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Chapter 10

PSY 220 Chapter Notes - Chapter 10: Scrotum, Pituitary Gland, Optic Chiasm


Department
Psychology
Course Code
PSY 220
Professor
Hurwitz Barry
Chapter
10

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PSY220- Psychobiology
CHAPTER 10 INTERNAL REGULATION
Main Ideas:
Many physiological and behavioral processes maintain a near constancy of certain
body variables. They anticipate needs as well as react to them.
Mammals and birds maintain constant body temperature as a way of staying ready
for rapid muscle activity at any temperature of the environment. They use both
behavioral and physiological processes to maintain temperature.
Thirst mechanisms respond to the osmotic pressure and total volume of the blood.
Hunger and satiety are regulated by many factors, including taste, stomach
distension, the availability of glucose to the cells, and chemicals released by the
fat cells. Many brain peptides help regulate feeding and satiety.
Every chemical reaction in a living body takes place in a water solution at a rate that
depends on the identity and concentration of molecules in the water and the temperature
of the solution.
Our behavior is organized to keep the right chemicals in the right proportions and at the
right temperature.
10.1- Temperature Regulation
Homeostasis (Walter B. Cannon 1929)- temperature regulation and other biological
processes that keep body variables within a fixed range
Homeostatic processes in animals trigger physiological and behavioral activities that keep
certain variables within a set range.
In many cases, this range is so narrow that we refer to it as a set point, a single value that
the body works to maintain.
Example: If calcium is deficient in your diet and its concentration in the blood begins to
fall below the set point of 0.16 g/L, storage deposits in your bones release additional
calcium into the blood.
Negative feedback- processes that reduce discrepancies from the set point
The body’s set points change from time to time; ex. your body maintains a higher
temperature during the day than at night, even if room temperature stays constant.
Allostasis- the adaptive way in which the body changes its set points depending on the
situation; much of this control depends on cells in the hypothalamus
Q: How does the idea of allostasis differ from homeostasis?

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A: Homeostasis is a set of processes that keep certain body variables within a fixed range.
Allostasis is an adjustment of that range, increasing it or decreasing it as circumstances
change.
An average young adult expends about 2,600 kilocalories (kcal) per day; most of this
energy goes to basal metabolism, the energy used to maintain a constant body
temperature while at rest.
Maintaining your body temperature requires about twice as much energy as do all other
activities combined.
Amphibians, reptiles, and most fish are poikilothermic, meaning that their body
temperature matches the temperature of their environment.
Poikilothermic animals lack physiological mechanisms of temperature regulation, such as
shivering and sweating.
Mammals and birds are homeothermic, except that certain species become
poikilothermic during hibernation.
Homeothermic animals use physiological mechanisms to maintain a nearly constant body
temperature despite changes in the temperature of the environment.
An animal generates heat in proportion to its total mass, but it radiates heat in proportion
to its surface area.
When the air is warmer than body temperature, humans sweat to expose water for
evaporation. As water evaporates, it cools the body. However, if the air is humid as well
as hot, the moisture does not evaporate.
You endanger your health if you cannot drink enough to replace the water you lose by
sweating; if you sweat without drinking, you start becoming dehydrated (low on water).
You then protect your body water by decreasing your sweat, despite the risk of
overheating.
Physiological mechanisms that increase body heat in a cold environment/decrease body
heat in a warm environment:
1. Shivering- muscle contractions generate heat
2. Decreased blood flow to the skin- prevents the blood from cooling too much
3. Fluffing out fur/ goose bumps- increases insulation
4. Put on more clothing/ take it off
5. Become more active to get warmer or less active to avoid overheating
6. Huddle with others
Mammals maintain a constant high body temperature of 37° C (98° F).

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From the standpoint of muscle activity, we gain an advantage by being as warm as
possible (a warmer animal has warmer muscles and therefore runs faster with less fatigue
than a cooler animal).
Mammals evolved a body temperature of 37° C for a reason. Maintaining higher
temperatures requires more fuel and energy, and beyond about 40° or 41° C, proteins
begin to break their bonds and lose their useful properties.
It is possible to evolve proteins that are stable at higher temperatures; ex. odd
microscopic animals called thermophiles survive in boiling water. However, to do so,
they need many extra chemical bonds to stabilize their proteins.
The enzymatic properties of a protein depend on its flexibility, so making proteins rigid
enough to withstand high temperatures makes them inactive at more moderate
temperatures.
Essentially, our body temperature of 37° C is a trade-off between the advantages of high
temperature for rapid movement and low temperature for protein stability.
Reproductive cells require a cooler environment than the rest of the body (this is why
birds lay eggs and sit on them rather than developing them internally at body temperature
105° F)
In most male mammals, the scrotum hangs outside the body, because sperm production
requires a cooler temperature than the rest of the body.
Q: What is the primary advantage of maintaining a constant high body temperature?
A: A constant high body temperature keeps the animal ready for rapid, prolonged muscle
activity even in cold weather.
Q: Why did mammals evolve a temperature of 37° C instead of some other temperature?
A: Animals gain an advantage in being as warm as possible and therefore as fast as
possible. However, proteins lose stability at temperatures much above 37° C.
The physiological changes that defend body temperature- such as shivering, sweating,
and changes in blood flow to the skin- depend on areas in and near the hypothalamus,
mainly the anterior hypothalamus and the preoptic area, which is just anterior to the
anterior hypothalamus. (It is called preoptic because it is near the optic chiasm, where the
optic nerves cross).
Because of the close relationship between the preoptic area and the anterior
hypothalamus, researchers often treat them as a single area: the preoptic area/anterior
thalamus, or POA/AH.
The POA/AH and a couple other hypothalamic areas send out input to the hindbrain’s
raphe nucleus, which controls the physiological mechanisms.
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