3. Principles of Hormone Action

Question 1

what are HORMONES

Answer 1

• one type of FIRST (or PRIMARY) MESSENGER
• molecules that have an effect on specific organs
• called TARGET ORGANS
• only cells with SPECIFIC RECEPTORS for the hormone will respond to the
  hormone
• called TARGET CELLS
• organs, tissues or cells lacking the specific receptors do not respond to
  the stimulating effects

Question 2

what are the 4 CLASSIFICATIONS of HORMONES

Answer 2

1. Lipid-Derived Hormones (Lipid-soluble)
2. Amino acid derivative hormones
3. Peptide hormones (hydrophilic)
4. Chemical messengers derived from fatty acids (eicosanoids)

Question 3

what is the primary class of LIPID HORMONES

Answer 3

STEROID HORMONES

Question 4

most LIPID HORMONES are DERIVED from…

Answer 4

CHOLESTEROL

• thus have a similar structure to it

Question 5

examples of LIPID HORMONES

Answer 5

• SEX-HORMONES
  (androgens, estrogens and progesterone)
• Hormones produced in ADRENAL GLANDS
  (Glucocorticoids and mineralocorticoids)

Question 6

FUNCTIONS of LIPID HORMONES include (3):

Answer 6

• WATER BALANCE
• SEXUAL DEVELOPMENT
• STRESS RESPONSE

Question 7

AMINO ACID DERIVATIVE HORMONES are SMALL molecules commonly DERIVED from.. (2)

Answer 7

TYROSINE &
TRYPTOPHAN

Question 8

examples of AMINO ACID DERIVATIVE HORMONES (2)

Answer 8

• THYROID hormone (lipid-soluble)
• CATECHOLAMINES (water-soluble)
  eg noradrenalin, adrenalin

Question 9

FUNCTIONS of AMINO ACID DERIVATIVE HORMONES include:

Answer 9

• Thyroid hormone regulates the development of organs
  and metabolism.
• Noradrenaline and adrenaline (catecholamines) increase
  heart rate, dilate blood vessels and cause the release of glucose during times of stress

Question 10

PEPTIDE HORMONES (hydrophilic) are…

Answer 10

CHAINS OF AMINO ACIDS (short or long)

Question 11

most HORMONES are..

Answer 11

PEPTIDE HORMONES

Question 12

examples of PEPTIDE HORMONES

Answer 12

FSH (small)
INSULIN (large)

PROLACTIN
GROWTH HORMONE
VASOPRESSIN
(pituitary)
ANP (which is produced by the heart -regulates homeostasis of the circulatory
system; released in response to high blood pressure and dilation of the atrium.)

Question 13

CHEMICAL MESENGERS derived from FATTY ACIDS
- EICOSANOIDS
are synthesised from..

Answer 13

ARACHIDONIC ACID
- 20-CARBON AMINO ACID

Question 14

CHEMICAL MESENGERS derived from FATTY ACIDS
- EICOSANOIDS…

Answer 14

• DEGRADE very EASILY
• do NOT GO FAR from production site

Question 15

unique characteristic of CHEMICAL MESENGERS derived from FATTY ACIDS
- EICOSANOIDS

Answer 15

they are produced and secreted by
NEARLY EVERY CELL in the body instead of just one gland.

Question 16

example of a CHEMICAL MESENGERS derived from FATTY ACIDS
- EICOSANOIDS

Answer 16

PROSTAGLANDIN

• Prostaglandins have a wide variety of functions ranging from
  uterine contractions to
  bronchodilation, inflammation and fever

(Aspirin acts on prostaglandins to reduce pain and fever)

Question 17

various roles of EICOSANOIDS include

Answer 17

inflammation,
blood pressure
blood clotting

Question 18

Endocrine, paracrine and autocrine

Answer 18

-paracrine signalling is
when NEIGHBOURING CELLS signal to each other

• Autocrine signalling is
  when a cell sends signals to ITSELF
• endocrine signalling uses the CIRCULATORY SYSTEM to transport ligands

Question 19

Binding of a ligand to a receptor changes…

Answer 19

changes its SHAPE or ACTIVITY

• allowing it to transmit a SIGNAL or directly
  produce a CHANGE inside of the cell

Question 20

RECEPTORS can be divided into 2 categories:

Answer 20

• INTRACELLULAR RECEPTORS
  (inside of the cell - in the cytoplasm or
  nucleus)
• CELL SURFACE RECEPTORS
  (embedded in the plasma membrane)

Question 21

What type of molecules reach INTRACELLULAR RECEPTORS

Answer 21

HYDROPHOBIC signalling molecules (ligands)

• DIFFUSE through plasma membrane

Question 22

RECEPTORS function as..

