BMED 3107Integrated Body Systems IVEndocrine & Reproductive SystemsDepartment of Health & Biomedical Sciences

Developmental Anatomy of the Endocrine system&Microscopic Anatomy of the Endocrine system

Embryology: Endocrine systemThe endocrine system resides within specific endocrine organs and both organs and tissues with other specific functions. Epithelia (ectoderm and endoderm) form the majority of the ductless endocrine glands. Differentiation of several also organs involves a epithelial/mesenchye interaction, seen in repeated in many differentiation of many different tissues.

Development of the HypothalamusThe diencephalon develops from the prosencephalon within the walls of the primitive third ventricle.The diencephalon gives rise to the epithalamus, thalamus, and hypothalamus.The Hypothalamus develops from the alar plate and floor plate ventral to the hypothalamic sulcus.

Development of the HypophysisThe pituitary gland (hypophysis) is attached to the hypothalamus by the pituitary stalk.The anterior lobe (Adenohypophysis) develops from Rathkes pouch, which is an ectodermal diverticulum of the primitive oral cavity (stomodeum).The posterior lobe (Neurophypophysis) develops from the infundibulum, which is a neuroectodermal ventral evagination of the hypothalamus.

Development of Pharyngeal apparatusThe pharyngeal apparatus consists of the pharyngeal arches, pharyngeal pouches, pharyngeal grooves, and pharyngeal membranes.

The pharyngeal apparatus is first observed in week 4 of development and gives the embryo its distinctive appearance.The pharyngeal apparatus contribute to the formation of structures in the head and neck.

Thymus Development

Thymus epithelium derives from Endoderm - third pharyngeal pouch Week 6 - diverticulum elongates, hollow then solid, ventral cell proliferation Thymic primordia - surrounded by neural crest mesenchyme, epithelia/mesenchyme interaction (Current research has shown that the human thymic epithelium derives solely from the third pharyngeal pouch -as in the mouse).

Development of the Thyroid glandIn the midline of the floor of the pharynx, the endodermal lining of the foregut forms the thyroid diverticulum. Thyroid diverticulum migrates caudally.During this migration, thyroid remain connected to the tongue by the thyroglossal duct, which later is obliterated.

Development of Parathyroid glandsParathyroid glands are derived from Endoderm - third and fourth pharyngeal pouches, could also have ectoderm and neural crest.3rd Pharyngeal Pouch - inferior parathyroid, initially descends with thymus 4th Pharyngeal Pouch - superior parathyroid Week 6 - diverticulum elongate, hollow then solid, dorsal cell proliferation Fetal parathyroids - respond to calcium levels, fetal calcium levels higher than maternal

Development of the Pancreas

The dorsal pancreatic bud is a direct outgrowth of foregut endoderm, whose formation is induced by the notochord. The ventral pancreatic duct is a direct outgrowth of foregut endoderm.

Isolated clumps of endodermal cells bud from the tubules and accumulate within the mesoderm to form islet cells in the following sequence (first last) alpha cells beta cells delta cells F (PP) cells. Because of the 90o clockwise rotation of duodenum, ventral bud rotates dorsally and fuses with the dorsal bud.

Development of the Suprarenal glandsInside the Adrenal (suprarenal) gland is an embryonic cortex formed by embryonic mesodermal cells which completely surrounds an innermost adrenal medulla derived embryologically from neural crest cells.(Neural crest cells differentiate into chromaffin cells)

During the fetal period and at birth, the suprarenal glands are very large due to the size of the fetal cortex.The zona glomerulosa and zona fasciculata of the adult cortex are present at birth, but the zona reticularis is not formed until age 3 years.

Histology: Endocrine systemHypophysis

Thyroid gland

Pineal gland

Parathyroid glands

Pancreas

Adrenal glands

HypophysisBecause of its dual origin (ectoderm/developing brain), the pituitary gland actually consists of two glands the posterior neurohypophysis and the anterior adenohypophysis united anatomically but with different functions.

The Neurohypophysis consists of a large part, the pars nervosa (PN) and the smaller infundibulum (IS-infundibular stalk) The Adenohypophysis has three parts: a large pars distalis (anterior lobe)(PD), the pars tuberalis (PT), which wraps around the infundibulum, and the thin pars intermedia (PI).

Adenohypophysis (Anterior lobe)The anterior lobe of the pituitary glands is derived from the hypophyseal pouch of the embryonic pharynx. The three parts of adenohypophysis are: pars distalis, pars tuberalis, and pars intermedia.Pars Distalis75% of the glandFibroblasts are present and produce reticular fibers supporting the cords of hormone-secreting cells.Common stains suggest two broad groups of cells based on staining affinity: chromofils (secretory cells) and chromophobes (C). Chromofils are also known as basophils (B) and acidophils (A) according to their affinity for basic or acidic dyes.Acidophilics include the somatotropic and mammotropic cells, while the basophilic cells are the gonadotropic, corticotropic, and thyrotropic cells.S-sinusoids

Pars Tuberalis Funnel-shaped region surrounding the infundibulum of neurohypophysis. Most of the cells are basophilic gonadotropic cells.

