Transcript Physiology of metabolic processes in the body. Composition of diet

Exchange of matters, energies and termoregulation. Role
of cavity of mouth in these reactions. State of hunger,
appetite and satiation.
The absorbed materials
Digested molecules of food, water
and minerals from the diet, are
absorbed from the cavity of the
upper small intestine.
The absorbed materials cross the
mucosa into the blood, and are
carried off in the bloodstream to
other parts of the body for storage or
further chemical change.
Protein
Foods such as meat, eggs, and beans consist of
large molecules of protein that must be digested
by enzymes before they can be used to build and
repair body tissues.
Digestion of proteins
An enzyme in the juice of the stomach starts the
digestion of swallowed protein. Further digestion
of the protein is completed in the small intestine.
Here, several enzymes from the pancreatic juice
and the lining of the intestine carry out the
breakdown of huge protein molecules into small
molecules called amino acids.
These small molecules can be absorbed from the
hollow of the small intestine into the blood and
then be carried to all parts of the body to build
the walls and other parts of cells.
Protein Metabolism
The first step in protein metabolism is to break it
into its constituent amino acids. These are absorbed
into the blood stream.
The second step is to break down the amino acids
into their constituent parts - catabolism. This
removes the nitrogen or amino group from the
amino acids. The process is called deamination.
Deamination breaks the amino group down into
ammonia and what is termed the carbon skeleton.
Ammonia is converted to urea, filtered through the
kidneys, and excreted in urine. The carbon skeleton-which is composed of carbon, hydrogen, and
oxygen--can then by used either for protein
synthesis, energy production (ATP), or converted to
glucose by gluconeogenesis.
Amino acids stimulate the release of
both glucagon and insulin
In a healthy person, a rise in blood amino
acid concentration stimulates the secretion
of both glucagon and insulin, so their
blood sugar remains stable.
The insulin is secreted to stimulate protein
synthesis - the uptake of amino acids into
muscle cells - making them less available
for gluconeogenesis. The glucagon is
secreted to stimulate the uptake of amino
acids into the cells of the liver for
gluconeogenesis.
Why are these two hormones battling for
opposing uses of the same amino acids?
Isn't that non-productive?
Actually, the phenomenon serves an important
purpose. The release of these two opposing
hormones ensures that the amino acids are used
for protein synthesis (because of the extra
insulin) but the blood sugar doesn't drop to
dangerously low levels, even if the meal was low
in carbohydrate.
As a result, blood glucose concentration remains
reasonably stable during protein metabolism.
The insulin and glucagon essentially cancel each
other out in terms of their effect on blood
glucose, while the insulin is still able to promote
protein synthesis.
Protein digestibility
An important aspect of protein metabolism is how
well or how poorly a given protein is digested by the
human body. Claims are sometimes made that
protein powders (especially predigested or
hydrolyzed proteins) are digested more efficiently
than whole food proteins.
Protein digestibility is measured by seeing how much
nitrogen is excreted in the feces compared to the
amount of nitrogen which is ingested. A correction is
made for the amount of nitrogen which is normally
lost in the feces. Therefore, digestibility research
examines how much more nitrogen is lost over
normal levels when a given protein is fed.
If an individual were fed 6,25 grams of protein, 1
gram of nitrogen was excreted in the feces.
Digestibility of common
proteins foods
Food source
Egg
Protein digestibility (%)
97
Milk and cheese
Mixed US diet
Peanut butter
Meat and fish
97
96
95
94
Whole wheat
Oatmeal
Soybeans
86
86
78
Rice
76
Protein quality
Protein quality is a topic of major debate, both in
the research world, as well as in the realm of
protein supplements. Arguments have been made
that one protein is of higher quality than another,
or that protein powders are superior to whole
food protein.
Protein quality refers, in a general sense, to how
well or poorly a given protein will be used by the
body.
More specifically, it refers to how well the
indispensable amino acid (AA) profile of a protein
matches the requirements of the body. However,
this should not suggest that the content of
dispensable AAs in a protein is irrelevant to
protein quality as the body.
Methods of measuring
protein quality
There most spread methods available to measure
protein quality are: chemical score, biological
value, protein efficiency ratio, and protein
digestibility corrected amino acid score.
The quality of a protein is directly related to the
physiological needs of the subject being studied.
