hunger and thirst

the process of actively maintaining internal conditions, particularly with respect to food and water availability and body temperature. Animals live in diverse environments because they can maintain homeostasis.

-> 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

-> animals sweat or pant like a dog (breath heavily); 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

Cold-blooded (ectotherm) animals are not very good at maintaining their body temperature, so their ability to move and function is highly dependent on the ambient temperature. When the temperature of warm-blooded (endotherm) animals deviates from a set point (~37 ˚C), the body launches corrective mechanisms.

When our body temperature becomes uncomfortable, we consciously experience a need state. Need states are motivating. They drive us (push us) to correct a specific problem. When a need becomes satisfied, we often experience relief or pleasure.

true, the anticipation of pleasure can motivate us (pull us) to perform an action, even in the absence of a corresponding need. Homeostatic needs and hedonic pleasures seem to activate overlapping neural circuits, as they give rise to indistinguishable sensations of craving, wanting, needing.

1- not enough water inside cells (osmometric thirst) 2- not enough blood (liquid) in our circulatory system (volumetric thirst)

water moves from areas of low salt concentration (low tonicity) to areas of high salt concentration (high tonicity). water goes where the salt (solute) concentrate is highest. Pure water has low tonicity; it is hypotonic. Salt water has high tonicity; it is hypertonic.

false: cell membranes limit diffusion. Molecules dissolved in water cannot easily cross a cell membrane. However, to some extent water can cross, which leads to osmosis

cells neither gain nor lose water.

cells absorb water and grow in size. (more salt inside the cell)

cells lose water and shrink in size. (more salt outside the cell)

neurons whose membrane potential is determined by the size of the cell. The release of neurotransmitter from osmoreceptors relates to the volume of these cells.

true

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. It is possible for cells to absorb too much water and explode, but this rarely happens because we quickly generate urine to eliminate excess water.

our extracellular fluid becomes hypertonic, causing water to move out of cells to eliminate the difference in tonicity across the membrane. Cells can shrink too much and die, but we experience osmometric thirst before that happens.

Low blood volume (hypovolemia) causes cells in the kidneys to release the enzyme renin, which initiates a cascade of chemical reactions. the hormone angiotensin 2 triggers corrective mechanisms in the body and brain. -retention of sodium -retention of water -increase in blood pressure -salt appetite -drinking People feel intense thirst when they lose a lot of blood.

true

Feelings of thirst relate to neural activity in the AV3V region of the hypothalamus (the anteroventral tip of the third ventricle). While the act of drinking immediately quenches thirst, it takes time for water to reach the AV3V region and neurons there generally remain active until water reaches them (long after people have stopped drinking).

they are part of the rapid satiety feedback mechanism. Rapid satiation may be a learned association between the act of drinking and the subsequent dissipation of thirst.

• sugar • fat • amino acids • nucleotides • salts and vitamins

urinating, sweating or breathing (Fat is broken down into water and carbon dioxide (which is exhaled)).

• excess water, salt, and sugar • urea from the breakdown of proteins • uric acid from the breakdown of nucleic acids

– It receives information from throughout the forebrain about the external environment (whether the room is safe, whether food is available, etc.) – It monitors hormone levels in the blood – And it indirectly receives information about digestive processes from the 10th cranial nerve (the vagus).