Histology - EGU Endocrine System PDF

Histology - EGU Endocrine System Endocrine glands = ductless glands Definition: - The sites of synthesis & secretion of hormones in certain amounts which spread thr...

Histology - EGU Endocrine System Endocrine glands = ductless glands Definition: - The sites of synthesis & secretion of hormones in certain amounts which spread throughout the body by the bloodstream where they act on target organs. - The endocrine & nervous system are the two main coordinating and integrating systems of the body, the two systems are linked through the hypothalamus --> which controls the secretion of many endocrine glands - The secretory cells discharge their hormones in the interstitial spaces from which they are rapidly absorbed into the circulatory system via fenestrated capillaries to reach the target organs and cells Endocrine system Endocrine glands Group of endocrine Dispersed endocrine cells cells in certain organs 1. Pituitary gland APUD cells 1. Pancreas (Islets of Langerhans) 2. Thyroid gland 2. Testis (leydig interstitial cells) 3. Parathyroid gland 3. Ovary (ovarian follicles & corpus 4. Suprarenal gland luteum) 5. Pineal gland 4. Placenta Types of hormones Steroid hormones Proteins & peptides Derivatives of amino acid tyrosine 1. Adrenal cortex (cortisol, 1. Anterior and Posterior 1. Thyroid hormones (Thyroxine & androgen& aldosterone) pituitary hormones triiodothyronine) are iodinated 2. Ovary (estrogen & 2. Parathyroid hormones forms of tyrosine derivatives progesterone) 3. Hormones of the pancreas 2. Adrenal medullary hormones 3. Testes (testosterone) (catecholamine) derived from 4. Placenta (estrogen & tyrosine progesterone). 1  Histology - EGU I-Steroid hormones (cholesterol derivatives): General structure of steroid secreting cells: EM: 1. Well developed smooth endoplasmic reticulum. 2. Mitochondria with tubular cristae. 3. Lipid droplets. LM: Eosinophilic & vacuolated cytoplasm. II- Proteins, Peptide; monoamines: General structure of protein secreting cells: EM: 1. Well developed rough endoplasmic reticulum. 2. Well developed Golgi apparatus. 3. Mitochondria with lamellar cristae. 4. Secretory granules. LM: 1. Euchromatic nucleus with prominent nucleolus. 2. Basophilic cytoplasm. Steroid secreting cells Protein secreting cells 1- H&E Acidophilic vacuolated cytoplasm. Basophilic cytoplasm. 2- Mitochondria With tubular cristae With lamellar cristae 3-Prominent Well-developed smooth Well-developed rough endoplasmic organelles endoplasmic reticulum. reticulum, Golgi apparatus. 4- Secretory Absent. Present. granules 5- Lipid droplets Present. Absent. 6- Sites Suprarenal cortex, gonads & Pituitary gland, thyroid gland, placenta. suprarenal medulla, parathyroid glands, pancreas. 2  Histology - EGU General structure of Endocrine Glands: - They are composed of: 1. A group of secretory cells. 2. Fenestrated blood capillaries (sinusoidal capillaries). - Endocrine glands are composed of a group of secretory cells of epithelial origin supported by a highly vascular CT. Cords Follicle Pituitary Gland Pituitary Gland (Hypophysis Cerebri): Anatomically: It is situated inside the hypophyseal fossa (sella turcica) of the sphenoid bone, connected to the brain by a stalk called the infundibulum & covered by the diaphragma sellae. Histologically: It is divided into: a. Anterior lobe (adenohypophysis): dark & cellular. - Cells of adenohypophysis are best differentiated by immunohistochemical staining of their specific hormones b. Posterior lobe (neurohypophysis): Pale & fibrous. 3  Histology - EGU I- Anterior lobe (Adenohypophysis): It lies anterior to the hypophyseal cleft. It is subdivided into 3 parts: 1. Pars distalis. 2. Pars tuberalis. 3. Pars intermedia. 