General
- See sphenoid anatomy
Embryology and derivation of the pituitary gland
Posterior pituitary
- Aka: neurohypophysis, pars nervosa
- Development:
- Derives from downward evagination of neural crest cells (brain neuroectoderm) from the floor of the third ventricle.
- The residual recess in the floor of the third ventricle is called the median eminence.
Anterior pituitary gland
- Aka: Adenohypophysis
- Development:
- From an
- Upward evagination of ectoderm of the stomatodeum (-depression ofwhich eventually forms the oropharynx) the evagination is known as Rathke’s pouch and is eventually separated from the oropharynx by the sphenoid bone.
- Failure of this separation results in a craniopharyngeal duct which can be a source of recurrent meningitis.
- Posterior surface of Rathke’s pouch forms the pars intermedium
- Remnants of Rathke’s pouch may persist (Rathke’s cleft) in the pars intermedius.
- Anterior portion forms the pars distalis.
- Comprised of
- Pars distalis (anterior lobe),
- Pars intermedia (intermediate lobe)
- Pars tuberalis (extension of adenohypophyseal cells surrounding the base of the pituitary stalk).
- The pituitary gland is functionally outside the blood-brain barrier.
- Portal circulation
- One of only two sites in the body having a portal circulation (the other being the liver).
- Distribution of the hormones trophologically
Intrasphenoidal endoscopic view of the sellar and parasellar areas
Abberviations
- A. = artery; A.C.A. = anterior cerebral artery; Ant. = anterior; Attach. = attachment; Bas. = basilar; Brs. = branches; Car. = carotico, carotid; Car. A. = carotid artery; Cav. = cavernous; Cav. Seg. = cavernous segment; Clin. = clinoid; CN = cranial nerve; Diaph. = diaphragm; Dist. = distal; Elev. = elevation; Eth. = ethmoid; Fiss. = fissure; For. = foramen; Hyp. = hypophyseal; Inf. = inferior; Lat. = lateral; Lig. = ligament; LOCR = lateral opticocarotid recess; M. = muscle; Max. = maxillary; Med. = medial; Memb. = membrane; Mid. = middle; N. = nerve; Oculom. = oculomotor; Ophth. = ophthalmic; Opt. = optico; Opticocar. = opticocarotid; Orb. = orbital; OS = optic strut; Pet. = petrous; Pet. Seg. = petrous segment; Pit. = pituitary; Plex. = plexus; Post. = posterior; Prom. = prominence; Proc. = process; Prox. = proximal; Pt. = point; Pterygopal. = pterygopalatine; Rec. = recess, rectus; Seg. = segment; Sphen. = sphenoid; Sup. = superior; Symp. N. = sympathetic nerve; Tr. = trunk; Tuberc. = tuberculum.
Intrasphenoidal diagrams
- The lateral opticocarotid recess extends into the optic strut in most specimens.
- The lateral aspect of the distal dural ring is located approximately 1 mm above the tuberculum recess and is medially continuous with the diaphragm attachment that is located at the level or slightly inferior to this recess (blue line).
- The proximal dural ring is located along the inferior border of the lateral opticocarotid recess and its projection extends medially toward the tuberculum recess (yellow dotted line).
- The middle clinoid when present (green shadowed area, green dotted lines) protrudes inside the cavernous sinus toward the anterior clinoid inferior and lateral to the medial opticocarotid point (point 4) and caroticosellar point (point 5).
- The caroticoclinoid ligament (light blue), when present, extends from the inferior aspect of the anterior clinoid to the middle clinoid (left side of the sellar wall).
- In cases with a caroticoclinoid ring, the proximal dural ring extends posterior to the carotid artery below the osseous ring and blends into the medial wall of the cavernous sinus (right side of the sellar wall).
- The middle clinoid base is located at the mid superior level of the sellar prominence directed posteriorly and superiorly to the anterior clinoid at approximately the center of the C-shape formed by the carotid prominence.