Diet and activity can affect how AAs are used in
the body. For example, long-duration endurance
activity tends to oxidize high quantities of the
branch-chain amino acids (BCAAs). In all
likelihood, there is no single protein that can be
rated as the highest quality for all situations.
Chemical score
Chemical score is method of rating proteins based on it's
chemical composition (more specifically it's indispensable AA
levels). To determine chemical score, a protein is picked as a
reference and other proteins are rated relative to that
reference protein.
Typically, egg protein has been used as the reference protein,
but this assumes that the amino acid profile of egg is the ideal
for humans.
Since chemical score is a relative, and not an absolute scale, it
is possible to have values greater than 100. If 5 grams of the
reference protein contains 800 mg of a certain amino acid, and
5 grams of the test protein contains 1000 mg of that same
amino acid, the second protein would be rated as 125% for
that amino acid.
The chemical score has little to do with how a food protein will
be used in the body and is rarely the only measure of protein
quality used to rate a protein.
Biological value (BV)
Biological value (BV) is probably one of the most commonly
used measures of a protein's quality. The BV of a protein is
given as the amount of nitrogen retained in the body
divided by the amount of nitrogen absorbed from that
protein. Therefore, digestibility of that protein is taken into
account. Thus:
BV = (nitrogen retained / nitrogen absorbed) * 100 %
A BV of 100 would indicate complete utilization of a given
dietary protein, in that 100% of the protein ingested was
stored in the body with none lost.
To measure BV, subjects are typically fed a zero protein diet
so that baseline losses of nitrogen can be measured (i.e.
the amount of nitrogen that is lost normally). Then the test
protein is fed at varying levels (generally 0.6, 0.5, 0.4 and
0.3 g/kg are fed) and a nitrogen balance study is done.
Some studies use longer periods of starvation and this is an
important consideration in evaluating the data.
BV of some
common
proteins
Table 2 presents the BV of
some common proteins.
Considering the high
protein intakes of most
strength athletes (2.0 g/kg
or higher) it is hard to see
how BV will play a
meaningful role in rating
proteins in this population.
In all likelihood, any decent
quality protein will be as
good as any other at these
types of protein intakes.
Protein
BV
whey
100
egg
100
milk
93
rice
86
casein, fish
and
75
beef
corn
peanut
flour
wheat
gluten
72
56
44
Protein efficiency ratio (PER)
PER is sometimes used to rate proteins and
represents the amount of weight gained (in grams)
relative the amount of protein consumed (in grams).
For example, a PER of 2.5 would mean that 2.5
grams of weight was gained for every gram of protein
ingested.
A recent animal study found that combinations of
animal (30% of total) and plant based proteins (70%
of total) had a higher PER value than the animal or
vegetable proteins eaten alone. This may have to do
with the proteins 'combining' to decrease the impact
of the limiting AA.
Individuals who wish to decrease their intake of
animal-based proteins may be able to achieve higher
PER values with a combination of animal and plant
based proteins than someone eating only animal
based proteins.
Protein digestibility corrected
amino acid score (PDCAAS)
PDCAAS is the newest method of protein quality to
be developed. It has also been suggested as the
ideal scale to rate proteins for their ability to meet
human requirements. Similar to chemical score, it
rates protein foods relative to a given reference
protein. In this case, the AA profile used is that one
determined to be ideal for children two to five years
old as its reference protein for adults.
Using the PDCAAS method, along with the proposed
AA reference patter, proteins which were previously
rated at poor quality, such as soy, have obtained
higher quality ratings. This is more in line with
studies showing that certain purified soy proteins,
such as Supro (tm) which is found in Twinlab Vegefuel, can maintain adults in nitrogen balance.
Summary of protein
quality
Although a variety of methods of measuring protein
quality have been proposed, none are perfect in rating
proteins for human use. While some methods of rating
protein are based on how well (or poorly) an animal
grows (or the nitrogen balance which is attained),
these methods provide no information on specific
amino acid requirements or protein synthesis at a
given tissue. Rather, only data regarding growth in the
whole body are obtained.
Another strategy to rate proteins is to compare the AA
profile in food protein to some reference protein.
Previously, food proteins such as egg or milk were
used as a reference but there has been a recent move
toward the use of an idealized reference pattern of
AAs to rate proteins. This assumes that the true
requirements for a given AA are known.
