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ANATOMICAL FEATURES OF THE ENDOCRINE GLANDS • • • • • • • • • • • • • • • • • • LEARNING OBJECTIVES At the end of this lecture, students should be able to, Understand the anatomy of the endocrine glands. Define the relations of these endocrine glands. Know Blood vessels supplying these endocrine glands. Know Nerve supply of these endocrine glands. ENDOCRINE GLANDS Control many body functions by releasing special chemical substances into the blood called hormones Act on target organs elsewhere in body Control and coordinate widespread processes, i.e. homeostasis, reproduction, growth and development, metabolism and response to stress. THE ENDOCRINE SYSTEM Consists of several glands located in various parts of the body i.e. Hypothalamus Pituitary Thyroid Parathyroid Adrenal Kidneys Pancreatic Islets Ovaries Testes PITUITARY GLAND • Lies in the hypophyseal fossa. • Covered by diaphragma sellae • On each side is a flange of dura matter separating the gland from the cavernous sinus. • Pia and arachnoid blend with the capsule of the gland. • Below the fossa lies the body of sphenoid containing sphenoidal air sinuses. • • • • • • • • Pitutary stalk slops down wards and forwards to the perforation in the diaphragma connecting posterior part of gland to the hypothalamus. Optic chaisma lies above the diaphragma sellae anterosuperior to the pitutary stalk. STRUCTURE OF PITUTARY GLAND Consists of anterior and posterior lobe. Anterior lobe or adenohypophysis develops from ectodermal sacule (rathke‟s pouch) of stomodeum and consists of pars anterior (distalis), pars tuberalis and rudimentary pars intermedia. Posterior lobe or neurohypophysis, develops from neuroectodermal growth from the floor of third ventricle and consists of pars posterior, infundabular stalk and median eminence. PARS ANTERIOR Accounts for 75% of gland and is highly vascular and consists of 50% chromophobe, 35% acidophils and15% basophils. Acidophils secrete growth hormones and prolactin. Basophils produce ACTH, TSH, FSH, LH. Pars tuberalis is small extension of the pars anterior along the pitutary stalk. Its function not known. Pars intermedia consists of colloid filled vesicles and secrete MSH. Its cells contain endorphins. • • • • • • • • PARS POSTERIOR Contains about 100,000 unmyelinated nerve fibers. Cell bodies in paraventricular nuclei secrete oxytocin. Cell bodies in supraoptic nuclei secrete antidiuretic hormone. Hormones are secreted from neurohypophysis. BLOOD SUPPLY Single inferior and several superior hypophyseal arteries arise from internal carotid arteries. Hypophyseal portal venous system forms, connecting hypothalamus and pitutary and carry hormones and releasing factors from pitutary. THYROID GLAND About 25g in weight and is enclosed by pretracheal fascia has two symmetrical lobes united by isthmus. Isthmus joins anterior surface of the lobes at their lower part, lies in front 2nd, 3rd and 4th tracheal rings. Pretracheal fascia is here fixed between them (It moves gland up and down during swallowing). On upper border of isthmus superior and inferior thyroid arteries form anastomosis. Tributaries of inferior thyroid veins emerge from its lower border. Lobes are pear shaped. Having narrow upper pole and broad lower pole. Triangular in cross section and possessing lateral, medial and posterior surface • • • • • • • • • • • LOBES OF THYROID GLAND Extends from oblique line on thyroid cartilage up to 6th tracheal ring sternothyroid and sternohyoid muscles cover lateral surface. Lower part of pharynx and upper esophagus lie behind. Posterior surface is related with medial part of common carotid artery. More laterally is internal jugular vein and parathyroid glands. RECURRENT LARYNGEAL NERVES Recurrent laryngeal nerves approach medial surface of gland from below and lie in or in front of groove between trachea and esophagus. Left nerve recurves around the arch of aorta in superior mediastinum. Right nerve recurves around right subclavian at the root of the neck, nerve either passes medial and lateral or through suspensory ligament of berry. PYRAMIDAL LOBE Upward projection from isthmus generally to the left of midline. It is caudal end of thyroglossal duct. It may be attached to the inferior border of the hyoid bone by fibrous tissue named levator glandulae thyroidae. Aberrant thyroid tissue may be found, near hyoid bone, in the tongue in the superior mediastinum and any where along the path of descent of thyroglossal duct. • • • • • • • • • • • • • • • • • • • • SUPERIOR THYROID ARTERY It is first branch from anterior aspect of external carotid artery. Pierces pretracheal fascia. Reaches the summit of upper pole in front of external laryngeal nerve. Divides in to anterior and posterior branch. Anterior branch runs down the isthmus and posterior branch runs down back of lobe and anastomosis with an ascending branch of inferior thyroid artery. Be ligated at upper pole or anterior or posterior branch