Hormone Synthesis and Action

Question 1

List 2 differences between endocrine and exocrine glands.

Answer 1

1 - Endocrine glands release secretions directly into the blood, whereas exocrine glands release their secretions onto surfaces.

2 - Endocrine glands are ductless whereas exocrine glands may be ducted.

Question 2

List 3 routes by which hormones can reach their targets.

Answer 2

1 - Endocrine.

2 - Autocrine.

3 - Paracrine.

Question 3

Describe the hypothalmo-pituitary-adrenal axis.

Answer 3

1 - The hypothalamus synthesises and releases corticotropin releasing hormone, which travels to the anterior pituitary gland.

2 - The anterior pituitary gland is stimulated to synthesise and release adrenocorticotropic hormone, which travels to the zona fasciculata of the adrenal gland.

3 - The zona fasciculata synthesises and releases cortisol, which acts through negative feedback to reduce the synthesis and release of corticotropin releasing hormone at the hypothalamus and adrenocorticotropic hormone at the pituitary.

Question 4

Describe the hypothalamic-pituitary-thyroid axis.

Answer 4

1 - The hypothalamus synthesises and releases thyrotropin releasing hormone, which travels to the anterior pituitary gland.

2 - The anterior pituitary gland is stimulated to release thyroid stimulating hormone, which travels to the thyroid gland.

3 - The thyroid gland synthesises and releases T3 and T4, which act through negative feedback to reduce the synthesis and release of thyrotropin releasing hormone at the hypothalamus and thyroid stimulating hormone at the anterior pituitary gland.

Question 5

List the three main groups of hormones.

Answer 5

1 - Protein / peptide hormones.

2 - Steroid hormones.

3 - Amine hormones.

Question 6

List two examples of protein / peptide hormones.

Answer 6

1 - Insulin.

2 - Thyrotropin releasing hormone.

Question 7

List two examples of steroid hormones.

Answer 7

1 - Cholesterol.

2 - Cortisol.

Question 8

List 3 examples of amine hormones.

Answer 8

1 - Tyrosine.

2 - Thyroxine.

3 - Noradrenaline.

Question 9

Are protein / peptide hormones hypdrophobic or hydrophilic?

Answer 9

Hydrophilic.

Question 10

In the anterior pituitary, which cells produce adrenocorticotropic hormone?

Answer 10

Corticotrophs.

Question 11

In the corticotroph, what is the pre-prohormone to adrenocorticotropic hormone?

Answer 11

Pre-pro-opiomelanocortin.

Question 12

How are TSH, LH, FSH and hCG related?

Answer 12

1 - They are all released from the anterior pituitary.

2 - All have an alpha and beta subunit, of which they share a common alpha subunit.

Question 13

What is the precursor of all steroid hormones?

Answer 13

Cholesterol.

Question 14

Are steroid hormones hydrophobic or hydrophilic?

Answer 14

Hydrophobic.

Question 15

In steroid hormone synthesis, what is the source of cholesterol?

Answer 15

Hydrolysis of esters.

Question 16

In steroid hormone synthesis, what is cholesterol converted to?

Where does this occur?

Answer 16

• Pregnenolone.

- In the mitochondria.

Question 17

What is the role of steroid acute regulatory protein (StAR) in steroid hormone synthesis?

Answer 17

To facilitate movement of cholesterol to the mitochondria.

Question 18

In steroid hormone synthesis, what regulates StAR activity?

Answer 18

Adrenocorticotropic hormone.

Question 19

Give an example of a hormone that is produced in the zona glomerulosa of the adrenal gland.

Answer 19

Aldosterone.

Question 20

Give an example of a hormone that is produced in the zona fasciculata of the adrenal gland.

Answer 20

Cortisol.

Question 21

Give an example of a class of hormone that is produced in the zona reticularis of the adrenal gland.

Answer 21

Adrenal androgens

Question 22

Why do increases in secretion of steroid hormones reflect accelerated rates of synthesis, whereas increases in secretion of peptide / protein hormones do not necessarily reflect accelerated rates of synthesis?

Answer 22

Because peptide / protein hormones can be stored, whereas steroid hormones cannot (as they are hydrophobic / lipophilic).

Question 23

What do the numbers ‘3’ and ‘4’ represent with T3 and T4?

Answer 23

The number of iodine atoms.

Question 24

Are amine hormones hydrophobic or hydrophilic?

Answer 24

Hydrophobic.

Question 25

Describe the process of thyroid hormone synthesis.

Answer 25

1 - I- and Na+ enter the follicular cell through an I- / Na+ symporter.

2 - Thyroglobulin is synthesised in the follicular cell (bound to many tyrosine residues) and released by exocytosis into the follicle colloid.

3 - I- exits the follicular cell into the follicle colloid via pendrin.

4 - Iodine is oxidised and binds to tyrosine residues that are bound to thyroglobulin to form either DIT (2 x I-) or MIT (1 x I-).

5 - Thyroglobulin and its iodinated tyrosine residues (MIT and DIT) re-enter the follicular cell by endocytosis.

6 - T3 is produced where DIT combines with MIT, whereas T4 is produced where DIT combines with DIT.

7 - A lysosome cleaves T3 and T4 from thyroglobulin.

Question 26

List 3 functions of carrier proteins for steroid and thyroid hormones.

Answer 26

1 - To increase solubility.

2 - To increase half-life.

3 - To maintain a reservoir of the hormone in the blood.

Question 27

What is the disadvantage of non-specific binding proteins?

Answer 27

They bind loosely.

Question 28

What is the name of the binding protein that is specific for thyroid hormones?

Answer 28

Thyroid binding globulin (TBG).

Question 29

What is the name of the binding protein that is specific for cortisol?

Answer 29

Cortisol binding globulin (CBG).

Question 30

Where is the site of action for protein / peptide hormones and steroid hormones?

Answer 30

• Protein / peptide hormones: Cell surface receptors.

- Steroid hormones: Intracellular receptors (cytoplasm or nuclear).

Question 31

What is the cause of dwarfism?

Answer 31

A deficiency of growth hormone.

Question 32

What is the cause of gigantism?

Answer 32

An excess of growth hormone.

Question 33

What is the cause of diabetes insipidus?

Answer 33

A deficiency of antidiuretic hormone.

Question 34

What is the cause of hypervolaemia?

Answer 34

An excess of antidiuretic hormone.

Question 35

What is the cause of diabetes mellitus?

Answer 35

A deficiency of insulin.