Endocrine organs

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Endocrine organs

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  • Endocrine organs

  • Endocrine organ classificationCentral organs:

    hypothalamus, hypophysis, pineal glandPeripheral organs:

    thyroid gland, parathyroid glands, adrenalsMixed organs:

    pancreas, gonads, placentaDiffuse neuroendocrine or APUD system

  • Endocrine gland tissue composition Nerves tissue:

    hypothalamus neurohypophysis pineal gland adrenal medulla Epithelial tissue:

    adenohypophysis thyroid gland parathyroid glands adrenal cortex

  • Endocrine organs are ductless glands Contain rich network of

    blood sinusoidal fenestrated capillarieslymphatic capillariesRelease hormones into

    the blood, lymph, and intracellular spaces Hormone chemistry: steroidsproteins glycoproteins amino acid derivatives

  • Endocrine system is regulating and controlling body systemHormones act on specific target cells interact with cell receptors (surface or nuclear)alter the target cell biological activity

    Control mechanisms: (a) endocrine (b) paracrine(c) autocrine

  • HypothalamusContains nuclei of neurosecretory cells

    Nuclei with large cells:

    Paraventricular nucleiSupraoptic nuclei

    Nuclei with small cells:

    Dorsomedial nucleiVentromedial nucleiArcuate or Infundibular nuclei

  • Neurosecretory cells secrete hormonesNeurosecretory cell axons leave the hypothalamusterminate on blood capillaries form the axovasal synapses in

    the neurohemal organs

  • Neurohemal organs contain axovasal synapsesPars nervosaMedian eminence

  • Hypothalamus nuclei with large neurosecretory cellsParaventricular nuclei oxytocinSupraoptic nuclei ADH

    Neurosecretory cell axons pass through the pituitary stalk

    (hypothalamohypophysial tract)enter the pars nervosaform axovasal synapses

  • Hypothalamus nuclei with small neurosecretory cellSecrete adenohypophyseal tropic hormones:releasing (liberins)inhibiting (statins)

    Neurosecretory cell axons:

    form axovasal synapses in the median eminenceon capillaries of the primary capillary network

  • Hypophysis (pituitary gland)lies beneath the brain is connected with the hypothalamus

    hypothalamohypophysial neuroendocrine system

  • Hypophysis anatomical subdivisionNeurohypophysis (nerves tissue)Pars nervosa (posterior lobe)Infundibulum

    Adenohypophysis (epithelial tissue)Pars distalis (anterior lobe)Pars intermediaPars tuberalis

  • Hypophysis developmentNeuroectoderm neurohypophysis Ectodermal epithelium of the oral cavity


  • Pars nervosa is not endocrine glandis the neurohemal organstores and releases hormones

    from the hypothalamus nuclei

  • Pars nervosa histologyunmyelinated nerve fibersglial cells pituicytesblood capillaries

  • Pars nervosa nerve fibersare axons of the neurosecretory cells

    from supraoptic and paraventricular nuclei of the hypothalamus

    form hypothalamohypophyseal tractconvey hormones to the pars nervosaform axovasal synapses on capillaries

  • Herring bodiesare dilated axon terminals accumulate secretory granulesrelease hormones to the bloodstream

  • Pars nervosa hormonesADHOxytocin

  • Adenohypophysisis true endocrine glandproduces and releases hormones

    Hormone chemistry:

    small proteinsglycoproteins

  • Adenohypophysis histologyendocrine epithelial cells (glandulocytes)loose connective tissue trabeculaesinusoidal fenestrated capillaries

    cells are arranged in adenomeres

  • Pars distalis cell typesAcidophilsBasophilsChromophobes

    acidophils and basophilscontain secretory granules

  • Pars distalis cell hormonesAcidophilsGH (STG)PL (LTH)BasophilsTSHLH and FSHACTH

  • Pars distalis chromophobes lack secretory granulesare partially degranulated secretory cells

    some of them are stem cells

  • Adenohypophysis pars intermediaEndocrine cells surround the colloid-filled cysts

    pseudofolliclessecrete hormonesMSHLPH

  • Adenohypophysis vascularizationsuperior hypophyseal artery

    primary capillary network

    in the median eminence portal veins

    secondary capillary network

    in the adenohypophysis hypophyseal veins

  • Adenohypophysis portal systemScanning EM

  • Portal system transports hypothalamic hormonesneurosecretory cells releaseliberinsstatinsin primary capillary network

    portal veins

    secondary capillary network

    of the adenohypophysis

  • Adenohypophysis is regulated by hypothalamic hormonesLiberins and statinsleave the secondary capillariesstimulate or inhibit adenohypophysis cells

  • Thyroid glandis located

    in anterior portion of the neckon the thyroid cartilage and upper trachea

    consists of

    two lateral lobesisthmuspyramidal lobe (may or may not be)

