12- Endocrine Sys & Appetite

Question 1

• what is homeostasis?
• give an outline of the control system of homeostasis.
• what are biological rhythms? give an example & what neurones are involved?
• Define neg & pos feedback
• how is body water controlled?

Answer 1

• not a steady state but a dynamic equilibrium, keeping the internal environment the same regardless of changes in external environment.
• stimulus, receptor (eg chemo,thermo,baro), afferent pathway(A before E) to control centre (determines set point), efferent pathway to effector.
• set point of control centre can vary, eg circadian rhythm changes w time, neurones =suprachaismatic nucleus, hormone melatonin from pineal gland sets bc.
• neg feebck=reversal of change away from normal, common, -pos feedbck=response changes variable further from norm eg blood clotting , childbirth.
• osmoreceptors in hypothalamus

Question 2

• define osmolality and osmolarity
• define an osmole
• what is the reference range for serum osmolality and what is it useful for?
• outline ADH and how it controls body fluid homeostasis.

Answer 2

• osmolality= number of osmoles/L (vol)
• osmolarity=number of osmoles /kg (mass)
• osmole=amount of substance that dissociates in sol to form 1 mole of osmotically active particles (1mM sol of NaCl=2 mOsm/L)
• ref=275 to 295 mOsm/kg useful when looking at low Na+ in blood.
• high blood osmolality= lots of Osm/kg (ie lots of ions, little water), detected by osmoreceptors, posterior pit. gland secretes more ADH, increased reabsorption of H2O, small vol of conc urine, brings osmolality down. Opp for low osmolality ie too much water.

Question 3

• outline how plasma glucose is controlled and what is the normal value?
• give the major organs of the endocrine system.
• give the 4 mechanisms of communication via hormones.
• what features in common do the endocrine and nervous systems have?
• give the 4 classes of hormones.

Answer 3

• increase in blood gluc sensed by beta cells, pancreas releases insulin, glycogenesis, stimulates glucose uptake into sk muscle and adipose. decrease, pancreas releases glucagon, glycogenolysis.
• hypothalamus, pituitary and thyroid glands, adrenal, pancreas, ovary and testes
  1) autocrine=hormone signal acts on same cell, 2)paracrine=hormone signal acts on neighbour 3)endocrine=far away 4)neurocrine=from neurone, down axon, through blood, to distal cell
• neurones and hormones can secrete, can both be depolarised, both work to maintain homeostasis.
• peptide=largest group, eg insulin, water sol , -aa derivative=eg adrenaline, adrenal medulla ones are water sol, thyroid hormones are lipid sol. -glycoproteins=largest, eg LH, FSH water sol. -steroid=from cholesterol eg cortisol, lipid sol.

Question 4

• how are hormones transported?
• what 3 factors determine hormone levels in blood? What concs do they normally circulate in blood?
• what’s the diff between lipid and water sol hormones in how they bind to receptors?

Answer 4

• some hormones can flow through blood, most need to be bound to proteins often specific ones, only the free form is active. role of carrier protein=increase solubility of hormone in plasma, increase half life
• 1=rate of production, 2=rate of delivery, 3=rate of degradation. Conc=pMol (10^-9)
• lipid sol hormones bind to intracellular receptors as they can cross the pm but water sol hormones bind to cell surface receptors eg G proteins and then have a 2nd messenger response.

Question 5

• where is appetite controlled? who is a key player in this?
• what 2 types of neurones are found in this key player?
• hormonal signals are sent from the gut to the hypothalamus, what are the 2 main hormones?

Answer 5

• controlled by the hypothalamus, the arcuate nucleus.
• 2: stimulatory neurones that promote hunger, inhibitory neurones that promote sateity (feeling full)
• ghrelin (grrr when hangry)= peptide hormone released from stomach when hungry, stims appetite, PYY (peptide tyrosine tyrosine) another peptide hormone release from ileum after feeding therefore suppresses appetite.

Question 6

• hormonal signals are also sent from the body to the hypothalamus. Name and describe these three hormones.
• what effect can a mutation in the leptin gene have?

Answer 6

• 1-leptin=peptide hormone released into blood by adipocytes, 2 effects in arcuate nucleus; stimulates inhibitory neurones, inhibits the excitatory neurones ie suppresses appetite main one
• 2-insulin=suppresses appetite
• 3-amylin=peptide hormone secreted by beta cells in pancreas, suppressed appetite
• mutation in lepton gene is shown to be linked to a lack of suppression of appetite and thus obesity. Leptin injection in these patients sees them return to normal size.