Veterinary Anatomy (DVT 10502) PDF

Veterinary Anatomy (DVT 10502) Danmaigoro Abubakar PhD Haemopoietic, Endocrine & Lymphatic System Senior Lecturer Department of Pre-clinical Science Faculty of Veterinary Medicine  2 Haemopoieti...

Veterinary Anatomy (DVT 10502) Danmaigoro Abubakar PhD Haemopoietic, Endocrine & Lymphatic System Senior Lecturer Department of Pre-clinical Science Faculty of Veterinary Medicine  2 Haemopoietic, Endocrine & Lymphatic System Overview Histology Endocrine system Pituitary Thyroid Parathyroid Adrenal Pineal gland Heamopoietic Lymphatic System  Endocrine System A gland of endocrine regulates metabolic activities of certain organs and tissues of the body by an organized collection of secretory epithelial cells. Exocrine glands deliver their secretions onto the surface of epithelia via ducts Endocrine glands consist of ductless glands, with distinct clusters of cells secrete hormones directly into the bloodstream thus, by a rich network of blood vessels. Endocrine glands include; Pituitary gland, Thyroid gland, Parathyroid gland, Pineal gland and suprarenal gland. Secretions can be: paracrine: hormones act on nearby tissues and cells; or neuroendocrine: hormones travel long distances through the blood to act on a specific ‘ target ’ organ, analogous to the co-ordinating activity of neurons. Endocrine glands can be: a component of a gland with both endocrine and exocrine functions (e.g., kidney, pancreas, and gonads); a discrete endocrine gland , that only has endocrine function, such as the pituitary (hypophysis), thyroid, parathyroid, adrenal, and pineal glands; A diffuse neuroendocrine system (e.g., cells in the gut, which secrete low molecular - weight peptides such as cholecystokinin and secretin). 3  The pituitary (or ‘hypophysis’) is found at the base of the brain, with two functional regions, the anterior and posterior lobes Pituitary The histological structure of the anterior and gland posterior lobes differs, and this reflects their different embryological origins. The anterior region (Adenohypophysis) originates from oral ectoderm, a primitive oral cavity called Rathke’s pouch, the remnants of which can still be seen in sections. 4  This region is the glandular epithelial part of the anterior pituitary, and it includes the pars distalis, pars intermedia, and pars tuberalis. The pars intermedia is found in a narrow region in the posterior part of the anterior pituitary and it also has its embryological origin in Rathke’ s pouch. Anterior pituitary gland (Adenohypophysis, Posterior pituitary gland Pars Distalis) (Neurohypophysis, Pars Stains “red” Nervosa) Pale staining Pituitary Gland  Adenohypophysis The anterior pituitary gland the adenohypophysis, develops from Rathke’s pouch, diverticulum of the oral ectoderm. Consist of Pars distalis Pars intermedia Pars tuberalis 7 The parenchyma cells of the pars distalis has affinity for dye are called chromophils (somototrophs and mammotrophs); while cells without affinity to dyes are called chromophobes. Chromophils: further divided into Acidophils (stains with acidic dye) and Basophils (stains with basic dyes). However, most abundant cells at the pars distalis are acidophils with large granules eg. Somatotrophs which have centrally placed nucleus, a moderate Golgi complex, and small rod- shaped mitochondria, with abundant RER and secretory granules which secretes somatotropin (growth hormone). Mammotrophs are arranged as individual cells rather than as clumps or clusters with golgi complex and large organells, they secrete protactin  Adenohypophysis – high power The adenohypophysis contains 3 cell types: -acidophils (stain red) -basophils (stain blue) -chromophobes (pale stain) Chromophobes are undifferentiated cells The adenohyphysis stains red-blue on low power because of the acidophils and basophils Hypophysis cerebri (cat) Pasrs distalis 92) Pars Intermdeia (3) Pars Nervosa (4) Pars Tuberalis (5) lumen of Rathke’s pouch 10 Neurohypophysis – high power The neurohypophysis resembles neural tissue, with glial cells, nerve fibers, nerve endings, and intra-axonal neurosecretory granules Precursors of ADH (vasopressin) and oxytocin are synthesized in the hypothalamus