Endocrinology

Question 1

Process of thyroid hormone synthesis

Answer 1

1) Thyrotropin releasing hormone produced in the hypothalamus stimulates the release of Thyroid stimulating hormone from the anterior pituitary gland.

2) Thyroid stimulating hormone binds to receptors on the thyroid gland.

3) Iodide is taken into the cell via a sodium iodide symporter (co transport/ secondary active transport)

4) (Thyroglobulin, a protein rich in tyrosine is stored in the follicle lumen as colloid) Thyroid peroxidase catalyses the iodination of thyroglobulin (iodide binds to tyrosine residues forming monoiodotyrosine and diiodotyrosine).

5) Coupling of a monoiodotyrosine and a diiodotyrosine gives Triiodothyronine (T3). Coupling of 2 diiodotyrosine gives thyroxine (T4) (T3 and T4 are thyroid hormones)

6) Iodinated thyroglobulin is brought into the follicular cell via endocytosis. Here, it undergoes proteolysis in lysosomes. (Cleaving the iodinated tyrosine residues)

7) Free T3 and T4 are released (steroid hormones). They are fat soluble and are carried by plasma proteins (Thyroxine binding globulin and albumin)

(Produced T4 and T3 have negative feedback loops on the production of TSH and thyrotropin releasing hormone)

Question 2

What is the precursor of thyroid hormone synthesis

Answer 2

Thyroglobulin

Question 3

What are the levels of Serum TSH, free T4 and free T3 in hyperthyroidism and hypothyroidism?

Answer 3

Hyperthyroidism
- Decreased serum TSH
- High serum T3 and T4

Hypothyroidism
- Increased serum TSH
- Low serum T3 and T4

Question 4

Signs and symptoms of hyperthyroidism and hypothyroidism (3 each)

Answer 4

Tachycardia
Weight loss
Increased appetite
Anxiety
Diplopia

(Bradycardia, weight gain, depression, heart failure - hypothyroidism)

Question 5

Actions of PTH on calcium and phosphate regulation

Answer 5

Increases calcium levels
1) Increases calcium reabsorption in the renal distal tubule
2) Increases intestinal calcium absorption via the activation of vitamin D
3) Increases calcium release from bone (promotes osteoclast activity)

Decreases phosphate levels
1) Decreases phosphate reabsorption in the kidneys

Question 6

How much serum calcium is free, how much is albumin bound?

Answer 6

50% each

Question 7

Function of calcitonin

Answer 7

Produced by thyroid parafollicular C cells

• Released in hypercalcemia to inhibit the action of osteoclasts and bone resorption

Question 8

Function of thyroxine

Answer 8

Regulation of weight

Control of metabolism

Regulation of body temperature

(Affects appetite as well)

Question 9

How is cortisol produced?

Answer 9

Stress hormone (hypoglycemia also can cause cortisol release)
1. Corticotropin releasing hormone from the hypothalamus stimulate the release of adrenocorticotropic hormone
2. ACTH binds to receptors on the zona fasciculate. Activating a G stimulatory protein —> which binds to GTP —> it then activates adenylate cyclase —> which converts ATP to cyclic AMP —> which in turn stimulates protein kinase A.
3. Protein kinase A stimulates the synthesis of cortisol (from cholesterol)
4. As cortisol is a steroid hormone, it needs to bind to protein transporters such as albumin(5%) and corticosteroid binding globulin (90%)

Cortisol has a negative feedback loop on CRH and ACTH

Question 10

Function/effects of cortisol

Answer 10

Stimulates muscles to increase protein degradation (increasing amino acid levels)

Promotes gluconeogenesis (with the amino acids)

Regulation of stress response

It depresses the immune system- to prevent overactive immune responses

• It increases blood pressure (via vasoconstriction)
• It decreases bone formation
• Decreases linear growth

Question 11

Definition of stress

Answer 11

The sum of the body’s response to adverse stimuli

(including infection, trauma, haemorrhage, psychological factors, etc)

Question 12

Most abundant adrenal androgen

What is the production of androgens regulated by?

Answer 12

Dehydroepiandrosterone

Production regulated by adrenocorticotropic hormone

Question 13

What is the definition of menopause?

What age does this happen?

Answer 13

Absence of menstruation for more than 12 months

48-52

Question 14

Describe menopause briefly

Answer 14

• Caused by a reduced sensitivity of the ovary to FSH and LH –> results in a reduction in oestrogen secretion –> less estrogen negatively feedback, causing FSH and LH levels to rise –> decrease in developing follicles also reduces amount of inhibin released –> causing FSH levels to rise further

Question 15

What are some signs you might expect in someone with premature menopause?

Answer 15

• Heart disease
• Mood and sexual disorders
• Increased risk of mortality
• Can increase chances of developing osteoporosis

Question 16

Function of androgens

Answer 16

Hormones that contribute to growth and reproduction in males and females

• Axillary, pubic in males and females + (facial hair in males)
• Libido in both genders
• Maintenance of muscle mass and strength

(might help with red blood cell production)

Question 17

Function of insulin

Answer 17

Increased glycogenesis
Increases glycolysis
Decreases gluconeogenesis
Increases lipogenesis
Increases fatty acid uptake in adipocytes

Question 18

Functions of glucagon

Answer 18

Decreased glycogenesis - increases glycogenolysis
Increased gluconeogenesis
Increased lipolysis
Stimulates ketogenesis