Chapter 9: Internal Regulation

Question 1

How does the idea of allostasis differ from homeostasis?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

Why did mammals evolve a temperature of
37C/98F instead of some other temperature?

Answer 3

Animals gain an advantage in being as warm as possible and therefore as fast as possible. However, proteins lose stability at temperatures much above
37C/98F.

Question 4

What are the sources of input to the POA/AH (preoptic area/anterior hypothalamus)

Answer 4

The POA/AH receives input from temperatures in the skin, the organs, and the hypothalamus. It also receives prostaglandins and histamines when the immune system detects an infection.

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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.

Question 7

Janella has been taking calcium supplements to support bone health. She is taking advantage of her body’s _____, meaning that if she can get her blood calcium level above 0.16 g/L, she knows that the excess calcium will be stored in her bones.
a. allostasis
b. set point
c. basal metabolism
d. negative feedback

Answer 7

set point

Janella’s body is working to keep her blood calcium levels at a set point of 0.16 g/L. If she exceeds that limit with the supplements, her body will try to restore her to the set point by storing the calcium in her bones and/or excreting it.

Question 8

Which of the following do scientists accept as an advantage of a high body temperature?
a. Mammals with a high body temperature can stay constantly ready for vigorous activity.
b. Organisms must spend more time searching for and consuming food.
c. Special care must be taken for reproductive cells, because they require a cooler environment.
d. Organisms need to stay close to 37°C so that proteins don’t lost their useful properties.

Answer 8

Mammals with a high body temperature can stay constantly ready for vigorous activity.

Correct. We eat a great deal to support our high metabolism so that even if the weather is cold, we can still run rapidly (or perform other vigorous activity) without great fatigue. This was evolutionarily worth having to constantly eat and search for food.

Question 9

Nolan has a fever. His doctor explains to him that a fever is a good thing because _____
a. his immune system functions better and many bacteria cannot grow well at the slightly higher temperature
b. an elevated temperature will kill viruses, so he should let it go as high as possible
c. it means the bacteria in the body have triggered the fever
d. the decreased set point will help him “sweat it out”

Answer 9

his immune system functions better and many bacteria cannot grow well at the slightly higher temperature

A fever is an increased set point initiated by the hypothalamus with the goal of raising the body temperature. Nolan’s doctor is relaying the research that has demonstrated that a mild temperature (less than 39°C) prevents many types of bacteria from growing and stimulates the immune system to function stronger.

Question 10

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

Answer 10

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.

Question 11

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

Answer 11

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

Question 12

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?

Answer 12

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 going to sleep at an unusual time.

Question 13

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

Answer 13

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

Question 14

What are the contributions of angiotensin II and aldosterone?

Answer 14

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

Question 15

Most of the time, humans drink ____ is needed.
a. more than
b. a little less than
c. exactly what
d. significantly less than

Answer 15

more than

Correct. Most of the time, humans drink more than is needed and excrete the excess. If there is a situation where there isn’t enough to drink, the pituitary can release vasopressin to conserve water.

Question 16

Bertha was swimming at the beach and accidentally swallowed some seawater. Several minutes later, she realized that she feels really thirsty. This is because the salt in the seawater ______.
a. caused her body to release aldosterone
b. resulted in osmotic thirst
c. caused her body to angiotensin II
d. resulted in hypovolemic thirst

Answer 16

resulted in osmotic thirst

Correct. There are two types of thirst: hypovolemic (results from a loss of fluids) and osmotic (results from consuming salt). In this case, Bertha accidentally consumed salty seawater, so she would be experiencing osmotic thirst.

Question 17

Jose recently had a stomach virus that resulted in him having severe diarrhea for several days. Although he was constantly trying to drink water, his doctor started to get concerned that he was experiencing ____ and suggested that he drink fluids that would restore his ___ levels along with water levels.
a. hypovolemic thirst; glucose
b. hypovolemic thirst; salt
c. osmotic thirst; salt
d. osmotic thirst; glucose

Answer 17

hypovolemic thirst; salt

Correct. Even though Jose is drinking water, he has probably lost a significant amount of water volume in his blood. This would include all the salts. Jose’s doctor suggested that to relieve the hypovolemic thirst (and avoid a dangerous dehydration state), he should also supplement his water intake with salt intake (probably in the form of an electrolyte drink).

Question 18

What evidence from rats suggests that bulimia resembles an addiction?

