5. Hyper/Hypo Thyroidism Flashcards
What percentage of hormone secreted by the thyroid is T4?
93%
Which thyroid hormone is more biologically active?
T3
Why are the actions of TH so sluggish?
Its actions are due to the transcription and translation of DNA, which is time consuming
What are the general effects of TH?
- Transcription of genes
2. Protein synthesis which increases the functional activity of the body
What are the metabolic effects of TH?
- Increases BMR
- Calorigenic/heat producing effect
- Synthesis and degradation of carbs, fat, protein
What is the function of TH on the nervous system in children?
Myelination
Development of CNS
What are the effects of TH on the cardiovascular system?
- Increased blood flow and cardiac output
- Increased heart rate
- Peripheral vasodilation (due to heat producing effect)
What are the effects of TH on growth?
- Stimulates GH secretion
- Increases production of IGF-1 by the liver
These both affect protein synthesis and skeletal growth
What effect does cold expose have on newborns?
Increases TRH secretion to increase calorigenic effect
What are the causes of hypothyroidism?
- Primary failure of the thyroid gland
- Autoimmune disease (Hashimoto)
- Deficiency of TRH or TSH
- Inadequate iodine
What are the symptoms of hypothyroidism?
- Low BMR
- Poor cold tolerance
- Weight gain
- Fatigue and drowsiness
- Slow, weak pulse
- Slow reflexes and mental responsiveness
- Decreased hair growth
- Scaly skin
- Husky voice
- Myxedema
What is myxedema?
Total lack of TH function
Water retaining carbohydrates bound to protein form excessive tissue gel
The increased ECF gives the body a puffy appearance
What is cretinism?
Hypothyroidism from birth
Presents as dwarfism, mental retardation
What is congenital cretinism?
Lack of thyroid from birth
What can endemic cretinism be caused by?
Genetic defect, thyroid doesn’t produce TH
Lack of iodine
How can endemic cretinism be treated?
Administering iodine or thyroxine
How is hypothyroidism diagnosed?
High TSH levels
Low thyroxine
What are the causes of hyperthyroidism?
- Graves’ disease
- Excess TRH/TSH
- Thyroid adenoma
What is Graves’ Disease?
Autoimmune disease
Involves the production of TSI or LATS which target TSH receptors, stimulating secretion and growth of thyroid
TSI and LATS not susceptible to negative feedback
What are the symptoms of hyperthyroidism?
- High BMR
- Increased heat production
- Increased appetite
- Decreased body weight
- Net degradation of carbs, fat and protein
- Increased HR and strength of contraction
- Excessive mental alertness
- Exophthalmos
What is exophthalmos?
Inflammation and swelling of eye muscles and fat behind eyes
Eyeballs bulge forwards
Eyelids unable to close: causes dry eyes and corneal ulceration
How is hyperthyroidism diagnosed?
Very low TSH
High thyroxine
What is the cause of goitre in hypothyroidism?
Hashimoto disease or lack iodine
Decreased TH causes secretion of TSH
TSH overstimulates thyroid, leading to hypertrophy and hyperplasia of gland
What is the cause of goitre in hyperthyroidism?
LATS promote thyroid growth
or excessive TSH is produced due to a hypothalamic or pituitary defect
