Chapter 12: Ingestive Behavior Flashcards
Homeostasis
Process by which the body’s substances and characteristics are maintained at their optimal level
Ingestive Behavior
Eating or drinking
Essential features of regulatory mechanism
- System variable
- Set point
- Detector
- Correctional mechanism
System variable
Variable that is controlled by regulatory mechanisms
Set Point
Optimal variable in regulatory mechanism
Detector
In regulatory process, mechanism that signals when system variable deviates from its set point
Correctional Mechanism
Mechanism that is capable of changes value of system variable
Negative Feedback
Process whereby effect produced by an action serves to diminish or terminate that action
Satiety Mechanism
Brain mechanism that causes cessation of hunger or thirst, produced by adequate and available supplies of nutrients or water
- Monitor activity of correctional mechanism, not system variables themselves
Intracellular Fluid
Fluid contained within cells
- Losing intracellular water deprives cells of ability to perform many chemical reactions and gaining water can cause membrane to rupture
Extracellular Fluid
All body fluids outside cells
- Interstitial fluid, blood plasma, and CSF
Intravascular Fluid
Fluid within blood vessels
- Volume of intravascular fluid must be closely regulated because of mechanism of operation of heart
Hypovolemia
Reduction in volume of intravascular fluid
Osmometric Thirst
Thirst produced by an increase in osmotic pressure of interstitial fluid relative to intracellular fluid, thus producing cellular dehydration
Osmosis
Movement of water through semipermeable membrane from region of low solute concentration to one high solute concentration
Osmoreceptors
Neurons that detects changes in solute concentration of interstitial fluid that surrounds it
- Located in lamina terminalis
Lamina terminalis
- Contains 2 specialized circumventricular organs: OVLT and SFO
- Found in hypothalamus, in region that borders anteroventral tip of 3rd ventricle (AV3V)
- Lack BBB
Volumetric Thirst
- Thirst produced by hypovolemia
- Involves loss of Na+ and water, volumetric thirst leads to salt appetite
- Cells in kidney detect decreases in blood flow
- In response to low blood volume, kidneys are responsible for presence of hormone angiotensin
- Baroreceptor cells
Angiotensin
Peptide hormone that constricts blood vessels, causes retention of Na+ and water and produces thirst band salt appetite
- Causes kidneys to conserve water and salt and increases blood pressure - Reduced blood flow to kidneys causes water and salt to be retained
Baroreceptor cells
Stretch sensitive and detect when blood volume in heart falls
- located in atria - reduced blood flow to heart increases drinking and severing nerves to atrial baroreceptor decreases drinking
Cells in liver convert glucose into […] and it is stored, and are stimulated to do so by presence of […]
Cells in liver convert glucose into glycogen and it is stored, and are stimulated to do so by presence of insulin
Glycogen
Polysaccharide often referred to as animal starch
- stored in liver and muscle - constitutes short-term store of nutrients
Insulin
Pancreatic hormone that facilitates entry of glucose and amino acids into cell, conversion of glucose —> and transport of fats into adipose tissue
- mice with mutation of insulin receptors in brain became obese
Fall in glucose is detected by cells in […]
Fall in glucose is detected by cells in pancreas and brain
- Pancreas responds by stopping its secretion of insulin and starting to secrete glucagon
Glucagon
Pancreatic hormone that promotes conversion of liver glycogen into glucose
Long-term reservoir consists of […]
Long-term reservoir consists of triglycerides
Triglycerides
- form of fat storage in adipose cells
- consists of molecule of glycerol joined with 3 fatty acids
Glycerol
Converted by liver into glucose
Fatty Acids
Can be metabolized by most cells of body expect for brain
Adipose tissues
Found beneath skin and abdominal cavity
- Cells are capable of absorbing nutrients from blood, converting them to triglycerides, and storing them - Size of fat cells is determined by amount of TAGs the cells contain
[…] is involved in breakdown and utilization of stored nutrients
Sympathetic Ns is involved in breakdown and utilization of stored nutrients
Fasting Phase
- Fall in glucose level causes pancreas to stop secreting insulin and to start secreting glucagon
- Absence of insulin means most of cells of body can no longer use glucose
- All glucose present in blood is reserved for CNS
- Fat cells break down TAGs into FA and glycerol
Absorptive Phase: Glucose
- level of glucose in blood rises
- Activity of sympathetic NS to decrease and activity of parasympathetic NS to increase
- Tells pancreas to stop secreting glucagon and begin secreting insulin
- Insulin permits all cells of body to use glucose as fuel
