Physiological Aspects of the Endocrine System Flashcards Preview

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Flashcards in Physiological Aspects of the Endocrine System Deck (46):
1

What is a hormone?

A chemical signal that enables an event in one part of the
body to have an effect elsewhere in the body.

2

What produces hormones?

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

3

How many hormones can an endocrine gland secrete?

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

4

What types of tissues secrete hormones

Nearly all tissues

5

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

Somatostatin

6

What are the 3 types of chemical signalling?

Autocrine
Paracrine
Endocrine

7

What does exocrine mean?

Outside the body

8

What is endocrine signalling?

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

9

What is autocrine signalling?

Signalling molecule that actually has an effect on itself

10

Give an example of autocrine signalling

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

11

What is paracrine signalling?

Signalling molecules that have an effect on cels around them

12

Give and example of paracrine signalling

E.g. nerves
Synapses affect other synapses

13

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

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

14

What are target cells?

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

15

Why is a cell a target?

Because it has a specific receptor for the hormone

16

What are the two types of hormone?

Proteins, peptides, amines
Steroids & Thyroid hormones

17

What is the structure of proteins peptides and amine hormones?

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

18

What is the structure of steroids & thyroid hormones

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

19

What are the sizes of polypeptides and protein hormones?

Size 3AA to 200AA

20

How are hormones initially assembled?

By pre pro ribosomes creating pro hormones

21

Where do pro hormones then go?

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

22

What happens to pro hormones in vesicles?

Can be cleaved to form active hormone

23

What are the steps of hormone synthesis?

Synthesis
Packaging
Storage
Secretion

24

What type of hormone is insulin?

Peptide hormone

25

What are the steps of the synthesis of insulin?

Preproinsulin
Proinsulin
Insulin- released as hormone
C peptide also released

26

How are steroid hormones synthesised?

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

27

What two ways can steroid hormones be released?

Free binding proteins
Bound steroids

28

Why can't steroid hormones be stored in vesicles?

As they are lipid soluble and can easily cross membranes

29

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

It has to be synthesised first

30

What are steroid hormones based on?

Cholestrol
Shape of ring and side chains vary

31

What is the mechanism of action of peptide hormones?

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

32

What is the mechanism of action of steroids?

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

33

What factors determine blood concentration of hormones?

The Rate of Secretion
Rates of Inactivation and Excretion

34

Whats are examples of the rate of secretion?

Neural control
Chemical control
Hormonal control
Feedback loops

35

What are examples of rates of inactivation and excretion?

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)

36

What is the Feedback in Endocrine Systems

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

37

What are multiple feedback loops?

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

38

What is a short loop?

Less sensitive than long loop

39

What is an ultrashort loop?

E.g. hypothalamus feedbacks on itself

40

How can cells change their sensitivity to a hormone?

By changing the number of receptors

41

What is receptor down-regulation?

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.

42

What does receptor down-regulation reduce?

Target cell's responsiveness

43

What is an example of a receptor down-regulation?

Prolonged high concentration of insulin down regulates its receptors

44

What is receptor up-regulation?

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

45

What is an example of a receptor up-regulation?

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

46

What is the clinical relevance of hormones?

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