Lecture 36: Metabolic Rate & Calcium Concentrations

Question 1

Where is the thyroid gland located?

Answer 1

On the anterior and lateral surfaces of the trachea, just below the larynx.

Question 2

Which hormones are secreted by the thyroid?

Answer 2

Thyroid hormone and Calcitonin.

Question 3

What is the thyroid gland composed of?

Answer 3

Small spherical sacs called follicles. Each follicle of surrounded by follicular cells, which is the site of thyroid hormone synthesis.

Parafollicular cells or C cells lie in clusters between follicles and make Calcitonin.

Question 4

Explain how thyroid hormone is synthesised.

Answer 4

Follicle cells release TGB protein into follicle.

Iodine reacts with the tyrosine in TGB., and iodised TGB moves into follicular cells.

Thyroid hormones detach from TGB as needed (T3 & T4)

Question 5

What are T3 & T4?

Answer 5

T3 is the active form of thyroid hormone, T4 is the more plentiful inactive form.

Question 6

Why is iodine so essential?

Answer 6

Required for thyroid hormone synthesis.

Question 7

Explain how thyroid hormone works.

Answer 7

Made in advance and stored (T4) until req. (even though LS).

Travels bound to carrier protein.

Detaches and enters target cell.

T3 binds to receptor.

Genes are activated, mRNA transcribed.

mRNA translates to proteins.

Question 8

How long does thyroid hormone take to respond?

Answer 8

45 mins - days.

Question 9

What is BMR?

Answer 9

Basal metabolic rate: the body’s rate of energy expenditure while AWAKE, at REST, LYING down, COMFORTABLE temperature and FASTED.

Question 10

What does thyroid hormone do?

Answer 10

Increased growth, alertness, metabolism.

Question 11

What is hypersecretion of thyroid hormone called?

Answer 11

Graves Disease. High metabolic rate, weight loss, increased HR, hair loss, thyroid swelling.

Question 12

How is Grave’s disease diagnosed?

Answer 12

Thyroid stimulating Immunoglobulin antibody assay, OR radioactive iodine scan.

Question 13

What is hyposecretion of thyroid hormone called?

Answer 13

Myxedema: Low metabolic rate, weight gain, cold intolerant, lethargic, slow HR.

Question 14

What is hyposecretion of thyroid hormone called in infants?

Answer 14

Cretinism: growth is retarded, brain develop. inhibited, caused by lack of iodine in mother’s diet.

Question 15

What is Goitre?

Answer 15

Iodine deficiency: can’t make TH. TRH and TSH secrete to try and make more TH –> overstimulation, growth of thyroid gland.

Question 16

Which 2 hormones regulate calcium homeostasis?

Answer 16

Parathyroid (PTH) and calcitonin.

Question 17

Where is calcitonin made?

Answer 17

Thyroid gland

Question 18

Calcitonin moves calcium from _____ to ______, whereas PTH does the opposite.

Answer 18

Blood -> Bone

Question 19

What is hypocalcaemia?

Answer 19

Low blood Ca2+: increased excitability, tremors, spasms.

Question 20

What concentration is hypoglycaemic?

Answer 20

below 2.2mmol/L

under 1.9mmol/L is paraesthesia, which can cause suffocation.

Question 21

What can cause hypoglycaemia?

Answer 21

Vit. D deficiency, diarrhoea, thyroid tumours, underactive parathyroid glands, pregnancy and lactation.

Question 22

Describe the symptoms of hyperglycaemia.

Answer 22

Less responsive nerves and muscle cells. at >3mmol/L can lead to depression.
At >3.5mmol/L, can lead to cardiac arrest.