- When present, the carotid cave is located between points 4 and 5.
- The chiasmatic sulcus can be referenced in the sphenoid sinus in the area above the tuberculum recess between both optic prominences.
- The distal dural ring is represented with a dark blue line, the proximal dural ring with a yellow line, the dotted lines indicate the locations where the dural rings are seen through the structures represented in the drawing. The dura mater has been removed except for a small piece of the diaphragm.
- A caroticoclinoid foramen is present on the right side, the proximal dural ring continues posteriorly blending into the periosteal dura below the osseous ring base.
- The middle clinoid (left side) is intracavernous, note the relationship of the distal and proximal dural rings that fuse posterior to the carotid artery medial to the anterior clinoid tip.
- The caroticoclinoid ligament (light blue) can be found in some cases as a medial extension of the proximal dural ring and has adhesions to the carotid artery, pituitary and middle clinoid, however, it does not form a different compartment in the cavernous sinus.
- This ligament may be present in cases without middle clinoid process and its sphenoidal extension is located in the theoretical position of the middle clinoid process in the medial edge of the carotid sulcus.
- The middle clinoid base is just inferior and lateral to the caroticosellar point and further inferior to the medial opticocarotid point.
- The anterior wall of the sphenoid sinus has been removed to expose the sellar wall and its recesses on the right side, and the intracranial aspects on the left side.
- The bone covering the left optic nerve and parasellar carotid has been removed.
- The optic strut base corresponds to the lateral opticocarotid recess, which lies anterolateral to the carotid sulcus.
- This three-dimensional perspective is partially lost with the endoscopic view that depicts the lateral opticocarotid recess as purely lateral to the carotid prominence.
- The middle clinoid and anterior clinoid processes are represented behind the carotid artery (dotted line).
Intrasphenoidal model
- The green dots are equivalent to the points explained in figure below
- The 2-mm ball probe end is a size reference, although all measurements between the marked points were performed directly from the endocranial surface to improve accuracy.
Intrasphenoidal endonasal dissection
- The bone over the internal carotid arteries, sella, and optic nerves has been drilled and the dura mater exposed.
- The dura mater covering the carotid arteries has been partially removed.
- Below and lateral to the point where the sellar prominence meets the internal carotid artery superiorly (medial opticocarotid point, green arrowheads), an indentation can be seen bilaterally (yellow arrows).
- This is the dural impression produced by the middle clinoid, located in the upper middle level of the sellar prominence.
- The right middle clinoid base is located at the center of the C-shaped anterior bend of the cavernous carotid artery.
- The middle clinoid is covered by the periosteal layer of the dura mater (yellow arrow).
- It protrudes into the cavernous sinus, with its base just below the projection level of the clinoid segment of the internal carotid artery according to intracranial dissections.
- The proximal dural ring is not identifiable from an endonasal view on the medial side of the artery.
- The dura mater over the internal carotid artery has been completely removed, revealing blue silicon filling the cavernous sinus at the site of the middle clinoid process.
Stepwise endoscopic dissection: anterio-lateral direction
- Anterior view. The mucosa has been removed to expose the bony prominences and recesses produced by the carotid artery, pituitary fossa, and optic nerve.
- The tuberculum recess, a shallow recess, extends upward into the tuberculum sella located at the junction of the planum sphenoidale and the anterior superior edge of the sella and laterally in the direction of the paired opticocarotid recesses demarcated superiorly by the optic canals and medially by the carotid arteries.
- The prominences overlying the carotid arteries are positioned lateral to the sella and clivus.
- The bone overlying the cavernous and terminal part of the petrous segments of the carotid arteries has been removed.
- Viewed by 45-degree lens, showing the course of the left petrous and cavernous segments of the carotid arteries in the wall of the sphenoid sinus.
- The anterior bend of the cavernous carotid is positioned behind the opticocarotid recess.
