B+B Chapter 9

How does allostasis differ from homeostasis?

Homeostasis keeps certain body variables within a fixed range by reacting to changes. Allostasis acts in advance to prevent or minimize changes.

What is the primary advantage of maintaining a constant high body temperature?

A constant high body temperature keeps an animal ready for rapid, prolonged muscle activity even in cold weather.

Why did mammals evolve a temperature of 37°C (98°F) instead of some other temperature?

Animals gain advantage in being as warm as possible and therefore as fast as possible. However, proteins lose stability at still higher temperatures.

What are the sources of input to the POA/AH?

The POA/AH receives input from temperatures in the skin and organs, and many cells sense their own temperature.

If you had damage to your POA/AH, what would happen to your body temperature?

You would be much less able to shiver, sweat, or control other physiological mechanisms that control body temperature. However, you could still try to find a place in the environment that keeps you close to your normal temperature.

What evidence indicates that fever is an adaptation to fight illness?

During a fever, the body will shiver or sweat to maintain its elevated temperature at a nearly constant level. Also, fish, reptiles, and immature mammals with infections use behavioral means to raise their temperature to a feverish level. Furthermore, a moderate fever inhibits bacterial growth and increases the probability of surviving a bacterial infection.

Allostasis

the adaptive way in which the body changes its set points depending on the situation

Basal metabolism

energy used to maintain a constant body temperature while at rest

Ectothermic

controlling temperature by relying on external sources of heat or cooling

Endothermic

controlling temperature by the body’s physiological mechanisms

Homeostasis

tendency to maintain a variable, such as temperature, within a fixed range

Negative feedback

homeostatic processes that reduce discrepancies from the set point

POA/AH

preoptic area/anterior hypothalamus - responsible for regulating body temperature

Set point

a value that the body works to maintain

What is allostasis?

a. Processes that react to any change to bring the body back to equilibrium

b. Processes that anticipate future needs

c. Random changes in the internal processes of the body

d. The ideal levels of all body variables

b. Processes that anticipate future needs

For most people, maintaining constant body temperature requires how much of the body’s total energy output?

a. One or two percent

b. About one-tenth

c. About one-third

d. About two-thirds

d. About two-thirds

How do reptiles and amphibians regulate their body temperature, if at all?

a. They move to a location with a more favorable temperature.

b. They use physiological mechanisms such as shivering and sweating.

c. They increase their metabolic rate.

d. They do not regulate their body temperature at all.

a. They move to a location with a more favorable temperature.

What is the primary advantage of maintaining a constant high body temperature?

a. It saves us the energy from having to look for a comfortable temperature.

b. It keeps the muscles ready for rapid, prolonged activity even in cold weather.

c. It enables the digestive system to process a greater variety of nutrients.

d. It enables us to survive in warmer climates.

b. It keeps the muscles ready for rapid, prolonged activity even in cold weather.

Cells in the POA/AH regulate body temperature by monitoring what?

a. Stomach secretions and muscle activity

b. Blood volume and the salt concentration in the blood

c. Skin temperature and the sugar concentration in the blood

d. Skin temperature and the temperature of the POA/AH itself

d. Skin temperature and the temperature of the POA/AH itself

When you have an infection, what causes the fever?

a. The infective agent stimulates the heart to beat faster.

b. The infective agent impairs the activity of the hypothalamus.

c. The immune system delivers chemicals that stimulate the hypothalamus.

d. The immune system decreases blood flow to the brain.

c. The immune system delivers chemicals that stimulate the hypothalamus.

Why is a very high body temperature dangerous?

a. Many proteins break down at high temperatures.

b. High temperatures interfere with muscle contractions.

c. High temperatures increase the ratio of excitation to inhibition in the brain.

d. High temperatures stimulate excessive eating and drinking.

a. Many proteins break down at high temperatures.

If you lacked vasopressin, would you drink more like a beaver or like a gerbil? Why?

If you lacked vasopressin, you would have to drink more like a beaver. You would excrete much fluid, so you would need to drink an equal amount to replace it.

Would adding salt to the body’s extracellular fluids increase or decrease osmotic thirst?

Adding salt to the extracellular fluids would increase osmotic thirst because it would draw water from the cells into the extracellular spaces.

Why are you likely to feel thirst just before bedtime? Would you feel just as thirsty if you went to sleep at an unusual time?

At bedtime, your body secretes vasopressin, which helps conserve water and also stimulates thirst. Both responses help you get through the night while you cannot drink. Your circadian rhythm triggers the increased vasopressin, so you would not feel as thirsty before sleep at an unusual time.

