Introduction to Endocrinology

Question 1

What are the three groups of hormone?

Answer 1

Protein/peptide
Steroid
Miscellaneous

Question 2

What are peptide hormones initially produced as? Give an example.

Answer 2

Inactive prohormones

E.g. ACTH is produced as pro-opiomelanocortin (POMC)

Question 3

Describe the synthesis of protein/peptide hormones.

Answer 3

Amino acids are delivered to the cell. These are used to synthesise the peptide hormones in the same way that all proteins are synthesised. Genome –> mRNA –> protein

Question 4

What are all steroid hormones derived from?

Answer 4

Cholesterol

Question 5

How is cholesterol stored in cells and what do they look like in the cell?

Answer 5

Cholesterol is delivered in LDLs and then it is stored as fatty acid esters, which appear as fatty droplets in the cell. Steroid producing cells have a lot of fat droplets.

Question 6

Where are most steroid hormones produced?

Answer 6

Adrenals and gonads

Question 7

What enzyme breaks down fatty acid esters?

Answer 7

Esterase

Question 8

Where does steroid hormone synthesis take place within the cell?

Answer 8

Mitochondrion

Question 9

How does cholesterol get into the mitochondrion?

Answer 9

Via StAR proteins (steroidogenic acute regulatory proteins)

Question 10

As all steroid hormones are derived from cholesterol, what determines the final hormone produced?

Answer 10

The combination of enzymes that are found within the cell

Question 11

State some key features of protein/polypeptide hormones and state how they are stored.

Answer 11

Protein/polypeptide hormones are stored in the cells that produce them. They have a short half life.

Question 12

How are steroid hormones transported/stored?

Answer 12

They are transported in the blood - bound to carrier/plamsa proteins such as albumin or other specific carriers such as cortisol and corticosteroid binding globulin(CBG).

Question 13

State two ways in which the steroid hormone equilibrium in the blood can be shifted.

Answer 13

1. Uptake of steroid hormones by tissue - leads to the release of some of the protein bound hormone to re-establish previous free steroid hormone levels.
2. Rise in plasma protein levels - more plasma proteins means that you are more likely that the plasma proteins will bind to the hormone so more protein bound hormone is formed.

Question 14

Give two examples of how the steroid hormone equilibrium can be shifted.

Answer 14

Cortisol is a stress hormone and in times of stress, more of the free cortisol enters the tissues so the free cortisol levels fall. Some of protein bind hormone release cortisol to maintain free steroid hormone blood levels.
In pregnancy more plasma proteins are synthesised.

Question 15

Describe the mechanism of action of ACTH in stimulating cortisol production.

Answer 15

1. ACTH receptors are usually G-protein coupled receptors.
2. Binding of ACTH to the receptor activates adenylate cyclase, which converts ATP to cAMP. The increase in cAMP activates Protein Kinase A.
3. Esterase is phosphorylated, and so cholesterol is liberated.
4. Phosphorylation of the StAR protein activates the StAR protein allowing cholesterol to move into the mitochondrion. This then stimulates steroid hormone production.

Question 16

What type of receptor do steroid hormones bind to and what is their mode of action on target cells

Answer 16

Intracellular receptors - they act as transcription factors

once bound to receptor they translocate to the nucleus and effect DNA transcription and subsequent translation

They change protein machinery of cell.

Question 17

Describe the feedback loop of ACTH and cortisol.

Answer 17

1. The anterior pituitary is stimulated by stress and ACTH is released.
2. ACTH acts on the adrenal gland to increase cortisol production. Cortisol reduces stress ( its function)
3. Cortisol returns to the anterior pituitary and switches off cortisol production.

NEGATIVE FEEDBACK

Question 18

What’s the pro-hormone for ACTH?

Answer 18

Pro-opiomelanocortin ( POMC)

Question 19

How long do peptide hormones last in blood and why?

Answer 19

A few minutes - they have a quick discrete action

Peptide hormones are broken down quickly via enzymatic action

Question 20

Which blood vessels are pituitary hormones secreted into?

Answer 20

pituitary capillary

Question 21

Provide an example of a peptide and steroid hormone

Answer 21

ACTH = peptide 
Cortisol = steroid

Question 22

What happens in terms of CBG during pregnancy?

Answer 22

Pregnancy increases CBG levels –> cortisol levels rise to ensure a constant level of free hormone available to tissues

Question 23

What’s the main rate limiting step for steroid hormone synthesis?

Answer 23

Transporting cholesterol into the mitochondria

Question 24

What determines the final steroid hormone product?

Answer 24

The enzymes present in certain cells determines the final steroid hormone product eg adrenal cortisol cells have enzymes to produce cortisol.

Question 25

What are the main difference between peptide and steroid hormone secretion

Answer 25

peptide - stored in vesicles and released via exocytosis when stimulated. REGULATED SECRETION
steroid - secreted in blood immediately since they are lipid soluble. CONSTITUTIVE SECRETION

Question 26

Whats plasma protein has the highest abundance within the blood?

Answer 26

albumin -not specific, can mop up most steroid hormones

Question 27

Provide an example of when steroid hormone are regulated via positive feedback

Answer 27

oestrogen and LH

Question 28

What type of hormones are secreted by the anterior pituitary?

Answer 28

protein/peptide