1. Pars distalis: It is composed of: A. Branching cords of polygonal cells. B. Surrounded by fenestrated sinusoidal capillaries. C. Supported by a network of reticular fibers. It consists of 2 types of cells: A. Chromophobes (52%): - Have weak affinity to stains. - They are cells smaller than the chromophils - Have a non-granular pale cytoplasm (few organelles). Function: They do not secrete hormones. They are reserve cells or degranulated chromophils. B. Chromophils (48%): - Have great affinity to stains. - They have granular darkly stained cytoplasm - They are classified according to their granules into two types: Acidophils: which have great affinity to acidic stains. Basophils: which have great affinity to basic stains. Chromophils Chromophobes 1- Percentage 48% 52% 2- size Larger Smaller 3- Cytoplasm Granular, dark Non granular, pale 4- Function Secretion of hormones A- Act as a reserve. B- Degranulated chromophils. 4  Histology - EGU a. Acidophils (37%): They secrete hormones of protein in nature. These cells are stained with periodic acid Schiff (PAS) reagent, which is a stain specific for glycoprotein molecules. They do not take the magenta red color of the stain They are periodic acid Schiff (PAS) negative. They are smaller than the basophils but contain larger secretory granules. EM: protein secreting cells. Acidophils are of two types: 1. Somatotrophs: secret growth hormone. 2. Mammotrophs: secret prolactin. Mammotrophs: (Lactotrophs) - The secretory granules in these cells are small, but in pregnant and lactating females they become large and numerous & are called pregnancy cells or Erdheim cells. - When suckling is terminated, lysosomes eliminate the excess secretory granules, a process known as crinophagy. b. Basophils (11%): They secrete hormones of glycoprotein in nature. They are PAS +ve. They are larger than the acidophils but contain smaller secretory granules. EM: protein secreting cells. Basophils are of three types: 1. Thyrotrophs: secrete thyroid stimulating hormone (TSH). 2. Gonadotrophs: They secrete two hormones: - Follicle stimulating hormone (FSH). - Luteinizing hormone (LH) 3. Corticotrophs: secrete adrenocorticotrophic hormone (ACTH). 5  Histology - EGU Acidophils Basophils 1- Percentage 37% 11% 2- Nature of hormones Protein Glycoprotein 3- PAS Negative Positive 4- size Smaller Larger 5- Granules Larger Smaller 6- Secretion Somatotrophs (growth h.) Thyrotrophs (TSH) Mammotrophs (prolactin) Gonadotrophs (FSH& LH) Corticotrophs (ACTH) 2. Pars Tuberalis: It is a superior extension that surrounds the infundibular stalk. It is highly vascular It's funnel (collar) shaped. It's formed of chromophobe: (basophils)-like cell Function: nonspecific. 3. Pars Intermedia: It lies between the pars distalis and pars nervosa. In humans, it is a rudimentary region. In lower animals, it is made up of colloid-filled follicles which represent remnants of Rathke's pouch. Function: nonspecific. 6  Histology - EGU It is a pale stained fibrous part, it lies posterior to the hypophyseal cleft The Infundibular stalk, which together with the surrounding pars tuberalis constitute the infundibulum Eosinophilic bodies branched plexus 7  Pituitary gland Pars tuberalis Infundibular stalk Pars nervosa Pars distalis Pars intermedia Which statement describes the acidophils? 1. They are larger than the basophils. 2. They are PAS +ve. 3. Their secretory granules are smaller than basophils. 4. They are more numerous than basophils. Thyroid gland Anatomically: It lies in the anterior aspect of the lower part of the neck. It consists of two lobes connected by an isthmus. Structure of thyroid gland : 1. Stroma: A double capsule: a. The outer: is the pretracheal fascia. b. The inner: is the true CT capsule of the gland. The CT capsule: send fibrous septa --> dividing the gland into incomplete lobes and lobules The stroma carries the blood vessels, nerves and lymphatics of the gland. Reticular fibers: form a network supporting the thyroid parenchyma reticular fibers: extend from the septa and forms a network supporting the thyroid parenchyma.