- The terminal petrous carotid passes above the foramen lacerum where it is joined by the vidian nerve, which underlies a prominence in the floor of the sphenoid sinus.
- The lateral recess extends laterally between the prominence overlying the V2 and the vidian canal.
- Viewed by 45-degree lens, showing the course of the left petrous and cavernous segments of the carotid arteries in the wall of the sphenoid sinus.
- The optic nerve has been exposed above the carotid artery medial to the opticocarotid recess.
- Endoscopic view (45-degree lens) from inside the sphenoid sinus into the left lateral recess.
- The lateral recess is a quadrangular area bordered by
- 3 prominences overlying structures in the sinus wall:
- The V2 superiorly
- The vidian nerve inferiorly
- The petrous segment of the carotid artery posteriorly
- Anteriorly: Anterior sinus wall between the foramen rotundum and vidian canal.
- A prominence over V3 can be seen when the lateral recess extends laterally to the foramen ovale.
- The bone covering the V2 and vidian nerve has been removed.
- The right lateral wall of the sphenoid sinus has been removed to expose the petrous and cavernous carotid, V1, V2, and V3, and the vidian and abducens nerves.
- The clivus has also been opened to expose the basilar artery and brainstem.
- The floor of the pituitary fossa has been removed and the gland pushed upward to expose the dorsum sellae in a dorsum type of the sphenoid sinus.
- A trapezoidal shaped floor of the sinus wall with the short base at the level of the tuberculum sellae has been opened to expose the dura on the planum.
- The exposure is limited laterally by the optic nerves and carotid arteries.
Anterior endoscopic view into the sphenoid sinus and assessment of degree of sphenoidal pneumatisation
- Showing both opticocarotid recesses.
- In this case, the pneumatisation of the opticocarotid recess extended through the optic strut and into the anterior clinoid process. The optic canals are exposed above, the prominences overlying the cavernous carotids medially, and the upper edge of the superior orbital fissures below the opticocarotid recesses.
- A probe has been passed into the right opticocarotid recess and into the anterior part of the anterior clinoid process.
- Axial computed tomography with image guidance showing that the probe has entered the pneumatized anterior clinoid process.
- A fiberoptic light has been positioned below the body of the sphenoid bone.
- This transillumination shows that the pneumatization has extended into both anterior clinoid processes, laterally beyond the right foramen rotundum to the medial edge of the foramen ovale, and posteriorly to the clivus.
Stepwise endoscopic dissection anterior to posterior
- Anterior view into a sphenoid sinus with the mucosa removed to show the relationships of the structures that can be exposed by the transsphenoidal approach.
- The structures in the exposure include the major sphenoidal septum, anterior sellar wall, and the prominences over the carotid arteries and optic canals.
- The tuberculum sellae and planum sphenoidale are located above the anterior sellar wall.
- The opticocarotid recess extends laterally between the carotid artery and optic canal.
- The bone in the walls of the sphenoid sinus has been removed while preserving the dura.
- The optic nerves, intercavernous carotids, and the pituitary gland are seen through the dura.
- The anterior bend of the intercavernous carotid bulges forward inside the dura immediately below the optic canals.
- The basilar sinus, which forms the largest connection between the paired cavernous sinuses, is situated behind the clivus and dorsum sellae.
- The inferior hypophyseal artery passes to the capsule of the posterior lobe. The optic nerve and ophthalmic artery can be seen through the optic sheath.
- The dura forming the medial and lower walls of the cavernous sinuses has been removed.
- Intercavernous sinuses connect the paired cavernous sinuses across the midline.
- The dura in the floor of the optic canals has been opened to expose the ophthalmic arteries and the optic nerves.
- The basilar sinus sits on the dorsum sellae and clivus and interconnects the posterior end of the paired cavernous sinuses.
- The venous space has been cleared to expose the intracavernous carotid and the anterior and posterior pituitary lobes.
- The inferior hypophyseal arteries arise from the meningohypophyseal branch of the intracavernous carotid and pass to the capsule of the posterior lobe.
