Introduction to the endocrine system

Question 1

Define endocrine system

Answer 1

A system that controls organ function through the secretion of chemicals from cells, tissues or glands which are then carried in the blood to the target organs where they influence the activity of the organ

Question 2

How do tissues detect hormones

Answer 2

The presence of specific receptors for the hormones on or in the cell

Question 3

How does neural communication work

Answer 3

Neurotransmitters released from presynaptic neurons travel across the synaptic cleft to the postsynaptic cell to influence its activity

Question 4

How does endocrine communication work

Answer 4

Hormones travel in the blood to their target hormones

Question 5

What is neuroendocrine

Answer 5

Endocrine and nervous system combine

Nerves release hormones which enter the blood and travel to target cells e.g hypothalamus and posterior pituitary axis

Question 6

How can one hormone produce a different effect in different cells

Answer 6

Because each cell can have a different receptor for the hormone which leads to a different downstream pathway

Question 7

How do exocrine glands deliver their secretions

Answer 7

Through ducts to the external environment including the GI tract e.g bile and saliva

Question 8

What are autocrine secretions

Answer 8

cells secrete chemicals that bind to receptors on the same cell

Question 9

What are paracrine secretions

Answer 9

Chemicals diffuse in the extracellular fluid to affect neighbouring cells

Question 10

What are peptide hormone composed of

Answer 10

chains of amino acids

Question 11

What are amino hormones derived from

Answer 11

one of two amino acids - tryptophan or tyrosine

Question 12

What are steroid hormones derived from

Answer 12

cholesterol

Question 13

What is one of the only amine hormones that comes from tryptophan

Answer 13

melatonin

Question 14

Describe the sequence of how peptide hormones get synthesised and then stored and released

Answer 14

They are synthesised by ribosomes as preprohormone until they are needed when the preprohormone is cleaved in the endoplasmic reticulum into prohormone and packaged into vesicles by the golgi apparatus with proteolytic enzymes until it is needed

Question 15

What do the proteolytic enzymes which are packaged with prohormone do

Answer 15

Break the prohormone into the active hormone

Question 16

What is C-peptide and why is it measured instead of insulin directly

Answer 16

Inactive fragment cleaved from insulin prohormone - it is measured instead of insulin directly due to insulin b eing metabolised 5x as fast

Question 17

What is the mechanism of action of peptide hormones

Answer 17

they are water soluble so dissolve in the plasma and travel easily but cannot cross cell membranes so they have to bind to receptors on the target cell

Question 18

What are the two receptors that peptide hormones usually bind to

Answer 18

GPCR
tyrosine kinase linked

Question 19

What is a GPCR

Answer 19

G protein coupled receptor
activates 2nd messenger system or ion channels which leads to modification of existing proteins

Question 20

What is the difference between tyrosine kinase linked receptors and G protein coupled receptors

Answer 20

GPCR have a rapid response while tyrosine kinase linked receptors are slower and longer lasting which is why they are associated with growth

Question 21

How are steroid hormones different to the other hormones in terms of production and storage

Answer 21

They are synthesised directly as needed and not stored like the other hormones

Question 22

Why can steroid hormones not be stored

Answer 22

They are highly lipophilic so can therefore not be retained within a lipid membrane

Question 23

How are steroid hormones transported in the blood considering they are poorly water soluble

Answer 23

They are transported bound to carrier proteins such as albumin - this protects them from enzymatic degredation

Question 24

Are steroid hormones quick or slow acting

Answer 24

Slow onset of action but action persists longer then peptide and amine hormones

Question 25

Where in the body are steroid hormones produced

Answer 25

Gonads
Placenta
Kidney
Adrenal cortex

Question 26

What steroid hormones are produced by the gonads

Answer 26

Sex steroids e.g testosterone and estrogen

Question 27

What steroid hormones are produced by the placenta

Answer 27

hCG, sex steroids

Question 28

What steroid hormones are produced by the kidney

Answer 28

Vitamin D3

Question 29

What steroid hormones are produced by the adrenal cortex

Answer 29

corticosteroids

Question 30

Why are steroid hormone receptors located within cells

Answer 30

Because steroid hormones are very lipophilic so can cross in and out of the cell membrane

Question 31

What is the effect of steroid hormones when they bind to their receptors

Answer 31

Their receptors change the gene expression at the nucleus so they either increase or decrease protein synthesis

Question 32

What do steroid hormones have to be to diffuse into target cells

Answer 32

unbound to plasma protein carriers

Question 33

What is the free hormone: protein bound hormone ratio in favour of

Answer 33

Protein bound is much in favour but free hormone is the physiologically important fraction