Chapter 9 Internal Regulation

What does the term "body weight set-point" refer to? How can it be altered?

The set-point theory suggests that body weight is regulated at a predetermined, or preferred, level by a feedback control mechanism.

osmotic thirst

(cellular dehydration ) • Antidiuretic hormone (ADH)/vasopressin: secreted by the posterior pituitary gland, enables the kidney to reabsorb water

What role does cellular dehydration play in regulating thirst? How is it detected? How can it be induced?

*An animal that becomes deficient in sodium shows an immediate strong preference for salty tastes, known as sodium specific hunger. Osmotic thirst! (Induced by eating salty food)

ventromedial hypothalamus (VMH)

*Damage results in hyperphagia *Rats will double or triple body weight after VMH lesions - food intake is greatly increased (more meals) *VMH lesioned rats produce more insulin

Paraventricular Nucleus (PVN)

*Damage to PVN results in hyperphagia *Rats eat larger meals.

Briefly summarize the digestive process for food.

*Digestion begins in the mouth, where enzymes in the saliva break down carbs. *The stomach stores food, and then a round sphincter muscle opens at the end of the stomach to release food to the small intestine. *The small intestine absorbs digested materials into the bloodstream. *The blood carries those chemicals to body cells that either use them or store them. *The large intestine absorbs water and minerals and lubricates the remaining materials to pass as feces.

Why do people become obese?

*Genetics- clearly genetics plays a role in the predisposition for obesity- not the only factor for most people however *Basal metabolism- low basal metabolism results in weight gain High basal metabolism helps maintain low or normal body weight *Conditioning/Learning

Describe the role of glucose, insulin, and glucagon in the regulation of hunger.

*Insulin enables glucose to enter cells where it is either used as fuel or stored as fat or glycogen. * High insulin levels produce hunger by reducing available glucose in the blood *Extremely low insulin levels (as in diabetes) also produce hunger by preventing glucose from entering the cells - thus, the cells are starving.

Describe the major fluid compartments of the body and how water moves between them?

*Intracellular: about 67% • Extracellular: about 33% • Water's movement between them is due to (Osmotic pressure). When the concentration of solutes across a semi-permeable membrane are not equal, the water moves to dilute it.

What role does the liver play in the regulation of eating?

*It has many important metabolic functions. It converts the nutrients in our diets into substances that the body can use, stores these substances. * It also takes up toxic substances and converts them into harmless substances or makes sure they are released from the body

What area of the brain is believed to be critical for temperature regulation? Why?

*Preoptic area and anterior hypothalamus (PAO/AH) *Monitors body temperature partly by monitoring its own temperature. *Preoptic area receives input from temperature sensitive receptors in the skin and spinal cord.

Poikilothermic (cold blooded)

*Refers to an animal whose body temperature is the same as their environment (Fish, reptiles, amphibians)

Homeothermic (warm blooded)

*Refers to animals that maintain a relatively constant body temperature (Mammals and birds)

What behavioral mechanisms do animals (and humans) use to regulate temperature?

*Shivering and sweating represent automatic mechanisms for controlling body temperature (Human). *Cold blooded animals choose their location within their environment in order to regulate their body temperature. *Warm blooded animals also use behavioral mechanisms to regulate body temperature.

Describe the role of stomach distention and CCK (cholecystokinin) in satiety?

*Stomach conveys information to the brain via the vagus and splanchnic nerves *There are stretch receptors in the walls of the stomach - thus stomach distension is a sufficient cue for satiety. *CCK decreases meal size by causing the sphincter muscle between the stomach and duodenum to close.

What role does basal metabolism play in weight regulation?

*This energy is used to support life-sustaining jobs, from breathing and pumping blood to maintaining body temperature. *Age makes a difference because the body loses muscle mass with aging, which slows down metabolism.

Describe the role of leukocytes and cytokines in the production of a fever. Which part of the brain do they affect?

*When the body is invaded by viruses, bacteria, leukocytes are mobilized to attack them. *Cytokines (small proteins) are released by leukocytes when bacteria or viruses invade the body and attack them. *Cytokines stimulate the vagus nerve to initiate a fever. *Low grade fever helps to fight the infection.

What role do oral factors play in the regulation of hunger?

*While taste and chewing contribute to the regulation of eating- these cues are not sufficient to produce satiety *(In Sham-Feeding Studies) all food (liquid diets are used) exits the digestive system via a tube attached to the stomach. In these studies, animals greatly increase the amount of food they eat.

Bulimia nervosa

*alternate between bingeing and purging *may have higher levels of peptide YY (PYY) *lower levels of CCK

Lateral hypothalamus

*hunger center so leads to aphasia dipsia *Eating less

Anorexia Nervosa (AN)

*unwillingness to eat *results in extreme weight loss *90% are female *may be a genetic predisposition

What neural mechanisms are involved in the regulation of drinking?

When the body's sodium reserves are low, the adrenal glands produce aldosterone, a hormone that causes the kidneys, salivary glands, and sweat glands to retain salt. Aldosterone and aldosterone II together change the properties of taste receptors on the tongue, neurons in the nucleus of the tractus solitarius, and neurons elsewhere in the brain to increase salt intake.

What is conditioned taste aversion?

a taste associated with nausea is avoided in the future

What role do the kidneys play in water regulation?

• ADH causes the kidneys to reabsorb water • Aldosterone causes the kidneys to reabsorb Na and other salts.

• Hypovolemia thirst:

• Renin: there are baroreceptors in the kidneys which detect low blood volume and release the enzyme renin • Renin causes proteins in blood to form angiotensin I • Angiotensin II: vasoconstrictor, constricts blood vessels, thus increasing blood pressure • Also stimulates the subfornical organ to initiate thirst so you drink • Subfornical organ is outside the BBB, relays information to a preoptic area in hypothalamus that helps control drinking