MBBS PRGRAM DEPARTMENT OF ANATOMY ENDOCRINE GLANDS Presented By PROF Dr / YOUSRY M SHAWKY
Characteristics of EG : 1. They have NO ducts and discharge their secretion (hormones) directly in blood. 2. They have rich blood Supply. 3. They are simple in structure: They consist of cords and plates of cells separated by blood vessels. ENDOCRINE GLANDS
It is a reddish-grey, ovoid body, about 12 mm in transverse and 8 mm in anteroposterior diameter and weighs about 500 mg. It lies within the hypophyseal fossa of the sphenoid bone. It is covered superiorly by a diaphragma sellae of dura mater which is pierced centrally by the infundibulum and separates the gland from the optic chiasma. Inferiorly & in front it is related to the sphenoid air sinus. It is related on either side to the cavernous sinus. It is related behind to dorsum sellae. Pituitary Gland (Hypophysis Cerebri)
The pituitary gland consists of : A) Anterior lobe (adenohypophysis) : Consists of: - Pars distalis - Pars tuberalis - Pars intermedia B) Posterior lobe (neurohypophysis) : Consists of pars nervosa which is connected by infundibulum (pituitary stalk) to the median eminence (tuber cinereum) of hypothalamus.
Pars distalis is formed of : Thick irregular cords of cells + blood sinusoids There are 2 types of cells: a) Chromophobes: About 50% of the cells. They are small, found in groups and have NO GRANULES in their cytoplasm. b) Chromophils: The other 50% of the cells. They have GRANULES in their cytoplasm and are larger than the chromophobes.There are 2 types of chromophil cells: — ACIDOPHILS (10%): have reddish cytoplasm. They secrete growth hormone (GH) & Prolactin (lactogenic) H. — BASOPHILS (40%): have bluish cytoplasm. They secrete TSH, ACTH, FSH & LH. In general basophils are larger in size and stain deeper than the acidophils.
Cells and hormones of the anterior pituitary gland & their functions Cell Hormone secreted Function Somatotropes (Acidophilic) Growth H (somatotropin) Stimulates body growth Mammotropes (Acidophilic) Prolactin (PRL) Stimulates milk production & secretion Thyrotropes (Basophilic) Thyroid Stimulating H (TSH) Stimulates production of thyroid H by follicular cells Gonadotropes (Basophilic) <ul><li>Follicle Stimulating Hormone (FSH. </li></ul><ul><li>Luteinizing H (LH) </li></ul>-Stimulates follicular cells in ovary & spermatogenesis in testis. - Stimulates production of estrogen & progesterone from the ovary & testosterone from the testis Corticotropes (Basophilic) Adreno-Cortico Trophic H (ACTH or corticotropin) Stimulates secretion of glucocorticoids & androgens from adrenal cortex
<ul><li>Pars nervosa contains : </li></ul><ul><li>a) Bundles of nerve fibers. </li></ul><ul><li>b) Cells called pituicytes. </li></ul><ul><li>c) homogenous intercellular substance: on fixation it precipitates to form Herring’s body. </li></ul><ul><li>The bundles of nerve fibers in the pars nervosa arise in the hypothalamus and descend to the posterior lobe forming the hypothalamo-hypophyseal tract (HHT). </li></ul><ul><li>The hormones secreted by nerve cells in the hypothalamus travel down along the HHT & accumulate at the end of the tract in pars nervosa as Herring’s bodies. </li></ul><ul><li>It secretes Vasopressin or ADH (Anti Diuretic H) & Oxytocin. </li></ul>
<ul><li>Lies in the lower part of the neck at the level of the 5 th cervical to the 1 st thoracic vertebrae. </li></ul><ul><li>It is formed of 2 lobes connected by an isthmus. </li></ul><ul><li>Each lobe pyramidal in shape with an apex, a base & 3 surfaces (medial, lateral & posterior). </li></ul><ul><li>Each lobe is about 5 x 3 x 2 cm (length x width x thickness). </li></ul><ul><li>The apex is at the level of oblique line of thyroid cartilage of the larynx. </li></ul><ul><li>The base is at the level of the 4 th or 5 th tracheal ring. </li></ul>THE THYROID GLAND
<ul><li>The anterior border is thin & related to the anterior branch of the superior thyroid artery. It is continuous below with the upper border of the isthmus. </li></ul><ul><li>The posterior border is rounded & is related below to the inferior thyroid artery and its anastomosis with the posterior branch of the superior thyroid artery. The parathyroid glands are usually related to this border. </li></ul>
