Lecture 7 General Medicine_3rd semester MICROSCOPIC STRUCTURE, HISTOPHYSIOLOGY AND DEVELOPMENT OF ENDOCRINE GLANDS Hormones – classification Components of the endocrine system Principles of humoral regulation n n n hormones = chemical signals used for communication between cells more than 60 hormones classified as Ø amino acids analogues and derivatives Ø peptide or protein hormones Ø steroid hormones receptors are chemically defined sites bound with cell membranes Endocrine system - endocrine glands - hypophysis, pineal, thyroid, parathyroid, and adrenal - endocrine cell groups located within glands with exocrine or other functions (islets of Langerhans in the pancreas, Leydig cells in testes, granulosa cells in ovaries, juxtaglomerular apparatus of kidneys, trophoblast cells of the placenta) - cells with endocrine function that are scattered in nonglandular organs (as a gut, stomach, trachea, etc.) - e.g. GEP cells n n n Endocrine glands (glandulae sine ductibus) - have no ducts - have exceptionally rich blood supply - secrete hormones that pass into the circulatory system and induce a response of specific target cells, tissues, or organs Ø hypophysis Ø epiphysis Ø thyroid gland Ø parathyroid gland Ø adrenal gland Ø islets of Langerhans Hypophysis (hypophysis cerebri, glandula pituitaria) n sella turcica n 0.6 – 0.7 g n nadenohypophysis: pars distalis (75 %) n(anterior lobe) pars intermedia n pars tuberalis n nneurohypophysis: infundibulum (infundibular stem) n(posterior lobe) pars nervosa Vývoj žláz s vnitřní sekrecí-1 lobes are enveloped by a thin common connective tissue capsule, from which delicate septa with blood vessels and nerves project into the parenchyma hypofýza_oběh kopie Blood supply: direct arterial supply has only neurohypophysis (from two sets of vessels - superior hypophyseal arteries and inferior hypophyseal arteries). The adenohypophysis is drained by hypophyseal portal veins, which arise from the primary capillary plexus in the region of the median eminence and infundibular stem F20_06 adenohyp1 Pars distalis is made up of cords of glandular cells among them are blood sinusoids Cells: - chromophobic cells -10-15% - chromophilic cells – acidophilic cells - 50 % – basophilic cells adenohyp Vývoj žláz s vnitřní sekrecí-4 Acidophils somatotropic cells lactotropic cells F20_07 by immunohistochemistry: Basophils adrenocorticotropic cells thyrotropic cells gonadotropicFSH cells gonadotropic LH cells F20_03 Pars intermedia consists of small cystic cavities (residua of Rathke´s pouch that are limited by basophilic and chromophobic cells; basophils produce MSH - melanocyte-stimulating hormone (in amphibians) - in the human its function is unclear Pars tuberalis surrounds infundibular stem, 25 – 60 mm thick, is highly vascularized and composed of clusters of basophils and chromophobic cells; basophils are supposed to secrete gonadotropic hormones (FSH, LH) Neurohypophysis (posterior lobe) composed of pars nervosa and infundibular stem The pars nervosa: - pituicytes - irregular-shaped cells with numerous processes - axoterminals and nonmyelinized nerve fibers (whose cell bodies are in the hypothalamus (nc. supraopticus, nc. paraventricularis, nc. tuberalis) -fenestrated capillaries - Function: release site of hormones: ADH (vazopresin) oxytocin synthetized by nerve cell bodies and are transported by axons in the infundibular stem or pars nervosa neurosecretion are seen at preaxoterminal sites as Herring´s bodies neurohyp F20_09 neurohyp1 Pars nervosa Infundibular stem: cca 100 000 neurites of nerve cells hypothalamic nuclei (tr. hypothalamohypophysealis) ncl. supraopticus a ncl. paraventricularis (large neurons) ncl. tuberales (nc.hypothalamicus ventromedialis et dorsomedialis, ncl. infundibularis) - small neurons axoterminals end near capillaries of the primary capillary plexus hypothalamic regulatory factors (inhibins and liberins) are transported via vv. portae hypophysis to the pars distalis F20_02 Development of the hypophysis 2 anlages adenohypophysis - ectoderm of the Rathke´s pouch neurohypophysis - neuroectoderm of the ventral wall of diencephalon Vývoj žláz s vnitřní sekrecí-46 the Rathke´s pouch occurs on day 21 as tubular invagination of the roof of stomodeum growing dorsocranially against the base of diencephalon at the same time, base of diencephalon proliferates to form resessus infundibuli during the 5th week ends of both invaginations meet each other being to enclose by common connective capsule in the course of the 6th week, Rathke´s pouch loses connection with the stomodeum, lumen rests of the pouch persist as Rathke´s cysts filled with colloid in the pars intermedia between weeks 12-14 cells start their differentiantion secretion of hormones begins with the end of the 4th month Vývoj žláz s vnitřní sekrecí-38 Hypophysis Development of the hypophysis vývojhypofýzy Vývoj žláz s vnitřní sekrecí-46 Epiphysis - pineal gland (corpus pineale) 0.1 – 0.2 g is of cone-shaped form, 5-8 x 5-5 mm enveloped by a thin capsule with delicate septae dividing the parenchyma into lobules They consist of two cell types: - pinealocytes - which are in majority and arranged in clumps or clusters; the cells are characterized by lobulated nucleus, prominent nucleoli, and membrane-bound granules in the cytoplasm - interstitial cells - about 5 % (modified astrocytes of fibrilar type) and - non-myelinized nerve fibres and blood capillary plexus Pineal gland of adults contains the calcified concretions called as brain sand or acervulus cerebri (corpora arenacea). The concretions differ from their surrounding by deep staining and concentric appearance Hormone: melatonin - inhibits steroidogenic activity of endocrine cells in gonads Note: the tumours of the pineal are often connected with a failure of gonadal function. epifýza epifýza1 epifýza2 Vývoj žláz s vnitřní sekrecí-45 Epiphysis gland develops from the roof diencephalon (epithalamus) to the end of the 1st month in the 3rd month first pinealocytes start to differentiate nGlandula thyreoidea (thyroid gland) n25 – 40 g nin the anterior of the neck, below the cricoid cart. n2 lobes + isthmus n nin 50 % of cases the pyramidal lobe (lobus pyramidalis) is nfound; it exits from the isthmus cranially n nconnective tissue capsule + septae nthe parenchyma organized into the lobules n nlobules are composed of the follicles, which nvary considerably in diameter and contain ngelatinous material called the colloid n nthe walls of follicles consist of simple epithelium nthat rests on a thin basal lamina and delicate nreticular network nthe epithelium involves mainly follicular cells, nwhich are squamous to columnar in dependance on the functional status nthe cells produce colloid; it consists of mucoproteins, proteolytic enzymes and a nglycoprotein called thyroglobulin – primary storage form of thyroid hormone ntriiodothyronine (T3) + tetraiodothyronine (thyroxin, T4) nparafolicular, light or C – cells (lie immediately adjacent to basal lamina) - calcitonin F20_24 F20_25 Follicles follicular cells 002 003 F20_27 F20_26 004 parafollicular cells F20_28 Vývoj žláz s vnitřní sekrecí-35 Thyroid gland endodermal origin first anlage occurs in embryos with 16 somits on ventral wall of pharynx between the median tongue bud (tuberculum impar) and copula by proliferation of cells initially thyroid diverticulum originates, it is solid and rapidly grows in length, it becomes a lumen - thyroglossal duct duct migrates caudally, its blind end start to proliferate and to form follicles (in the 7th week) secretion of colloid starts during the 11th week Vývoj žláz s vnitřní sekrecí-44 rests of the thyroglossal duct: foramen cecum on the tongue (cranially) : pyramidal lobe (caudally) nGlandulae parathyreoideae (parathyroid glands) n n2 paired oval bodies cca 6 -8 mm long nand 2-5 mm wide nlie on the dorsal aspects of both nlobes of the thyroid nweight of bodies is 0.2 g altogether n nthin connective tissue capsule ndelicate septae that divide gland into nsmall lobules n nthey are composed of closely packed groups nor cords of glandular cells that are of two ntypes: vchief (principal) cells nnumerous, 8-10 diameter, large accumulations of glycogen and lipid droplets ncells secrete parathyroide hormone (PTH) – regulate calcium level of the blood nPTH is essencial for life (tetany) voxyphil cells noccur singly or in groups, are larger than chief cells, stain intensely with eosin, ncontain elongated mitochondia with numerous cristae ncells increase in number after puberty n F20_30 F20_31 chief cells glparath F20_32 oxyphil cells Vývoj žláz s vnitřní sekrecí-42 Parathyroid gland superior pair of glands – from the 4th pharyngyel pouches inferior pair of glands – from the 3rd pharyngyel pouches Vývoj žláz s vnitřní sekrecí-43 Vývoj žláz s vnitřní sekrecí-42 Development of parathyroid bodies Vývoj žláz s vnitřní sekrecí-43 Development of parathyroid bodies F20_10 Glandula suprarenalis (suprarenal gland, adrenal gland) paired gland situated at upper pole of each kidney the right is triangular the left semilunar weight of 5 – 7 g capsule cortex – 80 % medulla F20_11 A schema of the adrenal gland F20_12 F20_13 The adrenal cortex: is composed of cord of glandular cells separated by blood sinusoids according to the arrangement of cells in cords - 3 layers of the cortex are distinguished zona glomerulosa zona fasciculata zona reticularis F20_14 F20_17 The adrenal medulla composed of large round or polyhedral cells arranged in clumps or short cords surrounded with framework of reticular fibers, containing numerous capillaries with fenestrae,venules, nerve fibers and solitary sympathetic neurones glandular cells called as chromaffin cells contain fine granular cytoplasm and secrete catecholamines 2 types of chromaffin cells: - secreting adrenalin or epinephrine (most - 96%) - secreting noradrenalin or norepinephrine (the rest) 001 Blood supply of the adrenal gland Vývoj žláz s vnitřní sekrecí-47 Adrenal gland its development begins during the 5th week cortex - coelomic mesoderm medulla - crista neuralis zona glomerulosa and fasciculata are developed at birth zona reticularis occurs around the 3rd postnatal year Nervový systém - 61 Endocrine glands- summary hypophysis: adenohypophysis - ectoderm of the stomodeum neurohypophysis - neuroectoderm of the diencephalon (base) epiphysis - neuroectoderm of the diencephalon (roof) thyroid gland - endoderm of the primitive pharynx parathyroid glands - endoderm of pharyngeal pouches (3rd, 4th) adrenal gland: cortex - coelomic mesoderm medulla - neural crest (crista neuralis) Langerhans islets - endoderm of the foregut (duodenum)