Thyroid_Gland_final (2).pptxllllllllllllllllll
- 1. Dr BS Kushwah Institute of Medical Sciences Department of Anatomy
- 2. Thyroid Gland – Anatomy & Clinical Correlation Group 6 – Anatomy Department, MBBS 1st Year Group Members:- ARYAN GUPTA (Roll No:26) ASHWARYA KUMARI (Roll No:27) ATUL CHANDRA MANI (Roll No:28) AYUSH GUPTA (Roll No:29) AYUSH NAYAK (Roll No:30)
- 3. Index 1)Introduction and Embryology 2)Gross Anatomy 3)Microscopic Anatomy 4)Blood Supply and Portal System
- 4. Introduction & Embryology of the Thyroid Gland
- 5. Introduction – Thyroid Gland • The thyroid gland is the largest endocrine gland, located in the lower anterior neck. • It spans from vertebral levels C5 to T1 and consists of two lobes connected by an isthmus. • Anatomically located anterior to the trachea, and inferior to the thyroid cartilage. • Its primary functions include regulation of metabolism, growth, and calcium balance. • Produces hormones: T3 (Triiodothyronine), T4 (Thyroxine), and Calcitonin. • Thyroid hormones regulate the basal metabolic rate, Calcitonin lowers blood calcium levels, secreted by parafollicular (C) cells.
- 7. Embryological Origin • Develops from a median endodermal thickening in the floor of the primitive pharynx • Site: Between tuberculum impar and copula (foramen cecum marks origin site) • Proliferation descends in front of the pharyngeal gut as a bilobed diverticulum • During this migration, thyroid remains connected to the tongue via the thyroglossal duct which opens in the tongue via the foramen cecum, which persists as a vestigial pit on the tongue (duct later degenerates).
- 9. Migration & Final Position • Migrates anterior to the hyoid bone and laryngeal cartilages • Reaches its final position in front of the trachea by the 7th week • Thyroglossal duct usually disappears; persistence may form cyst or fistula • A pyramidal lobe of the thyroid may be observed in as many as 50% of patients. This lobe represents a persistence of the inferior end of the thyroglossal duct that has failed to obliterate. • At final site: Gland forms two lobes connected by isthmus
- 11. Timeline of Thyroid Development • Week 3: • Originates from a median endodermal thickening in the floor of the primitive pharynx near the foramen cecum. • Week 4: • Forms a bilobed diverticulum and descends in front of the pharyngeal gut via the thyroglossal duct. • Week 5–7: • Reaches its final position anterior to the trachea. • Thyroglossal duct typically degenerates during this period. • Week 10–12: • Begins functional activity. • Starts producing T3 and T4 under TSH stimulation from the fetal pituitary. • Note: The thyroid is the first endocrine gland to develop, yet among the last to become functional in the fetus.
- 12. Functional Development • Begins Around Week 10–12 of Gestation • Initial Activity: • The thyroid gland begins to function by the end of the first trimester, around Week 10–12. • It is stimulated by TSH (thyroid-stimulating hormone) secreted by the fetal anterior pituitary. • Hormone Synthesis: • Follicular cells start producing thyroid hormones (T3 and T4). • Colloid (a gel-like substance that stores thyroglobulin) appears in the follicles. • These hormones are essential for: • Fetal brain development • Neurogenesis • Bone maturation • Parafollicular (C) Cells: • Derived from the ultimobranchial body (part of the 4th pharyngeal pouch). • Begin secreting calcitonin, which lowers blood calcium levels. • Special Note: • Despite being the first endocrine gland to form, the thyroid is among the last to become functionally active. • Maternal thyroid hormones cross the placenta before fetal production begins and are critical in early fetal development.
- 15. The ventral region of the fourth pouch gives rise to the ultimobranchial body, which is later incorporated into the thyroid gland. Cells of the ultimobranchial body give rise to the parafollicular cells, or C cells, of the thyroid gland. These cells secrete calcitonin, a hormone involved in regulation of the calcium level in the blood.
- 16. Clinical Relevance • Ectopic thyroid tissue: May be found along thyroglossal duct path • Thyroglossal cyst: Midline neck swelling, moves with swallowing or tongue protrusion • Lingual thyroid: Remnant at base of tongue (foramen cecum) • Agenesis or hemiagenesis can cause congenital hypothyroidism • Early development important for fetal brain maturation and skeletal growth
- 17. Ectopic Thyroid Tissue • Ectopic thyroid tissue refers to thyroid tissue located outside its normal position due to abnormal embryological migration. • Common Sites: - Most commonly found at the base of the tongue (Lingual Thyroid). - Can also be located anywhere along the thyroglossal duct path: from the foramen cecum to the anterior neck. • Clinical Importance: - Sometimes, the ectopic thyroid is the only functioning thyroid tissue in the body. - If removed without proper evaluation, it may result in complete thyroid hormone deficiency. • Diagnosis: - Always confirm the presence or absence of a normally located thyroid gland using imaging (e.g., thyroid scan or ultrasound) before surgical removal.
