13. Endocrine System Part 2 Flashcards
What is a neurohormone?
A neurohormone is any hormone produced and released by neuroendocrine cells (neurons that secrete hormones) into the blood
What part of the pituitary releases neurohormones?
The posterior pituitary
What is the process of the posterior pituitary releasing neurohormones?
- Hypothalamic neurons produce ADH and Oxytocin and transport them to the posterior pituitary
- Neurohormones released into the posterior pituitary travel into capillaries
How is the anterior pituitary regulated by the hypothalamus?
- The terminals of hypothalamic neurons release neurohormones (releasing factors) into the hypothalamic capillaries
- Neuohormones travel to anterior pituitary capillaries, are released into the anterior pituitary, then stimulate or inhibit release of hormones from anterior pituitary cells
- Anterior pituitary hormones released by anterior pituitary cells make their way into the bloodstream
What is the stimulus response model for the anterior pituitary regulation?
- External or internal stimuli
- Hypothalamus
- Releasing hormone
- Pituitary
- Pituitary hormone
- Target or endocrine gland
- Hormone
Where does negative feedback occur int he anterior pituitary stimulus response model?
- The pituitary hormone regulates the hypothalamus
- The hormone regulates the pituitary and the hypothalamus
What type of epithelial cells are in the thyroid gland?
Cuboidal
What is the process of the synthesis and secretion of thyroxin?
- A follicle cell takes up iodine from blood
- Cell synthesises thyroglobulin from tyrosine
- Thyroglobulin and iodine are secreted into the follicle lumen, then Thyroglobulin is iodinated
- Iodinated thyroglobulin is taken up by follicle cell by endocytosis
- Enzymes digest thyroglobulin into T3 and T4
- T3 and T4 secreted into blood
What are t3 or t4?
T3 has 3 iodine and is the active hormone
T4 has 4 iodine and is the precursor
What is the function of thyroxine?
Thyroxine regulates the metabolic rate of most cells
How is TSH regulated (show the stimulus response model)?
- External or internal stimuli
- Hypothalamus
- TRH
- Anterior pituitary
- TSH
- Thyroid gland
- Thyroxine
Where does negative feedback occur in the regulation of TSH?
- TSH regulates the hypothalamus
- Thyroxine inhibits the anterior pituitary and the hypothalamus
What are the target cells of thyroxin and what is its affect?
Thyroxine regulates metabolic rate and its target cells are most cells which have thyroxine receptors.
What are the symptoms of hyperthyroidism?
Weight loss and moist skin
What are the symptoms of hypothyroidism?
Weight gain and dry skin
How does goiter come about?
Goiter, an enlarged thyroid is associated with
- Hypothyroidism - very low levels of thyroxine
- Hyperthyroidism - very high levels of thyroxine
The regulation of what hormone is involved in diseases of the thyroid?
The regulation of TSH
What is hyperthyroidism?
An autoimmune disease where an antibody binds to the TSH receptor
Problem: This antibody receptor binding MIMICS binding of TSH to the TSh receptor on the thyroid glands.
- Leads to high levels of thyroxine and low levels of TSH
- Negative feedback but ineffectual
What is one cause of hypothyroidism?
- Low dietary iodine (follicle cells fail to make thyroxine)
- Autoimmune disease (hashimoto’s disease)
- Pituitary disease
- Thyroiditis
What is the problem that creates hypothyroidism?
🔸 Low thyroxine levels
🔸 No negative feedback of TSH so the thyroid gland continues to make thyroglobulin but poorly iodinated
🔸 Low iodine, low thyroxine, high TSH
No negative feedback