Pars Intermedia (PI)Thin zone of basophilic cells between the pars distalis (PD) and the pars nervosa (PN) of neurohypophysis. Pars intermedia develops from dorsal walls of hypophyseal pouch and usually contain colloid-filled cists (C)

Neurohypophysis (Posterior lobe)Neurohypophysis consists of the pars nervosa and the infundibular stalk.The pars nervosa does not contain secretory cells. It is composed of neural tissue, containing some 100,000 unmyelinated axons of secretory neurons situated in the supraoptic and paraventricular nuclei of the hypothalamus. Also present are highly branched glial cells (pituicytes) (P).

Hormones are transported axonally into the pars nervosa and accumulate in axonal dilations called neurosecretory bodies (Herring bodies) (NB)

Adrenal gland Located on the superior poles of each kidney Half-moon shape 4-6 cm long, 1-2 cm wide, 4-6 mm thick Covered by a dense CT capsule that send thin septa to the interior of the gland as a trabeculae. The stroma consists mainly of a rich network of reticular fibers that support the secretory cells.

The gland consists of two concentric layers: a yellowish peripheral layer, the adrenal cortex, and a reddish-brown central layer, the adrenal medulla.

Adrenal cortexCells have characteristics features of steroid-secreting cells. (central nuclei, acidophilic cytoplasm, lipid droplets, profuse SER)Zona Glomerulosa(15%)

Zona Fasciculata65-80%)

Zona Reticularis(10%)

Fetal Adrenal cortexAt birth in humans the adrenal gland is larger than of the adult and produced up to 200 mg of corticosteroids per day, twice that of an adult.At this age, a layer known as the fetal or provisional cortex, comprising 80% of the total gland, is present between the thin permanent cortex and an under-developed medulla.

Adrenal medullaAdrenal medulla is composed of large, pale-staining polyhedral cells arranged in cords or clumps and supported by a reticular fiber network.The hormone-secreting cells of adrenal medulla are chromaffin cells, which resemble sympathetic neurons lacking axons and dendrites.

PancreasThe pancreatic islets (Islets of Langerhans) are compact spherical masses of endocrine tissue embedded within the acinar exocrine tissue

Make up 1-2 % of the organs volume.

Each islet consists of polygonal or rounded cells, smaller, and more lightly stained than the surrounding acinar cells.A low-magnification micrograph reveals many islets stained lighter than the surrounding tissue. The white spots are adipocytes.

The major hormone-producing islet cells are most easily identified and studied by immunohistochemistry: Alpha cells usually located near the periphery of the islets (glucagon) Beta cells located centrally in islets (insulin) Delta cells scattered and much less abundant. (somatostatin) F (PP) cells more commonly located within the head of the pancreas (pancreatic polypeptide)C- capillaries

Thyroid glandThe parenchyma of the thyroid is composed of millions of rounded epithelial structures known as thyroid follicles. Each follicle consists of a simple epithelium and a central lumen filled with a gelatinous substance called colloid. The gland is covered by a fibrous capsule from which septa extend into the parenchyma, dividing it into lobules.C- capsule, S- septa, L- lumen

Follicular cells (F) range in shape from squamous to low columnar and the follicles are quite variable in diameter.Another endocrine cell type, the Parafollicular, or C, cells (C) derived from neural crest cells migrating into the area of embryonic foregut. C cells may be part of the follicular epithelium or present singly or in groups outside of follicles.The Lumen is surrounded by a simple epithelium in which the cell height ranges from squamous to low columnar.

Parathyroid glandsFour small oval masses each 3 x 6 mm with a total weight of about 0.4 g located on the back of the thyroid gland. Each gland is contained within a capsule of CT. (S- septa)Two types of cells are present in the Parathyroid glands:Chief (Principal) cells (P)Small polygonal cells with round nuclei and pale-staining acidophilic cytoplasm.Oxyphil cells (O)More common in the elderly. Acidophilic cytoplasm. May occur singly or in clumps

Pineal glandAlso known as Pineal body or Epiphysis.Small pine, cone-shaped organ5-8 mm in length and 3-5 mm width.150 mgDevelops with the brain from neuroectoderm in the roof of the diencephalon and is found in the posterior of the third ventricle, attached to the brain by a short stalk.

The secretory cells, pynealocytes (P), which have slightly basophilic cytoplasm and large, irregular euchromatic nuclei.Interstitial cells (A) resemble astrocytes.

A characteristic feature is the presence of an extracellular mineral deposit called a corpus arenaceum (CA)V- blood vessels , = capillaries

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