LECTURE 19 + 20 : ENDOCRINOLOGY

what are hormones? where do hormones bind? are these receptors specific?

hormones: chemical messengers that enter the blood and are transported to their target cells

-target cells contain receptors for their corresponding hormone

• binding of the hormone produces a response in their target cell and organ

• receptors are specific to the hormone

how do endocrine and exocrine glands differ structurally?

exocrine glands: secrete their products into ducts

• ex. sweat or salivary glands

endocrine glands: secrete products directly into the surrounding interstitial fluid —→ diffuse into the blood stream

• ex. thyroid gland

what are the 3 hormones classes?

• what molecule(s) are each classification of hormones synthesized from?

• provide an example of each

1. Amine Hormones

• synthesized from the amino acids tryptophan and tyrosine

• ex. epinephrine, melatonin, an dopamine

2. Peptide Hormones

• comprised of polypeptide chains

  • larger that amine hormones

• ex. insulin, glucagon, growth hormone, oxytocin, follicle-stimulating hormone

3. Steroid Hormones

• synthesized from cholesterol

• ex. cortisol, testosterone, estrogen

where are steroid hormones typically produced? what results in the synthesis of steroid hormones?

STEROID HORMONE SYNTHESIS

-primarily produced by the adrenal cortex and the gonads

steps:

1. hormone secreted by the anterior pituitary binds to G-protein coupled receptor

2. G-protein activates adenylyl cyclase —> formation of cAMP

3. cAMP activates protein kinase A —→ phosphorylates other intracellular proteins

4. proteins convert cholesterol to corresponding steroid hormone

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!!!signal transduction pathway activated by G-protein coupled receptor results in the conversion of cholesterol to our steroid hormone

*example of steroid hormone is cortisol

how do free hormones and bound hormones differ?

• which is hydrophobic? which is hydrophilic?

• where would each type of hormone bind?

free hormones: do not require a transport protein

• are hydrophilic and bind to G-protein coupled receptors embedded in the plasma membrane of their target cell

• ex. epinephrine and dopamine

bound hormones: require a transport protein

• are hydrophobic and require a transport protein in order to be transported within the blood

  • transporter proteins: albumin and globulin

• bind to receptors within the cell (typically within the nucleus)

  • ex. cortisol

what is up-regulation? how does this differ from down regulation?

• what triggers each process?

up-regulation: increase in the number of receptors present in the plasma membrane

• typically occurs following prolonged exposure to low concentration of the hormone

down-regulation: decrease in the number of receptors present in the plasma membrane

• typically occurs following prolonged exposure to high concentration of the hormone

what is permissiveness?

permissiveness: when one hormone requires the presence of a second hormone for the full effect to occur

ex. thyroid hormone and epinephrine

• Both thyroid hormone and epinephrine increase fatty acid release into the blood

• When both are released simultaneously, we see a substantial increase in fatty acid secretion into the blood

what are neurosecretory cells? where do they originate? where are the terminal ends found?

• what hormones do they produce?

• what are the targets of these hormones?

neurosecretory cells originate in the hypothalamus and project down into the posterior pituitary

produce and secrete the hormones:

1. oxytocin

• secreted by: posterior pituitary

  • produced by the neurosecretory cells of the hypothalamus

• target(s):

  • uterus —→ stimulates contractions during childbirth

  • mammary glands —→ stimulates milk production

2. antidiuretic hormone

• secreted by: posterior pituitary

  • produced by the neurodecretory cells of the hypothalamus

• target(s):

  • collecting ducts: within the kidneys —→ increases aquaporin density —→ increases water reabsorption —→ increases blood volume

• release triggered by dehydration/increases in blood osmolarity

for the remaining hormones you should know:

• the endocrine gland/structure/cell that secretes the hormone. be as specific as possible

• the target(s) of the hormone (where it binds)

• effect of the hormone

• what triggers the release of each hormone (when mentioned in the slides)

*thyroid stimulating hormone, adrenocorticotropic hormone, luteinizing and follicle stimulating hormone

1. thyroid stimulating hormone

• produced and secreted by: anterior pituitary

• target(s):

  • thyroid gland —→ stimulates the release of T3, T4, and calcitonin from thyroid gland

• release triggered by thyroid releasing hormone (produced in the hypothalamus)

2. adrenocorticotropic hormone

• produced and secreted by: anterior pituitary

• target(s):

  • adrenal cortex —→ stimulates the release of cortisol and androgens

• release triggered by the corticotropin releasing hormone (produced in the hypothalamus)

3. luteinizing and follicle stimulating hormone

• produced and secreted by: anterior pituitary

• target(s):

  • testes —→ stimulates sperm production

  • ovaries —→ maturation of the ovum

• release triggered by gonadotropin releasing hormone (produced in the hypothalamus)

for the remaining hormones you should know:

• the endocrine gland/structure/cell that secretes the hormone. be as specific as possible

• the target(s) of the hormone (where it binds)

• effect of the hormone

• what triggers the release of each hormone (when mentioned in the slides)

*growth hormone, prolactin, endorphins

4. growth hormone

• produced and secreted by: anterior pituitary

• target(s):

  • cartilage + bone —→ stimulates growth + development

  • skeletal muscle —→ stimulates muscle development

  • fat —→ decreased lipid stores/releases fatty acids into blood

• release triggered by growth hormone-releasing hormone (produced in the hypothalamus)