and transported to the pars nervosa where processing is completed  Pars intermedia (cat). The parenchymal cells are arranged in (1) column or in (2) follicles. (3) Blood vessels. PAS/orange G/haematoxylin. X 250˘˘ 12  The anterior pituitary gland: This region contains cords of epithelial cells, surrounded by a small amount of supporting connective tissue, and fenestrated capillaries. These cells secrete hormone in response to signals from the hypothalamus. There are three types of endocrine cell: Acidophils, which stain strongly with acidic dyes; Basophils, which stain strongly with basic dyes, and stain strongly with periodic acid – Schiff due to their high glycoprotein content; Chromophobes (weakly staining), which arresting (degranulated) chromophils. Acidophils and basophils secrete five different types of hormone, which are secreted into the surrounding fenestrated capillaries. Acidophils are made up of two main types of cell, which each secrete one type of peptide hormone, as follows. Somatotrophs (40 – 50% of cells) secrete the growth hormone (somatotropin), the main target of which is the chondrocytes in epithelial growth plates. Mammotrophs ( ∼ 15%) secrete prolactin that stimulates milk -producing tissue in the breast. 13  Basophils cells stain blulish and are made up of three main types of cell, which secrete glycoprotein hormones, as follows. Corticotrophs (∼20%) secret adrenocorticotropic hormone (ACTH), which targets the adrenal gland. Thyrotrophs (∼5%) secrete thyroid - stimulating hormone (TSH), which targets the thyroid gland. Gonadotrophs (∼10%) secrete gonadotropins. These include follicle - stimulating hormone (FSH), which targets the follicular cells of the ovaries (in women) or Sertoli cells of the testis (in men) and luteinizing hormone (LH), which promotes ovulation in women, or stimulates androgen release from the Leydig cells of testes in men. 14 Pituitary gland (Pars distalis ) 1 Eosinophlic alpha cell 2. Basophic Beta cell 3. Chromophobe Sinusoid 15  Chromophobes They have little cytoplasm with weakly stained cells in the pars distalis Folliculostellate cells Abundant cells found with the pars distalis Pars intermedia It lies between the pars distalis and pars nervosa and contains cysts that are remnants of Rathke’s pouch Characterized by many cuboidal cells-lined colloid – containing cysts (Rathke’s cysts). Pars tuberalis It surrounds the hypophyseal stalk and absent on the posterior aspect of the thin layers of the pia arachnoid-like connective tissue separating then the pars tuberalis from the infundibular stalk 16 17  Neurohypophysis The posterior region (Neurohypophysis) originates from nervous tissue in the brain – a downgrowth of the diencephalon. It has the following region: Median eminence, Infundibulum and Pars nervosa Hypothalamohypophyseal tract: Axons of neurosecretory cells of the supraoptic and paraventricular nuclei extend into the posterior pituitary as the hypothalamohypophyseal tract Pars nervosa Pars nervosa of the posterior pituitary gland receives terminals of the neurosecretory hypothalmohypophyseal tract. 18 Neurohypophysis – high power Hering bodies are large dilated axon terminal endings that are filled with accumulated neurosecretory granules 20  Avian pituitary gland The avian pituitary gland is similar to that of other mammals excepts for the absence of the pars intermedia 21  Thyroid gland The thyroid gland is located in the cervical region, ventral and lateral to the trachea at the neck, and contains two lobes. It contains many thyroid follicular lining cells, which produce thyroid hormones. Colloid is an inactive precursor of thyroid hormone bound to a glycoprotein (thyroglobulin). Follicles are cavities surrounded by epithelial cells (spherical follicular cells), which are surrounded by a dense capillary network. The size of the follicles varies with activity. 22  Epithelium of the follicles consist of follicular lining cells which vary from squamous to columnar in shape. Active follicular cells are columnar. The lining cells are acidophilic with numerous cytoplasmic secretory vesicles, a basal nucleus and microvilli on the apical surface.  