Introduction to Endocrine Flashcards
1
Q
Definition of endocrine system
A
A system that integrates and controls organ function via the secretion of chemicals (hormones) from tissues or glands, which are then carried in the blood to the target organs distal from the site of the hormone synthesis where they influence the activity of the target organ
2
Q
What do hormones cause in the target organ?
A
A change in activity
3
Q
Different types of chemicals in the body
A
Paracrine chemicals
Endocrine chemicals
Autocrine chemicals
Exocrine chemicals
4
Q
Where do paracrine chemicals act?
A
Local to the site of synthesis, do not travel to distant sites
5
Q
Example of a paracrine chemical
A
Histamine
6
Q
Where do exocrine chemicals act?
A
Released from exocrine glands via ducts to the external environment including the GI tract e.g. saliva, sweat, bile
7
Q
Where do autocrine chemicals act?
A
Act on/in the same cell that synthesises the hormone
8
Q
Example of an autocrine chemical
A
Cytokine
9
Q
How do tissues detect hormones?
A
Through the presence of specific receptors for that chemical on/in the cells.
10
Q
Where can receptors be for the hormones?
A
Either outside the cell or within the cell
11
Q
What are neurotransmitters released from?
A
Presynaptic neurones
12
Q
Where do neurotransmitters travel?
A
From presynaptic neurones
across the synaptic cleft
To postsynaptic cell to influence its activity
13
Q
Where do neurotransmitters act?
A
Locally within the synaptic cleft
14
Q
What two systems co-operate intimately to provide further control particularly for long term phenomena e.g. growth?
A
Endocrine and nervous systems
15
Q
When the endocrine and neuro systems combine, what occurs?
A
Nerves release hormones which enter the blood and travel to their target cells (distal site)
16
Q
Example of a neuroendocrine system
A
Hypothalamic posterior pituitary axis
17
Q
Example of a neuroendocrine hormone
A
Adrenaline
18
Q
Function of hormones / Neurotransmitters
A
Bring about changes in the activity of their target cells and tissues (increase or decrease in a particular activity)
19
Q
What does the pineal gland produce?
A
Melatonin
20
Q
What does the hypothalamus produce?
A
Trophic hormones
21
Q
What is the primary target of trophic hormones?
A
Anterior pituitary
22
Q
What does the posterior pituitary produce?
A
Oxytocin
Vasopressin (ADH)
23
Q
What does the anterior pituitary produce?
A
Prolactin Growth hormone Corticotrophin (ACTH) Thyrotropin FSH LH
24
Q
What is another name for growth hormone?
A
Somatotropin
25
What does the thyroid gland produce?
Triiodothyronine
Thyroxine
Calcitonin
26
What does the parathyroid gland produce?
Parathyroid hormone
27
What does the thymus gland produce?
Thymosin
| Thymopoietin
28
What hormone does the heart produce?
ANP
29
Function of ANP
increases Na excretion
30
What hormones does the liver produce?
Angiotensinogen
| Insulin-like growth factors
31
What hormones does the pancreas produce?
Insulin
Glucagon
Somatostatin
Pancreatic polypeptide
32
What does the adrenal cortex produce?
Aldosterone
Cortisol
Androgens
33
What does the adrenal medulla produce?
Epinephrine / norepinephrine
34
What hormones do the kidneys produce?
Erythropoietin
| 1,25-Dihydroxy-vitamin D3 (calciferol)
35
What hormone does the skin produce?
Vitamin D3
36
What hormones do the testis produce?
Androgens
| Inhibin
37
What hormones do the ovaries produce?
oestrogen
progesterone
inhibin
Relaxin (pregnancy)
38
How much endocrine hormone is needed to bring about a response?
Endocrine hormones exert their effects at very low concentrations because the receptors have a very high affinity for the hormone and therefore do not need a lot of hormone to bring about a response
39
How do endocrine hormones often have their actions terminated?
Via negative feedback loops
40
Where do endocrine hormones get metabolised?
Liver
| Kidneys
41
What Is the release of endocrine hormones controlled by?
Negative feedback loops
42
Types of endocrine hormones
Peptide/protein hormones
Steroid hormones
Amine hormones
43
Different structures of peptide/protein hormones
Composed of chains of amino acids
Can be very short e.g. 3 amino acids long (TRH)
Can be very long e.g. FSH
44
What are all steroid hormones derived from?
Cholesterol
45
Examples of steroid hormones
Oestrogen
| Progesterone
46
What are amine hormones derived from?
One of two amino acids - either
- Tryptophan
- Tyrosine
47
What is the only amine hormone is derived from tryptophan?
Melatonin
48
What amine hormones are derived from tyrosine?
All other amine hormones apart from melatonin
49
Examples of peptide hormones
TRH
FSH
Insulin
50
When are peptide hormones synthesised?
In advance of need
51
Where are peptide hormones stored and until when?
Vesicles until required
52
What is the initial protein of peptide hormones called and what is it produced by?
Preprohormone
| Produced by ribosomes
53
Features of the preprohormone
Large and inactive so no endocrine function in that form
54
Where are preprohormones cleaved and what are they cleaved into?
In the RER
| Into small but still inactive proteins called prohormones
55
What happens to prohormones?
Packaged into vesicles in the Golgi apparatus, along with proteolytic enzymes
56
What do the proteolytic enzymes stored with the prohormones do?
Break the prohormone down into active hormone and other fragments
57
Hormones and fragments after the breakdown of prohormones are stored where and until when?
