Histology Of Endocrine System PDF

Histology Of Endocrine System (By Prof. Dr. Iman Nabil) Endocrine glands= ductless glands Definition: the sites of synthesis & secretion of hormones which spread throughout the body by the bloodstream where they act on target organs. Endocrine Module Page...

Histology Of Endocrine System (By Prof. Dr. Iman Nabil) Endocrine glands= ductless glands Definition: the sites of synthesis & secretion of hormones which spread throughout the body by the bloodstream where they act on target organs. Endocrine Module Page 1 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) 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. Endocrine Module Page 2 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) Steroid secreting Protein secreting cells cells 1- H&E Acidophilic Basophilic cytoplasm. vacuolated cytoplasm. 2- Mitochondria With tubular cristae With lamellar cristae 3-Prominent Well-developed Well-developed rough organelles smooth endoplasmic endoplasmic reticulum, Golgi reticulum. apparatus. 4- Secretory Absent. Present. granules 5- Lipid droplets Present. Absent. 6- Sites Suprarenal cortex, Pituitary gland, thyroid gland, gonads& placenta. suprarenal medulla, parathyroid glands, pancreas. General structure of Endocrine Glands: They are composed of: 1- A group of secretory cells. 2- Fenestrated blood capillaries (sinusoidal capillaries). Cords Follicle Endocrine Module Page 3 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) 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. b) Posterior lobe (neurohypophysis): Pale&fibrous. Development of Pituitary gland: Endocrine Module Page 4 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) 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- Irregular 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: 1- 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. 2- 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. Endocrine Module Page 5 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) 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. a- Acidophils (37%): They secrete hormones of protein in nature. 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: 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. Endocrine Module Page 6 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) b- Basophils (11%): They secrete hormones of glycoprotein in nature. They are PAS +ve (except the corticotrophs which secrete a polypeptide hormone (so, it is 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). Acidophils Basophils 1- Percentage 37% 11% 2- Nature of Protein Glycoprotein hormones 3- PAS Negative Positive 4- size Smaller Larger 5- Granules Larger Smaller 6- Secretion Somatotrophs Thyrotrophs (TSH) (growth h.) Gonadotrophs Mammotrophs (FSH& LH) (prolactin) Corticotrophs (ACTH) Endocrine Module Page 7 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) 2- Pars Tuberalis: It is a superior extension that surrounds the infundibular stalk. It is highly vascular. It is formed of: cords of cells (show immunoreactivity to ACTH,FSH&LH). Function: nonspecific. 3- Pars Intermedia: It lies between the pars distalis and pars nervosa. In humans, it is a rudimentary region. It is made up of colloid-filled follicles which represents remnant of Rathke,s pouch. It is made up of: cords of faint basophilic cells with few secretory granules. Function: nonspecific. Endocrine Module Page 8 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) II- Posterior lobe (Neurohypophysis): It lies posterior to the hypophyseal cleft. It consists of 3 parts: 1-The Median Eminence: a funnel shaped downward extension of the hypothalamus. 2- The Infundibular stalk. 3- The Pars Nervosa: which is connected to the base of the brain by the infundibular stalk and the median eminence. Pars Nervosa : It consists of: 1- Unmyelinated axons of neurosecretory cells:  Their cell bodies present in the supraoptic& paraventricular nuclei of the hypothalamus.  Their axons form the hypothalamo-hypophyseal tract carrying the neurosecretion from the hypothalamic nuclei to the pars nervosa. 2- Herring bodies:  Acidophilic homogenous bodies.  Represent accumulation of neurosecretory granules at the dilated terminal ends of axons. 3- Pituicytes: modified glial cells to support nutrition& isolation. 