Sweat, its helpful,
sometimes distracting, its always with us. Lets examine it in more detail and
see what is really going on. Its more than just water on the skin. It involves
the skin, glands, hormones, electrical stimuli, and homeostasis. It can indicate
a normal healthy body or one which is very sick.
The secretion of
sweat serves, through evaporation, to cool the body. When "no
visible" perspiration is produced, the sweat glands release virtually pure
water. This thin invisible coating of water maintains the skin moisture and is
called "insensible perspiration". The glands of the skin must always
be producing water to keep the skin moist.
This insensible
perspiration may amount to 600 to 700 ml / day. The small amount of organic and
inorganic material that accumulates on the skin under these conditions is
probably associated with activity of sebaceous glands rather than with that of
the sweat glands. In circumstances in which visible sweat (sensible sweat) is
elaborated, its volume and composition vary and are determined by the rate of
evaporation, previous fluid intake, external temperature and humidity, and
hormonal factors.
Volumes as large as
14 liter per day have been recorded.
Both volume and salt content of sensible perspiration are influenced by
acclimation of the individual. Persons new to an environment that is hot and
humid produce copious quantities of salt laden perspiration, Na+ (sodium) and
Cl- (chloride) may be as high as 75 meq / l. Acclimated individuals,
however, produce
smaller volumes with a lower salt concentration.
Unreplaced loss of
large volumes of perspiration may result in hypertonic contraction. Miners' or stokers' cramps result from salt
loss under these circumstances and can be prevented by incorporation of small
amounts of salt in drinking water. In cystic fibrosis, a congenital defect
involving most or all of the glandular epithelial structures of the body, sweat
and tears are characteristically rich in salt.
When small volumes
of visible perspiration are elaborated, its concentration of nonprotein
nitrogenous materials slightly exceed that of the plasma from which it is
derived. This probably reflects evaporation of water from the elaborated sweat.
However, sweat glands may possess an active mechanism for the concentration of
lactic acid.
The lactate
concentration of the sweat of athletes far exceeds that present in plasma .
Specific gravities of 1.002 to 1.005 for sweat have been reported, and the pH
lies between 4.5 and 7.5. Approximate
concentration of electrolytes in sweat:
Na+
<85, K+ 3-6 ,
Ca ++ 3-5, <85,
CL-
HCO---
0-10,
Protein
trace Numbers are meq / l of water.
Lets look at secretion at the glandular
level. Sweat is a secretion of glands in the skin. Formation of interstitial
fluid from plasma may be described in physiochemical terms based on knowledge
of the diffusibility of water, the solutes of plasma, and the permeability of
the capillary wall to these substances.
The basis for the
differences between the composition of intracellular and extracellular fluid is
the existence of a mechanism whereby energy, derived from metabolic processes,
may be used to maintain the intracellular composition against an osmotic
gradient. Another situation, "secretion", is evident in which cells
are aligned in columnar fashion (tubes), bathed by interstitial fluid or plasma
on one side and fluid of different composition on the opposite side, and in
which differences in the composition of the two fluids cannot be accounted for
in terms of spontaneous diffusion, osmosis, or permeability.
The secretory
process, operating against an osmotic, electrochemical, or hydrostatic
gradient, again requires the harnessing of metabolically derived energy. This
energy is derived from the mitochondria in the cuboidal and columnar cells
which are secreting.
The secretory
process is characterized by (1) inhibition by interruption of cellular
metabolism, (2) cations and anions are transported simultaneously in equivalent
amounts in the same direction, in contrast to the Donnan equilibrium, (3)
nonelectrolites also participate, and (4) cells are so aligned that the
transported fluid leaves by a duct and the pressure within this duct is
independent of arterial pressure.
Mammalian
secretions include milk, sweat, tears, cerebrospinal fluid, aqueous humor, and
the fluids of the digestive tract. Among the more dramatic instances of
secretion are the elaboration of 0.16 N HCL by the stomach, secretion of almost
pure water by sweat glands, and removal of almost all glucose and Na+ from the
urine. The fundamental mechanisms may be , in each case, an adaptation of those
by means of which all cells maintain their internal composition. The mechanisms
involved in these active transfers have been extensively studied but remain
among the major unresolved areas of
biochemistry. The term "secretion" has also been generally
employed to describe the behavior of the ductless endocrine glands, although
the cells "do work" in synthesizing the material, the actual transfer
of the secretion operates with the osmotic gradient and no work need be done to
achieve the transfer.
