The Pituitary Flashcards
The pituitary = _______ (undergrowth)
The pituitary = Hypothesis (undergrowth of brain)
Neurohypophysis (neural part to undergrowth):
Median eminence
Infundibular Stalk (has upper and lower parts that correspond to capillaries)
Infunibular process (swelling) called pars nervosa
Adenohypophysis: (glandular w epi cells secreting)
pars intermedia not present in hoomans
pars tuberalis
pars distalis
Whats part ofthe of the anterior lobe and whats part of the posterior lobe?
Posterior Lobe:
Infundibular Process/pars nervosa
Pars intermedia
Anterior Lobe:
Pars Tuberalis
Pars Distalis
Draw the pituitary and it’s portions!
***note where the dividing line between the hypothalamus and the pituitary
Where is the pituitary?
Smack bang in the middle of your head.
Sits in a fossa within the sphenoid bone, there’s also a Sphenoid sinus present.
*Surgeries can be done via the nose thorugh this route
Sella Turcica: shaped like a turkish saddle, so that the pituitary is trapped in bone, and cannot be removed without it breaking.
What’s the function of the Sella Turcica?
A bone shaped like a turkish saddle, so that the pituitary is trapped in bone, and cannot be removed without it breaking, and you’d need to dissect bone.
Add in the pituitary coverings to the picture
IR: Infundibular Recess, or bottom of the 3rd ventricle
Black lines: Dura mater covers the pituitary with a fibrous membrane, which also runs across the bone.
Also splits and puts a tissue sheath over the top to protect it ‘Diaphragma Sella’ (DS). THis has an opening in it that allows the stalk through.
What is the origin of the pituitary?
During embryonic development, the outpouching roof of the the stomodeum (primitive mouth cavity), called Rathke’s Pouch is opposite a downward extension of neural tissue called then encancephalon.
The two move towards each other, and as the neurohypophyseal bud comes down it drags the developing 3rd ventricle of nerual tissue with it, creating a funnel shaped of brain tissue. The Rathke’s pouch moves upward, anterior to the downward part.
Eventually the Rathke’s pouch breaks off, and forms a vesicle, (*and sometimes you get left behind residual bits of tissue). Which makes up the ant. pituitary.
One is epithelial, and one bit is neural!!
The anterior pituitary is of ________ origin
The posterior pituitary is of ______ origin
The anterior pituitary is of epithelial origin (Rathke’s pouch)
The posterior pituitary is of neural origin (infundibulum)
What would happen if you tied off the blood vessels to the pituitary?
Menstruation would cease, as the pituitary can no longer function and release the hormones vital for reproductive function!
What arteries supply the pituitary portal system?
The superior hypophyseal and inferior hypophyseal arteries Which come of the Internal Carotids.
Superior hypohyseal: comes in at the top. Feeds a portal system to the pars distalis (therefore the median eminence and infundibular stalk)
Inferior hypophyseal: comes in under the post. pituitary. Feeds vessels in the lower capillary bed + PP capilaries (neurohypophysis and a little bit of the stalk)
Short axons go into the __________
Long axons go into the _________
Short axons go into the upper capillary bed of the pituitary
Long axons go into the lower capillary bed of the Pituitary
What branches off the Superior Hypophysial artery, and what does it supply?
The Trabecular Artery.
Goes straight into the Pars Distalis, bypassing he upper capillary bed to go to the lower cappilary bed.
**Therefore doesn’t supply the ant. pituitary as previously thought!
What are the blood supply summary points?
- Pars Distalis lacks direct arterial supply
- Median Eminence has an arterial supply but lacks significant venous drainage; other then the portal system to the pars distalis.
- Ample venous drainage from Pars Distalis
- The neural lobe; (pars nervosa) has it’s own arterial supply and venous drainage
**not all of the blood flow is one way, some of it flows back from the pituitary to hypothalamus in a short feed-back loop.
How does the Axis Function
- Neurones in the Hypothalamus secrete hormones which pass by axonal flow to axon terminals
- Hormones destined for the posterior pituitary are released directly into the systemic circulation.
- Hormones destined for the anterior pituitary travel via the portal blood vessels
- An alternative route to the pituitary is available.**
Whats the alternative route of hormones getting to the anterior pituitary?
Involves special cells called Tanycytes.
Where theaxons go not to the portal system, but to the 3rd ventricle, get into the fluid and run down primitive nerve cells tanycytes who’s fat axons go down to the anterior pituitary.
Describe the Cells of the Pars Distalis.
Two groups of cell types,
- Chromophils (do stain): acidophils and basophils
- Chromophobes (don’t stain)
Acidophils and basophils are both types of chromophil cells found in the pars distalis. How do they stain?
Acidophils stained by: acid stains- as they’re negatively charged
eg; orange G
Basophils stained by: basic stains- as they’re positively charge
eg; fushin in PAS
Acidophils ( a type of cell in the pars distalis), that is stained by orange G, has different sub groups which produce different hormones. What are these?
- Somatotrophs → Produce Growth Hormone (GH)
- Lactotrophs → Produce Prolactin (PRL)
Basophils ( a type of cell in the pars distalis), that is stained by Fushin in PAS), has different sub groups which produce different hormones. What are these?
- Gonadotrophs → LH and FSH
- Thyrotrophs → thyroid stimulating Hormone
- Corticotrophs → ACTH
What colours do acidophils and basophils stain and why?
Basophils stain magenta: due to the hormones produced have glycoprotein groups associated with them, will pick up a stain in a particular way. As glycoproteins are - and BPs are +
Acidophils stain yellow/orange: don’t have the ‘glyco’ carbohydrate group associated.
*exception is ACTH coticotroph
Clinical correlation of chromatophils?
- In pregnancy there’s a marked proliferation of acidophils (prolactin) to help develop other body tissues for birth
- Tumour of acidophils (in pituitary): lead to acromegaly if there’s excess GH
- Basophil Adenoma: cushings syndrome due to excess ACTH
Describe the histology of the Pars Tuberalis (not much to note)
Cytology: generaly chromatophobic (no stains)
Vascularity: rich in capillaries
Connections: some reports of connections to tanycytes
Hormones: LH, FSH and TSH in small amounts
Neural tissue: Axons, glial cells
Capillaries
Pars Nervosa: axons terminate on capillaries
*you can see the membrane bound hormone granules moving toward the capillairy wall for quick and efficient hormone release
Learn this summary slide
* other hormones produced from pars distalis is LH and FSH
