endocrinology Flashcards
what is essential between the physiological processes which take place simultaneously?
coordination between these processes
how is long distance communication achieved?
through a number of chemical substances,
which are secreted by the releasing cells and interact with specific receptors on the distant target cells.
what does endocrine signalling involve?
Involves hormone secretion into the blood by an endocrine gland.
what are neurohormones?
Hormones involved are initially released by neurones
how is the hypothalamus linked to the pituitary gland
by a portal blood system
how does the portal blood system between the hypothalamus and the pituitary gland function?
Hormone A by the hypothalamus triggers the release of hormone B by the anterior pituitary gland. Hormone B then activates a target site (often another endocrine organ).
identify the type of signalling; Cell signals to adjacent target cells. No transport through blood?
Paracrine signaling
what is autocrine signalling?
Cell signals to self by producing hormones that interact with its own receptors.
what are the main steps involved in hormonal communication?
- synthesis of hormone
- release of hormone
- transport of hormone to target site
- detection of hormone by specific receptor
- change in cellular metabolism
- removal of hormone
what endocrine hormones are found in the brain?
hypothalamus
pituitary
what part of the pituitary gland is the extension of the hypothalamus?
posterior
which of the pituitary is neuronal?
posterior
what constitutes the hypothalamic-hypophyseal portal system
blood vessels of the pituitary stalk
what is the function of the hypothalamic-hypophyseal portal system?
allow Neurohormones from the hypothalamus reach the APG through these vessels.
how are peptide hormone synthesized?
synthesized by ribosomes and RNA pulled directly from the individual’s genes.
how are steroid and amine hormones synthesized?
they are not coded by DNA, but the enzymes required for their biosynthesis is coded
what is the other name given to protein hormones?
secreted protein
what is the additional sequence generally added to protein hormones
pre pro sequence
what is the function of the endoplasmic reticulum in sequencing of peptide hormones?
it Disposes of the pre sequence.
what is the function of the golgi apparatus in sequencing of peptide hormones?
Packs hormones into secretory vesicles. Disposes of
the pro sequence.
give a common glucocorticoid?
cortisol
give a common mineralocorticoid?
aldosterone
where are glucocorticoid and mineralocorticoids produced?
adrenal cortex
is the first ring of testosterone aromatic?
no
what is the precursor to estradiol?
testosterone
what does aromatase do?
it removes the methyl group from testosterone and converts it to estradiol
what are thyroid hormones produced from?
tyrosine
what are the main thyroid hormones?
T3 and T4
how do hormone receptors function?
through lock and key mechanisms –> complimentary binding
what are some properties of hormone receptors?
specificity
affinity
saturable
measurable biological effects
how are hormone receptors regulated?
up regulated: increased activity or synthesis
downregulated: decreased activity or synthesis
what are the 3 ways for hormones to exert effects on a target cell?
- Direct effects on function at the cell membrane.
- Intracellular effects mediated by second messenger systems.
‣ G protein coupled receptors that produce cAMP is a common type of second messenger system. - Intracellular effects mediated by genomic or nuclear action.
which type of hormone generally exerts effect on cell mediated by genomic nuclear action?
steroid hormones
how does it function for the effect of cell to be mediated by genomic nuclear action?
the cell receptors goes into the nucleus to regulate gene transcription
how are hormonal secretions regulated?
through feedback mechanisms
what does an excess of hormone or hormone activity lead to in negative feedback loop?
diminished secretion of the hormone
what system has a double negative feedback loop?
the hypothalamic-pituitary end organ axis where feedback is exerted on hypothalamus and pituitary
whats happens if under stressful conditions there is an increase of plasma cortisol?
negative feedback loop will signal the hypothalamus to decrease production of CRH and the anterior pituitary will decrease ACTH production
what are the 2 tissues that make up the pituitary gland
anterior (adenohypophysis)
posterior (neurohypophysis)
what type of tissue is the anterior pituitary?
endocrine
what type of tissue is the posterior pituitary?
neural tissue
what do the neurohormones secreted by the hypothalamus mostly target?
the anterior pituitary
what does GnRH produced in the hypothalamus target in the anterior pituitary?
+ FSH and LH
what does GHRH produced in the hypothalamus target in the anterior pituitary?
