Endocrinology (lecture 25)

Question 1

GAP junction communication

Answer 1

Message transmitted directly from cell to cell

Specificity depends on anatomical location/proximity

Question 2

Synaptic communication

Answer 2

Message transmitted across synaptic cleft

Specificity depends on anatomical location and receptors

Question 3

Paracrine and autocrine communication

Answer 3

Message transmitted by diffusion in interstitial fluid

Specificty depends on receptors but also proximity

Autocrine = acts on itself 
Paracrine = acts on cells in local area

Question 4

Endocrine communication

Answer 4

Message transmitted by circulating body fluids - blood

Specificity depends on receptors

Question 5

Definition of endocrine system

Answer 5

Endocrine cells within endocrine glands release substances (hormones) which are conveyed by the blood stream & act on distant cells

Question 6

What are the 2 main controllers of the body?

Answer 6

Hypothalamus
Pituitary

They control the rest of the endocrine system

Question 7

What does the rest of the endocrine system do?

Answer 7

• Thyroid controls metabolism
• Parathyroids control calcium levels
• Thymus controls body temperature
• Adrenals release adrenaline/epinephrine
• Pancreas
• Ovaries & testes produce sex hormones

Question 8

What are the non-classical producers?

Answer 8

• Kidney
• Heart muscle
• Endothelium
• Platelets
• Adipocytes
• White blood cells

Question 9

What is a hormone?

Answer 9

Chemical messenger

Synthesised by specialised cells

Secreted into the blood in small amounts which acts on a specific receptor in target organs to regulate cellular function

Question 10

How do hormones interact with target cells?

Answer 10

• High affinity
• Synergistic
• Permissive
• Antagonistic
• Competitive

Question 11

High affinity interaction

Answer 11

Hormones are effective at low concentrations. They are normally found in the blood in the pico molar range

Question 12

Synergistic interaction

Answer 12

The effect of two hormones is greater than one alone

e.g. thyroid hormone and norepinephrine on heart rate

Question 13

Permissive interaction

Answer 13

The presence of one hormone is necessary for another to have an effect

e.g. thyroid hormone and aldosterone on Na/K pumps in kidney

Question 14

Antagonistic interaction

Answer 14

Two hormones oppose each other’s effects

e.g. insulin vs glucagon

Question 15

Competitive interaction

Answer 15

Two hormones, similar in structure, compete for the same receptor

e.g. epinephrine and norepinephrine

Question 16

What are the 3 classes of hormones based on chemical structure?

Answer 16

Steroids
Peptides
Amino acids

Question 17

What are steroid hormones

Answer 17

Synthesised from cholesterol
Lipiphilic – can cross membranes easily
Receptors tend to be inside the cell – in the nucleus
Very difficult to store as leak out of vesicles – produced on demand

Eg. Cortisol

Question 18

What are peptide hormones

Answer 18

Synthesised from amino acids
Most abundant hormone class
Hydrophilic – like water – don’t cross the membrane easily
Receptors are on the membrane – second messenger pathways involved

Eg. Growth hormone

Question 19

What are amino acid hormones

Answer 19

Synthesised from tyrosine
Some act like steroid hormones but some act like peptide hormones

Eg. Thyroid hormone & epinephrine

Question 20

Properties of steroid hormones?

Answer 20

Cholesterol produced predominantly in the liver

• Released immediately following synthesis
• Circulate in bound form – needs a carrier protein - bound to plasma proteins
• Act on intracellular receptors which then bind to DNA (hormone response elements) & regulate gene transcription

Have slow long lasting effects

Question 21

What action do steroid hormones have on receptors?

Answer 21

Inhibitory protein complex (Heat shock protein 90) is bound during the resting state, hiding the DNA binding domain

Hormone binds (allosterically) causing a conformational; change so the hinge opens up, exposing the DNA binding sites

Question 22

Properties of peptide hormones

Answer 22

Peptide hormones are between 3 & 332 amino acids in length – most are longer

Synthesised as preprohormones (inactive form) & stored prior to release & modified before release

Act on cell surface receptors then via 2nd messenger systems to cause effect in target cells

Question 23

Properties of amino acids

Answer 23

Amino acid hormones include thyroid hormone & epinephrine

Most synthesised from tyrosine

Stored for instant release

Different modes of action – TH has intracellular receptors, others act at the surface

Question 24

What action do peptide and amino acids have on the cAMP pathway?

Answer 24

1) Hormone binds to receptor
2) Leads to G protein which activates adenylate cyclase
3) cAMP produced
activates protein kinase A
4) phosphorylates many things changing the cells activity

Question 25

What action do peptide and amino acids have on the IP3 pathway?

Answer 25

Phospholipase C cuts phospholipids

PIP2 converted to IP3 and DAG

IP3 part falls off & binds to receptor on the sarcoplasmic reticulum to release calcium ions

Ca++ and DAG activate PKC

Question 26

What are the different types of hormone release?

Answer 26

Continuous
Pulsatile
Circadian
Exocytosis on stimulus

Question 27

How can you control hormone effects?

Answer 27

Modification 
Degradation 
Receptor down-regulation 
Termination of intracellular effects 
Negative feedback