36. Thyroid And Adrenal Hormones

Question 1

What are follicular cells?

Where are they found?

Answer 1

Cuboidal epithelial cells

Line the follicles of the thyroid

Question 2

Where is thyroid hormone stored?

Answer 2

In colloid composed on thyroglobulin

Question 3

What is secreted by parafollicular cells?

Answer 3

Calcitonin

Question 4

What is the purpose of thyroglobulin?

Answer 4

It is the site of synthesis and storage of T3 and T4

Question 5

What form of iodine is transported to the colloid?

Answer 5

Iodine TPO, oxidised form of dietary iodide

Question 6

How are T3 and T4 formed?

Answer 6

T3 formed by MIT and DIT coupling, T4 formed by 2 DIT

Question 7

How do T3 and T4 get from the colloid to the blood stream?

Answer 7

By endocytosis of thyroglobulin which is digested to release T3 and T4 which diffuse into the blood

Question 8

How are thyroid hormones circulated in the blood?

Answer 8

Bound to thyroid binding globulin (99.5%) or free (0.5%)

Question 9

Why is much of the T4 converted into T3 in the cell?

Answer 9

Nuclear receptors have a higher affinity for T3

Question 10

How does thyroid hormone binding to DNA affect the cell?

Answer 10

Initiates transcription and formation of multiple mRNAs

Question 11

What is the main function of thyroid hormone?

Answer 11

Increase metabolic activity of nearly all tissues

Increase BMR, number of mitochondria, Na+/K+ ATPase activity

Question 12

How does thyroid hormone affect the cardiovascular system?

Answer 12

Increases sympathetic NS activity, ie increases heart rate, contractility, CO, etc

Question 13

What stimulates TSH production?

Answer 13

Thyrotropin releasing hormone from hypothalamus

Question 14

How does TSH affect thyroid hormone production?

Answer 14

Increases secretion of T3 and T4

Question 15

What are the causes of congenital hypothyroidism?

Answer 15

Thyroid dysgenesis, thyroid dyshormonogenesis, thyroid receptor abnormalities, iodine deficiency

Question 16

What is a sign of thyroid disfunction?

Answer 16

High levels of TSH in babies, suggests thyroid gland is not responding

Question 17

What drug is used to treat hypothyroidism?

Answer 17

Levothyroxine

Converted into T3 in body

Question 18

What does the adrenal cortex produce?

What does the adrenal medulla produce?

Answer 18

Steroid hormones

Adrenaline, Noradrenaline, and dopamine

Question 19

What are the histological layers of the adrenal cortex?

Answer 19

Zona glomerulosa - clusters of small cells. Release aldosterone
Zona fasciculata - large cells in cords. Produces cortisol
Zona reticularis - small randomly arranged cells. produced adrenal androgens

Question 20

What are the effects of cortisol?

Answer 20

Gluconeogenesis, lipolysis, suppress release of insulin, breakdown of skeletal muscle protein, immune suppression

Question 21

How is cortisol secretion regulated?

Answer 21

By hormones produced in hypothalamus and anterior pituitary (HPA axis)

Question 22

What stimulates cortisol release?

Answer 22

CRH from hypothalamus stimulates ACTH from pituitary which stimulates cortisol production in adrenals

Question 23

When is cortisol secretion highest?

Answer 23

In the early morning, controlled by daylight exposure

Question 24

What is the role of cortisol in the stress response?

Answer 24

Maintains steady supply of glucose, suppresses immune system and has anti-inflammatory action to prepare for long term damage

Question 25

What is Cushing’s syndrome?

Answer 25

Prolonged exposure to excess cortisol (not caused by pituitary tumour)

Question 26

What are the symptoms of Cushing’s disease?

Answer 26

Red moon face, thin extremities, fat around back of neck and abdomen, thin skin, etc.