Chapter 10 Outline
THE REGULATION OF INTERNAL BODY STATES
I. Temperature Regulation
A. Basal Metabolism: Energy used to maintain a constant body temperature at rest.
B. Homeostasis: Biological processes which keep certain body variables within a fixed range. In mammals, temperature regulation, thirst and hunger are nearly homeostatic and not exactly homeostatic.
Set point: Level at which a homeostatic process maintains a variable.
C. Poikilothermic: Animals with body temperatures the same as their environment
D. Homeothermic: Animals with physiological mechanisms that maintain an almost constant body temperature despite variations in environmental temperature
Mammals maintain a body temperature of 37°C for two reasons: 1) Because they have less efficient mechanisms for cooling than heating thus it is important to have a body temperature warmer than the air. 2) Maintaining a high body temperature keeps the animal ready for rapid movement.
E. The brain region most critical for temperature control is the preoptic area of the hypothalamus (preoptic because it is near the optic chiasm). This area monitors body temperature by monitoring its own temperature and by receiving input from temperature-sensitive skin and spinal cord receptors.
F. The body temperature of fish, amphibians, and reptiles match that of their surroundings but rarely fluctuate tremendously because these animals choose their location within the environment. Mammals can also maintain their body temperature by behavioral means.
G. After infection by bacteria, viruses, or fungi, the body mobilizes its leukocytes (white blood cells) to attack these foreign substances. Leukocytes release a protein (interleukin-1) which causes the production of prostaglandin E1 and prostaglandin E2 (this causes cells in the preoptic area to raise body temperature)
H. Infant rat behavioral capacities are poor at room temperature but improve dramatically in temperatures kept above 30°C.
I. Tonic immobility: A limp and almost motionless body response (e.g., when a baby bird is grabbed by a predator). A motionless chick will eventually accumulate body heat;
when its body temperature reaches 41.4 degrees Celsius, it starts moving again.
II. Thirst
A. When your body needs water, the posterior pituitary gland releases vasopressin also known as antidiuretic hormone (ADH), which enables the kidneys to reabsorb water and secrete highly concentrated urine.
B. Thirst can be divided into two types: thirst due to an increase in solute concentrations (osmotic thirst) and thirst due to a loss of overall volume (hypovolemic thirst).
1. Osmotic pressure: The tendency of water to flow across a semipermeable membrane from an area of low concentration to areas of high concentration. In cells, the membrane works as a semipermeable membrane and water but not all solutes flows freely between the extraceUularfiuid (fluid outside the cell) and intracellularfiuid (fluid inside the cell).
2. Osmotic thirst: Occurs when certain neurons detect their own loss of water.
3. Organum Vasculosum Laminae Terminalis (OVLT): Area located around the third ventricle, the OVLT is most responsible for detecting osmotic pressure.
4. The supraoptic nucleus and paraventricular nucleus are brain areas located in the hypothalamus that control the rate at which the posterior pituitary gland releases vasopressin.
5. Neurons which control drinking are located in the lateral preoptic area of the
hypothalamus.
C. Hypovolemic thirst: Thirst based on blood volume (and therefore blood pressure) becoming too low, so that water and nutrients cannot get to the body's cells.
1. Baroreceptors: Receptors attached to large veins that determine the pressure of
blood returning to the heart.
2. When blood volume decreases, the kidneys release the hormone renin which splits a portion off angiotensinogen ( a large protein in the blood) to form angiotensin I which is then converted into angiotensin II; this hormone constricts blood vessels in order to reverse the loss of blood volume.
3. Subfornical organ (SFO): Adjoining the third ventricle of the brain, neurons in this brain area send information to the preoptic area after angiotensin stimulates its neurons.
4.  Synergistic effect: An effect that is more than the sum of two separate effects. Angiotensin and baroreceptors have a synergistic effect as less angiotensin is required to stimulate thirst if baroreceptors also indicate low blood pressure.
