Lecture 2 Flashcards
Neurohypophysis of the pituitary.
(This is the posterior pituitary).
Includes median eminence, infundibular stalk (upper and lower) and infundibular process (pars nervosa).
Adenohypophysis of the pituitary.
(This is the anterior pituitary).
Includes pars tuberalis and pars distalis.
Some mammals, not humans, have a pars intermedia
Posterior lobe of pituitary components
Infundibular process (pars nervosa)
+
Pars intermedia
Anterior lobe of pituitary components
Pars tuberalis
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Pars distalis
Anatomical location of pituitary
Sits in a fossa inside the spend bone -> pituitary fossa (in sphenoid sinus).
Surgical access -> through the nose / nasal cavity and through the sphenoid bone to the pituitary.
Diaphragma sella
A protective sheet of dura mater that goes around the pituitary and over the top with an opening for the stalk.
Origin of the pituitary (anterior and posterior)
** Diagrams on slides **
Primitive mouth cavity (stomodeum) –> Rathke’s pouch moves upwards towards the neurohypophyseal bud on the floor of the diencephalon.
Wrath’s pouch breaks off and becomes the anterior lobe. The neurohypophyseal forms the posterior lobe.
KEY POINT:
Anterior pituitary is of epithelial origin.
Posterior pituitary is of neural origin.
Blood supply to the hypothalamus / pituitary
Superior hypophyseal artery and inferior hypophyseal artery come of the internal carotid artery.
Flow of blood is not all one way - some flow from pituitary to hypothalamus i.e. short feedback loop.
Trabecular artery
Comes off the superior hypophyseal artery before it reaches the pituitary and passes through the pars distalis (does not supply here though) and to the lower capillary bed
Bloody supply of pars distalis
No direct arterial supply.
Blood supply of the median eminence
Has an arterial supply but lacks significant venous drainage - other than the portal system to the pars distalis.
Ample venous drainage from the pars distalis.
Blood supply of the neural lobe (pars nervosa)
Has its own arterial supply and venous drainage.
Blood supply direction
Not all one way - some flow from the pituitary to the hypothalamus i.e. a short feedback loop.
Overall functioning of the axis.
Neurones in the hypothalamus secrete hormones which pass via axonal flow to the axiom terminals.
Hormones destined for the posterior pituitary (vasopressin, oxytocin) are released directly into systemic circulation.
Hormones destined for the anterior pituitary (GnRH, TRH, somatostatin etc.) travel via the portal blood vessels.
An alternative route to the anterior pituitary involves special cells called tanycytes.
Tanycytes
An alternative route to the anterior pituitary.
Some of the axons go to the third ventricle. Hormones are released into the third ventricle and then tanycytes (large axon) run from the ventricle down to the capillary bed.
