Thyroid Systems Flashcards
Explain the hypothalamic regulation of thyroid function?
- Hypothalamus contains parvocellular neurosecretory cells that release Thyrotropin Releasing Hormones (TRH)
- Inflow of blood from superior hypophyseal artery carries hormones across to anterior pituritary
- The endocrine then releases to the vein Thyroid Stimulating Hormone- Thyrotropin (TSH)
What effect does the thyroid hormones have on basal metabolic rate
Raised O2 consumption
Raised CO2 and heat production
What effect does the thyroid hormones have on cardiovascular system
Increases heart rate and force of contraction
What effect does the thyroid hormones have on nervous system
Increases activity of sympathetic nervous system
Enhances the sensitivity to catecholamines
What effect does the thyroid hormones have on growth and maturation
Embryo development
CNS development
Linear growth (promotes growth hormone effect)
What role does C cells play in thyroid follices
Make calcitonin, lowers calcium levels by inhibiting bone breakdown- involved in managing calcium balance
How do you form the two types of iodinated molecules?
Combination of Thyroglobulin (contains high amount of tyrosine) with Iodine (I2) made form iodide (I-) taken up from the blood
What are the two couple of iodinated molecules called
MIT: mono-iodotyrosine- one iodine per tyrosine
DIT: di-iodotyrosine- two iodines per tyrosine
How do you produce Thyroxine (T4)
DIT (di-iodotyrosine) + DIT
How do you produce Triiodothyronine (T3)
MIT (mono-iodotyrosine) + MIT
Explain how the Thyroid hormones are released
- Follicular cells take up portion of colloid in lumen (endocytosis)
- Lysosomal enzymes in follicular cell break down the iodinated thyroglobulin, this creates T3 and T4
- T3 and T4 diffuse via the plasma membrane of the follicular cell into the blood
What is the role of TBG (thyroxine binding globulin)
Releases bound T3 and T4 to exert its biological effect
Needed to circulate blood stream as we know T3 and T4 have poor solubility in water
Which is more active between T3 and T4, explain
T3 is more active as it binds to the thyroid hormone with a higher affinity than T4
Local tissues convert T4 into T3 via removal of one iodine
Explain how thyroid hormones are transported around the body to have its targeted effect
- They are lipophilic in nature and are transported in blood stream bound to carrier protein (TBG and albumin)
- The activated receptor hormone complex can alter the gene expression
- Newly formed mRNA directs specific synthesis of specific proteins on ribosomes which bind to intracellular receptors on target cell
What are the three diseases associated with the thyroid hormone
Goitre
Cretinism
Grave’s disease
Describe what goitre is
Hypertrophy of thyroid gland (too much TSH stimulation)
Associated with hypo/hyperthyroidism forms
Association with autoimmune disease
What can hypothyroidism lead to symptom wise
Weight gain Cold intolerance Lethargy and depression Puffiness of skin and muscles Muscular weakness Sluggish Reflexes Reduced pulse and cardiac output
Describe what cretinism is
Hypothyroidism in kid that can cause fetal brain damage
Shortness
Obesity
Mental retardation
How do you treat hypothyroidism
Life long replacement with T4
Levothyroxine- identical to natural T4
What is the drug that is identical to T3 and T4 called
Liothyroxine- T3
Levothyroxine- T4
What is Hashimoto’s thyroiditis
An autoimmune disease that causes damage to the gland which can lead to hypothyroidism
What are the symptoms of hyperthyroidism
Weight loss Nervousness High cardiac output Heat intolerance Hand tremor eyeball protrusions
What is Grave’s disease
Cause of hyperthyroidism
Peculiar form of autoimmune disease
Reason: Thyroid stimulating antibody that mimics TSH
HIGH T3/T4, LOW TSH, goitre
How do you treat hyperthyroidism
Interfere with thyroid synthesis by blocking the thyroid peroxidase enzyme (prevents iodination of thyroglobulin)
Drug: CARBIMAZOLE
