Body Fluids - Copy

8/11/2019 Body Fluids - Copy

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The Body Fluids

Cerebrospinal fluid (CSF)is a clear colorless bodily fluid found in the brain and spine. It is

produced in the choroid plexus of the brain. It acts as a cushion or buffer for the brain's

cortex, providing a basic mechanical and immunological protection to the brain inside

the skull, and it serves a vital function in cerebral autoregulation of cerebral blood flow.

The CSF occupies the subarachnoid space (the space between the arachnoid mater

and the pia mater) and the ventricular system around and inside the brain and spinal

cord. It constitutes the content of the ventricles, cisterns, and sulci of the brain, as well

as the central canal of the spinal cord.

Production.

The brain produces roughly 500 mL of cerebrospinal fluid per day. This fluid is constantly

reabsorbed, so that only 100-160 mL is present at any one time.

Ependymal cells of the choroid plexus produce more than two thirds of CSF. The

choroid plexus is a venous plexus contained within the four ventricles of the brain,hollow structures inside the brain filled with CSF. The remainder of the CSF is produced

by the surfaces of the ventricles and by the lining surrounding the subarachnoid space.

Ependymal cells actively secrete sodium into the lateral ventricles. This creates osmotic

pressure and draws water into the CSF space. Chloride, with a negative charge,

maintains electroneutrality and moves with the positively-charged sodium. As a result,

CSF contains a higher concentration of sodium and chloride than blood plasma, but

less potassium, calcium and glucose and protein.

CSF serves several purposes:

Buoyancy: The actual mass of the human brain is about 1400 grams; however, the net

weight of the brain suspended in the CSF is equivalent to a mass of 25 grams. The braintherefore exists in neutral buoyancy, which allows the brain to maintain its density

without being impaired by its own weight, which would cut off blood supply and kill

neurons in the lower sections without CSF.

Protection: CSF protects the brain tissue from injury when jolted or hit. In certain

situations such as auto accidents or sports injuries, the CSF cannot protect the brain

from forced contact with the skull case, causing hemorrhaging, brain damage, and

sometimes death.

Chemical stability: CSF flows throughout the inner ventricular system in the brain and is

absorbed back into the bloodstream, rinsing the metabolic waste from the central

nervous system through the bloodbrain barrier. This allows for homeostatic regulation of

the distribution of neuroendocrine factors, to which slight changes can cause problems

or damage to the nervous system. For example, high glycine concentration disrupts

temperature and blood pressure control, and high CSF pH causes dizziness and

syncope. To use Davson's term, the CSF has a "sink action" by which the various

substances formed in the nervous tissue during its metabolic activity diffuse rapidly into

the CSF and are thus removed into the bloodstream as CSF is absorbed.

Prevention of brain ischemia: The prevention of brain ischemia is made by decreasing

the amount of CSF in the limited space inside the skull. This decreases total intracranial

pressure and facilitates blood perfusion.


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Clearing waste: CSF has been shown by the research group of Maiken Nedergaard to

be critical in the brain's glymphatic system, which plays an important role in flushing

metabolic toxins or waste from the brain's tissues' cellular interstitial fluid (ISF). CSF

flushing of wastes from brain tissue is further increased during sleep, which results from

the opening of extracellular channels controlled through the contraction of glials cells,

which allows for the rapid influx of CSF into the brain. These findings indicate that CSF

may play a large role during sleep in clearing metabolic waste, like beta amyloid, that

are produced by the activity in the awake brain.

Blood plasmais the pale-yellow liquid component of blood that normally holds the

blood cells in whole blood in suspension. It makes up about 55% of the body's total

blood volume.[1] It is the intravascular fluid part of extracellular fluid (all body fluid

outside of cells). It is mostly water (up to 95% by volume), and contains dissolved

proteins (6-8%) (i.e.albumins, globulins, and fibrinogen), glucose, clotting factors,

electrolytes (Na+, Ca2+, Mg2+, HCO3-, Cl-, etc.), hormones, and carbon dioxide

(plasma being the main medium for excretory product transportation). Plasma also

serves as the protein reserve of the human body. It plays a vital role in an intravascular

osmotic effect that keeps electrolytes in balanced form and protects the body frominfection and other blood disorders.

Blood plasma is prepared by spinning a tube of fresh blood containing an

anticoagulant in a centrifuge until the blood cells fall to the bottom of the tube. The

blood plasma is then poured or drawn off. Blood plasma has a density of approximately

1025 kg/m3, or 1.025 g/ml.

Blood serum is blood plasma without clotting factors; in other words, "pure" blood.

Plasmapheresis is a medical therapy that involves blood plasma extraction, treatment,

and reintegration.

Interstitial fluid (or tissue fluid)is a solution that bathes and surrounds the cells ofmulticellular animals. It is the main component of the extracellular fluid, which also

includes plasma and transcellular fluid. The interstitial fluid is found in the interstitial

spaces, also known as the tissue spaces.

