Homeostasis

1
Homeostasis

• Set zone and feedbackTemperatureHeat transfer
  productionThermoregulationFluid
  regulationThirst / Internal triggersSalt /
  food / energy regulationInsulin /
  MetabolismSatiety / Eating disorders

2
Set Zone and Feedback

• 3 regulatory systems
• Heat, food and water
• Motivated behavior
• Negative feedback
• To adjust around a range / set zone
• Obligatory losses (excretion, movement, energy
  consumption)
• Requires organisms to gain heat, water and food

3
Temperature Regulation

• Body temperature
• Cell cooling
• Bi-lipid layer disrupted by icicle formation
• Slowed chemical reactions / loss of energy
  production
• Anti-freeze in Mealworm beetles
• High temperatures
• Amino acid fusion
• Protein folding

4
Heat Transfer and Production

• Endotherms
• Regulation through metabolic processes
• Favorable environments
• Costly system
• Aerobic activity
• Metabolism of brown fat cells
• Shivering (birds)
• Constriction of blood vessels
• Increased thyroid hormone activity
• Ectotherms
• Regulation through behavior
• Anaerobic activity
• Changing exposure of body surface

5
Offspring Thermoregulation

• Birds
• Brood patch (egg and fledglings)
• Rats
• Mother crouching
• Pup rotation
• Brown fat deposits in shoulders

6
Nervous System Thermoregulation

• Hypothalamus
• Autonomic - POA
• Behavioral - Lateral hypothalamus
• Brainstem
• Spinal cord
• Skin receptors

7
Fluid Regulation

• Intracellular / Extracellular (buffer)
• Interstitial fluid, plasma, GI, bladder
• Water movement
• Aquaporins (protein channels for H2O movement)
• Osmosis
• Osmotic pressure
• Osmolality
• Solute concentration in a solution
• Iso- (0.9 NaCl), hyper- and hypotonic

8
Hypovolemic Thirst

• Hypovolemic
• Low extracellular volume
• Through blood loss or loss of other body fluids
• Heart and blood vessels have baroreceptors
  thatrecognize volume drop(s)
• Autonomic NS / Brain response
• Vasopressin / ADH (posterior pituitary gland)
• Diabetes insipidus (increased urination
  novasopressin / ADH)
• Vasoconstriction
• Water reduction from kidney to bladder

9
Renin-Angiotensin System
10
Osmotic Thirst

• Loss of H2O
• Perspiration, respiration, urination
• Salty food intake
• Osmoreceptors
• Respond to change in osmotic pressure
• Osmotically-receptive neurons
• POA, anterior hypothalamus, supraoptic nucleus,
  organum vasculosum of lamina terminalis (OVLT) -
  acircumventricular organ

11
Salt / Food / Energy Regulation

• Aldosterone
• Steroid hormone triggers kidney to preserve Na
• Food energy usage (75) (1 of 3 ways)
• Process newly ingested food (8)
• Basal metabolism (body heat, resting
  functions)(55)
• Active behavioral processes (12-13)
• Carbohydrates (glucose)
• Insulin converts glucose into glycogen (fat
  store)
• Glucagon breaks glycogen into glucose

12
Insulin / Metabolism

• Glucose transporters
• Glucodetectors (glucostats)
• Detect circulating glucose trigger insulin
  release
• Input from liver to vagus nerve to nucleus of
  solitary tract (NST)
• Diabetes mellitus (Type I v. Type II)
• Lack of insulin
• Type I juvenile onset
• Type II adult onset

13
Satiety

• OLD VIEW (VMH satiety center, LH hunger center)
• Arcuate nucleus (NPY/AgRP v. POMC/CART)
• Appetite control center insulin, leptin,
  ghrelin, Pyy3-36
• Leptin protein that brain monitors to regulate
  fat
• Ghrelin released by endocrine cells of stomach
  / appetite stimulant
• Pyy3-36 small/large intestine cells, released
  after a meal / appetite suppressant

14
Eating Disorders

• Anorexia nervosa
• Not yet evidence to suggest this is a
  physiologicaldisorder
• Has physiological consequences
• Can be fatal
• Bulimia nervosa
• Mismatch of biological make-up and desire for
  acertain body type
• Mutation of gene encoding MC4R receptor
• ?-melanocyte-stimulating hormone (?-MSH) -
  typically reduces appetite-stimulating effects of
  LH neurons
• Can be fatal

15
Take Home Message

• Set zone and feedback
• Temperature
• Heat transfer production
• Thermoregulation
• Fluid regulation
• Thirst / Internal triggers
• Salt / food / energy regulation
• Insulin / Metabolism
• Satiety / Eating disorders