<ul><li>The medial surface is related to : </li></ul><ul><li>Larynx, pharynx & external laryngeal nerve. </li></ul><ul><li>Trachea, esophagus & recurrent laryngeal nerve. </li></ul>Larynx Pharynx Esophagus Trachea Recurrent laryngeal n Ext laryngeal n Thyrocervical trunk Inferior thyroid artery CCA IJV
<ul><li>The lateral surface is related to : </li></ul><ul><li>Skin, superficial fascia with platysma m. </li></ul><ul><li>Deep fascia. </li></ul><ul><li>Muscles: sternomastoid, infrahyoid muscles (except thyrohyoid). </li></ul><ul><li>The posterior surface is related to : </li></ul><ul><li>Carotid sheath (overlapping common carotid artery). </li></ul><ul><li>The thyroid gland is found within the pretracheal fascia which is connected above to the thyroid cartilage that is why the galnd moves up & down with deglutition. </li></ul>sternomastoid infrahyoid muscles Carotid sheath Trachea Esophagus sternomastoid Pretracheal fascia
Thyroid isthmus : Lies opposite 2 nd & 3 rd tracheal rings & is covered by sternohyoid & sternothyroid muscles. It measures about 1.25 x 1.25 cm (length x width). The anterior branches of the superior thyroid arteries anastomose along its upper border. A conical pyramidal lobe is often present along its upper border (usually to the left). A fibrous or fibromuscular cord connects its apex to the hyoid bone (6) known as levator glandulae thyroideae (5).
<ul><li>Blood supply of thyroid gland : </li></ul><ul><li>Arterial supply : </li></ul><ul><li>Superior thyroid artery : Arises from the external carotid artery. It descends downwards & forwards to the gland accompanied by the external laryngeal nerve from which it becomes separated at the apex of the gland. It divides at the apex of the gland into anterior & posterior branches which descends on the anterior & posterior borders of the gland. </li></ul><ul><li>Inferior thyroid artery : Arises from the thyrocervical trunk of subclavian artery. It becomes related to the recurrent laryngeal nerve at the post surface of the gland. It gives ascending branch which anastomoses with the posterior branch of the superior thyroid artery. </li></ul><ul><li>Thyroidea ima artery : </li></ul><ul><li>A small artery that supplies the isthmus & arises from the arch of aorta or the brachiocephalic artery. </li></ul>
<ul><li>B) Venous drainage : </li></ul><ul><li>Thyroid gland is drained by: </li></ul><ul><li>Superior & middle thyroid veins which end usually in the internal jugular vein. </li></ul><ul><li>Inferior thyroid vein ends in the brachiocephalic vein. </li></ul><ul><li>Lymphatic drainage : </li></ul><ul><li>It is drained by lymph nodes beside the trachea (paratracheal nodes) and to deep cervical nodes inferior to the omohyoid muscle along the internal jugular vein. </li></ul>IJV IJV Brachiocephalic v middle thyroid vein middle thyroid vein inferior thyroid vein Superior thyroid vein
<ul><li>Clinical Anatomy </li></ul><ul><li>Any thyroid swelling is a goitre, which may press on related structures. Symptoms are most commonly due to pressure on the trachea or on the recurrent laryngeal nerves. </li></ul><ul><li>During thyroidectomy; if the external laryngeal nerve (which supplies cricothyroid muscle which tenses the vocal folds) is damaged, the voice becomes low pitched. </li></ul>
<ul><li>During tying of the superior thyroid artery, the external laryngeal nerve may be injured (tie it very near to the gland). </li></ul><ul><li>During tying of the inferior thyroid artery, the recurrent laryngeal nerve may be injured (tie it away from the gland). Temporary aphonia sometimes follows bruising of the nerve; complete division reduces the voice to a whisper. </li></ul><ul><li>In partial thyroidectomy the posterior parts of both lobes are left intact to preserve the parathyroid glands. </li></ul>
Histology of thyroid gland : The gland has a thin capsule of connective tissue, whose extensions divide it into masses of irregular form and size. The thyroid follicle forms the structural unit of the thyroid gland. Each follicle consists of follicular epithelium (simple cuboidal) and a central mass of colloid. Active follicles generally have "high" epithelium. Each follicle is surrounded by a delicate layer of loose connective tissue, containing a capillary network .
