Biological Regulation of Temperature, Thirst, and Hunger

Vocabulary-style flashcards based on lecture notes covering homeostatic mechanisms, temperature regulation, thirst, hunger, and eating disorders.

Homeostasis

Biological processes that keep certain body variables within a fixed range.

Set point

A single value that the body works to maintain, such as levels of water, oxygen, glucose, calcium, protein, fat, and acidity.

Negative feedback

Processes that reduce discrepancies from the set point.

Allostasis

The adaptive way in which the body anticipates needs depending on the situation.

Basal metabolism

Energy used to maintain a constant body temperature while at rest.

Poikilothermic (ectothermic)

The idea that body temperature matches that of the environment, characteristic of amphibians, reptiles, and most fish.

Homeothermic (endothermic)

The use of internal physiological mechanisms to maintain an almost constant body temperature, characteristic of mammals and birds.

POA/AH (preoptic area / anterior hypothalamus)

The brain area predominantly responsible for body temperature regulation; it receives input from temperature receptors and the immune system.

Constant High Body Temperature

Evolved in mammals at a level of $37^{\circ}\,\text{C}$ ($98^{\circ}\,\text{F}$) to support vigorous muscle activity while avoiding protein bond breakage.

Fever

An increased body temperature set point directed by the hypothalamus to help the immune system; fevers above $41^{\circ}\,\text{C}$ ($109^{\circ}\,\text{F}$) are life-threatening.

Vasopressin

A hormone released by the posterior pituitary that raises blood pressure and enables kidneys to reabsorb water; also known as antidiuretic hormone (ADH).

Osmotic thirst

A type of thirst resulting from eating salty foods which increases the concentration of solutes outside the cell.

Hypovolemic thirst

Thirst resulting from low volume of body fluids due to bleeding or sweating, associated with a drop in blood pressure.

Osmotic Pressure

The pressure created by solutes that causes water to flow across a semi-permeable membrane from low to high solute concentration; in mammals, the set point is $0.15\,M$.

OVLT and Subfornical Organ

Brain structures adjoining the third ventricle that detect osmotic pressure and the sodium content of the blood.

Angiotensin II

A hormone that constricts blood vessels to compensate for a drop in blood pressure and triggers neurons in the third ventricle to stimulate drinking.

Sodium-specific hunger

A strong craving for salty foods that develops automatically to restore solute levels in the blood during hypovolemic thirst.

Lactase

An intestinal enzyme necessary for metabolizing lactose, the sugar found in milk; levels usually decline after weaning in most mammals.

Sham feeding

Experiments where everything an animal eats leaks out of a tube, demonstrating that taste and chewing alone do not produce satiety.

Vagus nerve

The nerve that conveys information about the stretching of the stomach walls to the brain as a signal to stop eating.

Splanchnic nerves

Nerves that convey information about the nutrient contents of the stomach to the brain.

Duodenum

The part of the small intestine where significant nutrient absorption begins; its distention produces satiety.

Cholecystokinin (CCK)

A hormone released by the duodenum that regulates hunger by closing the sphincter between the stomach and duodenum and stimulating the vagus nerve.

Insulin

A pancreatic hormone that enables glucose to enter cells; high levels typically decrease hunger, but constantly high levels can cause weight gain.

Glucagon

A hormone released by the pancreas when glucose levels fall, stimulating the liver to convert stored glycogen to glucose.

Type I Diabetes

A condition where insulin levels remain low but blood glucose levels are high, leading to hunger despite internal starvation as glucose is excreted unused.

Leptin

A peptide produced by fat cells that signals the brain to increase or decrease eating; high levels increase physical activity and reduce eating.

Arcuate nucleus

A part of the hypothalamus containing neurons sensitive to both hunger and satiety signals; it receives input from ghrelin, insulin, and leptin.

Ghrelin

A neurotransmitter released in the brain and stomach that acts on the hypothalamus to increase appetite and trigger stomach contractions.

Paraventricular nucleus

A part of the hypothalamus that inhibits the lateral hypothalamus; the release of melanocortins here is important for limiting food intake.

Neuropeptide Y (NPY) and AgRP

Inhibitory transmitters that block the satiety action of the paraventricular nucleus and provoke overeating.

Lateral Hypothalamus

A brain area that controls insulin secretion, alters taste responsiveness, and increases the drive to eat; damage results in undereating and weight loss.

Ventromedial hypothalamus (VMH)

A brain area where output inhibits feeding; damage causes increased meal frequency, faster stomach emptying, and weight gain.

Bulimia nervosa

An eating disorder characterized by alternating between extreme dieting and binges of overeating, often associated with increased ghrelin levels.

Prader-Willi syndrome

A genetic condition marked by intellectual disability and obesity, characterized by high blood levels of ghrelin.

Syndromal obesity

Obesity caused by a medical condition, though most obesity relates to the combined influence of many genes and the environment.