We will begin here
with the composition of the skin, or, epithelial tissues. Epithelial tissues
cover all body surfaces, inside and outside. Nothing may enter the body without
passing through the epithelial tissue. The digestive system is in essence a
hollow tube passing through the body, and materials in the digestive system,
from mouth to anus, are not in the body until they pass through the epithelial
tissue.
Epithelial tissues make up the outer layer of
the skin, form the inner lining of body cavities, cover the organs inside these
cavities, and are the major tissue of glands. It always has a free
surface---one that is exposed to the outside or to an open space internally.
The underside of the tissue is anchored to connective tissue by a thin
nonliving layer called the basement membrane. Epithelial tissues lack blood
vessels, however, epithelial cells are nourished by substances that diffuse
from vessels in the underlying tissue, the lymph. Epithelial cells are tightly
packed together and there is little intercellular material between them. These
cells often form a protective barrier, as the skin, other epithelial functions
are secretion, absorption, excretion, and reproduction. Epithelial cells are classified according to
their shapes, arrangements and functions.
For example there
are single layersof cells called "simple", while those with many
layers are called "stratified". Thin flattened cells are
"squamous", cube like are called "cuboidal", and those that
are elongated are referred to as "columnar". Simple squamous cells
are found in the air sacs of the lungs where gas exchange takes place. Simple
cuboidal cells are found in various glands, such as the salivary glands,
thyroid gland, pancreas, liver, and some sweat glands. Simple columnar cells
are found in sweat glands, some secrete watery fluids, and some secrete
protective fluids called mucus (an oily substance). There are flasked shaped
cells scattered in among the columnar cells called goblet cells which also
assist with sweat production. Glandular
epithelial cells are found within the columnar and cubodial epithelium
and one or more cells constitute a gland. Those glands that secrete their
products into a duct are called "exocrine glands", and those that
secrete into tissue fluids or blood are called "endocrine glands".
Although a gland may be only a single cell (unicellular gland), as in the case
of goblet cells, most glands are composed of many cells (multicellular glands).
For example, exocrine glands that consist of
simple epithelial lined tubes opening to the surface are called
"tubular" glands, while those that are composed of one or more sac
like dilations connected to the surface by narrowed secretory ducts are called
"alveolar" glands.
Glandular secretions are classified according
to whether they are a cellular product or portion of the glandular cells.
Glands that secrete watery fluids (sweat) that diffuse through cell membranes
are called "merocrine" glands Those that release entire cells filled
with secretory products are "holocrine" glands, while those of the
intermediate type that lose small portions of their glandular cell bodies
during secretion are called "apocrain glands".
Now let us jump into the integumentary
system, that group of tissues referred to as the skin, hair, sebaceous glands
and sweat glands. The skin has three layers, the epidermis, dermis and
subcutaneous layer.
Hair develops in
hair follicles which have "arrector pili muscle", this muscle erects
the hair when you are cold or frightened or emotionally stimulated, i.e., goose
bumps. Sebaceous glands are holocrine glands that are usually associated with
hair follicles. They normally produce an oily secretion called sebum, which is
emptied into the hair follicle and helps to keep the hairs and skin soft,
pliable, and waterproof.
Under the action of
certain hormones the sebaceous glands may produce a less oily and more watery product. Sweat glands occur
in nearly all regions of the skin, but are most numerous in the palms and
soles. Each gland consists of a tiny tube that originates as a ball shaped coil
in the dermis or subcutaneous layer. The ball shaped coil is in reality a long
tube of tubular cells wound up in the shape of a ball. The open end exits onto
the surface of the skin. The tubular cells are sweat-secreting epithelial
cells. The opening at the surface is called a pore.
Some sweat glands, the apocrine glands,
respond to emotional stress via the action of hormones. They are responsible
for the skin's becoming moist when a person is upset or suffering from stage
fright. These glands are numerous in the armpits and groin and are usually
associated with hair follicles. They also become active when a person is
sexually stimulated. Other sweat glands, the eccrine glands, respond primarily
to elevated body temperatures. These glands are common on the forehead, neck,
and back, where they produce profuse sweating on hot days and during physical
exercise.
