Thyroid and Suprarenal Gland Dr Sandip Shah Dept of Anatomy BPKIHS
Thyroid GlandLower part of the front & sides of the neck.Weight-25gmCapsules—True capsule & false capsule IMPORTANCE
Location & Extent-C5-T1, embracing the upper part of the trachea.-Lobe =the middle of the thyroid cartilage to 4th -5th tracheal ring.-Isthmus = 2nd -4th tracheal ring. Suspensory Ligament of Berry Pyramidal lobe-Levator of TG
FunctionsA) Regulates the BMRB) Stimulates somatic & psychic growth.C) Plays an important role in calcium metabolism.
DevelopmentPharyngeal outgrowths that migrate caudally to their final position asdevelopment continues.Foramen caecum of the tongue indicates the site of origin and thethyroglossal duct marks the path of migration of the thyroid gland to itsfinal adult location.Thyroglossal duct usually disappears early in development, but remnantsmay persist as a cyst or as a connection to the foramen caecum (i.e. afistula).There may also be remains of the thyroid gland: associated with thetongue (a lingual thyroid); along the path of migration; or, upward fromthe gland along the path of the thyroglossal duct (a pyramidal lobe).
Lobes -Conical -- Apex, Base, 3 surfaces( Lat, Medial & Posterolateral), 2 borders( Ant & Post)• Ant border—Ant. Branch of the Sup thyroid art.• Post border—Inf. Thyroid art, parathyroid glands.
Relation• Apex—Upwards & Laterally, attached to the sternothyroid to the oblique line of the thyroid cartilage.• Base– 4th -5th tracheal ring.• Lateral –Sternothyroid, Sup. Belly of Omohyoid, Sternohyiod, Ant. Border of SCM muscle.• Medial – 2 tubes( Trachea & Oesophagus), 2 muscles( Inf.constrictor,Cricothyroid), 2 nerves( External & Recurrent laryngeal)• Posterolateral—Carotid sheath
Blood supplySup. & Inf thyroid artery SIGNIFICANCE STA- First branch of ECA Descent passing along the lateral margin of the thyrohyoid muscle, to reach the superior pole of the lateral lobe of the gland where it divides into anterior and posterior glandular branches:
• Inferior thyroid artery is a branch of the thyrocervical trunk, which arises from the first part of the subclavian artery .• It ascends along the medial edge of the anterior scalene muscle, passes posteriorly to the carotid sheath, and reaches the inferior pole of the lateral lobe of the thyroid gland.• Two br- inferior and ascending (parathyroid)
Thyroid ima arteryOccasionally(3%), a small thyroid ima arteryArises from the brachiocephalic trunk or the arch of the aortaAscends on the anterior surface of the trachea to supply the thyroid gland.
-Sup, middle ,inf thyroid vein ,4th Kochervein-Nerve supply—mainly from the middlecervical ganglion & partly from superior &inferior cervical ganglion .-Lymphatic – Deep cevical node.
Microanatomy• Unique among the human endocrine glands in that it stores large amounts of hormone in an inactive form within extracellular compartments in the centre of follicles; in contrast, other endocrine glands store only small quantities of hormones in intracellular sites.• Thyroid follicles store thyroglobulin, an iodinated glycoprotein, the storage form of thyroxine (T4) and tri-iodothyronine (T3).
• The follicles are lined by epithelial cells which are initially responsible for the synthesis of the glycoprotein component of thyroglobulin and for the conversion of iodide to iodine, the iodine linking to the glycoprotein in the follicle lumen.• When active thyroid hormone is required, the same thyroid epithelial cells remove some of the stored thyroid colloid and detach T3 and T4, which then pass through the cell into an adjacent capillary.• When inactive, thyroid epithelial cells are simple flat or cuboidal cells, but when actively synthesising or secreting thyroid hormone they are tall and columnar.
Thyroid C cell• Clear or light cell• Ultrastructural characteristics of neuroendocrine cells, the C cell or parafollicular cell C, is found in the thyroid gland as individual scattered cells in the follicle lining, or as small clumps in the interstices between follicles.• These cells secrete calcitonin, which is a physiological antagonist to parathormone and therefore lowers blood calcium levels by suppressing the osteoclastic resorption of bone.
Thyroid gland pathologyDiffusely or focally enlarged(numerous causes)Thyroid gland may under- or oversecrete the hormone thyroxine.• One of the commonest disorders of the thyroid gland is a multinodular goiter, which is a diffuse irregular enlargement of the thyroid gland with areas of thyroid hypertrophy and colloid cyst formation. Most patients are euthyroid (i.e. have normal serum thyroxine levels).• Immunological diseases may affect the thyroid gland and may overstimulate it to produce excessive thyroxine.• These diseases may be associated with other extrathyroid manifestations, which include exophthalmos, pretibial myxedema, and nail changes.• Other causes of diffuse thyroid stimulation include viral thyroiditis.• Some diseases may cause atrophy of the thyroid gland, leading to undersecretion of thyroxine (myxedema).
