Endocrine system Flashcards
what are the two communication systems in the body?
endocrine and nervous systems
In what two ways does communication of the endocrine system differ from communication in the nervous system?
route of communication
onset and duration of effects
what are the nine glands of the endocrine system?
pineal, hypothalamus, pituitary, thyroid, parathyroid, thymus, adrenal, pancreas, ovary/testis
Endocrine glands are ___ and require that ___ are released from a gland, and are transported in the ___/___ or other extracellular fluid to a ___ tissue.
ductless; hormones; blood/plasma; target
In order for there to be a response to a hormone or endocrine signal, what must the cells of a target tissue express?
functional receptors for that particular hormone
T/F. Specificity of responses is due to the presence of receptors, rather than the source of the signal.
True.
What are the three (four) major classes of hormones based on chemical structure?
- peptide and protein hormones
- steroid hormones
- amine hormones
- Eicosanoids
Peptide hormones are species specific and variability can exist due to ___.
glycosylations - affects the binding of hormones to the receptor
T/F. Peptides do not function as neurotransmitters. They only function as hormones.
False, the function as BOTH hormones and neurotransmitters. Examples include somatostatin and serotonin (5-HT).
In peptide hormone synthesis, the ___ is synthesized on ___ and includes extra amino acids and foldings.
preprohormone; ribosomes
The preprohormone forms the ___ by cleaving extra amino acids in the ___. Later it is packed into ___ ___ in the Golgi apparatus. Now, the hormone is called a ___.
prohormone; RER; secretory vesicles; hormone
When the hormone is secreted, what else is also released?
secretion of prohormone fragments from additional cleavage within the vesicle
what does packaging and storing peptide hormones permit?
the storage of large quantities for rapid release.
What does the use of precursor molecules prevent and limit?
prevents intracellular degradation
limits feedback efforts on the endocrine cells
Steroid hormones are ___ hormones, and are relatively ___ molecules.
lipid; small
T/F. Glandular sources of steroids are common.
False, glandular sources are rather limited.
What are the primary steroid producing organs?
gonads (ovaries/testes), adrenal CORTEX, and placenta
Where are steroids derived from?
cholesterol by a series of enzymatic reactions to produce FIVE different classes of steroids.
What are the five classes of steroids?
- progestagens
- androgens
- estrogens
- glucocorticoids
- mineralcorticoids
How is cholesterol produced?
de novo synthesis from acetyl CoA
T/F. Cholesterol is not a feature of all cells.
False, it is a feature of all cells because of cholesterol’s role as a membrane component.
Where is most of the cholesterol used for synthesis of steroid hormones derived from?
low density lipoproteins (LDLs)
LDLs in ___ are endocytosed into the steroidogenic cell and lysed to produce cholesterol ___ which are fairly ___-soluble.
circulation; esters; water
why is it a good thing that cholesterol esters are water-soluble?
so that they can be stored in lipid droplets. This causes the cells to appear white or fatty
The LDL is delivered to a ___ where the cholesteryl ___ is cleaved to yield free cholesterol to be utilized for membrane synthesis or is converted to ___ hormones and ___ acids.
lysosome; ester; steroid; bile
T/F. Cholesterol taken up by the cell inhibits the cell’s own cholesterol synthesis.
True.
How is steroid hormone synthesis is stimulated?
by peptide hormones from other glands
Once a steroid cell has been stimulated, what is the signaling cascade that results in the presence of free cholesterol in the cytoplasm?
- activate a G protein coupled receptor
- activate adenyl cyclase
- Increase cAMP
- activate PKA which stimulates the activity of cholesterol esterases
- Release of cholesterol from intracellular stores
What facilitates intracellular transport of cholesterol by binding to cholesterol and transporting it through the watery cytoplasm to the mitochondria?
steroid acute regulatory protein (StAR)
T/F. Steroid hormones cross the outer but not inner membrane of the mitochondria.
False, it crosses BOTH the outer and inner membranes
How and where is cholesterol converted into steroids?
by P450 enzymes in the mitochondria
What are P450 enzymes?
these are cytochrome P450 enzymes that add -OH or cleave C-C
Where are steroids shuffled for further enzyme modification?