The fluid secreted by sweat glands is mostly
water, although it contains small quantities of salts and certain wastes, such
as urea and uric acid. In this way , the secretion of sweat is, to a limited
degree, an excretory function also. The
body regulates its temperature by radiating heat or by evaporation of water
from its surface. When the body temperature is rising above normal, the nervous
system also stimulates sweat glands to become active and release fluid on to
the surface of the skin. As this fluid evaporates, it carries heat away from
the surface. The nervous system also signals blood vessels in the dermis to
dilate, bring more hot blood close to the surface, where it may be cooled by
the evaporating water.
In the case of
extreme cold the nervous system contracts the blood vessels and stops the
action of the sweat glands, shutting them off. Next we will examine the role
and actions of hormones in the production of sweat.
Body cells have
much in common with each other, yet those of different tissues vary in a number
of ways. Most of the trillions of cells within the human body are to small to
be seen without a microscope. Only the human egg cell can be seen with the
unaided eye, as a tiny speck. Cells vary in size, shape, and complexity,
determined by their function and purpose.
Secretory cells are
no exception, being specially constructed to do what they do with great
efficiency. Osmoregulatory cells, such as secretory, excretory and homeostatsis
epithelia act as highly specialized ionic pumps, and have special structural
features. The secretory cells of the sweat glands possess extensive systems of
smooth endoplasmic reticulum, dense populations of mitochondria containing
large numbers of cristae, and, frequently, extensive deep infoldings of the
cell membrane on the side of the cell where absorption is presumed to occur.
Lets take a quick
look at some of the cell contents. We know that cells are enclosed in a thin
membrane and that within this membrane there are hundreds more membranes
enclosing separate sections and organs of the cell. Of great interest to us are
the cytoplasm, endoplasmic reticulum, ribosomes, Golgi apparatus, and the
mitochondria. There are many other organs (organelles) in a cell, but these are
the ones of interest to us at this moment.
The cytoplasm is
the clear thick liquid (as seen by the eye) that fills the cell. The electron
microscope shows it to be filled with all kinds of cell machinery, networks of
tubules, membranes, and other organelles, no space is wasted. The activities of
the cell occur largely in its cytoplasm. It is there that food molecules are
received, processed and used, it is the site of the cells metabolic processes,
in which the other mentioned cytoplasmic organelles play specific roles.
The endoplasmic
reticulum is a complex network of interconnected membranes. Spaces between
these membranes form elongated canals called tubules. The network is connected
to the cells outer membrane , where it has openings to the outside of the cell.
It also connects to the other organelle and functions as a transporting
network, moving chemicals from one part to the other parts of the cell. The
endoplasmic reticulum also functions in the synthesis of the chemicals it is
distributing in the cell. A part of the membrane surface is smooth and part is
rough, having ribosomes on it. The smooth surface is very active in producing
secretory fluids.
The ribosomes
produce proteins, enzymes, other secretory products, which are used for cell
building and secreted outside of the cell.
The Golgi apparatus (named after Doctor Golgi) is composed of a group of
flattened, membranous sacs whose membranes are continuous with those of the
endoplasmic reticulum. The Golgi apparatus manufactures cellular secretions as
packages of glycoproteins which are released outside of the cell as secretion.
Mitochondria are
fairly large, fluid-filled sacs. They vary in size and can change shape; often
they can be observed moving about in the cytoplasm. The membrane surrounding a
mitochondrion has an outer and an inner layer. The inner layer is folded to
form partitions called cristae within the sac-like structure. Small particles
thought to be associated with enzymes are connected to the cristae. These
enzymes control the chemical reactions by which energy is released from the
glucose molecules. The mitochondria function in the transformation of this
energy into a form that is usable by cell parts. The mitochondria are the power
houses of the cell, changing incoming chemicals into chemicals that the cell
can use for energy. Secretory cells require large amounts of energy to
function, as all of their activities are against the normal gradients found in
normal cells. All cells have mitochondria, which supply ATP, to power the cell
activities. Cells that require larger amounts of energy have larger numbers of
mitochondria, a heart muscle cell will have as many as 50,000 in the cell, due
to the high energy requirement of the heart cell. Secretory cells, such as the
sweat cell have them in the many thousands. The more energy required, the more
mitochondria are found in the cell.
