Lecture 15 (H) PDF

Unified Lecture 15 THE ENDOCRINE GLANDS HIHD-211 TERM-3 Basic Science Department COSHP, KSAU-HS, KSA LEARNING OUTCOMES By the end of this session, you should be able to: 1. 2. 3. 4. 5. Recognize the different endocrine glands Differentiate between endocrine and apocrine glands Recognize the main cel...

Unified Lecture 15 THE ENDOCRINE GLANDS HIHD-211 TERM-3 Basic Science Department COSHP, KSAU-HS, KSA LEARNING OUTCOMES By the end of this session, you should be able to: 1. 2. 3. 4. 5. Recognize the different endocrine glands Differentiate between endocrine and apocrine glands Recognize the main cellular components in endocrine glands Recognize the structure of thyroid, parathyroid, pancreas, pituitary gland, and adrenal gland Correlate the morphological features with the tissue function Classification of Body Glands Body Glands Body Glands Exocrine glands retain “ducts” and secrete their products into it LO-2 Endocrine glands “ductless glands” product is released across cell membrane into interstitial spaces & enters capillaries ENDOCRINE GLANDS LO-1 ▪ The endocrine glands are responsible for the synthesis and secretion of chemical messengers known as hormones ▪ Hormones may ▪ Disseminate throughout the body by the bloodstream to act on specific target organs or affect a wide range tissues ▪ Act locally by specialized microcirculation Endocrine Glands The endocrine glands are composed of: ▪ islands of secretory epithelial cells the parenchyma ▪ supporting connective tissue, rich in blood & lymphatic capillaries, the stroma ▪ The parenchymal cells discharge the hormones into the interstitial space from which it is rapidly absorbed into the circulation ▪ Cells of the endocrine system have prominent nuclei, abundant mitochondria, endoplasmic reticulum, Golgi bodies and secretory vesicles. This reflects active hormone synthesis LO-1 Parts Of Endocrine System 1. Major endocrine organ: Whole organ act as an endocrine gland. Major function of the organ is synthesis, storage & secretion of hormones e.g. thyroid and pituitary gland 2. Endocrine component within other solid organ: Clusters of endocrine cells are embedded within other tissues e.g. pancreas, ovaries, testes, kidneys 3. Diffuse endocrine system: Scattered clumps of hormone secretory cells within an extensive epithelium e.g. GIT, Respiratory system producing paracrine effects (on adjacent non endocrine cells) LO-1 PITUITARY GLAND Pituitary is a small bean shaped gland located at the base of the brain in a bony cavity “Sella Turcica” (at base of skull) Pituitary gland is controlled by hypothalamus It consists of two main parts (anterior pituitary and posterior pituitary) which have different embryological origins LO-1 Dr. Ismail Memon Parts of the pituitary gland Anterior pituitary Adenohypophysis/Pars Distalis which develops from oral mucosa the Rathke's pouch Hormones of Anterior Pituitary (AP) 1. Growth hormone (GH) 2. Prolactin 3. Thyroid stimulating hormone (TSH) 4. Adrenocorticotrophic hormone (ACTH) 5. Follicular stimulating hormone (FSH) 6. Luteinizing hormone (LH) LO-5 Parts of the pituitary gland  Posterior pituitary Neurohypophysis/Pars Nervosa. It is a down growth of nervous tissue from the hypothalamus to which it remains joined by the pituitary stalk Hormone of Posterior Pituitary (PP) Antidiuretic hormone (ADH) Oxytocin LO-3 Pituitary Gland- Histology Anterior Pituitary has two major cell types based upon their appearance with H&E staining: 1. Chromophobes (Cp- 50%): The cells with weakly or pale staining cells, not associated with specific hormone secretion 2. Chromophils (50%): Cells with strongly staining cytoplasm. These have further two cell types i.e. Acidophils and basophils LO-3 Pituitary Gland- Histology Acidophils (35%) stain bright pink. Secrete ▪ GH by somatotrophs ▪ Prolactin by mammotrophs Basophils (15%) stain purple. Secrete ▪ TSH by thyrotrophs, ▪ ACTH by corticotrophs ▪ FSH and LH by gonadotrophs LO-3 Dr. Ismail Memon LO-5 Pituitary Gland- Histology ▪ ▪ ▪ Posterior Pituitary (PP): Composed of non myelinated axons with distended terminations to store hormones. These distensions are called Herring bodies (H) The cell bodies of these neurons are located in hypothalamus where they synthesize