Advertisement Upgrade to remove ads

Lecture 2 of 3 on Endocrine System/Endocrinology

Growth Hormone

Primary hormone involved in human growth; Secreted throughout life but declines with age; Produced by somatotroph cells in anterior pituitary gland; Stimulated by hypothalamic _ _RH release into the portal system; Inhibited by hypothalamic somatostatin and feedback mechanisms; Targets bone, liver, and fat tissues as main targets; This hormone has direct and indirect effects (indirect effects mediated by liver insulin-like growth factors--IGFs); Proliferation/survival effects = stimulates linear growth, increases organ growth, increases muscle mass; Stimulates lipolysis (decreases fat depots); This hormone responses mediated by 3 receptor signaling pathways (G protein coupled receptors, cytokine receptors, tyrosine receptor kinases)

Somatostatin

Negative regulator; Binds to G protein receptor; Found on all anterior pituitary cells; Pathway hypothalamus causes to damptem systems

Adipose Tissue

Direct effects of growth hormone on this; Stimulates lipolysis, increasing blood free fatty acid content; Decreases glucose uptake

Liver

Direct effects of growth hormone on this; Increases gluconeogenesis; Increases IGF production

Muscle

Direct effects of growth hormone on this; Stimulates amino acid uptake/protein syntehsis, increasing lean body mass; Decreases glucose uptake (net effect of glucose on all 3 tissues is increases blood glucose levels--diabetogenic)

Indirect effects of Growth Hormone

(From IGF signaling) Increase organ size and function (increased cell survival/proliferation/ differentiation); Stimulate bone condrocyte function at epiphyseal plates to enhance linear growth; Increase in lean muscle mass may be predominantly an IGF effect`

Thyroid Stimulating Hormone (TSH)

Regulated by hypothalamic TRH (thryoid hormone releasing hormone); TRH binds thyrotroph G protein coupled receptors for ___ (hormone) release); This hormone binds to thyroid follicular cells G protein coupled receptors for T3/T4 synthesis/release; T3/T4 are lypophilic and enters/binds to cytoplasmic steroid class of receptors in target cells

Thyroid Hormones

Regulates basal metabolic rate (BMR); Key in bone and nervous sytem development; Increases gut carbohydrate absorption; Decreases circulating cholesterol; Stimulates lipolysis; Increased protein breakdown (resulting in weight loss if food is not increased); Facilitates autonomic fucntion (ionotropic and chronotropic)

Thyroid Hormone (T3/T4) Biosynthesis

Dietary iodide is key substrate for synthesis on thyroglobulin (TG); Synthesis occurs in colloid; Products formed in cells; T3 is 4x more active; T4 is 20x more abundant; T4 is converted to T3 by deiodinases in tissues

Hyperthyroidism

Too much thyroid hormone; People are "hyper"; BMR 10-1000% above normal; Nervousness, fine tremor at the fingers; Weight loss, hyperphagia; Increase pule pressure, heat intolerant, sweating; Grave's disease

Grave's Disease

Related to hyperthyroidism; TSH antibodies activate thyroid receptors resulting in increased T3/T4 production (low circulating TSH)

Hypothyroidism

Too little thyroid hormone; BMR falls to 40% of normal; "Can't think", poor memory; Lethargic, listless; Skin dry, poor cold tolerance; Children with this develop poorly (dwarfed) and can show mental retardation (cretinism); Treatment = hormone supplements; Hashimoto's disease

Hashimoto's Disease

Related to hypothyroidism; Autoimmune antibodies destroy thyroid gland

Cretinism

Can develop in hypothyroid children; Children can show mental retardation

Parathyroid Hormone (PTH)

Involved in calcium homeostatsis; Produced by parathyroid gland; Activates G protein coupled receptors on target tissues (bone, kidney)

Calcium Homeostasis

Calcium importance = bone maintenance, nervous system signaling, muscle contraction/skeletal/smooth/cardiac, blood clotting, others; Three regulators = parathyroid hormone (PTH), vitamin D, calcitonin; Three integrated sites of action = bone (largest reservoir of body calcium), GI calcium absorption, kidney calcium excretion; Free (ionized) calcium is active (50% free-50% bound); PTH and blood calcium levels are tightly balanced; Drop in blood calcium leads to increased PTH release; PTH increases kidney calcium reabsorption (fast); PTH increases bone resorption to free calcium (slow); PTH stimulates kidney vitamin D synthesis (1,25-[OH]2D); 1,25-(OH)2D binds to GI steroid-type receptors to stimulate calcium absorption

Vitamin D

Involved in calcium homeostasis; Not one but class of compounds; Synthesis in 3 tissues (skin, liver, kidney); Parathyroid hormone (PTH) important in final synthesis of active vitamin D in kidney

Calcitonin

Peptide produced by thyroid C cells; Decreases blood calcium (opposite effects of PTH and vitamin D); Blood calcium so tightly coupled with PTH/vitamin D that calcitonin is more important development than in adults

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions above and try again

Example:

Reload the page to try again!

Reload

Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

NEW! Voice Recording

Create Set