ENDOCRINE SYSTEM

I.   INTRODUCTION
–  An endocrine gland secretes hormones into the bloodstream

–  hormone:  chemical messenger that regulates activity of other body cells

--  hormone levels are constantly adjusted by feedback loops

negative feedback loop: a stimulus causes an endocrine organ to release hormones,
*  the hormone helps bring the body back to homeostasis
*  once homestasis is achieved, the hormone release stops

–  endocrine system: all endocrine glands in the body
–  endocrine system overseen by hypothalamus

II.  PITUITARY GLAND (HYPOPHYSIS)
-- connected to hypothalamus via the infundibulum

A.  Posterior Pituitary:

*  axons from hypothalamus cells
*  stores two hormones made by hypothalamus:

1.  Oxytocin (OT):
*  stimulates uterine contractions/ induces labor
*  stimulates milk release in response to suckling infant
*  males: stimulates smooth muscle contraction in reproductive tract

2.  Antidiuretic Hormone (ADH):
*  diuresis = urine production
*  inhibits urine formation/production

*  ADH targets the kidneys

B.  Anterior Pituitary:

1.  Growth Hormone (GH):
*  stimulates cell growth and mitosis in most cells
* especially affects skeletal and muscular systems

2.  Thyroid Stimulating Hormone (TSH):
*  targets thyroid gland
*  stimulates thyroid to produce/release its own hormones

3.  Adrenocorticotropic Hormone (ACTH):
*  target organ: adrenal cortex
*  stimulates adrenal cortex to release its hormones

4.  Follicle Stimulating Hormone (FSH):
*  target organs: ovaries and testes

5.  Luteinizing Hormone (LH):
*  target organs: ovaries and testes

6.  Prolactin (PRL):
*  target organs: mammary glands
*  stimulates breast milk production

F L A T    P I G

III. THYROID GLAND
–  in front of trachea and below larynx

A.  Thyroid Hormone (TH):
*  increases cellular activity (metabolic rate) in most cells of body

B.  Calcitonin:
* encourages deposition of calcium and phosphorus from bloodstream into bone tissue
*  so it lowers blood calcium levels

IV.  PARATHYROID GLANDS
–  4 tiny oval masses behind thyroid
–  secrete parathyroid hormone (PTH)
* increases blood calcium levels

V.   ADRENAL (SUPRARENAL) GLANDS

A.  Adrenal Cortex:
*   releases corticosteroids

1.  one group of these steroids:

controls balance of sodium (Na+) and potassium (K+) ions in body fluids

2.  another (2nd) group of steroids

is responsible for helping keep blood sugar (glucose) levels constant
*   stimulate metabolism of glucose from fats and proteins

3.  another group of these steroids:

secrete small amounts of androgens (male sex hormones)
*  in females, some of these androgens are converted to estrogen

B.  Adrenal Medulla:
*  secretes epinephrine (adrenaline) and norepinephrine (noradrenaline)
*  help prolong “fight or flight” response started by sympathetic nervous system

VI.  PANCREAS
–  has both exocrine and endocrine functions
*  exocrine functions were discussed w/digestive system

–  Pancreatic islets: produce hormones

1.  Insulin:  lowers blood sugar (glucose) levels

*  enhances cells to pick up glucose
*  helps convert some glucose into glycogen (a carbohydrate)

2.  Glucagon: raises blood sugar levels

*  breaks down glycogen into glucose

VII. GONADS (OVARIES AND TESTES)

–  ovaries produce estrogen and progesterone
–  testes produce androgens (especially testosterone)
–  will discuss in reproductive system lectures

Which hormone is stored in the posterior pituitary?

a. growth hormone (GH)

b. luteinizing hormone (LH)

c. prolactin (PRL)

d. antidiuretic hormone (ADH)

e. adrenocorticotropic hormone (ACTH)

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