The mitochondria is
a separate living organism in its own right. It has its own membrane, its own
DNA, and all thats required to exist as a separate bacteria. It multiplies and
divides when more are needed, and when the cell divides each half will get its
starter group of mitochondria to populate it. Biologists now believe that long
ago the mitochondria were bacteria that formed a symbiotic relationship with
the living cell, a relationship that was to transform the cell so much that all
cells from yeasts through human beings could not survive without them. The
primitive algae did not have available extra energy, never had a way of
creating more energy, and never developed past the algae development. When
mitochondria formed a symbiotic relationship the primitive cell now had a way
of producing extra energy from foods, and in consequence became capable of
building larger more complex structures, creating electricity, doing forceful
secretions, moving about in its environment and actively pursuing food.
Evolution would have stopped without the mitochondria. The usual picture is
that an early cell tried to digest a mitochondria bacteria and it resisted
successfully and remained in the cell. Who knows, we do know it is there in all
our cells now. The ATP, which is the waste of the mitochondria is the energy
for the cell.
A molecule of
glucose enters the cell and is acted upon by enzymes, after nine successive
chemical reactions, the glucose molecule becomes two molecules of pyruvate,
which then enters the mitochondria. In the mitochondria the pyruvate is
processed to release energy in the form of electrons (the stuff of electricity)
which are immediately recaptured to make ATP (adenosine triphosphate) which in
turn is transported to all parts of the cell, providing the chemical power
needed by the cells components. As the energy is used from the ATP it becomes
ADP and returns back to the mitochondria for more energy, changing back into
ATP again. This happens million of times per second, per mitochondria, per
sweat cell, per sweat gland. Thats a lot of energy being created and used by
the sweat glands. A result of all this energy creation and use is water, a lot
of it, which is secreted by the cells through their membranes. Also the sodium-potassium
pumps go into high gear, producing a secretion of salt on the skin in the
water.
This whole process builds up in just seconds as the hormones and
electrical stimuli call for sweat. The mitochondria begin multiplying rapidly
and glucose intake rises sharply, ATP production goes into high gear and water
and salt begin coming from the cell within seconds of the demand for sweat. So
what is the sodium-potassium pump doing? For every glucose molecule that enters
the cell a sodium atom must accompany it, soon the cell will have to many
sodium atoms. The sodium-potassium pump will force sodium atoms out of the
cell, and in so doing this two potassium atoms come in for every three sodium
atoms forced out. This is good because the cell is constantly losing potassium
atoms in other chemical actions and they need to be replaced to maintain the
proper ionic balance. This forcing out of sodium and forcing in potassium use
energy which requires more glucose intake and round and round it goes. The
excess sodium appears in the sweat, mixed with the water in the ducts on its
way to the skin surface.
The term endocrine
is used to describe glands that secrete their products internally. For example,
thyroid and parathyroid glands are endocrine glands (ductless glands). Certain
other glands, such as sebaceous and sweat glands of the skin release their
products into ducts that lead to the outside of the body. Glands that secrete
externally are called exocrine glands.
As a group, the
endocrine glands are concerned with the regulation of metabolic processes. They
control the rates of certain chemical reactions, and aid in the transport of
substances through cell membranes, play vital roles in cell growth, and help
regulate water and electrolyte balance.
The chemicals secreted
by endocrine glands are called "hormones". They are released into the
extracellular spaces surrounding the gland, absorbed into the blood and carried
to all parts of the body. The physiological effect of a specific hormone is
often restricted to a certain tissue, called its target tissue. In other cases,
a particular hormone can affect nearly all body cells. Of the twelve major
hormone producing glands we will be most interested in the adrenal cortex
(outer region of the adrenal gland). Of the over two hundred identified
hormones we will concentrate on those that affect the sebaceous and sweat
glands.
Each kind of hormone has a unique molecular structure and a unique
action as well. However, all hormones are organic substances, usually steroids,
proteins, or amines. The steroids from the adrenal cortex have controlling
effects on the sebaceous and sweat glands. Some other hormones are suspected of
affecting the sweat glands also, and research is on going. Although it is not
yet totally clear how hormones exert influences on their target tissues, it is
recognized that they do so by acting on the cell membranes. According to this
idea, each kind of hormone molecule can combine with specific receptor sites
located on the membranes of its target cells.
