Overview Overview pituitary, or hypophysis, rests in sella turcica, a depression of the sphenoid bone primary function of pituitary is secretion of hormones anatomically, pituitary is divided into anterior and posterior pituitary Anterior Pituitary: Anatomy and Embryology Anterior pituitary anterior pituitary, or adenohypophysis, is the glandular component of the pituitary a collection of endocrine cells responsible for synthesis and secretion of anterior pituitary hormones consists of pars distalis, pars intermedia,and pars tuberalis embryological origin oral ectoderm (Rathke's pouch) upgrowth of oral ectoderm primitive oral cavity Anterior pituitary cell types various cell types are responsible for synthesis and secretion of various hormones gonadotrophs FSH and LH corticotrophs ACTH thyrotrophs TSH lactotrophs prolactin somatotrophs growth hormone (somatotropin) Histology chromophils anterior pituitary cells that contain granules that react with acidophilic/basophilic stains acidophils anterior pituitary cells (pars distalis) that contain granules that react with acidophilic stains responsible for synthesis and secretion of PiG hormones prolactin and growth hormone basophils anterior pituitary cells (pars distalis) that contain granules that react with basophilic stains responsible for synthesis and secretion of FLAT hormones FSH, LH, ACTH, TSH granules that contain FLAT hormones are PAS+ chromophobes anterior pituitary cells that lack granules and that do not react with acidophilic/basophilic stains e.g., stromal cells and degranulated chromophils Anterior Pituitary: Hormones Anterior pituitary hormones FLAT PiG FSH (follicle-stimulating hormone) LH (luteinizing hormone) ACTH (adrenocorticotropic hormone) TSH (thyroid-stimulating hormone) Prolactin Growth hormone (somatotropin) categories of hormones corticolipotropins ACTH and MSH (melanocyte-stimulating hormone) glycoprotein hormones FSH, LH, TSH somatomammotropins prolactin and growth hormone Cortiolipotropins synthesis overview corticolipotropins are derived from a single precursor, POMC POMC = pro-opiomelanocortin pathway details MSH corticolipotropin synthesis products (aka fragments) contain MSH increased MSH levels → skin pigmentation e.g., Addison's disease ↑ ACTH → ↑ MSH → skin pigmentation Glycoprotein hormones subunits of peptide hormones glycoprotein hormones contain 2 subunits: α and β subunit α subunits identical, β subunits non-identical hormone specificity determined by β subunit human chorionic gonadotropin (hCG) structurally related to glycoprotein hormone hCG contains identical α subunit Somatomammotropins prolactin growth hormone secretion pulsatile secretory pattern secretory bursts approximately every 2 hours ↑ in secretory bursts during exercise and sleep functions ↑ linear growth and muscle mass growth mediated by production of somatomedins aka insulin-like growth factors (IGFs) diabetogenic effect insulin resistance decreases glucose uptake and utilization "diabetogenic" growth hormone produces increases in blood glucose pathophysiology GH deficiency before puberty symptoms failure to grow short stature mild obesity delayed puberty treatment growth hormone replacement GH excess growth-hormone secreting pituitary adenoma causes acromegaly symptoms differ from pre-puberty vs post-puberty before puberty gigantism aka increased linear growth after puberty increased organ size increased hand and foot size enlargement of tongue coarsening of facial features insulin resistance and glucose intolerance treatment somatostatin analog (e.g., octreotide) Posterior Pituitary: Anatomy and Embryology posterior pituitary posterior pituitary, or neurohypophysis, is the neural portion of the pituitary a collection of unmyelinated axons axons extend from cell bodies in hypothalamus consists of pars nervosa, infundibular stalk, and median eminence neurophysins carry hormones made in the hypothalamus (ADH and oxytocin) from the hypothalamus to the posterior pituitary embryological origin neural ectoderm downgrowth of neural ectoderm (diencephalon) Posterior Pituitary: Hormones Antidiuretic hormone (ADH; vasopressin) synthesis hypothalamic supraoptic nucleus neuronal cell bodies synthesize ADH pro-hormone ADH pro-hormone contains ADH and neurophysin II ADH pro-hormones are packaged in secretory vesicles secretory vesicles are transported via axonal transport to nerve terminals nerve terminals in pars nervosa of posterior pituitary ADH pro-hormone processing occurs in secretory vesicles during axonal transport cleavage of neurophysin II and release of ADH hormone secretion action potential depolarizes nerve terminals neurosecretory vesicles fuse with plasma membrane releases ADH and neurophysin II into perivascular space of highly fenestrated capillaries by which ADH enters systemic circulation Oxytocin synthesis neuronal cell bodies of the hypothalamic paraventricular nucleus synthesize oxytocin pro-hormone oxytocin pro-hormone contains oxytocin and neurophysin I oxytocin pro-hormones are packaged in secretory vesicles secretory vesicles are transported via axonal transport to nerve terminals nerve terminals in pars nervosa of posterior pituitary oxytocin pro-hormone processing occurs in secretory vesicles during axonal transport cleavage of neurophysin I and release of oxytocin hormone secretion action potential depolarizes nerve terminals neurosecretory vesicles fuse with plasma membrane releases oxytocin and neurophysin I into perivascular space of highly fenestrated capillaries by which oxytocin enters systemic circulation