ANATOMY OF TYHROID GLAND
– Thyroid gland is an endocrine gland present in lower part of front and sides of neck.
– It regulates basal metabolic rate and has a important role in the calcium metabolism.
– It is roughly H shaped and It has 2 lobes and a isthmus.
* Situation and extent
– Gland lies against the C5, C6, C7 and T1 vertebrae.
– Each love extends from middle lobe of thyroid cartilage to fourth or fifth tracheal rings and Isthmus extends from second to third tracheal rings .
* Dimensions and weight
– Each lobe is measures about 2 inches ( length ) , one inch ( breadth ) and one inch ( thickness).
– The isthmus is 1/2 inch × 1/2 inch . And gland weighs about an average about 25g.
– It has a true capsule and a false capsule.
* Blood supply
– It has superior and inferior thyroid arteries.
• Superior thyroid artery : It is a branch of external carotid artery and supplies upper 1/3 rd of lobe and upper half of isthmus.
• Inferior thyroid artery : It is a branch of thyroid cervical trunk from subclavian artery.
It supplies lower 2/3 rd of lobe and lower half of isthmus.
* Venous drainage
– It has 3 veins
(1) Superior thyroid vein
(2) Middle thyroid vein
(3) Inferior thyroid vein.
* Structure and function
– It has 2 types of secretory cells : follicular and parafollicular cells
– The follicular cells secretes tri-iodo thyronine and tetra-iodo-thyronine.
– This stimulates basal metabolic rate and somatic and psyclic growth of individual.
– The parafollicular cells secretes thyrocalcitonine .
• Applied anatomy
– Goiter : any enlargement in thyroid gland
• THYROID HORMONES
– There are 3 types of thyroid hormones
(1) Tetra-iodo-thyramin ( T4) / thyroxin
(2) Tri-iodo-thyramin ( T3)
PHYSIOLOGY OF THYROID HORMONE
• Synthesis of T3 and T4
– These are produced by thryoid follicles.
– Thyroid follicles are made up of aceni which has a single layer of epithelial cells in centre.
– And it is filled with protein called as a colloid.
• Steps of thyroid hormone synthesis
1) Iodine trapping
– Iodide is present in the blood which is consumed in diet as iodine.
– When it passes through the thyroid gland it is actively taken up and is converted into iodide in acinar cells of thyroid gland.
– Iodine inside the cell is gets oxidised again back to iodine.
– Iodine binds with thyrosine and attached to thyroglobulin
– When the 2 molecules of iodine combined with thyrosine it forms diiodothyrosine.
– When only one molecules of iodine is combines with thyrosine it forms monoiodothyrosine.
– After the formation of diiodothyrosine and monoiodothyrosine , the two molecules of diiodothyrosine is combined to form T4 and one molecule of monoiodothyrosine and one molecule of diiodothyrosine combines to form T3.
5) Release of T3 and T4
– After the formation of T3 and T4 in colloid hormones along with thyroglobulin is taken into acinar cells.
– Lysozymes in the cell releases T3 and T4 from thyroglobulin and then T3 and T4 is released into blood.
– Thyroglobulin is recycled for further hormonal production.
• Functions or actions of thyroid hormone
1) Calorigenic action
– Thyroid hormone increases activity of sodium – potassium pump and there by stimulates BMR.
2) Effects on metabolism
– Carbohydrate metabolism
– Protein metabolism
– Lipid metabolism
– Vitamin metabolism
3) Effects on blood
– Stimulates erythropoiesis hence increase RBC and increase blood volume.
4) On Cardiovascular system
– Increase heart rate
– Increase force of contraction
– Increase cardiac output
– Increase SBP
– Decrease DBP
5) Effects of respiratory system
– Increase respiratory rate
– increase force of respiration
– Increase demand of oxygen
6) On GIT
– Increase Appetite and hunger
– Increase GIT secretion
– Increase GIT motility
7) On CNS
– Thyroid hormone is essential for fetal growth.
– Lack of thyroid hormone during intra uterine life produces mental retardation.
– Thyroid hormone increases blood flow the brain and maintains normal Function of brain .
