Regulating body temperature is essential to survival because it affects protein function, cellular membranes, etc. Even small elevations in temperature can result in heatstroke. The hypothalamus is the primary control center for detecting changes in temperature and receives input from skin receptors. When the hypothalamus determines that the body is hot, it causes vasodilation and sweating. Behaviorally, we respond to the that by stretching out to maximize surface area and shedding layers of clothing. We respond to cold by curling inward, snuggling up, and adding layers of clothing.

Monitoring fluid levels includes the intake of fluids as well as excretion. The intake of fluids is stimulated by specialized osmoreceptors in the brain that detect dehydration. These receptors communicate with the pituitary gland to stimulate the release of antidiuretic hormone (ADH), which in turn communicates with the kidneys to reduce urine production by reclaiming water. When blood volume is low, including when one has sustained an injury and is losing a significant amount of blood, hunger for sodium is stimulated to increase the concentration of salt in the blood, and thirst to replace the lost fluid. Excess fluid is managed internally through urination and sweating.

Hunger helps regulate the intake of nutrients into the body. Like body temperature, it is controlled by the hypothalamus, which receives information from the stomach, intestines and liver, as well as through the monitoring of blood glucose levels. The lateral hypothalamus brings on hunger, while the ventromedial hypothalamus depresses hunger. Ghrelin, released by the stomach and pancreas, heightens the sensation of hunger. Leptin, a hormone released by white adipose tissue (fat) reduces hunger.

In addition to directing the development of male and female sexual anatomy, sex hormones are responsible for the activation of sexual behavior. While estrogen and testosterone control sexual drive to a minimal extent in the short-term, long-term behavior can be guided by sex hormones. For example, the spike in feelings of sexual attraction during puberty is correlated with an increase in sex hormones.

We are more than beings driven simply by biological drives. When considering some of the higher levels of Maslow’s hierarchy, sociocultural factors likely play a large role in motivation. Also, lower levels of Maslow’s hierarchy are also included by sociocultural factors. For example, how a culture views body weight has an impact on the motivation of its members to reach some desired weight. In many cultures, such as that of the United States, where the media idolize a thinner image, people may change their eating habits to obtain that desired figure. In other cultures, being overweight is idolized as a sign of success and well being, so their members may strive to gain weight. Culture also influences taste preferences, the desire for fatty foods, and the amount of exercise that people get. Also, appetite is also related to mood. When feeling depressed, we may crave sweet or starchy foods to help boost the neurotransmitter serotonin, which has a calming effect. We may crave food simply for sensory stimulation when bored or may develop food aversions based on experiences of food poisoning. Hunger and other drives are far from simple innate biological drives- they are also influenced by experience.

 

Practice Questions

Khan Academy

 

MCAT Official Prep (AAMC)

Section Bank P/S Section Question 31

Section Bank P/S Section Passage 7 Question 53

Key Points

• Biological factors can play a large part in motivation. Responses to body temperature variations, fluid intake, weight variations, and sexual stimulation are regulated to a large extent by biological processes.

• For many physiological processes, it is theorized that bodies have a “set point” or a “sweet spot” at which things are in homeostasis. Our bodies also have mechanisms for detecting deviations from the set point and stimulating us to reach either internally or behaviorally to regain the set point. Responses to body temperature variations, fluid intake, weight variations, and sexual stimulation are regulated to a large extent by biological processes.

• When considering some of the higher levels of Maslow’s hierarchy, sociocultural factors likely play a large role in motivation. In addition, lower levels of Maslow’s hierarchy are also included by sociocultural factors.

Key Terms

Drive-reduction theory:  a theory that proposes deviations from homeostasis create physiological needs

Drive: acts of motivation like thirst or hunger that have primarily biological purposes

Homeostasis: the ability of a system or living organism to adjust its internal environment to maintain a stable equilibrium, such as the ability of warm-blooded animals to maintain a constant temperature

Maslow’s hierarchy: refers to Maslow’s theory that is based on the premise that humans are motivated by needs that are hierarchically ranked

Hypothalamus: located in the brain, is the primary control center for detecting changes in temperature

Osmoreceptors: receptors that monitor water levels in the body

Antidiuretic hormone: hormone from the pituitary gland that controls water levels

Gherlin: released by the stomach to promote hunger

Leptin: hormone secreted by fat tissue that reduces hunger

Estrogen: female sex hormone

Testosterone: male sex hormone