Histology 3.02 Endocrine System Quiz PDF

HISTOLOGY 3.02 ENDOCRINE SYSTEM WINSTON ABENA, MD | BELLATORUM OUTLINE 3 Primary Germ Layers I. Endocrine System VI....

HISTOLOGY 3.02 ENDOCRINE SYSTEM WINSTON ABENA, MD | BELLATORUM OUTLINE 3 Primary Germ Layers I. Endocrine System VI. Pineal Gland a. Ectoderm: Hypophysis, Adrenal Medulla, & II. Pituitary Gland VII. Endocrine Chromaffin Bodies A. Divisions and Subdivisions of Pancreas b. Mesoderm: Adrenal Cortex, Testes, & Ovaries Hypophysis Cerebri VIII. Diabetes c. Endoderm: Parenchymal Cells of the Thyroid, III. Thyroid Parathyroid, & Pancreatic Islets of Langerhans IV. Parathyroid Glands V. Adrenal Glands 3 Classes of Hormones VI. Hormones and Functions a. Steroid hormones ▪ Adrenocortical hormones (adrenal cortex) LEGENDS ▪ Testosterone (testis) Remember Lecturer Book Presentation ▪ Estrogen & progesterone (ovary) b. Protein hormones (prolactin & insulin) → secreted by hypophysis, pancreas, thyroid & I. ENDOCRINE SYSTEM parathyroid composed mainly of ductless gland whose secretions c. Amino acid analogues & derivatives (thyroxine (hormones) are passed directly into the blood or lymph & norepinephrine) – secreted by thyroid & adrenal circulation. medulla It consists of widely separate seemingly unrelated glands, Each endocrine gland secretes one or more specific which differentiate from epithelial cells derived from any of substances called hormones which are discharged from the 3 primary germ layers. cells of the endocrine gland into the blood or lymph Endocrine components of the body occur in 3 forms: circulation distributed to the tissue fluids 1. As separate entities which are pure endocrine in Hormones function → has an effect upon a particular tissue or organ or ▪ Pituitary gland (hypophysis) upon the body as a whole. ▪ Thyroid → the organs affected are termed target organs or ▪ Parathyroid receptors ▪ Suprarenal glands → Only a small quantity of hormones is required to 2. As scattered masses of endocrine tissue within produce an effect, usually an arousal or activation, exocrine glands or other organs but occasionally an inhibitory response ▪ Islets of Langerhans (pancreatic islets) → Some hormones do not enter target cells but instead ▪ Interstitial cells of the testis bind to receptors on the CM activating an enzyme, ▪ Corpora lutein of the ovary adenylcyclase ▪ Juxtaglomerular cells of the kidney ̶ increases concentrations of Cyclic Adenosine → these combined organs are called mixed glands Monophosphate (CAMP) which acts as a → like the liver, each hepatic cell exhibits both “second messenger” (to initiate the physiologic exocrine & endocrine functions, secreting bile response for which the particular cell is into the duct system & internal secretions directly programmed). into the blood vessels. Neuro-Endocrine System. 3. As isolated endocrine cells present in the lining → overlapping regulatory control (endocrine & epithelium of the GIT & respiratory tracts nervous) regarded as a single system ▪ terminal APUD (Amine Precursor Uptake → endocrine cells are regulated by neural Decarboxylation) cells. mechanisms. CT stroma of all endocrine glands is richly vascular Hormones may be secreted: II. PITUITARY GLAND 1. As rapidly as they are formed in some glands AKA Hypophysis Cerebri 2. When necessary in others Continuous with hypothalamus of brain 3. Stored until required Pea – shaped (0.5g) (1.5g in multiparous women) 4. These secretory patterns affect the microscopic & Controls many other glands such as the thyroid and ultrastructure of the parenchymal cells. adrenal glands, as well as the ovary and testes. in some endocrine glands, the secretion accumulates most complex of the endocrine glands, being composed within the cell of origin (Pancreatic Islets) of 2 different tissues Thyroid Gland it is buried in a bony fossa of the sphenoid bone (sella → secretory product is stored in a central vase turcica) and covered by an extension of the dura mater surrounded by secretory cells forming a follicle (diaphragma sellae) in the adrenal cortex, the secretion is released almost there is a small aperture in the diaphragm through which as rapidly as it is formed passes the hypophyseal stalk it is about the size of a small flattened grape located at the base of the brain TRANS TRANS Tullao, Acacio, Addatu, Pagud, Calamaza, Dagusen, Fabros, Pulido, Malawis, Cammayo, Pamittan, Garcia 1 of 13 3.02 Endocrine System it is considered one of the most important organs in the → it appears that most chromophobes are referred body despite its small size, producing at least 9 as Gamma Cells (Romer’s classification of hormones pituitary cells) it has neural & vascular connections with the brain to ̶ partially degranulated chromophils which it is attached by the infundibulum or (acidophils & basophils) and that only a small hypophyseal stalk percentage are considered reserve or non- Hypophyseal (Ratke) pouch: an outpocketing of secretory cells ectoderm from the roof of primitive mouth that grows cranially Acidophils (Alpha cells) → stain readily & are easily identified in ordinary A. Divisions and Subdivisions of Hypophysis Cerebri preparations a. Adenohypophysis (Anterior Lobe) → larger than chromophobes, cell bodies are distinct & → Glandular portion the cytoplasm is crowded with secretion granules → derived from the oral ectoderm (stained with eosin, acid fuchsin, orange G & → migrates dorsally from the Rathke’s pouch azocarmine) → typical endocrine organization → 2 types (based on affinity of granules to orange G & → clumps or cords of secretory cells separated by azocarmine): fenestrated capillaries or fenestrae a. Orangephils or Alpha Acidophils – cells united anatomically but with different functions whose granules take up the orange G of Azan ▪ Pars distalis stain ▪ Pars tuberalis b. Carminophils Or Epsilon Acidophils – cells ▪ Pars intermedia whose granules stain intensely with azocarmine Pars distalis 1. Somatotrope/somatotroph Largest subdivision of hypophysis (75%) → most abundant cell type Enclosed almost completely in a dense fibrous capsule → stains strongly with orange G or eosin Its parenchyma is formed of anastomosing cords & → tends to be rounded & has abundant granules clusters of epithelial cells separated from sinusoidal → it secretes the hormone somatotrophin capillaries by a meager amount of reticular fibers (stimulates general body growth, particularly Sinusoids growth of long bones of the epiphysis) → lined by an endothelium traditionally considered as → they are similar to the alpha cells of the phagocytes however under EM, it was not verified pancreatic islets & the C cells of the thyroid → therefore, it was no longer considered as part of the gland RES → At its periphery, the sinusoids continue into 2. Carminophils/Mammotrope/Mammotroph collecting venules that join the venous plexus in the → 2nd type of acidophil