On average, a person has about 10 litres (2.4 imperial gallons or ~2.9 US gal) of

interstitial fluid (they make up 16% of the total body weight), providing the cells of the

body with nutrients and a means of waste removal.

Production and removal

Plasma and interstitial fluid are very similar. This similarity exists because water, ions, and

small solutes are continuously exchanged between plasma and interstitial fluids acrossthe walls of capillaries. Plasma, the major component in blood, communicates freely

with interstitial fluid through pores and intercellular clefts in capillary endothelium.

Formation

Hydrostatic pressure is generated by the systolic force of the heart. It pushes water out

of the capillaries.


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The water potential is created due to the ability of small solutes to pass through the

walls of capillaries. This buildup of solutes induces osmosis. The water passes from a high

concentration (of water) outside of the vessels to a low concentration inside of the

vessels, in an attempt to reach an equilibrium. The osmotic pressure drives water back

into the vessels. Because the blood in the capillaries is constantly flowing, equilibrium is

never reached.

The balance between the two forces differs at different points on the capillaries. At the

arterial end of a vessel, the hydrostatic pressure is greater than the osmotic pressure, so

the net movement (see net flux) favors water and other solutes being passed into the

tissue fluid. At the venous end, the osmotic pressure is greater, so the net movement

favors substances being passed back into the capillary. This difference is created by the

direction of the flow of blood and the imbalance in solutes created by the net

movement of water favoring the tissue fluid.

Removal

To prevent a buildup of tissue fluid surrounding the cells in the tissue, the lymphatic

system plays a part in the transport of tissue fluid. Tissue fluid can pass into thesurrounding lymph vessels, and eventually ends up rejoining the blood.

Sometimes the removal of tissue fluid does not function correctly, and there is a build-

up. This can cause swelling, often around the feet and ankles, which is generally known

as edema. The position of swelling is due to the effects of gravity.

Amniotic Fluid

Development of amniotic fluidAmniotic fluid [AF] can be detected from the very beginning of formation of the

gestational sac (extra-embryonic coelom or chorionic cavity). This firstly water-like fluid

originates from the maternal plasma, and passes through the fetal membranes by

osmotic and hydrostatic forces. As the placental and fetal vessels develop, the fluid

passes through the fetal tissue, as the exsudatum of the skin. After the 20th-25th week of

pregnancy when the keratinization of skin occurs, the quantity of amniotic fluid begins

to depend on the factors that comprise the circulation of AF.

At first, amniotic fluid is mainly water with electrolytes, but by about the 12-14th week

the liquid also contains proteins, carbohydrates, lipids and phospholipids, and urea, all

of which aid in the growth of the fetus.

The volume of amniotic fluid is positively correlated with the growth of fetus. From the

10th to the 20th week it increases from 25ml to 400ml approximately. From the 8th week,

when the fetal kidneys begin to function, fetal urine is also present in the AF.

Approximately in the 10th week the breathing and swallowing of the fetus slightly

decrease the amount of AF, but neither urination nor swallowing contributes

significantly to AF quantity changes, until the 25th week, when keratinization of skin is


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complete. Then the relationship between AF and fetal growth stops. It reaches the

plateau of 800ml at the 28 week gestational age (GA). The amount of fluid declines to

roughly 400 ml at 42 weeks GA.

The forewaters are released when the amnion ruptures. This is commonly known as the

time when a woman's "water breaks". When this occurs during labour at term, it isknown as "spontaneous rupture of membranes" (SROM). If the rupture precedes labour

at term, however, it is referred to as "premature rupture of membranes" (PROM). The

majority of the hindwaters remain inside the womb until the baby is born. Artificial

rupture of membrane (ARM), a manual rupture of the amniotic sac, can also be

performed to release the fluid if the amnion has not spontaneously ruptured.

Functions of amniotic fluid

Amniotic fluid is inhaled and exhaled by the fetus. It is essential that fluid be breathed

into the lungs in order for them to develop normally. Swallowed amniotic fluid also

creates urine and contributes to the formation of meconium. Amniotic fluid protects the

developing baby by cushioning against blows to the mother's abdomen, allowing for

easier fetal movement and promoting muscular/skeletal development. Amniotic fluidswallowed by fetus help in the formation of gastrointestinal tract.

Gastric acidis a digestive fluid, formed in the stomach. It is composed of hydrochloric

acid (HCl) (around 0.5%, or 5000 parts per million) as high as 0.1 M, potassium chloride

(KCl) and sodium chloride (NaCl). The acid plays a key role in digestion of proteins, by

activating digestive enzymes, and making ingested proteins unravel so that digestive

enzymes break down the long chains of amino acids. Gastric acid is produced by cells

lining the stomach, which are coupled in feedback systems to increase acid

production when needed. Other cells in the stomach produce bicarbonate, a base, to

buffer the fluid, ensuring that it does not become too acidic. These cells also produce

mucus, which forms a viscous physical barrier to prevent gastric acid from damagingthe stomach. Cells in the beginning of the small intestine, or duodenum, further

produce large amounts of bicarbonate to completely neutralize any gastric acid that

passes further down into the digestive tract.

