Endocrine System PDF

11/7/24 Learning Objectives 1. Identify the hormones secreted by the...

11/7/24 Learning Objectives 1. Identify the hormones secreted by the endocrine glands and their target organs. Endocrine System 2. Describe the principal effect of the hormones By : Marc Anthony Cueto MD secreted by the endocrine glands. 3. Illustrate the different endocrine glands and identify their parts. 1 2 Endocrine System Endocrine System u The endocrine system, along with the nervous system, functions in the regulation of body activities. u The endocrine system coordinates functioning between u The nervous system acts through electrical impulses and different organs through hormones, which are released into neurotransmitters to cause muscle contraction and glandular the bloodstream from specific types of cells within secretion. endocrine (ductless) glands. u The effect is of short duration, measured in seconds, u Once in circulation, hormones affect function of the target and localized. tissue. Some hormones exert an effect on cells of the organ u The endocrine system acts through chemical messengers called from which they were released (paracrine effect), some hormones that influence growth, development, even on the same cell type (autocrine effect). and metabolic activities. u Hormones can be peptides of various sizes, steroids u The action of the endocrine system is measured in minutes, (derived from cholesterol), or amino acid derivatives. hours, or weeks and is more generalized than the action of the nervous system. 3 4 Hypothalamus-Pituitary Complex 5 6 1  11/7/24 Hypothalamus-Pituitary Complex Hypothalamus-Pituitary Complex : Hypothalamus u The hypothalamus–pituitary complex can be thought of as the “command center” of the endocrine system. u The hypothalamus is a structure of the diencephalon of the brain located anterior and inferior to the u This complex secretes several hormones that directly produce thalamus. It has both neural and endocrine functions, producing and secreting many hormones. responses in target tissues, as well as hormones that regulate the In addition, the hypothalamus is anatomically and synthesis and secretion of hormones of other glands. u functionally related to the pituitary gland (or hypophysis), a bean-sized organ suspended from it by u In addition, the hypothalamus–pituitary complex coordinates the a stem called the infundibulum (or pituitary stalk). messages of the endocrine and nervous systems. u The pituitary gland is cradled within the sella turcica of the sphenoid bone of the skull. u In many cases, a stimulus received by the nervous system must u It consists of two lobes that arise from distinct parts pass through the hypothalamus–pituitary complex to be of embryonic tissue: the posterior pituitary translated into hormones that can initiate a response. (neurohypophysis) is neural tissue, whereas the anterior pituitary (also known as the adenohypophysis) is glandular tissue that develops from the primitive digestive tract. 7 8 Hypothalamus-Pituitary Complex : Anterior Pituitary u Hypothalamic hormones are secreted by neurons, but enter the anterior pituitary through blood vessels. u Within the infundibulum is a bridge of capillaries that connects the hypothalamus to the anterior pituitary. u This network, called the hypophyseal portal system, allows hypothalamic hormones to be transported to the anterior pituitary without first entering the systemic circulation. u The system originates from the superior hypophyseal artery, which branches off the carotid arteries and transports blood to the hypothalamus. u The branches of the superior hypophyseal artery form the hypophyseal portal system. u Hypothalamic releasing and inhibiting hormones travel through a primary capillary plexus to the portal veins, which carry them into the anterior pituitary. u Hormones produced by the anterior pituitary (in response to releasing hormones) enter a secondary capillary plexus, and from there drain into the circulation. 