fibrous capsule → its cells are greatly increased in number during Name of hormone: name of target organ + suffix & after pregnancy “trophic” or “tropic” → they secrete a lactogenic hormone (prolactin, Classification of parenchymal cells according to luteotrophic hormone) which initiates & staining reaction: maintains the milk secretion after pregnancy, & 1. Chromophils (specific granule reaction, H&E) stimulates the corpus luteum of the a. Acidophils – stains well with eosin b. Basophils – stains well with aniline blue of Basophils (Beta cells) mallory’s or masson’s trichrome stains → are larger than the acidophils containing less numerous granules than in acidophils & which are 2. Chromophobes (reserve cells) smaller in diameter → Periodic Acid Schiff (PAS) stain → granules stain poorly with hematoxylin, but are ̶ selectively stains the basophilic granules stained deeply with methylene blue because of their content of glycoprotein → they are best identified by the Periodic Acid-Schiff it is considered the most meaningful (PAS) technique – strongly positive due to the histochemical method to identify different cell concentration of glycoproteins in their secretory categories granules → Immunohistochemistry – has confirmed at → 2 types of basophils: least 6 cell types in the pars distalis (using a. Thyrotrope/thyrotroph/beta-basophil hormonal negative feedback control of most → stains with aldehyde fuchsin & responding anterior pituitary hormones) to thyroidectomy → The cell boundaries are not easily visible in → secrete thyrotropic hormone (TSH) ordinary preparations & generally the cytoplasm → cells are relatively large & contain granules lacks specific granules principally concentrated within the → EM: many cells exhibit small secretory granules peripheral cytoplasm TRANS Tullao, Acacio, Addatu, Pagud, Calamaza, Dagusen, Fabros, Pulido, Malawis, Cammayo, Pamittan, Garcia 2 of 13 3.02 Endocrine System b. Gonadotrope/gonadotroph/delta-basophil o Adrenal cortex – lowering of resistance to → do not stain with aldehyde fuchsin, secretes stress & disorder in CHO metabolism gonadotropins, also includes corticotropes. Endocrine glands → secretes two hormones based on their → have a reciprocal inhibiting effect upon the granules (EM): hypophyseal function via the hypothalamus (anterior 1. Granules (250nm in dia.) – uniform in size lobe hormones) & tend to polarize to one side of the cell; → removal of the target organ results in hypertrophy of mitochondria & free ribosomes are the cells in the adenohypophysis responsible for the scattered evenly between sparse flattened secretion of the corresponding hormone cisternae of ER ▪ Thyroidectomy - ↑ basophil “thyroidectomy cells” ▪ Luteinizing hormone (LH) – in ▪ Castration – basophils become markedly females, stimulates conversion of enlarged castration cells ruptured ovarian follicle into a corpus luteum Adenohypophysis ▪ Interstitial cell stimulating → master gland of the endocrine system – because of hormone (ICSH) – in males, the multiple hormones produced & its role in the stimulates the testicular interstitial regulation of other exocrine glands endocrine cells to produce the male → regulated by hypothalamic centers (neurosecretory sex hormone (testosterone) cells: supraoptic & paraventricular nuclei) → produce 2. Granules (about 200nm in dia.) – releasing factors/hormones which are liberated in the irregularly dilated cisternae of rER contain perivascular spaces medium electron-dense material → carried by the hypophyseal-portal vessels to the pars ▪ Follicle stimulating hormone distalis where they cause release of specific pituitary (FSH) – in females, stimulates hormones growth of ovarian follicles ▪ FSH – in males, it acts on the Pituitary gland seminiferous epithelium to produce → is not only under direct & indirect feedback control by spermatozoa its target organs, but also under control by the CNS c. Corticotrophs/corticotropes → large basophilic cells, eccentric indented nu 5 Functional Cell Types → produce the hormone adrenocorticotropic 1. Somatotropes (Growth Hormone) hormone (ACTH) – affects the zona 2. Lactotropes (Prolactin) fasciculata & zona reticularis of the 3. Corticotropes (Adrenocorticotropic) suprarenal glands = secrete glucocorticoids 4. Gonadotropes (FSH, LH) & lipotropic hormone (LPH) 5. Thyrotropes (TSH) Acidophils Hormone secreted 6 Hormones Secreted by Pars Distalis Somatotrope somatotrophin 1. Somatotropin (Somatotropic Hormone, STH; Carminophils/Mammotrope prolactin, luteotrophic Growth Hormone, GH) hormone → stimulates body growth by promoting proliferation Basophils of cartilage cells in the epiphysis Thyrotrope/Beta-basophil thyrotropic hormone → Hypophysectomy – cessation of growth (can be (TSH) restored by administration of the hormone) Gonadotrope/Delta- Gonadotropins, → Anterior. lobe tumors: basophil corticotropes ▪ Gigantism – when they occur before closure Corticotropes adrenocorticotropic of epiphysis hormone (ACTH) ▪ Acromegaly – occur after epiphyseal closure; ↑ thickness of mandible and bones of skull, Function of Pars Distalis hands, & feet functions of the anterior hypophysis is multiple as shown → regulation of GH secretion: by the disabilities resulting from surgical removal or ▪ stimulated by Hypothalamic Releasing destruction by disease Factor (GHRF) ▪ Hypophysectomy – causes a cessation of general ▪ inhibited by the peptide hormone, somatostatin body growth & involution of: → Tumors are usually benign. 2/3 produce hormones o Gonads – responsible in maturation and causing symptoms. differentiation of primary ovarian follicle and → The functional tumors include those that secrete formation of spermatozoa prolactin, ACTH (Cushing’s Disease), Growth o Thyroid – lowering of Basal Metabolic Rate Hormone (Acromegaly), and TSH. (BMR) → Non-functioning Pituitary tumors – tumors that don’t secrete functional hormones TRANS Tullao, Acacio, Addatu, Pagud, Calamaza, Dagusen, Fabros, Pulido, Malawis, Cammayo, Pamittan, Garcia 3 of 13 3.02 Endocrine System 2. Prolactin (Mammotroph, Luteotropic Hormone, Pars Intermedia CTH) less well developed in man & is usually poorly defined → stimulates synthesis of milk proteins, lipids, & forms 2% of the hypophysis CHO it is composed of a thin layer of cells & vesicles which → its action is on mammary glands that have contain an acidophilic colloidal substance hypertrophied during pregnancy (under influence it lies in close relation to the residual lumen of estrogen and progesterone) cells lining the colloid: containing vesicles are commonly → regulation of PRL secretion: ciliated, and some are mucous-secreting a. hypophyseal inhibitory factors (PIL) Intermediate lobe b. dopamine – binds to specific receptors on → residual lumen of Rathke’s pouch mammotropes → this lobe is located between the pars distalis & the c. norepinephrine – binds to