Histology of Endocrine Glands 2024 PDF

Histology of the Endocrine Organs  Histology of the hypophysis cerebri (pituitary gland) Weighs 0.5 g in males and 1.5 g in multiparous women Has two parts developing from two different sources 1. Adenohypophysis (anterior lobe) 2. Neurophpophysis (posterior lobe)  Histolo...

Histology of the Endocrine Organs  Histology of the hypophysis cerebri (pituitary gland) Weighs 0.5 g in males and 1.5 g in multiparous women Has two parts developing from two different sources 1. Adenohypophysis (anterior lobe) 2. Neurophpophysis (posterior lobe)  Histology of adenohypophysis (anterior lobe) Is made up of three lobes known as: 1. Pars distalis (anterior lobe) 2. Pars intermedia 3. Pars tuberalis  Pars distalis (anterior lobe) Constitutes 75% of the hypophysis Is composed of the following threes cell types: 1. Chromophil cells a. Acidophils, make 40% i. Somatotrophs ii. Mammotrophs b. Basophils, make 10% I. Corticotrophs II. Thyrotrophs III. Gonadotrophs 2. Chromophob cells, make 50% 3. Folliculostellate cells Pars distalis (anterior lobe) Pars distalis (anterior lobe)  Pars distalis (anterior lobe) Regulation of Cells found in the Anterior Lobe of the Pituitary Gand  Chromophobs Small and weakly staining cells Have less cytoplasm than the chromophils Thought to be nonspecific stem cells or degranulated chromophils  Folliculostellate cells Nonsecretory cells with long processes interconnected by gap junctions Surround the hormone producing cells Functions may include: – Transmission of signals from pars tuberalis to pars distalis through their gap junction in addition to that of the hypophyseal portal vein system – Physical support  Pars intermedia Between pars distalis and pars nervosa, and have: 1. Colloids lined by cuboidal cells Thought to may have derived from folliculostellate cells or various hormone producing cells 2. Melanotropes as cords – Produce melanocyte stimulating hormone (β-MSH)  Pars tuberalis Funnel-shaped region surrounding hypophyseal stalk Is a highly vascular region containing veins of the hypothalamohypophyseal system Contains cords of cuboidal-low columnar basophilic cells – Produce no known specific hormone, but often show immunoreactivity for ACTH, FSH, and LH  Neurohypophysis (posterior pituitary gland) Mainly by nonmyelinated hypothalamohypophyseal tracts that arise from: 1. Supraoptic nuclei for production of equal amounts of both vasopressin (antidiuretic hormone, ADH) and oxytocin 2. Paraventricular nuclei for production of more oxytocin than ADH  Neurohypophysis (posterior pituitary gland) Vasopressin (antidiuretic hormone, ADH) causes: – Reabsorption of water by the kidneys – Vasoconstriction increasing the blood pressure Oxytocin functions in: – Contraction of myometrium during orgasm, menstruation and parturition – Contraction of myoepithelial cells increasing milk secretion  Neurohypophysis (posterior pituitary gland) Is divided into: 1. Median eminence 2. Infundibulum (stalk) 3. Pars nervosa  Pars nervosa 1. Receives the terminals of the hypothalamohypophyseal tracts, as Herring bodies 2. Contains neurohypophyseal cells (pituicytes) – Occupy about 25% of the volume of pars nervosa – Resemble astrocytes, and also have glial fibrillary acidic proteins (GFAP), and serves a supporting role 3. There are also fibroblasts and mast cells  Blood supply of the hypophysis Supplied by: 1. Superior hypophyseal arteries – Supply the pars tuberalis, median eminence and infundibulum – Take releasing & inhibiting factors of hypothalamic neurons to adenohypophysis via hypophyseal portal veins 2. Inferior hypophyseal arteries Mainly to neurohypophysis, with a small supply to the stalk Most of the anterior lobe of the pituitary gland has no direct arterial supply  Hypothalamus Coordinates most endocrine functions of the body and serves as one of the major controlling centers of the autonomic nervous system Produces numerous neurosecretory products – Oxytocin and ADH to pars nervosa – Other releasing and inhibiting polypeptides near the median eminence and infundibulum for the hypothalamohypophyseal portal system traveling to the pars distalis of the pituitary gland  Pineal gland (pineal body or epiphysis cerebri) A flattened, pine cone-shaped structure Measures 5 - 8mm high and 3 - 5mm in diameter and weighs 0.1 g – 0.2 g Divided into lobules by connective tissue septae extending from the pia mater Contains several types of cells, mainly: – Pinealcytes – Astrocytes-like cells  Pinealocytes Slightly basophilic cells with large irregular or lobulated nucleus occurring as clumps or cords Send one or two long processes with terminal dilatation to capillaries or other parenchymal cells Obtaining information about light and dark cycles from the retina via the retinohypothalamic tract, and produce: – Melatonin which is secreted at night and involved in the circadian (day/night cycle) and seasonal biorhythms – Other peptides  Astrocyte-like cells (Interstitial cells) Scattered cells making 5% of the cells of the gland Contain elongated nuclei that satin deeply than that of the pinealocytes Have long process with large number of intermediate filaments  Pineal gland Contains corpora arenacea (acervulus or brain sands) – Concretions of calcium phosphate and carbonate deposited in concentric ring on carrier proteins as orange matrix Increase in size with age and during short photoperiod, but decrease when the pineal gland is actively secreting  Histology of the thyroid Gland Divided into irregular lobes and lobules Thyroid follicles that vary in diameter from about 0.2 to 1.0 mm constitute the functional units of the gland Contains two types of cells 1. Follicular cells (principal cells) 2. Parafollicular cells (clear or C cells)  Thyroid follicles Lined by follicular cells – Simple basophilic epithelium that changes shape from squamous, when hypoactive to low columnar, when active Have colloids Contains gelatinous substance composed of about 3 months supply of triiodothyronine (T3) & tetraiodothyronine (T4, thyroxine) bound to thyroglobulin  Thyroid follicles The hormones regulate cell and tissue basal metabolism and heat production to influence body growth and development Regulated by TSH  Parafollicular cells (clear or C cells) Found as clusters or singly located in the periphery of the follicular epithelium and lie within the follicle basal lamina Pale staining cells with 2-3 times larger than the follicular cells Make only 0.1% of the epithelium  Parafollicular cells (clear or C cells) Produce calcitonin (thyrocalcitonin) which – Lowers blood calcium levels by suppressing osteoclasts and promotes calcium deposition in bones Regulated directly by blood calcium levels  Histology of the Parathyroid Gland Divided into poorly defined lobules Has some adipocytes which make about 60% - 70% of the gland in oldage Has mainly Chief (principal) cells, but also Oxyphil cells & Transitional cells  Histology of the Parathyroid Gland Chief (principal) cells Small and polygonal pale acidophilic cells Secrete parathyroid hormone that functions to: – Increases bone resorption by ostoclasts – Increases phosphate excretion and calcium reabsorption by the kidneys – Increase absorption of calcium by the intestinal mucosa – Regulated by the serum calcium level through a simple feedback system Histology of the Parathyroid Gland Oxyphil cells Small number of larger polygonal cells Stain deeply eosinophilic because of presence of mitochondria with variable shape and size that almost fill the cytoplasm with no secretory vesicles Transitional cells With smaller nuclei that stain deeply than the other cell types Both are believed to be different phases in the life cycle of a single cell type  Histology of the Adrenal Gland Has a thick capsule that sends trabeculae into the gland, and divided into: Outer cortex – Constitutes nearly 90% of the gland by weight 1. Zona glomerulosa 2. Zona fasciculata 3. Zona reticularis Inner medulla  Zona glomerulosa Outer layer making 15% of the gland’s volume ( and 15% of the cortical volume) As closely packed round or arched clusters (glomeruli) of small acidophilic columnar or pyramidal cells with densely staining spherical nuclei Produce mineralocorticoides, mostly aldosterone in response to angiotensin II and to a lesser extent by ACTH  Zona fasciculata About 65% of the volume of the gland (and 80% of the cortical volume) As radial columns or fascicles of one or two larger weakly acidophilic polyhedral cells thick with a lightly staining spherical nucleus Show features of steroid-secreting cells Cells have many lipid droplets as vacuoles, hence also known as spongiocytes Produce glucocorticoides, mainly cortisol and corticosterone Regulated by the CRH–ACTH feedback system  Zona reticularis Make 7% of the volume of the gland (and 5 – 7% of the cortical volume) As anastomotic network (reticulum) of irregular cords of small sized cells Several cells located near the medulla are with pyknotic nuclei Produce androgens – With negligible importance in males, but in the females stimulate growth of axillary and pubic hairs during puberty and adolescence Regulated by the feedback control of the CRH–ACTH system  Adrenal medulla Contains chromaffin cells and small number of ganglion cells Chromaffin cells – Modified postganglionic sympathetic neurons without processes – Stain deep brown with chrome salts giving positive chromaffin reaction  Chromaffin cells (pheochromocytes) Two types of cells: 1. Noradrenaline-storing cells – 20% of adrenal chromaffin cells – Contain larger & more dense granules with peripheral electron-lucent layer  Chromaffin cells (pheochromocytes) Two types of cells: 2. Adrenaline storing cells – 80% of adrenal chromaffin cells – Contain smaller and less dense granules filling the vesicle – Have enzyme phenyl ethanolamine-N-methyltransferase (PNMT) that convert noradrenaline into adrenaline  Ganglion cells Fewer in number Most are sympathetic, but a small number of parasympathetic neurons are also found Innervate adrenal cortical cells and blood vessels  Blood supply of adrenal gland Adrenal arteries make subcapsular arterial plexus which gives rise to: 1. Arteries to the capsule 2. Arteries to the cortex which branch to form the cortical capillaries that drain into the medullary capillaries 3. Arteries of the medulla which traverse the cortex without branching until they reach the medulla to form the medullary capillaries  Blood supply of adrenal gland A central adrenomedullary vein takes the blood out of the gland – Along with its tributaries have longitudinally oriented bundles of smooth muscle cells in the tunica media When contracts cause reduction in the volume of the adrenal gland to enhances the efflux of hormones from the adrenal medulla into the circulation  Fetal adrenal gland Has the following regions: 1. Fetal cortex (provisional cortex or fetal zone) – Irregular cords of large eosinophilic cells located centrally – With characteristic features of steroid secreting cells Spherical mitochondria with tubular cristae, small lipid droplets, an extensive sER that accounts for the eosinophilia of the cytoplasm, and multiple Golgi apparatus Involutes after birth  Fetal adrenal gland Has the following regions: 2. Permanent cortex – As a narrow region superficial to the fetal cortex – Made by basophilic cells with closely packed nuclei arranged in arched groups similar to the adult zona glomerulosa – Have small mitochondria with shelf-like cristae, abundant ribosomes, and small Golgi apparatus  Fetal adrenal gland Has the following regions: 3. Chromaffin cells – Scattered among the cells of the fetal cortex – No adrenal medulla, but forms later  Fetal adrenal gland Interacts with placenta for certain key enzymes one lacks, but present in the other for the synthesis of steroid hormones Precursor molecules are transported back and forth between the two organs for the synthesis of: – Glucocorticoids, aldosterone, androgens, and estrogens Is under the control of the CRH–ACTH feedback system