5.  Sodium-specific cravings (due to bleeding or excessive sweating) are caused by the release of aldosterone, a hormone which causes the kidneys, salivary glands, and sweat glands to conserve sodium and excrete more watery fluids than usual.
III. Hunger
A. Digestion begins in the mouth, where food is broken down by enzymes in the saliva.  Food then travels down the esophagus to the stomach, where hydrochloric acid and
enzymes digest proteins. The pyloric sphincter (located between the stomach and the intestines) is a round sphincter muscle which allows food to periodically enter the intestines. Food then enters the small intestine which is the main site for nutrient absorption into the bloodstream. These digested nutrients are carried by the blood to
cells throughout the body which use some of the nutrients and store the excess as glycogen, protein, and fat. The large intestine absorbs water and minerals and
lubricates remaining materials for excretion.
B. Many mammals lose their ability to metabolize lactose (sugar found in milk) after infancy due to decreased levels of the intestinal enzyme lactase. Worldwide most adult humans cannot consume large amounts of milk products.
C. Carnivore: An animal that eats meat.
D. Herbivore: An animal that eats plants.
E. Onmivore: An animal that eats both meat and plants.
F. Various behavioral strategies help to determine food selection including preference for sweet taste, avoidance of bitter taste, preference for familiar foods, and conditioned taste aversions (learned dislike of a food based on past experience with the food).
G. In sham-feeding experiments, everything an animal eats leaks out a tube connected to the esophagus or stomach (under these conditions, animals swallow several times as much as normal during each meal).
H. The vagus nerve (cranial nerve X) carries information to the brain regarding the stretching of stomach walls, providing a major basis for satiety.
I. The splanchnic nerves convey information about the nutrient contents of the stomach, carrying impulses from the spinal cord to the digestive organs and back.
J. The duodenum is part of the small intestine adjoining the stomach. Glucose produces satiety either through receptors in the duodenum or by causing it to release hormones with a satiating effect.
K. Cholecystokinin (CCK): A hormone released by the duodenum to inhibit appetite.
L. Insulin: Facilitates entry of glucose in the bloodstream into the body's cells.
M. Glucagon: Stimulates the liver to convert stored glycogen to glucose.
N. Diabetics eat more food than usual but lose weight because their body's cells are receiving little glucose due to poor insulin blood levels.
O. Obese people produce more insulin than do people of normal weight. The high levels of insulin cause more food than normal to be stored as fat and their appetite to return soon after a meal.
P.. Hypothalamus and feeding regulation
1. Lateral hypothalamus: A brain area important for the control of feeding. Damage to the lateral hypothalamus causes an animal to refuse food and water.
2. Ventromedial hypothalamus: Damage to this area leads to overeating and weight gain (these animals do not show an overall decrease in hunger because they consume bitter foods far less than normal).
3. Paraventricular nucleus (PVN): If damaged, rats eat larger meals rather than more frequent meals.
Q. Satiety Chemicals
1. Leptin: Released by fat cells, this protein circulates through the blood and notifies the rest of the body about current fat supplies. Hunger decreases with high leptin levels in the bloodstream.
2. Neuropeptide Y (NPY): A neuromodulator that inhibits the paraventricular nucleus, leading to an increase in eating.
R. Genes can control body weight in many ways, including metabolic rate. People with higher metabolic rates produce more heat than others do and radiate it to their environment (hence, maintaining a low weight).
S. Eating disorders
1. Anorexia nervosa: Disorder characterized by eating much less than one needs. Anorexics become very thin and sometimes die
2. Bulimia nervosa: Condition in which people alternate between dieting and overeating. Some individuals with this disorder force vomiting after meals. People with bulimia tend to have higher than normal levels of peptide YY, a neuromodulator with effects similar to NPY. Bulimics have lower than normal levels of (CCK) and signs of either decreased serotonin production or a reduced receptor sensitivity for serotonin. Drugs which increase serotonin activity (e.g., Fluoxetine) are often effective in treating bulimia.