Professor Eltuhami M Abdel-Magied 2017

The Endocrine System  This system consists of cells that produce hormones known as endocrine cells  Endocrine cells are epithelial cells that develop from all three germ layers (ectoderm, mesoderm and endoderm)  They are present in various parts of the body as: a. Solitary cells e.g. gut endocrine cells b. Small groups of cells e.g. pancreatic islets of Langerhans c. Independent glands e.g. the pituitary and thyroid 2017

The Endocrine Cells  Endocrine cells are furnished with the cytoplasmic organelles that are necessary for the synthesis and release of hormones  Protein / peptide hormone releasing endocrine cells are furnished with cisternae of rER  Steroid hormone releasing cells are furnished with tubules of sER  Both types have Golgi complexes (for hormone packaging) and vesicle (for storage or transport of the produced hormone) 2017

RER peptide hormone synthesis SER steroid hormone synthesis Golgi for Packaging Vesicles for storage or transport 2017

Endocrine Glands  Endocrine glands are ductless glands  They develop from a surface epithelium but loose connection with surface  They pass their secretions (hormones) directly into body fluids 2017

The Pituitary Gland  This is also known as hypophysis cerebri  It is located in the base of the cranium  Structurally and developmentally, the pituitary is the most complicated of endocrine glands  It produces numerous hormones  It has an anterior lobe and a posterior lobe 2017

Development The pituitary gland has two parts with different embryologic origins: o Adenohypophysis which develops from Rathke's pouch that develops from the roof of the primitive mouth o Neurohypophysis which develops from the infundibulum of the floor of the diencephalon. It remains connected to the brain throughout life April 2017

The Adenohypophysis  Adenohypophysis has three parts: A. Pars distalis B. Pars tuberalis C. Pars intermedia  Adenohypophysis has histological features characteristics of epithelial tissues  Depending on their affinity to dyes (stains), cells of the adenohypophysis are classified into chromophils (have affinity) and chromophobes (have no affinity to dyes)  Chromophils are further subdivided according to their staining reactions 2017

Parts of the Adenohypophysis Adenohypophysis consists of three parts: 1. Pars distalis is the largest part. It develops from the anterior wall of Rathke’s pouch. It constitutes the bulk of adenohypophysis and anterior lobe of the pituitary 2. Pars intermedia is remnant of posterior wall of Rathke’s pouch that is annexed to the pars nervosa (posterior lobe) 3. Pars tuberalis surrounds the infundibulum of neurohypophysis 2017

Cells of the Pars Distalis  Pars distalis consists of epithelial cells arranged in cords or clumps with blood capillaries in-between  Depending on affinity to stains, these cells are classified into chromophobes and chromophils  Chromophobes have no affinity to dyes. They appear pale and are considered reserve or exhausted cells  Chromophils have affinity to dyes. Those that stain with acidic dyes are called acidophils whereas those that stain with basic dyes are called basophils  Chromophils are further subdivided using special histochemical and immunohistological staining methods 2017

Chromophils  Currently, the different types of chromophils are designated by the type of hormones they produce  Somatotrophs produce GH and mammotrophs produce prolactin. They are both acidophils  Gonadotrophs, thyrotrophs and corticotrophs are basophils. Gonadotrophs produce FSH and LH, thyrotrophs produce TSH, corticotrophs produce ACTH  These five cell types can only be differentiated by immunohistological staining methpds  Electron microscopically, they are all characterized by cytoplasmic electron dense vesicle (of various size and density) 2017

Pars distalis is made of groups of epithelial cells and blood capillaries 2017 Capillary Capillary Capillary Endocrine cells

Cells of the pars distalis are either chromophobes or chromophils Chromophils have strong affinity to stainsChromophils have strong affinity to stains Chromophobes have week affinity to stains; they appear pale. They could be reserve cells or exhausted cellsChromophobes have week affinity to stains; they appear pale. They could be reserve cells or exhausted cells Chromophil Chromophobe April 2017

Chromophils are subdivided into acidophils and basophils A = acidophil B = basophil C = chromphobe 2017

Identification of the specific hormone producing cells of the adenohypophysis is possible only by immunohistochemical methods. Growth hormone producing cells are seen below 2017

Nuclei of hormone secreting cells of the pars distalis show abundance of euchromatin The cytoplasm contains electron dense granules of variable size, Golgi and mitochondria. Below is an electron micrograph of a somatotroph. somatotrophs produce growth hormone Nucleus

Chromophobes (Nonfunctional) Basophils Larger than Alfa Chromophils Adenohypophyseal Cells Aldehyde fuchsin -ve Orangophils (Somatotrophs Carminophils (Mammotrophs) Ratios of these cells vary according to Physiological status Aldehyde fuchsin +ve (Thyrotrophs) Acidophils (Alfa cells) GonadotrophsCorticotrophs 2017