+ GH
what does somatostatin produced in the hypothalamus target in the anterior pituitary?
- GH
- TSH
what does TRH produced in the hypothalamus target in the anterior pituitary?
+ TSH
+ prolactin
what is Prolactin release inhibiting hormone?
dopamine
what does CRH produced in the hypothalamus target in the anterior pituitary?
+ACTH
what are the hormones secreted by the posterior pituitary?
Arginine vasopressin. Oxytocin.
what type of hormones are the hypothalamic hormones?
all peptide except for PIH
what organ do FSH and LH affect?
gonads
what role do FSH and LH play in the gonads?
germ cell development
what organs does GH affect
liver and many more
what organs does TSH affect
thyroid
what is the main function of TSH?
regulates secretion of T3 and T4
what organs does prolactin affect
breast
what is the main function of prolactin?
Controls breast development and milk production in females.
Facilitates reproductive function for males.
what does ACTH induce?
cortisol secretions
how are oxytocin and vasopressin synthesized?
in two hypothalamic nuclei whose axons run down the pituitary stalk and terminate in the posterior pituitary close to capillary blood vessels.
where are the prohormones of oxytocin and vasopressin
• The prohormones are processed in the secretory granules during axonal transport.
what is the half life of oxytocin and vasopressin? why?
1-3 minutes
short half life = easier to control
what are the functions of oxytocin in females?
- uterine contractions in parturition
- milk ejection in response to suckling
- decreased anxiety and enhanced pro-social behaviors
effects of oxytocin in males?
- decreased anxiety and enhanced pro-social behaviors
- ejaculation
how much does the thyroid gland weight
~15-20g
is the thyroid gland greater in males or females?
females
how much healthy thryoid is actually needed for proper function
only ~ 3g
what is thyroglobulin?
huge protein (700 000 Da) that bathes inside thyroid
what is the function of thyroglobulin?
serves as a source of amine, will also function as storage for T3/T4 before released into blood
synthesis of thyroglobulin is under control of what?
-TSH on pituitary
what cells usually produce thyroglobulin and used by what cells
follicular cells of the thyroid and used entirely within the thyroid gland.
how many iodines does t4 & t3 have?
T4: 4
T3: 3
why is reverse T3 not a hormone
because it does not bind to T3/T4 receptors
what cells are able to able to trap iodine and transport it across the cell membrane against a chemical gradient (active transport).
thyroid follicular cells
what is the rate of synthesis of T3/T4 increased by?
TSH
what is the release of TSH controlled by?
TRH
what is the function of TSH
increases the production of T3/T4
what happens when T3/T4 in blood increases?
negative feedback decreases secretions of TRH and TSH
what happens in cases of iodine deficiency to T3/T4?
Levels in circulation decreases
what happens to TSH under iodine deficiency?
it is constantly stimulated causing for thyroid to enlarge
what are some of the effects of thyroid hormones?
stimulation of calorigenesis increase of glucose uptake in muscles promotes glycogen increased lipid synthesis stimulate protein synthesis stimulate GH secretion, maturation of nervous system
does thyroid hormones increased BMR?
yes thus greater need for oxygen as well
do thyroid hormones affect growth?
yes, growth of various organs and tissues along with development of the brain
what may absence of thyroid hormones lead to?
- Absence of thyroid hormones leads to decreases neuronal development.
- Absence of thyroid hormones at early stages of life leads to irreversible mental retardation.
how does the mechanism of action of thyroid hormones function?
same as steroid hormones
bind to target cell cognat receptors and alter transcription of the specific genes
what type of iodine is used in radioactive plants
stable iodine. it limits the amount of radioactive iodine that enters the thyroid
what type of iodine is used to treat thyroid cancers?
radioactive iodine
what are some of the consequences of hypothyroidism?
decreased levels of T3/T4
low BMR
goiter (not always present)
what are some of the consequences of hyperthyroidism?
elevated T3/T4
elevated BMR
goiter (primary or secondary origin)
what is myxedema?
it is the inability to synthesize active thyroid hormones (primary hypothyroidism)
what may be the causes to myxedema?
