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The Endocrine System
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Lesson 28-31 Endocrine systemHormones:
- Define hormones? chemical substance secreted by endocrine glands into the
circulation in small amounts and delivered to target tissues, where they produce
physiologic responses
➢ What are the classic endocrine(secretes hormones) glands?
- Hypothalamus
- Posterior pituitary glands
- Anterior pituitary
Then we have organs that produce hormones like:
> Thyroid: calcitonin
> Pancreas: insulin
> Adrenal medulla: epinephrine and norepinephrine
> Kidney: renin
> Adrenal cortex: cortisol, aldosterone
> Testes: testosterone
Hormone synthesis:
- 3 types of hormones depending on their synthesis:
- all of them are stored in secretory vesicles waiting to be released when signalled
● Peptide/protein hormones > synthesized from aas
● Steroid hormones> derivatives of cholesterol
● Amine hormones>derivatives of the aa tyrosine
Regulation of secretion:
- 2 mechanisms to control regulation=
➢ Neural mechanisms: CNS sends msg to the gland to begin secreting
➢ Feedback mechanisms: secretion of a particular hormone decreases or
increases secretion of the hormone
- Positive feedback>> secretion increases its secretion
- Negative feedback>> secretion of hormone decreases secretion
Negative feedback(autocontrol) has 2 main pathways
● Short loop=
1 gland that secretes the hormone is controlling in a short pathway, the effector
organs and the secretory organ( occurs in the Hypothalamic hipophysary(idk what this word is im
guessing the spelling based on fernando lol) access
, ● Long loops=
Effector organ that is secreting the hormone is the one that controls the controlling
organs for the secretion of the organ
When is positive feedback used? In an explosive process that needs a quick effect.
Ex, oxytocin=
- The delivery of a newborn causes a positive feedback to release oxytocin to begin
contraction and with increased stretching, oxytocin increases and increases
The mechanism of action for protein hormones:
- protein hormone action through extracellular receptors
➢ Show receptors in the membrane of the cell where the hormones bind to the
exterior of the cell and cause the desired effect.
The mechanism of action for steroid hormones:
- steroid hormone action through intracellular receptors
➢ derived from cholesterol so can cross through the membrane, show receptors
in cytoplasm of nucleus, bind to dna and replicate and transcribe from dna the
genes needed to produce the hormone
G proteins:
- G protein receptors Located on the membrane
- G protein is a trimeric protein made of an alpha, beta, and gamma subunit
- Alpha subunit capable to bind to GDP and GTP, and binds to GDP and detaches
from the rest of the protein and produces secondary messenger action
Secondary messengers action:
Adenylyl Cyclase(cAMP)=
- The alpha subunit from the G proteins activates Adenylyl cyclase by binding to GTP
and unbinding from The G protein.
- Adenylyl cyclase activates the increase in production of cAMP by degradation and
hydrolyzation of ATP. then activates protein kinase A which triggers phosphorylation
of proteins in the cytoplasm
Phospholipase C=
- Starts hydrolysis using Phospholipase C that transforms inositol diphosphate into
Diacylglycerol and IP3.
- Both Diaglycerol and IP3 interact with calcium to increase the levels of the protein
Kinase C concentration
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