- Extra glucose some is converted into glycogen which fills short-term carb reservoirs
- If glucose is left over, it is converted into fat and absorbed by fat cells
Absorptive Phase: Amino acids
- Small proportion are used to construct proteins and peptides
- Rest are converted to fats and stored in adipose tissue
Absorptive Phase: Fat
Stored in adipose tissue
Signals from Environment that start meal
- Time of day
- Presence of others
- Sensory signals, including sight or smell of food
Empty stomach and upper intestine (GI system) releases […] when digestive tract is empty
Empty stomach and upper intestine (GI system) releases ghrelin when digestive tract is empty
Ghrelin
Peptide hormone released by stomach that increases eating
- Produced by neurons in brain - Binds to receptors in hypothalamus - Increase with fasting and are reduced after meal - Relays signals from stomach and digestive tract to hypothalamus
Prader-Willi Syndrome
Obesity caused by almost continuous eating
- Chronic elevation in blood level of ghrelin, which remains high even after meal
Entry of food into […] suppresses ghrelin secretion
Entry of food into duodenum suppresses ghrelin secretion
Duodenum
First portion of small intestine, attached directly to stomach
- Contains ghrelin receptors
Hypoglycemia
Fall in blood glucose level is potent stimulus for hunger
Glucoprivation
Dramatic fall in level of glucose available to cells
- Can be caused by fall in blood level of glucose or by drugs that inhibit glucose metabolism
Lipoprivation
Dramatic fall in level of fatty acid available to cells
- Usually caused by drugs that inhibit fatty acid metabolism
2 sets of hunger detectors
- Brain receives glucoprivic hunger signal from liver through vagus nerve
- Lipoprivic hunger appears to be stimulated by receptors in liver
Brain contains detectors that monitor availability of […] inside BBB
Brain contains detectors that monitor availability of glucose inside BBB
Liver contains detectors that monitor availability of […] inside BBB
Liver contains detectors that monitor availability of nutrients inside BBB
After food reaches stomach it is mixed with […]
After food reaches stomach it is mixed with HCl and pepsin
Food is mixed with […], which continue digestive process
Food is mixed with bile and pancreatic enzymes, which continue digestive process
Duodenum controls rate of stomach emptying by secreting […]
Duodenum controls rate of stomach emptying by secreting cholecystokinin (CCK)
Cholecystokinin (CCK)
Hormone secreted by duodenum that regulates gastric motility and causes the gallbladder (cholecyst) to contract
- Appears to provide satiety signal transmitted to brain through vagus nerve - Response to presence of fats - Causes pyloris to constrict and inhibits gastic contractions - Blood levels is related to amount of nutrients that duodenum receives from the stomach - Doesn’t act directly on brain
Peptide YY3-36 (PYY)
Chemical produced by cells in GI tract and released by small intestine after meal in amounts proportional to calories that were just ingested
- Serves as satiety signal - Amount of PYY released after meal correlates positively with people’s ratings of satiety
Hepatic Portal Vein
Vein that transport blood from digestive system to liver
- When liver receives nutrients from intestines, it sends signal to brain that produces satiety - Signal continues satiety that was already started by signals from stomach and upper intestine
Ob Mouse
Strain of mice whose obesity and low metabolic rate are caused by mutation that prevents production of leptin
- OB gene normally produces leptin
Leptin
Hormone secreted by adipose tissue
- Decreases food intake and increases metabolic rate, primarily by inhibiting NPY-secreting neurons in arcuate nucleus
Decerebration
Surgical procedure that severs brain stem, disconnecting hindbrain from forebrain
- brain stem controls chewing and swallowing behaviors - Disconnects motor neurons of brain stem and spinal cord from neural circuits of cerebral hemispheres - Can distinguish between different tastes
[…] are parts of medulla that receive taste info from tongue and variety of sensory info from internal organ
Area postrema and nucleus of solitary tract (AP/NST) are parts of medulla that receive taste info from tongue and variety of sensory info from internal organ
[…] hypothalamus regulates hunger while […] hypothalamus regulates satiety
Lateral hypothalamus regulates hunger while ventromedial hypothalamus regulates satiety
Orexigens
“Appetite-inducing chemicals”
- MCH and ore in
- MCH appears to play more important role in stimulating feeding
- Endocannabinoids stimulate eating by increasing MCH and ore in release
Arcuate Nucleus
Nucleus in base of hypothalamus that controls secretions of anterior pituitary gland
- Contains NPY-secreting neurons involved in feeding in control of metabolism
