The pituitary gland: Flashcards
AKA
The hypophysis
Embryology: Development of pituitary gland
- Consists of 2 types of tissue
- Early in embryonic development, a finger of ectoderm grows upward from the roof of the mouth = Rathke’s pouch
– develops into ant. Pituitary gland. (adenohypophysis) - At same time the rathke’s pouch is developing, another finger of ectodermal tissue evaginates ventrally from the diencephalon (FB)
- Post pituitary gland comes from same structure that the hypothalamus divides from
- Extension of the ventral brain becomes the post-pituitary gland (neurohypophysis)
- Ultimately, the 2 tissues grow into one another and become tightly opposed, but their structures remain distinctly different (differ in embryological origins)
Summary:
1. Extension of diencephalon – infundibulum
2. Ectodermal outpocketing of buccopharyngeal membrane – Rathke’s pouch
The pituitary gland is a
Pea-sized oval structure
The pituitary gland is suspended from the
under side of the brain via the pituitary stalk (AKA infundibulum)
The pituitary gland sits within a small depression in the
sphenoid bone = sella turcica
diaphragm sellae
Sup surface of gland is covered with reflection of the dura matter = diaphragm sellae
This membrane has a central opening that allows passage of the infundibulum
Key anatomical relations:
Ant: sphenoid sinus
Post: Posterior intercavernous sinus and dorsum sellae (post wall of sella turcica)
Sup: Diaphragm sellae (fold of dura matter as well as optic chisma)
Inf: sphenoid sinus
Lat: cavernous sinus
Anatomically the pituitary gland is a 2-in-1 structure
Consisting of Ant. Pituitary and post pituitary
- have different embryonic origins and functions
Anterior/adenohypophysis is composed mostly of
glandular tissue, makes it different from post pit.
Anterior/adenohypophysis secretes
a number of hormones
Anterior/adenohypophysis is divided into 3 parts
Pars distalis - the largest section
Pars tuberalis - a collar of tissue that usually surrounds the infundibular stalk
Pars intermedia - a narrow band that is usually separated from the pars distalis by a hypophyseal cleft
Release of hormones from ant lobe
is under control of hypothalamus, which communicates with the ant pit lobe, via neurotransmitters that is secreted into the hypophysial portal vessels
These vessels ensure that hypothalamic hormones remain concentrated, rather than being diluted in systemic circulation.
Neurohypophysis/Posterior consists mainly of
nervous tissue (develops from diencephalon)
- Mainly neuronal projections extending mostly from the supraoptic and paraventricular nuclei of the hypothalamus
Neurohypophysis/Posterior secretes 2 hormones
ADH and oxytocin
ADH and oxytocin are produced by
the nuclei of the hypothalamus and then they are stored in the post pit gland.
Does the post pituitary gland synthesize any hormones?
No, only stores and releases from axons of hypothalamus neurosecretory cells.
- These axons release peptide hormones into the capillaries of the hypophyseal circulation
- These are then stored in neurosecretory vessels, before being secreted by the posterior pit. Into systemic circulation
The post pituitary gland is a
Direct extension of the hypothalamus
Neurohypophysis/Posterior consists of three parts:
Pars nervosa - the bulk of the posterior pituitary
Median emminence - the upper section of the neurohypophysis above the pars tuberalis
Infundibular stalk - the “stem” that connects the pars nervosa to the base of the brain
Arterial supply of the anterior pituitary gland
- Receives arterial blood supply from the superior hypophyseal artery
(branch of internal carotid artery) - The vessel first forms a capillary network around the hypothalamus
- Blood from this network is transported to a second capillary plexus surrounding the ant. Pit. Gland.
= Hypothalamo hypophyseal portal system - This system allows the hypothalamus to communicate with the ant pit gland via the release of neurotransmitters into the blood stream.
Arterial supply of the post pit gland and the infundibulum:
- Receives a rich blood supply from many arteries
- Superior hypophyseal artery, infundibular artery and the inferior hypophyseal artery
Vasculature of the pituitary gland:
- Is complex and unique
- While the ant and post lobe have the same venous drainage (anterior and posterior hypophyseal veins)
- They have individual arterial supply
