Anatomy of the Pituitary Gland Flashcards
What is the function of the endocrine glands?
Produce major hormones of the body, seven glands/[airs in the body
What is the diencephalon composed of?
The thalamus and hypothalamus
What does the diencephalon form?
The central core of the cerebellum = has connection to the left and right cerebral hemispheres, and the midbrain
What connects the hypothalamus to the pituitary gland?
The infundibulum (also called the pituitary stalk)
What is the pituitary gland divided into?
Anterior and posterior pituitaries
What is the embryonical origin of the anterior pituitary?
Rathke’s pouch = upwards protrusion of ectoderm into roof of the mouth
What is the embryonical origin of the posterior pituitary?
Finger of ectoderm invaginates ventrally from the diencephalon
How does the mature pituitary gland form?
By the eventual joining of the anterior and posterior pituitaries (form simultaneously)
What is the name for the anterior pituitary?
The adenohypophysis
What makes up the anterior pituitary, and what does it produce?
Components = pars distalis, pars tuberalis and pars intermedia
Responsible for synthesis and release of most pituitary hormones = GH, TSH, ACTH, FSH, LH, PRL
What is the other name for the posterior pituitary?
Neurohypophysis
What is the posterior pituitary composed of, and what is its function?
Made of pars nervosa, is actually an extension of brain
Releases ADH and OT (synthesised in hypothalamus)
What is the location of the pituitary gland?
Midline structure in the pituitary fossa of the sphenoid bone
Where is the pituitary fossa located?
Within the sella turcica (Turkish saddle) = lies immediately inferior to optic chiasm
What forms the optic chiasm?
Left and right optic nerves (CN II)
What structures pass posteriorly from the optic chiasm?
Right and left optic tracks
Where do the next axons in the visual pathway chain pass after synapsing in the thalamus?
Pass to the via cortex in the occipital lobe via the optic radiation
What is contained in the temporal retina?
Photoreceptors = rods and cones
What is contained in the nasal retina?
Photoreceptors = rods and cones
Where is the optic canal located?
In the sphenoid bone
What does the initial midline compression of the optic chiasm by a pituitary tumour cause?
Disrupts transmission of APs from nasal retina bilaterally
What does disruption of AP transmission from the nasal retina cause?
Patient loses ability to see structures in temporal side of visual field bilaterally (Bilateral hemianopia)
Patients still have normal vision in nasal field bilaterally
What are the two surgical approaches to accessing the pituitary gland?
Transcranial approach = subfrontal (under frontal lobe)
Transsphenoid approach = via nasal cavities and sphenoid sinus
What does the cribiform plate of the ethmoid bone form?
Roof of the nasal cavity
What does the vomer form?
Part of the nasal septum (inferior part)
What does the perpendicular part of the ethmoid bone form?
Superior part of the nasal septum
What are the nasal conchae found in the nasal cavity?
Superior and middle (of ethmoid bone), inferior
What are the paranasal sinuses?
Air-filled spaces within the bone surrounding the nasal cavities = lined by mucous secreting respiratory mucosa
What is the function of the paranasal sinuses?
Make mucous and drain into nasal cavities through ostia, reduce weight of skull and add resonance to voice
Where do the frontal sinuses usually connect?
In the midline = medial aspect of top of socket
What are some features of the ethmoid air cells?
Exists in three groups located between the nasal cavity and orbit
Where are the sphenoid sinuses located?
Within body of sphenoid = sometimes connect in midline
Where are the maxillary sinuses located?
Within each maxilla = known clinically as antrum
What are the different paranasal sinuses?
Frontal, maxillary and sphenoid sinuses, ethmoid air cells
What does the transsphenoid approach to accessing the pituitary gland require?
Surgical fracture of nasal septum, and the roof and floor of the sphenoid sinuses
What is the best approach to accessing the pituitary gland in complicated cases?
Le Fort I down-fracture
Where is the dura mater present?
Adherent to internal aspects of all bones of the cranial vault
What is the tentorium cerebelli?
Tough sheet of dura mater “tenting” over the cerebellum within the posterior cranial fossa
Why is there a central gap in the tentorium cerebelli?
To allow the brainstem to pass through
What is the diaphragm sellae?
Tough sheet of dura mater forming a roof over the pituitary fossa
What nerves are present within the cranial vault?
Internal carotid artery, basilar artery, vertebral artery, infundibulum, superior sagittal sinus, dural venous sinuses
What nerves are present in the cranial vault?
Optic nerve (CN II), abducent nerve (CN VI), trigeminal nerve (CN V), trochlear nerve (CN IV), oculomotor nerve (CN III)
What are the dural venous sinuses?
Venous channels within the dura mater that drain most of the venous blood from the cranial cavity into the internal jugular veins
Are the dural venous sinuses true veins?
No = not histologically veins, but function like them
What sinuses surround the pituitary gland?
Cavernous and intercavernous sinuses
Where do the dural venous sinuses drain into the internal jugular veins?
At the jugular foraminae in the floor of the posterior cranial fossa
What does the anterior intercavernous sinus connect?
The right and left cavernous sinuses = anterior to pituitary gland
What is the ophthalmic artery?
Branch of internal carotid artery = enters the orbit via the optic canal
What are some structures at risk of being damaged in pituitary gland surgery?
Optic chiasm, oculomotor nerve, trochlear nerve, trigeminal nerve, abducent nerve, cavernous sinus, internal carotid artery, dura mater
What is the function of the optic chiasm, and what can damage to it cause?
Conducts APs bilaterally from nasal retinae = damage causes bilateral hemianopia
What doses the oculomotor nerve supply?
Motor to muscles that move the eyeball
Parasympathetic to the sphincter muscle of the iris
What can damage to the oculomotor nerve cause?
Problems with several eye movements and dilated pupil (ipsilateral)
What does the trochlear nerve supply?
Motor to one muscle that moves the globe = damage causes problems with looking inferiorly and laterally (ipsilateral)
What does the trigeminal nerve supply?
Sensory to most of face and motor to muscles of chewing = damage causes sensory symptoms in face and difficulty chewing (ipsilateral)
What does the abducent nerve supply?
Motor to one muscle that moves the globe = damage causes problems with abduction of the eye (ipsilateral)
What is the function of the cavernous sinus and what does damage to it cause?
Drains venous blood = damage causes venous haemorrhage (ipsilateral)
What does damage to the internal carotid artery cause?
Catastrophic haemorrhage
What is the function of the dura mater, and what does damage to it cause?
Protects structures of the cranial cavity = damage causes cerebrospinal fluid leak
How do hormones get transported to the posterior pituitary?
Within the axoplasm by axoplasmic transport
What do hypothalamic neutrons secrete to affect the anterior pituitary?
Release stimulating or release inhibiting hormones
