Thyroid gland Flashcards
What is stored in thyroid follicles?
Thyroglobulin.
Where is the thyroid located?
Along the front of the trachea.
How are thyroid hormones synthesised?
Tyrosine combines with iodine multiple times to form mono-iodotyrosine, di-iodotyrosine which can then form thyroxine and triiodothyronine.
How does iodinated thyroglobulin enter the lumen?
Exocytosis.
How does stored thyroglobulin enter follicle cells?
Endocytosis.
What do lysosomal enzymes release?
T3 and T4.
What is T3 and T4?
Triiodothyronine and thyroxine.
What are key hormones involved that regulate the secretion of hormones in the thyroid?
Thyrotropin releasing hormone and thyroid stimulating hormone.
What does TSH cause?
Iodine uptake (by a pump mechanism), T3 and T4 synthesis and thyroglobulin breakdown by lysosomal proteases.
What happens when thyroglobulin breaksdown?
The thyroid hormones T3 and T4.
What are the thyroid hormones involved in?
Growth and development, protein, carboyhydrate and lipid metabolism, regulating energy metabolism, body temperature regulation and the regulation of the nervous system, cardiovascular system and musculo-skeletal and reproduction systems.
What is the majority of hormone released?
T4 - thyroxine.
How are most of the thyroid hormones found?
Bound by thyroid binding globulin, the rest are by thyroid binding prealbumin.
What types of thyroid hormones can enter target tissues?
Unbound hormones.
What are most of the physiological effects of thyroid hormones caused by?
T3 - triiodothyronine.
What do TH receptors do?
Regulate gene transcription.
What receptors can T3/T4 bind to?
Nuclear receptors that cause mRNA transcription and cause a change in cellular homeostasis and affect the rarget cell, or mitochondrial receptors that cause target cell responses.
How does thyroxine affect BMR?
It increases it significantly after a thyroxine injection, and then decreases after around 10 days.
How does thyroid hormone affect BMR?
There is an increase in Na-K ATPase that causes increased heat production, leading to increased BMR. It also causes increase size, number and surface area of mitochondria which results in an increased rate of ATP production, also increasing BMR.
How does increased protein metabolism raise BMR?
There is an increase in protease synthesis, an increased protein breakdown which requires energy, leading to an increased BMR.
How does thyroid hormones cause increased carbohydrate metabolism?
There is an increase in enzyme synthesis, which causes increased glycogenolysis, gluconeogenesis and glucose uptake by the GI tract, liver and muscle due to increased insulin release.
How do thyroid hormones cause increased fat metabolism?
There is increase lipase synthesis, resulting in increased lipid metabolism. There is also increased lipoprotein receptors on liver cells and increase bile cholesterol secretion, resulting in increased cholesterol secretion and decreased plasma cholesterol.
What are some of the physiological effects of TH?
Decreased body weight and increased apetie, increased secretions and motility from the GI tract, increase excitability of the CNS, increased muscle tension and force of contraction, increased respiration rate and depth, and increased cardiac output, vasodilation, blood volume and pulse pressure.
What is the result if there is underactive thyroid follicles?
High colloid levels, increased TSH and flattened cells.
What is the result of highly active thyroid follicles?
Low colloid levels and columnar cells.
What is hypothyroidism?
Increased TSH and decreased T4.
What can cause hypothyroidism?
An autoimmune disease, iodine deficiency or altered H-P activity.
What are some of the results of hypothyroidism?
Increased body weight, constipation, mental sluggishness, fatigue, muscle weakness and stiffness, decreased hair growth/hair loss, decreased cardiac output.
What is hyperthyroidism?
Increased rate of secretion.
What causes hyperthyroidism?
Autoimmune disease - antibodies bind to TSH receptors and continually activate them. Can also be caused by thyroid adenoma secreting large quantities of TH.
What are some of the effects of hyperthyroidism?
Decreased body weight, fatigue, heat intolerance, increased bowel movements, muscle weaknesses and tremors, excess hair growth and increased force of contraction in the the heart.
