Endocrinology1 Flashcards
Endocrinology is concerned with the study of the biosynthesis, storage, chemistry, and physiological function of hormones and with the cells of the endocrine glands and tissues that secrete them.
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The endocrine system is composed of a numerous (duct or ductless?) glands in different parts of the body, that secrete hormones directly into the ____ rather than into a ____ system.
ductless
blood
duct
Endocrine system is an anatomically and functionally connected system.
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Just functionally
endocrine glands can talk to one another
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one hormone may have several effects on different target organs
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one target organ can’t be affected by more than one hormone.
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The target cell/organ
-if the target cell does not have a receptor for the signaling molecule, it can still respond to the signal under some conditions
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It can’t
Paracrines
- local chemical messengers that exert their effects only on neighboring cells
- they are not transported in any quantity through the blood stream.
- E.g. histamine (involve in inflammatory response,causing localized vasodilatation)
(B)Autocrine
-in which a cell secretes substances that affect the function of the same cell by binding to the cell surface receptors.
(C)Neurotransmitters
- are very localized signaling molecules
- acting only across the space of the synapse, neuromuscular junction, or neuroeffector junction.
(D)Neuroendocrine
-in which neurons secrete substances (neurohormones) that reach the circulating blood and influence the function of cells at another location in the body
(E) Endocrine
- in which glands or specialized cells release into the circulating blood chemicals that influence the function of cells at another location in the body.
- They are the true long-range chemical messengers, secreted by the ductless glands.
Amines
- such as norepinephrine, epinephrine, and dopamine, are derived from single amino acids, in this case tyrosine.
- Thyroid hormones such as 3,5,3’-triiodothyronine (T3) and 3,5,3’,5’-tetraiodothyronine (thyroxine, T4) make up a subset of this class because they derive from the combination of two iodinated tyrosine amino acid residues.
- thyroid hormones
- stored in the protein thyroglobulin
- Hormone secretion occurs when the amines are split from thyroglobulin and the free hormones are then released into the blood stream.
- In the blood, most of the thyroid hormone combines with plasma proteins, which slowly releases the hormones to the target tissues.
- Act via the same mechanism as steroid hormones.
- Solubility:Thyroid hormones-lipophilic
Vc
Paracrines
- local chemical messengers that exert their effects only on ____ cells
- E.g. _____
neighboring
histamine
Paracrines are transported in only a little quantity through the blood stream.
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In no quantity
Histamine is involved in ______ response,causing localized _____
inflammatory
vasodilatation
Autocrine
-in which a cell secretes substances that affect the function of ____ cell by binding to the cell surface receptors.
the same
Neurotransmitters are slightly localized signaling molecules
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Very localized
Neuroendocrine
-in which ____ secrete substances (_____) that reach the circulating blood and influence the function of cells at another location in the body
neurons
neurohormones
Amines
-such as norepinephrine, epinephrine, and dopamine, are derived from _____ amino acids, in this case _______.
Single
tyrosine
Thyroid hormones such as ____-triiodothyronine (T3) and ____-tetraiodothyronine (thyroxine, T4) make up a subset of this class because they derive from the combination of __ iodinated ____ amino acid residues.
3,5,3’
3,5,3’,5’
two ; tyrosine
thyroid hormones
- stored in the protein ____
- Hormone secretion occurs when the ____ are split from ____ and the free hormones are then released into the blood stream.
thyroglobulin
amines
thyroglobulin
In the blood, most of the thyroid hormone combines with ____ , which slowly releases the hormones to the ___.
plasma proteins
target tissue
Thyroid hormones Act via the same mechanism as steroid hormones.
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Thyroid hormones are lipophobic
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Catecholamines
-Epinephrine and norepinephrine are formed in the ____, which normally secretes about four times more ____ than ____
adrenal medulla
epinephrine than norepinephrine.
Catecholamines are taken up into preformed vesicles and stored until secreted.