thyrotropes pars nervosa its parenchymal cells (melanotrophs) possess a faintly 3. Thyrotropic Hormone (TSH) basophilic cytoplasm & an eccentric nucleus, resembling → stimulates the thyroid gland by binding to specific the corticotrophs membrane receptors on the follicular cells EM: to differentiate corticotrophs from melanotrophs: (enhancing iodine transport & binding, ▪ Melanotrophs are polygonal & somewhat smaller thyroglobulin synthesis, and subsequent release ▪ Nucleus of melanotroph is smooth whereas that of of thyroid hormones & cell growth) the corticotroph is much indented → regulation of TSH secretion: ▪ The granules are very similar & impart the a. Stimulated by thyrotropic releasing basophilia to the cells hormones (TRH) ▪ Granules – 200 – 300µm, are presumably the b. EST - ↑s response of thyrotropes to TRH source of the melanocyte stimulating hormone c. Somatostatin - ↓s response (msh) or intermedin in that initiates production of melanin causing darkening of the skin 4. Follicle Stimulating Hormone (FSH) → promotes growth of antral follicles in the ovary in Addison’s disease the ♀, and the growth of testes & → Pigmentation is due to excess ACTH and MSH, both spermatogenesis in the ♂ of which have melanocyte stimulating properties → regulation of FSH secretion: During pregnancy – the darkening of the skin may also a. Stimulated by Gonadotropin Releasing result from increased release of one or both of these Hormone (GNRH) hormones b. Inhibited by estradiol 5. Luteinizing Hormone (LH) CELL TYPE → necessary for ovulation → it promotes PRG secretion by the ovary & Hormone General Specific Site of testosterone secretion by the Leydig cells of the Action testis → regulation of LH secretion: Growth Acidophil Somatotroph Skeletal a. Stimulated by Gonadotropin Releasing hormone (STH) (Somatotrope) tissues Hormone (GNRH) b. Negative feedback control by PRG Lactogenic or Acidophil Mammotroph Breast Luteotropic (Mammotrope) 6. Adrenocorticotropin (Adrenocorticotropic hormone (CTH) Hormone, ACTH; Corticotropin) Follicle Basophil Gonadotroph Ovary & → promotes hypertrophy & hyperplasia of adrenal Stimulating (Gonadotrope) Testis cortex (when given to normal subjects), especially Hormone (FSH) the zona fasciculata & zona reticularis, and Luteinizing Basophil Gonadotroph Ovary causes increased secretion of glucocorticoids, Hormone (LH) (Gonadotrope) mineralocorticoids, & androgens or Interstitial → hypophysectomy – atrophy of adrenal cortex Cell Gonadotroph Testis (prevented by ACTH injections) Stimulating (Gonadotrope) Hormone → regulation of ACTH secretion: (ICSH) a. Corticotropin Releasing Factor (CRF) – stimulates both synthesis & release of ACTH Adrenocorticot Basophil Corticotroph Supraren b. Negative feedback control of the glucocorticoid ropic Hormone al cortex (cortisol) (ACTH) o ↑ blood cortisol → (-) release of CRF Melanocyte Basophil Corticotroph Skin → (-) of pituitary response to CRF Stimulating Hormone (MSH) TRANS Tullao, Acacio, Addatu, Pagud, Calamaza, Dagusen, Fabros, Pulido, Malawis, Cammayo, Pamittan, Garcia 4 of 13 3.02 Endocrine System Pars Tuberalis → they are elaborated by the cytoplasmic granules of like the parenchyma of the pars distalis & intermedia, it neurosecretory cells of the supraoptic & takes its embryonic origin from Rathke's pouch paraventricular nuclei epithelium EM: (+) cytoplasmic vesicles which may be: it is the small superior portion of the pars distalis forming 1. synaptic vesicles of nerve fibers containing Ach a sleeve or collar of cells around the infundibular stalk 2. residual vesicles from which hormones were most highly vascularized subdivision of the hypophysis, extracted (oxytocin and vasopressin) since it is traversed by the major arterial supply for the → both hormones are linked to polypeptides anterior lobe & the hypothalamo-hypophyseal venous (neurophysins) during their transport down to portal system the H-H tract & in the neurosecretory granule – no significant physiological role has been determined; specific & contain cystine groups though small amounts of pars distalis hormones have been found here (LH, FSH, TSH) Oxytocin extension of anterior lobe along stalk like infundibulum → causes contraction of uterine smooth muscle during b. Neurohypophysis (Posterior Lobe) coitus & at the time of delivery → Extension of the CNS → it also causes contraction of the myoepithelial → Stores and releases secretory products from (basket) cells of the alveoli & ducts of the mammary hypothalamus gland → Only axons, glial cells (pituicytes), capillaries → it mediates the milk ejection reflex in response to → ventral invaginations from the floor of the suckling by lactating infants diencephalon (forebrain) → it is used clinically in obstetrics for induction of labor ▪ Pars nervosa synthesized by large neurons in the paraventricular ▪ Infundibular stem/stalk nuclei ▪ Median eminence of the tuber cinereum → portion of the hypophysis that is derived from the floor Vasopressin (ADH) of the 3rd ventricle of the brain (hypothalamus) → raises the BP by stimulating contraction of smooth → it includes the median eminence of the tuber muscle in the walls of blood vessels cinereum, the infundibular stalk, & the → it conserves body water by promoting reabsorption of infundibular process (pars nervosa) water in the DCT of the kidney (by increasing → all have the same nerve & blood supply, and contain permeability of the DCT & CD of kidney inhibiting the same active hormonal principle diuresis) → it consists of supportive cells resembling neuroglia → in large doses, causes contraction of intestinal & cells elsewhere in the CNS, the pituicytes, & the bronchial musculature terminal portions of the axons belonging to extrinsic Dehydrated: secrete ADH secretory neurons whose large cell bodies are synthesized by large neurons in the supraoptic located in the supraoptic & paraventricular nuclei of nuclei the hypothalamus (neurosecretory cells) ▪ Diabetes insipidus ̶ results when the nuclei of the hypothalamus are Pituicytes involved in tumor growth or injury → are small cells with short branching processes which end in relation either to blood vessels or to CT septa Blood Supply of Hypophysis → do not secrete a hormone & function like the neuroglia has unusual features & is intimately involved in control of of the CNS the secretory activity of the gland → within its cytoplasm are fat droplets, granules & Importance: it provides the avenue of control by the NS pigments (number of which increases with age) of the adenohypophysis, involving the release of special → they are present throughout the neurohypophysis & are hormones or releasing factors from the hypothalamic especially abundant in the Pars Nervosa nuclei (releasing factors are carried by the bloodstream → using silver stain, there are 4 types to the adenohypophysis where they control the release of ▪ Reticulo-pituicytes – center, near fiber tracks various pituitary hormones) ▪ Micropituicytes Distinguishing Feature: Portal System (artery arteriole- ▪ Fibropituicytes – near connective tissue support capillary plexus-portal veins-capillary (sinusoidal), plexus ▪ Adenopituicytes & the draining veins) Herring bodies Pituitary – is supplied by the superior hypophyseal → large accumulations of neurosecretory material in arteries which usually arise from the circle of Willis & the axoplasm of the fibers of H-H tract (stored inferior hypophyseal arteries from the internal carotids neuro-secretory corpuscles) Superior Hypophyseal Arteries → spherical masses of highly variable size, staining → supply the infundibulum, & the anterior lobe via a deeply with chrome aluminum hematoxylin portal system → found throughout the neurohypophysis but → form a ring interior to the circle of Willis sending particularly abundant in the pars nervosa capillaries to the infundibulum (infundibular process) TRANS Tullao, Acacio, Addatu, Pagud, Calamaza, Dagusen, Fabros, Pulido, Malawis, Cammayo, Pamittan, Garcia 5 of 13 3.02 Endocrine System arterioles – in the median eminence & upper ▪ ▪ iodine content of the food portion of the stalk terminate in looped sinusoidal capillaries forming an external Histological Organization (superficial plexus) Follicles ▪ vessels from this plexus unite to form the long → structural units of the gland, compose the lobules portal vessels passing superficially down to the → bigger follicles are found in the middle of the organ pars distalis & send branches that form the deep while the smaller ones are along the periphery plexus of vessels in the eminence (preponderance in human thyroid) ▪ deep vessels – eventually connect to the long → they also vary in shape, but usually are irregularly portal vessel spheroidal → Hypophyseo-portal system: long portal vessels, → the follicles are surrounded by an extremely thin short portal vessels (venules), capillaries basal lamina which is not resolved with the LM (eminence), sinusoidal capillaries (pars distalis) → store an intermediate form of hormone (thyroglobulin) outside cells in colloid rather than Inferior Hypophyseal Arteries in secretory granules within cells → serves mainly for the blood supply of the neural lobe with branches given off that anastomose with Development branches from the superior hypophyseal arteries to endodermal outpocketing from floor of pharynx supply the lower portion of the infundibulum & then point at which the anterior 2/3 of the tongue (1st the anterior lobe by a short portal system pharyngeal arch derivative) is joined by the posterior Veins from the neural lobe & those from the anterior lobe 1/3 of the tongue (3rd pharyngeal arch derivative) drain into the cavernous sinus guided by a duct, usually disappears Capillaries of the posterior lobe is smaller than the sinusoidal capillaries of the anterior lobe Follicular Epithelial Cells EM: (+) fenestrated type of endothelium in the sinusoidal capillaries (deficiencies within the endothelial vary in height but generally are simple cuboidal in the lining presumably facilitate the passage of secretory normal gland material into the vessel) when the gland is hypoactive, cells become low cuboidal or squamous Nerve Supply of Hypophysis when it is hyperactive, cells are tall columnar H-H tracts of unmyelinated nerve fibers that extend into its nucleus is spheroidal, centrally located, poor in the neural lobe from their cells of origin in the supraoptic chromatin & containing 1 or more nuclei & paraventricular nuclei tracts from other regions of the continuous row along the wall of the follicles hypothalamus to the upper part of the stalk there are no nerves to the anterior lobe Follicles although the parenchymal cells of the pars distalis are its cytoplasm is lightly basophilic, finely granular & devoid of nerve supply, there is evidence that they are containing rod-shaped or filamentous mitochondria that under nervous control vary in number with the activity of the cell its intercellular boundaries are distinct III. THYROID GLAND the fine structure of the follicular cells reflects both the weighs about 20 & 30g, shields the lower anterior region synthesis of glycoprotein & its resorption of the neck & may be palpated Follicular/Chief Cells it consists of 2 lateral lobes connected by a narrow → apical ends facing inward (towards the follicular isthmus – lies over the 2nd to 4th tracheal cartilages cavity); basal ends resting on a basal lamina the lateral lobes lie in relation to the superior part of the controlled by TSH, also known as thyrocytes trachea & inferior part of the larynx a median process (pyramidal lobe) is present extending Parafollicular Cells upward from the left sides of the isthmus → a small population of cells found between the beneath is a delicate layer of CT, the true capsule, which follicular cells & the basal lamina, and in the adheres closely to the gland interfollicular spaces it is penetrated by delicate trabeculae & septae that contains small amount of rough ER and large Golgi divides the gland into lobes & lobules, which in turn, are complexes composed of follicles → they produce calcitonin, “calcitonin cells” or C cells, the separation of the capsule into 2 layers facilitates “light cells”, ultimobranchial cells, or mitochondria- surgical removal of the gland rich cells it varies in size & structure in response to many factors → are larger than follicular cells & its nuclei are placed ▪ sex eccentrically ▪ temperature → they are the site of production of the blood calcium- ▪ nutrition lowering hormone, thyrocalcitonin or calcitonin ▪ age → they are of different embryonic origin from the ▪ reason follicular cells (neural crest cells) TRANS Tullao, Acacio, Addatu, Pagud, Calamaza, Dagusen, Fabros, Pulido, Malawis, Cammayo, Pamittan, Garcia 6 of 13 3.02 Endocrine System → since they contain serotonin & calcitonin, they are Functions of the Thyroid Gland often considered part of the Amine Precursor 1. to synthesize, store, and release hormones thyroxine Uptake & Decarboxylation System (APUD) (tetraiodothyronine) and tri-iodothyronine (that is → have a more eosinophilic cytoplasm due to the concerned with regulation of BMR) – function resides staining of its granules solely in the follicular epithelial cells → the structure of the cell is similar to the GH- 2. thyrocalcitonin (elaborated by parafollicular cells), a producing cells of the pituitary gland, although polypeptide that actively lowers blood calcium calcitonin can prevent bone resorption concentration, inhibits bone resorption Colloid Cells of Langerdorff ▪ hypercalcemia – stimulates its secretion → are slender cells with darkly staining cytoplasm that ▪ hypocalcemia – inhibits its secretion often appear to be filled with colloid, & they have 3. thyroxine increases