introduction/overview Flashcards
neuronal intracellular messenger
neurotransmitters at synaptic junctions, which act locally
ex: Ach, NE
endocrine intracellular messenger
release of hormones from specialized glands or cells into the blood circulation to influence the functions of target cells some distance away (insulin, ACTH, oxytocin)
neuroendocrine
secretion of products from neurons that reach the blood circulation and influence the function of target cells distance away (CRH)
paracrine
cell secretion products that diffuse into ECF and effect neighboring cells
autocrine
cell secretion products that affect function of the same cell by binding to cell surface receptors
cytokine
secreted cell proteins that function as autocrines, paracrines or endocrines and often act on a broad spectrum of target cells
(ex: IL, LT, TNF alpha)
acetylcholine mediates communication at _____ and _____ nerve terminals
parasympathetic and somatic
norepinephrine mediates communication at ____ nerve terminals
sympathetic
NTs are produced both _____ and _____
centrally and peripherally
what are the neurohormones secreted from neuroendocrine cells?
antidiuretic hormone (ADH/vasopressin) and oxytocin
what hormones do not directly interact with neuronal systems and are not under direct influence of neuronal activity for release?
neurohormones
what makes hormones?
hypothalamus
hormones reach anterior pituitary through ____ system
circulatory
the pancreas releases what hormones into what?
insulin (beta cells) and glucagon (alpha cells) into muscle, adipose, and liver
the adrenal medulla is controlled by____ and releases _____ into what?
controlled by CNS
releases epinephrine into muscle, adipose, liver
3 groups of hormones based on chemical structure or synthesis
- proteins and peptides (TRH, GH, insulin)
- steroids (derivatives of cholesterol–testosterone, cortisol, estrogen)
- derivatives of tyrosine (from thyroid gland T3 & T4 and adrenal medulla–epinephrine and norepinephrine)
protein/peptide hormones are made in the -_____
rough ER
preprohormone
initially formed protein that is larger than the active hormone
preprohormone is cleaved to form a _____ in ER
prohormone
the prohormone is packaged in secretary vesicle in the _____
golgi apparatus
with endocrine cell stimulation, hormone and co-peptides are released into extracellular fluid by ______
exocytosis
steroid synthesis, storage, and secretion
- little storage of hormone in steroid endocrine cells but there are large stores of cholesterol esters for synthesis of steroid hormones
- hormone diffuses through cell membrane into EC fluid
- cholesterol removed from plasma for synthesis, but there is also de novo synthesis of cholesterol from acetate
steroids are synthesized from _____
cholesterol
like ____, steroids are _______ thus cross membrane barriers readily
thyroid hormones
lipid soluble
____ is needed for formation of thyroid hormones and catecholamines
tyrosine
how are thryoid hormones formed?
by enzymatic action in cytosol/cytoplasm
-synthesized by iodination of tyrosine amino acid on thyroglobulin in follicles within thyroid gland
how are thyroid hormones stored?
- no storage in discrete granules
- large stores of thyroxine (T4) and triiodothyronine (T3) as part of large iodinated protein (thyroglobulin) that is stored in lumens of thyroid gland follicles
how do thyroid hormones leave the gland?
diffusion through cell membrane
thyroid hormones are _____ soluble
lipid
catecholamines (CAs)
- adrenal medullary and sympathetic nerve hormones
- epinephrine and norepinephrine
- formed by enzymatic action in cytosol
storage and synthesis of catecholamines
taken up into preformed vesicles and stored until secreted by process of exocytosis
the cortex of the adrenal gland makes ____
aldesterone and cortisol
the medulla of the adrenal gland makes
epinephrine mostly
a little norepinephrine
chromaffin cell secretions
epinephrine mostly
a little norep
size of hormones required to control most metabolic and endocrine functions
super small
1 picogram–> few micrograms
VERY POTENT
rate of daily secretion super small
rate of hormonal secretion is mostly controlled by ______ mechanism
negative feedback mechanism
explain negative feedback
endocrine glands over secrete hormones
when too much function/activation of target cell occurs, negative feedback to endocrine gland decreases secretary rate (prevents over-activity)
negative feedback helps maintain ____
homeostasis
surges of hormones also occur with ____
positive feedback
ex: LH during ovulation
examples of cyclical variations of hormone release
- cortisol
- melatonin
how are water soluble hormones transported?
(peptides and catecholamines)
-dissolved in plasma and transported from their sites of synthesis/release to target tissues
steroid and thyroid hormones circulate in blood mainly bound to ______
plasma proteins
-serve as reservoirs (not active)
how are hormones cleared from blood?
destruction
binding to tissues
excretion via liver (bile) and kidneys
hormone-receptor interaction is coupled to _____ that causes a _____ by altering the activity and/or amounts of enzymes, carrier proteins, etc
coupled to a signal-generating mechanism that causes a change in intracellular processes
different types of receptors
- intracellular receptor (thyroid hormone)
- ion channel-linked receptor (acetylcholine)
- G-protein linked/coupled receptor (epinephrine)
- enzyme-linked/catalytic receptor (insulin)
role of second messengers
- cell responses to protein/peptide and CA mediated by second messengers
- mediate hormone responses through intracellular mechanisms
- coupling of receptors to SMG systems intracellularly
adenylyl cyclase (AC-cAMP)
- hormone-receptor interaction stimulates the CM-bound enzyme adenylyl cyclase
- stimulation of AC results in synthesis of SMG, cyclic AMP (cAMP) via G protein
- cAMP activates kinase A (PKA)–> protein phosphorylation that activates/inactivates target enzymes
phospholipids and SMG generation
- hormone receptor interaction–> activates CM-bound enzyme phospholipase C (PLC)
- PLC causes phospholipids in CM to split into SMGs, DAG, and IP
- DAG activates PKC
- IP3 mobilizes calcium from IC stores –> enhancing activation of PKC
- phosphorylation of enzymes by PKC activates or deactivates enzymes mediating hormone responses
- DAG hydrolyzed to form arachidonic acid, a precursor for PGs
calcium-calmodulin system
- hormone-receptor interaction activates calcium channels in membrane–> calcium entry from outside
- some calcium can be mobilized by IC stores by hormone
- Ca ions intracellularly, bind with protein calmodulin, forming a complex that alters activity of Ca dep enzymes (myosin kinase) and IC reactions–> phys responses
G-protein-independent mechanisms/effects
- involve cGMP
- cGMP=second messenger that mediates the effects of atrial natriuretic peptide/factor (ANF) and NO without involving G protein–> cause direct activation of guanylyl cyclase to produce cGMP from GTP
- peptide hormones (insulin/leptin) bind to CM receptors to cause phos of IC receptor sites –> alters enzymatic activity
how does insulin produce its effects
via activation of large transmembrane glycoprotein insulin receptor having 2 alpha and 2 beta subunits linked by disulfide bonds to form heterotetramer
insulin receptor is a _____
tyrosine kinase
cell responses to ____ and ____ hormones are mediated by stimulating protein synthesis via intraceullar receptors
steroid and thyroid
- hormones enter cells and bind to IC receptors in cytoplasm or nucleus
- H/R interaction –> conformational change in receptor
- H/R complex binds to specific sites on DNA strands in chromosomes, resulting in activation of specific genes, transcription and translocation of mRNA to cytosol for protein synthesis
down-regulation of receptors can occur due to:
- inactivation of some receptor molecules
- inactivation of some IC protein signaling molecules
- temporary sequestration of receptor to inside of cell
- destruction of receptors by lysosomes
- decreased production of receptors
