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Psych 211 (neuro) > Hunger and Thirst > Flashcards

Hunger and Thirst Flashcards

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1
Q

What is homeostasis?

A
  • the process of actively maintaining internal conditions, particularly with respect to food and water availability and body temperature
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2
Q

What do cells require for survival?

A
  • a viable temperature and food and water
  • temperature cannot be too hot or cold
  • food and water availability must be above some threshold
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3
Q

What happens when the body is too cold?

A
  • basal metabolic rate increases; calories are burned to generate heat
  • the body shivers, a way of burning calories to generate heat
  • peripheral blood vessels constrict, moving blood to the interior of the body so less heat is lost through the skin
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4
Q

What happens when the body is too hot?

A
  • animals sweat or pant like a dog (breathe heavily); water evaporation has a cooling effect
  • peripheral blood vessels expand; blood moves closer to the skin so body heat can dissipate into the surrounding air
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5
Q

What are endotherm animals?

A
  • warm-blooded
  • temperature around 37 degrees Celsius
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6
Q

What are ectotherm animals?

A
  • cold-blooded
  • not very good at maintaining their body temperature
  • their ability to move and function is highly dependent on the ambient temperature
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7
Q

What is the thermostat metaphor?

A
  • thermostat measures temperature
  • when it falls below threshold, turns on heater or when it goes above it turns off the heater
  • similar to how brain works with eating and drinking
  • brain monitors water and calories
  • falls below level, triggers hunger and thirst
  • when eat or drink, know it is coming so can relax hunger and thirst
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8
Q

What happens when a need becomes satisfied?

A
  • experience relief or pleasure
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8
Q

What is a need state?

A
  • when our body temperature becomes uncomfortable, consciously experience a need state
  • motivating
  • drive us, push us to correct the specific problem
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9
Q

What can motivate us?

A
  • anticipation of pleasure can motivate us (pull us) to perform an action, even in the absence of a corresponding need
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10
Q

How do we lose water?

A
  • urinating
  • sweating
  • breathing
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11
Q

When do we consciously experience thirst?

A
  • when there is not enough water inside cells
  • when there is not enough blood (liquid) in our circulatory system
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12
Q

What are the steps in the regulation of thirst and fluid intake?

A
  • body loses water
  • detectors signal loss of water
  • drinking occurs (can be inhibition even before goes to stomach)
  • stomach fills with water, sends signal to brain
  • safety mechanism inhibits further drinking
    OR
  • water is absorbed, body fluids back to normal
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13
Q

What is tonicity?

A
  • the relative concentration of dissolved molecules (solutes in solution) on either side of a membrane that is permeable only to the solution, not to the solutes dissolve in it
  • tonicity describes the direction solvent will flow across a membrane that is only permeable to the solvent
  • the concentration of dissolved solutes
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14
Q

What is diffusion?

A
  • the process by which molecules move from areas of high concentration to areas of low concentration
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15
Q

What is osmosis?

A
  • the movement of a solution (solvent) from areas of high concentration (low tonicity) to areas of low concentration (high tonicity)
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16
Q

What is an isotonic solution?

A
  • similar concentrations of solute on either side of the membrane
  • cell will neither gain nor lose water
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17
Q

What is a hypotonic solution?

A
  • solute is less concentrated outside the cell than in, so water will enter the cell
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18
Q

What is an hypertonic solution?

A
  • solute is more concentrated outside the cell than in, so water will leave the cell
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19
Q

How much intracellular fluid is there?

A
  • 67%
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20
Q

What are the parts of extracellular fluid?

A
  • interstitial fluid
  • intravascular fluid (blood plasma)
  • cerebrospinal fluid
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21
Q

How much interstitial fluid is there?

A
  • 26%
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22
Q

How much intravascular fluid is there?

A
  • 7%
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23
Q

How much cerebrospinal fluid is there?

A
  • less than 1%
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24
Q

What do cells need?

