7.6 Thyroid and Parathyroid Flashcards
What is the width of the hypothalamus? How much does it weigh?
4cm, 15-20g
What cells make up most of the thyroid
Follicular Cells
What is the name of the middle of the thyroid bow tie?
Isthmus
What type of epithelium are follicular cells
Cuboidal Simple
What does thyroid colloid contain? What does this substance do?
- Thyroglobulin
- Protein backbone on which thyroid hormones are made
What hormones do c cells secrete?
Calcitonin
What is the function of calcitonin?
- Opposes parathyroid hormone
- Reduces bone resorption
Why does it makes sense that there are many capillaries in the thyroid?
It secretes hormone
True or false: iodine is essential in thyroid hormone manufacture
True. Think (hydrocarbon structure)
Which cell types do thyroid hormones act on?
All of them
What are the effects of thyroid hormones on metabolic pathways? How does this influence body temp?
- Boost energy metabolism
- Increase body temp
What are the effects of thyroid hormone on cellular differentiation and development?
Promote development and differentiation, including neurons and supporting cells of CNS`
What is the influence of T3 and T4 on TRH and TSH?
Decreases. It also inhibits synthesis of these hormones and receptors up to TSH secretion
Why does it make sense that most thyroid hormones are bound to carrier proteins in the blood (99.5%). What effect does this have on its biological activity?
- Large hydrocarbon structure, insoluble in plasma without protein
- Only biologically active when unbound
What are the non genomic effects of TSH?
- Enhances iodide pump activity (inc. iodide in thyroid)
- Inc. Iodination of tyrosine (inc. T3 and T4)
- Inc. Proteoysis of thyroglobulin (inc. T3 and T4 release)
What are the genomic effects of TSH?
Promotes transcription for:
- Iodide pump, thryoglobulin, T3 and T4 synthesis enzymes
- Nitric oxide synthase (vasodilation
-> inc. blood flow)
- Local growth factors (hyperplasia and hypertrophy of thyroid)
What are two carrier proteins that bind to thyroid hormones?
- Thyroxin binding globulin
- Albumin
What type of receptor are G protein receptors?
G-protein receptors
Where are thyroid receptors located?
In the nucleus of a cell, at regions of DNA called thyroid response elements
How do thyroid hormones increase the contractility of heart muscle?
- Increased calcium and sodium potassium pumps
- Increased beta adrenergic receptors
List two kinds of hormones that thyroid hormones are permissive to
- Growth hormone
- Catecholamines
Describe Hashimoto’s thyroiditis. What type of hypothyroidism is it?
Autoantibodies attack components of the thyroid hormone production and excretion system (e.g. thyroglobulin, TSH receptor). This is primary hypothyroidism
What is secondary hypothyroidism?
Caused by adenoma/destruction of pituitary gland
What it tertiary hypothyroidism?
Hypothalamic defecit (rare)
What it peripheral hypothyroidism?
Peripheral tissues do not respond appropriately to thyroid hormones. Often occur due to hereditary mutations in thyroid hormone receptors.
What three hormones are involved in calcium regulation?
- Parathyroid hormone
- Activated Vitamin D (Calcitriol)
- Calcitonin
How do the kidneys (in conjunction with PTH) help increase calcium reabsorption (beyond their regular function)?
PTH increases the activity of an enzyme produced in the kidney that converts vitamin D into its active form: calcitriol
How does PTH influence phosphate reabsorption
Increases
What type of hormone is vitamin D? What organs are involved in the activation of vitamin D into calcitriol?
- Steroid hormone
- Activated by kidneys and liver
How does PTH contribute to the activation of Vitamin D
Increase activity of kidney hydroxylases
Which three structures does calcitriol increase the concentration of to exert its effect?
- Calcium channels
- Calbindin (carries across cell)
- Calcium ATPase pumps, into extracellular fluid
What type of receptors are calcitonin receptors? Where are they found?
- G-protein coupled
- Found on osteoclasts, kidney, brain