Carbohydrates
An average American adult eats about half a
pound of carbohydrate each day. Some of our
most common foods contain mostly
carbohydrates. Examples are bread, potatoes,
pastries, candy, rice, spaghetti, fruits, and
vegetables. Many of these foods contain both
starch, which can be digested, and fiber, which
the body cannot digest.
The digestible carbohydrates are broken into
simpler molecules by enzymes in the saliva, in
juice produced by the pancreas, and in the lining
of the small intestine. Glucose and other
monocaccharides is carried through the
bloodstream to the liver, where it is stored or
used to provide energy for the work of the body.
Fates of dietary glucose
The major source of dietary carbohydrate for humans
is starch from consumed plant material. This is
supplemented with a small amount of glycogen from
animal tissue, disaccharides such as sucrose from
products containing refined sugar and lactose in milk.
Digestion in the gut converts all carbohydrate to
monosaccharides which are transported to the liver
and converted to glucose. The liver has a central role
in the storage and distribution within the body of all
fuels, including glucose.
Glucose in the body undergoes one of three metabolic
fates: it is catabolised to produce ATP; it is stored as
glycogen in liver and muscle; it is converted to fatty
acids. Once converted to fatty acids, these are stored
in adipose tissue as triglycerides.
Extracting Energy from
Glucose
Two different pathways are involved in the
metabolism of glucose: one anaerobic and one
aerobic.
The anaerobic process occurs in the cytoplasm
and is only moderately efficient.
The aerobic cycle takes place in the mitochondria
and is results in the greatest release of energy.
As the name implies, though, it requires oxygen.
Anaerobic Metabolism
Glucose in the bloodstream diffuses into the
cytoplasm and is locked there by
phosphorylation. A glucose molecule is then
rearranged slightly to fructose and
phosphorylated again to fructose diphosphate.
These steps actually require energy, in the form
of two ATPs per glucose. The fructose is then
cleaved to yield two glyceraldehyde phosphates
(GPs).
Finally, two more ATPs are produced as the
phosphoglycerates are oxidized to pyruvate.
Aerobic
Metabolism
Pyruvate is the
starting
molecule for
oxidative
phosphorylation
via the Krebb's
or citric acid
cycle.
In this process,
all of the C-C
and C-H bonds
of the pyruvate
will be
transferred to
oxygen.
Summary of
metabolism of glucose
Basically, the pyruvate is
oxidized to acetyl coenzyme
A, which can then bind with
the four carbon oxaloacetate
to generate a six carbon
citrate.
Carbons and hydrogens are
gradually cleaved from this
citrate until all that remains
is the four carbon
oxaloacetate we started
with. In the process, four
NADHs, one FADH and one
GTP are generated for each
starting pyruvate.
Anaerobic
Consumed
:
2 ATP
Produced:
8 ATP
Net:
6 ATP
Aerobic
Consume
d:
0 ATP
Produced: 2x 15 ATP
Net:
30 ATP
Gluconeogenesis
The process of conversion of lactate to
glucose is called gluconeogenesis, uses
some of the reactions of glycolysis (but in
the reverse direction) and some reactions
unique to this pathway to re-synthesise
glucose.
This pathway requires an energy input (as
ATP) but has, due to kidneys, the role of
maintaining a circulating glucose
concentration in the bloodstream (even in
the absence of dietary supply) and also
maintaining a glucose supply to fast twitch
muscle fibres.
Fats
Fat molecules are a rich source of energy for
the body. The first step in digestion of a fat is
to dissolve it into the watery content of the
intestinal cavity.
Fat digestion
The bile acids produced by the liver act as natural
detergents to dissolve fat in water and allow the
enzymes to break the large fat molecules into smaller
molecules, some of which are fatty acids and
cholesterol. The bile acids combine with the fatty
acids and cholesterol and help these molecules to
move into the cells of the mucosa. In these cells the
small molecules are formed back into large molecules,
most of which pass into vessels (called lymphatics)
near the intestine.
These small vessels carry the reformed fat to the
veins of the chest, and the blood carries the fat to
liver and than to storage depots in different parts of
the body.
Fat metabolism and
gluconeogenesis
Fatty acids cannot be used directly to
produce glucose. However, gycerol, a
product of fat metabolism, can and does
go through the gluconeogenic pathway to
produce glucose. Glycerol is a minor
component in fats, and accounts for only 9
to 15% of the total mass.