Gastric acid is produced by parietal cells (also called oxyntic cells) in the stomach. Its

secretion is a complex and relatively energetically expensive process. Parietal cells

contain an extensive secretory network (called canaliculi) from which the gastric acid is

secreted into the lumen of the stomach. These cells are part of epithelial fundic glands

in the gastric mucosa. The pH of gastric acid is 1.5 to 3.5 [2] in the human stomach

lumen, the acidity being maintained by the proton pump H+/K+ ATPase. The parietal

cell releases bicarbonate into the blood stream in the process, which causes atemporary rise of pH in the blood, known as alkaline tide.

The resulting highly acidic environment in the stomach lumen causes proteins from food

to lose their characteristic folded structure (or denature). This exposes the protein's

peptide bonds. The gastric chief cells of the stomach secrete enzymes for protein

breakdown (inactive pepsinogen and rennin). Hydrochloric acid activates pepsinogen

into the enzyme pepsin, which then helps digestion by breaking the bonds linking


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amino acids, a process known as proteolysis. In addition, many microorganisms have

their growth inhibited by such an acidic environment, which is helpful to prevent

infection.

Gastric acid secretion happens in several steps. Chloride and hydrogen ions are

secreted separately from the cytoplasm of parietal cells and mixed in the canaliculi.Gastric acid is then secreted into the lumen of the oxyntic gland and gradually reaches

the main stomach lumen. The exact manner in which the secreted acid reaches the

stomach lumen is controversial, as acid must first cross the relatively pH neutral gastric

mucus layer.

Chloride and sodium ions are secreted actively from the cytoplasm of the parietal cell

into the lumen of the canaliculus. This creates a negative potential of -40 mV to -70 mV

across the parietal cell membrane that causes potassium ions and a small number of

sodium ions to diffuse from the cytoplasm into the parietal cell canaliculi.

The enzyme carbonic anhydrase catalyses the reaction between carbon dioxide and

water to form carbonic acid. This acid immediately dissociates into hydrogen and

bicarbonate ions. The hydrogen ions leave the cell through H+/K+ ATPase antiporter

pumps.

At the same time sodium ions are actively reabsorbed. This means that the majority of

secreted K+ and Na+ ions return to the cytoplasm. In the canaliculus, secreted

hydrogen and chloride ions mix and are secreted into the lumen of the oxyntic gland.

The highest concentration that gastric acid reaches in the stomach is 160 mM in the

canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic

with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted

in the stomach lumen to a pH between 1 and 3.

There is a small continuous basal secretion of gastric acid between meals of usually less

than 10 mEq/hour.

There are three phases in the secretion of gastric acidwhich increase the secretion rate

in order to digest a meal:

The cephalic phase: Thirty percent of the total gastric acid secretions to be produced is

stimulated by anticipation of eating and the smell or taste of food. This signalling occurs

from higher centres in the brain through the vagus nerve. It activates parietal cells to

release acid and ECL cells to release histamine. The vagus nerve also releases gastrinreleasing peptide onto G cells. Finally, it also inhibits somatostatin release from D cells.

The gastric phase: About fifty percent of the total acid for a meal is secreted in this

phase. Acid secretion is stimulated by distension of the stomach and by amino acids

present in the food.


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The intestinal phase: The remaining 10% of acid is secreted when chyme enters the

small intestine, and is stimulated by small intestine distension and by amino acids. The

duodenal cells release entero-oxyntin which acts on parietal cells without affecting

gastrin.

The amniotic sac(also bag of waters) is the sac in which the fetus develops in amniotes.It is a thin but tough transparent pair of membranes, which hold a developing embryo

(and later fetus) until shortly before birth. The inner membrane, the amnion, contains the

amniotic fluid and the fetus. The outer membrane, the chorion, contains the amnion

and is part of the placenta. Its wall is the amnion, the inner of the two fetal membranes.

It encloses the amniotic cavity and the embryo. The amniotic cavity contains the

amniotic fluid. On the outer side, the amniotic sac is connected to the yolk sac, to the

allantois and, through the umbilical cord, to the placenta. Amniocentesis is a medical

procedure where fluid from the sac is sampled[9] to be used in prenatal diagnosis of

chromosomal abnormalities and fetal infections. If, after birth, the complete amniotic

sac or big parts of the membrane remain coating the newborn, this is called a caul.

When seen in the light, the amniotic sac is shiny and very smooth, but tough. Once thebaby is pushed out of the mother's abdomen, the umbilical cord, placenta, and

amniotic sac are pushed out in the after birth.

