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Pituitary gland


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Pituitary gland
• Embryonic origin
– Anterior pituitary gland (adenohypophysis)
• Rathke’s pouch
– Roof of the embryonic mouth
– Glandular tissue containing secretory cells

– Posterior pituitary gland (neurohypophysis)
• Infundibulum/brain floor)
– Part of the CNS
– Contains axons of the hypothalamic neurons

– Housed in a bony capsle called sella turcica


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• Anterior lobe
(predominant lobe)
– Differentiation of cells
• Spatiotemporal regulation
– Expression of cellspecific transcription
factor(s) at the specific
stage of development
– Concentration gradient
of soluble factors

• Sexually dimorphic
– Gonadotrophs in male –
predominantly LH
secreting cells
– Gonadotrophs in femaleequal distribution of LH
and FSH secreting cells


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• Pars tuberalis
– Dorsal extension of
anterior lobe
• Surrounds the
infundibulum

• Pars Intermedia
– Derived from anterior
pituitary cells adjacent
to infundibulum
• May not be clearly
defined in many
species


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• Pars nervosa
– Posterior lobe
– Extension of the CNS
– Contains axons of
hypothalamic neurons


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• Blood vessels
– Portal plexus from hypothalamus
• Median eminence
• Forms hypothalamic-portal circulation
• Bidirectional flow of blood
– Retrograde flow from the pituitary to hypothalamus
(short-loop feedback system)

– Systemic arteries
• Inferior hypophyseal arterial blanches
– Posterior pituitary gland


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Regulation of hormone secretion
• Hypothalamic level
– Releasing/inhibitory factors
• Transcription of mRNA
• Secretion of hormone

• Peripheral hormones
– Feedback system

• Autocrine/paracrine factors
• Net results
– Pulstatile secretion of pituitary hormones


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Role of transcription factors
• Determination of cell type lineage
– Temporal regulation of transcription cascade
• Homeodomain transcription factors

– Early differentiation
• Expression of Rpx and Ptx
• LIM homeodomain superfamily


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• Ptx superfamily
– Universal regulator of transcription within the anterior
pituitary
• Pit-1
– GH, PRL, TSH, and GHRH receptor mRNA transcription
– Interaction with other factors to induce commitment of cells to
differentiate (estrogen receptor, thyrotroph embryonic factor)
– Transcription of its own mRNA

• GATA-2
– Developmental regulation of alpha subunit expression
– Interaction with SF-1 and DAX-1 triggers differentiation into
gonadotrophs


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Endocrine cells
• Five types
– Corticotrophs
– Somatotrophs
– Lactotrophs/mammotrophs
– Thyrotrophs
– Gonadotrophs

• Staining characteristics
– Acidphils (stained with acidic dye)
– Basophils (stained with basic dye)


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Endocrine cells
• Corticotrophs
– Basophils
– 20 % of functional anterior pituitary gland cells
– Appears the earliest
• 8 weeks of gestation

– Clustered mainly in central median pituitary
wedge
– Large, irregularly shaped cells


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• Lactotrophs
– Acidophils
– Same stem cells as somatotrophs
• Could give rise to mammosomatotrophs
– Produce both GH and PRL

– 15-25 % of functional pituitary cells
• Two types
– Large polyhedral cells (found throughout the gland)
– Smaller angulated elongated cells (lateral wings and
median wedge)


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• Gonadotrophs
– Basophils
– 10-15 % of functional pituitary cells
– Contains two types of secretory glanules
• Large (350-450 mm)
• Small (150-250 mm)

– Secretion of two distinct hormones by the
same cells
• GnRH pulsatility


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• Somatotrophs
– Acidophils
– 35-45% of functional anterior pituitary cells
– Same stem cells as lactotrophs
• Mammosomatotrophs
• Differentiation induced by TRH or dopamine along
with estrogen

– Large secretory granules (700 mm)


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• Thyrotrophs
– Basophils
– 5 % of functional anterior pituitary cells
– Smaller in size
• Smaller secretory granules (120-150 mm)