6.2 - Introduction To The Endocrine System And Endocrine Control Of Apetite Flashcards
What is homeostasis?
A dynamic equilibrium
What are the main points of a control system?
1) stimulus
2) receptor … via afferent pathway…
3) control centre … via efferent pathway…
4) effector
What’s a biological rhythm?
small group of neurones in suprachiasmic nucleus detect cues from the environment (zeitgebers)
Keep body on a 24 hour cycle of
- sleep
- excersize
- eating and drinking
- social interaction
Long haul flights mess this synchrony up between environmental cues and body clock = jet lag.
Hormone melatonin from pineal gland helps set clock.
Define positive and negative feedback.
Positive = response in a way to change the variable even more in the direction of change e.g blood clotting
Negative = response is a way to reverse the direction of change
What do osmoreceptors d?
In hypothalamus, monitor osmotic pressure of blood plasma
What’s the difference between osmolarity and osmolality?
Osmolarity = the number of osmoles per litre of solution. VOLUME.
Osmolality = the number of osmoles per Kg of solution. MASS.
How is body fluid homeostasis maintained when you have a high blood osmolality?
1) high blood osmolarity = body needs to conserve water
2) detected by osmoreceptors in hypothalamus so you drink more as feel thirsty
3) posterior pituitary secrets more ADH
4) increased reabsorption of h20 from urine into blood in collecting ducts in kidney = concentrated urine and a small volume
How is plasma glucose maintained in a fed state?
1) pancreas releases insulin
2) insulin stimulates glycogenesis in liver and glucose uptake into tissues by GLUT4
3) plasma glucose declines
How is plasma glucose maintained in a fasted state?
1) pancreas releases glucagon
2) glucagon stimulates glycogeneolysis in liver
3) plasma glucose increases
What’s a hormone?
Chemical signals produced in endocrine glands or tissues that travel in the bloodstream to cause an effect on other tissues.
What are the classifications of hormones?
1) peptide/polypeptide
- largest group
- short chains of amino acid e.g insulin
- water soluble
2) amino acid derivatives
- adrenaline, noradrenaline, thyroid hormones
- adrenal medulla hormones h20 soluble
- thyroid hormones lipid soluble
3) glycoproteins
- large protein molecules made of subunits
- e.g thyroid stimulating hormones
- all water soluble
4) steroids
- derived from cholesterol
- e.g cortisol, adolesterone, testosterone
- all lipid soluble
How are hormones transported?
1) autocrine = acts on cell of origin
2) paracrine = acts of adjacent cells
3) endocrine = to distant cells
4) neuroscience = originates in neurone them goes into bloodstream
What is the role of carrier proteins in relation to hormones?
Free hormone + carrier = bound hormone Keeps it biologically inactive This means - increased solubility of hormone in plasma - increased half life - readily accessible reserve
What determines hormone levels in blood?
1) rate of production
2) rate of delivery
3) rate of degradation
What happens when G protein coupled receptors bind to hormones?
1) dissociation of G protein alpha subunit
2) activating if effector protein e.g adrenal cyclase
3) formation of second messenger cAMP
4) activation of protein kinase a
5) phosphorylation of target proteins and cellular response occours
What happens when a hormone binds to a tyrosine kinase receptor?
- dimerisation
- autophosphorylation
- recruitment of adapter proteins
- activation of protein kinase
- phosphorylation of target proteins
- cellular response
What us appetite controlled by?
Control centre is located in the hypothalamus
Hypothalamus contains several clusters of neurones ruffle red to as nuclei
It’s the arcuate nucleus that deals with nucleus
What neurones are in the arcuate nucleus?
Two types of primary neurones
1) stimulators neurones with neuropeptide Y and agouti related peptide. These promote hunger
2) inhibitory neurones contain POMC which yields several neurotransmitters including alpha MSH and B endorphin. These promote satiety.
What hormones go from the gut to the hypothalamus?
1) ghrelin
- released from stomach wall when empty
- stimulates excitatory primary neurones in arcuate nucleus = stimulates appetite
- filling of stomach inhibits ghrelin release
2) Peptide tyrosine tyrosine (PTT)
- released by cells in ileum and colon in response to feeding
- inhibits primary neurones of acrcuate nucleus and stimulates inhibitory neurones = suppresses appetite
What hormones from the body go to the hypothalamus for appetite control?
Leptin
- released by adipocytes
- stimulates POMC neurones
- inhibits excitably neurones
- overall suppresses appetite
Insulin
- suppresses appetite
Amylin
- secreted by B cells in Andreas
- suppress appetite
What’s leptin?
Hormone that suppresses appetite. If you miss the gene = be obese. Very rare, but patients respond well to leptin injections