Who would drink more pure water—someone with osmotic thirst or someone with hypovolemic thirst?

Someone with osmotic thirst would drink more water. Someone with hypovolemic thirst would drink more of a solution containing salts.

What are the contributions of angiotensin II and aldosterone?

Angiotensin II constricts the blood vessels, and stimulates neurons that produce hypovolemic thirst. Aldosterone causes the body to retain salt when blood volume is low.

Aldosterone

adrenal hormone that causes the body to retain salt

Angiotensin II

hormone that constricts the blood vessels, compensating for the drop in blood pressure; triggers thirst

Antidiuretic hormone (ADH)

hormone that enables the kidneys to reabsorb water from urine; also known as vasopressin

Lateral preoptic area

part of the hypothalamus that controls drinking

Osmotic pressure

tendency of water to flow across a semipermeable membrane from the area of low solute concentration to the area of high solute concentration

Osmotic thirst

thirst triggered by certain neurons that detect the loss of their own water

OVLT

organum vasculosum of the lamina terminalis - senses dynamics in sodium and water balance in body fluids.

Paraventricular nucleus (PVN)

part of the hypothalamus in which activity tends to limit meal size and damage leads to excessively large meals

Sodium-specific hunger

increased preference for salty tastes

Subfornical organ (SFO)

brain structure adjoining the third ventricle of the brain, where its cells monitor osmotic pressure and sodium concentration

Supraoptic nucleus

part of the hypothalamus that controls the release rate of vasopressin

Vasopressin

a hormone primarily involved in regulating water balance and blood pressure

What does vasopressin do?

a. It stimulates hypovolemic thirst.

b. It constricts blood vessels.

c. It increases digestion in the intestines.

d. It increases the deposit of calcium into the bones.

b. It constricts blood vessels.

What else does vasopressin do?

a. It prevents fluctuations of body temperature.

b. It increases salt appetite.

c. It makes urine more concentrated.

d. It increases the flow of glucose into the cells.

c. It makes urine more concentrated.

Which of these happens after you eat something salty?

a. The sodium-potassium pump becomes less active.

b. The sodium-potassium pump becomes more active.

c. Salt flows into the cells.

d. Water flows out of the cells.

d. Water flows out of the cells.

What would happen as a result of adding salt to the body’s extracellular fluids?

a. Increased osmotic thirst

b. Decreased osmotic thirst

c. Increased hypovolemic thirst

d. Decreased hypovolemic thirst

a. Increased osmotic thirst

What do the OVLT and the subfornical organ monitor?

a. Insulin and glucagon levels

b. Heart rate and body temperature

c. Osmotic pressure and blood volume

d. The balance between excitatory and inhibitory transmission

c. Osmotic pressure and blood volume

What is the most effective way to satisfy hypovolemic thirst?

a. Drink pure water slowly.

b. Drink pure water rapidly.

c. Drink water containing salt or other solutes.

d. Alternate between drinking water and drinking alcohol.

c. Drink water containing salt or other solutes.

What does aldosterone do?

a. It decreases appetite.

b. It helps the brain store long-term memories.

c. It helps the kidneys and other glands retain salt.

d. It helps the suprachiasmatic nucleus control the circadian rhythm.

c. It helps the kidneys and other glands retain salt.

Why do the genes for digesting lactose differ among parts of Africa?

African groups domesticated cattle at different times and independently evolved genes for digesting lactose.

What evidence showed that taste is not sufficient for satiety?

Animals that sham-feed do not become satiated, regardless of how much they taste.

What evidence shows that stomach distension is sufficient for satiety?

If a cuff is attached to the junction between the stomach and duodenum so that food cannot leave the stomach, an animal becomes satiated when the stomach is full.

What are two mechanisms by which CCK increases satiety?

What are two mechanisms by which CCK increases satiety?When the duodenum is distended, it releases CCK, which closes the sphincter muscle between the stomach and duodenum, increasing the rate at which the stomach distends. Also, neural signals from the intestines cause cells in the hypothalamus to release a shorter version of CCK as a neuromodulator.

Why do people with very low insulin levels eat so much? Why do people with constantly high levels eat so much?

Those with very low levels, as in type 1 diabetes, cannot get glucose to enter their cells, and therefore, they are constantly hungry. Those with constantly high levels deposit much of their glucose into fat and glycogen, so within a short time after a meal, the supply of blood glucose drops.

Why are leptin injections less helpful for most overweight people than for mice with a mutation in the leptin gene?