Fats are much less important than
proteins in the gluconeogenic process
Vitamins, water and salt
Another important part of our food that is absorbed
from the small intestine is the class of chemicals we
call vitamins. There are two different types of
vitamins, classified by the fluid in which they can be
dissolved:water-soluble vitamins (all the B vitamins
and vitamin C) and fat-soluble vitamins (vitamins A,
D, and K).
Most of the material absorbed from the cavity of the
small intestine is water in which salt is dissolved. The
salt and water come from the food and liquid we
swallow and the juices secreted by the many digestive
glands. In a healthy adult, more than a gallon of
water containing over an ounce of salt is absorbed
from the intestine every 24 hours.
Oxydation and ATP
Food energy is released through a chemical reaction with
oxygen in a process called oxidation. When this occurs
outside the body - for example the burning of oil (a fat) in a
lamp or the use of a flaming sugar cube (a carbohydrate)
as a decoration in a dessert - this energy is released as
heat and light. In the body however, food energy needs to
be released more slowly and in a form that can be
harnessed for basic cell functions and transformed into
mechanical movement by the muscle cells.
This is accomplished by "refining" the three basic food
materials (carbohydrate, fat, and protein), converting them
into a single common chemical compound adenosine
triphosphate (ATP). It is this ATP, synthesized as the cell
metabolizes (or breaks down) these three basic foods that
transfers the energy content of all foods to muscle action.
Isodinamia of substances
The energy contained in equal weights of
carbohydrate, fat, and protein is not the same.
Energy content is measured in Calories.
Carbohydrates and protein both contain 4.1
Calories per gram (120 Calories per ounce) while
the energy "density" of fat is more than double at
9 Calories per gram.
The disadvantage of fat as a fuel for exercise is
that it is metabolized through pathways that
differ from carbohydrates and can only support
an exercise level equivalent to 50% VO2 max. It
is an ideal fuel for endurance events, but
unacceptable for high level aerobic (or sprint)
type activities.
Energy Requirements
for Daily Activities
An average man of 70 kilograms who lies in bed all day uses
about 1650 Calories of energy. The process of eating and
digesting food increases the amount of energy used each day by
an additional 200 or more Calories, so that the same man lying in
bed and eating a reasonable diet requires a dietary intake of
aboul 1850 Calories per day. If he sits in a chair all day without
exercising, his total energy requirement reaches 2000 to 2250
Calories. Therefore, the approximate daily en- ergy requirement
for a very sedentary man performing only essential functions is
2000 Calories.
The amount of energy used to perform daily physical activi- ties
is normally about 25 per cent of the total energy expendi- ture,
but it can vary markedly in different individuals, depend- ing on
the types and amounts of physical activities. For example,
walking up stairs requires about 17 times as much energy as
lying in bed asleep. In general, over a 24-hour period, a person
performing heavy labor can achieve a maxi- mal rate of energy
utilization as great as 6000 to 7000 Calo- ries, or as much as 3.5
times the energy used under conditions of no physical activity.
Notion about basal
metabolism
Physiology of temperature
regulation and water-solt balance
Invertebrates generally
cannot adjust their body
temperatures and so are at
the mercy of the
environment. In
vertebrates, mechanisms
for maintaining body
temperature by adjusting
heat production and heat
loss have evolved. These
species are called "coldblooded"
(poikilothermic) because
their body temperature
fluctuates over a
considerable range.
In birds and mammals ,
the ' 'warm-blooded ' '
(homeothermic) animals,
a group of reflex responses
that are primarily
integrated in the
hypothalamus operate to
maintain body temperature
within a narrow range in
Poikilothermic
and
homeothermic
organisms
Temperature
balance
The balance between heat
production and heat loss is
continuously being
disturbed, either by changes
in metabolic rate (exercise
being the most powerful
influence) or by changes in
the external environment
that alter heat loss or gain.
The resulting changes in
body temperature are
detected by
thermoreceptors, which
initiate reflexes that change
the output of various
effectors so that heat
production and/or loss are
changed and body
temperature is restored
Normal Body Temperature
In homeothermic animals, the actual
temperature at which the body is
maintained varies from species to species
and, to a lesser degree, from individual to
individual. In humans, the traditional
normal value for the oral temperature is
37 °C (98.6 °F), but in one large series of
normal young adults, the morning oral
tem- perature averaged 36.7 °C, with a
standard deviation of 0.2 °C.
