Pituitary Gland and Hormones Review
Pituitary Gland: Structure and Location
Small gland located in a bony cavity (sella turcica) just below the hypothalamus
Connects to the hypothalamus by a thin stalk (infundibulum / pituitary stalk)
Two anatomically and functionally distinct lobes:
Posterior pituitary (neurohypophysis): composed of nervous tissue
Anterior pituitary (adenohypophysis): consists of glandular epithelial tissue
Intermediate pituitary (pars intermedia) is present in development and in some species; in humans it is largely regressed in adulthood
Hypothalamic Connections and Anatomy
Pituitary sits in relation to the hypothalamus and other brain structures; connection via infundibulum
Enlarged view shows the connection to the hypothalamus and its relation to rest of the brain
Hypothalamic-pituitary axis components:
Hypothalamic nuclei: Paraventricular nucleus, Supraoptic nucleus, Arcuate nucleus, Mammillary bodies, etc.
Hypothalamic tracts: Supraopticohypophyseal tract, Tuberohypophyseal tract, Hypothalamohypophyseal tract
Infundibulum (pituitary stalk) connects hypothalamus to the pituitary
Pars tuberalis surrounds the infundibulum and links to the anterior lobe
Neurohypophysis (posterior lobe) and Adenohypophysis (anterior lobe) receive distinct regulatory inputs
Key brain landmarks near pituitary: Optic chiasm, Lamina terminalis, Median eminence of tuber cinereum, Dorsomedial, Ventromedial, and Arcuate hypothalamic regions, Mammillary bodies
Neurohypophysis (Posterior Pituitary)
Part of the posterior lobe; does not synthesize hormones itself
Stores and releases two peptide hormones produced by hypothalamic magnocellular neurons:
Anti-diuretic hormone (ADH) / Vasopressin: conserves water during urine formation
Oxytocin: stimulates uterine contractions during childbirth and milk ejection during lactation
Structural/functional pathway:
Magnocellular neurons in the Paraventricular (PVN) and Supraoptic (SON) nuclei synthesize prohormones, package into secretory granules, and transport down axons via the hypothalamo-hypophyseal tract
Prohormone processing occurs within secretory granules; secretory vesicles are stored in the posterior pituitary (pars nervosa)
Exocytosis near capillary beds releases hormone along with neurophysin
Release is triggered by neuronal activity, delivering hormones directly into hypophyseal veins surrounding the posterior lobe
Referenced process steps (simplified):
Synthesis of prohormone → packaging with prohormone convertases → secretory granules
Intra-axonal transport → cleavage of prohormone → storage of secretory vesicles
Exocytosis near capillary bed → release of hormone and neurophysin
Hypothalamic-Neurohypophyseal System: Magnocellular Pathway
Magnocellular neurons located in PVN and SON
Key steps include: synthesis, packaging with neurophysin, axonal transport, storage, and release to regulate peripheral targets via the posterior pituitary
Anterior Pituitary (Adenohypophysis)
Secretes six peptide hormones produced within the pituitary:
Tropic hormones:
Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Growth hormone (GH)
Not a tropic hormone:
Prolactin (PRL)
The six hormones act on various target organs and tissues; regulation is via hypothalamic releasing/inhibiting hormones
Hypothalamic Releasing Hormones and Regulation of the Anterior Pituitary
Hypothalamic hormones that regulate the anterior pituitary include:
TRH ( Thyrotropin-releasing hormone )
CRH ( Corticotropin-releasing hormone )
GnRH ( Gonadotropin-releasing hormone )
GHRH ( Growth hormone-releasing hormone )
Dopamine – inhibitory
These releasing/inhibiting hormones control the secretion of the respective anterior pituitary hormones
Hypothalamic Regulation of Anterior Pituitary Hormones: Hormone Targets and Actions
TSH (from anterior pituitary) acts on the thyroid gland to promote thyroid hormone production; thyroid hormone includes T3 and T4