5. prolactin

• produced and secreted by: anterior pituitary

• target(s):

  • mammary glands —→ lactation (release of milk)

• released triggered by suckling

6. endorphins

• produced and secreted by: anterior pituitary

• target(s):

  • CNS —→ decrease sensation of pain

• release triggered by pain

for the remaining hormones you should know:

• the endocrine gland/structure/cell that secretes the hormone. be as specific as possible

• the target(s) of the hormone (where it binds)

• effect of the hormone

• what triggers the release of each hormone (when mentioned in the slides)

*melatonin, thymosin+thymopoietin+thymulin, T3+T4, calcitonin

7. melatonin

• produced and secreted by: pineal gland

• target(s):

  • CNS —→ regulates circadian rhythms

• release triggered by darkness

8. thymosin, thymopoietin, thymulin

• produced and secreted by: thymus

• involved in formation and maturation of T-cells —→ produces am immune response

9. T3 (triiodothyronine), T4 (tyroxine)

• produced and secreted by: thyroid gland

• target(s):

  • adipose —→ release of fatty acids into the blood

  • liver, muscle, neurons —→ increased metabolic rate (increased body temp with hypothyroidism)

  • GI tract —→ increased motility

• release triggered by thyroid stimulating hormone

10. calcitonin

• produced and secreted by: thyroid gland

• target(s): osteoclasts —→ inhibits activity

• release triggered by high blood Ca2+ levels

for the remaining hormones you should know:

• the endocrine gland/structure/cell that secretes the hormone. be as specific as possible

• the target(s) of the hormone (where it binds)

• effect of the hormone

• what triggers the release of each hormone (when mentioned in the slides)

*parathyroid hormone, leptin, epinephrine and norepinephrine

11. parathyroid hormone

• produced and secreted by: parathyroid gland

• target(s):

  • osteoclasts —→ stimulates —→ increases blood calcium levels

• release triggered by low blood Ca2+ levels

12. leptin

• produced and secreted by: adipose

• target(s): hypothalamus —→ appetite suppression

13. epinephrine and norepinephrine

• produced and released by: adrenal medulla

• target(s):

  • heart —→ increases heart rate and stroke volume

  • lungs —→ increases respiratory rate

  • liver —→ breakdown of glycogen to glucose

  • blood vessels —→ vasoconstriction (except int vessels carrying blood to skeletal muscles and the liver)

• release triggered by the sympathetic nervous system

for the remaining hormones you should know:

• the endocrine gland/structure/cell that secretes the hormone. be as specific as possible

• the target(s) of the hormone (where it binds)

• effect of the hormone

• what triggers the release of each hormone (when mentioned in the slides)

*cortisol, aldosterone, testosterone, estrogen and progesterone

14. cortisol

• produced and released by: zona reticularis and zona fasiculata

• target(s):

  • liver —→ breakdown of glycogen to glucose, conversion of lipids to glucose —→ increases blood sugar levels

  • muscle —→ decreases glucose uptake from blood; increases protein catabolism

  • adipose —→ conversion of lipids to glucose

• release triggered by adrenocorticotropic hormone

15. aldosterone

• produced and secreted by: zona glomerulosa

• target(s):

  • collecting ducts —→ increases Na+ and H2O reabsorption —→ increases blood volume

• release triggered by decrease in MAP and high blood K+ concentrations

16. testosterone

• produced and secreted by: testes

• target(s):

  • seminiferous tubules —→ production of sperm

  • thyroid cartilage —→ thickening during puberty

  • muscle mass and bone tissue—→ increases muscle mass and bone density

  • increases libido

  • increases facial and body hair growth

• production and release triggered by luteinizing hormone

17. estrogen and progestesrone

• produced and secreted by: ovaries

• target/effects:

  • maintain the female reproductive tract

  • reproduction —→ maturation and release of ovum

• release triggered by luteinizing hormone

what is aromatase? what does it convert?

enzyme responsible for converting testosterone to estradiol (estrogen)

what are the 2 endocrine cell types of the pancreas?

• which hormones does each secrete?

• when would each hormone be released? how does this help us regulate our blood sugar

  • know the basic blood sugar glucose feedback loops

BETA CELLS

• produce and release the hormone insulin

• target(s):

  • liver and muscle tissue —→ uptake glucose —→ stores as glycogen within the cell —→ lowers blood sugar levels

• released when blood sugar levels are high

ALPHA CELLS

• produce and release the hormone glucagon

• target(s):

  • liver —→ breakdown of glycogen into glucose monomers —→ increase blood sugar levels

• released when blood levels are low

blood glucose feedback loop: high blood sugar

• stimulus

• receptor

• integration center

• effector

• response

HIGH BLOOD SUGAR

stimulus: increased blood glucose

receptor: beta cells detects high blood glucose

integration center: beta cells —→ release insulin

effector: liver or muscle tissue

response: tissue uptakes glucose —→ decrease blood glucose

blood glucose feedback loop: low blood sugar

• stimulus

• receptor

• integration center

• effector

• response

LOW BLOOD SUGAR

stimulus: decreased blood glucose

receptor: alpha cells detects low blood glucose

integration center: alpha cells —→ release glucagon

effector: liver

response: glycogen —→ glucose —→ increase blood glucose