Temperature receptors
There are cold and warmth receptors.
Nerve fibers respond differently at
different levels of temperature. So a
person determines the different gradation
of thermal sensation by the relative
degrees of stimulation.
It is believed that the cold and warmth
receptors are stimulated by changes in
their metabolic rates or from chemical
stimulation of the endings as modified by
the temperature.
Sensory Nerve Endings in the
Skin
Central and peripheral
thermoreceptors
There are two categories of
thermoreceptors, one in the skin
(peripheral thermoreceptors) and
the other (central thermoreceptors)
in deep body structures, including the
hypothalamus, spinal cord, and
abdominal organs.
Since it is the core body temperature,
not the skin temperature, that is being
maintained relatively constant, the
central thermoreceptors provide the
essential negative-feedback component
of the reflexes.
Central control of touch and
temperature sensation
Almost all sensory information from the somatic
segments of the body enters the spinal cord through the
dorsal roots from the spinal nerves.
Sensory signals are carried through one or two
alternative sensory pathways: 1) the dorsal colomnmedial lemniscal system; 2) the anterolateral system.
All these fibers belong to spinothalamic tract.
Sensory information that must be transmitted rapidly or
with great spatial fidelity is transmitted mainly in the
dorsal colomn-medial lemniscal system.
Sensory impulses, which do not need to keep these
conditions, are transmitted mainly in the anterolateral
system. The anterolateral system can transmit pain,
warmth, cold and crude tactile sensation. Because of
the crossing of the medial lemnisci in the medulla, the
left side of the body is represented in the right side of
the thalamus, and the right side of the body is
represented in the left part of the thalamus.
Central processing of impulses
Cerebral cortex processes somatic sensory information
in somatosensory area I, and somatosensory area II.
Somatosensory area I has much more extensive spatial
orientation of the different parts of the body.
Somatosensory area II helps in association of somatic
sensory information with visceral sensation and body
activity. In general, thermal signals are transmitted in
pathways parallel to those for pain signals. On entering
the spinal cord the signals travel for a few segments
upward or downward and than terminate in dorsal
horns. Then nerve fibers cross to opposite anterolateral
sensory tract and terminate both the reticular areas of
the brain stem and the ventrobasal complex of
thalamus.
A few thermal signals are also relayed to the somatic
sensory cortex from the ventrobasal complex.
Furthermore, it is known that removal of the
postcentral gurus in the human brain being reduced but
does not abolish the ability to distinguish gradations of
temperature.
Role of the hypothalamus
An area of the hypothalamus serves as
the primary overall integrator of the
reflexes, but other brain centers also
exert some control over specific
components of the reflexes.
Output from the hypothalamus and the
other brain areas to the effectors is via:
(1) sympathetic nerves to the sweat
glands, skin arterioles, and the adrenal
medulla; and (2) motor neurons to the
skeletal muscles.
Control of Heat Loss by
Evaporation
Even in the absence of sweating, there is loss of
water by diffusion through the skin, which is not
waterproof. A similar amount is lost from the
respiratory lining during expiration.
These two losses are known as insensible water
loss and amount to approximately 600 ml/day in
human beings. Evaporation of this water accounts
for a significant fraction of total heat loss. In
contrast to this passive water loss, sweating
requires the active secretion of fluid by sweat
glands and its extrusion into ducts that carry it
to the skin surface.
Sympathetic nerves effect
Production of sweat is stimulated by
sympathetic nerves to the glands.
These nerves release acetylcholine rather
than the usual sympathetic
neurotransmitter norepinephrine.
Sweat is a dilute solution containing
sodium chloride as its major solute.
Sweating rates of over 4 L/h have been
reported; the evaporation of 4 L of water
would eliminate almost 2400 kcal from the
body.
Control of Heat Loss by
Radiation and Conduction
For purposes of temperature control, it is
convenient to view the body as a central
core surrounded by a shell consisting of
skin and subcutaneous tissue; we shall
refer to this complex outer shell simply as
skin.
It is the temperature of the central core
that is being regulated at approximately
37°C. As we shall see, the temperature of
the outer surface of the skin changes
markedly.
