Introduction to the Endocrine System

Question 1

What is the function of the endocrine system?

Answer 1

Integrates and controls organ function by the secretion of hormones

Question 2

What are hormones?

Answer 2

Chemicals released from cells, tissues or glands

Question 3

How are hormones transported around the body?

Answer 3

Blood

Question 4

What is meant by endocrine commuinication?

Answer 4

Hormones travelling through the blood to their target organs/tissues

Question 5

Describe the difference between neurotransmitters and endocrine hormones.

Answer 5

Neurotransmitters- released by nerves, cross the synapse and have local site of action.
Endocrine hormones- released by cell, travel in blood and have a distal site of action

Question 6

What happens if a chemical is neuroendocrine?

Answer 6

Nerves release hormones which enter the blood and travel to target cells

Question 7

Give an example of a neuroendocrine tissue.

Answer 7

Hypothalamus

Question 8

The response of target cells to a hormone is very specific. However, the same hormone can have different effects in different cells.

For example, what effect does insulin have when it binds in skeletal muscle/adipose tissue?

Answer 8

Increases glucose uptake

Question 9

The response of target cells to a hormone is very specific. However, the same hormone can have different effects in different cells.

For example, what effect does insulin have when it binds in the liver?

Answer 9

Increased glycogenesis
Decreased gluconeogenesis

Question 10

Endocrine glands are ductless.
Exocrine glands are ducted.
How do exocrine glands work?

Answer 10

Deliever their secretions to the external environment including the GIT

Question 11

Give some examples of exocrine secretions.

Answer 11

Sweat, bile, saliva

Question 12

Which type of glands have ducts?

Answer 12

Exocrine

Question 13

Which type gland are ductless?

Answer 13

Endocrine glands

Question 14

What is meant by autocrine secretions?

Answer 14

Cells secrete chemicals that bind to receptors on the same cell

Question 15

Give an example of a type of cell which produces autocrine secretions.

Answer 15

Cytokines

Question 16

What is meant by paracrine secretions?

Answer 16

Chemicals diffuse into the ECF to affect neighbouring cells

Question 17

Give an example of a cell which uses paracrine secretions.

Answer 17

Histamine

Question 18

Which type of hormonal secretions do not travel in the blood?

Answer 18

Autocrine and paracrine secretions.

Question 19

List some of the glands which have a purely endocrine function.

Answer 19

Thyroid gland
Adrenal gland
Pituitary gland
Hypothalamus

Question 20

Do hormones work at high or low concentrayions?

Answer 20

Low concentrations

->tiny changes in hormone levels can change function dramatically

Question 21

Describe the patter of endocrine hormone release.

Answer 21

Often released in short bursts

->this means 24hr monitoring is clinically required to get a realistic picture

Question 22

Name the three classes of hormone/

Answer 22

Peptide/protein hormones
Amine hormones
Steroid hormones

Question 23

Which classification of endocrine hormone is the most common?

Answer 23

Peptide/protein hormones

Question 24

What are peptide/protein hormones composed of?

Answer 24

Chains of amino acids

Question 25

What are amine hormones composed of?

Answer 25

All derived from either tryptophan or tyrosine

Question 26

In reality, only one hormone is derived from tryptophan and the rest come from tyrosine. What is the one hormone derived from tryptophan?

Answer 26

Melatonin

Question 27

What are steroid hormones dervived from?

Answer 27

Cholesterol

Question 28

Peptide hormones are initially synthesised as what in advance of need?

Answer 28

Preprohormones

Question 29

What happens to the preprohomones?

Answer 29

Cleaved into prohormones and stored in vesicles until required

Question 30

Where are the preprohormones synthesised?

Answer 30

Ribosomes

Question 31

Where are prohormones packaged into vesicles?

Answer 31

Golgi apparatus

Question 32

What else is packaged into the vesicles alongside the prohormone?

Answer 32

Proteolytic enzymes

Question 33

What role do the proteolytic enzymes play?

Answer 33

Breaks prohormone into active hormone and other inactive fragments ->worth noting that sometimes clinically it is more useful to measure the inactive fragments rather than the active ones, often done in measuring C-peptide in diabetes

Question 34

What is C-peptide?

Answer 34

Inactive fragment cleaved from insulin prohormone

Question 35

Why is C-peptide measured?