- Sympathetic nerves ascend on the carotid arteries.
- The abducens nerve passes through the cavernous sinus on the lateral side of the internal carotid artery and medial to the ophthalmic nerve.
- Oblique canal, superior orbital fissure, intracavernous carotid artery, and the maxillary nerve are exposed in the lateral wall of the sphenoid sinus.
- The bony depression between the carotid prominence and the optic canal, the opticocarotid recess, extends into the medial end of the optic strut.
- The broad round prominence below the opticocarotid recess is produced by the structures passing through the superior orbital fissure.
- Oblique view.
- The pituitary gland, intracavernous carotid artery, ophthalmic artery, and optic, ophthalmic, maxillary, oculomotor, and abducens nerves have been exposed.
- The abducens nerve courses medial to the ophthalmic nerve.
Transcranial view of the sellar and parasellar area
Abbreviations
- A. = artery; Ant. = anterior; Attach. = attachment; Bas. = basilar; Car. = carotid, carotico; Cav. = cavernous; Cist. = cistern; Clin. = clinoid; CN = cranial nerve; Diaph. = diaphragm; Dist. = distal; Elev. = elevation; Falc. = falciform; Gr. = greater; Hyp. = hypophyseal; Inf. = inferior; Intercav. = intercavernous; Interclin. = interclinoid; Lig. = ligament; Memb. = membrane; Men. Hyp. = meningohypophyseal; Mid. = middle; N. = nerve; Oculom. = oculomotor; Opt. = optico; OS = optic strut; Periost. = periosteal; Pet. = petrous; Petroclin. = petroclinoid; Petroling. = petrolingual; Petrosphen. = petrosphenoid; Pit. = pituitary; Post. = posterior; Prox. = proximal; Pt. = point; Seg. = segment; Sphen. = sphenoid; Tent. = tentorial; Tuberc. = tuberculum.
Specimen with a caroticoclinoid ring (green dotted lines)
- The caroticoclinoid ring is an osseous bridge formed by the fusion of the anterior clinoid process (ACP) and the middle clinoid process.
- The middle clinoid process itself is a prominence located on the medial side of the terminal part of the carotid sulcus, medial to the tip of the ACP.
- This fusion creates a bony ring or canal—the caroticoclinoidal foramen—through which the carotid segment of the ICA passes through
- The anterior clinoid process has been surgically removed.
- The III, IV, and V cranial nerves have been resected, along with both the anterior and posterior bends of the cavernous carotid artery.
- In the presence of a caroticoclinoid ring, the carotidoculomotor membrane continues posterior to the carotid artery below the osseous ring and continues the proximal dural ring (yellow dotted lines) all the way to the medial wall of the cavernous sinus.
- The osseous ring forms part of the roof of the cavernous sinus.
- The distal dural ring is represented by blue dotted lines.
Dural relationships and ligaments in the cavernous sinus
- Superolateral view; the left anterior clinoid has been removed.
- The proximal and distal dural rings in the lateral wall of the carotid artery delimit the clinoid segment of the carotid artery.
- These rings typically fuse at the posterior aspect of the carotid artery medial to the tip of the anterior clinoid process.
- Ligaments of the cavernous sinus, superior view.
- The dura mater forming the superior wall of the left cavernous sinus has been removed along with the posterior half of the distal dural ring to show the interclinoid ligament between the anterior and posterior clinoid processes and the anterior and posterior petroclinoid ligaments between the petrous apex and the anterior and posterior clinoids, respectively.
- The left anterior clinoid has been removed.
- The carotidoculomotor membrane forms the proximal dural ring when it meets the carotid medially.
- Blue silicon, representing the venous filling in the cavernous sinus, has been partially removed below the distal dural ring posteriorly.
- The proximal dural ring is not evident in the posterior and medial aspect of the carotid.
