1a. Overview + Peptide hormones

Question 1

Definition of the endocrine system

Answer 1

a system that integrates and controls organ function via secretion of chemicals (hormones) from cells, tissues or glands

• works with the nervous system

Question 2

Definition of endocrine hormones

Answer 2

chemicals secreted from cells, tissues or glands that are carried in the blood to target organs, distal from the site of hormone synthesis, where they influence the activity of that target organ

Question 3

Definition of paracrine hormones

Answer 3

act locally at the site of synthesis, do not travel distal to sites, diffuse in ECF to affect neighbouring cells e.g. histamine

Question 4

Definition of autocrine hormones

Answer 4

act on/in the same cell that synthesises the hormone e.g. cytokines

Question 5

Definition of exocrine hormones

Answer 5

released from exocrine glands via ducts to the external environment including the GI tract e.g. saliva, sweat, bile

Question 6

How does endocrine communication work

Answer 6

hormones travel in the blood to their target organs/tissues
- tissues detect hormones through specific receptors for that chemical on/in the cells

No receptor = No response

Question 7

Definition of neurotransmitter

Answer 7

a chemical released by the neurone - acts locally within the synaptic cleft

Question 8

How does neural communication work

Answer 8

neurotransmitters released from the presynaptic neutrons travel across the synaptic cleft to the postsynaptic cell to influence its activity

Question 9

Definition of neuroendocrine

Answer 9

the combined endocrine and nervous systems

Question 10

Definition of neuroendocrine hormones

Answer 10

chemicals released by nerves but entered into the blood to travel to their targets

Question 11

What makes the response to hormones highly specific despite them travelling all throughout the body

Answer 11

the presence of highly specific receptors on target cells

Question 12

How can the same hormone produce different effects in the body

Answer 12

when it interacts with a different target cell on a different target tissue

EXAMPLE:
insulin
1. skeletal muscle/adipose tissue - increased glucose uptake
2. liver - increased glycogenesis/decreased gluconeogenesis

Question 13

What physiological systems are involved in the endocrine system

Answer 13

reproductive, renal, GI

Question 14

what main glands are involved in the endocrine system

Answer 14

thyroid, adrenal, pituitary, hypothalamus

Question 15

name the 6 features of an endocrine hormone

Answer 15

1. produced by a cell or group of cells
2. secreted from those cells into blood
3. transported via the blood to distant targets
4. exert their effects at very low concentrations
5. act by binding to receptors on target tissues
6. have their action terminated, often via -ve feedback looks

Question 16

Why do hormones work at very low concentrations

Answer 16

hormone receptors have very high affinity to hormone - i.e. don’t need much of the hormone to create a large response

Question 17

what are the three groups of endocrine hormones

Answer 17

1. peptide/protein hormones (from chains of amino acids)
2. steroid hormones (from cholesterol)
3. amine hormones (from one of 2 amino acids - tryptophan or tyrosine)

Question 18

when are peptide hormones synthesised and stored

Answer 18

synthesised in advance of need and stored in vesicles until required

Question 19

What is the initial protein produced in peptide hormones

Answer 19

preprohormone - large and inactive, produced by ribosomes

Question 20

what are preprohormones

Answer 20

initial protein - contain one or more copies of the active hormone in their amino acid sequence

Question 21

what happens to preprohormones in the Rough ER

Answer 21

cleaved into smaller inactive units called prohormones

Question 22

what happens to prohormones in the golgi apparatus

Answer 22

packaged into vesicles along with proteolytic enzymes

Question 23

what do the proteolytic enzymes in the vesicles do

Answer 23

breaks down the prohormone into the active hormone and other fragments

Question 24

what happens to the vesicles when release is triggered (co-secretion)

Answer 24

the vesicles in the endocrine cells release all contents (hormones and fragments) into the plasma

Question 25

give an example of when measuring inactive fragments in the plasma can be used clinically

Answer 25

C-peptides in diabetes

Question 26

what is C-peptide

Answer 26

the inactive fragment cleaved from the insulin prohormone - levels in plasma or urine are often measured to indicate endogenous insulin production from the pancreas (as they are produced in equal amounts) BUT insulin is metabolised faster so C-peptide levels usually 5x higher

Question 27

Why is C-peptide measured in diabetics and not insulin directly

Answer 27

C-peptide reflects endogenous insulin production by the pancreas - so value is independent of synthetic insulin administration

Question 28

Peptide hormones are water soluble - what does this mean for transport and receptor placement

Answer 28

transport - hydrophilic so dissolve in plasma making transport via the blood simple and easy

receptors - lipophobic so cannot cross cell membrane therefore bind to membrane bound receptors on target cell

Question 29

Once bound most peptide hormones work via modulating which two pathways

Answer 29

1. G protein coupled receptor
2. Tyrosine kinase linked receptor

both signalling pathways

Question 30

How does the peptide hormone use the G Protein Couples Receptor

Answer 30

activates a 2nd messenger* system and/or ion channels leading to modification of existing proteins = RAPID RESPONSE

*may also alter gene expression

Question 31

How does the peptide hormone use the Tyrosine Kinase Linked Receptor

Answer 31

alters gene expression = SLOWER, longer lasting activity

Question 32

why does prolonged action of peptide hormones require continuous secretion

Answer 32

they have a very short half life in the plasma (minutes)

Question 33

where are peptide hormone receptors located

Answer 33

outside the cell on the membrane