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Similar to the ____ hormones, catecholamines are released from adrenal medullary cells by ____.
protein
exocytosis
catecholamines are hydrophilic
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Peptide and protein
- consist of ___ to more than ____ amino acid residues
- can have molecular weights as large as _____.
three
200
30,000
TRH contains ___ amino acid
3
FSH contains ___ amino acid
200
Polypeptides with 100 or more amino acids are called ___, and those with fewer than 100 amino acids are referred to as ___.
-They are synthesized on the ___ of the different endocrine cells first as larger proteins that are not biologically active ( _____hormones) and are cleaved to form smaller ___hormones.
proteins
peptides
RER
prepro; pro
Prohormones are then transferred to the ___ for packaging into secretory vesicles stored within the cytoplasm or bound to the cell membrane until their secretion is needed.
-When needed, the secretory vesicles fuse with the cell membrane and the granular contents are extruded into the interstitial fluid or directly into the blood stream by ____.
Golgi apparatuses
exocytosis
The peptide hormones are _____ soluble, allowing them to enter the circulatory system easily and be carried to their target tissues.
water
Steroid
- are converted from their parent compound, ____.
- Mammalian steroid hormones can be grouped into five groups by the receptors to which they bind: glucocorticoids, mineralocorticoids, androgens, estrogens, and progestagens.
- The chemical structure of steroid hormones is similar to ____.
cholesterol
cholesterol
Steroid hormones Are Stored.
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They aren’t
Much of the cholesterol in steroid-producing cells comes from the ____
plasma
Steroids are ____ soluble so, once synthesized, they simply diffuse ____ and enter the _____ and then the _____
lipid
across the cell membrane
interstitial fluid
blood.
*Mechanism of steroids -binding to ____ receptor -binding of hormone-receptor complex directly on target DNA -regulation of transcription of specific target genes -can induce production of specific proteins
intracellular
Factors affecting hormone concentrations
*neuroendocrine reflexes
-stimulation of the nervous sytem affects hormone production or release
-examples: stimulation of the ___ in cats and ___ causes release of ___ and subsequent ____ or _____ reflex
cervix
rabbits
LH
ovulation
milk ejection
circadian and circannual rhythms :
-temporal patterns of hormone release e.g. ____ rise in ADH e.g. pituitary hormones in seasonal breeding animals
nocturnal
Factors affecting hormone action:
- Number of receptors and strength of binding
- Presence of other hormones eg antagonists
- Second messenger systems
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Endocrine Disorders
(1) Hypersecretion
* primary : problem with ——- causes oversecretion
* secondary :______ causes target gland to overproduce the hormone in question
gland itself
overproduction of trophic hormone
Hyposecretion
- primary:
- _____ defect (e.g. lack of or mutated steroidogenic enzyme)
- ____ deficiency (e.g. lack of iodine which is necessary for synthesis of thyroid hormones)
- destruction of gland by___ or ___ (e.g. autoimmune destruction of pancreatic Beta cells which produce insulin)
- secondary
- _______ of trophic hormone
(3) Abnormal target cell responsiveness e.g. insulin resistance
- defect in _____
- disorder of _____ system
(4)Altered metabolism of hormone -example is effect of antibiotics on _____
genetic
dietary
disease or injury
underproduction
hormone receptors ; second messenger
oral contraceptives
MECHANISMS OF ACTION OF HORMONES
- The first step of a hormone’s action is to ___ to ______ at the ____ cell.
- When the hormone combines with its receptor, it initiates cascades of reactions in the cell, with each stage becoming more powerfully activated so that even ___ concentrations of the hormone can have a ____ effect.
bind
specific receptors
target
small
Large
Cells that lack receptors for the hormones do not respond.
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Receptors are usually highly specific for a single hormone and are located on the target cell membrane (___,___,_____hormones) or the target cell cytoplasm (different ____ hormones) or even the target cell nucleus (_____ hormones)
protein, peptide, and catecholamine
steroid
thyroid
Some Hormones Change Membrane Permeability. E.g. as ____ and ______
epinephrine
norepinephrine
Some Hormones Activate Genes by Binding with Intracellular Receptors. Several hormones, especially the ___ hormones and ____ hormones.
steroid
thyroid
Some Hormones activate (or occasionally inactivation) Intracellular Enzymes When They Combine with Their Receptors.e.g.
