Chapter TenThe Regulation of Internal Body States

Temperature Regulation

Homeostasis-keeping body variables within a fixed range

Set Point-a single value that the body works to maintain

Homeothermic-mammals and birds use physiological mechanisms to maintain an almost constant body temperature despite large variations in the temperature in the environment

Advantages of Consistent Body Temperature

Generally, we rest with temperature around 37o C

Advantages

Higher than air temperature so we don’t have to rely on inefficient methods to cool the body

Body is as warm as it can be without damaging necessary proteins

Rapid muscle contractions are more possible at this temperature

Temperature Regulation

Brain Mechanismspreoptic area is most critical

Behavioral MechanismsSeeking a warm place when cold, etc.

FeverProstaglandins stimulate a rise in temperature in response to

invading bacteria and viruses

Thirst and Related Processes

When the body needs water=thirst

Related Processes

Vasopressin-hormone released from posterior pituitary

constricts blood vessels

enables kidneys to reabsorb water

Types of Thirst

Osmotic Thirst

When solutes become concentrated outside the cell and water is extracted from inside cells

OVLT-organum vasculosum laminae terminalis

detects osmotic pressure

sends information to hypothalamus

paraventricular nucleus

supraoptic nucleus

lateral preoptic area

Figure 10.6  The consequence of a difference in osmotic pressure(a) A solute such as NaCl is more concentrated outside the cell than inside. (b)

Water flows by osmosis out of the cell until the concentrations are equal. Neurons in certain brain areas detect their own dehydration and trigger thirst.

Figure 10.3  Major subdivisions of the hypothalamus and pituitary

Types of Thirst

Hypovolemic Thirst

thirst resulting from low blood volume

Mechanisms

Baroreceptors-attached to large veins detect pressure of blood returning to the heart

Renin released by kidneys assists in creating high levels of angiotensin II which constricts blood vessels and signals brain to stimulate thirst

Table 10.1

Digestive System

Digestion

Begins with saliva in the mouth

Down esophagus

Stomach tears up food using acids and enzymes

Small Intestine-digested materials absorbed through small intestine

Large intestine-absorbs water and minerals

Influences on Food Selection

Food Preferencecarnivores-meatherbivores-plantsomnivores-meat and plants

FlavorFamiliarityPotential conditioned taste aversions-the tendency to form a dislike

to any food that has become associated with illnessEx: People receiving chemotherapy will develop a dislike for

fluids they consume during therapy

Bodily Influences on Hunger

Mouthoral sensations

StomachVagus nerve-transmits information on stomach distentionSplanchnic nerve-transmits information on nutrient content of

food being consumedIntestines

duodenum-once food reaches here, CCK is released and signals to stop eating

Glucose, Insulin, and Glucagon

Glucose-primary energy source for cells

Insulin-assists glucose entering cells

When high, hunger levels drop

Glucagon-stimulates liver to convert glycogen to glucose

The Hypothalamus and Eating Regulation

Lateral HypothalamusDamage to this area = animal refuses foodaxons extend to nucleus of the tractus solitarius in the medulla

possibly altering taste sensationsaxons extend to forebrain facilitating ingestion and swallowingactivates a circuit that excites dopamine cells initiating

reinforcement of behaviorssends axons to spinal cord controlling autonomic responses

such as digestive secretions

The Hypothalamus and Eating Regulation

Paraventricular NucleusDamage here = eating larger than normal meals

Ventromedial HypothalamusLesions to the VMH lead to finicky eating and sometimes to

overeatingThe overeating is due to eating more frequently than normal

Causesincreased stomach motility and secretionsleads to a lasting increase in insulin production

Satiety Signals and Eating Disorders

Hormones

Leptin-produced by fat cells and signal no need to eat

Neuropeptide Y-neuromodulator that inhibits the PVN of the hypothalamus and results in an increase in meal size

Figure 10.24  Relation among weight, leptin, NPY, and eatingOrdinarily, high levels of body fat produce leptin, which inhibits eating. Obese mice fail to produce leptin. Obese humans produce leptin but fail to

respond to it.

Genetics, Metabolic Rate, and Body Weight

Genetics-heritability of .4 to .7

Metabolic Rate-the higher the rate the more difficulty someone will have gaining weight

Ideas for Weight Loss

Increase exercise

Reduce consumption

Eating Disorders

Anorexia

defined-unwilling to eat, significantly underweight

occurs mostly in women during adolescence

Bulimia

defined-alternating between dieting and overeating

May be associated with alterations in PYY, CCK and serotonin