The acidophilic gel-like material called colloid is located in the center of the follicle. The two hormones secreted ( thyroxine or T4 and the more active tri - iodothyronine or T3) The pituitary hormone, thyroid - stimulating hormone (TSH), regulates their release by indirect action. The lining epithelium also contains parafollicular (clear) cells.  These cells secrete calcitonin, which regulates blood calcium levels. Parafollicular cells are scattered among the follicular cells, and while they can be recognized from their pale cytoplasm, they are difficult to identify with light microscopy. 26 Thyroid Gland Thyroid Follicles are filled with pink material which is colloid The follicles normally vary in size Thyroid follicle – high power Normal thyroid follicles are lined by a low cuboidal follicular epithelium Thyroid gland – high power Parafollicular cells (C- cells) lie between follicles and secrete Calcitonin  Parathyroid glands These consist of a pair of ovoid glands associated with the thyroid. Each gland is divided into lobules by connective tissue septa The parathyroid contains two types of cells. Chief (or principal) cells are small and pale, weakly eosinophilic staining, and contain cytoplasmic granules. They secrete parathyroid hormone (PTH). About 80% of the cells are inactive and have paler cytoplasm than active cells. PTH acts on the epithelial cells in the kidney (renal tubule) and osteoclasts in bone to raise Ca2+ levels in the blood (calcitonin) Oxyphil cells contain abundant mitochondria, do not secrete PTH, but may differentiate into chief cells. 30 31 Parathyroid Gland – low power Low power of parathyroid, showing random cords of cells. The parathyroid is somewhat lobulated in appearance and considerable adipose tissue is intermingled with secretory portions. Adipose tissue Cords of cells Parathyroid Gland – high power Chief cells Oxyphil cells 2 cells types of the Parathyroid: Chief cells secrete parathormone (PTH). They have large round nuclei with a small amount of clear cytoplasm. Oxyphil cells have smaller, darker nuclei and relatively larger amount of cytoplasm. The significance of the oxyphil cells is not clear.  Suprarenal glands Adrenal glands These are a pair of glands, one associated with each kidney. Each gland contains two main regions, an outer cortex and an inner medulla, which contain different types of endocrine tissue. The embryological origin of the cortex is similar to that of the gonads. The embryological origin of the medulla is similar to that of the sympathetic nervous system. 34 Adrenal Gland – Low power capsule cortex medulla Adrenal Cortex –low power Mineralocorticoids - Zona glomerulosa aldosterone Glucocorticoids – Zona fasciculata Cortisol, corticosterone Androgens– dehydroepiandrosteron Zona reticularis e 37 38  The cortex contains three regions which secrete different hormones, all of which are based on cholesterol (steroid hormones). Zona glomerulosa: The zona glomerulosa (ZG) is the outermost zone of the adrenal cortex. It secretes mineralocorticoids , which are important for fluid homeostasis (e.g., aldosterone, which regulates absorption/uptake of K + and Na + levels in the kidney). The secretory cells are arranged in irregular ovoid clusters (glomeruli) surrounded by trabeculae, which contain capillaries. The nuclei of the cells stain strongly, and the cytoplasm of these cells is darker than those in the next zone, the zona fasciculata, as there are fewer lipid droplets in these cells. 39  Zona fasciculata: The zona fasciculata (ZF) is the middle zone of the adrenal cortex. It secretes glucocorticoids, which are important for carbohydrate, protein, and lipid metabolism (e.g., cortisol, which raises blood glucose and cellular synthesis of glycogen).  The pituitary hormone adrenocorticotropic hormone (ACTH) regulates cortisol secretion. The secretory cells are arranged in cords, often one cell thick, surrounded by fi ne strands of supporting tissue. The nuclei stain strongly, the cytoplasm looks pale and foamy ’ due to the lipid droplets, and it is rich in smooth endoplasmic reticulum (ER) and mitochondria. Zona reticularis: The zona reticularis (ZR) is the innermost layer of the cortex. It secretes sex hormones (androgens) and small amounts of glucocorticoids.  