be ligated in order to avoid damage to external laryngeal nerve. Inferior thyroid artery arises from thyrocervical trunk. Arches upward medially and behind carotid sheath and then loops down to the lower pole of gland. Divides out side pretracheal fascia. Branches pierce fascia separately Recurrent laryngeal nerve always behind pretracheal fascia. Ligating it lateral to gland or its branches separately can safeguard nerve. Branches are ascending cervical artery and smaller pharyngeal, esophageal, laryngeal and tracheal branches. Thyroidea ima artery present in 3% of individuals. Enters lower pole of isthmus. .Arises from brachiocephalic trunk, arch of aorta or right common carotid artery. Venous drainage of thyroid gland Superior thyroid veins follow superior thyroid artery and opens into internal jugular vein or facial vein. Middle thyroid vein crosses internal carotid vein. Inferior thyroid veins drain mainly in to brachiocephalic vein Lymphatic drainage Mainly to deep cervical nodes. A few pass to prelaryangeal, pretracheal and paratracheal nodes. And few drain directly into thoracic duct. • • • • • • • • • • • • • • • PARATHYROID GLAND Are small and lie behind the lobes of thyroid gland. Superior parathyroid glands More constant in position. Usually within the thyroid‟s pretracheal facial capsule. Lie at the middle of the back of the thyroid lobe. At level with first tracheal ring above the inferior thyroid artery INFERIOR PARATHYROID GLAND Is less constant in position. Usually with in pretracheal facial sheath behind lower pole may be gland it self or outside facial sheath, in the neck or in superior or posterior mediastinum. Not necessary at same level on each side. Are brownish yellow and thyroid is deep red. Blood supply of parathyroid Inferior thyroid artery. Or anastomosis between superior and inferior thyroid arteries. Minute veins joins thyroid veins. Parathyroid hormone (PTH) – Stimulates Ca2+ release from bone – Promotes intestinal absorption and renal tubular reabsorption of calcium Underactivity – Decrease serum Ca2+ • Hypocalcemic tetany • Seizures • Laryngospasm. – – Overactivity Increased serum Ca2+ • Pathological fractures • Hypertension • Renal stones • Altered mental status “Bones, stones, hypertones, abdominal moans” ADRENAL GLAND • • • • • • • • • • • • • • • • • Among most important and vital endocrine organ Small bilateral, yellowish and retroperitoneal organ Lies just above kidney in gerota‟s fascia. Right adrenal is triangular, related to upper pole Right kidney Left adrenal is crescent shaped, related to upper and medial part Left kidney Size :Right is 3 – 6 cm long and left one is 0.9 – 3.6 cm. Width is 2-3 cm. Weight is 3-5 gm. approximately. Adrenal cortex consists of three distinct zones Zona Glomerulosa. Small cells with intermediate number of lipid inclusion. Zona Fasiculata. large foamy cells secondary to lipid inclusion - 75% of cortex. Zona Reticularis. Consists of compact cytoplasm and few lipid inclusions. Adrenal cortex produces Glucocorticoids (Zona Fasiculata) Mineralocorticoids (Zona Glomerulosa) Adrenal androgens (Zona Reticularis) Adrenal medulla produces Epinephrine (adrenaline) Norepinephrine (noradrenaline) Help increase in cardiac output, vascular resistance and mediate stress response All are absolutely required for life • • • • • • • • • • • • • • • • • • • FUNCTIONS Aldosterone helps in Na reabsorption & potassium excretion & preventing dehydration Cortisol stimulate protein breakdown, inhibition of tissue response in injury & antagonism to action of insulin Androgens helps in early development of male sex organ in childhood VASCULAR SUPPLY Blood to adrenal supplied by, Inferior phrenic artery (superiorly), aorta (medially) renal artery (inferiorly) Rt. adrenal : Superior and inferior suprarenal arteries. Lt. adrenal : Middle & inferior suprarenal arteries VENOUS DRAINAGE Right Adrenal. Drained to IVC via suprarenal vein Left Adrenal. Drained into left suprarenal vein or directly to IVC Lymphatic drainage. Drained to Para-aortic and Para- caval lymph nodes PANCREAS Gland with both exocrine and endocrine functions is 6-10 inch in length and 60-100 gram in weight. Location: Retro-peritoneal, at the level of 2nd lumbar vertebral. Extends obliquely towards left. Parts of pancreas: Head, neck, body and tail Endodermal in origin. Develops from ventral and dorsal pancreatic buds. Ventral bud rotates posteriorly and becomes the uncinate process and inferior part of head of pancreas Dorsal bud becomes superior part of head, neck, body and tail Ventral bud duct fuses with dorsal bud duct to become main pancreatic duct (Wirsung) • • • • Head of pancreas Includes uncinate process Flattened 2 – 3 cm thick In the „C‟ shaped concavity of duodenum. • • • • • • • • • • • • • • • • • • • • • • Neck of pancreas 2.5 cm in length Superior border relates to the pylorus Superior mesenteric vessels emerge from the inferior border Posteriorly, SMV and splenic vein confluence to form portal