9 10 Hypothalamus-Pituitary Complex : Hypothalamus-Pituitary Complex : Anterior Pituitary (Adenohypophysis) Posterior Pituitary (Neurohypophysis) u The posterior pituitary is actually an extension of the u The anterior pituitary originates from neurons of the paraventricular and supraoptic nuclei the digestive tract in the embryo and of the hypothalamus. The cell bodies of these regions rest in the hypothalamus, but their axons descend as migrates toward the brain during the hypothalamic–hypophyseal tract within the infundibulum, and end in axon terminals that fetal development. comprise the posterior pituitary. u The posterior pituitary gland does not produce u There are three regions: the pars hormones, but rather stores and secretes hormones distalis is the most anterior, the pars produced by the hypothalamus. intermedia is adjacent to the u The paraventricular nuclei produce the hormone oxytocin, whereas the supraoptic nuclei produce ADH. These hormones travel along the axons into posterior pituitary, and the pars storage sites in the axon terminals of the posterior tuberalis is a slender “tube” that pituitary. wraps the infundibulum. u In response to signals from the same hypothalamic neurons, the hormones are released from the axon terminals into the bloodstream. 11 12 2  11/7/24 13 14 Anterior Lobe Lesions u Hypersecretion of anterior lobe hormones (hyperpituitarism) is almost always selective, although occasionally a tumor hypersecretes both growth hormone and prolactin. u The anterior pituitary hormones most commonly secreted in excess are GH (as in acromegaly, gigantism), prolactin (as in galactorrhea), and ACTH (as in the pituitary type of Cushing Pituitary Lesions syndrome). u Hyposecretion of anterior lobe hormones (hypopituitarism) may be generalized, usually due to a pituitary tumor, or is idiopathic or may involve the selective loss of one or a few pituitary hormones. 15 16 Gigantism and Acromegaly Gigantism and Acromegaly u Gigantism and Acromegaly are syndromes of u In adults with acromegaly, coarse body hair increases and the skin thickens and excessive secretion of growth hormone frequently darkens. (hypersomatotropism) that are nearly always due to a pituitary adenoma. u The size and function of sebaceous and sweat glands increase, such that u In gigantism, This rare condition occurs if GH patients frequently complain of hypersecretion begins in childhood, before excessive perspiration and offensive closure of the epiphyses. Skeletal growth body odor. velocity and ultim ate stature are increased, u Overgrowth of the mandible leads to but little bony deformity occurs. protrusion of the jaw (prognathism) and u However, soft-tissue swelling occurs, and the malocclusion of teeth. peripheral nerves are enlarged. Delayed u Cartilaginous proliferation of the larynx puberty or hypogonadotropic hypogonadism leads to a deep, husky voice. is also frequently present, resulting in a eunuchoid habitus. 17 18 3  11/7/24 Gigantism and Acromegaly Gigantism and Acromegaly u The tongue is frequently enlarged and furrowed. In long-standing acromegaly, u Diagnosis is clinical and by skull costal cartilage growth leads to a barrel and hand x-rays and measurement chest. of growth hormone levels. u Peripheral neuropathies occur commonly because of compression of nerves by u Treatment involves removal or adjacent fibrous tissue and endoneural destruction of the responsible fibrous proliferation. Headaches are adenoma. com m on because of the pituitary tum or. u Bitemporal hemianopia may develop if suprasellar extension compresses the optic chiasm. u The heart, liver, kidneys, spleen, thyroid gland, parathyroid glands, and pancreas are larger than normal. 19 20 Growth Hormone Deficiency Galactorrhea u Growth hormone deficiency (GHD) is a medical u Galactorrhea is lactation in men or in women who are not condition in which the body produces insufficient growth hormone. breastfeeding. u Growth hormone, also called somatotropin, is u It is generally due to a prolactin-secreting pituitary adenoma. a polypeptide hormone which stimulates growth and cell reproduction. If this hormone u Abnormal lactation is not defined quantitatively; it is milk release is lacking, stunted or even halted growth may that is inappropriate, persistent, or worrisome to the patient. become apparent. u Spontaneous lactation is more unusual than milk released in response u Children with this disorder may grow slowly and puberty may be delayed by several years to manual expression. or indefinitely. u The milk is white. u Growth hormone deficiency has no single definite cause. It can be caused by mutations u Women with galactorrhea commonly also have amenorrhea or of specific genes, damage to the pituitary oligomenorrhea. gland, Turner's syndrome, poor nutrition, or even stress (leading to psychogenic u Diagnosis is by measurement of prolactin levels and imaging tests. dwarfism). u Treatment involves tumor inhibition with dopamine agonist drugs and u Treatment is GH replacement therapy. sometimes removal or destruction of the adenoma. 