Introduction To The Endocrine System Flashcards
What is the purpose of the endocrine system?
◦ Regulation of multiple organs to meet growth and reproduction demands
◦ Major role in homeostasis
What are the classical endocrine glands?
Hypothalamus Anterior/posterior pituitary Thyroid Parathyroid Adrenal cortex/medulla Gonads Pancreas Placenta
What major hormones does the hypothalamus produce?
- ADH (PVN)
* Oxytocin (SO)
* TRH
* GRH
* GHRH
* GnRH
* Somatostatin
* Dopamine
What major hormones does the anterior pituitary produce?
- ACTH
* TSH
* Growth hormone
* Prolactin
* FSH
* LH
* MSH
What major hormones does the posterior pituitary produce?
- Oxytocin
* ADH
What major hormones does the thyroid produce?
- Thyroxine (T4)
* Triiodothyronine (T3)
* Calcitonin (CT)
What major hormones does the Parathyroid produce?
• Parathyroid hormone (PTH)
What major hormones does the adrenal cortex produce?
- Cortisol
* Aldosterone
* Androgens
What major hormones does the adrenal medulla produce?
- Epi
* Norepinephrine
What major hormones do the Testes produce?
- Androgens (esp. testosterone)
* Inhibin
What major hormones do the Ovaries produce?
- Estrogens (estradiol)
* Progesterone
* Inhibin
* Relaxin
What major hormones do the Pancreatic Islets produce?
- Insulin
* Glucagon
* Somatostatin
What major hormones does the Placenta produce?
- HCG
* hPL
* Estriol
* Progesterone
What major hormones does the corpus luteum produce?
- Estradiol
* Progesterone
Where are there endocrine cells in a non-endocrine organ?
Adipose Kidneys Liver Heart GI tract
What major hormones do the Kidneys release?
◦ Renin
◦ 1,25 Dihydroxycholecalciferol
What can also modify hormones?
Examples?
Peripheral conversion
Angiotensin II
Vit. D from sun
What constitutes a proteins?
Polypeptide with >100 AAs
What constitutes a peptide?
Polypeptide with < or equal to 100 AAs
Are protein/peptide hormones lipid or water soluble?
Water soluble
How are protein/peptide hormones synthesized?
‣ Synthesized as Non-functional pre-prohormone
‣ Modified in ER —> pro-hormone —> Golgi apparatus s
‣ Packed into vesicles
‣ Cleaved by proteolytic enzymes to form functional hormone
What are protein/peptide hormones stored in?
When are they secreted?
Example?
In secretory vesicles
Secreted w/ endocrine stimulus
(Increased intracellular Ca —> increase cAMP —> PKA activation)
What are examples of steroid hormones?
‣ Cortisol ‣ Aldosterone ‣ Estradiol ‣ Estriol ‣ Progesterone ‣ Testosterone ‣ 1,25-dihydroxycholecalciferol
Are steroid hormones lipid or water soluble?
Lipid soluble
How are steroid hormones synthesized?
‣ From cholesterol
‣ modifications of cholesterol via addition or removal of side chains, hydroxylation or aromatization of the steroid nucleus
Where are steroid hormones synthesized at?
• Adrenal cortex, gonads, corpus luteum, placenta
How are steroid hormones stored? Secreted?
They are not stored
Secreted by adrenal cortex, gonads, corpus luteum, placenta
What are the 2 groups of amine hormones?
Catelcholamines
Thyroid hormones
How are catelcholamine hormones synthesized?
Secreted?
‣ Derived from Tyrosine
‣ Synthesized in cytosolic and secretory granules
‣ Secretion: Act thru cell membrane assoc. receptors
How are thyroid hormones synthesized? Secreted?
‣ Synthesized by Thryoid gland
‣ Stored as thyroglobulin in follicles w/in the gland
‣ Secretion: Cross cell membrane & act thru nuclear receptors
What two mechanisms control hormone secretion?
Neural and feedback
What is the neural mechanism that controls hormone secretion?
‣ Neuronal input to endocrine cell increases or decrease hormonal secretion
What is an example of neural mechanism of controlling hormone secretion?
sympathetic preganglionic innervation to adrenal medulla = causes release of Catecholamines into circulation
What mechanism is more common in controlling hormone secretion, neural or feedback
Feedback
How does the feedback mechanism for controlling hormonal secretion work?
element of pathway feeds back, directly or indirectly, on endocrine gland to change secretion rate
What is a positve endocrine feedback ?
◦ Hormone action causes additional secretion of hormone
◦ Uncommon in biological system
What can a positive endocrine feedback lead to?
Example?
‣ Can lead to explosive event
• Ovulation or labor contractions
What is a Negative Endocrine Feedback?
Purpose?