- 19. Thyroglossal Duct Anomalies •The thyroglossal duct normally degenerates after the thyroid descends. •Persistence leads to: • Thyroglossal duct cyst: A midline neck swelling arising from a remnant of the thyroglossal duct, commonly found near or just below the hyoid bone, but may also occur at the base of the tongue or near thyroid cartilage. •Thyroglossal fistula: May form secondarily after cyst rupture or may be congenital; presents as a canal connecting the cyst to the skin surface.
- 21. Agenesis or Hemiagenesis: •Complete or partial failure of thyroid formation. •Leads to congenital hypothyroidism, risking cretinism, growth retardation, and developmental delay. •Requires early detection through newborn screening. Importance in Fetal Development: •Thyroid hormones are essential for brain and skeletal development. •Maternal thyroid hormones support the fetus until its own thyroid becomes functional (~week 12).
- 22. THYROID GLAND GROSS ANATOMY BY ASHWARYA KUMARI ROLL NO -27
- 23. THYROID GLAND • ENDOCRINE GLAND ,SITUATED IN THE LOWER PART OF THE FRONT AND SIDES OF THE NECK. • EXTENDS : FROM OBLIQUE LINE OF THYROID CARTILAGE TO THE 5TH OR 6TH TRACHEAL RING. • LIE AGAINST C5, C6 ,C7 & T1 • CONSIST RIGHT & LEFT LOBES, JOINED BY ISTHMUS. • A 3RD PYRAMIDAL LOBE MAY PROJECT UPWARDS FROM THE ISTHMUS. • CAPSULES: TWO ;TRUE & FALSE • LARGER IN FEMALES THAN MALES • DEVELOPMENT: FROM THE ENDODERM OF THE FLOOR OF PRIMITIVE ORAL CAVITY IN THE REGION OF THE FUTURE FORAMEN CAECUM AND ULTIMOBRACHIAL BODY.
- 24. RELATIONS OF THE LOBE THE LOBES ARE CONICAL IN SHAPE HAVING APEX BASE THREE SURFACES:LATERAL, MEDIAL, POSTEROLATERAL TWO BORDERS:ANTERIOR AND POSTERIOR APEX: DIRECTED UPWARDS AND SLIGHTLY LATERALLY. BASE: ON LEVEL WITH THE 4TH OR 5TH TRACHEAL RING. LATERAL SURFACE : CONVEX AND COVERED BY • STERNOHYOID • SUPERIOR BELLY OF OMOHYOID • STERNOTHYROID • ANTERIOR BORDER OF STERNOCLEIDOMASTOID
- 25. MEDIAL SURFACE: • 2 TUBES – TRACHEA AND OESOPHAGUS • 2 MUSCLES – INFERIOR CONSTRICTOR AND CRICOTHYROID • 2 NERVES- EXTERNAL LARYNGEAL AND RECURRENT LARYNGEAL
- 26. POSTEROLATERAL SURFACE : CAROTID SHEATH AND OVERLAPS COMMON CAROTID ARTERY ANTERIOR BORDER: ANTERIOR BRANCH OF SUPERIOR THYROID ARTERY POSTERIOR BORDER: SEPARATES MEDIAL AND POSTERIOR SURFACES INFERIOR THYROID ARTERY ANASTOMOSIS BETWEEN SUPERIOR AND INFERIOR THYROID ARTERIES PARATHYROID GLANDS ON LEFT SIDE THORACIC DUCT
- 27. RELATIONS OF ISTHMUS ANTERIOR SURFACES : COVERED BY STERNOTHYROID AND STERNOHYOID ANTERIOR JUGULAR VEIN CONNECTS LOWER BODY PARTS OF THE 2 LOBES . FASCIA AND SKIN POSTERIOR SURFACES : 2ND TO 4TH TRACHEAL RINGS. UPPER BORDER: ANASTOMOSIS B ETWEEN RIGHT AND LEFT SUPERIOR THYROID ARTERIES . LOWER BORDER : INFERIOR THYROID VEINS
- 28. Microscopic Anatomy of thyroid gland
- 30. Histology of thyroid gland • Thyroid gland is covered by thin connective tissue capsule. Septa arising from capsule divide the gland into number of lobules. • • Thyroid gland is made up of follicles lined by simple cuboidal epithelium (ranges from squamous to low columnar) with rounded nuclei. • • Lumen of follicle contains pink homogeneous colloid material that consists of thyroglobulin.
- 31. • Few parafollicular/C-cells are present in relation to follicles. C-cells secrete calcitonin that reduces blood calcium levels. • • In between follicles, rich vascular connective tissue is present.