Heat Exchange in the Skin
Nonshivering thermogenesis
Muscle contraction is not the only process
controlled in temperature-regulating reflexes.
In most experimental animals, chronic cold
exposure induces an increase in metabolic rate
(heat production) that is not due to increased
muscle activity and is termed nonshivering
thermogenesis.
Its causes are an increased adrenal secretion
of epinephrine and increased sympathetic
activity to adipose tissue, with some
contribution by thyroid hormone as well.
However, nonshivering thermogenesis is quite
minimal, if present at all, in adult human
beings, and there is no increased secretion of
thyroid hormone in response to cold.
Nonshivering thermogenesis does occur in
Shivering thermogenesis
Changes in muscle activity constitute the major
control of heat production for temperature
regulation. The first muscle changes in response
to a decrease in core body temperature are a
gradual and general increase in skeletal-muscle
contraction.
This may lead to shivering, which consists of
oscillating rhythmical muscle contractions and
relaxations occurring at a rapid rate. During
shivering, the efferent motor nerves to the
skeletal muscles are influenced by descending
pathways under the primary control of the
hypothalamus. Because almost no external work is
performed by shivering, virtually all the energy
liberated by the metabolic machinery appears as
internal heat and is known as shivering
thermogenesis. People also use their muscles for
voluntary heat-producing activities such as foot
stamping and hand clapping.
Termoregulatory muscular tonus
Primarily on the muscle response to
cold; the opposite muscle reactions
occur in response to heat. Basal muscle
contraction is reflexly decreased, and
voluntary movement is also diminished.
These attempts to reduce heat
production are relatively limited,
however, both because basal muscle
contraction is quite low to start with
and because any increased core
temperature produced by the heat acts
directly on cells to increase metabolic
rate.
Scheme of reflex arc
The skin’s effectiveness as an
insulator
The skin’s effectiveness as an insulator is subject
to physiological control by a change in the blood
flow to it. The more blood reaching the skin from
the core, the more closely the skin’s temperature
approaches that of the core. In effect, the blood
vessels diminish the insulating capacity of the skin
by carrying heat to the surface to be lost to the
external environment.
These vessels are controlled largely by
vasoconstrictor sympathetic nerves, the firing rate
of which is reflexly increased in response to cold
and decreased in response to heat. There is also a
population of sympathetic neurons to the skin
whose neurotransmitters cause active
vasodilation. Certain areas of skin participate
much more than others in all these vasomotor
responses, and so skin temperatures vary with
location.
Loosing heat by panting
Some mammals lose heat by panting. This
rapid, shallow breathing greatly increases the
amount of water vaporized in the mouth and
respiratory passages and therefore the
amount of heat lost. Because the breathing is
shallow, it produces relatively little change in
the composition of alveolar air.
The relative contribution of each of the
processes that transfer heat away from the
body varies with the environmental
temperature. At 21 °C, vaporization is a minor
component in humans at rest. As the
environmental temperature approaches body
temperature, radiation losses decline and
vaporization losses increase.
Effect of relative humidity
It is essential to recognize that sweat
must evaporate in order to exert its
cooling effect. The most important factor
determining evaporation rate is the watervapor concentration of the air—that is, the
relative humidity.
The discomfort suffered on humid days is
due to the failure of evaporation; the
sweat glands continue to secrete, but the
sweat simply remains on the skin or drips
off.
Head Thermogram
Infrared (IR)
radiation is
electromagnetic
radiation of a
wavelength longer
than that of visible
light, but shorter than
that of radio waves.
The name means
"below red" (from the
Latin infra, "below"),
red being the color of
visible light of longest
wavelength. Infrared
radiation spans three
orders of magnitude
and has wavelengths
between
Infrared thermography
Infrared
thermography is
a non-contact,
non-destructive
test method that
utilizes a thermal
imager to detect,
display and
record thermal
patterns and
temperatures
across the
surface of an
object.
Thermal imaging
Thermography,
or thermal
imaging, is a type
of infrared
imaging.
Thermographic
cameras detect
radiation in the
infrared range of
the
electromagnetic
spectrum (roughly
900–14,000
nanometers or
0.9–14 µm) and
produce images of
that radiation.
Thermology
Thermology is the medical science that derives
diagnostic indications from highly detailed and
sensitive infrared images of the human body.