The aqueous humouris a transparent, gelatinous fluid similar to plasma, but containing

low protein concentrations. It is secreted from the ciliary epithelium, a structure

supporting the lens.[1] It is located in the anterior and posterior chambers of the eye,

the space between the lens and the cornea. It is not to be confused with vitreous

humour, which is contained within the larger cavity of the eye behind the lens.

Composition

Amino acids: transported by ciliary muscles

98% water

Electrolytes

Ascorbic acid

Glutathione

Function

Maintains the intraocular pressure and inflates the globe of the eye.

Provides nutrition (e.g. amino acids and glucose) for the avascular ocular tissues;

posterior cornea, trabecular meshwork, lens, and anterior vitreous. May serve to transport ascorbate in the anterior segment to act as an

antioxidant agent.

Presence of immunoglobulins indicate a role in immune response to defend

against pathogens.

Provides inflation for expansion of the cornea and thus increased protection

against dust, wind, pollen grains and some pathogens.


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Bile or gallis a bitter-tasting, dark green to yellowish brown fluid, produced by the liver

of most vertebrates, that aids the digestion of lipids in the small intestine. In humans, bile

is produced continuously by the liver (liver bile), stored and concentrated in the

gallbladder (gallbladder bile) and when the organism eats, is discharged into the

duodenum. The composition of gallbladder bile is 92% water, 6% bile salts, 0.3% bilirubin,

0.9-2.4% fats (Cholesterol, fatty acids and lecithin), and 200 mEq/L inorganic salts.

Physiological functions

Bile acts to some extent as a surfactant, helping to emulsify the lipids in food. Bile salt

anions are hydrophilic on one side and hydrophobic on the other side; consequently,

they tend to aggregate around droplets of lipids (triglycerides and phospholipids) to

form micelles, with the hydrophobic sides towards the fat and hydrophilic sides facing

outwards. The hydrophilic sides are negatively charged, and this charge prevents fat

droplets coated with bile from re-aggregating into larger fat particles. Ordinarily, the

micelles in the duodenum have a diameter of around 1433 m.

The dispersion of food fat into micelles thus provides a greatly increased surface area

for the action of the enzyme pancreatic lipase, which actually digests the triglycerides,

and is able to reach the fatty core through gaps between the bile salts. A triglyceride is

broken down into two fatty acids and a monoglyceride, which are absorbed by the villi

on the intestine walls. After being transferred across the intestinal membrane, the fatty

acids reform into triglycerides, before being absorbed into the lymphatic system

through lacteals. Without bile salts, most of the lipids in food would be excreted in feces,

undigested.

Since bile increases the absorption of fats, it is an important part of the absorption of

the fat-soluble substances, such as the vitamins A, D, E and K.

Besides its digestive function, bile serves also as the route of excretion for bilirubin, a

byproduct of red blood cells recycled by the liver. Bilirubin derives from hemoglobin by

glucuronidation.

Bile is alkaline and also has the function of neutralizing any excess stomach acid before

it enters the duodenum, the first section of the small intestine. Bile salts also act as

bactericides, destroying many of the microbes that may be present in the food.

Chymeis the semifluid mass of partly digested food expelled by the stomach into theduodenum.

Also known as "chymus", it is the liquid substance found in the stomach before passing

through the pyloric valve and entering the duodenum. It results from the mechanical

and chemical breakdown of a bolus and consists of partially digested food, water,

hydrochloric acid, and various digestive enzymes. Chyme slowly passes through the

pyloric sphincter and into the duodenum, where the extraction of nutrients begins.


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Depending on the quantity and contents of the meal, the stomach will digest the food

into chyme in anywhere between 40 minutes to a few hours.

With a pH of around 2, chyme emerging from the stomach is very acidic. To raise its pH,

the duodenum secretes a hormone, cholecystokinin (CCK), which causes the gall

bladder to contract, releasing alkaline bile into the duodenum. The duodenum alsoproduces the hormone secretin to stimulate the pancreatic secretion of large amounts

of sodium bicarbonate, which raises the chyme's pH to 7 before it reaches the jejunum.

As it is protected by a thick layer of mucus and utilizes the neutralizing actions of the

sodium bicarbonate and bile, the duodenum is not as sensitive to highly acidic chyme

as the rest of the small intestine.

At a pH of 7, the enzymes that were present from the stomach are no longer active. This

then leads into the further breakdown of the nutrients still present by anaerobic

bacteria which at the same time help to package the remains. These bacteria also

help synthesize vitamin B and vitamin K.

Breast milkis the milk produced by the breasts (or mammary glands) of a human

female for her infant offspring. Milk is the primary source of nutrition for newborns before

they are able to eat and digest other foods; older infants and toddlers may continue to

be breastfed, either exclusively or in combination with other foods.