4- Rich fenestrated blood capillaries. Neurosecretion: 1-Oxytocin Acts on smooth muscles of the uterus&mammary glands 2- Vasopressin (ADH)(ADH)(ADH): ↑ water reabsorption from collecting ducts → concentrated urine. Endocrine Module Page 9 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) Blood supply of pituitary gland: Inhibiting & releasing hormones Hypophyseal portal system 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. Endocrine Module Page 10 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) 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.  CT septa: dividing the gland into incomplete lobes & lobules.  Reticular fibers: form a network supporting the thyroid parenchyma. 2- Parenchyma:  It is composed of follicles.  The follicles are surrounded by network of fenestrated blood capillaries.  They contain a gelatinous acidophilic material in their lumina called colloid.  They are lined by cuboidal cells of two types: follicular cells & parafollicular cells. Endocrine Module Page 11 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) 1- Follicular cells: Function: Synthesis & secretion of thyroid hormones (T3&T4). LM: 1- Shape: simple cuboidal cells. 2- Nucleus: central& rounded. 3- Cytoplasm: basophilic. N.B: The cells change their shape according to the degree of activity:  Columnar when they are active.  Squamous when they are inactive. Steps of synthesis of thyroid hormones: 1- Synthesis of thyroglobulin (glycoprotein): A- The protein part of the thyroglobulin are synthesized from the amino acids tyrosine by the rough endoplasmic reticulum. B- The Golgi apparatus adds carbohydrate to the protein to form the thyroglobulin& packed into secretory vesicles. C- The secretory vesicles are discharged into the lumen of the follicle by exocytosis where thyroglobulin contributes in the formation of the colloid. 2- Uptake of iodide:  The follicular cells trap the iodide from the capillaries oxidation into iodine released into the follicular lumen. 3- Iodination of thyroglobulin: takes place in the colloid to form monoiodotyrosine& diiodotyrosine. 4- Formation of T3 & T4: by coupling reaction in the colloid, where they are stored in the lumen of the follicle. Endocrine Module Page 12  Histology Of Endocrine System (By Prof. Dr. Iman Nabil) 5- Release of T3 & T4:  In response to TSH endocytosis of the colloid in endocytotic vesicles by the follicular cells fusion of the vesicles with lysosomes hydrolysis release of T3&T4 blood stream. How does the follicular cell adapt to its function? EM A-Basally: Numerous profiles of rER. B- Apically: 1- Supranuclear Golgi. 2- Secretory vesicles containing thyroglobulin. 3- Microvilli. 4- Endocytotic vesicles & lysosomes. The thyroid gland is unique gland which stores its hormone precursor as a colloid extracellular and not intracellular Endocrine Module Page 13 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) 2-Parafollicular (Clear cells or C cells): Function: synthesis & secretion of calcitonin. They are found as part of the follicular epithelium, in between the follicular cells or as isolated clusters between the follicles. Number: 0.1% of the follicular epithelium. LM:  Size: larger than the follicular cells.  Cytoplasm: pale (clear cells). Their basal surfaces rest on the follicular basement membrane but their apical surfaces never reach the lumen of the follicles. How does the parafollicular cell adapt to its function? EM: Polypeptides secreting cells:  Moderate amount of organelles.  Infra nuclear Golgi (Why).  The secretory granules are small & basal (Why). The Interfollicular cells: They are tangentially cut follicles so appear as clumps of cells without lumen. They may be follicular or parafollicular cells. Endocrine Module Page 14 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) Follicular cells Parafollicular cells 1- Size Smaller Larger 2- Number Numerous Few 3- Extension Reach the lumen Never reach the lumen 4- Cytoplasm Basophilic Pale basophilic 5- rER Rich, basally Moderate 5- Golgi Supranuclear Infranuclear 5- Lysosomes Numerous Less 6- Secretion Stored extracellular Stored intracellular, inside secretory granules. 7-Function Secrete T3&T4 Secrete calcitonin Anatomically: 4 glands situated behind thyroid gland. Structure of parathyroid : gland I-Stroma:  CT capsule: of that of the thyroid gland.  