exam 2

What part of motivation is thirst

a drive

what does thirst motivate us to do

stay hydrated

what is the biggest danger in the world

dehydration

how many days does it take to die of dehydration

three

what percent of out body is water

70%

how do we obtain water

eating and drinking

how do we lose water

alcohol, defecating, urinating, seating, exhaling, evaporating (speaking)

caffein is NOT a...

diuretic

who created the dry mouth theory

walter cannon

hypothesis of dry mouth theory

we drink because our mouths are dry

evidence against dry mouth theory

-people without salivary glands
-unable to feel level of wetness in mouth
-sham-drinking experiments

sham-drinking experiment

-done in dogs
-dog drinks water, water is syphoned out of the stomach through fistula/cannula

cause of thirst

depletion of water from the body's cells

what holds water inside the body

intracellular and extracellular compartments

what compartments hold majority of water in body

intracellular compartments

where are extracellular compartments

in the cells and blood

what is a set point

the certain amount of substance required to maintain homeostasis

what substances must be maintained for homeostasis

the amount of solute per salt in the cells and blood

what happens with low levels of salt AND water

low levels \= thirst
extreme drop \= DEATH

what are the two kinds of thirst

osmotic and hypovolemic

way to remember osmotic thirst

osmotic \= osmosis

way to remember hypovolemic thirst

volemic \= volume
deals with water in the blood

what is osmotic thirst

deals with movement of molecules from high to low concentration through a barrier
-loss of water \= osmotic thirst

what kind of membrane do cells have

a semipermeable membrane

what is a semipermeable membrane

only permits some things through

what enters the cell after eating salty food

more salt

movement of salt and water through membrane

-salt can not pass immediately through membrane
-balance maintained by water moving OUTSIDE cell to return to equilibrium

why doesn't sugar cause as much thirst

-sugar is much more permeable
-much less/almost no water has to exit the cells after eating sugar.. therefore no thirst

who discovered the brain signal that tells you to drink

dr. andersson (1953)

what part of the brain tells us to drink

the osmoreceptors

what are osmoreceptors

neurons that become active when low in water, make you thirsty

what kind of thirst is the most common

osmotic thirst

why do we feel hypovolemic thirst

when there is a loss of water between cells and blood
-also loss of sodium

fitzsimmons hypovolemic thirst experiment

-put balloon in vena cava of dogs heart (decreased blood flow).. mimics hypovolemic thirst
-dog started drinking

what are baroreceptors

receptors in the right atrium that measure pressure
-determine level of stretch on atrium to assess level of blood flow coming through

what causes baroreceptors to send a signal to brain

lack of stretch on the atrium

what is triggered by the baroreceptors

-triggers the posterior pituitary gland to release vasopressin
-vasopressin tells kidneys to retain water

function of vasopressin

an anti-diuretic hormone

what do the kidney's detect

low blood pressure

what hormones do the kidneys release when blood pressure is low

renin

what does renin do

turns angiotensinogen into angiotensin I to angiotensin II

function of angiotensin

constricts blood vessels, activates subfornical organ in brain, stimulates posterior pituitary to release vasopressin, stimulates adrenal glands to secrete aldosterone

purpose of constricting blood vessels

increases pressure so blood can travel to destination faster

purpose of stimulating adrenal glands to secrete aldosterone

helps to retain salt and makes you crave salt

how do you know when a function is important?

it has redundancies.. if one system shuts down it has a million others to back it up

why do people with high blood pressure need to cut salt from diet

more salt \= more water flow out of cells... heart is already struggling to pump blood so salt doubles responsibility

hangovers have similar symptoms to...

