73 - HPA Axis Flashcards
Where is the median eminence (ME), w/r/t the hypothalamus?
What’s important about it?
- Floor of the hypothalamus
- Convergence point for axons
What hypothalamic nucleus is important for sleep?
SCN (suprachiasmatic nucleus)
What hypothalamic nucleus is important for feeding behavior/satiety?
ARC (arcuate nucleus)
What hypothalamic nucleus is important for thirst?
PVN (paraventricular nucleus)
What hypothalamic nucleus is important for reproduction?
POA (preoptic nucleus)
What hypothalamic nucleus is important for circadian rhythms?
SCN
What hypothalamic nucleus is important for mood/emotions/stress?
PVN/ARC
What hypothalamic nucleus is important for body temp?
POA
What hypothalamic nucleus is important for BP?
PVN
Name the major hypothalamic-releasing factors/hormones (7)
GnRH, GnIH, CRH, TRH, GHRH, SS, Dopamine.
What hypothalamic nucleus releases GnRH/GnIH?
Scattered; POA has majority
What hypothalamic nucleus releases CRH?
PVN (parvocellular)
What hypothalamic nucleus releases TRH?
PVN
What hypothalamic nucleus releases GHRH?
ARC
What hypothalamic nucleus releases Somatostatin (SS)?
What is the function of SS?
Periventricular Nucleus (PeVN) - GHRH inhibitor
What hypothalamic nucleus releases dopamine?
ARC
What type of hormones are most of the hypothalamic releasing hormones?
What are the exceptions?
Peptides
- Dopamine (Amine)
What cells are the pituitary targets of GnRH/GnIH?
What do these cells synthesize?
- Gonadotrophs
- FSH/LH
What cells are the pituitary targets of CRH?
What do these cells synthesize?
- Corticotrophs
- ACTH
What cells are the pituitary targets of TRH?
What do these cells synthesize?
- Thyrotrophs
- TSH
What cells are the pituitary targets of GHRH/SS?
What do these cells synthesize?
- Somatotrophs
- GH
What cells are the pituitary targets of dopamine?
What do these cells synthesize?
- Lactotrophs
- PRL
What is the common target of all hypothalamic-releasing hormones?
They all target the anterior pituitary
Explain where you’d find cell bodies for GnRH. Which nucleus has most of them?
- Scattered throughout the forebrain
- Largest concentration in POA
There are relatively few cell bodies that have GnRH (~1500-2000). Why are they scattered throughout the forebrain?
Redundant for species survival (need to be able to have offspring even if part of the hypothalamus is damaged)
How many AA’s long is GnRH?
10 AAs (decapeptide)
What is the receptor for GnRH?
GPCR (like most peptide hormones)
In what pattern is GnRH released?
Pulsatile
What type of dz Kallman syndrome?
What is the pathology?
What are the characteristics?
- Rare, genetic, occurs more commonly in men (heritable, x-linked, less commonly autosomal)
- GnRH neurons fail to migrate to CNS from olfactory placode
- Reproductive failure, anosmia
Regarding pulsativity of GnRH, high frequency stimulate release of _____ and low freq stimulates release of _____.
- LH
- FSH
(therefore each stimulated at separate times)
How is the anterior pituitary connect to the hypothalamus?
Hypophyseal portal system (vascular connection)
What a. gives rise to the capillary plexus in the anterior pituitary?
What is the name of this plexus?
- Superior hypophyseal artery
- Capillary plexus/portal plexus
W/in the ME, the capillary/portal plexus becomes the ________________.
Primary capillary plexus
The primary capillary plexus drains into __________________ to become the __________________.
- Hypophyseal portal veins
- Secondary capillary plexus
Where is GnRH pulsativity measured?
Hypophyseal portal vein (b/w primary and secondary capillary plexi)
TSH, FSH, LH, and hCG all share a common ________ subunit and have different ________ subunits.
