Physiological Aspects of the Endocrine System

Question 1

What is a hormone?

Answer 1

A chemical signal that enables an event in one part of the

body to have an effect elsewhere in the body.

Question 2

What produces hormones?

Answer 2

May be produced from specialist organs – endocrine
glands – e.g. thyroid gland
May be produced from cells distributed around the body
– e.g. endothelial cells

Question 3

How many hormones can an endocrine gland secrete?

Answer 3

Two or more different hormones
E.g. Thyroid Gland
T3 and T4- follicular cells
Calcitonin- parafollicular celks

Question 4

What types of tissues secrete hormones

Answer 4

Nearly all tissues

Question 5

Give an example of a hormone that is secreted at multiple sites

Answer 5

Somatostatin

Question 6

What are the 3 types of chemical signalling?

Answer 6

Autocrine
Paracrine
Endocrine

Question 7

What does exocrine mean?

Answer 7

Outside the body

Question 8

What is endocrine signalling?

Answer 8

Within the body, directly into the blood stream, transported to target cells

Question 9

What is autocrine signalling?

Answer 9

Signalling molecule that actually has an effect on itself

Question 10

Give an example of autocrine signalling

Answer 10

E.g. T cells, produce growth signals which have effect on themselves

Question 11

What is paracrine signalling?

Answer 11

Signalling molecules that have an effect on cels around them

Question 12

Give and example of paracrine signalling

Answer 12

E.g. nerves

Synapses affect other synapses

Question 13

Some cells can have multiple modes of signalling, give an example of this

Answer 13

Insulin
Has both endocrine and exocrine functions
Beta cells- produce insulin
Endocrine- has effect on multiple cells e.g. adipose, liver and skeletal muscle to enable uptake of glucose
Autocrine- when insulin is released it has some sort of subsequent release from its cells

Question 14

What are target cells?

Answer 14

A particular hormone usually affects only a limited number of cells, these limited cells are target cells

Question 15

Why is a cell a target?

Answer 15

Because it has a specific receptor for the hormone

Question 16

What are the two types of hormone?

Answer 16

Proteins, peptides, amines

Steroids & Thyroid hormones

Question 17

What is the structure of proteins peptides and amine hormones?

Answer 17

Hydrophilic (can’t cross membrane)
Cell surface receptors, act via second messenger system
Circulate primarily dissolved in plasma

Question 18

What is the structure of steroids & thyroid hormones

Answer 18

Hydrophobic (Can easily pass across membrane)
Intracellular receptors, promote or suppress gene transcription
Circulate primarily bound to plasma proteins

Question 19

What are the sizes of polypeptides and protein hormones?

Answer 19

Size 3AA to 200AA

Question 20

How are hormones initially assembled?

Answer 20

By pre pro ribosomes creating pro hormones

Question 21

Where do pro hormones then go?

Answer 21

Golgi aparatus where it is packaged and put into vesicles where it can be stored

Question 22

What happens to pro hormones in vesicles?

Answer 22

Can be cleaved to form active hormone

Question 23

What are the steps of hormone synthesis?

Answer 23

Synthesis
Packaging
Storage
Secretion

Question 24

What type of hormone is insulin?

Answer 24

Peptide hormone

Question 25

What are the steps of the synthesis of insulin?

Answer 25

Preproinsulin Proinsulin Insulin- released as hormone C peptide also released

Question 26

How are steroid hormones synthesised?

Answer 26

Stimulus Synthesis of precursor Synthesis of enzyme These two join and are released

Question 27

What two ways can steroid hormones be released?

Answer 27

Free binding proteins | Bound steroids

Question 28

Why can't steroid hormones be stored in vesicles?

Answer 28

As they are lipid soluble and can easily cross membranes

Question 29

Why does it take longer for a steroid hormone to have effect?

Answer 29

It has to be synthesised first

Question 30

What are steroid hormones based on?

Answer 30

Cholestrol | Shape of ring and side chains vary

Question 31

What is the mechanism of action of peptide hormones?

Answer 31

Peptide hormone binds to a receptor on cell surface membrane Once in the cell a inactive secondary messenger is activated which iniates a protein kinase cascade The peptide hormone then enters the nucleus where it acts as a transcription factor which switches on gene for a specific protein

Question 32

What is the mechanism of action of steroids?

Answer 32

The steroid hormone enters the cytoplasm Steroid hormone binds with steroid receptor to form a hormone-receptor complex This then enters the nucleus In the nucleus, the complex binds to receptor sites on chromatin activating mRNA transcription

Question 33

What factors determine blood concentration of hormones?

Answer 33

The Rate of Secretion | Rates of Inactivation and Excretion

Question 34

Whats are examples of the rate of secretion?

Answer 34

Neural control Chemical control Hormonal control Feedback loops

Question 35

What are examples of rates of inactivation and excretion?

Answer 35

Peptide hormones – degraded in target tissues, have short half-life in the blood (minutes to hours) Steroid hormones – usually metabolised in the liver and eliminated in the urine. Longer half-life (hours to days)

Question 36

What is the Feedback in Endocrine Systems

Answer 36

``` Stimulus – Fall in Blood Calcium Controlled condition – Blood Calcium Level Receptors – Calcium receptor on parathyroid cell membrane Control Centre – Parathyroid Gland Effectors – Bones, Kidneys Response – increased calcium release from bones, and increased calcium re-uptake in kidneys ```

Question 37

What are multiple feedback loops?

Answer 37

More than one feedback loop | I.e. Long loop, short loop, ultra short loop

Question 38

What is a short loop?

Answer 38

Less sensitive than long loop

Question 39

What is an ultrashort loop?

Answer 39

E.g. hypothalamus feedbacks on itself

Question 40

How can cells change their sensitivity to a hormone?

Answer 40

By changing the number of receptors

Question 41

What is receptor down-regulation?

Answer 41

When a high extracellular concentration of the hormone is maintained for some time, the total number of target cell receptors for that hormone may decrease.

Question 42

What does receptor down-regulation reduce?

Answer 42

Target cell's responsiveness

Question 43

What is an example of a receptor down-regulation?

Answer 43

Prolonged high concentration of insulin down regulates its receptors

Question 44

What is receptor up-regulation?

Answer 44

When cells are exposed for a prolonged period to very low concentrations of a hormone, they may develop more receptors and have increased sensitivity.

Question 45

What is an example of a receptor up-regulation?

Answer 45

Prolactin increases the number of its receptors in the breast for breastfeeding.

Question 46

What is the clinical relevance of hormones?

Answer 46

Thyroid Disease- autoimmune disease Iodine disease- hormone isn’t synthesised Hypothalamic or Pituitary disease- e.g. tumour prevent production Absent thyroid hormone receptor TRB- producing thyroid but cells can’t act