thyroid and parathyroid glands

Question 1

wheres thyroid gland located

Answer 1

Located below larynx/voice box - two lobes

Question 2

explain follicular and parafollicular cells in the thyroid gland

Answer 2

Follicular cells that surround follicles/ follicular cells secrete thyroxin (T4) (4 atoms of iodine) & triiodothyronine (T3) (3 atoms of Iodine)
- Stored in follicle

Parafollicular cells (C-cells) function is in producing calcitonin

Question 3

what do T4 and T3 increase

Answer 3

basal metabolic rate, protein synthesis & growth

Question 4

how do thyroid hormones help control blood level

Answer 4

Blood level is controlled via feedback through hypothalamus

Increased body ATP demand can also raise blood levels

Question 5

what does the thyroid hormone calcitonin do

Answer 5

Calcitonin inhibits osteoclasts which cause decrease in blood Ca2+

The blood calcium levels feedback to control calcitonin secretion

Question 6

explain the process of releasing thyroid hormones in the body

Answer 6

1. low blood levels of thyroid hormones or low low metabolic rate stimulate release of TRH (thyrotropin-releasing hormone)
2. TRH, carried by hypophyseal portal veins to anterior pituitary, stimulates release of TSH (thyroid stimulating hormone)
3. TSH released into blood stimulates thyroid follicular cells
4. thyroid hormones released into blood by follicular cells
5. elevated level of thyroid hormones inhibit release of TRH ns TSH (negative feedback)

Question 7

describe the shape and location of the parathyroid glands

Answer 7

Small round endocrine masses, a pair either side located in posterior aspect of thyroid gland

Question 8

what cells release parathyroid hormones (PTH)

Answer 8

chief cells

Question 9

what do parathyroid hormones regulate and how

Answer 9

calcium, magnesium & phosphate

by increasing blood calcium levels and decreasing blood phosphate levels.

• Increases number & activity of osteoclasts
• Slows loss of Ca2+ & Mg2+ in urine
• Promotes production of calcitriol from vitamin D which increases rate of calcium, magnesium & phosphate absorption in GI tract
• Controlled by blood calcium levels

Question 10

explain the steps in the stimulation of the parathyroid hormone and what it does in the body once stimulated

Answer 10

1. high levels of calcium in blood stimulates thyroid gland parafollicular cells to release more CT (calcitonin)
2. calcitonin inhibits osteoclasts, thus decreasing blood calcium levels
3. low level of calcium in blood stimulates parathyroid gland chief cells to release more PTH (parathyroid hormone)
4. PTH promotes release of calcium from bone extracellular matrix into blood and slows loss of calcium in urine, thus increasing blood calcium levels
5. PTH also stimulates the kidneys to release calcitriol
6. calcitriol stimulates increased absorption of calcium from foods, which increases blood calcium levels