Production

Under the influence of the hormones prolactin and oxytocin, women produce milk after

childbirth to feed the baby. The initial milk produced is referred to as colostrum, which is

high in the immunoglobulin IgA, which coats the gastrointestinal tract. This helps to

protect the newborn until its own immune system is functioning properly. It also creates

a mild laxative effect, expelling meconium and helping to prevent the build-up of

bilirubin (a contributory factor in jaundice).

Actual inability to produce enough milk is rare, with studies showing that mothers from

developing countries experiencing nutritional hardship still produce amounts of milk of

similar quality to that of mothers in developed countries. There are many reasons a

mother may not produce enough breast milk. Some of the most common reasons are

an improper latch (i.e., the baby does not connect efficiently with the nipple), not

nursing or pumping enough to meet supply, certain medications (including estrogen-

containing hormonal contraceptives), illness, and dehydration. A rarer reason is

Sheehan's syndrome, also known as postpartum hypopituitarism, which is associated

with prolactin deficiency: This syndrome may require hormone replacement.

The amount of milk produced depends on how often the mother is nursing and/or

pumping; the more the mother nurses her baby, or pumps, the more milk is produced. It

is very helpful to nurse on demand - to nurse when the baby wants to nurse rather than

on a schedule. If pumping, it is helpful to have an electric high-grade pump so that all

of the milk ducts are stimulated. Galactagogues increase milk supply, although there

are risks for even herbal ones, therefore non-pharmaceutical methods should be tried

first.


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Perspiration (sweating, transpiration, or diaphoresis)is the production of fluids secreted

by the sweat glands in the skin of mammals.

Two types of sweat glands can be found in humans: eccrine glands and apocrine

glands. The eccrine sweat glands are distributed over much of the body.

In humans, sweating is primarily a means of thermoregulation which is achieved by the

water-rich secretion of the eccrine glands. Maximum sweat rates of an adult can be up

to 2-4 liters per hour or 10-14 liters per day (10-15 g/minm), but is less in children prior to

puberty. Evaporation of sweat from the skin surface has a cooling effect due to

evaporative cooling. Hence, in hot weather, or when the individual's muscles heat up

due to exertion, more sweat is produced. Animals with few sweat glands, such as dogs,

accomplish similar temperature regulation results by panting, which evaporates water

from the moist lining of the oral cavity and pharynx.

Primates and horses have armpits that sweat like those of humans. Although sweating is

found in a wide variety of mammals, relatively few, such as humans and horses,

produce large amounts of sweat in order to cool down.

Mechanism

Sweating allows the body to regulate its temperature. Sweating is controlled from a

center in the preoptic and anterior regions of the brain's hypothalamus, where

thermosensitive neurons are located. The heat-regulatory function of the hypothalamus

is also affected by inputs from temperature receptors in the skin. High skin temperature

reduces the hypothalamic set point for sweating and increases the gain of the

hypothalamic feedback system in response to variations in core temperature. Overall,

however, the sweating response to a rise in hypothalamic ('core') temperature is much

larger than the response to the same increase in average skin temperature.

Sweating causes a decrease in core temperature through evaporative cooling at the

skin surface. As high energy molecules evaporate from the skin, releasing energy

absorbed from the body, the skin and superficial vessels decrease in temperature.

Cooled venous blood then returns to the body's core and counteracts rising core

temperatures.

There are two situations in which the nerves will stimulate the sweat glands, causing

perspiration: during physical heat and during emotional stress. In general, emotionally

induced sweating is restricted to palms, soles, armpits, and sometimes the forehead,

while physical heat-induced sweating occurs throughout the body.

People have an average of two to four million sweat glands. But how much sweat is

released by each gland is determined by many factors, including gender, genetics,

environmental conditions, age or fitness level. Two of the major contributors to sweat

rate are an individual's fitness level and weight. If an individual weighs more, sweat rate

is likely to increase because the body must exert more energy to function and there is

more body mass to cool down. On the other hand, a fit person will start sweating earlier


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and easier. As someone becomes fit, the body becomes more efficient at regulating

the body's temperature and sweat glands adapt along with the body's other systems.

Sweat is not pure water; it always contains a small amount (0.21%) of solute. When a

person moves from a cold climate to a hot climate, adaptive changes occur in the

sweating mechanisms of the person. This process is referred to as acclimatisation: themaximum rate of sweating increases and its solute composition decreases. The volume

of water lost in sweat daily is highly variable, ranging from 100 to 8,000 mL/day. The

solute loss can be as much as 350 mmol/day (or 90 mmol/day acclimatised) of sodium

under the most extreme conditions. During average intensity exercise, sweat losses can

average up to 2 litres of water/hour. In a cool climate and in the absence of exercise,

sodium loss can be very low (less than 5 mmols/day). Sodium concentration in sweat is

30-65 mmol/l, depending on the degree of acclimatisation.