CT septa.  Network of reticular fibers: support the parenchymal cells. II-Parenchyma: It consists of cords of polygonal cells surrounded by a rich network of fenestrated blood capillaries. The cells are of 2 types: Chief & oxyphil cells. Endocrine Module Page 15  Histology Of Endocrine System (By Prof. Dr. Iman Nabil) A- The chief cells: Function: Secretion of parathyroid hormone. Number: numerous. LM:  Shape: small polygonal cells  Nucleus: large vesicular nuclei  Cytoplasm: pale (WHY). How does the chief cell adapt to its function? EM: Polypeptide secreting cells  The cytoplasm contains moderate amount of organelles (rER, Golgi complex, mitochondria& secretory granules.  Glycogen granules& lipid droplets: cause the pale cytoplasm seen with the LM. Parathyroid gland Endocrine Module Page 16  Histology Of Endocrine System (By Prof. Dr. Iman Nabil) B- Oxyphil cells Function: Unknown. Number: few. LM:  Shape: large polygonal.  Nucleus: small& dense.  Cytoplasm: deep eosinophilic (Why). EM: The cytoplasm contains many mitochondria. With increasing age:  The chief cells are replaced by fat cells which may constitute more than 50% of the gland.  The number of oxyphil cells increases. Chief cell Oxyphil cell 1- Size Smaller Larger 2- Number Numerous Few 3- Cytoplasm Pale Deep acidophilic 4- Nucleus Large& vesicular Small & dense 5- rER More Less 6- Mitochondria Less Numerous 7- Function Secretion of Unknown parathyroid hormone Endocrine Module Page 17 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) Which statement is the best to describe the pointed cell? 1- It secretes the parathyroid hormone. 2- Its Golgi complex is basal. 3- It is the most numerous cell type. 4- It is stained by the acidic stain. Anatomically: Two glands, each one situated at the upper pole of the kidney. Histologically: Each gland consists of a cortex& medulla. Structure of suprarenal glands : I-Cortex:  Yellow in color (Why).  It originates from the mesoderm.  It constitutes 80- 90% of the gland. II- Medulla:  Reddish brown in color (Why).  It originates from the neural crest (the same origin as the sympathetic nervous system).  It is considered as a modified sympathetic ganglion, where the neurons have acquired an endocrine activity and secrete catecholamines. Structure of suprarenal glands : A- Stroma:  A connective tissue capsule.  A CT septa.  A network of reticular fibers. Endocrine Module Page 18 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) B- Parenchyma: it is divided the cortex & the medulla. I- Suprarenal Cortex: It is the steroid secreting portion of the gland. It is divided into 3 zones: 1- Zona glomerulosa (15% of the cortex): Secretes mineralocorticoids mainly aldosterone control blood volume& blood pressure. 2- Zona fasiculata (65-80%): Secretes glucocorticoids control CHO, fat & protein metabolism. 3- Zona reticularis (7%): Secretes androgen development of axillary& pubic hair in females. Structure of cells in adrenal cortex: Steroid secreting cells: LM:  Cytoplasm: acidophilic& vacuolated. EM:  Abundant sER.  Mitochondria with tubular cristae.  Lipid droplets: they are numerous in zona fasiculata & less in zona glomerulosa and reticularis. Endocrine Module Page 19 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) A- Zona Glomerulosa: LM:  It lies immediately under the capsule.  Arrangement of the cells: in closely packed arched clusters surrounded by fenestrated blood capillaries.  Shape of the cells: columnar.  Nucleus: dense.  Cytoplasm: acidophilic & slightly vacuolated. EM: The cells show the ultrastructural features of steroid secreting cells with few lipid droplets. B- Zona Fsciculata: LM:  It is the middle layer of the cortex  Arrangement of the cells: in long straight cords, perpendicular to the capsule.  The cords are one or two cells thick& separated by sinusoidal blood capillaries.  Shape of the cell: large polyhedral.  Nucleus: large& pale.  Cytoplasm: pale acidophilic& highly vacuolated so called spongiocytes. EM: The cells show the ultrastructural features of steroid secreting cells with numerous lipid droplets. Endocrine Module Page 20 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) C- Zona Reticularis: LM:  It is the inner layer of the cortex.  