ME04 - Introduction to Endocrine Flashcards
Local chemical messengers secreted by cells into the ex
tracellular fluid & affect neighboring cells of a different
type
Paracrine/Juxtacrine (Histamine)
Affects cells of the same type
Secreted by cells into the ECF and affects the function of
the same cells that produced them by binding to cell sur
face receptors
Autocrines
Peptides secreted by cells into the ECF & can func
tion as autocrines, paracrines or endocrine hormones
Cytokines
Example of Cytokines
a. interleukins & lymphokines ? secreted by
helper cells & act on other cells of the immune system
b. Leptin (adipokines) ? secreted by adipocytes
Secreted by neurons into the circulating blood and influ
ence the function of cells at another location in the body
Neuroendocrine Hormones
Example of Neuroendocrine Hormones
ADH, OTC, & hypophysiotropic hormones
Released by endocrine glands into blood stream & influence function of target cells
Some affect almost all cells & organs (GH, Thyroid hormone, Catecholamines)
Other affect specific tissues (ACTH, TSH, FSH & LH)
Secreted by ductless glands in the endocrine system
Endocrine Hormones
Function of Endocrine Hormones
Play important role in homeostasis
Essential to the maintenance of the life & well being of an individual & of the species
Chemical Messengers
Secreted into the blood and acts on another location
Hormones
Main site of inactivation
Liver
Mechanism for removal of hormones
Kidneys, Liver
General Characteristics of Hormones
- Secreted by specific group of cells
- Thrown directly into circulation
- Exert effects on target tissues which are distant from the source of hormone
- Do not create an additional or new function, only modify or alter functions that already exists.
- Rate of secretion fluctuates. Increases when there is a need for it; minimal when need not present.
- Do not stay in the circulation forever
- Can undergo inactivation
- Main site of inactivation: LIVER
- Can be removed from circulation through kidneys.
- Plasma concentration of hormones tested by determining
Forms of Chemical Signaling
Autocrine ? cell targets itself
Signaling across gap junctions ? Cell targets a cell connected by gap junctions
Paracrine ? Cell targets nearby cell
Endocrine ? Cell targets a distant cell through the bloodstream
Hormones synthesized and secreteed by dedicated Endocrine Glands
Pituitary Gland ? GH, Prolactin, ACTH, TSH, FSH, LH
Thyroid Gland ? T4,T3, Calcitonin
Parathyroid Gland ? PTH
Islets of langerhans ? Insulin, Glucagon, Somatostatin
Adrenal Gland ? Epinephrine, NorEpi, Cortisol, Aldosterone, DHEAS
Ovaries ? Estradiol, Progesterone, inhibin
Testes ? Testosterone, AMH, Inhibin
Hormones Synthesized in Organs with Primary Function other than Endocrine
Brain (Hypothalamus) ? ADH, Vasopressin, Oxytocin, CRH, TRH, GnRH, GHRH, Somatostatin, Dopamine
Brain (Pineal Gland) ? Melatonin
Heart ? ANP
Kidney ? Erythropoietin
Adipose Tissue ? Leptin, Adiponectin
Stomach ? Gastrin, Somatostatin, Ghrelin
Intestines ? Secretin, Cholecystikinin, GLP-1, GLP-2, GIP, Motilin, IGF-1
Liver ? IGF-1
Classify Hormones
- PROTEIN HORMONE
- More common, Stored in vesicles
- BIOGENIC AMINES
- derivatives of tyrosine
- thyroid hormones (T3 & T4), adrenal medullary hormones
- derivative of histidine:
- histamine (mast cells inconnective tissues)
- derivatives of tryptophan
- melatonin (pineal gland)
- serotonin (blood platelets)
- derivatives of tyrosine
- STEROID HORMONE
- derivative of Cholesterol
- Synthesized as needed
Produces new proteins from DNA
Lipid-soluble
Reflection Coefficient closer to 0
STEROID HORMONES
Slow-acting; To produce 2 proteins from DNA
Modifies existing proteins
Water-soluble
Reflection Coefficient closer to 1
Protein Hormones - facilitates signals; Faster
Types of Hormone Receptor
G-PROTEIN LINKED HORMONE RECEPTORS
Transmembrane proteins loop in and out of the cell membrane seven times
