LECTURE 11 (Thyroid & Adrenals)

Question 1

Describe Thyroid Histology

Answer 1

• Thyroid gland contains “follicles”
• Follicles filled with COLLOID (protein materials)
• Thyroid hormone synthesised by follicular cells

Question 2

What are the different types of Thyroid dysfunction?

Answer 2

Hypothyroidism & Hyperthyroidism

Question 3

What does Iodine deficiency lead to?

Answer 3

Hypothyroidism

Explanation: Thyroid hormones contain Iodine -> normal level of iodine in diet is mandatory -> Iodine mixed in table salt to prevent iodine deficiency

Question 4

What are the two types of thyroid hormones synthesised in the body?

Answer 4

• T3 - Triiodothyronine
• T4 - Thyroxine

Question 5

What are Thyroid hormones synthesised from?

Answer 5

Tyrosine & Iodine

Question 6

What is Thyroglobulin?

Answer 6

• Large protein produced by thyroid follicular cells
• “backbone” containing numerous tyrosine molecules

Question 7

What must happen to iodide in our diet for thyroid hormone synthesis?

Answer 7

1) Taken up by follicular cells
2) Oxidised to I2 “OXIDATION”
3) Added to organic/carbon structures “ORGANIFICATION”

Question 8

What are the symptoms of Hypothyroidism?

Answer 8

• Weight gain
• Puffy face
• Decreased sweating
• Constipation
• Slow heart rate
• Irregular and heavy periods

Question 9

What are the symptoms of Hyperthyroidism?

Answer 9

• Weight loss or gain
• Diarrhoea
• Increased sweating
• Racing heart
• Short and light periods

Question 10

Which symptoms are found in both Hypothyroidism and Hyperthyroidism?

Answer 10

• Fatigue
• Insomnia
• Hair loss

Question 11

Describe Thyroid hormon synthesis

Answer 11

1)Iodide enters the Follicular cell via NA-IODINE SYMPORTER with Sodium
2) “OXIDATION” Iodide is oxidised to I2 via THYROID PEROXIDASE
3) “ORGANIFICATION” Tyrosine + Iodine (I2) is converted to either MONOIODOTYROSINE (MIT) [1 iodine] or DIIODOTYROSINE (DIT) [2 iodine] via THYROID PEROXIDASE
4) “COUPLING REACTIONS” MIT + DIT = TRIIODOTHYRONINE (T3) or DIT + DIT = THYROXINE (T4)

Question 12

What is the function of Thyroid Peroxidase (TPO)?

Answer 12

It catalyses
- Oxidation of iodide
- Organification into MIT/DIT
- Coupling of MIT/DIT into T3/T4

Question 13

TPO antibodies are common in which disease?

Answer 13

Autoimmune thyroid disease

Question 14

What is produced more, T3 or T4?

Answer 14

T4 (>90% of thyroid hormone produced in T4)

Explanation: More T4 is produced but more T3 is needed since it is a more POTENT hormone, thus T4 must be converted to T3 via 5’-DEIODINASE

Question 15

Which enzyme converts T4 to T3?

Answer 15

5’-DEIODINASE

[most conversion occurs in peripheral tissues]

Question 16

What are some different Hyperthyroid medications?

Answer 16

• Propylthiouracil (PTU)
• Methimazole
• Propranolol

Question 17

Describe the MOA of Propylthiouracil (PTU)

Answer 17

• Inhibits TPO (Thyroid peroxidase) -> decreases T3/T4 from thyroid gland
• Inhibits 5’-deiodinase -> decreased T4 into T3 conversion in peripheral tissues

Question 18

Describe the MOA of Methimazole

Answer 18

Inhibits TPO (Thyroid peroxidase) -> decreases T3/T4 from thyroid gland

Question 19

Describe the MOA of Propranolol

Answer 19

• Beta-blocker
• Weak inhibitor of 5’deiodinase
• Used in thyrotoxicosis (inappropriately high levels of thyroid hormones) -> blocks catecholamines + T4 to T3 conversion

Question 20

Describe the Adrenal glands

Answer 20

• Located above kidneys
• CORTEX synthesises 3 groups of hormones (Mineralocorticoids, Glucocorticoids & Androgens)
• MEDULLA synthesises Epinephrine & Norepinephrine -> sympathetic nervous system control

Question 21

Which parts of the cortex synthesises the three different groups of hormones?

Answer 21

• Zona Glomerulosa = Mineralocorticoids (Aldosterone)
  [regulated by Angiotensin II]
• Zona Fasciculata = Glucocorticoids (Cortisol)
  [regulated by ACTH + CRH]
• Zona Reticularis = Androgens (DHEA)
  [regulated by ACTH + CRH]

Question 22

What is the HPA axis?

Answer 22

A major neuroendocrine system that controls reactions to stress

Hypothalamus produces CRH (Corticotrophin-releasing hormone) -> Pituitary gland produces ACTH (Adrenocorticotropic hormone) -> Adrenal gland produces Cortisol

Question 23

What are the Effects of Cortisol?

Answer 23

• Increased serum glucose
  [induces glucose production in liver since increased synthesis of glucose-6-phosphatase + PEPCK -> gluconeogenesis & less glucose taken up peripherally + more glycogen storage in liver]
• Fat deposition
  [activation of lipolysis in adipocytes -> stimulate adipocyte growth]
• Long-term steroid use -> diabetes
  [enhanced effects of glucagon and epinephrine -> long-term leads to insulin resistance]
• Muscle atrophy
• Thin skin, Easy bruising & Striae (stretch marks)
  [blunted epidermal cell division in skin]
• Osteopenia & Osteoporosis
  [Inhibits osteoblasts]

Question 24

What is Cushing’s syndrome?

Answer 24

A set of symptoms resulting from exposure to increased levels of cortisol - Endogenous or exogenous sources of excess cortisol

CAUSES:
- Long-term use of glucocorticoid medications
- Pituitary tumour (Cushing’s disease)
- Ectopic ACTH-producing tumour
- Adrenal tumour

SYMPTOMS:
- Moon face
- Buffalo hump
- Muscle wasting & thin extremities
- Stretch marks, weight gain, obesity & easy bruising
= Skin & bone thinning

FEMALES:
- Hirsutism (where women have thick, dark hair on their face, neck, chest, tummy, lower back, buttocks or thighs)
- Menstrual changes
- Decreased Libido