A
  • cells take in salts and other solutes as needed from extracellular fluid
  • across time, intracellular solute concentrations are fairly stable, while extracellular solute concentrations vary according to what we eat and drink
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25
Q

What happens when we drink water?

A
  • it lowers the tonicity of extracellular fluid, causing cells to expand in size as water moves into them from the extracellular fluid
  • excess water is eliminated by urine production
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26
Q

What happens when we consume salt?

A
  • it increases the tonicity of extracellular fluid, causing cells to shrink in size as water moves out of them
  • this physical contraction of cells triggers osmometric thirst
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27
Q

What is osmometric thirst?

A
  • not enough water inside cells
  • hypertonic (salty) solutions cause cellular dehydration (cells lose water and shrink in size)
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28
Q

What are osmoreceptors?

A
  • neurons whose membrane potential is sensitive to the size of the cell
  • release of neurotransmitter from osmoreceptors relates to the volume of these cells
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29
Q

What is volumetric thirst?

A
  • when there is not enough blood circulating in the body
  • people feel an intense thirst after they lose a lot of blood
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30
Q

What is low blood pressure?

A
  • causes cells in the kidneys to release an enzyme called renin
  • initiates a cascade of chemical reactions in the blood
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31
Q

What is hypovolemia?

A
  • not enough volume of blood
  • reduced flow of blood to kidneys
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32
Q

What does the kidney do when hypovolemia?

A
  • release renin into blood
  • renin converts angiotensinogen into angiotensin I
  • angiotensin II signals not enough blood
  • retention of sodium
  • retention of water
  • increase in blood pressure
  • salt appetite
  • drinking
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33
Q

Feelings of thirst relate to neural activity in what brain regions?

A
  • few different regions
  • particularly a hypothalamic area known as anteroventral tip of the third ventricle (the AV3V region)
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34
Q

Where are the neurons that are activated by feelings of thirst?

A
  • feelings of thirst activate neurons in the AV3V region as well as anterior cingulate cortex
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35
Q

What does drinking do?

A
  • quenches feelings of thirst
  • some thirst related neural activity immediately dissipates upon drinking (before water reaches the relevant cells)
  • AV3V neurons generally remain active until the water reaches them (long after people have stopped drinking)
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36
Q

What do cold sensors and sensory fibers do?

A
  • cold sensors in the mouth and sensory fibers in the stomach are part of the rapid satiety feedback mechanism
  • make mouth cold then feel less thirsty
37
Q

What is the main satiety mechanism?

A
  • may be a learned association between the act of drinking and the dissipation of thirst
38
Q

What does food mostly consist of?

A
  • sugars (carbs)
  • lipids (triglycerides)
  • amino acids (proteins)
39
Q

What does the pancreas do?

A
  • monitors blood glucose levels
40
Q

What does the pancreas do when blood glucose is high?

A
  • the pancreas releases insulin
41
Q

What does the pancreas do when blood glucose is low?

A
  • the pancreas releases glucagon
42
Q

What does insulin do in terms of blood glucose?

A
  • causes blood glucose to be stored as glycogen (in liver and muscle cells)
43
Q

What does glucagon do in terms of blood glucose?

A
  • causes glycogen to be broken down into glucose
44
Q

What is glycogen?

A
  • represents our short-term storage of glucose
  • build up glycogen levels when we eat (when insulin is released)
  • deplete glycogen levels between meals
  • can store up to 2000 calories
45
Q

How do cells in the brain absorb glucose?

A
  • cells in the brain can always take in glucose (using a glucose transporter)
  • glucose transporter works in the absence of insulin, so can always internalize sugar
46
Q

How do cells outside the brain absorb glucose?

A
  • use a glucose transporter that requires insulin to be functional
  • use a glucose transporter that requires insulin to be functional
47
Q

What do cells outside the body do in the absence of insulin?

A
  • cells in the body cannot take in glucose
  • they can only take in ketones (made from break down of fatty acids into glucose?) for energy
48
Q

What does insulin do in terms of blood lipids?