Insulin
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Insulin+receptor Leads to formation of an activated ____.This ____ promotes _____ of several different substances inside the cell.
OR
*Leads to formation of activated enzyme _____.This cyclase in turn catalyzes the formation of ____, called a second messenger because it is not the hormone itself that directly institutes the intracellular changes; instead, it is the ____ that serves as a second messenger to cause these effects.
Kinase
Kinase
phosphorylation
adenylyl cyclase
cAMP
cAMP
STEROIDS
- The steroid hormone enters the ____ of the cell, where it binds with a specific receptor protein.
- The combined receptor protein-hormone then diffuses into or is transported into the ____.
- The combination binds at specific points on the ____ strands in the chromosomes which activates formation of ____.
- The mRNA diffuses into the ____, where it promotes the translation process at the ribosomes to form new proteins
cytoplasm
nucleus
DNA
messenger RNA
cytoplasm
the measurement of hormones, their precursors, and their metabolic end products are done using the method of
______( ___ )
Or
_______ ( _____ )
radioimmunoassay; RIA
Enzyme-linked immunosorbent assay
Feedback Systems
-Feedback systems are the primary means by which the endocrine system maintains a relatively constant rate of secretion
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Homeostasis is the general rule for the endocrine system
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Types of feedback
____ feedback
____ feedback
Negative
Positive
Negative Feedback:
-It prevents Overactivity of Hormone Systems.
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testosterone feeds back on LH to increase LH release
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Inhibits it
_____ feedback occurs when homeostasis is not the goal
Positive
the surge of luteinizing hormone (LH) that occurs as a result of the stimulatory effect of _____ on the _____ before ______.
-The secreted LH then acts on the _____ to stimulate additional secretion of _____, which in turn causes more secretion of LH.
- Eventually, LH reaches an appropriate concentration, and typical negative feedback control of hormone secretion is then exerted.
- the output of the system stimulates the input, which then stimulates more output, which stimulates more input, etc.
estrogen
anterior pituitary
ovulation
ovaries
estrogen
Cyclical-variations:
-Superimposed on the negative and positive feedback control of hormone secretion are ____ variations in hormone release influenced by seasonal changes, various stages of development and aging, the diurnal (daily) cycle, or sleep.
-E.g. secretion of growth hormone is markedly increased during the ____ period of sleep but is reduced during the ____ stages of sleep.
periodic
early
later
The concentrations of hormones required to control most metabolic and endocrine functions are (small or large?)
Small
Corpus Luteum produces which hormone (s)?
Estradiol and progesterone
____ of the cervix causes the posterior pituitary to secrete ____ which In turn, stimulates ______ , which causes _______.
In this example, the explosive event is _______
Dilation
oxytocin
uterine contraction
further dilation of the cervix
parturition
If more hormone is required to produce 50% of the maximal response, then there has been a ___ease in sensitivity of the target tissue. If less hormone is required, there has been an _____ease in sensitivity of the target tissue.
Decr
Incre
Human growth hormone contains ___ amino acids in a straight-chain polypeptide with ___ internal disulfide bridges.
191
2
The gene for growth hormone is a member of a family of genes for related peptides,_____ and ______.
prolactin
human placental lactogen
Human growth hormone is structurally similar to prolactin
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Prolactin, a ___–amino acid straight-chain polypeptide with ___ disulfide bridges, has ____% homology with growth hormone.
198
3
75
Human placental lactogen, a ____–amino acid straight-chain polypeptide with __ disulfide bridges, has ___% homology.
191
2
80
Growth hormone is secreted in a _____ pattern, with bursts of secretion occurring approximately every ____ hours.
pulsatile
2
The largest secretory burst of growth hormone occurs within __ of falling asleep (during sleep stages ___ and ____).