vein Body of pancreas Elongated. Anterior surface, separated from stomach by lesser sac. Posterior surface, related to aorta, Lt. adrenal gland, Lt. renal vessels and upper 1/3rd of Lt. kidney Splenic vein runs embedded in the post. surface closer to the superior border Inferior surface is covered by transverse mesocolon Tail of pancreas Narrow, short segment Lies at the level of the 12th thoracic vertebra Ends within the splenic hilum. Anteriorly, related to splenic flexure of colon May be injured during splenectomy. PANCREATIC DUCT Main duct (Wirsung) runs the entire length of pancreas and joins CBD at the ampulla of Vater 2 – 4 mm in diameter, drains up to 20 secondary branches Ductal pressure is 15 – 30 mm Hg (vs. 7 – 17 in CBD) thus preventing reflux and damage to pancreatic duct Lesser duct (Santorini) drains superior portion of head and empties separately into 2nd portion of duodenum ARTERIAL SUPPLY • Celiac Superior pancreaticoduodenal artery which divides into anterior and posterior branches • SMA Inferior pancreaticoduodenal artery which divides into anterior and posterior branches Anterior and posterior collateral arcade between the superior and inferior PDA supply head • Body and tail supplied by splenic artery by about 10 branches • Three big branches from splenic are Dorsal pancreatic artery Pancreatica Magna (midportion of body) Caudal pancreatic artery (tail) • • • • • • • • • • • • • • • • • • • VENOUS DRAINAGE OF PANCREAS Follows arterial supply Anterior and posterior arcades drain head and the body Splenic vein drains the body and tail Major drainage areas are Suprapancreatic PV Retropancreatic PV Splenic vein Infrapancreatic SMV Ultimately, into portal vein Lymphatic drainage Rich periacinar network that drain into 5 nodal groups Superior nodes Anterior nodes Inferior nodes Posterior PD nodes Splenic nodes • • • • • • • • INNERVATION OF PANCREAS Sympathetic fibers from the splanchnic nerves Parasympathetic fibers from the vagus Both give rise to intrapancreatic periacinar plexuses Parasympathetic fibers stimulate both exocrine and endocrine secretion Sympathetic fibers have a predominantly inhibitory effect HISTOLOGY-ENDOCRINE PANCREAS Accounts for only 2% of the pancreatic mass Nests of cells - islets of Langerhans Four major cell types – Alpha (A) cells secrete glucagon – Beta (B) cells secrete insulin – Delta (D) cells secrete somatostatin – F cells secrete pancreatic polypeptide B cells are centrally located within the islet and constitute 70% of the islet mass • • • • • INSULIN Synthesized in the B cells of the islets of Langerhans 80% of the islet cell mass must be surgically removed before diabetes becomes clinically apparent Proinsulin, is transported from the endoplasmic reticulum to the Golgi complex where it is packaged into granules and cleaved into insulin and a residual connecting peptide, or C peptide Major stimulants – Glucose, amino acids, glucagon, GIP, CCK, sulfonylurea compounds, β-Sympathetic fibers Major inhibitors – somatostatin, amylin, pancreastatin, α-sympathetic fibers • • • • • • • • • • • • Glucagon Secreted by the A cells of the islet Glucagon elevates blood glucose levels through the stimulation of glycogenolysis and gluconeogenesis Major stimulants – Aminoacids, Cholinergic fibers, β-Sympathetic fibers Major inhibitors Glucose, insulin, somatostatin, α-sympathetic fibers Somatostatin Secreted by the D cells of the islet Inhibits the release of growth hormone Inhibits the release of almost all peptide hormones Inhibits gastric, pancreatic, and biliary secretion Used to treat both endocrine and exocrine disorders • PINEAL GLAND Located within the Diencephalon Melatonin – Inhibits ovarian hormones – May regulate the body‟s internal clock • HYPOTHALAMUS Produces several releasing and inhibiting factors that stimulate or inhibit anterior pituitary‟s secretion of hormones. • • • Produces hormones that are stored in and released from posterior pituitary HYPOTHALAMUS Also responsible for: – Regulation of water balance – Esophageal swallowing – Body temperature regulation (shivering) – Food/water intake (appetite) – Sleep-wake cycle – Autonomic functions • • • • OVARIES Located in the abdominal cavity adjacent to the uterus Under the control of LH and FSH from the anterior pituitary Produce ovum for reproduction Produce hormones – estrogen – progesterone – Functions include sexual development and preparation of the uterus for implantation of the egg OVARIES • • Estrogen – Development of female secondary sexual characteristics – Development of endometrium Progesterone – – Promotes conditions required for pregnancy Stabilization of endometrium TESTES • • • • Located in the scrotum Controlled by anterior pituitary hormones FSH and LH Produce sperm for reproduction Produce testosterone – promotes male growth and masculinization – promotes development and maintenance of male sexual characteristics -----------------------------------------------------------------------------------