Composition

Sweat contains mainly water. It also contains minerals, lactate, and urea. Mineral

composition varies with the individual, their acclimatisation to heat, exercise and

sweating, the particular stress source (sauna, etc.), the duration of sweating, and thecomposition of minerals in the body. An indication of the minerals content is sodium (0.9

gram/liter), potassium (0.2 g/l), calcium (0.015 g/l), magnesium (0.0013 g/l).[12] Also

many other trace elements are excreted in sweat, again an indication of their

concentration is (although measurements can vary fifteenfold) zinc (0.4 mill igrams/liter),

copper (0.30.8 mg/l), iron (1 mg/l), chromium (0.1 mg/l), nickel (0.05 mg/l), lead (0.05

mg/l).[13][14] Probably many other less-abundant trace minerals leave the body

through sweating with correspondingly lower concentrations. Some exogenous organic

compounds make their way into sweat as exemplified by an unidentified odiferous

"maple syrup" scented compound in several of the species in the mushroom genus

Lactarius.[15] In humans, sweat is hypoosmotic relative to plasma [16] (i.e. less salty).

Sweat typically is found at moderately acidic to neutral pH levels, typically between 4.5and 7.0.

Urineis a liquid by-product of the body secreted by the kidneys through a process

called urination and excreted through the urethra. Cellular metabolism generates

numerous by-products, many rich in nitrogen, that require clearance from the

bloodstream. These by-products are eventually expelled from the body during

urination, the primary method for excreting water-soluble chemicals from the body.

These chemicals can be detected and analyzed by urinalysis. Certain disease

conditions can result in pathogen-contaminated urine.

PhysiologyMost animals have excretory systems for elimination of soluble toxic wastes. In humans,

soluble wastes are excreted primarily by the urinary system and, to a lesser extent in

terms of urea removed, by perspiration. The urinary system consists of the kidneys,

ureters, urinary bladder, and urethra. The system produces urine by a process of

filtration, reabsorption, and tubular secretion. The kidneys extract the soluble wastes

from the bloodstream, as well as excess water, sugars, and a variety of other

compounds. The resulting urine contains high concentrations of urea and other


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substances, including toxins. Urine flows from the kidney through the ureter, bladder,

and finally the urethra before passing from the body.

Composition

Exhaustive detailed description of the composition of human urine can be found in

NASA Contractor Report No. NASA CR-1802, D. F. Putnam, July 1971. That report

provided detailed chemical analyses for inorganic and organic constituents, methods

of analysis, chemical and physical properties and its behavior during concentrative

processes such as evaporation, distillation and other physiochemical operations. Urine is

an aqueous solution of greater than 95% water, with the remaining constituents, in order

of decreasing concentration urea 9.3 g/L, chloride 1.87 g/L, sodium 1.17 g/L, potassium

0.750 g/L, creatinine 0.670 g/L and other dissolved ions, inorganic and organic

compounds.

Urine is sterile until it reaches the urethra, where epithelial cells lining the urethra are

colonized by facultatively anaerobic Gram negative rods and cocci. Current research

suggests urine is not even sterile in the bladder. Regardless, subsequent to elimination

from the body, urine can acquire strong odors due to bacterial action,[citation

needed] and in particular the release of ammonia from the breakdown of urea.Some diseases alter the quantity and consistency of urine, such as diabetes introducing

sugar. Consuming beets can result in beeturia (pink/red urine containing betanin) for

some 1014% of the population.

Chemical analysis

Urine is principally water. It also contains an assortment of inorganic salts and organic

compounds, including proteins, hormones, and a wide range of metabolites, varying by

what is introduced into the body.

Color

Urine varies in appearance, depending principally upon a body's level of hydration, aswell as other factors. Normal urine is a transparent solution ranging from colorless to

amber but is usually a pale yellow. In the urine of a healthy individual the color comes

primarily from the presence of urobilin. Urobilin in turn is a final waste product resulting

from the breakdown of heme from hemoglobin during the destruction of aging blood

cells.

Colorless urine indicates over-hydration, generally preferable to dehydration (though it

can remove essential salts from the body). Colorless urine in drug tests can suggest an

attempt to avoid detection of illicit drugs in the bloodstream through over-hydration.

Dark yellow urine is often indicative of dehydration.

Yellowing/light orange may be caused by removal of excess B vitamins from the

bloodstream.Certain medications such as rifampin and phenazopyridine can cause orange urine.

Bloody urine is termed hematuria, a symptom of a wide variety of medical conditions.

Dark orange to brown urine can be a symptom of jaundice, rhabdomyolysis, or Gilbert's

syndrome.

Black or dark-colored urine is referred to as melanuria and may be caused by a

melanoma.

Pinkish urine can result from the consumption of beets.

Greenish urine can result from the consumption of asparagus.


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Reddish or brown urine may be caused by porphyria (not to be confused with the

harmless, temporary pink or reddish tint caused by beeturia).

Blue urine can be caused by the ingestion of methylene blue (e.g., in medications).