Thermology is sometimes referred to as medical
infrared imaging or tele-thermology and utilizes
highly resolute and sensitive infrared
(thermographic) cameras. Thermology is
completely non-contact and involves no form of
energy imparted onto or into the body.
Thermology has recognized applications in breast
oncology, chiropractic, dentistry, neurology,
orthopedics, occupational medicine, pain
management, vascular medicine/cardiology and
veterinary medicine.
Behavioral mechanisms
There are three behavioral mechanisms for altering
heat loss by radiation and conduction: changes in
surface area, changes in clothing, and choice of
surroundings.
Curling up into a ball, hunching the shoulders, and
similar maneuvers in response to cold reduce the
surface area exposed to the environment, thereby
decreasing heat loss by radiation and conduction. In
human beings, clothing is also an important
component of temperature regulation, substituting for
the insulating effects of feathers in birds and fur in
other mammals. The outer surface of the clothes
forms the true “exterior” of the body surface.
The skin loses heat directly to the air space trapped
by the clothes, which in turn pick up heat from the
inner air layer and transfer it to the external
environment. The insulating ability of clothing is
determined primarily by the thickness of the trapped
air layer.
Clothing and body
temperature
Clothing is important not only at low temperatures
but also at very high temperatures. When the
environmental temperature is greater than body
temperature, conduction favors heat gain rather
than heat loss.
Heat gain also occurs by radiation during exposure
to the sun. People therefore insulate themselves in
such situations by wearing clothes. The clothing,
however, must be loose so as to allow adequate
movement of air to permit evaporation. White
clothing is cooler since it reflects more radiant
energy, which dark colors absorb. Loose-fitting,
light-colored clothes are far more cooling than
going nude in a hot environment and during direct
exposure to the sun.
The third behavioral mechanism
The third behavioral mechanism for
altering heat loss is to seek out
warmer or colder surroundings, as
for example by moving from a shady
spot into the sunlight.
Raising or lowering the thermostat of
a house or turning on an air
conditioner also fits this category.
Integration of Effector
Mechanisms
By altering heat loss, changes in skin blood flow alone can
regulate body temperature over a range of environmental
temperatures (approximately 25 to 30°C or 75 to 86°F for a
nude individual) known as the thermoneutral zone.
At temperatures lower than this, even maximal
vasoconstriction cannot prevent heat loss from exceeding heat
production, and the body must increase its heat production to
maintain temperature. At environmental temperatures above
the thermoneutral zone, even maximal vasodilation cannot
eliminate heat as fast as it is produced, and another heat-loss
mechanism—sweating—is therefore brought strongly into play.
Since at environmental temperatures above that of the body,
heat is actually added to the body by radiation and
conduction, evaporation is the sole mechanism for heat loss.
A person’s ability to tolerate such temperatures is determined
by the humidity and by his/her maximal sweating rate.
Summary of Effector Mechanisms in
Temperature Regulation
Peculiarities of temperature homeostasis in
children
Newborns thermoregulatory system is well
developed, but in newborns different condition of
temperature exchange and present some
peculiarities of thermoregulation. Children have
another than adults ratio of body surface and
weight.
Body square is more than body weight that is
why lost of temperature increase and regime of
temperature comfort change in side of increase of
external temperature to 32-34 °C. Big body
square developed condition for more intensive
cool and heating. Children have more thin thermo
isolative layer of subcutaneous fat.
Role of brown fat
In newborns very important role in thermo regulative
processes has brown fat. It’s present under the skin of
neck, between scapulars. That gives condition for
blood supply of brain, where the cells are very sensate
to disbalance of temperature homeostasis. Brown fat is
well innervated by sympathetic nerves and well
provided with blood.
In the cells of brown fat small drops of fat are present.
In a white cells there is only one drop of fat. Quantity
of mitochondria, cytochroms is greater in brown fat.
Speed of fat acids oxidation 20 times higher, but
absent synthesis and hydrolysis of ATP, that is why the
heat produced immediately. That is caused by presents
of special membrane polypeptide – termogenine. When
it is necessary increase of brown fat oxygenation may
be added to increase the heat production in 2-3 times.
Children, especially of first year life, do not so sensitive
as adult to change of temperature homeostasis. That's
why they don't cry when they lost heat.