Answer 35

Indicated endogenous insulin production from pancreas ->can be measured in plasma or urine

Question 36

How do the levels of C-peptide compare to levels of endogenous insulin and why?

Answer 36

Levels of C-peptide usually 5x higher. This is because insulin is metabolised faster.

Question 37

Why would you measure C-peptide levels and not insulin levels when determining pancreas function?

Answer 37

In those w Type 1 diabetes, they will be taking synthetic insulin which will also be measured and does not relate to pancreas function

Question 38

Are peptide hormones water soluble?

Answer 38

Yes ->this means they dissolve easily in plasma making these hormones easily transportable in the blood

Question 39

As peptide hormones are water soluble, this means they cannot simply cross cell membranes. How do they do it?

Answer 39

Bind to receptors on the target cell

Question 40

Which type of receptors do most peptide hormones target?

Answer 40

G-protein coupled receptor Tyrosine kinase linked receptors

Question 41

GCPR and tyrosine kinase linked receptors result in what?

Answer 41

Phosphorylation of intracellular target proteins, changing their activity.

Question 42

Do peptide hormones generate fast or slow responses?

Answer 42

Fast

Question 43

Are water-soluble peptide hormones hydrophobic or hydrophilic?

Answer 43

Hydrophilic

Question 44

RECAP- which enzymes phosphorylate target proteins?

Answer 44

Kinase enzymes

Question 45

In terms of peptide hormone signal transduction, hormones coupled to which type of receptor leads to rapid responses?

Answer 45

G-coupled protein receptors (GCPR)

Question 46

In terms of peptide hormone signal transduction, hormones coupled to which type of receptor leads to slower, long lasting responses?

Answer 46

Tyrosine kinase linked receptor

Question 47

RECAP- the majority of amine hormones are dervobed from which amino acid?

Answer 47

Tyrosine

Question 48

List some amine hormones.

Answer 48

Dopamine, norepinephrine, epinephrine (catecholamines) Tetraiodothyronine, triiodothyronine (thyroid hormones)

Question 49

Which other type of hormones do catecholamines have similar mechanisms to?

Answer 49

Peptide hormones

Question 50

Which other type of hormones do thyroid hormones have similar mechanisms to?

Answer 50

Steroid hormones

Question 51

Which type of hormone is synthesised when required and not stored?

Answer 51

Steroid hormones

Question 52

Why are steroid hormones only synthesised when required?

Answer 52

They are highly lipophilic so cannot be retained within lipid membranes

Question 53

Steroid hormones are poorly soluble in water. Therefore, how are they transported?

Answer 53

Bound to proteins such as albumin

Question 54

Describe the onset of action of steroid hormones

Answer 54

Slow onset but action lasts much longer than peptide or amine hormones

Question 55

What produces steroid hormones?

Answer 55

Gonads (testes and ovaries) Placenta Kidney Adrenal cortex

Question 56

Which type of steroid hormones are produced in the gonads?

Answer 56

Sex steroids

Question 57

Which type of steroid hormone are produced by the placenta?

Answer 57

hCG Sex steroids

Question 58

Which type of steroid hormone are produced by the kidneys?

Answer 58

Vitamin D3

Question 59

Which type of steroid hormone are produced by the adrenal cortex?

Answer 59

Corticosteroids

Question 60

Are steroid hormones lipophilic or hydrophilic?

Answer 60

Lipophilic ->this means they can readily cross the plasma membrane and enter cells which means they have intracellular receptors

Question 61

What happens when there is activation of intracellular receptors by steroid hormones?

Answer 61

Changes in gene expression which in turns affects protein synthesis

Question 62

There is a small amount of unbound/ free steroid/thyroid hormone. What can this hormone do that bound hormone cannot?

Answer 62

Cross capillary walls to target cells. ->amount of free hormone is a lot less than the amount of hormone bound to protein

Question 63

In order to calculate total plasma hormone levels, what do you need to do?

Answer 63

Free hormone = complex (bound) hormone

Question 64

Thyroid hormones act like steroid hormones but are actually which type of hormone?

Answer 64

Amine hormones

Question 65

Are thyroid hormones or lipophilic or hydrophilic?

Answer 65

Lipophilic ->act like steroid hormones

Question 66

The vast majority of hormone secretion is controlled by which mechanism?

Answer 66

Negative feedback

Question 67

Neuroendocrine pathways also respond to which other type of feedback as well as negative feedback?

Answer 67

Neural feedback loops