A
  • causes fatty acids to be stored as triglycerides in adipose tissue (fat cells)
49
Q

What does glucagon do in terms of blood lipids?

A
  • causes triglycerides to be broken down into fatty acids
50
Q

What are triglycerides?

A
  • represent our long-term storage of energy
51
Q

What does the liver do?

A
  • converts glycerol into sugar and fatty acids into ketones
52
Q

What happens in the presence of insulin?

A
  • all cells can use glucose for energy
  • glucose is stored for later use
  • when digestive system contains food (absorptive phase)
53
Q

What happens in the presence of glucagon?

A
  • glycogen is broken down into glucose for cells in the brain
  • cells in the body switch to using ketones (from fatty acids) for energy
  • when digestive system is empty (fasting phase)
54
Q

What do cells in the liver monitor?

A
  • glucose levels
  • this information is brought to the brain by the 10th cranial nerve (the vagus)
55
Q

What are some controllers of hunger?

A
  • blood glucose levels
  • stomach releases different signaling molecules when empty and when full; some reach brain and influence hunger
56
Q

How is an empty stomach communicated?

A
  • by the stomach’s release of a peptide called ghrelin
  • levels of circulating ghrelin increase with hunger and fall with satiation
  • exogenous administration of ghrelin increases hunger and food intake
57
Q

What can reduce hunger?

A
  • swelling of the stomach can slightly reduce, but it mostly just causes a bloated feeling
58
Q

What are the peptides that are released by the stomach and intestines when food is consumed?

A
  • the hormones CCK and GLP-1
59
Q

What do CCK and GLP-1 do?

A
  • regulate the release of digestive enzymes and insulin
  • released by the intestines in proportion to the number of calories ingested
  • their entry into the brain elicits feelings of satiety
60
Q

What does CCK do?

A
  • repeated administration of CCK to healthy people does not reliably cause sustained weight loss
  • sometimes decreases meal size, but people typically respond by eating small meals more frequently
61
Q

What does GLP-1 do?

A
  • GLP-1 agonists have recently proven to be highly effective in reducing hunger and weight in most people
  • these drugs were initially developed to boost insulin signaling in diabetics
62
Q

What does the body monitor?

A
  • blood glucose
  • food in the stomach
  • fat levels
63
Q

Why does the body monitor fat levels?

A
  • body wants to ensure there is enough fat to make it between meals
64
Q

What happens when animals are force fed?

A
  • become heavier than normal
  • reduce food intake once it regains control over how much it eats
  • body weight goes up but food intake goes down
  • after stop being force fed, body weight will go back down and food intake back up until it is regulated
65
Q

What is leptin?

A
  • a circulating hormone
  • secreted by adipocytes (fat cells)
  • leptin levels correlate with the amount of fat in the body
  • to some extent, leptin levels regulate the sensitivity of hypothalamic neurons to short-term satiety signals (CCK and GLP-1)
66
Q

How do leptin levels increase?

A
  • as fat cells grow and proliferate, leptin levels increase
67
Q

What happens if leptin levels fall below some threshold?

A
  • feel intense hunger
68
Q

What does exogenous leptin administration do?

A
  • slightly decrease meal size in healthy people, but this effect is short-lived
  • lifesaver for people who are unable to produce leptin due to a genetic mutation
69
Q

What is congenital leptin deficiency?

A
  • brain thinks there is no fat in body so think they’re in feeding emergency and eat a lot
  • rare in humans
70
Q

What is an ob mouse?

A
  • strain of mice whose obesity and low metabolic rate are caused by mutation that prevents production of leptin
71
Q

When are emergency hunger circuits activated?

A
  • when a specific critical need to eat or not eat overrides energy homeostasis circuitry
72
Q

What are the types of emergency hunger circuits?

A
  • glucoprivation (hypoglycemia)
  • lipoprivation
73
Q

What is glucoprivation (hypoglycemia)?