Answer 22

ligand-dependent TRANSCRIPTION FACTORS

Question 23

how do RECEPTORS function as ligand-dependent TRANSCRIPTION FACTORS?

hormone-receptor complex binds to…

Answer 23

• the hormone-receptor complex BINDS to PROMOTER REGIONS of responsive GENES and STIMULATE/INHIBIT TRANSCRIPTION
• SELECTIVELY affecting TRANSCRIPTION of genes
• CONCENTRATIONS of respective PROTEINS ALTERED
  -CHANGE IN PHENOTYPE OF CELL

Question 24

3 main components of CELL-SURFACE RECEPTORS

Answer 24

1. An external ligand binding domain- extracellular domain
2. A hydrophobic membrane spanning region
3. Intracellular domain inside the cell

Question 25

3 types of CELL-SURFACE RECEPTORS

Answer 25

- G PROTEIN-LINKED - ENZYME-LINKED - ION CHANNEL-LINKED

Question 26

What happens when a ligand binds to a G-PROTEIN COUPLED RECEPTOR

Answer 26

- G-PROTEIN IS ACTIVATED (membrane protein) eg used by Catecholamines

Question 27

what does an INACTIVE G-PROTEIN have on its ALPHA subunit

Answer 27

GDP

Question 28

What happens when a G-Protein is activated

Answer 28

- ALPHA SUBUNIT swaps GDP for GTP ALPHA subunit dissociates from the BETA and GAMMA subunits and triggers a cellular response

Question 29

What does the GTP-BOUND ALPHA SUBUNIT do after dissociating from other G-protein subunits

Answer 29

- BINDS to and ACTIVATES ADENYLATE CYCLASE - activated adenylate cyclase catalyses CONVERSION of ATP to CAMP and PYROPHOSPHATE - cAMP ACTIVATES PROTEIN KINASE A (secondary messenger) which PHOSPHORYLATES and activates other proteins and triggers further responses

Question 30

how does the alpha-subunit return to its original place on inactivated G-protein

Answer 30

GTP HYDROLYSED to GDP - signalling molecule comes off the receptor Alpha subunit comes back together with the receptor and beta and gamma subunits

Question 31

What are ENZYME-LINKED RECEPTORS

Answer 31

Cell-surface receptors with intracellular domains that are associated with an ENZYME - Normally have large extracellular and intracellular domains - When a ligand binds to the extracellular domain, a signal is transferred that ACTIVATES THE ENZYME component of the receptor which leads to a response eg. Insulin binding to tyrosine-kinase receptor

Question 32

what happens when a ligand binds to an ION-CHANNEL LINKED RECEPTOR

Answer 32

CONFORMATIONAL CHANGE in the STRUCTURE - allows IONS to PASS THROUGH eg. neurons

Question 33

what happens when Ions pass through ION CHANNEL- LINKED RECEPTOR

Answer 33

Change the ACTIVTY of ION-BINDING ENZYMES and VOLTAGE-SENSITIVE CHANNELS - to produce a response

Question 34

multiple hormones can...

Answer 34

utilize the same second messenger system

Question 35

a single hormone can...

Answer 35

utilize more than one second messenger system

Question 36

what do we get in DOWN-REGULATION of RECEPTORS

Answer 36

LINGAND-INDUCED DESENSITIZATION or INTERNALIZATION of receptor

Question 37

How do you get DOWN-REGULATION of RECEPTORS

Answer 37

Receptors CHRONICALLY EXPOSED to an EXCESSIVE AMOUNT of a LIGAND (endogenous mediators or from exogenous drugs)

Question 38

what is UP-REGULATION of RECEPTORS

Answer 38

SUPER-SENSITIZED CELLS - cell makes extra receptors on the surface (so any small amount of that ligand can bind)

Question 39

how do you get UP-REGULATION of RECEPTORS

Answer 39

- REPEATED EXPOSURE to an ANTAGONISTIC DRUG or - PROLONGED ABSENCE of the LIGAND

Question 40

What do RECEPTOR AGONISTS cause

Answer 40

DOWN-REGULATION of their respective receptor

Question 41

What do RECEPTOR ANTAGONISTS cause

Answer 41

UP-REGULATION of their respective receptor may also damage receptors faster than they upregulate (internalization of receptors due to antagonism)

Question 42

How are hormones secreted (pattern)

Answer 42

Hormone secretion often follows a RHYTHM or is PULSATILE secreted in a burst-like or episodic manner rather than constantly.

Question 43

how is melatonin secretion (pattern)

Answer 43

Melatonin secretion is related to the length of the NIGHT Also melatonin profiles show a SEASONAL pattern (increased production in winter)

Question 44

example of DIRECT and INDIRECT EFFECTS of hormones eg growth hormone

Answer 44

DIRECT EFFECTS: growth hormone binds to GH Receptors on Fat Cells, stimulating break down of triglycerides INDIRECT EFFECTS: Insulin-like Growth Factor-I (IGF-I) secreted in response to GH. The majority of the growth promoting effects of GH are actually due to IGF-I acting on its target cells.