dehydration

who coined the gastric contractions theory

walter cannon

gastric contractions theory

no gastric contractions \= no more hunger

evidence against gastric contractions theory

-people without stomachs still get hungry
-balloon in stomach only momentarily reduced hunger

what are orosensory factors

smell, texture, hearing... neck up feelings

sham-feeding experiment

-same as sham drinking but with eating
-dogs get all orosensory senses of eating without getting full
-time between meals decreases but amount of food eaten remains the same
-showed that only satisfying orosensory senses is not enough

who coined the drop in blood glucose theory

gene mayer

what is the blood glucose theory

a drop in available blood glucose causes hunger
-glucose stimulates certain neurons in the brain

where are the "glucostats"

in an area of the hypothalamus called the ventromedial hypothalamic nucleus (VMH)

how was the ventromedial hypothalamic nucleus found

scientists lesioned (destroyed) the hypothalamus.. when VMH was hit, the individual survived but continuously ate and gained weight

what is the static phase

when a patient with VMH lesions evens out (amount of food eaten) but still consumes SIGNIFICANTLY more than control individual

function of the ventromedial hypothalamic nucleus

controls eating (satiety)... limits food intake

what happens to individuals with lesions to the lateral hypothalamus

they stop eating!!!!
-would eat when forced but had little to no interest in food

function of lateral hypothalamus

controls the initiation of eating
-controls appetite.. lights up even when thinking about food

what is the "center" controlled by lateral hypothalamus

hunger center.. lesions \= undereating

what is the "center" controlled by ventromedial hypothalamic nucleus (VMH)

satiety center... lesions \= overeating

other explanations about overeating when VMH is lesioned

lesions also destroyed connections to peripheral nervous system, brain didn't recognize already conserved energy

other explanations about undereating when LH is lesioned

lesions also destroyed dopamine neurons responsible for reward, and motor neurons
-LH is also connected to drinking... no drinking \= no eating

what does norepinephrine control

hunger

medicines that cause weight gain control what chemical

norepinephrine

what does serotonin control

satiety

medicines that cause undereating activate what chemical

serotonin

Kennedy's lipostatic theory stated

appetite/hunger is controlled by body fat
-you are hungry when you lose fat and satiated when you gain it

kennedy's experiment for hunger theory

-experiment on prisoners
-are TONS of food and gained body fat

kennedy's hunger theory is good for what?

long term weight maintenance

what kind of tissue are fat cells

adipose tissues
\=fat cells are endocrine glands

what hormone do fat cells secrete

leptin

what does leptin control

satiety
-when leptin is low, brain activates TONS of hormones for you to eat
-like the "E" in your car

how was the function of leptin discovered

-mice without leptin were significantly fatter
-being fatter is phenotype for no leptin or no leptin receptors

obesity \= \_______ leptin

more leptin, less ghrelin

when is obesity usually identifiable

around 3 years old

BMI for obesity

greater than or equal to 30

how to calculate BMI

weight (kg) / height (m^2)

underweight BMI

less than or equal to 18

healthy weight BMI

around 18/19 to 25

overweight (preobesity) BMI

25 to 29

graphs shape of death risk for BMI

-obese and underweight are highest risk
-healthy weight is least risk

what is obesity a risk factor for...?

EVERYTHING

percentage of people overweight in america

72%

percentage of people obese in america

38%

what is the second most preventable cause of death

obesity

how many die of obesity a year

400,000

most preventable cause of death

smoking

cause of obesity

eating more calories than we expend OR expending less calories than we eat

people with obesity show no evidence for..

laziness, lack of will power, or slow metabolism

signal to stop eating in people with obesity

its compromised.. stopping eating is HARD

commonalities of people who keep wight off

-WALKING WHENEVER POSSIBLE
-low fat diets
-weigh themselves once a week
-meal planning

max pounds to lose in one week

2 pounds

what percentage of obesity is genetic

65%

how many genes code for BMI

300 genes
-satiety levels, food preference, exercise, etc

what percentage of obesity is environmental

35%

dieting is insufficient when...

you're cutting out entire food groups (proteins, lipids, carbs)
-your brain will crave each no matter what

best way to measure for appropriate weight

waist circumference

why do we use waist circumference

waist is the location of all vital organs, so fat surrounding will directly effect their performance