  • Thyroid histologic compositionfolliclesconnective tissue stromacapillaries

  • Follicles are the thyroid morpho-functional unitsare spherical cyst-like compartmentsconsist ofbasal laminaepithelial cells - thyrocytescolloid

  • Thyroid follicles are surrounded by rich capillary networkcapillaries are

    fenestrated sinusoidal

  • Thyrocytes or follicular cellsare epithelial cellsarise from the endodermare cuboidal in shaperest on the basal membraneare in contact with the colloid

  • Thyrocytes secrete protein hormonesThyroxine (tetraiodothyronine) T4Triiodothyronine T3

    Hormones regulate cell and tissue basal metabolism cell growth and cell differentiation

  • Colloid takes part in hormone synthesisColloid contains thyroglobulin - iodinated glycoproteinseveral enzymes

    Thyroglobulin is inactive storage form of the thyroid hormones

  • synthesis and secretion of thyroglobulinconcentration of iodide, oxidation to iodine,

    and release to the colloidformation of T3 and T4 hormones by iodinationresorption of colloid by endocytosisrelease of hormones from cells into circulation

    resorption vacuoles

  • Hyperfunction and hypofunction of the thyroid gland

    HyperfunctionHypofunctionFollicular cell shapeColumnarFlatFollicle diameter SmallerLarger Colloid volumeDecreasesIncreasesResorption vacuolesMore in numberLess in number

  • Thyrocytes are the adenohypophysis-dependent cellsare stimulated by TSH from the pars distalisrelease of T3 and T4 is regulated by

    a simple feed-back system

  • Parafollicular cells or C-cellsarise from the neural crestoccur in follicle wall or interfollicular spacescontain numerous secretory granules

  • Parafollicular cells secrete protein hormone calcitoninlowers the blood calcium level

    suppresses bone resorptionstimulates bone calcification

    are the adenohypiphysis-independent cells are regulated by the blood calcium level

  • Parathyroid glandare two pairs: superior and inferiorassociated with the thyroid

  • Parathyroid gland histologyepithelial endocrine cellsloose connective tissuesinusoidal fenestrated capillaries

  • Endocrine cells are arranged in cordsPrincipal or chief cells parathyroid hormone (PTH)Oxyphil cells (unknown function)

  • Parathyroid hormone is antagonist to calcitonin increases the blood calcium level

    stimulates bone resorptionreduces the kidney calcium excretionactivates the intestine calcium absorption

  • Parathyroid gland is the adenohypophysis-independent is directly regulated by the blood calcium level

    Simple feedback system:

    low calcium levels

    stimulate PTH secretion

    high calcium levels

    inhibit PTH secretion

  • Adrenal (suprarenal) glandsare paired glandsare located at the kidney superior poles

    are subdivided in cortex and medulla

  • Adrenal gland blood vesselsShort cortical arteries

    cortical capillaries medullary capillaries medullary veins Long cortical arteries

    medullary capillariesmedullary veins

  • Adrenal gland vascularization

  • Adrenal cortexarises from the mesodermconsists of epithelial cellssecretes steroid hormonesis adenohypophysis-dependent

  • Adrenal cortex zonationZona glomerulosa

    Zona fasciculata

    Zona reticularis

  • Zona glomerulosacells are arranged in ovoid clusterssecretes mineralocorticoids (aldosterone)is regulated by renin-angiotensin system

    and ACTH

  • Aldosterone effectsstimulates

    sodium resorption and potassium excretion in the kidney, salivary glands and sweat glands

  • Zona fasciculatacells are arranged in long straight cords

  • Zona fasciculata cell ultrastructure is characteristics of steroid-secreting cells:well-developed SERnumerous mitochondria with tubular

    and vesicular cristaewell-developed Golgi complexnumerous lipid droplets

  • Zona fasciculata secretionsecretes glucocorticoids (cortisol, corticosterone)hormone effects:

    regulate gluconeogenesis and glycogenesisdepress immune and inflammatory response

  • Regulation of Zona fasciculata activityis under control of ACTH

  • Zona reticulariscells are arranged in anastomosing cords

  • Zona reticularis secretionsecretes weak androgens

    (dehydroepiandrosterone)is under ACTH control

  • Adrenal medullaarises from the neural crestconsists of modified neural cellssecretes catecholamine hormonesis adenohypophysis-independent

  • Adrenal medulla cells are called chromaffin cellssecrete norepinephrine and epinephrine

    are regulated by preganglionic sympathetic nerve fibers glucocorticoids induce norepinephrine to epinephrin


  • Adrenal medulla hormone effectsrise in blood pressuredilation of the coronary vesselsincrease in the heart rate

  • The END

    Thank you for attention!