Those mice fail to produce leptin. Nearly all overweight people produce enough leptin, and extra leptin only weakly suppresses appetite.

Name three hormones that increase satiety and one that increases hunger.

Insulin, CCK, and leptin increase satiety. Ghrelin increases hunger.

How does the inhibitory transmission from the hunger cells lead to increased eating?

The output inhibits the paraventricular nucleus, and thereby stops it from inhibiting the lateral hypothalamus.

What is the role of melanocortins?

Melanocortins excite neurons in the paraventricular nucleus, and therefore decrease appetite.

How does the lateral hypothalamus facilitate feeding?

Activity of the lateral hypothalamus improves taste, enhances cortical responses to food, and increases secretions of digestive juices.

In what way does eating increase after damage in and around the ventromedial hypothalamus? After damage to the paraventricular nucleus?

Animals with damage to the ventromedial hypothalamus eat more frequent meals. Animals with damage to the paraventricular nucleus of the hypothalamus eat larger meals.

Lateral hypothalamus

Undereating, weight loss, low insulin level (because of damage to cell bodies); underarousal, under responsiveness (because of damage to passing axons)

Ventromedial hypothalamus

Increased meal frequency, weight gain, high insulin level

Paraventricular nucleus

Increased meal size, especially increased carbohydrate intake during the first meal of the active period of the day

Why did the Pima begin gaining weight in the mid-1900s?

They shifted from a diet of local plants that were seasonally available to a calorie-rich diet that is available throughout the year.

Why are over-the-counter weight-loss supplements risky?

Some of them contain unapproved chemicals not listed on the label.

What evidence from rats suggests that bulimia resembles an addiction?

Rats that alternate between food deprivation and a very sweet diet gradually eat more and more, and they react to deprivation of the sweet diet with head shaking and teeth chattering, like the symptoms of morphine withdrawal.

If rats are limited to eating for one hour a day, what determines whether or not they will lose weight?

If the room is cool and the rats have access to a running wheel, they will exercise enough to keep warm, which causes them to lose weight.

Anorexia Nervosa

disorder characterized by refusal to eat enough to remain healthy

Arcuate nucleus

hypothalamic area with sets of neurons for hunger and satiety

Bulimia nervosa

a condition in which people alternate between binges of overeating and periods of strict dieting

cholecystokinin (CCK)

stimulation of pancreatic secretion and gall-bladder contraction, regulation of gastrointestinal motility and induction of satiety

duodenum

part of the small intestine adjoining the stomach; first digestive site that absorbs nutrients

ghrelin

chemical released by the stomach during a period of food deprivation; also released as a neurotransmitter in the brain, where it stimulates eating

glucagon

pancreatic hormone that stimulates the liver to convert stored glycogen to glucose

insulin

pancreatic hormone that enables glucose to enter the cells

lactase

intestinal enzyme that metabolizes lactose

Most Southeast Asians limit their consumption of milk because of what?

a. Their enzymes

b. Their taste buds

c. Their surface-to-volume ratio

d. Their olfactory sensitivity

a. Their enzymes

How does eating more carbohydrates increase tryptophan in the brain?

a. Digesting carbohydrates increases blood pressure.

b. Eating carbohydrates increases the appetite for eating proteins.

c. The brain converts carbohydrates into tryptophan.

d. Increased insulin removes phenylalanine from circulation.

d. Increased insulin removes phenylalanine from circulation

When food distends the duodenum, the duodenum releases the hormone CCK. By what peripheral mechanism (outside the brain) does it increase satiety?

a. CCK increases stomach contractions.

b. CCK tightens the sphincter muscle between the stomach and the duodenum.

c. CCK increases the ability of nutrients to enter cells.

d. CCK decreases metabolic rate.

b. CCK tightens the sphincter muscle between the stomach and the duodenum.

What is the effect of CCK on appetite?

a. It increases appetite.

b. It limits the size of a meal.

c. It decreases the frequency of meals.

d. It produces nausea.

b. It limits the size of a meal.

Which of these does insulin do?

a. It helps the intestines digest glucose.

b. It helps glucose enter cells.

c. It converts glucose into glutamate.

d. It converts stored fats into glucose.

b. It helps glucose enter cells.

What causes Type 2 diabetes?

a. The pituitary gland decreases its secretion of releasing hormones.

b. The pancreas stops making or releasing insulin.

c. Cells become insensitive to the effects of insulin.

d. The intestines decrease their ability to absorb glucose.

c. Cells become insensitive to the effects of insulin.

