Hypothalamus-Pituitary Relationship Flashcards
What are the nuclei of the hypothalamus?
PVN (Paraventricular Nucleus) POA (Preoptic Nucleus) ARC (Arcuate Nucleus) SCN/SC (Suprachiasmatic Nucleus) SON (Supraoptic Nucleus)
What is the median eminence?
The floor of the hypothalamus and the convergence point for axons
What are some general hypothalamic functions and the associated nuclei?
Sleep - SCN Feeding behavior/Satiety - ARC Thirst - PVN Reproduction - POA Circadian Rhythms - SCN Mood/Emotions/Stress - PVN/ARC Body Temp - POA Blood Pressure - PVN
What are some important hypothalamic releasing hormones?
GnRH (inhibited by GnIH) CRH TRH GHRH Somatostatin Dopamine
What do the hypothalamic releasing factors target?
the anterior pituitary
Discuss the type, origin, target, second messengers, and function GnRH
Peptide hormone (10AA) The brain nuclei are scattered, but the POA has majority Gonadotropes - FSH and LH IP3/DAG/PKC (via GPCR) Reproduction
Discuss the type, origin, target, second messengers, and function of CRH
Peptide (41AA) PVN Corticotrope - ACTH cAMP Glucocorticoids - Pleiotropic effects
Discuss the type, origin, target, second messengers, and function of TRH
peptide (3AA) PVN Thyrotrope - TSH IP3/DAG/PKC Thyroid Hormone - pleiotropic effects
Discuss the type, origin, target, second messengers, and function of GHRH
peptide (44AA) ARC Somatotrope - GH cAMP Growth and development
Discuss the type, origin, target, second messengers, and function of somatostatin
peptide (14AA) periventricular (PeVN) Somatotrope cAMP Inhibits GH
Discuss the type, origin, target, and function of dopamine
amine
ARC
Lactotrope - prolactin
Milk production
Discuss Kallman’s syndrome
genetic disease where neurons fail to enter the CNS
characterized by sterility and anosmia
X-linked: Kal1
autosomal: Kal2
Describe the hypophyseal portal system
vascular connections between the hypothalamus and pituitary gland
Describe the connections of the hypophyseal portal system
the anterior pituitary axons release hormones into the superior hypophyseal artery which carries them to the anterior pituitary
What is the importance of hormone pulsatility?
Can help in the sensitization problem
TSH, FSH, LH, hCG all require the common subunit alpha-glycoprotein subunit (alpha-GSU): Pulse frequency can determine which subunit & subsequent hormone is released
What are the two major pathways of the hypothalamic-pituitary connection?
Tuberoinfundibular system
Neurohypophyseal tract
Discuss the tuberoinfundibular system
Comprises all neurons that send projections to the median eminence - they have a portal system
Hormones target the anterior pituitary via the capillary system (endocrine)
Discuss the Neurohypophyseal tract
comprises neurons whose axons terminate in the posterior pituitary - does NOT have a portal system
What are the different anatomical landmarks of the anterior pituitary?
Pars distalis (90%) Pars intermedia Pars tuberalis
What are the different anatomical landmarks of the posterior pituitary?
Pars nervosa
Infundibulum (stalk)
What is another name of the anterior pituitary and what kind of tissue is it made up of?
Adenohypophysis
made up of glandular tissue: cords of epithelial cells
What is another name for the posterior pituitary and what kind of tissue is it made up of?
Neurohypophysis
made up of neural tissue: terminal axons and glial cells
What is the blood supply of the posterior pituitary?
via inferior hypophyseal artery - has it’s own capillary bed, does not use a portal system
From where do the axons that terminate in the neurohypophysis originate?
Magnocellular axons
What are the major hormones of the neurohypophysis?
Arginine vasopressin (AVN) and oxytocin (OXY)
How do the hormones synthesized in magnocellular axons reach the neurohypophysis to be released?
Axonal transport
What are Herring bodies?
Dilations of unmyelinated axons near their terminals (terminal end of axons where hormones are temporarily stored)
Contain vesicles of either AVP or Oxytocin plus a binding protein, neurophysin
What is the significance of the median eminence (ME)?
the interface for all hypophysiotrophic hormones
Discuss some anatomical features of the median eminence
Lies outside the BBB (signals don’t have to cross BBB to reach the ME) and forms the floor of the third ventricle
What are the 5 major cell types in the anterior pituitary?
Acidophils (40%): somatotrophs and lactotrophes
Basophils (10%): corticotrophs, gonadotrophs, thyrotrophs
Chromophobes (50%)
What do somatotrophs secrete?
Growth hormone (GH)
What do lactotrophs secrete?
Prolactin (lactation)
What do corticotrophs secrete?
ACTH (stress)
What do gonadotrophs secrete?
LH/FSH (reproduction)
What do thyrotrophs secrete?
TSH
What do chromophobes do?
paracrine actions
Where is ACTH generally secreted?
centrally
Where is GH/PRL generally secreted?
in the periphery
Where is TSH generally secreted?
Anteriorly
Do hormones have a circadian rhythm?
Yep!
