EH 9 Intro To Endocrine System And Appetite Flashcards
Homeostasis definition
The maintenance of a stable environment within a dynamic equilibrium using negative feedback systems
Features of a control system
1- stimulus
2- receptors
Afferent pathway
3- control centre
Efferent pathway
4- effector
Negative feeback
What detects position and movement?
Proprioreceptors
What detects dangerous stimuli?
Nociceptors
What does the control centre do and where is it located?
Hypothalamus + pituitary gland
Determines set point
Analyses afferent input
Determines response
How do biological rhythms arise?
Set points varying over time
What is the suprachiasmatic nucleus and what does it set?
Biological clock in hypothalamus
Sets the circadian/diurnal rhythm
What does melatonin set and where is released from?
Circadian/diurnal rhythm
Pineal gland
What are zeitgebers?
Examples
Environmental cues
Examples: lights, temp, exercise
Hormone definition
Molecule secreted by endocrine gland into bloodstream to act on distant target cells
What conc. are horomones in the blood?
Very low concentration
Four classifications of hormones
Peptide
Glycoproteins
Amino acid devrivatives
Steroids
What classifications of hormones are water soluble/
Glycoproteins
Peptide
Some amino acid derivative - (nor)adrenaline
What classifications of hormones are lipid soluble?
Steroids
Some amino acid derivatives-thyroid hormone
Describe peptide hormones + examples
Water soluble
Free in plasma
Examples: insulin, glucagon growth hormone
Describe Glycoproteins hormones + examples
Water soluble
Free in plasma
Examples- LH, FSH, TSH
Describe Amino acid derivatives hormones + examples
- (Nor)adrenaline - water soluble - free in plasma
- Thyroid horomone - lipid soluble - bound to carrier protein TBG
- melatonin
Describe Steroid hormones + examples
Lipid soluble
Derived from cholesterol
Bound to carrier proteins
Examples- cortisol, aldosterone, testosterone, oestrogen
How are water soluble hormones transported in the blood?
Free in plasma
How are lipid soluble hormones transported in blood?
Bound to carrier proteins
Role of carrier proteins
Increase solubility of hormone in plasma
Transports lipid soluble hormones in blood
Increase half life
Readily accessible reverse
Endocrine communication
Hormone released into blood and carried to distant target cells
Neurocrine communication
Hormone transported down axon from neurone + released into blood to distant target cell
Paracrine communication
Hormone carried short distance to adjacent ell via interstitial fluid
Autocrine communication
Hormone acts back on original cell
In what type of communication does the hormone act back on original cell?
Autocrine
In what type of communication does the hormone act on adjacent cells via interstitial fluid?
Paracrine
In what communication does the hormone travel down the axon from the neurone?
Neurocrine
In what communication does the horomone travel in the blood to distant target cells?
Endocrine
Neurocrine
Factors determining hormone levels
- rate of production - synthesis and secretion
- rate of delivery - increased blood flow = increased hormone delivers
- rate of degradation - metabolism + excretion
Are lipid or water hormone receptors faster?
Water- triggers mechanism already set out
Where do water soluble hormones bind to?
Can’t pass through plasma membrane
Bind to extra cellular/cell surface receptors
Two extracellular receptors
G protein coupled receptor
Tyrosine kinase
How does G protein coupled receptor initiate a response?
1- binding of hormone to receptor
2- dissociation of G protein alpha subunit
3- activation of effector protein
4- formation of secondary messenger
5- activation of protein kinase
6-phosphorylation of target proteins
7- cellular response
How does tyrosine kinase initiate a response?
1- hormone binds to receptor
2- dimerisation
3- autophosphorylatio of tyrosines
4- activation of protein kinase
5- phosphorylation of target protein
6- cellular response
What receptors do lipid soluble hormones bind to?
Can pass through plasma membrane
Bind to intracellular receptors in cytoplasm or nucleus
Modulate gene transcription
How to lipid soluble hormones initiate a response?
1- hormone bind to receptor
2- receptor bind to DNA sequence with HRE- hormone response element
3- expression of new protein mediates effect of hormone
DNA > mRNA > new protein > cellular response
What is the appetite control centre?
Arcuate nucleus
What controls the feeling of fullness?
Satiety centre
Where is the satiety centre?
Hypothalamus
Nuclei meaning in hypothalamus
Several clusters of neurones
What do excitatory/stimulators neurones in the arcuate centre do?
Promote hunger
Via NPY and AgRP
What does the inhibitory neurone in the arcuate centre do?
Suppresses appetite
Via release of POMC > alpha MSH and beta endorphin
Promote satiety
What do primary neurones on the arcuate centre do?
Sense metabolite and hormone levels
What do secondary neurones do?
Receive inputs from primary neurones
Co-ordinate an appropriate response via vagus nerve
What nerve do secondary neurones express a response via?
Vagus nerve
What hormone stimulates appetite?
Ghrelin - ‘growling’
What hormones suppress appetite?
PYY - peptide tyrosine tyrosine
Leptin
Insulin
Amylin
Ghrelin
Stimulates appetite
Released from stomach wall when empty
Filling of stomach inhibits release
Ghrelin effect on arcuate nucleus
Stimulates excitatory neurones
Stimulates appetite
Peptide tyrosine tyrosine PYY
Suppresses appetite
Released by ileum and colon - small intestine
PYY effect on arcuate nucleus
Stimulates inhibitory neurones
Inhibits excitatory neurones
Leptin
Suppresses appetite
Released into blood by adipocytes
Leptin effect on arcuate nucleus
Stimulates inhibitory neurones
Inhibits excitatory neurones
Insulin
Suppresses appetite
Released by beta cells in pancreas
Amylin
Suppresses appetite
Released by beta cells in pancreas
Decrease glucagon secretion
Slows gastric emptying
When is are cortisol levels at the highest?
8am
What hormones effect appetite from the gut?
Ghrelin - stimulates
PYY - suppresses
What hormones effect appetite from the body?
Leptin
Amylin
Insulin
Suppress appetite