Lecture 27

Question 1

Where is the thyroid gland located?

Answer 1

• Immediately below larynx,
  anterior and on each side of
  trachea

Question 2

What are the 2 lobes of the thyroid called?

Answer 2

right lateral lobe and left lateral lobe

Question 3

What connects the 2 lobes of the thyroid?

Answer 3

Isthmus

Question 4

What hormones does the thyroid secrete? Which is there more of?

Answer 4

• Thyroxine (T4) and Triiodothyronine (T3)
• most in blood is T4, convrted to T3 in tissues

Question 5

What is the thyroid gland composed of?

Answer 5

• made of follicles
• Follicles filled with a large glycoprotein (thyroglobulin) secreted by cuboidal cells that
  comprise the follicular walls

Question 6

What are Parafollicular (C-cells) and what do they do?

Answer 6

• lie between follicles and secrete calcitonin (peptide)
• Reduces osteoclast activity
• Inhibits reabsorption of calcium by kidney

Question 7

How does the Synthesis and Release of Thyroid Hormones work?

Answer 7

• Iodides in blood actively transported into the cells of the follicles
• Iodide oxidised which then binds to tyrosine residues of
  thyroglobulin.
• Iodotyrosine residues become coupled to each other to produce T3 and T4
• Thyroid hormones stored within follicles in association with thyroglobulin
• Iodinated thyroglobulin taken up into follicle cells
• Lysosymes in cytoplasm fuse with vesicles and digest thyroglobul in molecules to release T3 and T4
• T3 and T4 then diffuse into surrounding capillaries
• Thyroid hormones transported in blood bound to plasma proteins

Question 8

How is thyroid hormone secretion controlled?

Answer 8

• Thyrotropin releasing hormone (TRH) is secreted by hypothalamic neurons
  and enters the hypothalamichypophyseal-portal capillaries
• TRH travels to anterior pituitary to cause release of Thyroid Stimulating Hormone (TSH)
• TSH released by anterior pituitary which stimulates synthesis and secretion of thyroid hormones
• Thyroid hormones exert negative feedback control of TSH (anterior pituitary) and TRH (hypothalamus)

Question 9

What is the most important action thyroid hormones?

Answer 9

Increases Basal Metabolic Rate (BMR)

Question 10

What form is calcium stored in in the bones?

Answer 10

Hydroxyapatite and mobilizable salts

Question 11

Where are the parathyroid hormones?

Answer 11

• Partially embedded in the posterior surface of the lateral lobes of the thyroid gland.

Question 12

Parathyroid hormone is secreted in response to…

Answer 12

LOW ECF calcium concentration

Question 13

What is the parathyroid made of?

Answer 13

• 2 cells
• Chief cells or principal cells which produce parathyroid
  hormone (PTH)
• Oxyphil cells, not normally present before puberty may be
  modified or depleted
  chief cells as numbers
  increase with age, help with identification of parathyroid tissue

Question 14

How do we go from 7- dehydrocholesterol in skin from UV to active vitamin deez nuts?

Answer 14

7- dehydrocholesterol in skin > cholecalciferol (can be from diet, vitamin D) > 25-hydroxycholecalciferol (25 HCC) in liver > 1,25-dihydroxycholecalciferol (1.25 DHCC) (calcitriol = active Vit D) in kidneys

Question 15

infantile hypothyroidism is caused by what?

Answer 15

• absent or poorly functioning thyroid gland
• poorly functioning pituitary
• lack of iodine in mother’s diet

Question 16

what are the effects of infantile hypothyroidism?

Answer 16

• Low Metabolic rate
• Delayed growth and neural development
• swelling around eyes and tongue

Question 17

what is simple goitre

Answer 17

• i.e. not associated with any other
  disease process e.g. cancer or
  autoimmune process
• May be due to Iodine deficiency
• Low levels of thyroid hormones
• High TSH
  » excessive growth of
  thyroid tissue

Question 18

what is hashimoto’s thyroiditis

Answer 18

• where immune cells attack own
  thyroid gland
• Thyroid swollen but produces less thyroid hormone than usual

Question 19

what is graves disease

Answer 19

• hyperthyroidism
• Autoimmune disease whereby antibodies attach to TSH
  receptors and act to stimulate (rather than destroy) the
  thyroid cells
• This leads to overproduction of thyroid hormones
  HYPERthyroidism as well as an associated goitre
• The antibodies can also cause swelling of tissues
  around/behind they eyes&raquo_space; exopthalmus

Question 20

what is ricketts

Answer 20

Lack of Vit D and/or dietary calcium in children&raquo_space; inadequate calcification of
new bone. Weakened, bowed lower limb bones and abnormal epiphyseal plates

Question 21

what is osteomalacia

Answer 21

In adults, lack of Vit D and/or calcium can result in
abnormal mineralization of mature bone, weaker, proner to atypical fractures