SER
How do different cells or tissues make different steroids?
due to differences in the enzymes the cell synthesizes
T/F. Steroids are water-soluble so they are stored until needed.
False, steroids are LIPID-soluble so they are not stored and none of the intermediates can be stored.
How is the synthesis of steroids regulated?
by regulating the peptide hormone that stimulates their synthesis, the synthesis of steroidogenic enzymes, and/or the number of steroidogenic cells.
List the simplified pathway for steroid biosynthesis.
- cholesterol
- progestagens (progesterone)
- corticosteroids OR androgens (testosterone)
- estrogens (estradiol)
What type of hormones are derived from the amino acid tyrosine?
amine hormones
what are the four amine hormones?
T3/T4, norepinephrine, epinephrine, dopamine
Thyroid hormones are synthesized in the ___ gland where ___ and ___ are produced by the ___ of tyrosine at one or two carbons and combining iodinated molecules.
thyroid; T3; T4; iodination
Catecholamines or catecholaminergic hormones are synthesized in the ___ ___ or ___.
adrenal MEDULLA; hypothalamus
Match
- Norepinephrine (NE) (noradrenaline)
- Epinephrine (E) (adrenaline)
- Dopamine (DA)
A. Adrenal medulla
B. Hypothalamus
- A
- A
- B
Catecholamines are common ___ so other neurons, like the ___ nervous system, make them.
neurotransmitters; autonomic
T/F. NE, E, & DA are peptide-like with respect to solubility and receptors.
True, they are hydrophilic/polar
T/F. Most hormones are secreted in short bursts with the timing of the bursts controlled by an upstream signal.
True. NO hormone is released in between vesicular release or the next round of steroid synthesis.
The pattern of secretion produces variability in blood concentrations of hormones. Why does this produce a decrease in hormone concentrations between bursts?
due to clearance or metabolism of circulating hormones. example of T and LH
What is the circadian secretion due to?
reduced pulsatility, but can also be due to changes in amplitude. example GH and cortisol
Patterns of secretion are controlled by what three factors?
- plasma concentrations of a nutrient, eg GH and glucose
- neural control, eg neurons have rhythmic firing pattern
- hormonal control, eg GnRH - LH - T
T/F. Hydrophilic hormones readily dissolve in plasma when being transported.
True.
Lipophilic hormones require ___ proteins to increase their ___ in the plasma.
carrier; solubility
Where are carrier or binding proteins synthesized?
liver
How does the use of carriers affect the availability of hormone?
hormone must be released from carrier in order to bind to receptor
[free hormone] is a function of [binding protein]
How are binding proteins protective?
they protect the hormone from degradation and clearance
What organs contain enzymes that break down or inactivate a hormone? How is the done?
Liver and kidneys, but some degradation occurs in the blood due to the action of circulating enzymes
hydrolysis or sulfation
*note that in some cases, circulating prohormones are activated
Which type of hormones are highly susceptible to enzymatic degradation? Which are not and why?
Catecholamines and peptides are highly susceptible to enzymatic degradation
Steroid and thyroid hormones are less susceptible because they attach to binding proteins in the blood.
The amount of hormone circulating in the blood is a function of what?
what has been synthesized/secreted combined with the rate of clearance.
Peptide and catecholamine receptors (for hydrophilic hormones) are found where? Why?
They are on the cell surface/in plasma membrane because they are too large and/or too hydrophobic to pass through membrane
Peptide and catecholamine receptor activation causes a signal transduction pathway that facilitates a response within the cell to an extracellular signal known as what?
a second messenger system
What do ionotropic responses open?
ion channels, Ca2+, Na+, K+
___ responses alter cell activity, ___ proteins including second messengers move things around like receptors and vesicles.
Metabotropic; phosphorylate
T/F. Both rapid AND delayed responses are possible with peptide hormones and catecholamines.
True.
Which type of response includes responses to Ca2+ influx and protein phosphorylation? Which type occurs when the second messenger system alters protein synthesis?
rapid
delayed
Where are receptors for lipophilic hormones found?
Steroid or thyroid hormone receptors are found intracellularly and/or in the nucleus.