21 22 SIADH vs Diabetes Insipidus Posterior Lobe Lesions 23 24 4  11/7/24 Thyroid and Parathyroid gland Thyroid gland u The thyroid gland is anterior in the u The thyroid and parathyroid glands are endocrine neck below and lateral to the glands positioned anteriorly in the neck. thyroid cartilage. u It consists of two lateral lobes u Both glands begin as pharyngeal outgrowths that (which cover the anterolateral migrate caudally to their final position as development surfaces of the trachea, the cricoid cartilage, and the lower part of the continues. thyroid cartilage) with an isthmus that connects the lateral lobes and u The thyroid gland is a large, unpaired gland, while the crosses the anterior surfaces of the parathyroid glands, usually four in number, are small second and third tracheal cartilages. and are on the posterior surface of the thyroid gland. 25 26 Thyroid gland Thyroid gland u The thyroid gland arises as a u Lying deep to the sternohyoid, median outgrowth from the floor sternothyroid, and omohyoid of the pharynx near the base of muscles, the thyroid gland is in the tongue. the visceral compartment of the u The foramen cecum of the tongue neck. indicates the site of origin and the u This compartment also includes thyroglossal duct marks the path of the pharynx, trachea, and migration of the thyroid gland to esophagus and is surrounded by its final adult location. the pretracheal layers of fascia. u The thyroglossal duct usually disappears early in development, but remnants may persist as a cyst or as a connection to the foramen cecum (i.e., a fistula). 27 28 How to find the Thyroid gland Thyroid gland – Arterial supply – Superior u The left and right lobes of the thyroid gland are in the thyroid artery anterior triangles in the lower neck on either side of the airway and digestive tract inferior to the position of the oblique line of the thyroid cartilage u The superior thyroid artery is the first u In fact, the sternothyroid muscles, which attach branch of the external carotid artery. It superiorly to the oblique lines, lie anterior to the lobes descends, passing along the lateral margin of the thyroid gland and prevent the lobes from moving of the thyrohyoid muscle, to reach the upward in the neck. superior pole of the lateral lobe of the u The lobes of the thyroid gland can be most easily gland where it divides into anterior and palpated by finding the thyroid prominence and arch of the cricoid cartilage and then feeling posterolateral to posterior glandular branches: the larynx. u the anterior glandular branch passes u The isthmus of the thyroid gland crosses anterior to the along the superior border of the upper end of the trachea and can be easily palpated in thyroid gland and anastomoses with its the midline inferior to the arch of the cricoid. twin from the opposite side across the u The presence of the isthmus of the thyroid gland makes isthmus; palpating the tracheal cartilages difficult in the neck. Also, the presence of the isthmus of the thyroid gland u the posterior glandular branch passes and the associated vessels found in and crossing the to the posterior side of the gland and midline makes it difficult to artificially enter the airway anteriorly through the trachea. This procedure, a may anastomose with the inferior tracheostomy, is a surgical procedure. thyroid artery. 