Histology: Basic & Systematic - Endocrine System PDF

ANAT2241 Histology: Basic & Systematic Endocrine System Dr. Reza Shirazi Department of Anatomy, School of Medical Sciences Faculty of Medicine & Health, UNSW Sydney [email protected] Image by Dr John Abramyan, University of Michigan Resources Recommended reading: Textbook chapter (Whe...

ANAT2241 Histology: Basic & Systematic Endocrine System Dr. Reza Shirazi Department of Anatomy, School of Medical Sciences Faculty of Medicine & Health, UNSW Sydney [email protected] Image by Dr John Abramyan, University of Michigan Resources Recommended reading: Textbook chapter (Wheather's online): Endocrine System Textbook chapter (Junqueira’s Basic Histology: Text and Atlas, 16e online): Endocrine System University of Michigan Histology and Virtual Microscopy Learning Resources Chapman Histology https://www.youtube.com/channel/UCvSvCkHjCbHn8aGd6OPno_A/featured Learning Objectives 1. To understand and identify the basic components of the pituitary gland 2. To be able to describe the Hypothalamic-hypophyseal portal system 3. To be able to identify the two components of adrenal gland 4. To be able to understand different zones of adrenal cortex 5. To be able to understand endocrine component of pancreas 6. To be able to understand the histology of thyroid and parathyroid glands 7. To be able to understand the histology of pineal gland Endocrine System Secretory cells of endocrine glands: • Release their products, hormones, into the neighboring vascularized compartment • No secretory duct • Epithelial in origin • Aggregated as cords or clusters Hormones types: 1- Steroid: • Ovary • Testis • Adrenal cortex 2- Peptides, polypeptides, and proteins: • • • • • Hypothalamus Hypophysis Thyroid Parathyroid Pancreas 3- Amino acids and their derivatives: • Neurons • Adrenal medulla • Thyroid Endocrine System Secretions types of endocrine cells: 1- Endocrine secretion: • Into the neighboring vascularized compartment 2- Paracrine secretion: • Act on target cells only a short distance away: § With localized dispersal in interstitial fluid OR § Through short loops of blood vessels 3- Juxtacrine secretion: • A signaling molecule remains on the secreting cell’s surface or adjacent extracellular matrix and affects target cells when the cells make contact 4- Autocrine secretion: • Cells may produce molecules that act on themselves or on cells of the same type Source: Michael H. Ross: Histology: a Text and Atlas, 7th Edition Copyright © 2016 Wolters Kluwer Health Endocrine System: Locations of the Major Endocrine Glands Location of endocrine cells: • Endocrine glands • Located in other organs such as: § § § § § § Heart Thymus Gut Kidneys Testis Ovaries Pituitary Gland (Hypophysis) Location: • Below the brain in a small cavity on the sphenoid bone, the sella turcica Composed of: 1- Glandular tissue (epithelial tissue) [anterior pituitary or adenohypophysis] 2- Neurosecretory tissue [posterior pituitary or neurohypophysis] Source: Richard L. Drake: Gray’s Anatomy for Students, 4th Edition Copyright © 2020 Elsevier Inc. Pituitary Gland (Hypophysis) Embryological origins of pituitary gland: 1- Adenohypophysis (Oral component): • Outpocketing of ectoderm from the roof of the primitive mouth • Grows cranially • Forms hypophyseal (Rathke) pouch • Separates from the primitive mouth 2- Neurohypophysis (neural component): • Neurohypophyseal bud growing down from the floor of the future diencephalon • Forms a stalk (infundibulum) • Remains attached to the brain Pituitary Gland (Hypophysis) Composed of two glands: 1- Adenohypophysis (anterior pituitary): • Retains histologic features of glandular tissue • Locate anteriorly • Including: § Pars distalis § Pars tuberalis; wraps around the infundibulum § Pars intermedia; adjacent to pars nervosa 2- Neurohypophysis (posterior pituitary): • Retains histologic features of brain tissue • Located posteriorly • Including: § Pars nervosa § Infundibulum; attached