Stored in vesicles in the endocrine cells
| Until release is triggered where all vesicle contents are released into the plasma
58
What is the release of all vesicle contents (inactive and active fragments) called?
Co-secretion
59
How can inactive fragments in the plasma be useful clinically and how? Then give an example
They can be measured
They tend not to be metabolised as quickly as hormones and so can be detected clinically
C peptide in diabetes
60
What is C peptide?
The inactive fragment cleaved from the insulin prohormone
61
What does C peptide measurement indicate?
Endogenous insulin production from the pancreas (produced in equal amounts)
62
C peptide levels compared to insulin levels and why
C peptide levels are approx. 5x higher than endogenous insulin release levels
Because insulin is metabolised faster
63
Solubility of peptide hormones
Water soluble
64
Where can water soluble hormones move?
Dissolve easily in plasma so transport via the blood is simple and easy
Cannot cross cell membrane
65
Where are the hormone receptors for peptide hormones?
Membrane bound receptors on outside of cells
66
Speed of peptide hormone reactions once bound to the receptors
Fast (secs - mins)
67
Peptide hormone pathways
GPCR (G-protein coupled receptors) signalling pathway
| Tyrosine kinase linked signalling pathway
68
Other names for hormones being water soluble
Hydrophilic
| Lipophobic
69
How does a peptide hormone activating a G protein coupled receptor work?
2nd messenger system activation and / or ion channels
Modification of existing protein
Rapid response
70
How does a peptide hormone activating a tyrosine kinase linked receptor work?
Alters gene expression
| Slower, longer lasting activity
71
What may 2nd messengers also do in peptide hormone reactions?
Alter gene expression
72
When are steroid hormones synthesised?
Directly as needed
73
Solubility of steroid hormones and what this means for their storage
Highly lipophilic / lipid soluble
| So cannot be retained within lipid membranes and so cannot be stored
74
How are steroid hormones transported in the blood?
Bound to carrier proteins such as albumin
75
Function of carrier proteins transporting steroid hormones
Stabilises their transport through the plasma
| Protects them from metabolic enzymatic degradation - massively increasing their half life
76
Examples of steroid hormones and what they are produced by..
Gonads - sex steroids
Placenta - hCG, sex steroids
Kidneys - vitamin D3
Adrenal cortex - corticosteriods
77
How is which specific steroid hormone is derived from cholesterol determined?
By different cells having different enzymes synthesising different derivatives of cholesterol
78
Where are receptors for steroid hormones found?
Inside cells (cytoplasmic or nuclear receptors)
79
What do steroid hormones do once bound to receptors and what is this called?
Triggers either activation or repression (inhibition) of gene function within the nucleus
Genes control the synthesis of proteins so these hormones either increase of decrease protein synthesis
This is called the genomic effect
80
What does the relatively slow process of steroid hormones cause?
A lag time between hormone release and biological effect (hours to days) but the effect persists for around the same time
81
Examples of amine hormones
Dopamine
Norepinephrine
Epinephrine
82
Where is dopamine released from?
The brain
83
Where is norepinephrine released from?
Neurones
84
Where is epinephrine released from?
The adrenal medulla
85
Function of melatonin
Regulates circadian rhythm
86
What is the only amine hormone not derived from tyrosine and what is it derived from?
Melatonin - derived from tryptophan
87
Two types of amine hormones derived from tyrosine
Catecholamines
| Thyroid hormones
88
Mechanism of action of catecholamines
Similar mechanism to peptide hormones as they are HYDROPHILIC
89
Mechanism of action of thyroid hormones
Similar mechanism to steroid hormones as they are LIPOPHILIC
90
What is the physiologically important fraction of steroid/thyroid hormones in the plasma? Why?
The small amount of unbound free steroid/thyroid hormone
| Because only free hormone can diffuse across capillary walls to target cells (lipophilic)
91
What is the free hormone : hormone-protein complex ratio of steroid hormones much in favour of?
Bound hormone
92
What is an important fact of the level of free (active) hormone of the lipophilic hormones in the plasma?
The levels remain constant
93
What does the Law of Mass Action dictate?
As free hormone leaves the plasma (taken up by cells) more hormone is released from the carriers
94
Equation for total plasma hormone in lipophilic hormones
Total plasma (hormone) = free hormone + complexed hormone
95
Types of carrier protein in the plasma for steroid/thyroid hormones
Specific = corticosteriod binding globulin
| Non specific = albumin
96
What does the reservoir of steroid in the plasma result in?
Prolonged effect
97
What does the concentration of hormone in the blood depend on?
Rate of secretion
| Rate of removal
98
How are hormones removed and where does this occur?
Excretion or metabolic transformation
| Mainly occurs in liver and kidneys
99
Which types of hormones are excreted quickly and easily due to their short half life? (mins - hours)
Catecholamines
| Peptide hormones
100
Which types of hormones take hours and days to excrete or metabolise and why is this?
Steroid hormones
Thyroid hormones
Because they are protein bound
101
What happens to the target cells after prolonged exposure to a low hormone concentration in the plasma?
Up regulation
| = increase in no. of hormone receptors on the target tissues
102
What happens to the target cells after prolonged exposure to high concentration of the hormone in the plasma?
Down regulation
| = decrease in the receptor number on target tissues
103
Definition of permissive effects
The presence of one hormone enhances the effects of another
104
Definition of half life
Time taken for the plasma concentration to fall by one half