8) Effects on skeletal muscles
– thyroid hormones are protein catabolic hormones
– They Decrease size and bulk of skeletal muscle
9) Effect on sleep
– Decreases sleep
10) Effect on Reproductive system
– Increases metabolic rate in reproductive system
– In females excess thyroid hormones produces oligomenoria
– In males , excess thyroid hormones produces impotence,
11) Effect on other endocrine glands
– Stimulates activity of endocrine gland.
12) On growth
– Stimulates bone growth and skeletal growth before puberty .
– Increased secretion of thyroid hormone is called as Hyperthyroidism.
1) Grave’s disease : primary
2) Thyroid adenoma : secondary.
• Grave’s disease
– It is an autoimmune disease.
√ B – lymphocytes produces autoimmune antibodies ( thyroid stimulating autoantibodies )
√ They start acting like TSH
√ Hypersecretion of thyroid hormone
• Signs and symptoms
– Exoptalmus proptosis ( protrusion of eye balls due to edematous swelling of retro-orbital tissues leading to optic nerve damage )
– Patient is unable to close eye
– Can lead to dryness of cornea
– Infection , ulceration
– Increased BP
– Cardiac failure
– Hypermobility of intestine which causes vomiting and diarrhea
– Increase muscular weakness
– Edema over skin bones
– Whitish discolouration of skin
– Hair loss
– Mild tremor
– Heat intolerance
6) Oligomenorrhea / Amenorrhea in females
1) Thyroid function test
– T3 , T4 is increased
– TSH is decreased
2) Detection of autoantibodies against thyroglobulin
3) Radioactive iodine uptake is increased
4) Fine needle aspiration
– Hyperplasia of thyroid cells
1) Anti-thyroid drugs
– Helps to suppress production of thyroid hormone
2) Beta – blockers
– To relieve Tachycardia and heart rate
3) Radioactive iodine
– Destruction of functional thyroid cells
* Secondary hyperthyroidism
– Thyroid adenoma
– Sometimes , a localized tumor develops in the functional thyroid cells ( thyroid adenoma ) which secretes large quantity of thyroid hormone.
– Depresses the production of TSH.
– Decreased secretion of thyroid hormone is called as hypothyroidism.
– Primary hypothyroidism : Decreased function of thyroid gland.
– Secondary hypothyroidism : Decreased secretion of thyroid hormone.
– Hypothyroidism in adults.
– Life threatening complication of hypothyroidism.
– Patient goes in state of coma.
– Deposition of myxedematous tissues of various organ.
– Responsible for organ dysfunction
1) Disease of thyroid gland
2) Iodine deficiency.
3) Deficiency of TSH
4) Auto immune
5) GI bleeding
6) Trauma or physical stress
7) Use of sedative diuretics.
*Signs and symptoms of MYXEDEMA
1) Edematous appearence throughout the body
2) Moon face
– Swelling of face
– Bagginess under eyes
– puffiness of face
– Non-pitting type of edema
* General features
2) Weight gain
3) Frog like husky voice
5) Skin – Dry skin
Thick and rough
6) CVS – Bradycardia
7) CNS – Depression
8) Muscle – Stiffness
9) GIT – Constipation
– Iron deficiency anemia.
– Pernicious anemia
– Decrease RBC synthesis
11) Reproductive – Menorrhagia
√ Thyroid function test
– T3 and T4 decreases and TSH increases.
√ Radioactive iodine uptake decrease
√ Fine needle aspiration
– decreased thyroid cells.
– Replacement therapy
– Thyroxine therapy
– Supplementation of thyroid hormone.
– Hypothyroidism in children .
– Congenital absence of thyroid gland
– Genetic disorder
– lack of iodine in diet.
* Features of Cretinism
1) At the time of birth , a newborn baby with hypothyroidism may appear normal because Thyroxine has been supplied from mother.
-But after weeks baby starts developing sluggish movements and croaking sound while crying .
– If not treated early , the baby will be mentally retarded permanently
2) Skeletal growth is affected more than the soft tissues.
– Bloated body.
– Tongue becomes big and there is a dripping of saliva.
– Obstruction in swallowing and breathing.