Receptor + ___ forms a DNA-binding protein that regulates ___. These responses are ___ because protein synthesis takes time.
ligand; transcription; delayed
T/F. There are membrane receptors for steroid hormones.
True. These receptors control rapid, non-genomic responses.
What is the central control of the endocrine function?
the hypothalamus and pituitary glands
What forms the floor of the diencephalon and surrounds the 3rd ventricle?
hypothalamus
The ___ gland lies below the hypothalamus in a depression in the sphenoid bone called the ___ ___. What is another name for this gland?
pituitary; sella turcica; hypophysis
The ___ is the stalk of tissue that connects the pituitary gland to the base or ___ ___ of the hypothalamus.
infundibulum; median eminence
Which structure contains several nuclei or clusters of neuronal cell bodies?
the hypothalamus
The anterior pituitary gland or ___ develops from an outpocketing of the ___ ___ that pinches off from the ___ of the mouth and lies above the ___.
adenohypophysis; oral ectoderm; roof; palate
The ___ pituitary gland or neurohypophysis buds off the ___ of the hypothalamus and is suspended below the brain by the ___.
posterior; floor; infundibulum
Which portion of the pituitary gland contains the axon terminals of neurons within two hypothalamic nuclei that passed thru the infundibulum?
posterior pituitary gland
What two hormones are released from the posterior pituitary gland?
oxytocin and vasopressin
T/F. Oxytocin and vasopressin are steroid hormones.
False, they are peptide hormones.
Posterior pituitary hormones are synthesized in the neuronal cell bodies in the ___ and ___ nuclei and secretory vesicles are stored in the axon terminals within the posterior pituitary.
supraoptic; paraventricular nuclei
Posterior pituitary hormones are released into ___ of the systemic circulation in response to ___ ___ in the hypothalamic neurons.
capillaries; action potentials
T/F. The posterior pituitary synthesizes hormones in addition to receiving some from the hypothalamus.
False, NO hormones are synthesized in the posterior pituitary - it is simply the site of release for hormones synthesized in the hypothalamus.
What are the functions of oxytocin and vasopressin?
Oxytocin stimulates smooth muscle contraction
Vassopressin (or antidiuretic hormone) has actions in the kidney and blood vessels to regulate blood pressure.
T/F. The anterior pituitary gland is an extension of the hypothalamus.
False, it is NOT an extension of the hypothalamus, but it is regulated by hormones secreted by hypothalamic neurons.
Hypothalamic neurons secrete ___ or releasing hormones whose axon terminals lie in the ___ ___. At the base of this structure are the ___ blood vessels.
hypophysiotropic; median eminence; portal
How do hypothalamic hormones get transported to the anterior pituitary?
they are transported in the blood within the portal vessels of the anterior pituitary
T/F. Releasing hormones are only stimulatory.
False, most are stimulatory but there are a few inhibitory ones.
In the anterior pituitary there are ___ (5/6) different cell types that produce ___ (5/6) PRIMARY hormones in response to different hypophysiotropic hormones.
5; 6
T/F. Hypophysiotropic hormones are often found elsewhere in the nervous system and they are NOT all peptides.
True. Dopamine is not a peptide hormone, it is a catecholamine.
What is often referred to as the neuroendocrine system?
the hypothalmo-pituitary portion of the endocrine system
Hypothalamus + pituitary + target = an ___
axis
What are the six primary hormones produced by the anterior pituitary gland?
FLAT PiG = FSH, LH, ACTH, TSH, PRL, GH
What other hormones come from the anterior pituitary?
Beta-lipotropin and Beta-endorphin
What are the products of proopiomelanocortin (POMC)?
ACTH, Beta-lipotropin and Beta-endorphin
What is a precursor polypeptide synthesized in corticotrophs that is cleaved to yield multiple peptides with varied actions and target tissues?
POMC
In addition to secreted hypophysiotropic hormones being stimulatory or inhibitory, how else can they be controlled?
by other hormones via feedback mechanisms
___-loop feedback is self-regulated by product/hormone of ultimate target tissue (eg. cortisol and ACTH/CRH).
Long
Short-loop negative feedback occurs when the hormone from ___(1st/2nd) gland in the axis affects the action of the ___(1st/2nd) gland (eg. LH and GNRH).
2nd; 1st
