Endocrine System

Endocrine-System.ppt 1

Endocrine System

“Raging Hormones!”


Endocrine System

•Odd organ system– Compare to nervous sys.,

digestive sys.

•Endocrine glands usually not connected– Considered a “system”

because of functional similarity


Endocrine System

•Endocrine glands– Masses of epithelial tissue– Cells secrete into

interstitial spaces,– Secretions (hormones)

diffuse into blood– No ducts!

•Contrast to exocrine glands


Endocrine System

•“Hormone”– Chemical messenger

secreted into blood and carried to “target cells” where it alters activity.

•Other chemical messengers– Autocrines– Paracrines


Hormones

•3-4 Chemical Types– Steroids– Amines– Peptides– (Eicosanoids)

• Mostly paracrines• Leukotrienes• Prostaglandins


Hormones

•Steroids– Derivatives of

cholesterol– Four covalently-

bonded rings– Adrenal cortex– Gonads


Hormones•A

mines– Derivatives of tyrosine,

an amino acid– Thyroid hormones

• Thyroxine (T4)

• Triiodothyronine (T3)

– Adrenal medulla• Epinephrine• Norepinephrine

– Usually neurotransmitter


Hormones•P

eptides– “Chains” of amino acids

• 4 – 200+ amino acids

– Hypothalamus– Pituitary (Ant. & Post.)– Islets of Langerhans– Parathyroid hormone– Digestive system

hormones


Mechanisms of Hormone Action

•Lipid-soluble steroids & thyroid hormones– Diffuse through plasma

membrane– Enter nucleus– Forms “hormone-receptor

complex”– H-R complex binds to

chromosome to activate/inactivate gene(s)



•Peptides & water-soluble amines– Hormone (A) binds to

receptor on cell surface– Activates G- protein– Activates adenylate cyclase

• Converts ATP to cAMP– cAMP activates protein

kinases, which produce final effect.



•Peptides & water-soluble amines– Other Hormone (B) binds

to receptor on cell surface– Activates G- protein– Inhibits adenylate cyclase

• Stops ATP to cAMP inhibits final effect of

first hormone

Endocrine System

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