1hour
III
IV
Factors stimulating Growth Hormone Secretion
______ glucose concentration
_______ free fatty acid concentration
__-Adrenergic agonists
Decreased
Decreased
β
Factors affecting Growth Hormone Secretion
Pregnancy Fasting or starvation Stage III and IV sleep Obesity Arginine Senescence
Inhibits
Stimulate
Stimulate
Inhibits
Stimulate
Inhibits
Factors affecting Growth Hormone Secretion
Hormones of puberty Somatostatin Exercise Somatomedins Growth hormone Stress
Stimulate
Inhibits
Stimulate
Inhibits
Inhibits
Stimulate
The highest rates of growth hormone secretion occur during ____, and the lowest rates occur in _____.
puberty
senescence
GHRH stimulates growth hormone secretion by utilizing ______ as second messengers.
both cAMP and IP3/Ca2+
Somatostatin is also secreted by the _____ and acts on the somatotrophs to inhibit _____ secretion.
hypothalamus
growth hormone
Somatostatin inhibits growth hormone secretion by ____ the action of ____ on the somatotroph.
blocking
GHRH
Somatostatin binds to its own membrane receptor, which is coupled to ____ by a G_ protein, inhibiting the generation of _____ and decreasing growth hormone secretion.
adenylyl cyclase
i
cAMP
direct actions of growth hormone are mediated by _____ receptors.
Indirect actions of growth hormone are mediated through the production of ______ in the ____.
tyrosine kinase associated
somatomedins (or IGFs)
liver
Some IGF receptors are similar to the insulin receptor, having ______ activity and exhibiting _____
intrinsic tyrosine kinase
Autophosphorylation
growth hormone causes ____ease in blood insulin levels
Incr
Growth hormone causes insulin resistance
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linear growth, protein synthesis and organ growth work of growth hormone is mainly carried out by ????
Somatomedins
Growth hormone deficiency in children is treated with ________.
human growth hormone replacement
Laron dwarfism, in which growth hormone levels are _____ and treatment with growth hormone is ______.
In these individuals, ______ are defective; thus growth hormone cannot cause production of ____ in target tissues.
elevated
ineffective
growth hormone receptors
IGFs
Excess growth hormone Secretion after puberty cause insulin _____ and glucose _______
Resistance
Intolerance
Conditions with excess secretion of growth hormone are treated with __________ (e.g., ______ )
somatostatin analogues
octreotide
TRH is a stimulator of prolactin secretion
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Hypothyroidism causes ____prolactinaemia
Hyper
Factors Affecting Prolactin Secretion
Dopamine antagonists Sleep Stress Bromocriptine Somatostatin Prolactin
Stimulates
Stimulates
Stimulates
Inhibits
Inhibits
Inhibits
pregnancy does not have to occur for lactation to be possible
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Lactation occurs during pregnancy
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prolactin inhibits ovulation
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In males with high prolactin levels (e.g., due to a ______), there is a parallel (stimulatory or inhibitory?) effect on ____ secretion and ______, resulting in ______.
prolactinoma
inhibitory
GnRH
spermatogenesis
Infertility
The major symptoms of excess prolactin secretion are _____ and _____
galactorrhea and infertility
Factors Affecting Antidiuretic Hormone Secretion
Pain Nausea ANP Hyperglycemia (change to hypo that stimulates) Nicotine Ethanol α-Adrenergic agonists Opiates Antineoplastic drugs
Stimulates
Stimulates
Inhibits
Inhibits
Stimulates
Inhibits
Inhibits
Stimulates
Stimulates
To increase water permeability, ADH uses V_ receptor
To contract vascular smooth muscle uses V_ receptor
2
1
SIADH is treated with an ADH antagonist such as ______ or ______
demeclocycline
water restriction.
Opiods stimulate oxytocin secretion
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It inhibits
Suckling is required for oxytocin secretion
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It’s not