- In some specimens, there is a carotico clinoid ligament between the anterior clinoid and middle clinoid (when present) or medial border of the carotid sulcus at the level of the anterior bend of the carotid artery (when the middle clinoid is absent).
- Further removal of blue silicon of the left cavernous sinus.
- This ligament blends into the carotidoculomotor membrane and is directed to the periosteal layer covering the middle clinoid process or medial aspect of the carotid sulcus.
- It may have adherences to the internal carotid artery and to the meningeal layer of the dura mater covering the pituitary.
- Further removal of blue silicon of the left cavernous sinus.
- This ligament blends into the carotidoculomotor membrane and is directed to the periosteal layer covering the middle clinoid process or medial aspect of the carotid sulcus.
- It may have adherences to the internal carotid artery and to the meningeal layer of the dura mater covering the pituitary.
- The left half of the pituitary gland has been removed to show the meningeal layer covering the gland and the periosteal layer covering the sellar wall of the sphenoid sinus.
- Both of them form part of the medial wall of the cavernous sinus.
Stepwise microscopic dissection: superior to inferior
- Showing the intracranial correlation of the recesses and referenced points in the sellar wall of the sphenoid sinus, superior intracranial view.
- After brain removal, the dura mater covering the right anterior clinoid process has been removed.
- The 1-mm perforations are enhanced with green circles for clarity.
- The right anterior clinoid process has been drilled, view of the 3 reference points (6, 7, 8) of the lateral opticocarotid recess corresponding to the optic strut.
- Note the point corresponding to the deepest and middle part of the tuberculum recess (1).
- The proximal and distal dural rings and the carotidoculomotor membrane are exposed.
- The middle clinoid process is not visualized as it is located below the level of the posterior junction of the proximal and distal dural rings at the tip of the anterior clinoid.
- The dural rings have been incised to retract laterally the right carotid artery, and the periosteal layer of the dura mater has been removed.
- The medial opticocarotid point (4) and caroticosellar point (5) are exposed with the middle clinoid (yellow dotted line).
- The caroticosellar and medial opticocarotid points are superior to the middle clinoid.
- Bilateral dissection showing both junction points and bilateral prominence of the middle clinoid processes.
Superior view of the sellar region
- The sella is located between the cavernous sinuses.
- The diaphragm, which usually separates the sella from the suprasellar cisterns, is absent in this case.
- The oculomotor nerves enter the roof of the cavernous sinus where there is a narrow cistern around the nerve.
- The oculomotor triangle, the triangular patch of dura through which the oculomotor nerve enters the dura in the cavernous sinus roof, is positioned between the anterior and posterior clinoid processes and the petrous apex.
- The roof of the cavernous sinus extends forward under the anterior clinoid process.
- The dura covering the anterior clinoid process and optic canal has been removed.
- The outer layer of dura in the lateral wall of the cavernous sinus has been removed to expose the thin inner layer of the lateral sinus wall and the lateral surface of Meckel’s cave.
- The falciform ligament, the dural fold extending above the optic nerve proximal to the nerve’s entrance into the optic canal, extends from the anterior clinoid to the tuberculum.
- The inner layer of the lateral sinus wall has been removed to expose the nerves coursing in the wall of the cavernous sinus and middle fossa.
- The oculomotor nerve enters the narrow oculomotor cistern in the sinus roof and passes forward along the lower margin of the anterior clinoid process.
- Enlarged view.
- A probe has been passed between the optic nerve and the falciform ligament.
- The dissector can be seen through the dura proximal to the osseous optic canal.
- The anterior clinoid is located lateral to the optic nerve and internal carotid artery and above the oculomotor nerve.
- The dura covering the dorsum sellae, basilar sinus, and posterior clinoid process has been removed.
- The oculomotor nerve passes forward lateral to the posterior clinoid and below the anterior clinoid.
- An abnormal bony projection extends laterally from the right posterior clinoid below the oculomotor nerve toward the petrous apex.
