May 17, 2016 - Pituitary Physiology Flashcards
Stalk
The stalk contains vasculature that connects the hypothalamus to the anterior pituitary.
It also contains neurons and axons which connects the hypothalamus to the posterior pituitary.
Pituitary Development
The brain has a little outpouch that wraps around the outpouch from the roof of the mouth (Rathke’s pouch).
Over development, Rathke’s pouch detaches from the roof of the mouth and becomes the anterior pituitary gland, while the outpouch from the brain becomes the posterior pituitary gland.
Hormones of the Anterior
ACTH
TSH
LH / FSH
GH
Prolactin
Hormones of the Posterior
ADH
Oxytocin
Development of Cell Types
Different cell types that secrete different hormones are needed in the pituitary.
These come from undifferentiated stem cells that need certain transcription factors in order to become these cells. In some individuals with mutations and stuff in some of these transcription factors, they can be deficienct in the cells that secrete certain hormones and therefore become deficient in hormones.
Stalk Damage
The stalk is very susceptible to shear forces.
If it is sheared, the anterior pituitary can infract because you lose 2/3 of the blood.
2/3 of the blood comes through the stock from the superior hypophyseal artery long portal vessels, while 1/3 of the blood comes from the short portal vessel of the inferior hypophyseal artery.
Anterior pituitary has dual venous supply.
Structures Around Pituitary
On the top, there is the optic chiasma
On the sides are cranial nerves 3, 4, and 5 which affect peripheral vision.
On the bottom there is the sphenoid sinus
Posterior Pituitary on MRI
Shows up as a bright spot
Sheehan’s Syndrome
During post-partum hemorrhage, blood is shunted to the core organs and the pituitary, because of the dual venous blood supply, actually infarcts on the anterior side. Can become deficient in hormones.
Rarely seen today because of good obstetrical care.
Pituitary Function and Radiation
Years after radiation, you can see a decline in hormone levels.
Growth hormone is the first to fail, then ACTH, then LH/FSH, and last is TSH.
Dopamine and Prolactin
Dopamine levels inhibit prolactin production.
Prolactin is only necessary for a few select times, at which point dopamine levels are suppressed and prolactin is made.
Measuring Hypothalamic Releasing Hormones
YOU CANT
You can measure all the pituitary hormones though and the target gland hormones.
Most Important Hormone
ACTH
Without cortisol you will die.
Skin and Excess ACTH
Because melanin is in the same pathway as ACTH, if you have excess signalling peptide to make more ACTH, you will also activate melanin and become dark-skinned
Approach to Low Cortisol
You need to look at ACTH levels.
If ACTH levels are low, this is a central problem as it should be secreting high levels to stimulate cortisol. If levels are high, this indicates an adrenal problem because the adrenals are not responding to the high ACTH.