cell metabolism, thus is concerned pyknotic nuclei with development, differentiation, and growth → degenerating follicular cells & may be sloughed into ▪ Hypothyroidism: infant (cretinism); adult the lumen of the follicle, adding their contents, (myxedema) including nucleoproteins & proteolytic enzymes to ▪ Hyperthyroidism: (overactivity) exophthalmic the colloid goiter Colloid 4. it has certain interrelation with the ant. pituitary gland → an acidophilic homogenous staining substance found ▪ Thyroidectomy – (+) hypertrophy of anterior lobe within the lumen of the thyroid follicle with degranulation of alpha cells & the appearance → it contains the hormone, thyroxin, which is secreted of the “thyroidectomy cells” by the follicular epithelium Thyroid Hormones → vacuoles of varying size, rbcs, & desquamated glandular cells are found within the colloid mass Essential to normal growth and development → Inactive follicles – stains basophil Critical for early brain development → Active follicles – stains weakly basophil or acidophil Also stimulate gene expression for GH → it represents a reserve of secretion that is rich in Increase basal metabolic rate, fat metabolism, heart rate nucleoproteins (basophilia), and contains and body temperature thyroglobulin & enzymes Thyroxine ▪ Thyroglobulin – is a glycoprotein containing → Modified amino acid that contains four atoms of several iodinated AAs, proportion of which vary iodine from follicle to follicle; it stains deeply with PAS → Accelerates oxidative metabolism throughout the ▪ the secretory process is complex and involves body synthesis of the TH, temporary storage, and → Hypothyroidism – deficiency of thyroxine, causes release into the perifollicular capillaries; goiter, decreased heart rate, lethargy, obesity, and synthesis & release may occur both at the same decreased mental alertness time → Hyperthyroidism – too much thyroxine, profuse ▪ Thyroid cells – remove iodine rapidly from the perspiration, high body temperature, increased bloodstream & concentrate it → major part of the metabolic rate, high blood pressure, loss of weight, iodine is incorporated in follicles in an organic and irritability form and in colloid; Iodine within the colloid are present in the form of: Blood Vessels & Nerves o Di-iodothyronine it has a rich plexus of blood & lymph capillaries which are o Tri-iodothyronine in intimate relation to the follicular epithelium o Tetraiodothyronine (thyroxine) bound to blood capillaries – are of the fenestrated variety, which globulin aid in the passage of the hormone into the capillary lumen → release: thyroglobulin is first recovered from the arteries – contain pad-like thickenings beneath the colloid by the process of pinocytosis (at the apex intima at places where they branch, they assist in lysosomes) → breakdown: thyroxine → tri- shunting the blood to different parts of the gland as the iodothyronine → passes thru bases of follicular cells arteries contract into the underlying capillary plexuses numerous myelinated nerve fibers are found in the walls Production of Thyroid hormone of the thyroid arteries – most are vasomotor in function 1. thyroglobulin is produced 2. iodide uptake from the blood though Na/I symporters IV. PARATHYROID GLANDS (pendrin pumps) location: near thyroid glands but variable 3. iodination of tyrosyl residues thin connective tissue separates from thyroid 4. formation of T3 and T4 from cells of 3rd and 4th pharyngeal arches 5. endocytosis of iodinated thyroglobulin small yellowish-brown oval bodies which lie in close 6. secretion of T3 and T4 relation to the thyroid gland they are usually in 2 pairs; although accessory glands occur frequently, the upper parathyroid lie on the TRANS Tullao, Acacio, Addatu, Pagud, Calamaza, Dagusen, Fabros, Pulido, Malawis, Cammayo, Pamittan, Garcia 7 of 13 3.02 Endocrine System posterior surface of the thyroid, whereas the lower ones → EM: (+) concentration of elongated are in relation to the lower poles of the thyroid lobes mitochondria with numerous closely spaced because of the origin of their parenchymal cells from the cristae; small Golgi apparatus & scarce ER endodermal epithelium of the 3rd & 4th pharyngeal → LM: (+) eosinophilic granules (abundant pouches, respectively, they are designated sometimes as mitochondria) parathyroid III & IV Parathyroid III both cell types are arranged irregularly in cords or clumps → are associated with the thymus during the 1st part that are supported by a delicate vascular fibroreticular of its caudal migration, before detaching from the stroma (containing the blood vessels & nerves; fats – with thymus & become associated with the dorsal increasing age, they show an increase in amount so as surface of the thyroid with oxyphil cells & colloid) Parathyroid IV → detach from the rest of the pharyngeal epithelium & Blood Vessels & Nerves later become associated with the thyroid have a rich blood supply; larger vessels follow the septa → as a consequence, parathyroid III becomes the into the interior of the gland inferior Parathyroid, and parathyroid IV become the the highly permeable fenestrated type of capillary is less superior Parathyroid numerous (+) delicate septa which pass inward from the capsule, compared to the thyroid carry blood vessels & few nerve fibers into the gland (+) plexus of veins the CT of the capsule & of the septa contains fat cells that unmyelinated nerve fibers (vasomotor) – scanty increase in number with age Parenchyma Functions of Parathyroid Gland → It is supported by a network of reticular fibers which 1. Elaborate the parathyroid hormone (parathormone) – in is composed of masses and cords of epithelial cells regulation of calcium metabolism; it is produced principally by the dark chief cells 2 types of epithelial cells ▪ ↓ plasma calcium conc. → (+) release of hormone → 1. Chief/Principal cells (+) withdrawal of bone calcium ̶ majority, secrete parathyroid hormone (PTH) ▪ Hormone – stimulates the transformation of ̶ smaller & more numerous osteogenic cells into osteoclasts ̶ polygonal in shape with a centrally placed ▪ Removal/atrophy of the gland - ↓ blood calcium; vesicular nucleus & a pale, slightly acidophilic accompanied by nervous hyperexcitability & muscular cytoplasm spasm (tetany) → death ̶ (+) coarse granules of lipofuscin pigment with ▪ Calcium deficiency (rickets) – (+) hypertrophy a considerable amount of glycogen; (+) small ▪ Tumors or hyperplasia → hyperparathyroidism = secretory granules – secrete parathormone deposition of calcium in soft tissues (calcification), ̶ EM: (+) cisternae & granular ER that has a hypercalcemia & extensive bone resorption tendency to accumulate at the cell periphery ̶ Effects of Hyperparathyroidism: weakness, ▪ Clear chief cells – have large vesicular nuclei thirst, dizziness, calcification of blood vessel & a clear, pale-staining cytoplasm