Answer 18

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

Question 19

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

Answer 19

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

Question 20

For someone who is trying to lose weight, why would it be a good idea to cut down on sweets altogether?

Answer 20

Sugars provide many calories. Although fructose provides fewer calories for a given amount of sweet taste, it is less effective at triggering a sense of satiety. People who try to satisfy their sweet cravings with artificial sweeteners do not generally cut down on total calories. Furthermore, artificial sweeteners promote the types of intestinal bacteria that are associated with type 2 diabetes.

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

Why do most Southeast Asian adults avoid drinking much milk?

Answer 23

Most Southeast Asian adults lack the genes that help digest lactose, the main sugar in milk.

Question 24

What evidence indicates that taste is not sufficient for satiety?

Answer 24

Animals that sham-feed chew and taste their food but do not become satiated.

Question 25

What evidence shows that stomach distension is sufficient for satiety?

Answer 25

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.

Question 26

What are two mechanisms by which CCK increases satiety?

Answer 26

When the duodenum is distended, it releases CCK, which closes the sphincter muscle between the stomach and duodenum. CCK therefore increases the rate at which the stomach distends. Also, neural signals from the intestines cause certain cells in the hypothalamus to release CCK as a neurotransmitter, and at its receptors, it triggers decreased feeding.

Question 27

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

Answer 27

Those with very low levels, as in type 1 diabetes, cannot get glucose to enter their cells, and therefore, they are constantly hungry. They pass much of their nutrition in the urine and feces. 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.

Question 28

What would happen to someone’s appetite if insulin levels and glucagon levels were both high?

Answer 28

When glucagon levels rise, stored glycogen is converted to glucose, which enters the blood. If insulin levels are high also, the glucose entering the blood is free to enter all the cells. So the result would be decreased appetite.

Question 29

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

Answer 29

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

Question 30

In what ways does the lateral hypothalamus facilitate feeding?

Answer 30

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

Question 31

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

Answer 31

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

Question 32

Regarding human digestion, _____ can be broken down in the mouth, whereas _____ must be digested in the stomach.
a. carbohydrates; proteins
b. proteins; carbohydrates
c. proteins; fats
d. carbohydrates; fats

Answer 32

Carbohydrates; proteins

Correct. Digestion begins in the mouth, where enzymes in saliva can break down carbohydrates. Swallowed food enters the stomach, where acids and enzymes break down proteins. Finally, it is sent to the small intestine where additional enzymes break down fats.

Question 33

Evidence from a 6,500-year-old piece of chewing gum (Battersby, 1997) suggests that ____.
a. chewing gum can replace eating certain meals
b. people have always liked candy
c. chewing gum can preserve tooth health
d. the urge to chew is strong

Answer 33

the urge to chew is strong

Correct. The piece of gum came from birch-bark tar and probably tasted bad. However, the urge to chew is strong and a teenager or child likely chewed the gum anyway.

Question 34

The _____ nucleus of the _____ has one set of neurons sensitive to hunger signals and a second set sensitive to satiety signals.
a. lateral; pituitary
b. arcuate; pituitary
c. lateral; hypothalamus
d. arcuate; hypothalamus

Answer 34

arcuate;hypothalamus

Correct. The arcuate nucleus of the hypothalamus has one set of neurons sensitive to hunger signals and a second set sensitive to satiety signals. The hunger neurons are sometimes referred to as the NPY/AgRP neurons and the satiety neurons are referred to as POMC/CART neurons because of the distinct neurotransmitters released by each.

Question 35

Shavon is sitting in a cold classroom. To keep from feeling cold, she might shiver, have changes in heart rate and metabolism, and changes in the blood flow to her skin. This is all controlled by her _____.
a. subfornical organ
b. nucleus of the tractus solitarius
c. raphe nucleus
d. paraventricular nucleus

Answer 35

raphe nucleus

Correct. When sensory information is sent to Shavon’s brain about her being cold, her preoptic area/anterior hypothalamus (POA/AH) send output to the raphe nucleus in the hindbrain. The raphe nucleus then allows her to attempt to warm herself up by shivering, and so on.

Question 36

When blood volume drops, the kidneys release the enzyme ____.
a. angiotensin II
b. vasopressin
c. renin
d. aldosterone

Answer 36

renin
Correct. When blood volume is low, the kidneys release the hormone renin. Renin helps form angiotensin I, which is converted into angiotensin II. Angiotensin II constricts the blood vessels, compensating for the drop in blood pressure, and helps trigger thirst.