Which part of the body secretes leptin?

a. The duodenum

b. The fat cells

c. The stomach

d. The liver

b. The fat cells

How do the “hunger” cells of the arcuate nucleus increase eating?

a. By inhibiting the paraventricular nucleus

b. By stimulating the lateral hypothalamus

c. By stimulating the ventromedial hypothalamus

d. By inhibiting the sphincter muscle between the stomach and the duodenum

a. By inhibiting the paraventricular nucleus

Which part of the body secretes ghrelin?

a. The duodenum

b. The fat cells

c. The stomach

d. The liver

c. The stomach

What do variants in the FTO gene do?

a. They increase the probability of bulimia nervosa.

b. They alter the metabolism of lactose.

c. They produce monogenetic obesity.

d. They increase the probability of weight gain.

d. They increase the probability of weight gain.

How has the prevalence of obesity changed since the availability of high-fructose corn syrup and artificially sweetened diet beverages?

a. Each of them helped lower the prevalence of obesity.

b. High-fructose corn syrup helped lower obesity rates, but diet drinks did not.

c. Diet drinks helped lower obesity rates, but high-fructose corn syrup did not.

d. The prevalence of obesity has increased after the availability of both of them.

d. The prevalence of obesity has increased after the availability of both of them.

The drug that is most effective for weight control binds to receptors for what chemical?

a. Dopamine

b. Insulin

c. Serotonin

d. Glucagon-like protein 1

d. Glucagon-like protein 1

Bulimia nervosa has been compared to which of the following?

a. Borderline personality disorder

b. Paranoid schizophrenia

c. Drug addiction

d. Fear of heights

c. Drug addiction

Temperature regulation is a likely explanation for which aspect of anorexia nervosa?

a. Higher prevalence in women than men

b. Increased exercise

c. Fear of becoming fat

d. Age of onset

b. Increased exercise

Which physiological mechanism is used to cool the human body in hot temperatures?

a. Radiation

b. Decreased metabolism

c. Removing clothing

d. Evaporation

d. Evaporation

Shifting blood flow away from the skin is a strategy the body uses to manage which of the following?

a. Cold temperatures

b. Dehydration

c. Inadequate sweating

d. Hot temperatures

a. Cold temperatures

One benefit of endothermy is that the animal can always keep warm and therefore is constantly ready for vigorous activity, regardless of the air temperature.

a. True

b. False

a. True

Which of the following terms refers to the tendency of water to flow across a semipermeable membrane from an area of low solute concentration to an area of higher concentration?

a. Hypovolemic thirst

b. Reverse osmosis

c. Osmotic pressure

d. Solute pressure

c. Osmotic pressure

Which structure increases drinking in reaction to osmotic thirst?

a. Paraventricular nucleus

b. Supraoptic nucleus

c. Lateral preoptic area

d. Subfornical organ

c. Lateral preoptic area

After you eat or drink, changes in blood osmotic pressure happen almost immediately.

a. True

b. False

b. False

Which of the following is a major site for absorbing nutrients?

a. Stomach

b. Esophagus

c. Large intestine

d. Duodenum

d. Duodenum

Which hormone stimulates the liver to convert some of its stored glycogen back to glucose?

a. Insulin

b. Cholecystokinin

c. Glucagon

d. Leptin

c. Glucagon

In general, the mechanisms that promote hunger are stronger and more insistent than those for satiety.

a. True

b. False

a. True

Menstruation or extensive sweating tends to increase the preference for what taste?

a. Sweet

b. Sour

c. Salty

d. Bitter

c. Salty

Which of the following causes osmotic thirst?

a. Eating salty foods

b. A decrease in blood volume

c. Activity by the immune system

d. Decreased body temperature

a. Eating salty foods

What does insulin do?

a. It tightens the muscle between the stomach and the duodenum.

b. It breaks down carbohydrates into smaller molecules.

c. It helps glucose enter cells.

d. It helps nutrients cross from the intestine into the blood.

c. It helps glucose enter cells.

Is a fever helpful in any way? If so, what?

a. No, a fever is harmful.

b. Yes, a fever increases alertness.

c. Yes, a fever inhibits the growth of bacteria.

d. Yes, a fever improves appetite.

c. Yes, a fever inhibits the growth of bacteria.

What advantage do endothermic animals have?

a. They do not need to shiver or sweat.

b. Their bodies are optimized for the environment in which they live.

c. They can remain active when the environment is cool.

d. They need little fuel to maintain their body temperature.

c. They can remain active when the environment is cool.