which walls contains few granules 2. Has a direct effect upon ion transport in the kidney ▪ Dark chief cells – have smaller nuclei & finely 3. It decreases the conc. Of phosphate ion in the blood granular cytoplasm (electron-dense & ▪ ↓ parathyroid activity à ↑ phosphate conc. in blood bounded by a membrane) ▪ Parathyroids – respond directly to blood calcium ▪ Both forms are rich in glycogen levels & are not under the control of other endocrine ̶ in normal adult, only about ⅓ of the chief cells are glands or the NS actively synthesizing & secreting parathormone ▪ Parathormone – demands for its production remains ̶ Active cells: usually stain a little darker in LM fairly constant since calcium is readily available from ̶ Less active cells: have a smaller Golgi complex, bones & the diet few or no secretory granules, considerable ▪ there are no specialized storage or mobilization glycogen & lipofuscin pigment requirements for this hormone; thus, the parathyroid chief cells are relatively inactive in contrast to other 2. Oxyphil cells endocrine glands → no known secretory role, singly or in clusters, acidophilic V. ADRENAL GLANDS → do not appear in man until near the end of the Upper poles of kidneys, embedded in fat. first decade & are not abundant until puberty; Are a pair of roughly triangular, flattened yellowish organs its function is still uncertain embedded in the retroperitoneal adipose tissue close to → they are larger than chief cells but fewer in the cranial pole of each kidney number, occurring singly or in small groups Left adrenal is crescentic while the right is pyramidal in → have a small, darkly staining nucleus & a shape, with a combined weight of 10 – 12g; the left being strongly acidophilic cytoplasm somewhat heavier than the right TRANS Tullao, Acacio, Addatu, Pagud, Calamaza, Dagusen, Fabros, Pulido, Malawis, Cammayo, Pamittan, Garcia 8 of 13 3.02 Endocrine System They are composite organs consisting functionally & lipid droplets: composed of cholesterol (more ▪ structurally of 2 distinct parts: concentrated in the outer ⅔ of the zone), FA, a. Cortex (inter-renal tissue) – mesoderm; bright & neutral fat yellow in color (outer part), reddish brown (inner (responsible for fatty acid synthesis) zone) ▪ inner ⅓ of the zone – relatively free of lipid b. Medulla (chromaffin tissue) – ectoderm; thin, gray material; more basophilic due to its granular in color ER → Secretory cells: General Structure ▪ cholesterol esters – serve as a precursor for Epithelial parenchyma – is supported by a delicate steroid hormone synthesis by these cells’ fibroreticular tissue richly provided with capillaries & considerable amounts of ascorbic acid sinusoids; thus, it is considered to be among the most ▪ ACTH – causes rapid depletion of vascular glands (like the thyroid) cholesterol & ascorbic acid The adrenal substance is divided into an outer yellowish → secretory cells: appear vacuolated and spongy, cortex & an inner dark, & more vascular medulla are called “spongiocytes” (believed to be the yellowish color of the cortex is due to the presence responsible for the secretion of the cortical of fat droplets within the cells, while the medulla is dark hormones) brown or gray due to the large amount of blood it contains → EM: much developed smooth-surfaced ER; & to the presence of chromaffin granules in the cells tubular villous cristae; large Golgi apparatus with It lacks hilum lysosomes & deposits of lipochrome pigments (older individuals) Adrenal Cortex secrete glucocorticoids especially cortisol it is classically divided into 3 zones according to differences in the cord-like arrangement of its cells: a. Zona glomerulosa (outer) c. Zona reticularis (inner) → it is the thin layer just beneath the capsule → the thinnest & less distinct of the 3 zones cell consisting of closely packed clusters and cords form an anastomosing arcades of columnar cells arranged in spheroidal → its transition from the fasciculata is gradual groups which normally show no central lumen or → cytoplasm contains fewer lipid droplets toward in hooked, horseshoe-shaped, or slightly coiled the medulla, there is a variable number of “light” columns & “dark” cells → they are continuous with the cell columns of the ▪ Light cells – nuclei are pale staining zona fasciculata ▪ Dark cells – nuclei are shrunken & hyper- → EM: most characteristic feature of cytoplasm – chromatic containing large accumulations of smooth surfaced ER forming an anastomosing lipofuscin pigment network of tubules ▪ the cells in this zone possess an abundance of the agranular variety of ER → (+) filamentous mitochondria with lamellar cristae, juxtanuclear Golgi apparatus, microvilli Adrenal Medulla on surface Columnar/Pyramidal cell: closely packed, Medullary (Chromaffin cells) – large, pale staining rounded or arched cords w/ many capillaries. Chromaffin cells are responsible for the storage and Steroids made are mineralocorticoids and the secretion of either epinephrine or norepinephrine. principal product is aldosterone Modified neurons without processes Glucocorticoids from cortex control them b. Zona fasciculata (middle) Sympathetic nerve fibers reach these cells, stimulate → the thick broadest zone composed of cell cords them to release epinephrine from the bloodstream coursing parallel to one another in a radial Fight or Flight response direction toward the medulla cords the boundary between the zona reticularis of the cortex & → consists of polyhedral cells larger than those medulla is usually irregular in man with some columns of found in the zona glomerulosa cortical cells projecting into the medulla → are usually one or 2 cells in width separated by a its cells are epithelioid, ovoid, or polyhedral arranged in longitudinally oriented meshwork of sinusoidal rounded groups or short anastomosing cords surrounded capillaries by venules & capillaries → Secretory cells: generally cuboidal or they have large vesicular nuclei & their cytoplasm polyhedral in shape, sometimes are binucleate; contains fine granules (chromaffin) which become brown these are numerous fatty cells possessing a pale when the tissue is fixed in a solution containing potassium staining or vesicular nucleus with less dense dichromate (Zenker’s fixative) chromatin & a cytoplasm containing plenty of fat the resulting brown coloration of the granules in the droplets that is responsible for the yellowish color cytoplasm with chromium salts is called the “chromaffin of the cortex or pheochrome reaction” – this is believed to be due to the oxidation of the catecholamines, epinephrine, & TRANS Tullao, Acacio, Addatu, Pagud, Calamaza, Dagusen, Fabros, Pulido, Malawis, Cammayo, Pamittan, Garcia 9 of 13 3.02 Endocrine System norepinephrine contained within the granules of the cells; Zona glomerulosa after treatment with ferric chloride, the medulla is colored ̶ secrete