ANBI Module 1

Endocrinology

the study of the endocrine glands and their secretions

Endon + krinein =

within + to secrete

Endocrine glands

ductless glands that secrete hormones into the blood

Classical endocrine secreting glands

• Thyroid

• pituitary

Clinical endocrinology

Ethiology and treatment of human endocrine diseases

comparative endocrinology

• Learn more about the functions of hormones

  • How animals adapt to dissimilar enviros

Behavioral endocrinology

how hormones regulate behaviour

Endocrine toxicology

• endocrine disrupting chemicals and impact on humans and animal health

Hormone classical definition

• A substance secreted by specialized cells and released into a vascular system (bloodstream) or tissue fluid causing a response in target cells elsewhere in the body

• Response is mediated by receptors specific to hormone in target tissues

Issues with the hormone definition

• not always produced by glands

• not unihormonal

• multiple production sites

• transport not only thru blood

Major functions of hormones

• growth and dev

• homeostasis

• metabolism

• behavioral regulation

• immune function

Why do we have endocrine system

• multicellular forms need a way to coordinate and comm

• chemical signalling

• compliments nervous system

3 components of endo system

1. Gland/cell (secrete hormones)

2. Hormone (chemical products, released upon stimulation)

3. Target organ (express hormone specific receptors, biological response)

Exocrine glands

release secretions via a duct into an epithelial surface

Epithelial cells

• skin cells but not necessarily on outside

  • GI tract, resp tract

Endocrine glands

• ductless and release substances directly into blood/lymph

• water sol (exocytosis)

• lipid sol (diffusion)

Hormone classification based on

• type of signaling

• chemical structure

• solubility

solubility of hormones

• water vs fat sol (type of receptor)

• blood is mostly water

  • water sol receptors on outside of cells bc cant go thru lipid membrane

Endocrine signaling

hormones enter bloodstream/lymph and bind to hormone receptors in target cells of DISTANT organs

Endocrine signaling ex.

Beta cells in islets of Langerhans in pancreas produce and release insulin into blood where it travels to many tissues including liver signaling it to store glucose in form of glycogen

Paracrine signaling

hormones bind to cells near the cell that released them (same organ/tissue), often degrade quickly or taken up regularly (interstitial space)

Autocrine signalling

hormone produced biological effect on same cell that it has released it

Autocrine signaling ex

• lining of mammalian endometrium responds to oxytocin to cause production of prostaglandins (cause contractions)

• tumor cells (estrogen in breast cancer cells)

• growth hormone in pituitary cells

Intracrine signaling

• when hormone is synthesized and acts intracellularly

  • DOES NOT leave cell

Intracrine ex

• Precursor sex steroid hormones are synthesized and then are converted by enzymes to active androgens/estrogens which bind to receptors within the same cell

• Vit D (calcitriol) converted to its active form within target cells and acts intracellularly

Neuroendocrine

chemical is produced by neuron or nervous tissue and is released into bloodstream to act on another cell type

Neuroendocrine ex

• Adrenalin, dopamine, oxytocin

Hormones vs neurotransmitters

• endocrine cells vs neurons

• vesicles, diffusion vs action potential, vesicles

• variable distance vs short

• slow speeds vs fast

• depends on receptor vs specific to post synaptic neuron

Peptide and protein hormones

• proteins are more complex

• common hormone type

• made of chain aa

• preprohormones → prohormones → active hormones

• stored in secretory vesicles and released by exocytosis

• water sol

• act quickly, short half life

hormone processing

• uses enzymes on aa hormone

  • until end product, are inactive

Preprohormone

large, inactive precursor

Prohormone

smaller, inactive (proteolytic, post translational mod)

Peptide/protein hormones

bind surface membrane receptors, cellular response thru signal transduction system