29 30 5  11/7/24 Thyroid gland – Arterial supply – Inferior Venous and Lymphatic drainage of the thyroid artery Thyroid gland u The inferior thyroid artery is a branch of the thyrocervical trunk, which arises from the first u Three veins drain the thyroid gland: part of the subclavian artery. It ascends along the medial edge of the anterior scalene muscle, u the superior thyroid vein primarily drains the area supplied by the superior thyroid passes posteriorly to the carotid sheath, and artery; reaches the inferior pole of the lateral lobe of the u the middle and inferior thyroid veins drain the rest of the thyroid gland. thyroid gland. u At the thyroid gland the inferior thyroid artery divides into an: u The superior and middle thyroid veins drain into the u inferior branch, which supplies the lower part of internal jugular vein, and the inferior thyroid veins empty the thyroid gland and anastomoses with the into the right and left brachiocephalic veins, respectively. posterior branch of the superior thyroid artery; and u an ascending branch, which supplies the parathyroid glands. u Lymphatic drainage of the thyroid gland is to nodes beside u Occasionally, a small thyroid ima artery arises the trachea (paratracheal nodes) and to deep cervical from the brachiocephalic trunk or the arch of the nodes inferior to the omohyoid muscle along the internal aorta and ascends on the anterior surface of the trachea to supply the thyroid gland. jugular vein. 31 32 33 34 Parathyroid glands u The parathyroid glands are two pairs of small, ovoid, yellowish structures on the deep surface of the lateral lobes of the thyroid gland. They are designated as the superior and inferior parathyroidglands. However, their position is quite variable and they may be anywhere from the carotid bifurcation superiorly to the mediastinum inferiorly. u Derived from the third (the inferior parathyroid glands) and fourth (the superior parathyroid glands) pharyngeal pouches, these paired structures migrate to their final adult position and are named accordingly. u The arteries supplying the parathyroid glands are the inferior thyroid arteries, and venous and lymphatic drainage follows that described for the thyroid gland. 35 36 6  11/7/24 Thyroid Disorders 37 38 Simple Non-Toxic Goiter u Simple nontoxic goiter, which may be diffuse or nodular, is noncancerous hypertrophy of the thyroid without hyperthyroidism, hypothyroidism, or inflammation. u Except in severe iodine deficiency, thyroid function is normal and patients are asymptomatic except for an obviously enlarged, nontender thyroid. Simple non-toxic goiter u Diagnosis is clinical and with determination of normal thyroid function. u Treatm ent is directed at the underlying cause, but partial surgical rem oval m ay be required for very large goiters. 39 40 Hyperthyroid (Thyrotoxicosis) u Hyperthyroidism may result from increased synthesis and secretion of thyroid hormones (thyroxine [T 4 ] and triiodothyronine [T 3 ]) from the thyroid, caused by thyroid stim ulators in the blood or by autonom ous thyroid hyperfunction. u It can also result from excessive release of thyroid hormone from the thyroid without increased synthesis. u Such release is commonly caused by the destructive changes of various types Hyperthyroidism (Thyrotoxicosis) of thyroiditis. Various clinical syndromes also cause hyperthyroidism. 41 42 7  11/7/24 Hyperthyroidism (Thyrotoxicosis) Hyperthyroidism (Thyrotoxicosis) u The clinical presentation may be dramatic or u Signs may include warm, moist skin; tremor; tachycardia; widened pulse pressure; atrial fibrillation; and palpitations. subtle. u Eye signs include stare, eyelid lag, eyelid retraction, and mild u A goiter or nodule may be present. conjunctival injection and are largely due to excessive adrenergic stimulation. u Many common symptoms of hyperthyroidism u Infiltrative dermopathy, also called pretibial myxedema (a confusing are similar to those of adrenergic excess, such term, because myxedema suggests hypothyroidism), is characterized by nonpitting infiltration by proteinaceous ground substance, usually as nervousness, palpitations, hyperactivity, in the pretibial area. increased sweating, heat hypersensitivity, u The lesion is often pruritic and erythematous in its early stages and fatigue, increased appetite, weight loss, subsequently becomes brawny. Infiltrative dermopathy may appear years before or after hyperthyroidism. insomnia, weakness, and frequent bowel movements (occasionally diarrhea). u Hypomenorrhea may be present. 43 44 Grave’s Disease u the most common cause of hyperthyroidism, is characterized by hyperthyroidism and one or more of the following: u Goiter u Exophthalmos u Infiltrative dermopathy u Graves disease is caused by an autoantibody against the thyroid receptor for thyroid- stimulating hormone (TSH); unlike most Hypothyroidism autoantibodies, which are inhibitory, this autoantibody is stimulatory, thus causing continuous synthesis and secretion of excess T 4 and T 3. 