth plates)
      • this increases blood glucose
      • increases release of fatty acids from adipose tissue
      • increases protein synthesis
    • Negative feedback loop - GH and somatomedins decrease GH
  • PRL - Prolactin
    • Stimulated by oxytocin, TRH, and estrogen
    • Supply and demand (infant suckling, which increases oxytocin, and more PRL)
    • Inhibited by dopamine
    • PRL stimulates glandular tissue in breasts, milk production, mobilizes calcium from the bone for milk production, and stimulates the immune system (I'm guessing to be put into the milk as passive immunity for the baby)
  • ACTH - AdrenoCorticoTropic hormone
    • It's a big chain - CRH from hypothalamus --> ACTH from anterior pituitary ---> cortisol from adrenal cortex ---> decreases CRH and ACTH by way of negative feedback
Thyroid - C cells
  • Calcitonin
    • Stimulated by increased blood calcium levels
    • Inhibited by decreased blood calcium levels (negative feedback loop - supply and demand)
    • Stimulates calcium uptake into bones resulting in a decreased blood calcium level.
Parathyroid Gland
  • PTH - Parathyroid hormones
    • Opposite of calcitonin (stimulated by low blood calcium, inhibited by high blood calcium)
    • Mobilizes calcium from bone
    • Decreases rate of calcium excretion by kidneys
    • Lowers phosphate in blood
    • Activates vitamin D in kidney - stimulates calcium absorption in the intestine
*Calcium is needed for muscle and nerve function, so Calcitonin and PTH work together to maintain the proper balance of calcium in the blood for use in these areas.

Adrenal Medulla
  •  Epinephrine and norepinephrine
    • Stimulated by - sympathetic nervous system, exercise, hypoglycemia, injury, hypotension
    • Stimulates glycogenolysis in liver and muscles
    • Gluconeogenesis in liver
    • Lactic acid production in muscles
    • Increases heart rate
Adrenal Cortex
  • Cortisol - Glucocorticoids
    •  CRH (corticotropin releasing hormone) from the hypothalamus stimulates ACTH from the anterior pituitary which stimulates cortisol to be released from the adrenal cortex
    • Inhibits inflammatory response
    • Inhibits immune system functions
    • Inhibits cytokines (chemical messengers that call for more immune system helpers)
    • Stimulates gluconeogenesis, glycogen storage, and raising of plasma glucose levels
    • Increases fatty acid mobilization
    • Increases break down of protein to amino acids
*Now I understand - this is why I don't get sick until after a stressful situation is over (like finals or a big project).  I often get sick right after big things like that.  It's because the high stress I'm under leads to high cortisol which suppresses my immune system functions.  That's kind of scary to think that I have levels of cortisol high enough to keep me from having symptoms of sickness for that long.
  • Aldosterone - mineralocoricoids
    • Made in adrenal cortex
    • Angiotensin II in plasma or elevated serum potassium stimulates it
    • Causes sodium reabsorption and potassium excretion by kidneys
  • Glucagon
    • responds to low blood glucose
    • mobilizes glucose into the blood (through glycogenolysis, gluconeogenesis, ketone body formation)
    • Prevents hypoglycemia
  • Insulin
    • responds to high blood glucose and/or amino acids
    • allows cells to take in glucose and/or amino acids (this is pretty cool- when insulin is on the receptor, the cell puts a bunch of channels out into its membrane to allow glucose to enter.  As soon as insulin leaves the receptor, the cell endocytoses the channels back into the cell to wait for the next time.
    • stimulates glycogen synthesis, lipogenesis, protein synthesis
    • inhibits lypolysis and ketone formation

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