Arrangement of the cells: in irregular cords enclosing fenestrated capillaries in between.  Shape of the cell: small polyhedral.  Cytoplasm: acidophilic& slightly vacuolated.  Dark cells: are seen near the medulla. They have dark cytoplasm with pyknotic nuclei, suggesting that they are degenerating cells.  Lipofuscin pigments: are present in this layer. EM: The cells show the ultrastructural features of steroid secreting cells with few lipid droplets. NB: Steroid secreting cells Never store their Hormones. Zona glomerulosa Zona fasiculata Zona reticularis 1- Percentage 15% 65-80% 7% 2-Arrangement Closely packed arches Long straight Irregular cords cords 3- Shape of Columnar Large polyhedral Small polyhedral the cells 4- Nucleus Dense Large& pale 5- Cytoplasm Acidophilic& slightly Acidophilic& highly Acidophilic& vacuolated vacuolated slightly vacuolated 6-Lipid Few Numerous Few droplets 7- Function Secrets Secretes Secretes mineralocorticoids glucocorticoids androgen Endocrine Module Page 21 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) II- Suprarenal Medulla: It contains two types of cells: 1-Chromaffin cells: secrete catecholamines (epinephrine&norepinephrine). 2- Sympathetic ganglion cells. 1- Chromaffin cells = Pheochromocytes: They are called chromaffin cells due to the affinity of their granules to react with chromium salts and give brown color (chromaffin reaction). LM:  Arrangement of the cells: in irregular cords enclosing the blood capillaries.  Shape of the cell: large ovoid.  Nucleus: large spherical.  Cytoplasm: pale basophilic. EM: polypeptide secreting cells  Moderate amount of rER, prominent Golgi and secretory granules. Endocrine Module Page 22 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) -Adrenal medulla is considered as modified sympathetic ganglia -Chromaffin cells are modified postganglionic neurons 2- Sympathetic ganglion cells: Functions: A-Modulate the secretory activity of the cortex. B- Innervate the blood vessels of the cortex. Blood supply of the adrenal gland: The medulla has a dual blood supply: 1- Arterial: from the medullary arterioles. 2- Venous: from the cortical sinusoids draining the cortex (glucocorticoids reaching the medulla are essential for production of epinephrine by chromaffin cells). Which statement describes the spongiocytes? 1- They contain lipofuscin pigments in their cytoplasm. 2- They are arranged in long straight cords. 3- Their nuclei are dense. 4- They store their secretion inside the secretory granules. Endocrine Module Page 23  Histology Of Endocrine System (By Prof. Dr. Iman Nabil) Anatomically: Pancreas is one of the largest glands of the digestive tube. It lies in C- shaped cavity of the duodenum. It is divided into head, body & tail. Histologically: It is a mixed gland: composed of both exocrine (described in GIT module) & endocrine parts. The endocrine pancreas (The Islets Of Langerhans) The islets of Langerhans are more numerous in the tail than in the head & the body of the pancreas. They appear in histological sections as lightly stained areas (Why). Histological structure of islets of Langerhans A- Stroma:  They are not encapsulated.  Supported by network of reticular fibers. B- Parenchyma: LM: Arrangement of the cells: in short cords and separated by network of fenestrated blood capillaries. Shape of the cells: polygonal. Cytoplasm: pale basophilic Endocrine Module Page 24  Histology Of Endocrine System (By Prof. Dr. Iman Nabil) EM: Polypeptide secreting cells Moderate amount of rER, Golgi complex & secretory granules. 3 main types of cells can be identified: A cells, B cells& D cells. How to differentiate between the cells of the islets? 1- Histochemistry. 2- Immunohistochemistry. 3- Electron microscope (by their secretory granules). 1-A cells (alpha): Function: secretion of glucagon increases blood sugar level. Size: large. Number: 20%. Site: at the periphery of the islet. EM: the secretory granules are numerous and have a homogeneous dense core. 2-B cells (Beta): Functions: 1- Secretion of insulin lower blood sugar level. 