45 46 Hypothyroidism Cretinism u a condition of severely stunted physical and mental u Hypothyroidism is thyroid hormone deficiency. growth due to untreated congenital deficiency of u Symptoms may include cold intolerance, constipation, forgetfulness, and thyroid hormones (congenital hypothyroidism). personality changes. u Thyroid gland may be congenitally absent u Modest weight gain is largely the result of fluid retention and decreased u In this case the child is physically and mentally metabolism. retarded. u Infant screening test detects the hypo secretion of u Paresthesias of the hands and feet are common, often due to carpal-tarsal this hormone. tunnel syndrome caused by deposition of proteinaceous ground substance in the ligaments around the wrist and ankle. u Characteristic features : u thick skin that becomes dry, wrinkled and sallow u Women with hypothyroidism may develop menorrhagia or secondary amenorrhea. u tongue is enlarged, lips thickened u The facial expression is dull; the voice is hoarse and speech is slow; facial u mouth is open and drooling saliva puffiness and periorbital swelling occur due to infiltration with the u enlargement of the abdomen mucopolysaccharides hyaluronic acid and chondroitin sulfate; eyelids droop u Delayed motor development because of decreased adrenergic drive; hair is sparse, coarse, and dry; and the skin is coarse, dry, scaly, and thick. u Coarse hair u Managem ent includes treatm ent of the cause and adm inistration of thyroxine. u Short stature (dwarfism) 47 48 8  11/7/24 Adrenal Glands u The adrenal glands are wedges of glandular and neuroendocrine tissue adhering to the top of the kidneys by a fibrous capsule. u The adrenal glands have a rich blood supply and experience one of the highest rates of blood flow in the body. u They are served by several arteries branching off the aorta, including the suprarenal and renal arteries. u Blood flows to each adrenal gland at the adrenal cortex and then drains into the adrenal medulla. u Adrenal hormones are released into the circulation via the left and right suprarenal veins. 49 50 Adrenal Glands Pheochromocytoma u The adrenal gland consists of an u Pheochromocytoma is a catecholamine-secreting tumor of chromaffin cells (NOREPINEPHRINE) typically located in the adrenal medulla. outer cortex of glandular tissue and u S/Sx : an inner medulla of nervous tissue. u sudden & severe hypertension u The cortex itself is divided into u Heart racing & palpitations three zones: the zona glomerulosa, u Sudden headache the zona fasciculata, and the zona u Heavy sweating reticularis. u Diagnosis is by measuring catecholamine products in blood or urine. u Each region secretes its own set of u Imaging tests, especially CT or MRI, help localize tumors. hormones. u Treatment involves removal of the tumor when possible. u Drug therapy for control of BP includes α-blockade, usually combined with β-blockade. 51 52 Pancreas Pancreas u The pancreas lies m ostly posterior to the stom ach. It extends across the posterior abdom inal w all from the duodenum , on u The pancreatic duct begins in the tail of the the right, to the spleen, on the left. pancreas. It passes to the right through the body u The pancreas is (secondarily) retroperitoneal except for a of the pancreas and, after entering the head of sm all part of its tail and consists of a head, uncinate process, the pancreas, turns inferiorly. neck, body, and tail. u In the lower part of the head of the pancreas, the u The head of the pancreas lies w ithin the C-shaped pancreatic duct joins the bile duct. The joining of concavity of the duodenum. these two structures forms the hepatopancreatic u Projecting from the low er part of the head is the ampulla (ampulla of Vater), which enters the uncinate process, w hich passes posterior to the superior descending (second) part of the duodenum at the m esenteric vessels. major duodenal papilla. Surrounding the ampulla is the sphincter of ampulla (sphincter of Oddi), u The neck of the pancreas is anterior to the superior which is a collection of smooth muscles. m esenteric vessels. Posterior to the neck of the pancreas, the superior m esenteric and splenic veins join to form the u The accessory pancreatic duct empties into the portal vein. duodenum