Top Banner
The Thyroid Gland
34

The Thyroid Gland

Jan 14, 2016

Download

Documents

mILOS

The Thyroid Gland. The Thyroid Gland. Largest endocrine glands in the body, Weighing ~ 20-25g. Functions early in life for the development of brain cells (forming nerve terminals/ synapse/ dendrites/ myelin). Figure 18.11a. The Thyroid Gland---Structure. Figure 18.11b, c. Figure 18.12b. - PowerPoint PPT Presentation
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: The Thyroid Gland

The Thyroid Gland

Page 2: The Thyroid Gland

The Thyroid Gland

Figure 18.11a

Largest endocrine glands in the body,

Weighing ~ 20-25g.

Functions early in life for the development of brain cells (forming nerve terminals/ synapse/ dendrites/ myelin)

Page 3: The Thyroid Gland

The Thyroid Gland---Structure

Page 4: The Thyroid Gland

Figure 18.11b, c

Page 5: The Thyroid Gland

Figure 18.12b

Page 6: The Thyroid Gland

The Thyroid Gland - Function

酪氨酸

Page 7: The Thyroid Gland

Biosynthesis of Thyroid Hormones

Iodine:

- Distribution: the sea- Source: food (and drink), in the form of I-.

The international recommended intake of iodine : 150 mg/day (1/3 is absorbed in the thyroid)

The total iodine in the thyroid: 8-10 mg (90% of the total iodine in body)

Thyroglobulin (TG):

- Homodimer glycoprotein

- Carrier of iodotyrosine

- The storage form of thyroid hormones

Page 8: The Thyroid Gland

Biosynthesis of Thyroid Hormones

Page 9: The Thyroid Gland

The Thyroid Gland - Production of T3 and T4

Page 10: The Thyroid Gland
Page 11: The Thyroid Gland
Page 12: The Thyroid Gland

Figure 18.12a

Page 13: The Thyroid Gland

The sodium/iodide symporter ( 同向转运体, NIS) is an intrinsic membrane protein that mediates the active transport of iodide into the thyroid and other tissues

Iodide trap – active transport:

thyroid peroxidase, TPO

Page 14: The Thyroid Gland

The activation of the iodine is the precondition of tyrosine iodination:

Page 15: The Thyroid Gland

Condensation of iodinated tyrosine:

Page 16: The Thyroid Gland

The storage and release of thyroid hormones

Storage–In the follicles–In the form of TG–For 2 ~3 months

Release–Stimulated by TSH

T3 = 1.8 ~2.9 nmol/L

T4 = 65 ~156 nmol/L

rT3 = 0.2 ~0.8 nmol/L

Page 17: The Thyroid Gland

Binding form: 99%

Thyroid hormones attached to thyroid binding globulins (TBG)– Some are attached to transthyretin(甲状腺素运载蛋白) ,

Thyroxine-binding prealbulmin (TBPA,甲状腺素结合前白蛋白 ) or albumin

–Slowly released to the tissue cells, slower for T4 due to its higher affinity

–Slow onset and long duration of action

Free form: 1% ( T3)

Transport of thyroid hormones

Page 18: The Thyroid Gland

Metabolism of thyroid hormones

DeiodinationDeiodinase

T4 → T3 (45%), in coldnessT4→ rT3 (55%), in pregnancy, hungry, stress, kidney failure

Locations: liver, kidney, skeletal muscle

Page 19: The Thyroid Gland

The Thyroid Gland - Regulation of Secretion

Page 20: The Thyroid Gland

Effects of T3 and T4 on the Body

Proper development of the nervous system in the fetus;

Maintain a person's alertness, responsiveness, and emotional state.

Page 21: The Thyroid Gland

Essential for growth in children - Promote bone formation and maturation, and the development of brain (fetus and baby)

Synergistic effect(协同效应) with GH, IGF-1, insulin and other growth factors

Cretinism: deficiency of thyroid hormone during the period of fetal and early neonatal development; short, stocky stature & mental retardation

Page 22: The Thyroid Gland

Permissive Effects on catecholamines

– Up-regulate beta-adrenergic receptors in many tissues (heart and nervous system)

– Potentiate (↑the effect of, being synergistic) actions of catecholamines (i.e. hyperthyroidism resembles symptoms of hypersecretion of epinephrine/norepinephrine)

Page 23: The Thyroid Gland

Effects of T3 and T4 on the Body: Calorigenic effect

Page 24: The Thyroid Gland

Carbohydrate metabolism

–↑glucose oxidation,↑effect of glucagon, cortisol and GH–↑glucogenesis and glycogenolysisToo much TH →↑blood glucose (Diabetes)

Fat metabolism–↑lipolysis (Triglyceride → FFA + glycerol)–↑oxidation of FFA–↓serum cholesterol (excretion into GI)

Protein metabolism–↑Protein synthesis (normal)–↑Protein catabolism (hyperthyroidism)

Page 25: The Thyroid Gland

Effects on Nervous System

A key role on the CNS-maturation during perinatal period

↑ wakefulness, alertness, responsiveness to various stimuli, auditory sense, awareness of hunger, memory and learning capacity

Normal emotional tone also depends on proper thyroid hormone

↑ the speed and amplitude of peripheral nerve reflexes

Hyperthyroidism: hyperexcitability, insomnia, loss of concentration

Hypothyroidism: mental retardation, sleepiness

myxedema

Page 26: The Thyroid Gland

Effects on cardiovascular system

↑ blood flow and cardiac output–↑metabolism →↑utilization of O2 & ↑metabolic end products from tissue →vasodilatation–↑cardiac output ensures sufficient O2 delivery to the tissues

↑ heart rate

–↑adrenergic activity (↑response to adrenaline/noradrenaline)–↑enzymatic activity

Affect heart strength–slightly increase of thyroid hormone increases heart strength–marked increase of thyroid hormone decreases heart strength

↑stroke volume + ↓peripheral resistance →pulse pressure ↑

Page 27: The Thyroid Gland

Effects on gastrointestinal system

Increase appetite and food intakeIncrease secretion of digestive juicesIncrease mobility of GI tract – hyperthyroidism: diarrhea

Effects on muscleshyperthyroidism →muscle weakening (catabolic effect), fine muscle tremor (characteristic sign)hypothyroidism →muscles sluggish

Effects on other endocrine glands↑secretion of insulin and cortisol

Effects on sexual function– loss of libido– impotency– abnormal menstruation

Page 28: The Thyroid Gland

Working mechanism of thyroid hormones

– T3 and T4 act by binding to nuclear receptors– T3 has 10 times the affinity for thyroid receptor as T4– ↑ Transcription of large numbers of genes– ↑ Synthesis of great numbers of proteins

Page 29: The Thyroid Gland

The HPT axis

Wolff - Chaikoff Effect(autoregulation by Iodine)– low Iodine intake stimulates ‘iodide trap’– high Iodine intake (>2 mg/day) inhibits ‘iodine trap’ and TH synthesis

T4 is converted into T3 in pituitary and T3 acts as the final effector to turn off TSH

Page 30: The Thyroid Gland

– TRH

Tripeptide;↑ TSH secretion; Cold TRH release ↑

PLC-DAG-PKC途径调节靶基因转录,促进 TSH合成

IP3-Ca2+途径促进 TSH爆发性释放

Page 31: The Thyroid Gland

– TSH

• Glycoprotein

• ↑ T3, T4 synthesis and release

• ↑ thyroid cell size

• cAMP mediated mechanism

Page 32: The Thyroid Gland

The Thyroid Gland- Diseases: Goiter

Page 33: The Thyroid Gland
Page 34: The Thyroid Gland