Blue urine stains can be caused by blue diaper syndrome.

Purple urine may be due to purple urine bag syndrome.

Odor

The odor of normal human urine can reflect what has been consumed or specific

diseases. For example, an individual with diabetes mellitus may present a sweetened

urine odor. This can be due to kidney diseases as well, such as kidney stones.

Eating asparagus can cause a strong odor reminiscent of the vegetable caused by the

body's breakdown of asparagusic acid. Likewise consumption of saffron, alcohol,

coffee, tuna fish, and onion can result in telltale scents.[citation needed] Particularly

spicy foods can have a similar effect, as their compounds pass through the kidneys

without being fully broken down before exiting the body.

Turbidity

Turbid (cloudy) urine may be a symptom of a bacterial infection, but can also becaused by crystallization of salts such as calcium phosphate.

pH

The pH of urine can vary between 4.6 and 8, with neutral (7) being norm. In persons with

hyperuricosuria, acidic urine can contribute to the formation of stones of uric acid in

the kidneys, ureters, or bladder. Urine pH can be monitored by a physician[12] or at

home.

A diet high in citrus, vegetables, or dairy can increase urine pH (more basic). Some

drugs also can increase urine pH, including acetazolamide, potassium citrate, and

sodium bicarbonate.[citation needed]

A diet high in meat can decrease urine pH (more acidic).[citation needed]Cranberries, popularly thought to decrease the pH of urine, have actually been shown

not to acidify urine. Drugs that can decrease urine pH include ammonium chloride,

chlorothiazide diuretics, and methenamine mandelate.

Volume

Average urine production in adult humans is about 12 L per day, depending on state

of hydration, activity level, environmental factors, weight, and the individual's health.

Producing too much or too little urine needs medical attention. Polyuria is a condition of

excessive production of urine (> 2.5 L/day), oliguria when < 400 mL are produced, and

anuria one of < 100 mL per day.

Density or specific gravityNormal urine density or specific gravity values vary between 1.0031.035 (gcm3),and

any deviations may be associated with urinary disorders.

Synovial fluid is a viscous, non-Newtonian fluid found in the cavities of synovial joints.

With its yolk-like consistency ("synovial" partially derives from ovum, Latin for egg), the

principal role of synovial fluid is to reduce friction between the articular cartilage of

synovial joints during movement.


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Structure

The inner membrane of synovial joints is called the synovial membrane and secretes

synovial fluid into the joint cavity. The fluid contains hyaluronic acid secreted by

fibroblast-like cells in the synovial membrane and interstitial fluid filtered from the blood

plasma. This fluid forms a thin layer (roughly 50 m) at the surface of cartilage and also

seeps into microcavities and irregularities in the articular cartilage surface, filling all

empty space.[2] The fluid in articular cartilage effectively serves as a synovial fluid

reserve. During movement, the synovial fluid held in the cartilage is squeezed out

mechanically to maintain a layer of fluid on the cartilage surface (so-called weeping

lubrication). The functions of the synovial fluid include:

reduction of frictionsynovial fluid lubricates the articulating joints

shock absorptionas a dilatant fluid, synovial fluid is characterized by the rare quality

of becoming more viscous under applied pressure; the synovial fluid in diarthrotic joints

becomes thick the moment shear is applied in order to protect the joint and

subsequently, thins to normal viscosity instantaneously to resume its lubricating function

between shocks

nutrient and waste transportationthe fluid supplies oxygen and nutrients and

removes carbon dioxide and metabolic wastes from the chondrocytes within the

surrounding cartilage.

Composition

Synovial tissue is sterile and composed of vascularized connective tissue that lacks a

basement membrane. Two cell types (type A and type B) are present: Type A is derived

from blood monocytes, and it removes the wear-and-tear debris from the synovial fluid.

Type B produces synovial fluid. Synovial fluid is made of hyaluronic acid and lubricin,

proteinases, and collagenases. Synovial fluid exhibits non-Newtonian flowcharacteristics; the viscosity coefficient is not a constant and the fluid is not linearly

viscous. Synovial fluid has thixotropic characteristics; viscosity decreases and the fluid

thins over a period of continued stress.

Normal synovial fluid contains 34 mg/ml hyaluronan (hyaluronic acid), a polymer of

disaccharides composed of D-glucuronic acid and D-N-acetylglucosamine joined by

alternating beta-1,4 and beta-1,3 glycosidic bonds. Hyaluronan is synthesized by the

synovial membrane and secreted into the joint cavity to increase the viscosity and

elasticity of articular cartilages and to lubricate the surfaces between synovium and

cartilage.

Synovial fluid contains lubricin (also known as PRG4) as a second lubricating

component, secreted by synovial fibroblasts. Chiefly, it is responsible for so-called

boundary-layer lubrication, which reduces friction between opposing surfaces of

cartilage. There also is some evidence that it helps regulate synovial cell growth.