- athrophy of thyroid
- hasimoto’s disease (destruction of cellular compartment by antibodies)
- non toxic goiter
when do symptoms for infantile hypothyroidism appear and why?
after a few month of birth, before in belly, thyroid hormones are supplied from the mother via placenta
what may infantile hypothyroidism lead to?
growth and mental retardation leads to
cretinism.
what is Secondary hypothyroidism.?
Failure to synthesizes TSH in the pituitary gland.
what is teritary hypothyroidism?
Failure to synthesizes TRH in the hypothalamus.
how can hypotheroidism be treated?
administration of synthroid
what is graves disease?
toxic diffuse goiter/ a form of hyperthyroidism
how is graves disease caused?
autoimmune disease where LATS mimic the action of TSH and constantly stimulate the release of T3/T4
what are the forms of primary hyperthryroidism?
graves disease and thyroid adenoma
what happens in secondary hypothyroidism?
No negative feedback from increased levels of T3/T4. TSH synthesis is autonomous.
what causes secondary hypothyroidism?
often a tumor to the pituitary
what causes tertiary hypothyroidism?
hypothalamic tumor
what happens in tertiary hypothyroidism?
No negative feedback from high T3/T4 to decrease thyrotropin releasing hormone secretions (TRH).
what treatments can be used for hyperthyroidism?
surgery
remplacement therapy
use drugs that block thyroid hormone synthesis
what are the main functions of CA2+
◦ Essential structural component of the skeleton.
◦ Normal blood clotting.
◦ Maintenance of the transmembrane potential with Na+ and K+.
◦ Excitability of nervous tissue.
◦ Muscle contraction.
◦ Release of hormones and neurotransmitters.
what is the general concentration of calcium intra/extracellular?
10mg/100 mL
how are plasma levels maintaiuned?
exchanges between bones and plasma
what hormones greatly impact levels of circulating calcium?
parathyroid hormone
calcitonin
vitamin D
which hormones increase levels of circulating calcium? which decreases?
parathyroid and vit D increase
decrease: calcitonin
calcium from diet is obtained through where?
duodenum and upper jejunum
what hormone increases calcium deposition in bones?
calcitonin
what hormone increases Ca2+ loss via kidneys?
calcitonin
what happens if plasma calcium is below 10mg/100mL
the parathyroid homrone will stimulate the
Reabsorption of Ca++ from the kidney.
◦ Removal of Ca++ from bones (bone resorption).
how many parathyroid glands do we have?
4
what happens if a parathyroid gland is removed?
will cause a severe drop in plasma calcium levels.
A Drop in plasma [Ca++] causes tetanic convulsions and death.
what is the structure of parathyroid hormone? what is needed for its full function?
84 AA but only the 34 from N terminal are needed for full activity
what is the name given to Parathyroid hormone before it is proteolytically cleaved?
preproparathyroid hormone
what is the half life of parathyroid hormone?
3-18 minutes
how does PTH increases levels of plasma calcium?
- bone resortion; increases demineralization of the bone
- kidney reabsorption from proximal convoluted tubules
- stimualtes synthesis of vitamin D (Active form)
- along with Vit D they increase absorption of Ca2+ in the gut
where does vitamin D synthesis take place?
kidneys
what controls PTH levels?
levels of circulating ca2+
what symptoms are associated with hypoparathyroidism?
Low plasma Ca++ (hypocalcemia).
‣ Production of biologically active vitamin D is decreased.
‣ More serious clinical problems - Tetany & convulsions.
• Ca++ < 7mg/100ml leads to increased neural overexcitability = muscle spasms.
• Spasms of laryngeal muscles may lead to death by asphyxiation.
how can hypoparathyroidism be treated?
administration of active vitamin D and Ca2+ supplements
what is hyperfunction of parathyroids generally caused by?
parathyroid adenoma
what symptoms are associated with hyperparathyroidism?
- high vitamin D
- high bone resorption and kidney reabsorption
- high ca2+ in circulation (kidney stones)
what serious problems can arise from hyperparathyroidism?
- cardiac arythmias
- depreessed neuromuscular excitability
- calcium deposition on the walls of the blood vessels
what treatment is used for hyperparathyroidism?