- The basilar sinus crosses the back of the dorsum and upper clivus and communicates widely with the posterior edge of the paired cavernous sinuses.
- The abducens nerve passes through the lower margin of the basilar sinus.
- An anterior intercavernous passes along the anterior margin of the sella.
- The posterior part of the cavernous sinus has been cleared to expose the abducens passing through Dorello’s canal, which is roofed by the petrosphenoidal ligament.
- The anterior clinoid process has been removed to expose the clinoid segment of the internal carotid artery defined by the upper and lower dural rings.
- The upper ring is formed by the dura extending medially from the upper surface of the anterior clinoid.
- The lower dural ring is formed by the dura, which extends medially from the lower margin of the anterior clinoid and separates the lower clinoid margin from the oculomotor nerve.
- Posterosuperior view of the sella.
- The dorsum and posterior clinoid have been removed to expose the posterior lobe of the pituitary, which was hidden below the dorsum.
- The abducens nerve is exposed below the petrosphenoidal ligament.
- The trigeminal nerve has been reflected forward to expose the petroligand ligament, which extends above the internal carotid artery just proximal to the artery’s entry into the cavernous sinus.
- Enlarged view of the petroliquand and petrosphenoidal ligaments.
- The inferior hypophyseal artery passes to the capsule of the posterior lobe.
- The greater petrosal nerve courses medially and is joined by the deep petrosal branch of the periarterial carotid plexus to form the vidian nerve.
- Enlarged view.
- The carotid artery protrudes medially to deform the lateral surface of the anterior lobe of the pituitary gland.
- A tongue of anterior lobe extends laterally above the intercavernous carotid.
Stepwise microscopic dissection inferior to superior
A., artery; Ant., anterior; Bas., basilar; Cap., capitus; Cav., cavernous; CN, cranial nerve; Eth., ethmoid; Eust., eustachian; Hyp., hypophyseal; Inf., inferior; Infraorb., infraorbital; Long., longus; M., muscle; Max., maxillary; N., nerve; Ophth., ophthalmic; Perp., perpendicular; Pet., petrous; Post., posterior; Proc., process; Pteryg., pterygoid; Rec., rectus; Seg., segment; Sphen., sphenoid; Sup., superior.
- The right half of the floor of the sphenoid sinus has been removed to expose the sellar floor and the part of the sphenoid sinus below the planum and tuberculum.
- On the specimen’s left side, the eustachian tube, pterygoid process, and posterior part of the maxillary sinus have been preserved.
- On the right side, the medial portion of the eustachian tube and the pterygoid process have been removed.
- This exposes the right mandibular nerve exiting the foramen ovale and the maxillary nerve exiting the foramen rotundum and passing forward as the infraorbital nerve.
- The pterygopalatine ganglion is located in the pterygopalatine fossa behind the maxillary sinus in the lateral wall of the nasal cavity.
- The right pterygoid process has been removed to expose the vidian canal, in which the vidian nerve travels to reach the pterygopalatine ganglion.
- The bone below the petrous carotid has been removed up to the point where the artery turns upward to enter the posterior part of the cavernous sinus.
- Part of the vomer, perpendicular ethmoid plate, and floor of the sphenoid sinus have been removed to expose the cavernous sinus, intracavernous carotid, and the pituitary gland.
- The floor of the optic canals have been removed to expose the ophthalmic arteries coursing below the optic nerves.
- The cavernous sinus surrounds the intracavernous carotid.
- An anterior intercavernous sinus crosses the anterior margin of the gland.
- Some of the upper clivus has been removed to expose the basilar sinus, which sits on the back of the dorsum and is the largest connection between the cavernous sinuses.
- The venous spaces around the pituitary gland have been cleared to expose the petrous and intracavernous carotid segments.
- Enlarged view of the pituitary gland, intracavernous carotid, and the optic nerves and ophthalmic arteries.
- The inferior hypophyseal arteries pass to the posterior lobe.