to hypothalamus (X30; H&E; Pituitary gland) • PD: pars distalis • PI: pars intermediate • PT: pars tuberalis • IS: infundibular stalk • PN: pars nervosa The Hypothalamic-Hypophyseal Tract & Blood Supply Routes connecting pituitary gland to the hypothalamus: 1- Hypothalamic-hypophyseal tract • A bundle of axons coursing into the neurohypophysis from two important hypothalamic nuclei (supraoptic and the paraventricular nuclei) 2- Vascular portal system • Carrying small regulatory peptides from the hypothalamus to the adenohypophysis The Hypothalamic-Hypophyseal Tract & Blood Supply Blood supply: Arteries: 1- Superior hypophyseal arteries; supply: • Median eminence • Infundibular stalk 2- Inferior hypophyseal arteries; supply: • Neurohypophysis Veins: • Hypophyseal veins Vascular portal system in pituitary gland Adenohypophysis (Anterior Pituitary): (1) Pars distalis Accounts for 75% of the adenohypophysis Surrounded by a thin fibrous capsule Hormones produced by the pars distalis: • Widespread functional activities • Regulate: § § § § § Almost all other endocrine glands Milk production Ovarian function Sperm production Metabolism of muscle, bone, and adipose tissue Adenohypophysis (Anterior Pituitary): (1) Pars distalis Histological architecture: • Cords of endocrine cells interspersed with fenestrated capillaries and supporting reticular connective tissue Contains two groups of cells based on the histologic staining: 1- Chromophils; in which hormone is stored in cytoplasmic granules; including: • Basophils • Acidophils 2- Chromophobes; including : • Stem and undifferentiated progenitor cells • Any degranulated cells (X400; H&E; Pars distalis) • A: acidophils • B: basophils • C: chromophobes • IS: capillaries and sinusoids Adenohypophysis (Anterior Pituitary): (1) Pars distalis Source: Michael H. Ross: Histology: a Text and Atlas, 7th Edition Copyright © 2016 Wolters Kluwer Health (X640; Brilliant crystal scarlet, aniline blue, and Martius yellow; Pars distalis) • Ac: acidophils • Bas: basophils • Ch: chromophobes (X400; H&E; Pars distalis) • A: acidophils • B: basophils • C: chromophobes • IS: capillaries and sinusoids (X400; Gomori trichrome; Pars distalis) • A: acidophils • B: basophils • C: chromophobes • IS: capillaries and sinusoids Adenohypophysis (Anterior Pituitary): (1) Pars distalis Subtypes of acidophilic cells: • Identified by their granular morphology in the TEM or more easily by immunohistochemistry • Named according to their hormone’s target cells: 1- Somatotrophs/somatotrophic cells; 50% of the cells of the pars distalis; secrete: § Somatotropin (growth hormone) 2- Lactotrophs/lactotrophic cells; secrete: § Prolactin (PRL) (X10000; TEM; somatotropic cells) • G: Golgi complexes • N: euchromatic nuclei (X400; Hematoxylin counterstain; somatotropic cells) • Antibody against somatotropin Adenohypophysis (Anterior Pituitary): (1) Pars distalis Subtypes of basophilic cells (named according to their hormone’s target cells) 1- Corticotrophs; secrete: § § Adrenal corticotropin (adrenocortical trophic hormone (ACTH)) β-Lipotropin (β-LPH) 2- Gonadotrophs; secrete: § § FSH LH 3- Thyrotrophs: the least abundant; secrete: § Thyrotropin Adenohypophysis (Anterior Pituitary): (2) Pars tuberalis A smaller funnel-shaped part surrounding the infundibulum Mainly composed of: • Gonadotrophs Adenohypophysis (Anterior Pituitary): (3) Pars intermedia A narrow region between pars distalis and pars nervosa Overall functional significance: • Remains uncertain Composed of: 1- Basophils (corticotrophs) 2- Chromophobes: • Best-developed and active during fetal life • Produce two forms of melanocytestimulating hormone (MSH) 3- Colloid-filled cysts (X56; H&E; Pars intermedia) • PD: pars distalis • PI: pars intermediate • PN: pars nervosa • B: basophils • C: colloid-filled cysts Adenohypophysis (Anterior Pituitary): (3) Pars intermedia (X120; Toluidine blue; Pars intermedia) • CF: colloid Source: Michael H. Ross: Histology: a Text and Atlas, 7th Edition Copyright © 2016 Wolters Kluwer Health Neurohypophysis (posterior hypophysis) Composed of: 1- Pars nervosa 2- Infundibular stalk Neurohypophysis (posterior hypophysis) Histological architecture: neural tissue 1- Unmyelinated axons of large secretory neurons whose cells bodies located in: • Supraoptic nucleus; produce: § vasopressin/ADH • Paraventricular nucleus; produce: § Oxytocin Transportation of produced hormones: • Axonal transportation • Accumulate in axonal dilations called neurosecretory bodies or Herring bodies § Visible in the light microscope as faintly eosinophilic structures 2- Glial cells (pituicytes) • Look like astrocytes • The most abundant cells type in neurohypophysis 3- Capillaries (X400; H&E; Pars nervosa) • NB: neurosecretory (Herring) bodies • P: pituicyte • C: capillary Adrenal (Suprarenal) Gland Paired organs lying near the superior poles of the kidneys Covered by a dense connective tissue capsule that sends thin trabeculae into the gland’s parenchyma Stroma; consists mainly of: • Reticular fibers supporting the secretory cells and microvasculature Histological structure: Composed of two concentric regions which can be considered two different glands with different embryologic origins: 1- Cortex • Outer yellowish region 2- Medulla • Inner reddish-brown region Adrenal (Suprarenal) Gland: Blood Supply Source: Michael H. Ross: Histology: a Text and Atlas, 7th Edition Copyright © 2016 Wolters Kluwer Health Adrenal (Suprarenal) Gland: (1) Cortex Containing steroid-secreting cells Steroid hormones: • Involves close collaboration between SER and mitochondria • Not stored in granules like proteins • Diffuse freely from cells through the plasma membrane, as small lipid-soluble molecules Composed of 3 concentric zones: 1- Zona glomerulosa 2- Zona fasciculata 3- Zona reticularis Adrenal (Suprarenal) Gland: (1) Cortex Source: Michael H. Ross: Histology: a Text and Atlas, 7th Edition Copyright © 2016 Wolters Kluwer Health Adrenal Cortex: (1) Zona glomerulosa Immediately beneath the capsule 15% of the cortex Rich in capillary Composed of closely packed, rounded or arched cord with columnar or pyramidal cells Products: 1- Mineralocorticoids • Affects uptake of Na+, K+, and water by cells of renal tubules 2- Aldosterone; major product: • The major regulator of salt balance, which acts to stimulate Na+ reabsorption in the distal convoluted tubules (DCT) (X20; H&E; Adrenal cortex) • G: zonae glomerulosa • F: fasciculata • R: reticularis • M: medulla (a-f: X20; Mallory trichrome; Adrenal cortex) • C: capsule • M: medulla Adrenal Cortex: (2) Zona fasciculata 65-80% of the cortex Composed of long cords with large polyhedral cells Products: 1- Glucocorticoids, especially cortisol: • Affects carbohydrates metabolism • Cortisol: • (A) Suppresses many immune functions • (B) Induce fat metabolization and muscle proteolysis 2- Small amount of androgen Controlled by: ACTH (X20; H&E; Adrenal cortex) • G: zonae glomerulosa • F: fasciculata • R: reticularis • M: medulla (a-f: X20; Mallory trichrome; Adrenal cortex) • C: capsule • M: medulla Adrenal Cortex: (3) Zona reticularis Innermost zone 10% of the cortex Composed of network of irregular cords with smaller cells Stained heavily due to fewer lipid droplets and more lipofuscin pigments Products: 1- Weak androgens (main production); including: • Dehydroepiandrosterone (DHEA) 2- Cortisol Controlled by: ACTH (X20; H&E; Adrenal cortex) • G: zonae glomerulosa • F: fasciculata • R: reticularis • M: medulla (a-f: X20; Mallory trichrome; Adrenal cortex) • C: capsule • M: medulla Adrenal medulla Composed of: • Large, pale-staining polyhedral cells • Arranged in cords or clumps • Supported by a reticular fiber network Medullary parenchymal cells: Chromaffin cells • Modified sympathetic postganglionic neurons • Lacking axons and dendrites and specialized as secretory cells • Unlike cells in the cortex, contain many granules for