Make use of G-Proteins
ENZYME-LINKED HORMONE RECEPTORS
Passes through the membranes only once
Makes use of intracellular enzymes directly
E.g. Leptin and its use of Tyrosine Kinase
G Proteins
- Heterotrimeric GTP-binding Proteins
- Act as TRANSDUCERS
- Link hormone receptors with 2nd messenger systems (Intracellular Enzymes and Ion Channels)
Intracellular Enzymes and Ion Channels
May be Gs Protein (stimulatory) or Gi Proteins (inhibitory)
3 subunits: alpha, beta, gamma
The Second-Messenger System
? cAMP/cGMP
? IP3/DAG
? Calcium-Calmodulin
? Tyrosine Kinase
Most common 2nd Messenger System
cAMP/cGMP System
MECHANISM
Alpha subunit of G proteins activates Adenylate cyclase and together with ATP ?>forms cAMP ?> activates protein kinase A
Used by all Hypothalamic Hormones EXCEPT CRH
- Mediates smooth muscle contraction by hor-mone/neutrotransmitter (e.g. Motilin in the GI)
Phospholipid System (IP3/DAG)
- MECHANISM
Phospholipase C ?> PIP2 ?>PIP2 splits into IP3(releases Calcium) and DAG (activates protein kinase C)
Used by Insulin, Growth factors, EPO, Leptin
Tyrosine Kinase
Pathway»_space; G protein»_space; Protein Kinase
cAMP»_space; Gs INC cAMP; Gi DEC cAMP; Adenylate Cyclase»_space; Protein Kinase A
IP3/DAG»_space; Gq INC IP3/DAG; Phospholipase C»_space; Protein Kinase C
cGMP»_space;———————-»_space; Protein Kinase G
Tyrosine Kinase»_space; ———-»_space; Tyrosine Kinase/ JAK-STAT
Intracellular (Steroid Hormones)
Must be transported bound to a protein in the blood
Lipid Soluble Hormones
Active form of Lipid Soluble Hormones
FREE, UNBOUND FORM
What is the Mechanism of Hormonal Action
On the target cell, the hormone in combination
with the receptor cells act by any of the following
mechanisms:
1. Alternating the permeability of cell membrane
- Neurotransmitter substances
- Activating the intracellular enzyme
- Protein hormones & catecholamines - Activating the gene
- Thyroid & steroid hormones
Mechanism for Regulation of Hormone Effects
MECHANISMS
- Hormone Secretion
- Hormone Receptors
Differentiate Negative from Positive Feedback
NEGATIVE FEEDBACK
?Products inhibit Precursors?
More common
E.g. Cortisol inhibiting ACTH Secretion from the Pituitary
POSITIVE FEEDBACK
?Products stimulate Precursors?
Rare, exploding
E.g. surge of LH before ovulation, Oxytocin during deli-very and lactation
Differentiate Down-Regulation from UP-Regulation of Receptors
DOWN-REGULATION OF RECEPTORS Decrease in: - Receptor Number - Receptor Affinity - E.g. in the uterus, progesterone down-regulates its own receptor and the receptor for estrogen
UP-REGULATION OF RECEPTORS Increase in: - Receptor Number - Receptor Affinity - E.g. in the ovary, estrogen up-regulates its own re-ceptor and that of LH
3 types of Hormone Interactions
Synergistic Effects | Permissive Effects | Antagonistic Effects
Differentiate 2 Types of Synergistic Effec ts (Additive & Complementary)
- ADDITIVE EFFECTS
- E.g. Epinephrine & NE effects on the heart
- COMPLEMENTARY EFFECTS
- E.g. FSH & Testosterone effects on spermatogenesis
Differentiate Permissive Effects vs Antagonistic Effects
. PERMISSIVE EFFECTS
- E.g. Cortisol has permissive effects on Epi & NE with regards to blood vessels; T3 has permissive effects on Epi with regards to lipolysis
ANTAGONISTIC EFFECTS
- E.g. Estrogen blocking Prolactin effects on the breasts during pregnancy
Equal to the rate of disappearance of hormone from the plasma/concentration of hormone in each milliliter of plasma
Metabolic Clearance Rate
Mechanisms: Tissue Destruction, Tissue binding, Bile Excretion, Urine Excretion
Hormone»_space; Pituitary target
GnRH >> FSH, LH CRH >> ACTH (B-LPH) TRH >> TSH (PRL) GHRH >> Somatotropin (GH) PRH >> TRH PIH >> Lactotrophs (PRL) MRH >> MSH MIH >> MSH
Where Oxytocin is produced
Paraventricular nuclei
Where ADH is produced
Supraoptic nuclei
Where hormones are stoed
Posterior Pituitary