- The superior hypophyseal arteries arise in the chiasmatic cistern and pass medially to reach the stalk and chiasm.
Blood supply
Arterial
- Cavernous segment of ICA → Meningiohypophyseal trunk → inferior hypophyseal artery
- Ophthalmic segment of ICA → Superior hypophyseal artery
- A slight contralateral oblique view, an LAO of right ICA injection
- Superior hypophyseal (white arrow, with an infundibulum)
- Supplying the pituitary stalk (black arrows).
- Inferior hypophyseal (dashed white arrow)
- Supply of the posterior pituitary (dashed black arrow)
Venous
- Anterior lobe of the pituitary flows → small hypophyseal veins → network of veins overlying the pituitary surface → drains laterally into the cavernous sinuses → inferior petrosal sinuses → posteriorly and caudally and enter the jugular bulb at the skull base
Pituitary hormones
- Releases 8 hormones
6 from the anterior pituitary
General
- Hypothalamic hormones are released in a pulsatile fashion from neurons of the tuber cinereum (a hypothalamic nucleus) that are conveyed via the tubero-hypophyseal tract (a parvocellular system) to their terminus in the median eminence of the pituitary stalk.
- These hypophyseal hormones are released into capillaries of the hypophyseal portal circulation, which carries them via the pituitary stalk to a second capillary bed in the anterior pituitary where they control release of hormones by adenohypophyseal gland cells.
Propiomelanocortin (POMC)
- AKA proopiomelanocortin
- 241 amino acid polypeptide hormone precursor
- Synthesized primarily in corticotroph cell of the anterior pituitary (but also found in the hypothalamus).
- Contains amino acid sequences for ACTH, alpha-melanocyte-stimulating hormone (α-MSH), β-lipotropin, γ-lipotropin, β-endorphin and metenkephalin.
Corticotropin AKA adrenocorticotrophic hormone (ACTH)
- A 39 amino acid trophic hormone synthesized from POMC. The first 13 amino acids at the amino terminal of ACTH are identical to α-MSH. Active half-life is ≈ 10 minutes. Produces a diurnal peak in cortisol (the highest peak occurs in the early morning, with a second, lesser peak in the late afternoon) and also increases in response to stress. Control: CRH from the hypothalamus stimulates the release of ACTH.
Prolactin (PRL)
- AKA somatomammotropin.
- 199 amino-acid protein weighing 23,000 daltons.
- Levels are higher in females than males, and are higher still in pregnancy
- Secretion
- Secreted in pulsatile fashion with a frequency and amplitude that varies during menstrual cycle
- (Range: 5–27 ng/ml)
- (≈ 9 pulses/ 24 hours in the late luteal phase,
- ≈ 14 pulses/24 hours in the late follicular phase,
- The pulse amplitude increases from early to late follicular and luteal phases).
- Diurnal variation:
- Levels begin to rise 1 hour after the onset of sleep,
- Peak ≈ 5:00–7:00 AM,
- Nadir in midmorning after awakening.
- Heterogeneity of the molecule may produce different results between bioassays and immunoassays.
- Control:
- PRL is the only pituitary hormone predominantly under inhibitory control from the hypothalamus by prolactin releasing inhibitory factors (PIFs), with dopamine being the primary PIF.
- Prolactin releasing factors (PRFs) include:
- Thyrotropin-releasing hormone (TRH)
- Vasoactive intestinal peptide (VIP).
- The physiologic role of PRFs is not established. For DDx of hyperprolactinemia see
Growth hormone (GH)
- A 191 amino-acid polypeptide trophic hormone.
- Pulsatile secretion (≈ 5–10 pulses/ 24 hours, primarily at night, up to 30 mcg/L), levels may be undetectable (< 0.2 mcg/L) by standard assays between pulses.14
- Function
- Mainly through
- Insulin-like growth factor-1 (IGF-1) (Aka somatomedin-C)
- Protein secreted primarily by the liver in response to GH that is responsible for most of GH’s systemic effects (see levels (p.757)).
