PSYC211 Hunger and Thirst

homeostasis

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

osmosis

the movement of water from areas of low tonicity to areas of high tonicity

tonicity

the concentration of dissolved solutes

isotonic solutions

cells neither gain nor lose water (normal cell)

hypotonic solutions

cells absorb water and grow in size (swollen cell)

hypertonic solutions

cells lose water and shrink in size (shrunken cell)

osmoreceptors

neurons whose membrane potential is determined by the size of the cell

volumetric thirst

occurs when there is not enough blood circulating in the body; the heart needs a certain amount of blood to keep beating

hypovolemia

low blood volume, causes cells in the kidneys to release the enzyme renin, which initiates a cascade of chemical reactions

angiotensin 2

hormone that triggers corrective mechanisms in the body and brain

insulin

hormone released by pancreas when BG is high

glucagon

hormone released by pancreas when BG is low

ghrelin

peptide released by the stomach when the stomach and intestines are empty (in between meals)

glucoprivation (hypoglycemia)

- dangerously low blood-glucose levels, triggers intense feelings of hunger

- can result from excessive insulin signaling as well as from drugs that inhibit glucose metabolism

lipoprivation

dangerously low amounts of body fat or available free fatty acids

AGRP/NPY neurons

promote hunger, are activated by ghrelin and inhibited by leptin and CCK

POMC neurons

inhibit hunger, are inhibited by ghrelin and activated by leptin and CCK

when the body is too cold...

- 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

when the body is too hot...

- animals sweat or pant, water evaporation has a cooling effect

- peripheral blood vessels expand, blood moves closer to - the skin so body heat can more easily dissipate into the surrounding air

AV3V region of the hypothalamus

feelings of thirst relate to neural activity here

osmometric thirst

occurs when there is not enough water inside cells

when we drink pure water...

our extracellular fluid becomes hypotonic, causing water to move into cells to eliminate the difference in tonicity across the membrane

when we consume salt...

our extracellular fluid becomes hypertonic, causing water to move out of cells to eliminate the difference in tonicity across the membrane

insulin causes blood-glucose to be stored as...

glycogen (in liver and muscle cells)

glucagon & glycogen

- glucagon causes glycogen to be broken back down into glucose

- glycogen represents our short-term storage of glucose

- we build up glycogen levels whenever insulin is released

- we deplete glycogen levels whenever glucagon is released

- glycogen can store up to 2000 calories

triglycerides

fatty acids are stored as this in adipose tissue, used for long-term energy

CCK and GLP-1

hormones released by the intestines in proportion to the number of calories ingested, regulate the release of digestive enzymes and insulin

PVN (hypothalamus)

where firing rates track leptin levels, animals feel intense hunger when certain of these cells stop firing, even though excess stimulation of these cells does not reliably reduce hunger

Prader-Willi syndrome

- rare chromosomal abnormality in which a gene critical for the development/survival of a population of hypothalamic PVN neurons is deleted

- between 2 and 8 years of age, people with this condition develop a heightened, permanent and painful sensation of hunger, a feeling of starving to death