ACTH acts on the adrenal cortex to promote cortisol production; cortisol participates in metabolic actions and stress response
GH acts on liver and other tissues to stimulate IGF-I production and growth of soft tissues, bone, and other targets; GH has direct and indirect (IGF-1 mediated) effects
FSH and LH act on the gonads to regulate sex hormone secretion (estrogen, progesterone, testosterone) and gametogenesis (ova and sperm)
PRL acts on mammary glands to promote milk production
Hormones and their peripheral target organs (illustrative mappings):
TSH → Thyroid gland; thyroid hormone synthesis and release
ACTH → Adrenal cortex; cortisol production
GH → Liver (and other tissues) to produce IGF-1; growth and metabolic effects
FSH/LH → Gonads; sex hormone production and gametogenesis
PRL → Mammary glands; milk production
Peripheral hormones and intermediary actions:
IGF-1 mediates many growth-promoting effects of GH
Sex steroids provide feedback to hypothalamus and anterior pituitary to regulate release
Thyroid hormones (T3/T4) and cortisol provide feedback to hypothalamus and pituitary
Receptor and signaling notes:
PRL receptor (JAK/STAT–linked)
GH receptor (JAK/STAT–linked)
FSH/LH receptors (Gs-linked GPCRs)
TSH receptor (Gs-linked GPCR)
MC2R (ACTH receptor) (Gs-linked GPCR)
Endocrine target status: some targets are endocrine glands; others are directly responsive tissues (e.g., IGF-1 production by liver influences growth)
Short vs. Long Feedback Loops
Primary hypothalamic regulation involves releasing/inhibiting hormones (TRH, CRH, GnRH, GHRH) and dopamine
Short feedback loops: peripheral hormones influence the pituitary and hypothalamus directly
Long feedback loops: peripheral hormones (e.g., T3/T4, cortisol, estrogens/testosterone) provide negative feedback to hypothalamus and pituitary to modulate hormone release
Key hormone–receptor interactions and examples of regulatory dynamics:
Prolactin has autoregulatory and receptor-mediated feedback mechanisms
GH and IGF-1 provide negative feedback at the level of the hypothalamus and pituitary
Listed cell types and their regulating hormones (simplified):
Corticotrope: ACTH; regulated by CRH and cortisol; CRH stimulates, cortisol provides feedback
Thyrotrope: TSH; regulated by TRH and thyroid hormones
Gonadotrope: FSH and LH; regulated by GnRH and sex steroids
Somatotrope: GH; regulated by GHRH and somatostatin
Lactotrope: PRL; regulated by dopamine (inhibitory) and other stimuli
Tropic hormones and target organs: a note that many receptors are located on endocrine glands and mediate endocrine cascades via signaling pathways
Pituitary Blood Flow and Portal System
Blood supply and drainage pattern:
Superior hypophyseal arteries feed into the primary capillary plexus within the pituitary stalk/infundibulum
Long portal veins connect to the secondary capillary plexus in the anterior lobe (hypophyseal portal system)
Short portal veins connect the primary and secondary plexuses
The anterior lobe is supplied by the hypophyseal portal system; the posterior lobe is served by directly entering arteries (inferior hypophyseal arteries) and draining via hypophyseal veins
Venous drainage:
Posterior lobe drains into hypophyseal veins → cavernous sinus → inferior petrosal sinus → jugular vein
Structural components shown in the portal system diagram include:
Fibrous tissue, primary plexus, long portal veins, trabecular arteries, short portal veins, secondary plexus, inferior hypophyseal arteries/veins, and the connections to the cavernous sinus
Pituitary Development: Embryology and Key Signals
Embryonic origins:
Rathke's pouch (oral ectoderm) forms the anterior pituitary (adenohypophysis)
Infundibulum (diencephalon floor) forms the posterior pituitary (neurohypophysis) along with the neurohypophyseal stalk
Median eminence and infundibular stem become part of the hypothalamic-pituitary axis
Early developmental interactions:
