Lecture 1 - Introduction to Endocrinology

Question 1

3 groups of hormones:

Answer 1

Proteins/polypeptides Steroid Miscellaneous

Question 2

Synthesis of protein hormones - ACTH Adenocorticotrophic hormone

Answer 2

DNA codes for mRNA of POMC mRNA makes POMC using a.a. from blood POMC modified in Golgi Exported in vesicles where enzymes cut off the ‘pro’ bit ACTH vesicles accumulate under surface Wait for signal ACTH is then exocytosed into blood

Question 3

Where is ACTH produced?

Answer 3

Anterior Pituitary

Question 4

Synthesis of steroid hormones - cortisol

Answer 4

Cholesterol delivered to cell as LDLs Then stored as Fatty Acid Esters Esterase breaks down the FAE Cholesterol enters the mitochondria via StAR proteins Enzymes in mitochondria catalyse the steps to convert cholesterol into steroid cortisol is then secreted into cytoplasm and then into blood

Question 5

What is the precursor molecule to all steroids?

Answer 5

Cholesterol

Question 6

Where are most steroid hormones produced?

Answer 6

In the adrenal glands or gonads

Question 7

Where are steroids synthesised in the cell?

Answer 7

Mitochondria

Question 8

What is the rate limiting step for cholesterol synthesis?

Answer 8

Cholesterol entry into mitochondria via StAR

Question 9

Differences between polypeptide and steroid hormone secretion

Answer 9

PH stored in vesicles in the cell, waiting for signal SH secreted into blood stream as soon as produced

Question 10

How do protein hormones travel around the body?

Answer 10

Secreted into blood

Travel unbound - so sensitive to enzymatic breakdown Very short half lives - usually matter of minutes Stored in production tissues

Question 11

How do steroid hormones travel around the body?

Answer 11

Stored in blood Bind to plasma proteins - Albumin (mops up large amount but non-specific interaction) Each steroid has specific plasma proteins eg: Coricosteroid Binding Globulin (Cortisol) Vast majority of SH bound to plasma proteins in blood SMALL AMOUNT free - which can move into tissues

Question 12

What is the equilibrium equation in the blood for protein hormones?

Answer 12

Hormone + Plasma proteins <=> Protein Bound Hormone

Question 13

To maintain equilibrium of SH in blood, how does the equilibrium react when decrease of SH occurs?

Answer 13

Less unbound SH Equilibrium shifts to left, releasing more bound hormone *Endocrine cells are stimulated to produce more SH* (Occurs with any shift in equilibrium)

Question 14

What is the mechanism of action of protein hormones to cause an effect on the cell?

Answer 14

ACTH binds to G-protein coupled receptor Activates Adenylate Cyclase - Causes ATP -> cAMP Increase of cAMP activates Protein Kinase A (PKA) PKA phosphorylates esterase, releasing cholesterol from LDLs StAR is phosphorylated, hence activated StAR allows cholesterol to enter the mitochondrion Stimulating SH production

Question 15

What is the mechanism of action of steroid hormones to cause a reaction?

Answer 15

Free SH enter cells via diffusion SH binds into intracellular receptors Complex translocates to nucleus Affects DNA transcription, translocation CHANGE PROTEIN MACHINERY WITHIN CELL

Question 16

How does hormone feedback work?

Answer 16

NEGATIVE FEEDBACK The hormone switches off its own production Hormones are usually released as a homeostatic process so will need to be switched off e.g. after cortisol is released, it returns to anterior pituitary and switches ACTH off

Question 17

What are the different endocrine glands present in the human body?

Answer 17