16.7, 16.8 Thyroid/Parathyroid Glands Flashcards
Butterfly shaped gland in anterior neck on the trachea, just inferior to larynx
Thyroid gland
Median mass connecting two lateral lobes
Isthmus
Hollow sphere of epithelial follicular cells that produce thyroglobulin; Also known as principal cells
Located in thyroid gland
Follicles
Thick fluid containing thyroglobulin proteins with attached iodine, from which thyroid hormone is produced
Colloid
Cells that produce and secrete calcitonin hormone located around follicles
Parafollicular cells
Cells that secrete thyroid hormone
Follicular cells
Body’s major metabolic hormone; Found in two forms:
T4 (Thyroxine) - Major form that consists of two tyrosine molecules with four bound iodine atoms
T3 (Triiodothyronine) - Form that has two tyrosines with three iodine atoms
Lipid soluble like steroid; must travel in bloodstream bound carriers
Thyroid hormone (TH)
Hormone that increases basal metabolic rate and heat production (Calorigenic effect)
Regulates tissue growth and development (Skeletal/NS)
Permissive for epinephrine and norepinephrine
Thyroid hormone (TH)
- Follicular cells take iodinated thyroglobulin via endocytosis
- Endosomes fuse with lysosomes
- Lysosome enzymes digest iodinated thyroglobulin and liberate thyroid hormones (T3 and T4)
- Thyroid hormones diffuse out into the blood and bind to carrier proteins
Synthesis of TH
Occurs by negative feedback
Decrease in TH stimulate release of TSH
Increase TH inhibit release of TSH
TRH can overcome negative feedback during pregnancy or exposure to cold
Regulation of TH
Hyposecretion of TH
Symptoms: low metabolic rate, thick/dry skin, puffy eyes, feeling chilled, constipation, edema, lethargy
Deficient iodine = goiter development (mass on thyroid)
Myxedema
Poor development of thyroid gland in children
May be asymptomatic or present with weak cry, poor feeding, constipation, prolonged jaundice
Congenital hypothyroidism
Most common condition of hyperthyroidism; autoimmune disease
Immune system makes abnormal antibodies directed against self cells and bind; Mimics TSH
Symptoms: elevated metabolic rate, sweating, rapid and irregular heartbeat, weight loss, bulging eyes
Treatment: Surgical removal
Grave’s disease
Produced by parafollicular cells in response to high Ca2+ levels
Antagonist to parathyroid hormone (PTH)
Increased levels has bone-sparing effect
Calcitonin
4-8 small yellow-brown glands embedded in posterior aspect of thyroid; Contain oxyphil cells and parathyroid cells (secrete PTH)
Parathyroid gland
Hormone that raises blood calcium levels by stimulating osteoclasts to digest bone matrix to release into blood
Enhances reabsorption of Ca2+ by kidneys; Promotes activation of vit. D by kidneys
Most important in Ca2+ homeostasis
Target organs: skeleton, kidneys, intestine
Parathyroid hormone (PTH)
Excess PTH; Usually due to parathyroid gland tumor
Causes kidney stones, spontaneous bone fracture
Hyperparathyroidism
Severe bone disorder, spontaneous fracturing
Osteitis fibrosa cystica
Insufficient PTH; May follow parathyroid gland removal or trauma
Tingling, muscle twitching, convulsions
Hypoparathyroidism
Paired, pyramid shaped organs atop kidneys
Split into two: Adrenal cortex, Adrenal medulla
Adrenal glands
Three outer layers that produce corticosteroids (ZG, ZF, ZR)
Adrenal cortex