Rathke's pouch grows toward the brain and induces development of adenohypophysis; stalk regresses as the pouch forms the anterior lobe
Infundibulum forms the posterior lobe and neurohypophysis
Pars tuberalis surrounds the infundibulum
Pars intermedia is present in development; in adults it may be regressed/undetectable
Components and adult anatomy (from development):
Adenohypophysis includes Pars distalis and Pars tuberalis; Pars intermedia is lost or reduced
Neurohypophysis includes Pars nervosa; fluid-filled spaces can persist as remnants of Rathke's pouch lumen
Key transcription factors and lineage specification (from developmental schematics):
GATA-2, Prop-1, NeuroD1, Tpit, LIF, Pit-1 drive lineage specification in Rathke’s pouch
Pit-1 drives differentiation of somatotropes, lactotropes, and certain gonadotropes
Gonadotropes, Thyrotropes, Lactotropes, Somatotropes, and Corticotropes arise from Rathke’s pouch lineage
Additional progenitor and patterning factors involved in Rathke’s pouch development include:
Six3/6, Lhx3, Hesx1, Sox2, Sox1/2/3, Notch1/2, Jagged1, Hes1
BMP2, BMP4, Wnt4, FGF8/10/18, SHH (not explicitly listed but commonly implicated in pituitary development), and Pax family members in broader contexts
Rhythms of development and morphological events:
Rathke’s pouch proliferates from oral ectoderm and expands toward the diencephalon
The stalk of Rathke’s pouch regresses; mesenchymal interactions and bone formation (developing sphenoid bone) envelop the pituitary
Median eminence and infundibulum form the hypothalamic connection to the posterior pituitary
Notable structural remnants and anatomy references:
Optic chiasma, pars tuberalis, pars distalis, pars intermedia (lost in adult), infundibular stem, infundibular process, pars nervosa, fluid-filled spaces from lumen remnants
Model of developmental gene regulation (illustrative):
Lineage commitment and organogenesis are driven by a network of transcription factors and signaling molecules; proto-typical pathways include GATA2/Prop1/NeuroD1/Tpit/Pit-1 in adenohypophysis specification and Sox2/Notch/Jagged in progenitor maintenance and differentiation
Key Hormonal Relationships and Practical Implications
The hypothalamic-pituitary axis integrates neural and endocrine signals to regulate metabolism, growth, reproduction, and stress responses
Hormone release is tightly coupled to feedback from target organs (thyroid hormones, cortisol, sex steroids, IGF-1)
Understanding pituitary development helps explain congenital deficiencies and syndromes related to pituitary hormone production
The posterior pituitary’s storage-and-release mechanism illustrates a neuroendocrine interface where neural signals trigger endocrine outcomes
Quick Reference: Hormones and Targets (Summary)
Anterior Pituitary Hormones
TSH → Thyroid gland; thyroid hormone production and metabolic effects
ACTH → Adrenal cortex; cortisol production
FSH/LH → Gonads; sex hormone production and gametogenesis
GH → Liver (and other tissues); IGF-1 production; growth and metabolic effects
PRL → Mammary glands; milk production
Posterior Pituitary Hormones
ADH (vasopressin) → Kidneys; water reabsorption
Oxytocin → Uterus and mammary glands; contraction and milk ejection
Releasing/Inhibiting Hormones
TRH, CRH, GnRH, GHRH → Stimulate respective pituitary hormones
Dopamine → Inhibits prolactin release
Feedback Signals
Peripheral hormones (T3/T4, cortisol, estrogens/testosterone/progesterone, IGF-1) feed back to hypothalamus/pituitary to regulate release
Notable Biochemical Details
Prolactin molecular weight: ca. 23 kDa
Growth hormone molecular weight: ca. 22 kDa
CRH: 41-aa peptide; GHRH: 44-aa peptide; PRL receptor and GH receptor signaling via JAK/STAT pathways
CRH, TRH, GnRH, GHRH are short peptide hormones with specific receptor signaling mechanisms
Receptor/Signal Examples
FSH/LH receptors: Gs-linked GPCRs
TSH receptor: Gs-linked GPCR
ACTH receptor (MC2R): Gs-linked GPCR