hormones called Mineralocorticoids green (Aldosterone & Deoxycorticosterone) which are Application of histochemical methods to chromaffin cells concerned with fluid & electrolyte balance indicate the presence of 2 types of cells derived from the Zona fasciculata & reticularis neural crest ectoderm: ̶ secrete the hormones: a. cells containing epinephrine (epinephrocytes) – o Glucocorticoids (cortisol, cortisone & high affinity for azocarmine positive acid corticosterone) – concerned with the phosphatase reaction & negative reaction with iodate metabolism of CHO, CHONS, & fat or silver o Female sex hormones (EST & PRG) & b. cells containing norepinephrine androgen hormones (norepinephrocytes) – are autofluorescent, give >sex hormones are found in the distal end of argentaffin & potassium iodate reactions, have a low Z. fasciculata (small amount) and upper affinity for azocarmine & a negative acid region of Z. reticularis (numerous) phosphatase reaction → normal activity of the suprarenal cortex – is partially most prominent feature of these cells in EM is the under the control of the ACTH of the adenohypophysis presence of large numbers of membrane-bound dense that affects principally the zona fasciculata granules → Hypophysectomy – results in marked atrophy of the in glutaraldehyde fixation, 2 populations of cell: zona fasciculata & reticularis but little effect on zona a. cells that store EPI – have granules that contain a glomerulosa; atrophy can be prevented by ACTH very electron-dense core eccentric in location injection b. cells that store NE – have granules that are relatively → large doses of cortisol – suppresses hypophyseal homogenous & less electron-dense secretion of ACTH = atrophy of inner zones of adrenal the mitochondria are not prominent; cisternae of the cortex granular ER are arranged in small parallel arrays; Golgi → Glucocorticoids – also have effects upon apparatus contain dense material believed to be a inflammatory response of the CTs & upon the immune precursor of the secretory granules system; they are widely utilized in the treatment of mechanism of hormone release: exocytosis allergies, rheumatic fever, arthritis, & other production of catecholamines: inflammatory diseases; in surgical organ grafting, it is → uses tyrosine from the liver → DOPA → dopamine often given to suppress the rejection reaction (cytoplasm) → NE (chromaffin granules) → EPI → relationship exist between adrenal cortex & the (cytoplasm) reproductive system: removal of adrenals = loss of >NE and EPI- responsive for cholinergic receptors libido (males) & abnormal cycles (females) >associated with post-ganglionic type of → Cushing’s disease/hyperadrenocorticism – a synapses condition in which the adrenal cortex is hyperplastic secretory cells of the adrenal medulla have many producing excessive amounts of ACTH similarities to postganglionic neurons: → Addison’s disease/hypoadrenocorticism – is due to ▪ both are derived from neural crest in the embryo & destruction of the adrenal cortex by TB or other innervated by preganglionic sympathetic fibers infections, resulting in chronic insufficiency of the ▪ both secrete norepinephrine production of the hormone difference of medullary cells from postganglionic 2. Adrenal Medulla neurons: responsible for automatic responses (immediate) ▪ neurons cannot convert NE to EPI → not essential to life ▪ neurons secrete at nerve endings → enables an individual to respond to emergency ▪ medullary cells secrete into the interstitium from situations which the hormone enters the blood vessels → secretes the hormone, catecholamines (EPI, NE) center of medulla: (+) several large veins with a → EPI (vasoconstrictor) – has relatively very little prominent tunica media & contains longitudinally effect upon metabolism, but causes a marked ↑ BP disposed smooth muscles causing a bulging into the with very little effect upon CO; it is the principal lumen; (+) sympathetic ganglion cells occur singly or in transmitter substance of adrenergic neurons small groups (neurohumor) Hormones and Functions Regeneration 1. Adrenal Cortex cells of the adrenal cortex show a capacity for → it is concerned with a variety of body functions such as: regeneration in comparison to those of the medulla a. maintenance of fluid & electrolyte balance b. maintenance of CHO balance Blood Supply & Lymphatic Drainage c. maintenance of the normal function of cellular Adrenal glands – are highly vascular organs; each elements of the CT gland is supplied by 3 arteries (superior, middle, & inferior suprarenals) coming from different sources → enter the capsule at various points giving off branches: TRANS Tullao, Acacio, Addatu, Pagud, Calamaza, Dagusen, Fabros, Pulido, Malawis, Cammayo, Pamittan, Garcia 10 of 13 3.02 Endocrine System ▪ some ramify in the stroma of the cortex between → irregular in shape, well-developed Golgi the clumps of the cells → zona reticularis → complex, sparse ER & small number of collecting vein (medullary boundary); no venous glycogen particles system in the cortex → with numerous membrane-limited electron ▪ others go directly towards the medulla where they opaque granules resembling those of the ramify into several capillaries & sinusoids adrenal medulla Medulla – has a dual blood supply: → histochemical methods indicate presence of a. through the cortical sinusoids that anastomose with catecholamine principally NE its capillary bed across the junction between the → are usually separated from the blood by a cortex & medulla barrier consisting of a thin supporting cell, b. through the medullary arteries from the capsule basal lamina, and the endothelium → these directly to the medulla vascular relationships are significant as it is Capillaries of the medulla – empty into the same not yet clear whether the paraganglion cells collecting veins that drain the cortex & which later join have an endocrine function to form the large central veins of the medulla and 2. Supporting cells emerge as the suprarenal vein from the gland → surround each of the chief cells Cells lining the medullary capillaries – endothelium → nucleus is elongated & the cytoplasm is Cortical sinusoids – endothelium; ct macrophages devoid of secretory granules Lymphatics: found only in the capsule & cortical trabeculae, and the CT around the large central veins there are abundant capillaries lined by very attenuated of the medulla endothelial cells that exhibit occasional fenestrae Arteries enter capsule via 2 routes Carotid & Aortic Bodies a. Cortical capillaries → they function as chemoreceptors and are associated b. Medullary arterioles with small islands of chromaffin cells Central adrenomedullary vein → Aortic Chromaffin Bodies (Lumbar Paraganglia) → Tunica media has conspicuous, longitudinally ̶ are relatively large, irregularly paired masses oriented bundles of smooth muscle formed by a