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Endocrinology Introduction


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What is the advantage of the nervous system?
It is fast and specific because there are physical, ANATOMICAL connections between Neurotransmitters and target cells.
what are the messengers that communicate in the nervous system? What is their effect?
Neurotransmitters - they act on receptors, to open and close ion channels.
What is the difference between ionotropic and metabotropic receptors?
Metabotropic receptors open ion channels with G proteins, indirectly.
What are examples of
-Ionotropic receptors?
-Metatotropic receptors?
Iono: GABA a

Metabo: adrenergic receptors
What's faster, Nervous or endocrine system?
Why is endocrine slower?
Because messengers (hormones) travel in the blood
What gives the endocrine system specificity?
Whether or not the a cell has a receptor or not
What is a target cell?
The cell with a receptor specific for one hormone
What are paracrines?
chemical messengers that exert an effect in the same area that the cell that made the hormone is - affects its neighbors.
What are autocrines?
chemical messengers that release into Interstitial fluid and act on the very cell that secreted it.
What are the 6 fuctions of the endocrine system?
1. Control metabolism
2. Control ECF vol/composition
3. Regulate Digestive tract secretions and motility of the digesting food inside it.
4. Adaptation to stress and hostile environments
5. Coordination of growth and development
6. Regulation of reproduction
What are the 6 Steroid hormones?
Sex hormones (androgens/estrogens/progestins)
Calciferols - (VitD)
What are the steroid hormones made from?
Cholesterol - don't need a surface receptor b/c they are lipid-soluble.
When you measure a hormone in the body, what amount do you measure?
The TOTAL amount: what's bound to carrier proteins, and what's free in the plasma.
What amount of the hormone has its effect on targets?
Only what is free in plasma; only a small fraction of total hormone.
What are the Peptide and Protein hormones?
Hypothalamic hormones
Pituitary hormones
GI hormones
PAncreatic hormones
more (parathyroid, calcitonin, EPO, IGF-1, angiotensin II, erythropoeitin, ANP)
How do peptide and protein hormones tell the target to do something?
By binding to the surface receptor.
What are the amino acid derivative hormones?
Thyroid hormones
Which two hormone categories need an intracellular receptor, but not a surface receptor?
Steroids and Thyroid hormones.
What are the catecholamines?
Epinephrine, norepinephrine, dopamine.
What are the thyroid hormones?
Thyroxine and Triiodothyronine
how do thyroid an steroid hormones effect their targets?
By diffusing through the cell membrane, binding a receptor, which binds a DNA or mRNA segment and alters protein synthesis.
What type of hormones bind to a cell surface receptor to act?
-Peptide hormones
What are the 2 messengers involved in 2nd messenger systems?
1: the hormone
2: the second messenger
What are the steps (in general) of an ACTIVATING 2nd msngr system?
1. Hormone binds receptor
2. Receptor couples to Gs
3. Coupling stimulates Adenylate Cyclase to form cAMP
4. cAMP stimulates protein kinase A (PKA) to phosphorylate proteins and gives the EFFECT.
What are two ways a cAMP/Adenylyl Cyclase system can effect a response?
-If the G protein 2nd msgr is Gs, it will STIMULATE adenylyl cyclase;
-If the G protein 2nd msgr is Gi, it will INHIBIT adenylyl cyclase.
What are the 6 types of 2nd msgr systems?
1. Regulate cAMP formation
2. Activate Phospholipase C
3. Activate PHospholipase A2
4. Regulate cGMP formation
5. Open cell membrane ion channels.
6. Receptors which are protein kinases themselves.
How does the phospholipase C 2nd msgr system work?
1. Hormone binds a receptor;
2. Binding activates Gq and turns on PLC.
3. PLC forms IP3 and DAG.
4.IP3 makes Ca2+ release from intracell. stores (ER)
5. Released Calcium has biological effects, DAG activates PKC.
What does Calcium released by IP3 do?
1. Activates calmodulin (in smooth muscle)
2. Activates Protein Kinase C (PKC)
3. Causes hormone/neurotransmit. release
What does DAG do?
Activates PKC, which phosphorylates proteins and gives biological effects.
What is the phospholipase A2 2nd msgr system for?
Generating Eicosanoids
What in the world are Eicosanoids?
Byproducts of arachadonic acid.
When catalyzed by COX, they produce prostaglandins.
What is COX?
Cyclooxygenase, an enzyme that catalyzes formation of prostaglandins from arachadonic acid.
Why are prostaglandins good?
They cause a fever, which fights bacterial infection.
What inhibits prostaglandins and fevers?
What hormone uses the cGMP 2nd msgr system?
Epinephrine; it binds its receptor and increases cGMP.
What two types of hormones use the 2nd msgr sytem where the receptor is itself a protein kinase?
-Growth factors
What hormones are use the PLC (phospholipase C) pathway?
-Smooth msucle contraction also activates PLC.
Whats an example of a biological system that experiences both inhibitory and stimulatory effects on cAMP and Adenylyl C?
What 2 types of receptors are on the SA node?
What binds to each?
-Muscarinic; Dopamine binds
-Beta-adrenergic; Epi binds.
What happens when the muscarinic receptor gets bound on SA node?
It activates the receptor and Gi protein INHIBITS adenylyl cyclase from activating PKA.
What happens when the adrenergic receptor gets bound on SA node?
it activates the receptor and Gs protein STIMULATES adenylyl cyclase; Protein Kinase A is stimulated to phosphorylate proteins for the effect.
Use the Growth Hormone producing cell as an example of cAMP 2nd msgr signalling.
GHRH binds the Adrenergic receptor; causes Gs to stimulate Adenylyl cyclase, activating PKC to phosphorylate proteins and release Growth Hormone!
somatostatin binds muscarinic receptor; causes Gi to inhibit Adenylyl cyclase so no Growth hormone is produced!
How are 2nd msgr systems used in the glucose/glycogen equilibrium?
the enzymes that catalyze glycogen synthesis and glycogen breakdown (phosphatase and synthase) are only active when phosphorylated.
How can one phosphorylate those enzymes needed for making glycogen and breaking it down?
by using the 2nd msgr system.
Insulin binds a receptor and causes the phosphorylation of Glycogen synthase, so glucose will be STORED away in the closet for later.

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