Once the hormone-receptor
combinations have been made, certain enzyme molecules (adenyl cyclase) are
activated within the membrane and diffuse into the cells cytoplasm. There the
enzymes cause cytoplasmic ATP (adenosine triphosphate) molecules to be converted
into "cyclic AMP" (adenosine monophosphate). The cyclic AMP brings
about the desired cellular changes, i.e., secrete more, secrete less, or change
secretion content. In other words, a hormone that stimulates activity in a
particular target cell may do so by initiating the formation of cyclic AMP. The
cyclic AMP, in turn, may cause changes in the cells membrane permeability, in
the number of enzyme molecules present, or in the rate at which certain
substances are synthesized by the cell----changes recognized as the hormones
effect.
Now we get to the
pituitary gland which is attached to the hypothalamus gland by the pituitary
stalk. The pituitary secretions are controlled by the brain which is in turn
stimulated by nerve impulses originating in the hypothalamus. The hypothalamus
receives information from nearly all parts of the nervous system. This
information includes data concerning a persons emotional state, body
temperature, blood nutrient concentrations, ionic balance and so forth. The
hypothalamus signals the pituitary gland to release hormones.
The hormone of interest to us is the ACTH (adrenocorticotropic hormone) which
controls the manufacture and secretion of certain hormones from the outer
layer, or cortex, of the adrenal gland. The adrenal glands are located atop
each kidney. The outer part of the gland is called the adrenal cortex and
it produces a number of different hormones, of which about thirty have been
identified. These hormones are all steroids, and unlike the medullary
(inner adrenal layer) hormones---which a person can live without---
those of the adrenal cortex are vital. In the absence of adrenal cortex
secretions a person will die within a week.
The hormones from
the cortex are in three groups, mineralocorticoids which regulate the concentrations
of extracellular electrolytes. Glucocorticoids which influence metabolism of
carbohydrates, proteins and fats. Sex hormones which have effects on sexual
characteristics.
Of the
mineralocorticoids which are manufactured by the cells in the outer zone (zona
glomerulosa) of the cortex the most important is "aldosterone". It
controls the water conservation or promotion by acting on the blood volume and
pressure. It also controls balance of sodium and potassium ions in the body.
This is accomplished by regulating the urine and sweat.
Of the various
glucocorticoids, the hormone responsible for the greatest amount of activity is
"cortisol" (hydrocortisone), a substance structurally similar to
aldosterone. Its action is controlled by the ACTH from the pituitary gland, and
effects cell membranes and stimulates liver cells and adipose tissue.
As we can plainly
see, hormones have control of most bodily functions involving regulation of the
homeostasis and the sweat glands play an important role . The sweat glands are
controlled by nerve impulses, and hormones.
It has been said
that the skin is our first line of defense, almost true, the symbiotic bacteria
on the skin are our first line of defense. These bacteria are kept moist by the
insensible sweat and nurtured by the nutrients in the sweat. Different areas of
the skin have various strains of bacteria populating it. These bacteria destroy foreign
dangerous bacteria landing on the skin. The toxic waste of our friendly skin bacteria has been
synthesized and used as antibiotics for many years now, some of the antibiotics
developed from analysis of the skin bacteria toxins are streptomycin,
aureomycin, terramycin and neoycin.
Care should be
taken during body hygiene to preserve the integrity of the bacterial colonies
on the skin. A healthy individual will not smell from the normal sweat and
bacteria on the skin. Smell is caused by improper hygiene permitting the
destruction of our normal bacterial colonies. Using excess oil removing soaps
and harsh cleansers destroys the insensible water/oil layer and bacteria.
Rubbing the skin until it
is pink (sign of a
raw wound) is very bad. Loss of the layer of dead protective skin cells is not
good hygiene. Normally hot water is all that is needed to remove dirt from the
surface of the body, without damaging the water/oil layer or bacterial
colonies.