2- Secretion of C-peptide: as a consequence of insulin production. It prevents neuropathy and other symptoms of diabetic vascular deterioration. Measuring its level can give an idea about the viable beta cell mass. 3- Secretion of GABA (γ amino butyric acid): suppress glucagon secretion. Size of the cells: small. Number: 70% of the islet cells. Site: centrally located within the islet. EM: their secretory granules have a rectangular crystalline dense core surrounded by an electron lucent halo. Endocrine Module Page 25 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) 3-D cells (Delta): Function: secretion of somatostatin inhibits secretion of GH, insulin & glucagon. Number: 5 - 10% of the islet cells. Site: at the periphery of the islet. Alpha Beta Delta Number 20% 70% 5-10% Site Periphery Central Periphery Size Large Small Small Granules: Granules with Granules with rectangular EM homogenous crystalline dense core dense core surrounded by an electro lucent halo. Function Glucagon Insulin, C peptide&GABA Somatostatin Endocrine Module Page 26 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) Definition: single or small groups of endocrine cells with diffuse distribution in different tissues and organs of the body. These cells secrete hormones, usually peptides. They synthesize monoamines by the uptake of amine precursors and their decarboxylation( APUD cells=Amine Precursor Uptake & Decarboxylation). Modes of action of their hormones: 1- Paracrine: act on the neighboring cells. 2- Autocrine: act on the cell that secrete the hormone itself. 3- Endocrine: act on target cells in remote tissue. Endocrine Module Page 27 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) How to identify the DNES in histological sections? 1- H&E: These cells are not well seen. 2- Special stain:  chromium salts (chromaffin cells).  silver salts (argentaffin cells). 3- Immunohistochemical stain: using antibodies against their peptide hormone. Chromaffin cells Argentaffin cells Structure of DNES: EM: 1- Shape: pyramidal with narrow apex and a wide base. 2- Cytoplasm: polypeptide secreting cells with moderate amount of organelles due to slow rate & small amount of secretion:  rER.  Mitochondria.  Golgi apparatus.  Secretory granules. Endocrine Module Page 28 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) Types of DNES: 1-Open type: the cell has long microvilli extending into the lumen of the organ. 2- Closed type: where the cell apex is covered by other epithelial cells of the organs. Distribution of DNES:  Gastrointestinal tract (enteroendocrine cells).  Respiratory system.  Supraoptic and paraventricular hypothalamic nuclei.  Parafollicular cells of thyroid gland.  Chief cells of parathyroid gland.  Chromaffin cells of the suprarenal medulla.  Cells of islets of Langerhans.  Pinealocytes. What is the correct statement about the alpha cells of the Islets of Langerhans? 1- They are centrally located within the Islets. 2- They are the most numerous cell types. 3- Their secretory granules have electron dense core. 4- They secret somatostatin. Endocrine Module Page 29 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) Site: on the posterior part of third ventricle at the mid line between two cerebral hemispheres. Structure: It is covered by pia matter which sends CT septa carrying the blood vessels. It consists of 2 types of cells: A- Pinealocytes (secretory cells). B- Glial cells (resemble astrocytes): for support. Pinelocytes : Shape: branching with long tortuous processes end as flat dilatations near blood capillaries (WHY). Nucleus: large, lobulated with prominent nucleoli. Cytoplasm: pale basophilic (WHY) with secretory vesicles. Function: secretion of melatonin. Corpora arenacea (brain sand) Definition: Formation of calcified bodies which increase in number & size by age. Importance: it can be used as a clinical landmark for the midline location of the pineal gland during radiological examination of the brain. Endocrine Module Page 30 Histology Of Endocrine System (By Prof. Dr. Iman Nabil) Functions of melatonin 1- Controls circadian rhythm. 2- Induces feeling of sleepiness. 3- Decreases gonadotropin. 4- Protects CNS from oxidative stress. Which statement is not describing the histological structure of the pineal gland? 1- It has no capsule. 2- It has a profuse blood supply. 3- The cytoplasm of the secretory cells contain rER, Golgi and secretory vesicles. 4- The corpora arenacea increases with age. Endocrine Module Page 31