Adrenal medulla This region contains strongly basophilic staining cells (they do not contain any lipid in their cytoplasm. These cells actively secrete peptide - based hormones, for example, the catecholamines norepinephrine ( noradrenaline ) and epinephrine (adrenaline ). This region is rich in venous channels, which drain blood from the sinusoids of the cortex, pass through the medulla, and drain into the medullary vein. The sympathetic nervous system controls secretion of these hormones. Their targets are the adrenergic receptors in the heart, blood vessels, bronchioles, visceral muscle, skeletal muscle, and in the liver, where they promote glycolysis (breakdown of glycogen). 42  Epiphysis cerebri (Pineal gland) The pineal gland (epiphysis cerebri) is a dorsal evagination of the diecephalon, attached by a stalk to the dorsal wall for the third ventricle of the cerebrum. It is covered by a capsule and trabeculae of the pia mater and is divided into by connective tissue septa. The parenchyma is composed primarily of pinealocytes, small epithelioid cells with round nuclei and acidophic cytoplasm, supported by neuroglia cells. The gland secretes melatonin & serotonin 43 44  Thymus The thymus, blocking the entry of antigenic material into the spaces between them (the blood – thymus barrier ). In addition, cortical epithelial cells secrete the hormones for T - cell growth and development (thymosin, thymulin, and thymopoietin). The medulla contains Hassall’ s corpuscles, which contain flat, non - secreting, keratinized epithelial cells (type VI epithelioreticular cells), arranged in concentric layers. They secrete cytokines and thymic stromal lymphopoietin, which activates dendritic cells. 45 Photomicrograph of the thymus 46  Secondary Lymphoid - Lymph Node It is small soft tissue that has fibrous CT capsule surrounded by adipose tissue. It convex surface perforated by afferent lymph vessels with valves with the hilum at the concave surface of the lymph node. Histologically, the lymph node subdivided into three regions Cortex, Paracortex and Medulla. All the region have sinusoids, enlarged endothelially line space. 47 Photomicrograph of the lymph node 48  Cortex of the lymph node The cortex is further subdivided into compartments that house B-cells and secondary lymphoid nodules Its capsule are dense, irregular, collageneous CT that moves into the formation of trabeculae and hilum The centre of the lymphoid nodules are stained paler, house germinal centres (Secondary nodules) Peripherally, compose of dense accumulation of small lymphocytes at migrate away from the origin. The region is also referred to as The Germinal Centre with 3 zone, Dark zone, basal light zone & apical light zone 49 Photomicrograph of the lymph node zones 50  Paracortex of the Lymph node Its is a region between the cortex and medulla. It houses mostly T- cells Serve as the thymus-dependent zone of the lymph node. The Antigen presenting cells (APCs) eg Langerhans cells from the skin and dendritic cells from mucosa migrate to the region to present their epitope –MHC complex to the T- helper cells High endothelial venules (HEVs) are also found within paracortex 51  Medulla of the lymph node The medulla region composed of large tortuous lymph sinuses surrounded by lymphoid cells that are organized in clusters 52  Spleen The spleen is the largest lymphoid organ in the body. It is a well organised “tree” of branching arterial vessels with the smaller branches ending up as sinusoidal system. The organ is surrounded by a fibrous capsule of connective tissue, stemming from which are TRABECULAE support the vasculature It has a convex surface and concave aspect, know as the hilum Its dense, irregular fibro-elastic connective tissue capsule. The spleen function not only on immunological capacity, T and B cell proliferation but also act in filter of the blood in destroying old erythrocytes. 