pack Flashcards
How many secretory cell types does the adenohypophysis have?
5 secretory cell types
How many hormones does the adenohypophysis secrete?
6 hormones
What regulates the adenohypophysis’s endocrine functions?
The hypothalamus
What is the hypothalamic–pituitary axis?
It is the functional connection between the brain and hormone regulation.
What are the 5 cell types of the adenohypophysis?
Somatotropes, Lactotropes, Thyrotropes, Corticotropes, and Gonadotropes.
What do somatotropes produce and what type of cell are they?
Acidophils, Produce GH
What do Lactotropes produce and what type of cell are they?
Acidophils, Produce prolactin
What do Thyrotropes produce and what type of cell are they?
Basophils, Produces TSH
What do Corticotropes produce and what type of cell are they?
Basophils, Produce ACTH
What do Gonadotropes produce and what type of cell are they?
Basophils, Produce FSH LH
What is the most numerous cell type in the Pars distalis?
Somatotropes
What cell bodies does the hypophysiotropic region of the hypothalamus contain?
Parvocellular cell bodies
Where do the parvocellular cell bodies extend their axons?
Towards the median eminence
How do the hormones released by the parvocellular cell bodies reach the adenohypophysis?
They reach it through a system of fenestrated capillaries through a main plexus then through the hypophyseal portal vessels to the secondary plexus where they reach the pars distalis of the adenohypophysis.
What hormone does not decrease in production even if the pituitary stalk is damaged?
Prolactin
How many endocrine axes are there?
5
What does each endocrine axis break down into?
Three levels: Hypothalamic neurons, Anterior pituitary cells, Peripheral endocrine glands.
What is primary, secondary, and tertiary endocrine disease?
Primary: Failure at peripheral gland. Secondary: Failure at the anterior pituitary cells. Tertiary: Failure at peripheral endocrine gland (eg. thyroid).
What is short loop and long loop feedback?
Short loop: Feedback from the hormones of the anterior pituitary onto the hypothalamus. Long loop: Feedback from the peripheral hormones from the target tissue onto the anterior pituitary and hypothalamus.
If the trophic hormone is high (e.g. TSH), but the target gland hormone is low (e.g. T4), what might be the cause?
The problem is caused by failure at the target gland.
If the trophic hormone is low (e.g. TSH), and the target gland hormone is low (e.g. T4), what might be the cause?
Trophic hormone deficiency
If the trophic hormone is high (e.g. TSH), and the target gland hormone is high (e.g. T4), what might be the cause?
Autonomous secretion of pituitary hormone or resistance to target gland hormone’s negative feedback.
If the trophic hormone is low (e.g. TSH), but the target gland hormone is high (e.g. T4), what might be the cause?
Autonomous secretion of target gland hormone
What hormone do parvocellular neurons synthesize?
Corticotropin Releasing hormone (CRH)
What exactly does CRH do?
CRH induces corticotrope cells in the pars distalis to increase the expression of the POMC gene which increases the production of the POMC prohormone which is then cleaved into ACTH and B-LPH.
What effects does abnormally high levels of ACTH and B-LPH have on melanin?
When ACTH is at supraphysiological levels (e.g. Addison disease) then ACTH can bind to the MC1R and along with β-LPH induces melanin deposition in melanocytes in the skin leading to skin darkening.
Where and what type of receptor does ACTH bind to?
ACTH binds to the melanocortin-2 receptor (MC2R) on cells in the zona fasciculata of the adrenal cortex.
What does ACTH stimulate the secretion of?
ACTH stimulates the adrenal cortex to synthesize the glucocorticoids, cortisol and corticosterone. The cortex also synthesizes androgens – dehydroepiandrosterone (DHEA).
At what time of the day does the secretion of ACTH peak?
Early in the morning.
What can severe chronic depression lead to?
Hyper secretion of CRH is a factor in the development of tertiary hypercortisolism.
What hormone does the parvocellular neurons synthesize that is related to the thyroid?
Thyroid releasing hormone (TRH)
What does TRH stimulate the secretion of?
It stimulates the secretion of TSH from the anterior pituitary.
What type of peptide is TRH?
It is a tripeptide.
What is TRH synthesized from?
TRH is synthesized as a larger prohormone that contains six copies of TRH within its sequence.
What are the three glycoprotein hormones of the anterior pituitary?
TSH, LH, FSH
What is the composition of TSH?
TSH is a heterodimer of α-glycoprotein subunit (α-GSU), and a β-subunit (β-TSH).
How do the subunits of TSH differ from those of FSH and LH?
The α-GSU is common to TSH, FSH, and LH, whereas the β subunit is hormone specific.
What does glycosylation of the subunits found in TSH do?
Glycosylation of the subunits increases their stability in circulation and enhances the affinity and specificity of the TSH.
Where is GnRH produced?
GnRH is produced by a subset of parvocellular hypothalamic GnRH neurons.
What is the hormone that FSH increases the secretion of in both genders?
Inhibin
What is kallman syndrome?
A syndrome that causes hypogonadotropic hypogondasim
due to lack of secretion of GnRH and therefore a lack of FSH and LH
Patients also usually don’t have a sense of smell
What are the symptoms of Kallman syndrome?
Small penis/undescended testicles at birth
lack of sexual development at puberty
No sense of smell
What does GH stimulate the secretion of in the liver?
insulin like
growth factor (IGF-I)
What is another protein synthesized by the anterior pituitary that is similar to GH?
PRL
and
human placental lactogen (hPL)
What peptide does the hypothalmus use to inhibit the release of GH and TSH?
Somatostatin
Remember that GH is released by Somatotrophs
What does Gherlin do in relation to GH and how does it work on receptors?
It stimulates the release of GH from GHS-R on somatotropes
What is the form the 50% of GH is in serum?
50% of GH in
serum is bound to GH-binding protein (GHBP)
How are IGFs transported in serum?
IGFs are transported in serum bound to IGF
binding proteins (IGFBP)
What are the two ways the IGF-1 inhibits GH?
IGF-1 inhibits GH secretion from
somatotropes and stimulates somatostatin release from hypothalamus
The receptor of what other anterior pituitary hormone can GH stimulate?
Human GH can also act as an agonist of the PRL receptor
Makes sense since GH is similar to PRL
Where is GHBP derived from and how does this explain the symptoms of Laron syndrome?
GHBP is derived from N terminal of the GH receptor
Individuals with Laron syndrome, who lack normal GH receptors but have normal GH secretion, do not have detectable GHBP in their serum
