Download Follicles And Colloid

Follicles and Colloid
– Follicular
Epithelial Cells
–Colloidstores thyroid
hormone
Parafollicular Cells(C cells)
Follicles and Colloid
• Calcitonin
Thyroglobulin
• Iodinated tyrosine molecules
• Tetraiodothyronine = T4
=Thyroxine
• Triiodothyronine = T3
• Reverse T3 = rT3 = an isomer
• 1) Synthesis of Thyroglobulin
– Follicular epithelial cells
– Tyrosine
– Secreted into the Colloid
• 2) Iodide Trapping
– Plasma into Epithelial Cells
– Thiocyanates can block
1
h
• 3) Oxidation of Iodide
– Thyroid peroxidase
• 4) Organification
– MIT(monoiodothyronine)
– DIT(diiodothyronine)
• oxidizes Iodide to form Iodine
TPO
I¯
Ð I
– Thiouracils can block
• DIT + MIT = T3(10%) rT3 (<1%)
• DIT + DIT = T4(90%)
Secretion of Thyroid Hormones
• T4 and T3 released
from cell into plasma
• 5) STORAGE
Thryoglobulin
• Tyrosine and I are
recycled
Concept of Bound vs.
Unbound
• Thyroxine binding globulin
(75% T-4; 75% T-3)
• Transthyretin
(15% T-4; 0% T-3)
• Thyroxine binding albumin
• Concepts
• Clinical Implications
(10% T-4; 25% T-3)
2
Thyroid Stimulating Hormone
*
•
•
•
•
Enhances Iodide trapping
Enhances synthesis of T4 and T3
Enhances the endocytosis of the colloid
Enhances the proteolysis of the
thyroglobulin
• Enhances the release of T4 and T3
* Starvation inhibits this enzyme
• Maturational/Differentiational
Mechanism of Action
• Neurological Effects
• Growth
• Metabolic Actions
• Sympathomimetic Effect
• Reproduction
Hypothyroidism
• Primary - failure of
gland itself
• Secondary - TRH or
TSH related
deficiency
• Nutritional (most
common world)
• Hashimoto thyroiditus
most common U.S.
3
• Symptoms (Infants and
Children)
–
–
–
–
–
R.D.S.
Retarded Bone Age
Mental Retardation
Stunted Growth
Delayed or absent sexual
maturity
Hypothyroidism
Treatment
– THYROXINE PREPARATIONS
• LEVOXYL
• SYNTHROID
• LEVOTHYROID
• Symptoms (Adults)
–
–
–
–
–
–
Low BMR
Poor resistance to cold
Weight gain
Slow thinking
Thin and brittle hair
Weakness, fatigue,
lethargy
– MYXEDEMA
Hyperthyroidism (Thyrotoxicosis)
• Graves’ Disease
• Symptoms
–
–
–
–
Increased BMR
Heat Intolerance
Increased appetite
Elevated HR and
arrhythmias,
– Nervous, irritable
– Exopthalmus
Hyperthyroidism
• Treatment
– Surgery
– 131I
– Thiouracils
– (PROPACIL)
4
Goiter
• Enlarged Thyroid Gland
• Hyperthyroidism or Hypothyroidism
• Iodide deficiency
5