Introduction to Endocrine Physiology

Question 1

True or False: Hormones are produced by organs.

Answer 1

False - hormones can be produced by individual cells

Question 2

True or False: Hormones must be released into the blood stream.

Answer 2

False - there is paracrine/autocrine signaling, chemical mediators may be diffused into the interstitial space

Question 3

True or False: Hormones exert its specific function.

Answer 3

True. (hehehe)

Question 4

What are the types of hormones according to structure?

Answer 4

• amino acid derivatives/amines
• proteins, peptides, and glycoproteins
• steroids - prostanoids/prostaglandins

Question 5

Enumerate the amino acid/amine hormones

Answer 5

• thyroid homones
• catecholamines
• melatonin

Question 6

How are thyroid hormones synthesized?

Answer 6

Iodination of benzene ring of tyrosine

Question 7

Give examples of thyroid hormones.

Answer 7

• T3 or triiodothyronine
• T4 or thyroxine

Question 8

How are catecholamines synthesized?

Answer 8

Introduction of a second hydroxyl group in the benzene ring of tyrosine

Question 9

Give examples of catecholamines.

Answer 9

norepinephrine, epinephrine, dopamine

Question 10

How is melatonin synthesized?

Answer 10

Acetylation of the aliphatic amino group and hydroxylation of the indole ring of tryptophan

Question 11

Enumerate the protein/glycoprotein hormones

Answer 11

• thyrotropin-releasing hormone (TRH), growth hormone (GH), and luteinizing hormone (LH)
• insulin

Question 12

What is peculiar about TRH, GH, and LH?

Answer 12

They all come from a common ancestral gene; they have similar basic structures but with different functions

Question 13

What is the smallest hormone? Where is it produced?

Answer 13

TRH (3 amino acids), produced in the hypothalamus

Question 14

What is peculiar about insulin production?

Answer 14

Analogues (from alternative splicing and post-translational modification) of insulin produce slightly different effects. This is significant for some patients that are resistant to certain types of insulin

Question 16

Enumerate the steroid hormones

Answer 16

• cortisol - glucocorticoid - aldosterone - mineralocorticoid - DHEA-S, androstenedione - sex hormones - vitamin D metabolites

Question 17

How are steroids produced?

Answer 17

Cholesterol undergoes modification of side chains, hydroxylation, and ring formation.

Question 18

How are prostanoids or prostaglandins produced?

Answer 18

addition of oxygen atoms and cyclization of arachidonic acid

Question 19

How are peptide and steroid hormones stored?

Answer 19

Peptide hormones are usually stored in granules, while steroids are usually free in the cytoplasm

Question 20

How are peptide and steroid hormones transported in the blood?

Answer 20

Peptide hormones are usually free (faster action), while steroids are usually bound to transport proteins.

Question 21

What are the types of hormones according to mechanism of action?

Answer 21

• hormones that bind to intracellular receptors (i.e. lipophilic hormones)
• hormones that bind to cell-surface receptors

Question 22

How are hormones classified according to function?

Answer 22

• reproduction
• growth and development
• homeostasis
• energy availability

Question 23

Types of cell-to-cell interactions:

Answer 23

• autocrine (short distance to cells of the same type)
• paracrine (short distance to cells of different type)
• endocrine (long distance via blood stream)
• neurocrine (long distance via blood stream produced by a nerve cell)

Question 24

preprohormone vs prohormone vs hormone

Answer 24

• preprohormone - produced in ribosomes; signal peptide is still attached
• prohormone - produced in RER; signal peptide is cleaved off
• hormone - produced in Golgi apparatus; copeptide is cleaved off; stored in granules

Question 25

examples of special precursor molecules:

Answer 25

• propiomelanocortin (POMC) - precursor for ACTH (adenocorticotropic hormone)
• glucagon precursor - precursor for glucagon (pancreas) or glucagon-like peptide (GLP, in L cells of intestine)

Question 26

Types of hormone release

Answer 26

* **vesicular** e.g. proteins, peptides, and catecholamines (stored in granules) * **non-vesicular** e.g. steroids and eicosanoids (lipophilic hormones), diffuse across plasma membrane out of the cell * **hybrid** (combination) e.g. thyroid hormones

Question 27

How are non-vesicular hormones protected from degradation?

Answer 27

by being bound to transport proteins e.g. **thyroglobulin** for thyroid hormones and **cortisol-binding protein** for cortisol

Question 28

mechanism of peptide hormone release

Answer 28

**Stimulus-secretion coupling** 1. Stimulus (*depends* on hormone) 2. Activation of second messenger (only for some). 3. Increase in *intracellular calcium* drives *contraction of microtubules and microfilaments* attached to secretory granules 4. Bring secretory granules to cell membrane 5. Granule fuses with cell membrane 6. Hormone is released (*exocytosis*).

Question 29

How are steroids transported?

Answer 29

Steroids are *bound to transport proteins*, to protect them from metabolism and renal clearance (wastage)

Question 30

How are peptide hormones transported?

Answer 30

Free - short-lived, destroyed by circulating proteases, have immediate effect

Question 31

protein hormones that are bound to carrier protein:

Answer 31

GH and IGF-1

Question 32

Cells that eventually receive the hormone in circulation

Answer 32

target cells

Question 33

specialized structure that will bind a particular hormone

Answer 33

receptor

Question 34

Parts of the receptor

Answer 34

* **recognition domain** - binds to the hormone * **coupling domain** - involved in signal transduction; *intracellular*, mediates signaling of receptor

Question 35

three conditions for hormone to produce an effect

Answer 35

1. Hormone must be *recognized* by receptor. 2. Hormone-Receptor Complex must have the ability to produce *signal generation* in cytoplasm/nucleus. 3. There must be available effector proteins/enzymes and other machinery to manifest response.

Question 36

Will there be an effect if receptor is weakly bound to a homologue of the original hormone?

Answer 36

Yes, and the effects are those produced by the original hormone.

Question 37

Significance of **Human Chorionic Gonadotropin (HCG)**

Answer 37

* structural *homologue* of **TSH (thyroid-stimulating hormone)** and **LH (luteinizing hormone)** * released *during pregnancy* by placenta * may activate thyroid hormones * causes **gestational transient thyrotoxicosis** associated with **hyperemesis gravidarum** (morning sickness)

Question 38

Hormone mechanisms of action

Answer 38

* G-protein-linked receptors * G-protein second messengers * enzyme-linked receptors

Question 39

How many subunits are there in a G-protein? Enumerate:

Answer 39

three: alpha, beta, and gamma

Question 40

What are the functions of the subunits of G-proteins?

Answer 40

alpha-subunit - binds to receptors, to effector molecules, and to GDP and GTP beta-gamma-subunit (dimer) - may serve to attach the G-protein to the plasma membrane

Question 41

What are the basic components of a G-protein pathway?

Answer 41

* Receptor * G-protein complex * Target enzyme or channel

Question 42

Cation required for the G-protein cycle

Answer 42

Mg²⁺

Question 43

What are the main effector systems used by G-proteins?

Answer 43

* adenylyl cyclase-cAMP system * plasma membrane phospholipids/phospholipase C pathway * calcium-calmodulin system

Question 44

What does the adenylyl cyclase-cAMP system do?

Answer 44

It catalyzes the formation of cAMP from ATP with Mg²⁺ as cofactor. This increases the intracellular cAMP levels.