Body fluids
The cells that make up the bodies of all but the simplest
multicellular animals, both aquatic and terrestrial, exist in
an '''internal sea" of extracellular fluid (ECF) enclosed
within the integument of the animal. From this fluid, the
cells take up 02 and nutrients; into it, they discharge
metabolic waste products. The ECF is more dilute than
present-day sea water, but its composition closely
resembles that of theprimordial oceans in which,
presumably, all life originated.
In animals with a closed vascular system, the ECFis divided
into 2 components: the interstitial fluid andthe circulating
blood plasma. The plasma and thecellular elements of the
blood, principally red bloodcells, fill the vascular system,
and together they consti-tute the total blood volume.The
interstitial fluid isthat part of the ECF that is outside the
vascular system,bathing the cells. The special fluids
lumped together astranscetlular fluids are discussed below.
About a thirdof the total body water (TBW) is extracellular;
theremaining two-thirds are intracellular (intracellularfluid).
Size of the Fluid Compartments
In the average young adult male, 18% of the
bodyweight is protein and related substances,
7% is mineral, and 15% is fat.
The remaining 60% is water. The intracellular
component of the body wateraccounts for
about 40% of body weight and the
extracellular component for about 20%.
Approximately 25% of the extracellular
component is in the vascularsystem (plasma
== 5% of body weight) and 75% out-side
the blood vessels (interstitial fluid = 15% of
bodyweight).
The total blood volume is about 8% of
bodyweight.
Extracellular Fluid Volume
The ECF volume is difficult to measure because
the limits of this space are ill defined and because
fewsubstances mix rapidly in all parts of the space
while remaining exclusively extracellular. The
lymph cannot be separated from the ECF and is
measured with it. Many substances enter the
cercbrospinal fluid (CSF) slowly because of the
blood-brain barrier.
Equilibration is slow with joint fluid and aqueous
humor and with the ECF In relatively avascular
tissues such as dense connective tissue, cartilage,
and some parts of bone. Substances that distribute
in ECF appear in glandular secretions and in the
contents of the gastrointestinal tract. Because they
are not strictly part of the ECF, these fluids, as
well as CSF, me fluids in the eye, and a few other
special fluids, are called transcellular fluids.
Their volume is relatively small.
Interstitial Fluid Volume
The interstitial fluid space cannot be measured
directly, since it is difficult to sample interstitial
fluid and since substances that equilibrate in
interstitial fluid also equilibrate in plasma. The
volume of the interstitial fluid can be calculated
by subtracting the plasma volume from the ECF
volume.
The ECF volume/intracellular fluid volume ratio is
larger in infants and children than it is in adults,
but the absolute volume of ECF in children is, of
course, smaller than it is in adults. Therefore,
dehydration develops more rapidly and is
frequently more severe in children than in adults.
Intracellular Fluid Volume
The intracellular fluid volume cannot be
measured directly, but it can be calculated by
subtracting the ECF volume from the total body
water (TBW). TBW can be measured by the
same dilution principle used to measure the
other body spaces. Deuterium oxide (D;0, heavy
water) is most frequently used. D20 has
properties that are slightly different from H20,
but in equilibration experiments for measuring
body water it gives accurate results. Tritium
oxide and aminopyrine have also been used for
this purpose.
The water content of lean body tissue is constant
at 71 -72 mL/100 g of tissue, but since fat is
relatively free of water, the ratio of TBW to body
weight varies with the amount of fat present. In
young men, water constitutes about 60% of
body weight. The values for women are
somewhat lower.
The distribution of electrolytes in the various
compartments
The composition of intracellular fluid
varies somewhat depending upon the
nature and function of the cell.
Eelectrolyte concentrations differ markedly
in the various compartments. The most
striking differences are the relatively low
content of protein anions in interstitial
fluid compared to intracellular fluid and
plasma, and the fact that Na+ and C- are
largely extracellular, whereas most of the
K+ is intracellular.
Size of the Fluid Compartments
In the average young adult male, 18 % of the
body weight is protein and related substances,
7 % is mineral, and 15 % is fat. The
remaining 60 % is water.
The intracellular component of the body
water accounts for about 40 % of body
weight and the extra cellular component
for about 20 %.
Approximately 10 % of the body water is
inside the blood vessels.
Interstitial fluid = 15 % of body weight.
The total blood volume is about 6-8 % of
body weight.