- 33. BLOOD SUPPLY OF THYROID GLAND
- 35. ARTERIAL SUPPLY THE gland is highly vascular and is supplied by the following arteries 1.SUPERIOR THYROID ARTERY :- It is the branch of the external carotid artery . 2.INFERIOR THYROID ARTERY :- It is the branch of the thyrocervical trunk 3.THYROIDEA IMA ARTERY ( in 30 % cases ) :- It is a branch of the brachiocephalic trunk 4.ACCESSORY THYROID ARTERY :- They arise from the tracheal and esophageal artreries
- 36. COURSES AND BRANCHES OF THYROIDAL ARTERIES Superior Thyroid Artery • Runs downwards & forwards with external laryngeal nerve • Divides at apex into anterior & posterior branches • Anastomoses at anterior border and with inferior thyroid artery posterior branc • Supplies upper 1/3 of lobe and upper isthmus Inferior Thyroid Artery • Runs upwards along medial border of scalenus anterior • Passes behind carotid sheath to thyroid lobe • Related to recurrent laryngeal nerve (variable positions) • Gives 4-5 branches, ascending branch anastomoses with superior thyroid artery posterior branch • Supplies lower 2/3 of lobe and lower isthmus
- 37. VEINOUS DRAINAGE OF THYROID GLAND 1.Superior thyroid vein: It emerges at the upper pole of the thyroid lobe, runs upwards and laterally, and drains into the internal jugular vein. 2.Middle thyroid vein: This short, wide venous channel emerges at the middle of the lobe to soon enter the internal jugular vein. 3.Inferior thyroid vein/veins: They emerge at the lower border of the isthmus, form plexus in front of the trachea and then run downwards to drain into the left brachiocephalic vein. 4.Sometimes a fourth vein, the thyroid vein (of Kocher) emerges between the middle and inferior thyroid veins to drain into the internal jugular vein.
- 38. Portal system of thyroid gland The portal system of the thyroid gland refers to the specialized blood circulation that involves the thyroid gland and its regulation by the hypothalamus and pituitary gland. In the thyroid, the "portal system" is typically associated with the hypothalamo-pituitary-thyroid (HPT) axis and the regulation of thyroid hormones
- 39. In the context of the hypothalamic-pituitary-thyroid axis, thyroid hormone regulation follows a different form of portal-like system: Hypothalamus secretes TRH (Thyrotropin-Releasing Hormone). TRH travels through the hypophyseal portal system (a specialized system of blood vessels) to reach the anterior pituitary. The anterior pituitary then secretes TSH (Thyroid Stimulating Hormone) into the bloodstream, which signals the thyroid gland to produce and release T3 and T4 thyroid hormones. This is the regulatory pathway that maintains thyroid hormone levels in the body, with the "portal" referring to the circulation of hormones between the hypothalamus and pituitary gland, directing the thyroid's activity.
- 40. Why It's Not a True Portal System? A true portal system, like the hepatic portal system, involves blood passing through two capillary beds before returning to systemic circulation. In the thyroid, blood flows from arteries to capillaries and then directly to veins, without a second capillary network. Thus, the thyroid's vascular system is better described as a highly vascularized network optimized for hormone secretion rather than a portal system
- 41. CLINICAL CORRELATION Presented by:- AYUSH NAYAK ROLL:- 30
- 42. Swelling of the Thyroid Gland and Movement on Swallowing:- • The thyroid gland is invested in a sheath derived from the pretracheal fascia. This tethers the gland to the larynx and the trachea and explains why the thyroid gland follows the movements of the larynx in swallowing. This information is important because any pathologic neck swelling that is part of the thyroid gland will move upward when the patient is asked to swallow.
- 43. The Thyroid Gland and the Airway:- • The close relationship between the trachea and the lobes of the thyroid gland commonly results in pressure on the trachea in patients with pathologic enlargement of the thyroid
- 44. Retrosternal Goiter:- • The attachment of the sternothyroid muscles to the thyroid cartilage effectively binds down the thyroid gland to the larynx and limits upward expansion of the gland. There being no limitation to downward expansion, it is not uncommon for a pathologically enlarged thyroid gland to extend downward behind the sternum. A retrosternal goiter (any abnormal enlargement of the thyroid gland) can compress the trachea and cause dangerous dyspnea; it can also cause severe venous compression.
- 45. Thyroid Arteries and Important Nerves:- • It should be remembered that the two main arteries supplying the thyroid gland are closely related to important nerves that can be damaged during thyroidectomy operations. The superior thyroid artery on each side is related to the external laryngeal nerve, which supplies the cricothyroid muscle. The terminal branches of the inferior thyroid artery on each side are related to the recurrent laryngeal nerve. Damage to the external laryngeal nerve results in an inability to tense the vocal folds and in hoarseness. For the results of damage to the recurrent laryngeal nerve.
- 46. Thyroidectomy and Parathyroid Glands:- • The parathyroid glands are usually four in number and are closely related to the posterior surface of the thyroid gland. In partial thyroidectomy, the posterior part of the thyroid gland is left undisturbed so that the parathyroid glands are not damaged. The development of the inferior parathyroid glands is closely associated with the thymus. For this reason, it is not uncommon for the surgeon to find the inferior parathyroid glands in the superior mediastinum because they have been pulled down into the thorax by the thymus.
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