文档介绍：Section 3 Thyroid Gland
冯鉴强教授
anization
• the first endocrine gland to be recognized by those symptoms associated with excess or deficient function
• consists of two lobes, one on each side of trachea below cricoids cartilage(环状软骨)
• Lobes posed of spherical follicles formed by a single layer of epithelial cells that surround a lumen filled with a gel-like substance called colloid(胶质) composed of thyroglobulin(TG), the precursor(前体)of thyroid hormones
• thyroid epithelial cells secrete thyroid hormones (T4,T3) and synthesize TG
• parafollicular cells secrete calcitonin, CT,降钙素
Thyroid Hormones( TH)
TH including thyroxin(T4),3,5,3’,5’-triiodothyronine(T3) and rT3(逆-三碘甲腺原氨酸)(no biological activity)(Fig 11-15)
Synthesis and secretion of thyroid hormones
Iodine is required for formation of thyroxin
About 500mg of ingested are required each year; about 1mg/week
International standard: 150μg/d
To prevent iodine deficiency, salt is iodized with sodium iodide (iodide : NaCl = 1:100,000)
Absorbed from gastrointestinal tract in the same manner as chloride
Synthesis and secretion of TH include 4 stages
(1)Iodide Trapping(碘捕获)
Uptake of iodide ions (I¯) from the blood by epithelial cells of the follicle via an active transport system that co-transports Na+ ions into the cell
transport of iodine including 2 steps
① at basal membrane, transported actively into cell against electrical-chemical gradient by a sodium-iodide symportor(钠-碘同向转运体,也称Na+-I-泵)
I¯ concentration inside thyroid gland is 20~25 times than in the blood
The resting membrane potential of epithelia cell is about -40~-50mV
Na+-I- pump requires energy provided by Na+-K+-ATPase
ATP →Na+-K+-ATPase activity↑→ extracellular Na+↑→Na+ diffuse inside↑→I¯ transported by Na+-I¯ pump↑(I iodine: 2 Na+-contransport,协同转运)
②Some ions: ClO4¯,SCN¯,NO3¯: pete against I¯ transport
③TSH: to stimulate and hypophysectomy greatly diminishes the activity of iodide pump.
-¹³¹I be used to test ability of iodide trapping and func