Introduction to Endocrinology

Question 1

Differences between endocrine, paracrine and autocrine?

Answer 1

Endocrine - Hormone acts on target cell at distance from source
Paracrine - Hormone acts on nearby target cell
Autocrine - Hormone acts on its own producing cell

Question 2

3 hormone classes?

Answer 2

Protein/polypeptide hormones
Steroid hormones
Miscellaneous

Question 3

Example of a protein/polypeptide hormone?

Answer 3

Adrenocorticotrophic hormone (ACTH)

Question 4

Example of a steroid hormone?

Answer 4

Cortisol

Question 5

Precursor molecule for ACTH?

Answer 5

POMC - pro-opiomelanocortin

Question 6

Where is POMC produced?

Answer 6

Anterior pituitary gland

Question 7

Process of POMC generation to final production of ACTH?

Answer 7

Amino acids enter cytoplasm of corticotroph cells in anterior pituitary gland stimulating transcription and translation of POMC in ER
Vesicles contains POMC are transported into Golgi where they undergo post-translational modification and processing by enzymes to form ACTH
ACTH is stored in vesicles within the cell ready for stress signal for exocytosis

Question 8

What is the major stress hormone of the body?

Answer 8

Cortisol

Question 9

Stimulus and initiation for cortisol production?

Answer 9

Stress stimulus causes breakdown of fatty acid esters using enzymes, esterase, liberating cholesterol to begin cortisol synthesis

Question 10

Transportation of cholesterol after liberation and production of cortisol process?

Answer 10

Liberated cholesterol is transported into mitochondria via StAR proteins (availability limits rate of cholesterol production)
Once in the mitochondria, cholesterol is converted to the steroid hormone of choice i.e. Cortisol

Question 11

Difference in degree of mediation in protein hormone and steroid hormone release?

Answer 11

Protein hormone - stored in cytoplasmic vesicles until signal arrives to exocytose and release hormone
Steroid hormone - diffuses across plasma membrane of adrenal cortical cell straight into blood circulation as soon as it is produced

Question 12

What molecules do steroid hormones bind to in the blood to prevent degradation during transport?

Answer 12

PLASMA PROTEINS

Question 13

Low affinity, high capacity transport protein for steroid hormones? (general transporter, not overly specific to any one molecule)

Answer 13

Albumin

Question 14

High affinity, low capacity protein for steroid hormones?

Answer 14

Binding globulins

e.g. cortisol-binding globulin

Question 15

What state must steroid hormones be in the blood to be biologically active?

Answer 15

Free, unbound to plasma proteins

- if bound, they have no effect, however only a small proportion of steroid hormone in the blood is unbound

Question 16

Describe the equilibrium of free hormone to plasma protein-bound hormone and how it is affected?

Answer 16

An equilibrium forms between plasma protein bound hormone and free hormone in the blood
When there is increased uptake of free hormone by target tissue, its concentration will decrease and equilibrium will shift leading to dissociation of plasma protein bound hormone and increased hormone production from the endocrine gland
This also works in the opposite direction leading to an increase in plasma protein bound hormone in the blood

Question 17

Process of ACTH action and effect?

Answer 17

ACTH transport to adrenal cortical cells in adrenal glands via the blood
Binds to ACTH G-protein linked receptor
Activates adenylate cyclase which increases conversion of ATP to cAMP
cAMP increase activates protein kinase A which stimulates increased cholesterol release from fatty acid esters and increased uptake of cholesterol into mitochondria via StAR proteins
OVERALL EFFECT IS INCREASED CORTISOL SYNTHESIS

Question 18

Mechanism of action of steroid hormones?

Answer 18

Free steroid hormones freely diffuse across plasma membrane of target cell
Bind to intracellular receptor
Complex translocated into the nucleus where protein transcription is modified for production of a new protein or increased specific protein production

Question 19

Describe the negative feedback cycle involving ACTH-mediated cortisol production?

Answer 19

Stress stimulates synthesis/release of ACTH from anterior pituitary
ACTH stimulates synthesis/release of cortisol from adrenal gland into the bloodstream
Cortisol acts on anterior pituitary inhibiting synthesis of ACTH