Paraventricular Nucleus (PVN)
Nucleus of hypothalamus located adjacent to dorsal third ventricle
- Contains neurons involved in control of ANS and posterior pituitary
Anorexigens
“Appetite- suppressing chemicals”
- CART and a-MSH
Melanocortin-4 Receptor (MC4R)
Receptor found in brain that binds with a-MSH and AgRP
- Plays role in control of appetite
PYY binds with an inhibitory autoreceptors found on […] neurons in […] of hypothalamus
PYY binds with an inhibitory autoreceptors found on NPY/AgRP neurons in arcuate nucleus of hypothalamus
Melanin-concentrating hormone (MCH)
Location of cell bodies: Lateral hypothalamus
Location of terminals: neocortex, PAG, reticular formation, thalamus, LC neurons in spinal cord that control sympathetic NS
Interaction with other peptides: Activated by NPY/AgRP; Inhibited by leptin and CART/ a-MSH
Physiological/ behavioral effects: eating; decreased metabolic rate
Orexin
Location of cell bodies: Lateral hypothalamus
Location of terminals: neocortex, PAG, reticular formation, thalamus, LC neurons in spinal cord that control sympathetic NS
Interaction with other peptides: Activated by NPY/AgRP; Inhibited by leptin and CART/ a-MSH
Physiological/ behavioral effects: eating; decreased metabolic rate
Neuropeptide Y (NPY)
Location of cell bodies: Arcuate nucleus of hypothalamus
Location of terminals:Paraventricular nucleus, MCH and orexin neurons of lateral hypothalamus
Interaction with other peptides: activated by ghrelin; inhibited by leptin
Physiological/ behavioral effects:eating; decreased metabolic rate; stimulates insulin and glucocorticoid secretion; decrease TAG breakdown; decreased body temperature
Agouti-related protein (AgRP)
Location of cell bodies: Arcuate nucleus of hypothalamus
Location of terminals:Paraventricular nucleus, MCH and orexin neurons of lateral hypothalamus
Interaction with other peptides: inhibited by leptin
Physiological/ behavioral effects:eating; decreased metabolic rate; acts as antagonist at MC4-R
Cocaine-and- amphetamine regulated transcript (CART)
Location of cell bodies: arcuate nucleus of hypothalamus
Location of terminals; paraventricular nucleus, lateral hypothalamus, PAG matter, neurons in spinal cord that control sympathetic NS
Interaction with other peptides: activated by leptin
Physiological/ behavioral effects: Suppression of eating; increased metabolic rate
a-Melanocyte Stimulating Hormone (a-MSH)
Location of cell bodies: arcuate nucleus of hypothalamus
Location of terminals; paraventricular nucleus, lateral hypothalamus, PAG matter, neurons in spinal cord that control sympathetic NS
Interaction with other peptides: activated by leptin
Physiological/ behavioral effects: Suppression of eating; increased metabolic rate; acts as agonist at MC4 receptors
Roux-en-Y gastric bypass (RYGB)
Produces small pouch is attached to lower portion of intestines
- Produce small stomach whose contents enter jejunum and bypass duodenum - Can cause iron and Vit B12 deficiency - Decreased ghrelin secretion - Increased blood levels of PYY
Anorexia Nervosa
Disorder that most frequently afflicts young women
- Exaggerated concern with overweight that leads to excessive dieting and often compulsive exercising - Can lead to starvation
Bulimia Nervosa
Bouts of excessive hunger and eating, often followed by forced vomiting or purging with laxative
Binge-Eating Disroder
Disorders that includes bouts of excessive eating
Sensation of thirst involves […]
Sensation of thirst involves anterior cingulate cortex
Osmosensory transduction occurs in […]
Osmosensory transduction occurs in magnocellular neurosecretory cells (MNCs)
Subfornical Organ and Thirst
small organ located in confluence of lateral ventricles, attached to underside of the fornix
Neurons in the SFO send their axons to […]
Neurons in the SFO send their axons to median preoptic nucleus
Median Preoptic Nucleus
small nucleus wrapped around the front of anterior commissure, a fiber bundle that connects amygdala and anterior temporal lobe
Satiety Signals
- Short-Term: entry of food into stomach; nutrient detectors activated
- Long-Term: arise in the adipose tissue (long-term nutrient reservoir)
Liver Satiety Signals
- Last stage of satiety
- Nutrient detectors in liver send signal after nutrients received from intestines
- Glucose and fructose through hepatic portal vein there was reduction of food intake
- Fructose can’t cross BBB and is metabolized poorly by cells in rest of the body
Reinforcement, Stress, and Food
DA and CRH involved in relapses of addictive behaviors
Pharmacological Interventions for Obesity
- Fenfluramine- serotonin agonists
- Rimonabant
Fenfluramine- serotonin agonists
pulmonary hypertension and damage to heart valves
Rimonabant
blocks CB1 receptors
- suppresses appetite, weight loss, increases HDL
- more depressive moods, anxiety, and suicide risk