<ul><li>Para follicular or C cells are located near the follicular basement lamina but separated from the lumen of the follicle by follicular epithelium. These cells secrete calcitonin and may be difficult to identify. They are somewhat larger and lighter staining than follicular cells. </li></ul>
PARATHYROID GLANDS The parathyroid glands are small, yellowish-brown, ovoid or lentiform in shape, usually lying between the posterior borders of the thyroid gland and its capsule. They are commonly about 6 x 3 x 1 mm, each weighs about 50 mg. Usually there are two on each side, one superior and one inferior. The superior parathyroid glands are more constant in location than the inferior and are usually midway along the posterior thyroid borders. The inferior pair may be : (1) Above or below the inferior thyroid arteries. (2) In the thyroid gland near its base.
Histology of parathyroid glands: <ul><li>The parathyroid gland has a capsule and is well vascularized. solid cell cords form the gland. </li></ul><ul><li>- principal (chief) cells have a slightly eosinophilic cytoplasm. They produce parathyroid hormone (PTH) </li></ul><ul><li>- oxyphil cells: are larger and very eosinophilic. The function of oxyphil cells is unknown but they may also secrete PTH. </li></ul><ul><li>- Adipose tissue is frequently found in this gland in older individuals. </li></ul>
THE SUPRARENAL (ADRENAL) GLANDS Phrenic a Renal v IVC Hilum Hilum 1 2 3 Renal a They are two small flat yellowish bodies, situated on the upper renal ends. They are enclosed in renal fascia but separated from the kidneys by fibrous tissue. Each in adults measures about 5 X 3 X 1 cm weighing about 5 grams. At birth the gland is about 1/3 the size of a kidney but in adults only 1/13. Right Left Shape Pyramidal semilunar Anterior Relations Liver & IVC Stomach & Pancreas Posterior Relations Diaphragm Medial Relations Celiac ganglion Inferior Relations The kidney Arterial supply: - Superior suprarenal a (1) from the phrenic - Middle suprarenal a (2) from the aorta. - Inferior suprarenal a (3) from the renal Venous drainage Right suprarenal vein drains to IVC Left suprarenal drains to the renal v. The hilum Directed forwards Directed downwards
<ul><li>HISTOLOGY OF ADRENAL GLANDS </li></ul><ul><li>The human adrenal gland is roughly triangular in cross section. </li></ul><ul><li>It is divided into cortex and medulla . </li></ul><ul><li>A) ADRENAL CORTEX : </li></ul><ul><li>The cortex is divided into three zones: </li></ul><ul><li>zona glomerulosa is composed of cells grouped in an ovoid configuration. </li></ul><ul><li>It secretes mineralocorticoids (aldosterone). </li></ul><ul><li>zona fasciculata is composed of lipid-droplet laden cells arranged in radial columns. </li></ul><ul><li>It secretes glucocorticoids (cortisol). </li></ul><ul><li>zona reticularis is composed of a loose meshwork configuration. </li></ul><ul><li>It secretes androgens . </li></ul>
B) ADRENAL MEDULLA : The principal cells of the medulla are the chromaffin cells which can be considered as modified post-ganglionic sympathetic neurons that lack dendrites and axons. They secretes adrenaline & noradrenaline . The medulla contains a large central vein.
THE PANCREAS <ul><li>It is both exocrine & endocrine gland. </li></ul><ul><li>The endocrine part secretes insulin, glucagon & somatostatin hormones which control glucose level in the blood. </li></ul><ul><li>The exocrine part secretes digestive enzymes for proteins, carbohydrates & fat through the main & accessory pancreatic ducts. </li></ul><ul><li>It lies on the posterior abdominal wall behind the stomach. </li></ul><ul><li>It is divided into 4 parts: head, neck, body & tail. </li></ul><ul><li>Its head is surrounded by the duodenum & in front of aorta & IVC. </li></ul>
<ul><li>Structurally, the pancreas consists of serous acini with scattered islets of endocrine tissue. </li></ul><ul><li>ISLETS OF LANGERHANS : </li></ul><ul><li>These are clusters of lighter staining cells. The islets are composed of three cell types: alpha cells, beta cells, and delta cells. These cells cannot be readily distinguished without special stains. </li></ul><ul><li>Alpha cells (15-20%) : </li></ul><ul><li>are found at the periphery and secrete glucagon. </li></ul><ul><li>Beta cells (70%) : </li></ul><ul><li>are found more centrally and secrete insulin. </li></ul><ul><li>Delta cells (5-10%) : </li></ul><ul><li>are found throughout the islet and secrete somatostatin. </li></ul>