Ultrasound easily demonstrates their nature and position, andtreatment is by surgical excision and Nuclear Scan
Thyroid gland Thyroidectomy - For benign diseases such as multinodular goiter. possibility of damaging other structures when carrying out a thyroidectomy, namely• The parathyroid glands (which may be excised en masse with the thyroid gland),• The recurrent laryngeal nerve,• The sympathetic trunk, and• Rarely, the nerves of the carotid sheath.
• Pair of important endocrine glands situated on the posterior abdominal wall• Over the upper pole of the kidneys behind the peritoneum• lies in the Epigastrium, in front of the crus of the diaphragm, opposite the vertebral end of the 11th intercostal space and the 12th rib.
• 50 mm in height, 30mm in breadth, 10 mm in thickness, 5 gm in weight.• They are made up of 2 partsa) An outer cortex- mesodermal origin which secrets a number of steriod hormones.b) An inner medulla- neural crest origin, which is made up of chromaffin cells and secrets adrenalin & noradrenallin (catecholamines)
Right LeftShape Pyramidal SemilunarParts Apex-bare area of liver Upper end-close to spleen Base-upper pole of right liver Lower end – hilum left veinAnterior surface IVC, Bare area of liver Cardiac end of stomach,pancreas with splenic arteryPosterior Rt crus of diaphragm,rt kidney Left crus of diaphragm,leftsurface kidneyAnterior border Hilum-right hilum --------Medial border Coeliac ganglia Coeliac gangliaLateral border Liver stomach
• The vascular system of the cortex C consists of an anastomosing network of capillary sinusoids supplied by branches of the subcapsular plexus, known as short cortical arteries.• The medulla is supplied by long cortical arteries which descend from the subcapsular plexus through the cortex into the medulla where they ramify into a rich network of dilated capillaries surrounding the medullary secretory cells.
• Adrenal cortex has a similar embryological origin to the gonads and, like them, secretes a variety of steroid hormones all structurally related to their common precursor, cholesterol. The adrenal steroids may be divided into three functional classes, mineralocorticoids, glucocorticoids and sex hormones. The mineralocorticoids are concerned with electrolyte and fluid homeostasis. The glucocorticoids have a wide range of effects on carbohydrate, protein and lipid metabolism. Small quantities of sex hormones are secreted by the adrenal cortex and supplement gonadal sex hormone secretion.• Adrenal medulla secretes the catecholamine hormones, adrenaline (epinephrine) and noradrenaline (norepinephrine).
• The zona glomerulosa G(1/5th) is composed of cells arranged in irregular ovoid clusters separated by delicate fibrous trabeculae T continuous with the fibrocollagenous capsule Cap; both the trabeculae and inner capsule contain prominent capillaries.• The cells have round nuclei and less cytoplasm than the cells in the adjacent zona fasciculata.• The cytoplasm contains plentiful smooth endoplasmic reticulum and numerous mitochondria, but with only scanty lipid droplets.
• The zona fasciculata(3/5 th) is the middle and broadest of the three cortical zones.• It consists of narrow columns and cords of cells, often only one cell thick, separated by fine strands of collagen and wide bore capillaries.• The cell cytoplasm is abundant and pale staining due to the large number of lipid droplets present; mitochondria and smooth endoplasmic reticulum are also abundant.
• The zona reticularis(1/5th) R is the thin innermost layer of the adrenal cortex, and lies next to the adrenal medulla M.• It consists of an irregular network of branching cords and clusters of glandular cells separated by numerous wide diameter capillaries.• The zona reticularis cells are much smaller than those of the adjacent zona fasciculata with less cytoplasm.• The cytoplasm is darker staining because it contains considerably fewer lipid droplets. Brown lipofuscin pigment is sometimes seen in the cells of this layer.• The zona reticularis secretes small quantities of androgens and glucocorticoids.
Adrenal medulla• The adrenal medulla secretes the amines adrenaline (epinephrine) and noradrenaline (norepinephrine) under the control of the sympathetic nervous system.• When stained with the standard H [amp ] E method the adrenal medulla is composed of clusters of cells with granular, faintly basophilic cytoplasm, with numerous capillaries in their fine supporting stroma.• Venous channels V draining blood from the sinusoids of the cortex pass through the medulla towards the central medullary vein.
APPLIED ANATOMY• The excess hormone may be produced by a benign tumour (adrenal cortical adenoma) or a malignant tumour (adrenal cortical carcinoma), or by diffuse hyperplasia of the adrenal cortex.• Destruction of both adrenals (for example, by autoimmune adrenalitis or, in former years, by tuberculosis) leads to failure of secretion of all adrenal cortical hormones (hypoadrenalism), leading to the clinical syndrome called Addisons disease (weakness, tiredness, skin pigmentation, postural hypotension, hypovolaemia and low blood sodium).
• More common is hyperadrenalism where there is excess secretion of one or more of the cortical hormones, mainly glucocorticoids (producing Cushings syndrome- obesity,hirustism diabetes and hypogonadism) or mineralocorticoids (producing Conns syndrome) or virilism(excessive androgens may cause masculinization) or male excessive estrogen cause feminisation—breast enlargement• Children-excessive sex hormones cause adrenogenital syndrome— pseudohermaphroidism• Tumor of medulla-Pheochromocytoma---HTN,Excessive sweating,pallor of skin