Chapter 5: Thirst, Hunger, Elimination

Question 1

Extracellular Thirst

Answer 1

Accounts for 1/3 of total water in body
Water outside cells (in blood, CSF, body cavities)
Induced by perspiration, blood loss, diarrhea, heavy menstrual bleeding
Blood volume and blood pressure decrease
Requires replacement of electrolytes and water

Question 2

Extracellular Thirst Mechanisms

Drop in blood pressure lead to…

Answer 2

Leads to activation of baroreceptors (blood pressure receptors) in kidneys
Activation of baroreceptors triggers release of renin from kidneys
Renin is an enzyme that produces angiotensin in blood
Angiotensin causes vasoconstriction
Angiotensin causes hypothalamus and pituitary to increase production of vasopressin (anti-diuretic hormone –prevents urination)
Angiotensin causes adrenal gland to release aldosterone from adrenal cortex
Aldosterone causes kidneys to increase sodium reabsorption
Vasopressin causes kidneys to increase water reabsorption

Question 3

How does angiotensin stimulate production of vasopressin

Answer 3

Subfornical Organ
• Located outside BBB
• Contains osmoreceptors and also responds to angiotensin
• Neurons in subfornical organ project to hypothalamus

Question 4

Cellular Thirst

Answer 4

Accounts for 2/3 of total water in body
Water inside cells
Induced by excess salt consumption or severe thirst (dehydration)
Excess salt consumption or severe thirst leads to increased extracellular sodium
Osmotic force draws water out of cells (cell shrinks)
Extracellular thirst will occur before cellular

Question 5

Concentrated saline (salt) applied around third ventricle …

Answer 5

induces drinking

Question 6

Distilled water applied around third ventricle …

Answer 6

causes drinking cessation

Question 7

Feeding (Absorptive) Phase

Answer 7

Insulin release from pancreas
Glucose from blood moves into cells, glucose–>glycogen
Energy stored
Parasympathetic

Question 8

Fasting (Utilization) Phase

Answer 8

Glucagon release from pancreas
Glycogen stores from cells metabolized to glucose and released into blood
Liberates stored energy
Sympathetic

Question 9

Ghrelin

Answer 9

• Secreted by epithelial cells lining empty stomach, as well as intestines and pancreas
• Ghrelin levels in blood rise during fasting
• Signals hunger & stimulates feeding
• Inhibits vagus nerve (signals parasympathetic system)
• Crosses BBB via transport system (get into hypothalamus)

Question 10

Cholecystokinin (CCK)

Answer 10

• Released when food reaches the intestines (duodenum)
• Stimulates digestion of fat and protein
• Injecting CCK reduces feeding and food seeking behaviour
• Receptors in many areas, influence on hypothalamus directly and through vagus nerve
• Receptors in many areas of brain stimulate vagus nerve

Question 11

Orexin

Answer 11

• Produced in the Lateral Hypothalamus
• Causes craving of food
• Increases meal size by suppressing inhibitory feedback

Question 12

Neuropeptide Y (NPY)

Answer 12

• NPY neurons found in arcuate nucleus of hypothalamus
• NPY active during hunger
• NPY less active in well-fed state
• Stimulates hunger
• Injecting NPY into hypothalamus of rats leads to ravenous and frantic eating behaviours
• Obesity can be associated with excessive NPY
• Chronic stress and a high fat, high sugar diet are associated with excess NPY in studies of mice and monkeys

Question 13

Leptin

Answer 13

• Secreted by adipose tissue
• Decreases food intake
• Increases metabolism
• Involved in long-term regulation of body weight and fat stores
• Does not necessarily have immediate effects on hunger and satiety

Question 14

Lesion the ventromedial hypothalamus (VMH)

Answer 14

Hyperphagia (overeating)

Therefore, Natural role of VMH is to inhibit/reduce feeding

Question 15

Lesion the lateral hypothalamus (LH)

Answer 15

Aphagia (failure to eat/drink)

Therefore, Natural role of LH is to stimulate/promote eating behaviour

Question 16

Leptin vs Ghrelin

- For NPY & Orexin

Answer 16

Leptin
Inhibits NPY secreting neurons in the arcuate nucleus of the hypothalamus
Inhibits Orexin producing cells
Decreases food intake

Ghrelin
Activates NPY secreting neurons in the arcuate nucleus of the hypothalamus
Stimulates Orexin producing cells
Increases food intake

Question 17

Glucose

Answer 17

Decreased glucose in cells stimulates hunger
Hunger and feeding correlate with low blood sugar

Glucose in hepatic portal vein reduces appetite
Liver information delivered to the hypothalamus via the vagus nerve

Question 18

Blood Glucose

Answer 18

• Levels detected by hepatic portal vein
• Info sent to hypothalamus via vagus nerve
• Involved in hunger regulation
• NOT used as a source of energy

Question 19

Intracellular Glucose

Answer 19

• Used as a source of energy
• Cells capable of signalling in response to low intracellular glucose
• Involved in hunger regulation (when we are hungry)

Question 20

Insulin

Answer 20

• decrease blood glucose by increasing intracellular glucose

* decrease in intracellular glucose increases hunger

Question 21

Diabetes

Answer 21

• increase in blood glucose
• decrease in intracellular glucose
• increase hunger

Question 22

Social influences on Hunger

Herman et al. (2003)

Answer 22

• All female, eat 1-3 hrs before study
• Rate how hunger they are right now
• In high category, told people before them rated high hunger
• In low category, all fake data provided said they were not hungry
• Participants believed their hunger levels should match those that are around them
• Both high and low ate the same amount of cookies

Question 23

Social influences on Hunger
De Castro (1994)

Answer 23

• Individuals are not alone when eating (unlike last study)
• Participants had diet journals
• When with other people (partners/family), eat more food and faster
• When eating with friends, eat slower but still more than when alone
• Females eat more when with a male than other female friends
• No difference in males

Question 24

Sweetness

Answer 24

Sweet foods provide rapid energy with little metabolic cost
Tongue can directly sense sweetness

Newborns (smile with sugar water, innate preference)
Anencephalic infants (born w/o forebrain)--prefer sugar water over distilled water

Question 25

Saltiness

Answer 25

Tongue can directly sense saltiness
Herbivores will travel great distances for salt; Carnivores usually obtain sufficient dietary salt; Omnivores vary depending on the environment
Salt deprivation will cause animals to drink very high salinity solutions

Question 26

Avoidance

Answer 26

Learning to avoid sickening foods is rapid and single-trial, and does not follow conventional laws of learning

Question 27

Dietary Neophobia

Answer 27

Animals tend to avoid foods that they have never previously eaten

Question 28

Area Postrema

Answer 28

Controls vomiting reflex in response to toxins in food

Strong release of vasopressin from posterior pituitary can induce vomiting