fusion of paraganglia → Constriction causes adrenal gland volume to ̶ located retroperitoneally & lie ventrolaterally decrease, enhancing efflux of hormones from to the aorta at about the level of the origin of gland like squeezing a wet sponge. the inferior mesenteric artery Organs with dual blood supply: Liver, thyroid and → clinical significance: involved in production of medulla chromaffin tumors similar to those of suprarenal medulla (pheochromocytoma) Nerve Supply also responsive to autonomic nervous system Splanchnic nerves → unmyelinated nerve fibers à capsule → cortex → trabeculae → medulla (preganglionic VI. PINEAL GLAND (EPIPHYSIS CEREBRI) fibers in medullary cells) is slightly flattened, cone-shaped appendage of the brain few ganglion cells in medulla measuring 8 – 12mm in length & 5 – 8mm in width (+) splanchnic nerves = ↑ EPI its base is constricted to form a hollow peduncle by which section of splanchnic nerves = (-) secretory activity of it is attached to the roof of the 3rd ventricle with the pineal medullary cells recess (narrow prolongation of the III ventricle) extending up into it Paraganglia (Chromaffin System) it is covered by the pia mater except at its attachment, involves several scattered groups of cells that are similar forming a thin capsule from which CT trabeculae in many ways to medullary cells of the suprarenal glands invaginate the parenchyma of the organ dividing into these are clusters of epithelioid cells that give a poorly defined lobules – numerous blood vessels & chromaffin reaction nerves are carried by this capsule and trabeculae. cells of the paraganglia & cells of the adrenal medulla 2 types of cells (being similar in morphology & embryonic origin), make ▪ Pinealocytes (95%) – clumps/cords of cells up the so-called chromaffin system ▪ Glial cells (5%) – like astrocytes of brain it is present in many organs receiving sympathetic innervation (liver, kidney, heart, ovary, & testis) Microscopic Anatomy its largest group is the paired para-optic bodies of 2 Types of Cells in the Parenchyma Zuckerkandl (Lumbar aortic paraganglia) which is 1. Pinealocytes/Chief cells/Epithelioid cells located in the CT located at the junction of the inferior → H & E: composed of cords of pale staining mesenteric artery with the aorta epithelioid cells with large nuclei & prominent its component cells are chromaffin cells that stain nucleoli; lightly staining cytoplasm positively with chromic & osmic acid → del Rio-Hortega 2 types of Parenchymal cells ̶ irregularly shaped cells 1. Chief cells ̶ have a long tortuous cytoplasmic process radiating from the cords toward the CT TRANS Tullao, Acacio, Addatu, Pagud, Calamaza, Dagusen, Fabros, Pulido, Malawis, Cammayo, Pamittan, Garcia 11 of 13 3.02 Endocrine System septa with club-shaped terminations or Longer days of spring allow gonads to develop as bulbous swellings on or near blood melatonin inhibits gonadal releasing hormones vessels Seasonal Affective Disorder (SAD) – emotional states → EM: numerous free ribosomes in the at high altitudes in winter cytoplasm, abundant tubular & vesicular elements of atypical agranular ER, & Functions of Pineal Gland moderately abundant fairly large mitochondria 1. Antigonadotropic – inhibitory action on the maturation → a distinctive feature is the presence of of the gonads abundant microtubules; (+) lipid droplets, 2. Secretion of high level of melatonin & serotonin, and an lipochrome pigments, & lysosomes – enzyme hydroxyindole-o-methyltransferase (HIOMT) that cytoplasm has a role in the synthesis of melatonin from serotonin → (+) Grumose Bodies – dense-cored ▪ Melatonin membrane-bound granules reminiscent of ̶ produces blanching of melanophores (an effect primary lysosomes (near the Golgi apparatus, opposite that of melanocyte stimulating along the cell process, & in the terminals) hormone) → constitute the bulk of the organ ̶ its synthesis is influenced by light probably via 2. Interstitial/Neuroglia/Supportive cells/ the sympathetic ns Epiphyseal Gliocytes Melanocyte stimulating hormone - located → they occur in the perivascular area & between the anterior and posterior pituitary (pars between the clusters of pinealocytes intermedia) → nuclei are elongated & stain more deeply 3. It has a high concentration of NE (neurotransmitter) than those of the parenchymal cells 4. It may also produce arginine vasopressin (a peptide → cytoplasm appears more basophilic & drawn that is an antagonist to LH & FSH) out into long processes or extensions surrounding pineal cells & their processes, VII. ENDOCRINE PANCREAS as well as sympathetic nerves & nerve the endocrine portion of the pancreas has scattered richly endings vascularized small masses of endocrine cells known as → it represents about 5% of the cells in the the pancreatic islets of Langerhans pineal body their secretion (insulin) is poured directly into the → considered as glial elements (astrocyte) bloodstream, having no functional communication with → (+) filaments in their cytoplasm – “stellate the duct system of the gland astrocytes” H & E: appear as spheroidal masses of pale staining cells → (+) rER unevenly distributed in compact arranged in the form of irregular anastomosing cords; masses there are numerous blood capillaries closely adjacent to → (+) primary and secondary lysosomes the epithelial cells between the cords Islet cells Corpora arenacea → pale staining than the surrounding acinar cells Brain sand, psammoma bodies, acervulus cerebri, sand → they are clearly demarcated from the surrounding granules acinar tissue by a thin reticulum containing the these are mulberry-shaped concretions which are capillaries extracellular lamellated bodies composed of concentric capillaries are fenestrated layer of a mineralized organic matrix (composed mainly → they are more abundant in the tail of the pancreas of calcium phosphates & carbonates) than in the head they increase gradually in size & number (old age) embryonic in origin Mallory-azan stain: 3 types of granular cells Nerve Supply a. Alpha cells (A cell) → contains granules that are insoluble in alcohol Myelinated nerve fibers (some) – derived from the → its granules are relatively large & colored brilliant trabecular & post. Commissures red Unmyelinated nerve fibers (most) – derived from the → less numerous & have a tendency to be situated sympathetic fibers originating from the post. cervical around the periphery of the islet ganglia → they elaborate glucagon which has an opposite unmyelinated nerve endings – have a beaded action to that of insulin (it causes an ↑ of blood appearance sugar level) Measures light intensity/ Duration → they have also shown the presence of gastrin which has been associated in cases of islet cell Circadian rhythms – day/night cycle tumors (gastrin hypersecretion & severe gastric During the day, substances produced in the pineal gland