It also contains phagocytic cells that remove microbes and the debris that results from

normal wear and tear in the joint.


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Salivais a watery substance located in the mouths of animals, secreted by the salivary

glands. Human saliva is 99.5% water, while the other 0.5% consists of electrolytes, mucus,

glycoproteins, enzymes, and antibacterial compounds such as secretory IgA and

lysozyme. The enzymes found in saliva are essential in beginning the process ofdigestion of dietary starches and fats. These enzymes also play a role in breaking down

food particles entrapped within dental crevices, protecting teeth from bacterial decay.

Furthermore, saliva serves a lubricative function, wetting food and permitting the

initiation of swallowing, and protecting the mucosal surfaces of the oral cavity from

desiccation.

Various species have special uses for saliva that go beyond predigestion. Some swifts

use their gummy saliva to build nests. Aerodramus nests are prized for use in bird's nest

soup. Cobras, vipers, and certain other members of the venom clade hunt with

venomous saliva injected by fangs. Some arthropods, such as spiders and caterpillars,

create thread from salivary glands.

Functions

Saliva contributes to the digestion of food and to the maintenance of oral hygiene.

Without normal salivary function the frequency of dental carries, gum disease

(gingivitis), and other oral problems increases significantly.

1.

Lubricant

Saliva coats the oral mucosa, mechanically protecting it from trauma during

eating, swallowing and speaking. In persons with little saliva (xerostomia),

soreness of the mouth is very common, and the food (especially dry food) sticks

to the inside of the mouth.

2.

Digestion

The digestive functions of saliva include moistening food and helping to create a

food bolus. This lubricative function of saliva allows the food bolus to be passed

easily from the mouth into the esophagus. Saliva contains the enzyme amylase,

also called ptyalin, which is capable of breaking down starch into simpler sugars

such as maltose and dextrin that can be further broken down in the small

intestine. Only about 30% starch digestion takes place in the mouth cavity.

Salivary glands also secrete salivary lipase (a more potent form of lipase) to

begin fat digestion. Salivary lipase plays a large role in fat digestion in newborn

infants as their pancreatic lipase still needs some time to develop.

3. Antimicrobial function

Saliva has both a mechanical cleansing action and a specific (immunoglobulins,

e.g. IgA) and non-specific immunologic action (e.g. lysozyme, lactoferrin and

myeloperoxidase). These factors control the micro-organisms that survive in the

mouth. It also has a protective function, helping to prevent dental plaque build-


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up on the teeth and washing away adhered food particles. Saliva is also key in

preventing ascending infections of the salivary glands (e.g. parotitis).

4.

Ion reservoir, buffer function

Saliva is supersaturated with various ions. Certain salivary proteins prevents

precipitation, which would form salts. These ions act as a buffer, keeping the

acidity of the mouth within a certain range, typically pH 6.27.4. This prevents

minerals in the dental hard tissues from dissolving.

5.

Hormonal function

Saliva secretes carbonic anhydrase (gustin), which is thought to play a role in the

development of taste buds.

6. Role in taste

Saliva is very important in the sense of taste. It is the liquid medium in which

chemicals are carried to taste receptor cells (mostly associated with lingual

papillae). Persons with little saliva often complain of dysgeusia (i.e. disordered

taste, e.g. reduced ability to taste, or having a bad, metallic taste at all times).

7. Wound licking

A common belief is that saliva contained in the mouth has natural disinfectants,

which leads people to believe it is beneficial to "lick their wounds". Researchers

at the University of Florida at Gainesville have discovered a protein called nerve

growth factor (NGF) in the saliva of mice. Wounds doused with NGF healed

twice as fast as untreated and unlicked wounds; therefore, saliva can help to

heal wound in some species. NGF has not been found in human saliva; however,

researchers find human saliva contains such antibacterial agents as secretory

IgA, lactoferrin, lysozyme and peroxidase.[7] It has not been shown that human

licking of wounds disinfects them, but licking is likely to help clean the wound byremoving larger contaminants such as dirt and may help to directly remove

infective bodies by brushing them away. Therefore, licking would be a way of

wiping off pathogens, useful if clean water is not available to the animal or

person. The mouth of animals is the habitat of many bacteria, some pathogenic.

Some diseases, such as herpes, can be transmitted through the mouth. Animal

and human bites are routinely treated with systemic antibiotics because of the

risk of septicemia.

8. Glue to construct bird nests

Many birds in the swift family, Apodidae, produce a viscous saliva during nesting

season to glue together materials to construct a nest.[8] Two species of swifts inthe genus Aerodramus build their nests using only their saliva, the base for bird's

nest soup.

References:

Boron, Walter F. (2003). Medical Physiology: A Cellular And Molecular Approach.

Elsevier/Saunders


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Maton, Anthea (1993). Human Biology and Health. Prentice Hall. ISBN 0-13-981176-1.

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