53  Spleen The capsule are thickened at the hilum, due to the presence of the arteries, nerve and lymphatic vessels The trabeculae from the capsule, carry blood vessels to the parenchyma of the spleen The smaller branches of the arterial supply forms the white pulp of the spleen. Its has three-dimensional network of reticular fibers and associated network of reticular cells 54  Spleen The Spleen has a gray area surrounded by a red area (White Pulp and Red Pulp) The trabecular arteries has a loosely tunica adventitia and are infiltrated by sheath of lymphocytes referred to as peri-arterial lymphatic sheath (PALS). The terminal end of the sheath are subdivided into short, parallel branches known as penicullar arteries which has 3 regions 1. Pulp arteriole 2. Sheathed arteriole 3. Terminal arterial capillaries The splenic sinuses are drained by small veins of the pulp to the splenic vein and portal vein 55 Photomicrograph of the spleen capsule showing both the white and red pulp  White Pulp and Marginal Zone The structure of the white pulp is closely associated with the central arteriole. The PALS that surrounds the central arteriole is composed of T lymphocytes PALS and lymphoid nodules constitute the white pulp with T and B cells stationed in specific locations. The white pulp is surrounded by the marginal zone, that separates the white pulp from the red pulp. The Marginal zone is composed of plasma cells, T and B cells lymphocytes, macrophages, and interdigitating dendritic cells with marginal sinuses. 57  Red Pulp The red pulp resembles a “sponge”, composed of splenic sinuses and cords. The splenic sinuses is surrounded by reticular fibers which are arranged perpendicular to the longitudinal axis of the sinuses and are coated by basal lamina. The splenic cords are composed of a loose network of reticular fibers, that are enveloped by stellate reticular cells. 58  Red Pulp Photomicrograph of the spleen capsule showing Red pulp containing the red cells and macrophages 59  The lymphoid vessels are efferent vessels through which lymphocytes migrate to the splenic lymph nodes. The spleen is a highly vascular organ being it a blood filter organ. 60  White Pulp Photomicrograph of the spleen capsule showing White pulp containing the central arteriole 61 Endocrine Pancreas Cells in the islets of Langerhans Alpha – secrete glucagon Beta – secrete insulin Delta – secrete somatostatin and gastrin PP – secrete pancreatic polypeptide  Endocrine Pancreas Islets of Langerhans Low power High power  Mucosa-Associated Lymphoid Tissue (MALT) MALT compose of a non encapsulated, localized lymphocyte infiltration and lymphoid nodules in the mucosal of the Gastrointestinal (gut-associated lymphoid tissue GALT), Respiratory (bronchus-associated lymphatic tissue BALT), tonsils and Urinary tract. GALT is composed of aggregated lymphoid follicles along the length of the gastrointestinal tract known as Peyer’s patches which composes of B cells surrounded by looser region of T cells and numerous APCs 64 Photomicrograph of the MALT 65  BALT similar to Peyer’s patches except that they are located on the bronchi, especially at the region where bronchi and bronchioles bifurcate. Tonsils Tonsil are mostly incompletely encapsulated aggregate lymphoid nodules Palatine Pharyngeal Lingual The palatine tonsil has numerous lymphoid nodules, with many display germinal centre with active B cells 66 Photomicrograph of the palatine tonsil 67  Pharyngeal and Lingual tonsil It is similar to the palatine tonsil but in complete capsule with the crypts shallow and longitudinal unfolding called Pleats The lingual tonsil has a single crypts that receives ducts of mucous minor salivary glands 68 Photomicrograph of the pharyngeal and Lingual tonsil 69 Pancreas 70  Tutorial Q Pitutary Gland On low power and high power sections distinguish the adenohypophysis (anterior pituitary) from the neurohypophysis (posterior pituitary). List the 2 hormones that are secreted by the hypothalamus and stored in the posterior pituitary. Explain in general terms the staining patterns of chromophobes, basophils and acidophils of the anterior pituitary. List the 6 hormones secreted by the anterior pituitary and the cell type by which they are each secreted. Thyroid Gland On H&E stained sections, identify thyroid follicles and colloid. Describe the cell type that lines thyroid follicles. List the hormone produced by the parafollicular cells of the thyroid gland. Q&A  #END Thank You