A
  • dangerously low blood glucose levels can cause intense hunger
  • not enough immediately available sugar in the blood
  • can result from excessive insulin signaling and from drugs that inhibit glucose metabolism
74
Q

What is lipoprivation?

A
  • dangerously low levels of fat
  • not enough fat on the body or free fatty acids in the blood
  • can be caused by drugs that inhibit fatty acid metabolism
75
Q

What does the brain do when it senses that energy stores are dangerously low?

A
  • insulin release is suppressed, and glucagon release is triggered
  • short-term satiety signals are ignored
  • energy expenditure slows (basal metabolic rate), halting growth and reproductive systems
  • a potent and sustained feeling of hunger takes hold
76
Q

What is diabetes?

A
  • a condition where people are either insensitive to insulin signaling or they do release enough insulin
  • results in high blood glucose levels and an inability to store glucose as fat
77
Q

What happens if diabetes is not treated?

A
  • leads to intense thirst and progressive weight loss
  • as fat cells become depleted, leptin levels fall, and a lipoprivation- related feeding emergency takes hold, resulting in intense hunger, even if there is tons of glucose in the blood
  • often led to death before insulin treatments were discovered
78
Q

What is the hypothalamus?

A
  • key regulator of hunger
79
Q

What happens in the arcuate nucleus of the hypothalamus in terms of hunger?

A
  • two cell populations have opposing influences on hunger
  • AGRP/NPY neurons
  • POMC neurons
80
Q

What does stimulation of one cell population (AGRP and NPY) do?

A
  • Stimulation of one cell population – the neurons that co-release the peptides AGRP and NPY – causes dramatic overeating
  • Leptin and other satiety signals inhibit these neurons
81
Q

What do AGRP/NPY neurons do?

A
  • promote hunger
  • inhibited by leptin and activated by ghrelin
82
Q

What do POMC neurons do?

A
  • inhibit hunger
  • activated by leptin and inhibited by ghrelin
83
Q

What do the two cell population do?

A
  • Feelings of hunger partially relate the balance of activity between these two cell populations
  • project to the paraventricular nucleus (PVN) of the hypothalamus
  • Some neurons in this area stop firing when the body has dangerously low levels of fat (leptin)
84
Q

What does PVN activity do?

A
  • Artificially increasing PVN neuron activity does not substantially/reliably change hunger
  • the inhibition of some cells in this area can generate intense hunger
  • seem to trigger a lipoprivation response
85
Q

What is Prader-Willi syndrome?

A
  • a rare chromosomal abnormality in which up to 7 genes are deleted from chromosome 15
  • one of these genes is critical for the development/survival of a population of PVN neurons
86
Q

What do people suffer with Prader-Willi syndrome?

A
  • born with very low muscle mass and have little interest in eating
  • develop a heightened, permanent and painful sensation of hunger
  • most die of obesity- related causes
  • sensations of satiety to tell them to stop eating or to throw up
  • can accidentally consume enough food in a single binge to fatally rupture their stomach
87
Q

What is the modern obesity epidemic?

A
  • world is changing much faster than our genes are, and some people’s genes are not well-suited to our current food environment
  • hedonic aspect to hunger
  • Food can be delicious and reinforcing even when people are not hungry
88
Q

Why is there variability in body fat?

A
  • About 50% of the variability in people’s body fat is due to genetic differences
  • Natural variations in metabolic efficiency are one of the most important factors
89
Q

What can treat obesity?

A
  • pharmacological treatments to control weight
  • surgeries have developed that limit the amount of food that can be eaten during a meal
90
Q

What is bariatric surgery?

A
  • modifies the stomach, small intestine, or both
  • most effective form is called the Roux-en-Y gastric bypass (RYGB)
91
Q

What is RYGB surgery?

A
  • the second part of small intestine (the jejunum) is cut and attached to the top of the stomach
  • the stomach is also stapled to make it much smaller
  • results in reductions in hunger over time

Psych 211 (neuro) (21 decks)

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