The daily
requirement for water under usual environmental conditions results in a daily
obligatory loss of approximately 1,500 ml of water by normal human adults. Of
this, about 600 ml is lost through the skin as insensible perspiration, 400 ml
in the expired air, and 500 ml in the urine. Thats about half of your water
loss via the sweat glands, which can produce copious amounts of water on demand
of the bodies homeostasis systems. Any excess intake of water over this
obligatory total volume appears as an increased urine volume. When the intake
is less than this obligatory 1,500 ml, the difference must be at the expense of
the total body water. Since the
oxidation of glucose and lipid, in an amount sufficient to yield 2000 Cal/day,
results in formation of about 300 ml of water, there remains an obligatory
water intake of the order of 1,200 ml/day. This 1,200 ml can be composed of
drinking water or water in the foods you eat, but it must come from somewhere
or you will become dehydrated.
The average person
goes around in a dehydrated state and wonder why they can not function well or
think straight. The secret is to drink lots of water, don't worry if its to
much, the body will get rid of the excess it does not need via the sweat and
urine. Now, 500 ml is about two cups of water, so you need to drink on average
about 5 cups of water a day. Thats all, just five cups of water a day, where ever they came up with this six glasses
a day thing I don't know. A glass is not a recognized unit of measure, you do
not use a glass of milk and a glass of onions ,or a half glass of flour when
measuring, the glass is not a unit of measure. Its really easy to drink five
cups of water a day, a shake is four cups and coffee will be many cups a day
and then we drink milk and also put milk on the cereal, and then have some
chocolate milk and maybe a soda pop, and some plain old water when coming in
from the garden, so drinking five cups of water is really easy.
In contrast to the
water requirement, there is no equivalent obligatory loss of Na+ or Cl- (salt)
under normal conditions. Adults on a diet devoid of Na+ and Cl- lose these ions
in the urine for only a few days, after which the urine becomes virtually salt
free, all other circumstances remaining constant. The body is now reabsorbing
all Na+ and Cl- ions and conserving them. During periods of high sweating more
salt must be taken in. The average diet provides 100 to 200 meq of Na+ and Cl-
(salt) per day, all of which, except for small amounts in sweat and feces, is
excreted in the urine. In the absence of dietary K+, urinary excretion of
approximately 40 to 60 meq of K+ per day occurs for a few days, after which
urine losses diminish to about 10 meq a day.
Several events can occur that will cause the hormones to swing into
action with the sweat glands. These are disturbances in the bodies osmotic
pressure, volume of body blood, blood pressure, volume of extracellular fluids
and alterations in the composition of the electrolyte (ionic) and water
balance. If you are sitting at a meal and begin to sweat as you eat, you have a
serious problem and should see a physician right away. This is a sure sign of a
cardiac problem relating to blood pressure and blood volume control, left
untreated it will lead to death. Observing your sweat will give us many clues
as to the proper or improper functioning of the body. Keep in mind that the
hormone aldosterone is a principal hormone in regulating homeostasis and it
also regulates the sweat glands. So
when aldosterone is running, the sweat glands alert you that your body is
struggling to correct imbalances somewhere in it.
Occasionally, under
heat stress, the temperature regulating ability of the body fails and the
function of the temperature regulating center breaks down. In such a case, the
body temperature may rise rapidly, accompanied by a dry skin and the absence of
sweating. This condition is called "heat stroke".
Another condition
that may be observed in heat-exposed individuals is "heat
exhaustion". In this condition , the temperature regulating mechanisms are
functional, but as the result of extreme sweating (fluid loss) and vasodilation
to lose heat, the individual may collapse and display low blood pressure
(hypotention) and a cool , clammy skin with little rise in body temperature.
Heat stroke in general is a much more serious condition than heat exhaustion,
however, both require immediate health care.
Now, high blood
pressure is connected with sweat disorders. The high blood pressure
(hypertension) is a common disease of the cardiovascular system. The elevated
pressure is sometimes related to arteriosclerosis or kidney disease, which is
also connected with the elasticity of the arterial walls and narrowing of the
lumens of these vessels.
When the blood flow to the
kidneys is altered an enzyme called renin is released which in turn causes
angiotensin (a plasma protein) to be produced, which in its turn triggers the
adrenal cortex to release more of the hormone aldosterone. Which of course gets
the sweat glands involved in the cardiac problem. Yes, the sweat glands are a
good indicator of how the health of the body is doing.
Take good care of
your sweat glands and they will take care of you.
Happy sweating,
when needed.
--The end--
Bless you
Bob Lee