hormones of posterior pituitary and transport down via pituitary stalk to posterior pituitary. The purple colored structures are the nuclei of the supporting cells the pituicytes. LO-4 THYROID GLAND It is a butterfly shaped gland in the neck, in front of the trachea The functional unit is thyroid gland is the thyroid follicle It is a unique gland as it stores inactive hormone in large quantities (collide) in extra-cellular space, in centre of the follicle It has two types of cells, the follicular cells and parafollicular cells The follicular cells produce Iodine containing, triiodothyronine/T3 and tetraiodothyronine /T4 (thyroxine) which are stored in form of thyroglobulin The parafollicular cells secrete the Calcitonin LO-3 THYROID GLAND- Histology ▪ ▪ ▪ Gland is enveloped by fibrous capsule and contain the thyroid follicles Follicles are spherical structure composed of a single layer of cuboidal epithelium resting on a basement membrane and contain colloid (thyroglobulin inactive form of hormone secreted by follicular cells) in their centers When inactive, the follicular cells are simple cuboidal, but when actively synthesizing hormone they become columnar LO-4 THYROID GLAND- Histology When required, follicular cells remove some of the stored colloid and detach T3 and T4, which then pass through the cell into an adjacent capillary. LO-5 THYROID GLAND- Histology ▪ ▪ ▪ ▪ Second type of endocrine cells in the thyroid are the Parafollicular C cell C cells are scattered in the follicle lining, or as small clumps in between follicles Less prominent and are usually identified by special stains Secrete Calcitonin LO-3 Dr. Ismail Memon PARATHYROID GLANDS Two pairs of small oval glands are situated on the posterior borders of the thyroid gland It secretes Parathormone (PTH) which regulates blood calcium levels Histology: ▪ Covered by thin fibrous capsule ▪ Glandular cells are intermixed with adipose tissue ▪ Glandular cells are of two types: ▪ Chief or Principal Cells (P): small cells with central nuclei and pale pink cytoplasm ▪ Synthesize and secrete PTH ▪ Oxyphil cells (O): eosinophilic cytoplasm, do not secrete PTH and increase in number with age LO-3 ADRENAL GLANDS (SUPRARENAL GLANDS) Small endocrine glands on the upper pole of each kidney ▪ Contain two types of endocrine tissue with different embryological origins & functions Two components of the adrenal gland are: ▪ Adrenal Cortex; an outer part that secretes steroid hormones, the: ▪ 1. Mineralocorticoids 2. Glucocorticoid 3. Sex hormones ▪ Adrenal Medulla; an inner core that secretes catecholamines i.e. adrenaline & noradrenaline LO-5 ADRENAL GLANDS - Histology Low magnification: Adrenal gland has Fibrous Capsule F Outer Cortex C Inner Medulla M LO-4 F ADRENAL GLANDS - Histology Adrenal cortex: Three histological zones Zona Glomerulosa; is an outermost layer of cortex underneath the capsule where cells are arranged in round clusters. It produces mineralocorticoids ▪ ▪ ▪ Zona Fasciculata; is intermediate layer where cells are arranged in parallel columns (fascicles). It produces glucocorticoids Zona Reticularis; is innermost layer adjacent to the medulla where cells are arranged in irregular cords. It produces sex steroids LO-3 ADRENAL GLANDS - Histology Adrenal Medulla is composed of clusters of cells (granular, lightly basophilic cytoplasm), with numerous capillaries. ▪ ▪ ▪ Catecholamine granules stain brown with chrome salts, so are called “Chromaffin cells”(Cc) Gc-ganglion cell LO-3 PANCREAS ▪ Major exocrine gland with important endocrine cells and functions ▪ The endocrine part of the pancreas consists of isolated clusters of cells i.e. “Islets of Langerhans”, scattered throughout the exocrine glandular tissue IL-islets of Langerha ns IL LO-4 ENDOCRINE PANCREAS Islets of Langerhans are groups of secretory cells with numerous capillaries, surrounded by a thin capsule ▪ Endocrine cells are small with pale cytoplasm ▪ The cell types and hormones of islets of Langerhans are: ▪ Alpha cells: (15-20% of islet cells) glucagon ▪ Beta cells: (65-80%) insulin ▪ Delta cells: (3-10%) somatostatin ▪ PP cells: (3-5%)pancreatic polypeptide ▪ Exocrine part is made up of pancreatic acini which stain strongly ▪ Epsilon cells: motilin, serotonin, substance P (