Surgery to remove the affected parathyroid glands & replacement therapy (1,25,D3 + Ca++).
what sources of food can vitamin D be found in?
cod liver oil
fatty fish
why is vitamin D technically not a vitamin?
because it can be synthesized from cholesterol
how is vitamin D synthesized?
UVB light + 7-dehydrocholesterol in skin.
◦ 25-hydroxylation in the liver (
◦ 1-hydroxylation in the kidney and several
peripheral tissues (PTH controlled).
‣ The end result is 1,25-
dihydroxyvitamin D3.
what functions does vitamin D have?
Increase Ca++ absorption from the intestine. ◦ Regulates the immune system - Anti- inflammatory. ◦ Anticancer properties.
what happens to vit D synthesis if calcium is low?high?
low: increased production of Ca2+ along with PTH
high: depressed synthesis
what will low levels of vitamin D cause?
osteomalacia in adults
rickets in growing individuals
what can absence of UVB cause?
VIT D deficency which may lead to bone demineralization
is a certain skin tone more prone to being vit D deficenct?
darker skin tones
what happens to patient with renal failture?
tends to have vit D deficency since 1-hydroxylase is not produced
what are the 2 causes to congenital rickets?
- lack of enzymes to produce vit D
- lack of VDR (bald)
what is calcitonin?
a 32 SS peptide
what manufactures calcitonin?
parafollicular C cell of the thyroid gland
is calcitonin as important as vit D and PTH on calcium homeostasis?
no, unless thyroid gland is removed
where are the adrenal glands located?
above kidney
are the adrenal glands heavier in males or females?
males
under the microscope, what does the adrenal cortex look like?
large lipid containing endothelial cell
under the microscope, what does the adrenal medulla look like?
chromaffin cells- fine brown granules when fixed with potassium
bichromate.
what part of the adrenal is derived from the mesoderm?
cortex
what part of the adrenal is derived from the neural crest?
medulla
what is produced by the adrenal cortex?
glucocorticoids, mineralocorticoids, progestins
what is produced by the adrenal medulla?
catecholamines & some peptide hormones
the cortex is composed of 3 distinct layers which are?
zona glomerulosa
zona fasciculata
zona reticularis
what is produced in the zona glomerulosa?
mineralocorticoids due to presence of 18-hydroxylase
what is produced in the zona fasciculata
mainly glucocorticoids due to presence of 17a-hydroxylase
what is produced in the zona reticularis
glucocorticois, progestins, androgens, estrogens
where do steroid hormones interact with steroid hormone receptors?
in the cytoplasm
do steroid need active transport to travel across the cell membrane?
no
where does regulation of transcription of steroid hormones take place?
inside the nucleus
what are the main roles of mienralocorticoids?
- Controls sodium metabolism by increasing the reabsorption of Na+ by the kidney.
- Affects the plasma concentration of K+ and H+.
what needs to be done in order to attain balance when pumping out certain ions?
balance is achieved as other ions get pumped in
what happens if aldosterone is in hypofunction?
High [H+] in circulation
what are some of the effects of glucocorticoids?
- salt retention (less than mineralocorticoids)
- effect on protein and cho metabolism
- effect on lipid metabolism
- antiinflammatory and immunosupressive properties
- decrease of protein matrix of the bone
how do glucocorticoids impact CHO and proteins?
increase break down of proteins into CHO along with decrease glucose uptake in muscles rapidly causes increase of blood sugar. if prolonged it may cause adrenal diabetes
how do glucocorticoids impact lipid metabolism?
FFA become the primary source of energy, but isn’t fully oxidized which leads to ketosis (acetone breathe) and may also lead to hyperlipidemia and hypercholesterolemia.
don glucocorticoid decrease or increase histamine production?
decrease; good for allergic reactions
what happens to wounds under high levels of glucocorticoids?
do not properly heal since inflammatory response is reduced
how are secretions of glucocorticoids controleled?
negative feedback on hypothalamus and anterior pituitary
what is ACTH?
a 39 AA peptide hormone produced by anterior pituitary
what may cause for adrenal hyperplasia?
11B- hydroxylase deficency causes for cortisol not to be produced and ACTH is left uncheck
how can adrenal hyperplasia be treated?
the deficency needs to be corrected and the ACTH levels need to be restored
