13. Endocrine System Part 2

Question 1

What is a neurohormone?

Answer 1

A neurohormone is any hormone produced and released by neuroendocrine cells (neurons that secrete hormones) into the blood

Question 2

What part of the pituitary releases neurohormones?

Answer 2

The posterior pituitary

Question 3

What is the process of the posterior pituitary releasing neurohormones?

Answer 3

1. Hypothalamic neurons produce ADH and Oxytocin and transport them to the posterior pituitary
2. Neurohormones released into the posterior pituitary travel into capillaries

Question 4

How is the anterior pituitary regulated by the hypothalamus?

Answer 4

1. The terminals of hypothalamic neurons release neurohormones (releasing factors) into the hypothalamic capillaries
2. Neuohormones travel to anterior pituitary capillaries, are released into the anterior pituitary, then stimulate or inhibit release of hormones from anterior pituitary cells
3. Anterior pituitary hormones released by anterior pituitary cells make their way into the bloodstream

Question 5

What is the stimulus response model for the anterior pituitary regulation?

Answer 5

• External or internal stimuli
• Hypothalamus
• Releasing hormone
• Pituitary
• Pituitary hormone
• Target or endocrine gland
• Hormone

Question 6

Where does negative feedback occur int he anterior pituitary stimulus response model?

Answer 6

• The pituitary hormone regulates the hypothalamus

- The hormone regulates the pituitary and the hypothalamus

Question 7

What type of epithelial cells are in the thyroid gland?

Answer 7

Cuboidal

Question 8

What is the process of the synthesis and secretion of thyroxin?

Answer 8

1. A follicle cell takes up iodine from blood
2. Cell synthesises thyroglobulin from tyrosine
3. Thyroglobulin and iodine are secreted into the follicle lumen, then Thyroglobulin is iodinated
4. Iodinated thyroglobulin is taken up by follicle cell by endocytosis
5. Enzymes digest thyroglobulin into T3 and T4
6. T3 and T4 secreted into blood

Question 9

What are t3 or t4?

Answer 9

T3 has 3 iodine and is the active hormone

T4 has 4 iodine and is the precursor

Question 10

What is the function of thyroxine?

Answer 10

Thyroxine regulates the metabolic rate of most cells

Question 11

How is TSH regulated (show the stimulus response model)?

Answer 11

• External or internal stimuli
• Hypothalamus
• TRH
• Anterior pituitary
• TSH
• Thyroid gland
• Thyroxine

Question 12

Where does negative feedback occur in the regulation of TSH?

Answer 12

• TSH regulates the hypothalamus

- Thyroxine inhibits the anterior pituitary and the hypothalamus

Question 13

What are the target cells of thyroxin and what is its affect?

Answer 13

Thyroxine regulates metabolic rate and its target cells are most cells which have thyroxine receptors.

Question 14

What are the symptoms of hyperthyroidism?

Answer 14

Weight loss and moist skin

Question 15

What are the symptoms of hypothyroidism?

Answer 15

Weight gain and dry skin

Question 16

How does goiter come about?

Answer 16

Goiter, an enlarged thyroid is associated with

1. Hypothyroidism - very low levels of thyroxine
2. Hyperthyroidism - very high levels of thyroxine

Question 17

The regulation of what hormone is involved in diseases of the thyroid?

Answer 17

The regulation of TSH

Question 18

What is hyperthyroidism?

Answer 18

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

Question 19

What is one cause of hypothyroidism?

Answer 19

• Low dietary iodine (follicle cells fail to make thyroxine)
• Autoimmune disease (hashimoto’s disease)
• Pituitary disease
• Thyroiditis

Question 20

What is the problem that creates hypothyroidism?

Answer 20

🔸 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

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