Pituitary gland

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

• Anterior lobe (predominant lobe)– Differentiation of cells

• Spatiotemporal regulation– Expression of cell-

specific 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 female-equal distribution of LH and FSH secreting cells

• 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

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

hypothalamic neurons

• 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

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

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

• 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

Endocrine cells

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

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

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

• 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)

• Gonadotrophs– Basophils– 10-15 % of functional pituitary cells– Contains two types of secretory glanules

• Large (350-450 m) • Small (150-250 m)

– Secretion of two distinct hormones by the same cells

• GnRH pulsatility

• 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 m)

• Thyrotrophs– Basophils– 5 % of functional anterior pituitary cells– Smaller in size

• Smaller secretory granules (120-150 m)