Endocrynologie Flashcards
(39 cards)
What is endocrinology?
- Coordination of physiological processes
ex: coorodinating mvt, respiration, circulation, digestion, excretion, metabolism all at once
endocrine system + CNS = major coordinating factors - Long distance communication
communicating between cells through chemical substances secreted by releasing cells and interact with specific receptors → specific physiological effects
What are the 2 type of signalling ?
Paracrine Signaling:
Very local, could be direct contact with target cell
Autocrine Signaling:
Cell releasing a hormone and has specific receptor on its surface (subcategory of paracrine but cell comunicates with itself)
What are the steps of hormone communication?
- Synthesis (of hormone by endocrine cell (or neutron in case of neurohormone)
- Release (of hormone …)
- Transport of hormone/neurhormone to target site by blood stream
- Detection of hormone/neurhormone by specific receptor protein on target cell
- Change in metabolism triggered by hormone
- Removal of the hormone (terminates the cellular response)
*Each step = potential source of signalling/response
How does the Hypothalamic-Pituitary signaling work?
Hypothalamic neurohormones released from hypothalamus (?) and inhibit/activates activity of 6 types of hormones-producing cells in the anterior pituitary
neurohormones are called releasing hormones/factors or inhibiting hormones/factor
What are the different classes of hormones and what are they base one?
Based on their structure
Glycoproteins (encoded by genes)
Polypeptides (encoded by genes)
Steroids (small molecules)
Amines (small molecules)
Ion Calcium (considered hormone bc calcium sensing receptors
How are hormones produced?
First produced as pre-hormones (synthesis on ribosomes)
prehormones → prohormones (Rough endoplasmic reticulum)
Hormones stored into vesicles with other peptides and are released from the cell
What are 4 important steroid hormones?
Cortisol
Aldosterone
Testosterone
Estradiol (Estrogene)
What is a unique feature of the Thyroid hormones?
They have Iodine in their structure
What are the properties of hormone receptors?
- Specificity: recognition of 1 single hormone/hormone family
- Affinity: Bonding hormone at its physiological concentration
- Should show saturability: finit # receptors
- Measureable biological effect: effect = response du to interaction of hormone with its receptor
What can be the issues in regulation of the receptors?
Upregulated → either by increasing their activity in response to hormone or their synthesis
Downregulated → either by decreasing their activity of their synthesis
What are the 3 mechanisms by which a hormone can exert effetc on a target cell?
- Direct effects on function at cell membrane
ex: insuline receptor activates glucose membrane carrier (to bring glucose into the cell) - intracellular effects mediated by second messenger systems
*First messenger = the hormone that binds to the receptor → ATP converted to cAMP - intracellular effects mediated by genomic of nuclear action
*Signaling by nuclear receptors including receptors for steroid hormones → steroid hormones have receptors inside the cytoplasm (not on cell surface), not at the surface and go into the nucleus to act on protein synthesis and alter functional response
By what mechanism is hormone secretion regulated?
Feedback mechanisms (negative most of the time, an excess of hormone leads to diminution of its sercretion)
How does the plasma Ca2+ regulation negative feeback loop work?
What organs are concerned by Ca2+?
Low plasma → ↑ stimulation of parathyroid gland → ↑ Synthesis/release of parathyroid hormone → ↑ PTH → Action on bond, kidney, gut → ↑ plasma Ca2+
Bond, kidney, gut!
*Negative feedback loop when Ca2+ plasma increases, decreases stimulation of parathyroid glands
What are the complete names of these acronymes ?
CRH
ACTH
CRH = corticotopin releasing hormone (secretion in hypothalamus)
ACTH = adrenocorticotopic hormone (secretion in anterior pituiraty gland)
cortisol (glucocorticoid) (secretion in adrenal cortex)
How does the regulation mechanism of stress work?