just above the major duodenal papilla u The body of the pancreas is elongate and extends from at the minor duodenal papilla. the neck to the tail of the pancreas. u The tail of the pancreas passes betw een layers of the splenorenal ligam ent. 53 54 9  11/7/24 Exocrine Pancreas Endocrine Pancreas u Distributed throughout the gland are groups of u It consists of a large number of lobules made up of small specialized cells called the pancreatic islets (of alveoli, the walls of which consist of secretory cells. Langerhans). Alpha cells – glucagon u Each lobule is drained by a tiny duct and these unite u Beta cells – insulin eventually to form the pancreatic duct, which extends the u Delta cells – somatostatin whole length of the gland and opens into the duodenum. u u PP cells – pancreatic polypeptide u Just before entering the duodenum the pancreatic duct joins u The islets have no ducts so the hormones the common bile duct to form the hepatopancreatic ampulla. diffuse directly into the blood. The duodenal opening of the ampulla is controlled by the u The function of the endocrine pancreas is to hepatopancreatic sphincter (of Oddi). secrete the hormones insulin and glucagon, which are principally concerned with control of u The function of the exocrine pancreas is to produce blood glucose levels. pancreatic juice containing enzymes that digest carbohydrates, proteins and fats. 55 56 Function of the Pancreas u As part of the endocrine system, the pancreas secretes two main hormones that are vital to regulating glucose (also known as blood sugar) level: u Insulin. The pancreas secretes this hormone to lower blood glucose when levels get too high. u Glucagon: The pancreas secretes this hormone to increase blood glucose when levels get too low. u Balanced blood glucose levels play a significant role in the liver, kidneys, Testes & Ovaries and even brain. Proper secretion of these hormones is important to many bodily systems, such as your nervous system and cardiovascular system. 57 58 Testes Testes u The testes are located within the scrotum, u Inside the scrotum, the testes are covered with the epididymis situated on the almost entirely by the tunica vaginalis, a closed posterolateral aspect of each sac of parietal peritoneal origin that contains a testicle. Commonly, the left testicle lies lower small amount of viscous fluid. than the right. They are suspended from the abdomen by the spermatic cord – u This sac covers the anterior surface and sides of collection of vessels, nerves and ducts that each testicle and works much like the peritoneal supply the testes. sac, lubricating the surfaces of the testes and allowing for friction-free movement. u Originally, the testes are located on the posterior abdominal wall. During u The testicular parenchyma is protected by embryonic development they descend down the tunica albuginea, a fibrous capsule that the abdomen, and through the inguinal canal encloses the testes. It penetrates into the to reach the scrotum. They carry their parenchyma of each testicle with diaphragms, neurovascular and lymphatic supply with dividing it into lobules. them. 59 60 10  11/7/24 Testes Ovaries u The female gonads are called the ovaries u The testes have an ellipsoid shape. They consist of a series of lobules, each u The ovaries are paired, oval organs attached to containing seminiferous tubules supported the posterior surface of the broad ligament of the by interstitial tissue. uterus by the mesovarium (a fold of peritoneum, continuous with the outer surface of the ovaries). u The seminiferous tubules are lined by Sertoli u Neurovascular structures enter the hilum of the cells that aid the maturation process of the spermatozoa. ovary via the mesovarium. u In the interstitial tissue lie the Leydig cells that u The main functions of the ovaries are: are responsible for testosterone production. u To produce oocytes (female gametes) in preparation for fertilization. u Spermatozoa are produced in the seminiferous tubules. The developing sperm travels through u To produce the sex steroid the tubules, collecting in the rete testes. hormones estrogen and progesterone, in response to pituitary gonadotrophins (LH and FSH). u Ducts known as efferent tubules transport the sperm from the rete testes to the epididymis for storage and maturation. 61 62 Thank you ! 63 64 11