Page 1007 - Fundamentals of anatomy physiology

994 Unit 5 Environmental Exchange greater than 37.2°C (99°F). We discussed fevers when we ex-
With increasing age and size, an infant’s body temperature
becomes more stable. As a result, brown fat becomes less im-
portant. With increased body size, skeletal muscle mass, and
insulation, shivering thermogenesis becomes more effective in
raising body temperature. Adults have little, if any, brown fat.
Thermoregulatory Variations among Adults. Adults of a
given body weight may differ in their thermal responses due to
variations in body mass and tissue distribution. Adipose tissue
is an excellent insulator. It conducts heat at only about one-
third the rate of other tissues. As a result, people with a more
substantial layer of subcutaneous fat may not begin to shiver
until long after their thinner companions.
Two otherwise similar individuals may also differ in their
response to temperature changes because their hypothalamic
“thermostats” are at different settings. We all experience daily
oscillations in body temperature. Temperatures peak during
the day or early evening. They fall 1°C–2°C (1.8°F–3.6°F) at
night. The ovulatory cycle also causes temperature fluctuations
in women, as you will see in Chapter 28.
Individuals vary in the timing of their maximum tempera-
ture setting. Some have a series of peaks, with an afternoon low.
The origin of these patterns is unclear. The patterns do not re-
sult from daily activity regimens. For example, the temperatures
of people who work at night still peak during the same range of
times as the rest of the population.
Fevers
Any elevated body temperature is called pyrexia (pı.-REK-se.-
uh). Pyrexia is usually temporary. A fever is a body temperature
Related Clinical Terms
25 anorexia: Persistent loss of appetite.
anorexia nervosa: Eating disorder occurring primarily among girls
and women characterized by a desire to lose, or not gain, weight
through starvation, due to a distorted view of the person’s own
body. There are typically two types: strict diet and exercise, and
binging and purging.
binge-purge syndrome: Eating disorder characterized by excessive
eating followed by periods of fasting or self-induced vomiting.
bulimia: An eating disorder usually characterized by episodic binge
eating that is followed by feelings of guilt, depression, and self-
condemnation. It is often associated with steps taken to lose
weight, such as self-induced vomiting, the use of laxatives, diet-
ing, or fasting.
eating disorders: Psychological problems that result in inadequate
or excessive food consumption. Examples include anorexia ner-
vosa and bulimia.
familial hypercholesterolemia: The most common inherited type
of hyperlipidemia characterized by high levels of lipids in one’s
blood. It affects one in every 500 children born, who then pre-
sent with LDL levels in excess of 190.
amined innate (nonspecific) immunity. p. 828 Fevers occur
for a variety of reasons, not all of them pathological. In young
children, transient fevers with no ill effects can result from ex-
ercise in warm weather. Similar exercise-related elevations were
rarely seen in adults until running marathons became popular.
Temperatures from 39°C to 41°C (103°F to 109°F) may result.
For this reason, competitions are usually held when the air tem-
perature is below 28°C (82°F).
Fevers can also result from the following factors:
Abnormalities that affect the entire thermoregulatory
mechanism, such as heat exhaustion or heat stroke.
Clinical problems that restrict blood flow, such as conges-
tive heart failure.
Conditions that impair sweat gland activity, such as drug
reactions and some skin conditions.
The resetting of the hypothalamic “thermostat” by circulat-
ing pyrogens—most notably, interleukin-1.
Checkpoint
19. How would the BMR of a pregnant woman compare
with her own BMR before she became pregnant?
20. What effect does peripheral vasoconstriction on a hot
day have on an individual’s body temperature?
21. Why do infants have greater problems with
thermoregulation than adults?
See the blue Answers tab at the back of the book.
heat cramps: A condition that usually follows heavy sweating due
to strenuous activity that causes a loss of salt in the body and re-
sults in painful muscle spasms in the abdomen, arms, or legs.
hyperuricemia: A condition in which the plasma uric acid level ex-
ceeds 7.4 mg/dL. It can result in the condition called gout.
ketonuria: The presence of ketone bodies in the urine.
kwashiorkor: A form of malnutrition due to a protein deficiency
in the diet that typically affects young children in tropical
regions.
marasmus: Severe malnourishment that causes a child’s weight to
fall significantly below the standards set for children of similar
age.
orexigenic: Having a stimulating effect on the appetite.
pica: Tendency or craving for substances other than normal food.
Possible organic causes are iron deficiency, lead encephalopathy,
pregnancy, and zinc deficiency.
protein-calorie malnutrition (PCM): A severe deficiency of pro-
tein in the diet in addition to inadequate caloric intake. It results
in the condition termed kwashiorkor.
skin-fold test: Test to estimate the amount of body fat on a person.