Stress or other inputs from other brain areas → INCREASE in CRH secretion (in Hypothalamus) → increase in plasma CRH → INCREASE in ACTH secretion (in anterior pituitary gland) → increase in plasma ACTH → INCREASE cortisol secretion (in adrenal cortex) → increase cortisol in plasma → target cell (of cortisol) responds to increase in cortisol
Résumé: CRH → ACTH → cortisol
Hypothalamus → anterior pituitary gland → adrenal cortex → target cell
*Negative feedback mechanism acts on hypothalamus secretion of CRH and anterior pituitary gland secretion of ACTH
What are the 2 parts of the pituitary gland?
Anterior pituitary gland → endocrine tissue
Posterior pituitary gland → neural tissue
Which important hormone is not encoded by genes?
Prolactin-inhibiting hormone
PIH, Dopamine
*but component necessary for dopamine synthesis are encoded by genes
What is the pathway of Oxytocin and Vasopressin?
Posterior Pituitary Gland does Neurohypohysis !!
Outgrowth of hypothalamus (connected to pituitary stalk)
Secretion of Oxytocin and Vasopressin (antidiuretic hormone - ADH)
Oxytocin and vasopressin synthesized in 2 hypothalamic nuclei (supra topic nucleus and paraventricular nucleus) *axons run down the pituitary stalk and terminate in posterior pituitary close to capillary blood vessels
*In axons, during transport, prohormones are processed in secretory granules (secretory granule travels the axon)
Mature hormone liberated from the Neurophysins I (for Oxytocin) and II (for vasopressin aka ADH)
Neurophysins = carrier molecules
ADH → Kidneys
Oxytocin → Uterus and Lactating mammary gland
*Circulating half-life of 1-3mins
What is the circulating half-time of oxytocin and vasopressin?
Why?
1-3 min to allow tight control
What are the roles of oxytocin ?
Females:
Parturition → uterus very sensitve to oxytocin at end of pregnancy, dilaiton uterine cervix causes oxytocin → uterine contraction
Milk ejection → response to stimulus of suckling, Causes milk filled ducts to contract and squeeze milk out
Behavioural effects → anxiety, enhances bonding, pro-social behaviour
Males:
Ejaculation → Oxytocin surge during sexual activity → epididimial passage of sperm and ejaculation
Behavioural effects → anxiety, enhances bonding, pro-social behaviour
What are characteristics of Colloid? Thyroglobulin? Thyroid Gland?
Colloid: major component = thyroglobulin, a large protein of 700,000 Da, Follicles in thyroid filled with colloid
Colloid contains thyroid hormone thyroxine (T4) and triiodothyronine (T3)
Thyroglobulin = protein your thyroid gland makes
Thyrglobulin = type of storage for T3, T4 before release
T3 and T4 are split off of it and enter blood where they bind to special plasma proteins
Synthesis of thyroglobulin under control of TSH of pituitary gland
Thyroid gland:
15 to 20 g (varies w/ diet, sex, etc.)
Larger in females than males
Only 3g of healthy thyroid needed to maintain euthyroid state (normal functional state)
What are the complete words for T3 and T4?
Thyroid hormone thyroxine
Triiodothyronine
What are the Tyroid hormones containing iodine (and their %?
What about the presence of iodine in the Thyroid hormones?
T4 = 90%
T3 = 9%
reverse T3 = 0.9%
-Availability of iodine limited in diet, etc.
- Cellular mechanisms developped for concentration, utilization of iodine in thyroid gland
- Thyroid follicular gland able to trap iodide and transport across the cell againsat chemical gradient (active transport)
How are the thyroid hormones synthesised?
- I- from plasma carried into thyroid follicular gland
- I- oxidized to Iodine (I2)
- I2 used of iodination of tyrosine residues of thyroglobulin (TGB) → forms monoiodotyrosine (MIT) + diiodotyrosine (DIT)
so I2 + TGB → MIT + DIT - Oxidative coupling of 2 DIT → Thyroxine (T4)
oxidative coupling of 1 MIT + 1 DIT → triiodothyronine (T3) - Hormones stored linked to thyroglobulin until go to plasma
*Rate of synthesis (all steps) ↑ by TSH