storage and secretion of catecholamines: § Epinephrine (adrenaline): 80% of secreted catecholamines from the adrenal medulla § Norepinephrine (noradrenaline) (X200; H&E; Adrenal medulla) (X33000; TEM; Adrenal medulla) • NE: norepinephrine-secreting cells • E: epinephrine-secreting cells Adrenal medulla Innervated by preganglionic sympathetic neurons: • Stimulate the release of epinephrine and norepinephrine during stress and intense emotional reactions Epinephrine: • Increases heart rate • Dilates bronchioles • Dilates arteries of cardiac and skeletal muscle • Stimulate glycogen breakdown, elevating blood glucose levels Norepinephrine: • Constricts vessels of the digestive system and skin • Increasing blood flow to the heart, muscles, and brain • Stimulate glycogen breakdown, elevating blood glucose levels (X200; H&E; Adrenal medulla) (X33000; TEM; Adrenal medulla) • NE: norepinephrine-secreting cells • E: epinephrine-secreting cells Adrenal medulla (X120; H&E; Outer cortex) (X120; H&E; Deep cortex and medulla) Source: Michael H. Ross: Histology: a Text and Atlas, 7th Edition Copyright © 2016 Wolters Kluwer Health Pancreatic Islets (Islets of Langerhans) • Compact spherical or ovoid masses of endocrine cells embedded within the acinar exocrine tissue of the pancreas • Most islets contain several hundred cells, but some have only a few cells • More than 1 million islets in pancreas, mostly in the gland’s narrow tail region • Constitute 1%-2% of the organ’s total volume • A very thin reticular capsule surrounds each islet, separating it from the adjacent acinar tissue (X55; H&E; Pancreatic islets) • C: fenestrated capillaries (X12.5; H&E; Pancreatic islets) Source: Richard L. Drake: Gray’s Anatomy for Students, 4th Edition Copyright © 2020 Elsevier Inc. (X40; H&E; Pancreatic islets) • C: fenestrated capillaries (X300; Modified aldehyde fuchsin and light green; Pancreatic islets) Pancreatic Islets (Islets of Langerhans) The cells of islets: • • • • Polygonal or rounded Smaller More lightly stained than the surrounding acinar cells Arranged in cords separated by fenestrated capillaries Major human islet cells (most easily identified and localized by immunohistochemical staining): 1- α or A cells: • Secrete primarily glucagon • Abundant and scattered through most islets 2- β or B cells: • Produce insulin • About twice as abundant as α cells • Usually scattered 3- δ or D cells: • Secreting somatostatin • Much less abundant than the other major cell types 4- PP cells: • A minor cell type • Secrete pancreatic polypeptide Thyroid Gland Located anterior and inferior to the larynx Consists of two lobes united by an isthmus Covered by a fibrous capsule from which septa extend into the parenchyma: • Dividing it into lobules • Carrying blood vessels, nerves, and lymphatics Products: 1- Thyroxine (tetra-iodothyronine or T4) • Help control the basal metabolic rate in cells throughout the body 2- Tri-iodothyronine (T3) • Help control the basal metabolic rate in cells throughout the body, as well as the polypeptide hormone 3- Calcitonin • Inhibits osteoclast activity Thyroid Gland Parenchyma: • Millions of rounded epithelial thyroid follicles of variable diameter, each with simple epithelium and a central lumen densely filled with gelatinous acidophilic colloid (X12; H&E; Thyroid gland) • C: capsule • S: septa (X200; H&E; Thyroid gland) • L: lumen • C: C cells Specific features: • Only endocrine gland in which a large quantity of secretory product is stored • Storage is outside the cells: § In the colloid of the follicle lumen § Contains thyroglobulin (he precursor for the active thyroid hormones): ü T3 ü T4 c and d (X400; H&E; Thyroid gland) • T: thyrocytes • C: C cells (X400; Mallory trichrome; Thyroid gland) • T: thyrocytes • C: C cells Thyroid Gland Cell types: (X12; H&E; Thyroid gland) • C: capsule • S: septa (X200; H&E; Thyroid gland) • L: lumen • C: C cells 1- Thyrocytes: • Range in shape from squamous to low columnar § Active glands: have more follicles of low columnar epithelium § Hypoactive glands: with mostly squamous follicular cells 2- Parafollicular cell or C cell: • Found inside the basal lamina of the follicular epithelium or as isolated clusters between follicles • Larger than follicular cells • Stain less intensely • Produce calcitonin § Triggered by elevated blood Ca2+ levels § Inhibits osteoclast activity c and d (X400; H&E; Thyroid gland) • T: thyrocytes • C: C cells (X400; Mallory trichrome; Thyroid gland) • T: thyrocytes • C: C cells Thyroid Gland (X500; H&E; Pineal gland) • Arrows: blood capillaries between the follicles Parathyroid Glands Four small ovoid masses Location: • On the back of the thyroid gland • Usually embedded in the larger gland’s capsule Each contained within a thin capsule from which septa extend into the gland Histological feature: • Stroma: a sparse reticular tissue supporting dense elongated clusters of secretory cells • Parenchyma: 1- Principal (chief) cells 2- Oxyphil cells Parathyroid Glands: (1) Principal (Chief) Cells Endocrine cells Small polygonal cells with round nuclei and palestaining (X60; H&E; Parathyroid gland) • S: septa • P: principal cells • O: oxyphil cells Slightly acidophilic cytoplasm Product: • Parathyroid hormone (parathormone: PTH) § An important regulator of blood calcium levels With increasing age: • Many secretory cells are replaced with adipocytes, which may constitute more than 50% of the gland in older people (X200; H&E; Parathyroid gland) • C: capillaries Parathyroid Glands: (2) Oxyphil Cells Much smaller populations of the cells Often clustered Sometimes also present in parathyroid glands, more commonly in older individuals Much larger than the principal cells Characterized by: • Very acidophilic cytoplasm (X60; H&E; Parathyroid gland) • S: septa • P: principal cells • O: oxyphil cells Parathyroid Glands (X175; H&E; Parathyroid gland) • Cap: capsule • BV: blood vessel • AC: adipose cells Parathyroid Glands (Medium power; H&E; Parathyroid gland) • G: glandular elements • A: adipose tissue (High power; H&E; Parathyroid gland) • P: principal cells • O: oxyphil cells • C: capillaries Pineal Gland (Epiphysis Cerebri) Regulates the daily rhythms of bodily activities A small, pine cone-shaped organ Location: • In the posterior wall of the third ventricle Covered by: • Connective tissue of the pia mater § From which septa containing small blood vessels emerge and subdivide variously sized lobules Source: Richard L. Drake: Gray’s Anatomy for Students, 4th Edition Copyright © 2020 Elsevier Inc. Pineal Gland (Epiphysis Cerebri) Cell types: 1- Pinealocytes • Prominent and abundant secretory cells • Slightly basophilic cytoplasm • Irregular euchromatic nuclei • Produce melatonin § Promoted by darkness § Inhibited by daylight 2- Interstitial glial cells • Modified astrocytes • Represent about 5% of the cells • With elongated nuclei more heavily stained than those of pinealocytes • Usually found in: § Perivascular areas § Between the groups of pinealocytes (X200; H&E; Pineal gland) • S: septa • V: venules • CA: corpus arenaceum (X400; H&E; Pineal gland) • P: pinealocytes • A: astrocytes • V: blood vessels • CA: corpus arenaceum • Arrow: Capillaries Pineal Gland (Epiphysis Cerebri) A characteristic feature of the pineal gland: • Concretions of calcium and magnesium salts: corpora arenacea (brain sand) § Formed by mineralization of extracellular protein deposits § May appear during childhood and gradually increase in number and size with age, with no apparent effect on the gland’s function (X200; H&E; Pineal gland) • S: septa • V: venules • CA: corpus arenaceum (X400; H&E; Pineal gland) • P: pinealocytes • A: astrocytes • V: blood vessels • CA: corpus arenaceum • Arrow: Capillaries Pineal Gland (Epiphysis Cerebri) (X250; H&E; Pineal gland) • BV: blood vessels (Medium power; H&E; Pineal gland) • P: Pinealocytes • N: neuroglial cells (astrocytes) • S: pineal sand