- Alpha (common)
- Beta
*What is the 2nd messenger pw of GnRH? (recall: GPCR)
GPCR -> PLC-beta -> PIP2 -> IP3/DAG -> Ca2+ + PKC -> release of FSH/LH
What are the key differences in the GnRH 2nd msger pw that occur w/hormone synthesis vs. hormone release?
- Synthesis: PIP2 -> DAG -> PKC -> ^FSH/LH synthesis
- Release: PIP2 -> IP3 -> Ca2+ -> ^FSH/LH release
What’s another name for the anterior pituitary?
Posterior?
- Ant: Adenohypohpysis
- Post: Neurohypophysis
(Pituitary = hypophysis)
What are the names of the 2 major connections b/w hypothalamus and pituitary?
- Tuberoinfundibular system
- Neurohypophyseal tract
What comprises the tuberoinfundibular system?
All neurons that send axonal projections to the ME. Hormones target the anterior pituitary through the capillary system (endocrine).
What comprises the neurohypophyseal tract?
Neurons whose axons terminate in the posterior pituitary (no portal system).
Name the regions of the anterior pituitary. Which is the largest?
- Pars distalis (90%)
- Pars tuberalis
- Pars intermedia
Name the regions of the posterior pituitary.
- Pars nervosa
- Infundibulum (stalk)
What is the anterior pit derived from?
Embryonic foregut (glandular tissue + cords of epithelial cells)
What is the posterior pit derived from?
Neuroectoderm (terminal axons + glial cells)
Axons from___________ neurons terminate in neurohypophysis.
magnocellular
What artery supplies the posterior pituitary, even though it doesn’t rely on a plexus?
Inferior hypophyseal artery (anterior supplied by superior hypophyseal artery.
What are the major hormones released from the posterior pituitary?
AVP and OXY
What are herring bodies?
- In posterior pituitary
- Dilations of unmyelenated axons near the terminals
The _____________ is the interface for all hypophysiotrophic hormones
ME
What is special about the ME, in terms of its relationship with the blood?
Lies outside the BBB?
- Forms the floor of the 3rd ventricle.
What are the categorical names of the different cells of the anterior pituitary? (not corticotrope, etc)
Acidophils, basophils, and chromophobes (paracrine)
Which are most abundant- acidophils, basophils, or chromophobes?
- Chromophobes (50%)
- Acidophils (40%)
- Basophils (10%)
On staining, what is the appearance of acidophils, basophils, and chromophobes?
- Acidophils: light stain
- Basophils: dark stain
- Chromophobes: clear
What cells fall under the category of acidophils?
Basophils?
Acidophils: somatotrophs, lactotrophs
Basophils: corticotophs, thyrotrophs, gonadotrophs
In regional distribution of the anterior pituitary, where are the lactotrophs?
Lateral
In regional distribution of the anterior pituitary, where are the corticotrophs?
Center
In regional distribution of the anterior pituitary, where are the thyrotrophs?
Most anterior (away from posterior pituitary)
In regional distribution of the anterior pituitary, where are the somatotrophs?
Lateral
In regional distribution of the anterior pituitary, where are the gonadotrophs?
Scattered
Which of the anterior pituitary cells are most numerous?
Least?
- Somatotrophs
- Thyrotrophs
Axons from___________ neurons terminate in adenohypophysis.
parvocellular
When is the circadian peak of plasma GH?
Night
When is the circadian peak of plasma ACTH?
Morning
Kallman syndrome is a relatively rare disorder that manifests in patients as infertility and anosmia. Which one of the following best explains the link between reproductive disorders and anosmia?
A. GnRH inhibits olfactory signaling pathways
B. GnRH neurons originate from the olfactory placode
C. GnRH neurons fail to extend their axons to the olfactory area in the brain
D. GnRH is overexpressed in the brain
E. GnRH neurons migrate from the brain to the olfactory placode during development
B. GnRH neurons originate from the olfactory placode