- GH also acts directly on epiphyseal endplates of long bone to stimulate chondrocyte proliferation.
- Inc release
- GH-releasing hormone (GHRH) from the arcuate nucleus
- Inc. pituitary secretion and
- Inc. synthesis and transcription.
- Dec. release
- Somatostatin from the periventricular nucleus.
- GH release is also stimulated by ghrelin,15 a peptide synthesized primarily in the GI tract in response to certain nutrients (may act partially or totally via hypothalamic GHRH).
Thyrotropin
- AKA thyroid stimulating hormone (TSH)
- Inc. release
- TRH
- Inc. release
- Inc. synthesis
- Dec. release
- Somatostatin
- Glycoprotein trophic hormone secreted by thyrotroph cells of the anterior pituitary. Control: TSH is also under dual hypothalamic control.
Gonadotropins
- Follicle stimulating hormone (FSH) and luteinizing hormone (LH) (AKA lutropin)
- Inc release
- Gonadotropin releasing hormone (GnRH)
- Made in preoptic area of the hypothalamus.
2 from the posterior pituitary
Antidiuretic hormone (ADH)
General
- AKA arginine vasopressin (AVP)
- A nanopeptide hormone
Source
- ADH is synthesised in the hypothalamus, specifically in the supraoptic and paraventricular nuclei.
- Magnocellular portion of the supraoptic nucleus of the hypothalamus.
- Conveyed along axons in the supraoptichypophyseal tract to the posterior pituitary gland where it is released into the systemic circulation.
- It is then stored and secreted by the posterior pituitary gland.
ADH release regulation
- ADH release is increased by
- Increased serum osmolality (Most potent)
- Osmoreceptors in hypothalamus - day to day
- Reduction of intravascular volume (Less potent)
- Baroreceptors in brainstem and great vessels - emergency
- Glucocorticoid deficiency
- ADH release decreased by
- Exogenous glucocorticoids and adrenergic drugs.
Function: ADH result from binding of the hormone to specific membrane-bound receptors on the surface of target cells.
- Increase the permeability of the distal renal tubules → increased reabsorption of water through insertion of aquaporin channels into the principal cells of the renal collecting duct → diluting the circulating blood + producing a concentrated urine
- Vasoconstrictor through V₁-receptors.
- Vasopressin, being an ADH analog, is a potent vasopressor that can be used to increase organ perfusion in septic shock.
Clinical Relevance:
- In central diabetes insipidus (DI), ADH levels are decreased.
- Hyponatraemia is very common in clinical practice
- Type of morbidity depends on onset/duration of hyponatraemia, i.e. acute or chronic
- Treatment decisions hinge on:
- Whether the condition is acute or chronic
- Presence or absence of symptoms
- Volume status of the patient
- Cortisol deficiency is an important potential cause—especially relevant with macro-sellar lesions
- Monitoring is essential when treating hyponatraemia
- Collaboration with an endocrinologist is encouraged—stay responsive during therapy
- Vasopressin cans stimulate acth release
- If you have a sella mass (craniopharyngioma), patient has a masked DI because the cortisol is low so body can't loose water but when cortisol is replace with HC then DI will formed
- In nephrogenic DI, ADH levels can be normal or increased.
- Nephrogenic DI can be caused by a mutation in the V₂-receptor.
- Desmopressin, which is an ADH analog, is a treatment for central DI and nocturnal enuresis.
Oxytocin
- A nonapeptide.
- A neurotransmitter as well as a hormone.
- Made in
- Magnocellular neuroendocrine neurons (not gland cells) in the supraoptic and paraventricular nuclei of the hypothalamus
- Conveyed along axons in the supraoptic-hypophyseal tract, also via the pituitary stalk, to the posterior pituitary gland where they are released into the circulation.
- Function
- Milk let down reflex for breastfeeding
- Uterine contraction during labour.
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