◦ Hormone action inhbits further secretion of the hormone
◦ Confers stability by keeping a physiological parameter (i.e. blood glucose level) w/in a normal range
What is the pathway for a LONG feedback loop?
‣ Hormone released from peripheral endocrine gland (3rd tier)
—-goes back to —->
1st tier (hypothalamus) and 2nd tier (pituitary)
What is the pathway for a SHORT feedback loop?
Hormone from 2nd tier (pituitary)
—>
1st tier (hypothalamus)
What is the ULTRA SHORT feedback loop?
Gland inhibits its own secretions
How is the hypothalamus regulated?
By descending and ascending neuronal inputs
From Suprachiasmatic nucleus, pineal glands, physiological stress
What is the “first tier” of the endocrine axes?
Hypothalmus
What does the suprachiasmatic nucleus Regulate? How?
Hypothalamus
Thru imposing circadian rhythm on secretion of hypothalamic releasing hormone and endocrine axes
What does the pineal gland regulate? How?
Hypothalamus
Releases melatonin to feed back to SCN re: info about day and night
What does physiological stress regulate? How?
Hypothalamus
Influences the release of hormones from hypothalamus
How is sensitivity defined?
[hormone] that produces 50% of maximal response (EC50)
What is the dose-response relationship regulate?
Responsiveness of target tissue
How can you change the responsiveness of tissues to hormones?
Change # of receptors
Change affinity of receptors for hormones
What are the mechanisms for up-regulation ?
When would you upregulate?
◦ Increase # of receptors OR sensitivity of target tissue
when hormone level is low
What are the mechanisms for down-regulation ?
When would you downregulate?
◦ Reduce # of receptors OR sensitivity of target tissue
when hormone levels are high (Chronic)
How would you enact up-regulation?
‣ Increasing synthesis of new receptors
‣ Decreasing degradation of old
‣ Activating receptors
How do you enact down-regulation ?
‣ Decreasing receptor synthesis
‣ Increasing degradation of receptors
‣ Inactivating/desensitizing receptors
What are the hormones that act thru adenylyl cyclase pathway?
What is the mechanism?
ACTH, LH, FSH, TSH, Glucagon
1st messenger hormone —> receptor
Gs activated —> primary effector-adenylyl cyclase
2nd messenger cAMP —> 5AMP —> PKA active now = secondary effector
PKA —> phosphorylate proteins
—> physiological actions
What hormones will act thru Phospholipase C pathway?
GnRH, TRH, Oxytocin
What is the mechanism of hormone action using the Phospholipase C pathway?
1st messenger hormones —> receptor
Gq activated —> Phospholipase C (primary effector)
Phospholipase C —> IP3, DAG, Ca (2nd messenger)
—> PKC or Calmodulin (secondary effector)
How do steroid hormones diffuse into target cell?
Diffuse UNbound to plasma protein carriers
What is the signal transduction pathway for steroid hormones?
Steroid diffuses into target cell
Bind steroid hormone r. On cytoplasm or NUCLEUS
If nucl —> binds DNA, activating/repressing 1 or more genes
Activated genes —> new mRNA —> mRNA back to cytoplasm —> Translation at ER —> new proteins made for cell processes
What do steroid hormones that bind to membrane receptors do?
Use second messenger system to create RAPID response
What is Guanylyl Cyclase do when activate?
Convert GTP to cGMP
CGMP —> activates cGMP kinase
Relax vascular smooth muscle
What are the 2 categories for tyrosine kinases?
- Receptor tyrosine kinases
2. Tyrosine kinase associated receptors (jak-stat)
What are the characteristics of Receptor Tyrosine Kinases?
When active, what will they do?
Have intrinsic tyrosine kinase activity
Will phosphorylates downstream proteins
What are the characteristics of Tyrosine Kinase Associated Receptors?
What will they do when active?
associate non-covalently to proteins that have kinase activity
Active kinase phosphylates downstream proteins
What is the relationship to the amount of hormone bound to protein and its half life and clearance?
Increase protein binding by hormone
Will
INCREASE 1/2 half
DECREASE metabolic rate (clearance)
What are the three tiers of the endocrine system?
Tier 1: hypothalamus
Tier 2: pituitary
Tier 3: target of pituitary
What are the three general classes of hormones?
Proteins and peptides
Amines
Steroids
What are endocrine cells?
Release hormone thru blood which can act on a DISTANT cell that will then produce an effect
What is a paracrine cell?
Acts on NEARBY cell using hormone and then that cell will have effect
What is an Autocrine cell?
Acts on the SIGNALING cell using hormone released by itself
What are neuroendocrine cells?
Cells that receive neuronal input
(NTRs released by nerve cells or neruocsecretroy cells)
and release hormone into blood to act on distant cell