endocrinology: pituitary

Question 1

what is main site of hormone release

Answer 1

pituitary gland

Question 2

what kind of molecules can hormones be

Answer 2

amines, peptides or steroids

Question 3

where are peptide hormones secreted

Answer 3

pituitary gland, parathyroid, heart, stomach, liver and kidney

Question 4

where are amines secreted

Answer 4

amines derived from tyrosine are secreted from thyroid and adrenal medulla

Question 5

what are steroid hormones, where are they secreted and how do they act

Answer 5

steroids are lipids derived from cholesterol, secreted by gonads, adrenal cortex and placenta, including testosterone and estradiol

steroid hormones bind to nuclear membrane receptors producing acitvated hormone receptor complex, which binds to DNA activating specific genes

steroid hormones use transport proteins called globins which carry them in the intracellular aqueous environment.

Question 6

how does developmental origin of organs effect hormone secretion

Answer 6

glands of ectodermal and endodermal origin during development produce peptide and amine hormones, mesodermal glands produce steroid hormones.

Question 7

how do hormones produced in brain reach circulation

Answer 7

hormones are produced in brain, transported down axons to the posterior pituitary, anterior pituitary has vascular supply which convey signals causing release in hormone

Question 8

where does synthesis of posterior pituitary hormones occur

Answer 8

synthesis of posterior pituitary hormones occurs in cell bodies of magnocellular neurones (PVN (paraventricular nucleus) and SON(supraoptic nucleus)), axonal transport from hypothalamus to posterior pituitary

Question 9

what are cells types in the pituitary that can be differentiated by dye, what hormones do they secrete

Answer 9

when anterior pituitary tissue is stained with dyes such as hematoxylin and eosin, 3 distinct types of epithelial cells; acidophils whose cytoplasm stain red/pink, basophils whose cytoplasm stain blue/purple and chromophobes cytoplasm stains poorly

acidophils contain polypeptide hormones: somatotropes and lactotropes

basophils contain glycoprotein hormones: thyrotropes and gonadotropes as well as corticotropes which produce ACTH which is polypeptide

chromophobes have minimal or no hormonal content, may be acidophils or basophils which are depleted of hormone or stem cells which have not yet differentiated

Question 10

where is thyroid stimulating hormone produced, what is its effect

Answer 10

thyrotrophs, stimulates synthesis and secretion of thyroid hormones, these cells are in anterior pituitary

Question 11

where are LH and FSH produced, what is their function

Answer 11

gonadotrophs in anterior pituitary, stimulate steroid biosynthesis and germ cell maturation in gonads, stimulat ovaries,

Question 12

where is ACTH produced, what is its function

Answer 12

corticotrophs in anterior pituiary, stimulates steroid in adrenal cortex

Question 13

where is growth hormone produced, what are its effects

Answer 13

somatotrophs in anterior pituitary, stimulates growth via IGF-1

Question 14

where is prolactin produced, what are its effects

Answer 14

lactotrophs in anterior pituitary, lactation

Question 15

which anterior hormones are glycoproteins

Answer 15

TSH, LH and FSH are heterodimeric glycoproteins, they have common alpha subunit and different specific beta subunits

Question 16

what is structure of peptide hormones of anterior pituitary

Answer 16

ACTH it is a 39AA long fragment of POMC

growth hormone and prolactin are 190 AA peptides

Question 17

where is melanocyte stimulating hormone secreted

Answer 17

in the intermediate lobe which is between posterior and anterior pituitary

Question 18

what role does hypothalamus have in pituitary endocrinology

Answer 18

synthesis and secretion of anterior hormones can be under control of hypothalamic releasing hormones and hypothalamic inhibitory factors

Question 19

what hormones are produced by the hypothalamus, what are their effects on other hormones

Answer 19

TRH released from hypothalamus stimulates TSH

GnRH stimulates LH and FSH

CRH stimulates ACTH

GHRH stimulates growth hormone

somatostatin inhibits growth
hormone

stimulatory hormones from hypothalamus increase stimulation of either adenylate cyclase or phospholipase C

Question 20

describe the axis involved in growth hormone

Answer 20

GHRH released from hypothalamus, causes stimulation of growth hormone from anterior pituitary

growth hormone stimulates IGF-1 release, which produces negative feedback to growth hormone and GHRH

IGF-1 is produced in the liver, somatostatin produced in hypothalamus inhibits growth hormone

stress also inhibits GHRH

Question 21

how is prolactin release controlled

Answer 21

negative control by dopamine

Question 22

describe the HPT axis

Answer 22

THR from hypothalamus stimulates TSH which stimulates thyroid hormones T3 and T4, all hormones provide negative feedback to previous hormones

Question 23

describe the HPG axis

Answer 23

GnRH stimulates LH and FSH which stimulate progesterone, oestradiol and testosterone

all hormones inhibit previous hormones that stimulate them

Question 24

what is HPA axis

Answer 24

CRH from hypothalamus stimulates ACTH from anterior pituitary which stimulates cortisol production in adrenal medulla

usual axis negative feedback

Question 25

what are the different levels of feedback in hormone axes

Answer 25

short loop negative feedback from anterior pituitary to hypothalamus
long loop is from outside hypothalamo-pituitary complex, effects of gonadal steroids and corticosteroids
higher brain centres can over ride negative feedback, example; chronic stress overrides negative feedback on CRH and ACTH and increases negative feedback on GnRH and GHRH

Question 26

what may cause lack/ too much of pituitary hormones, what are effects of this

Answer 26

functional disconnection of pituitary gland may happen due to cranial trauma, pressure on pituitary stalk (due to a tumour) or inflammation/infection, defects in migration of hypothalamic neurones

hyposecretion of anterior pituitary hormones; due to rare mutation in genes, can cause dwarfism, may be due to radiation harming somatotrophs which are sensitive

hypersecretion of anterior pituitary hormones; most common functional pituitary tumors; prolactinomas; cause lactation (galactorrhea) and infertility (suppression of HPG axis)

GH hypersecretion causes giantism in infancy or acromegaly in adults

Question 27

what are hormones secreted by posterior pituitary

Answer 27

2 posterior hormones; oxytocin and vasopressin, both 9AAs long, only differ in 2 AAs, both packed in grandules and secreted with carrier proteins called neurophysins

Question 28

how does vasopressin regulate body water

Answer 28

vasopressin increases water permeability of water duct via aquaporins, increases urea permeability and salt reabsorption

cells in hypothalamus measure osmolality of the blood plasma

Vasopressin produced in supraoptic and paraventricular nuclei transported to and released from posterior pituitary

vasopressin also regulates blood pressure via urine volume

standard osmolality of blood plasma is 290 mOsm/kg

Question 29

what is oxytocin, how is it produced

Answer 29

oxytocin stimulates milk ejection, smooth muscle contraction in uterus at birth, establishes maternal behaviour

oxytocin secretion is stimulated by positive feedback mediated by neural reflexes, causing suckling reflex and fergusson reflex