Chromophils, the Hormones they Produce and their EM features Granules ( EM ) HormoneNameType nm oval or rod-shape GH (STH) SomatotrophsAcidophils 200 nm (600nm in pregnancy ProlactinMammotrophs nm round FSH, LH GonadotrophsBasophils Small nm TSHThyrotrophs Large nm ACTH, LPH Corticotrophs 18 LPH = Lipotropic hormone April 2017

Trophic Hormones of the Pars Distalis  Pituitary hormones control the activity of some other glands and tissues. They have trophic effects on those glands and tissues  Pars Distalis produces TSH, ACTH, FSH, LH (ICSH), Prolactin and GH.  Prolactin and GH are produced by acidophils whereas the rest are produced by basophils Controlled by Acidophils Controlled by Basophils 2017

Pars Intermedia  Pars intermedia lies between Pars nervosa and Pars distalis  It is separated from Pars distalis by remnants of Rathke’s pouch (RP).  Its epithelial cells may be surround colloid filled cysts.  Pars intermedia also contains basophils and chromophobes.  Its basophils may produce ACTH, LPH, MSH (melanocyte stimulating hormone) and endorphins 2017 Pars Nervosa Pars Distalis Pars Intermedia

Pars tuberalis  Pars tuberalis contains endocrine epithelial cells arranged in short cords or clusters separated by capillaries and veins  Some of the cells are gonadotrophs  The high vascularity of the pars tuberalis is related to the hypophyseal portal system (primary capillaries, veins and secondary capillaries)  Pars tuberalis may contain follicles lined by cuboidal cells 2017

Pars Tuberalis surrounding the infundibular stalk and contains hypophyseal portal vessels April

Pars Tuberalis and Hypophyseal Portal System  Releasing hormones are synthesized in nerve cell bodies within the hypothalamus and are carried along their axons to endings in the median eminence  Then they are carried to capillaries (primary) which unite to form portal veins that break up into another set of capillaries (secondary) in the pars distalis  Releasing hormones stimulate chromophils 2017

Neurohypophysis  The neurohypophysis consists of the pars nervosa and infundibulum (connected to hypothalamus)  It contains unmyelinated nerve fibers, nerve endings, pituicytes (glial cells) and capillaries  The nerve fibers and endings belong to neurosecretory neurons whose cell bodies are located in the hypothalamus (PV or SO nuclei)  ADH and Oxytocin are synthesized in the cell bodies of these neurons, then transmitted via their axons to nerve ending in pars nervosa where they are secreted into capillaries.  Nerve endings filled with secretions are visible with LM; these are known as Herring bodies 2017

Neurohypophysis  Neurohypophysis consists of unmyelinated nerve fibers, nerve endings (Herring bodies), glial cells (pituicytes) and capillaries  Two hormones (ADH and Oxytocin) are secreted by neurohypophysis  Both hormones are synthesized in nerve cell bodies present in the hypothalamus  They are then carried by axons of these neurons along the hypothalamo-hypophyseal tract to nerve endings in pars nervosa  From there they are released into blood capillaries 2017

Arrow = Herring body 2017 Neurohypophysis Consists of unmyelinated axons, nerve endings (Herring bodies), glial cells (pituicytes) and capillaries

Hypothalamo- hypophyseal (pituitary) relations [neurosecretory neurons and hypophyseal portal system] Hypophyseal Portal System April 2017

Target Organs and Tissues for Pituitary Hormones 2017

The Pineal Gland  Also Known as the Epiphysis cerebri  It is a small body located on the roof the third ventricle of the brain. It is about 7mm in diameter. It develops from the roof of the diencephalon and remains connected to it by the pineal stalk (contains nerve fibers from the hypothalamus and adjacent regions of the brain).  The pineal gland is surrounded by a connective tissue capsule continuous with the meninges (pia mater)  It contains two types of cells; pinealocytes and interstitial cells  The gland controls onset of puberty and may adjust changes in day length (biological clock & Jet lag) 24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م29

Pinealocytes, Interstitial Cells and Brain Sand  Pineolcytes (chief cells) are the functional parenchymal (epitheloid) cells of the gland. They secrete melatonin and serotonin. Adjacent cells have intercellular junctions including gap junctions, which facilitate interactions between cells.  Interstitial cells are supportive neuroglial cells (astrocytes).  The pineal gland contains calcified concretions known as corpora arenacea (brain sand, acervuli) containing calcium and phosphorus. For this reason the pineal body forms a medial intracranial landmark visible in X- rays, CT scans and MRI. These concretions become more prominent with age. 24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م24/10/ :33 م30

Pineal Gland April