COMPOSITION
OF THE BODY FLUIDS
mirka.rovenska@lfmotol.cuni.cz
Body fluids:
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Digestive juices (saliva, gastric juice, pancreatic secretions,
bile, secretions of the small intestine)
Plasma
Cerebrospinal fluid
Urine
Sweat
Tears
Amniotic fluid
Compartmentalization of the
body water
H2O [l]
H2O [% of body
weight]
H2O [portion of
total body water]
Intracelullar fluid
28
40
~ 2/3
Extracellular fluid
14
20
~ 1/3
- interstitial fluid
11
16
26 %
- intravasal fluid:
plasma, lymph
3–4
5
7%
1-2
2
2%
42
60
Compartment
- transcellular fluid
Total
Note: transcellular fluid includes pleural, peritoneal, and cerebrospinal fluid, fluid in the
urinary tract, and in the lumen of GIT. Under pathological conditions, originally small
amount of water can increase several folds (e.g. ascites...).
Extra- versus intracellular fluid
Important for homeostasis!
Deviations of the levels are dangerous!!!
Composition of digestive juices
Digestive juice
Saliva
Gastric juice
Pancreatic secretion
Bile
Secretion of small int.
Feces
Saliva
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Function: initiation of food digestion; excretion of certain drugs
(morphine) and inorganic substances (I, Hg, Pb)
99,5% water; the rest consists of:
inorganic salts (1/3): chlorides, phosphates, bicarbonate, sodium,
potassium
org. compounds (2/3):
 glycoproteins (mucins) acting as lubricants facilitating mastication
and swallowing; have a high content of O-linked (to Ser, Thr)
oligosaccharides, usually containing NeuAc, GalNAc
 antibodies – secretory IgA
 enzymes
Enzymes in saliva
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-amylase: partial hydrolysis of starch and glycogen, yielding maltose,
maltotriose, and (1-6)-oligosaccharides – dextrines;
in saliva not very significant (rapid inactivation of the enzyme in stomach)
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lysozyme – hydrolyzes the glycosidic bonds in peptidoglycan of bacterial
cell walls (and thus helps to fight bacteria)
Gastric juice
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Water – 99,4%; inorganic salts (chlorides)
HCl – creates the acid environment (pH~1-2 in adults), denatures proteins
(making them more susceptible to proteolysis), and kills bacteria
Mucins – form mucus which protects the stomach from the gastric juice
Peptides: gastrin – produced by G-cells of the stomach, stimulates
secretion of HCl and pepsinogen
Proteins:
 albumin, IgA, amylase from saliva (denaturated)
 intrinsic factor (glycoprotein secreted by parietal cells of the gastric
mucosa, binds vitamin B12 and facilitates its absorption in the ileum)
 proenzymes (zymogens)
Protein concentration – low (<50mg/ml); the amount of albumin is
elevated in gastropathies
Enzymes of the gastric juice
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Pepsin:
 inactive zymogen pepsinogen is activated to pepsin by H+ which is
followed by rapid autocatalysis;
 pH optimum ~1-3
 endopeptidase – cleaves proteins into polypeptide fragments,
mainly between Tyr/Phe and Glu/Asp…most important digestive
process in stomach
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Acid-stable lipase – cleaves triacylglycerols, yielding fatty acids and
1,2-diacylglycerols
Pancreatic secretion
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Alkaline (pH = 7,5-8,9), together with the bile and secretion of the
intestine neutralizes HCl from the stomach
HCO3- concentration is higher than in plasma
Contains various enzymes participating in cleavage of high-molecular
dietary constituents; many of these enzymes are secreted as zymogens:
 trypsinogen – activated to trypsin by enterokinase; then trypsin itself
activates other zymogens:
 chymotrypsinogen, proelastase, procarboxypeptidase
Enzymes of the pancreatic juice
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Endopeptidases: trypsin, chymotrypsin, elastase; cleave proteins/polypeptides into oligopeptides
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Exopeptidases – carboxypeptidases: cleave off amino acids from the
C-terminus of oligopeptides
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Endoglycosidases: -amylase
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RNAses (ribonucleases),DNAses (deoxyribonucleases)
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Pancreatic lipase – hydrolyzes triacylglycerols in the presence of the bile
salts, phospholipids (emulsification), colipase and phospholipase A2.
Products: mixture of 2-monoacylglycerols, FAs, and glycerol
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Cholesterol esterase – hydrolysis of cholesteryl esters
Bile
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Water: 96-98%
Inorganic salts
Bile salts (acids): e.g. cholic acid, deoxycholic acid; may be conjugated
with glycine or taurine
Bile pigments: bilirubin and products of its conversion: urobilinogen,
urobilin, sterkobilin
Cholesterol
Phospholipids – lecithin
Roles of the bile:
 bile acids facilitate absorption of the products of lipid digestion (FAs,
monoacylglycerols) and of the compounds dissolved in lipids, such as
vitamins A, K
 neutralization of chyme (HCO3-)
 excretion of cholesterol, bile pigments, drugs, inorganic substances
(Cu, Zn, Hg)
cholic acid
glycine
bilirubin
intestinal bacteria
glycocholic acid
lecithin = phosphatidylcholin
Secretion of the small intestine
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Water, inorganic compounds – NaHCO3
Mucus – formed by mucins, protects the intestinal epithelium
Cholecystokinin, secretin – peptides secreted by the cells of the small
intestine: cholecystokinin stimulates the secretion of pancreatic juice rich
in enzymes, secretin of that rich in NaHCO3
Enzymes – mainly anchored in the intestinal surface:
 disaccharidases, oligosaccharidases (maltase, sucrase, lactase)
 aminopeptidases and dipeptidases – cleave oligopeptides produced by
the action of endopeptidases and carboxypeptidases
 polynucleotidases – cleave the polynucleotide chain into nucleotides
 phosphatases – remove phosphate from organic phosphates
(glycerolphosphate) and nucleotides
 nucleosidases – phosphorolysis of nucleosides to bases and pentose
phosphates
Amniotic fluid
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In early embryogenesis, the composition is being influenced by free
transport of compounds between the foetus (extracellular fluid) and AF
(before keratinisation of the skin occurs around 25th week)
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Two major sources of AF in the second half of gestation:
 fetal urine (first enters the amniotic space around the 10th week)
 secretion of fetal lungs
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As the foetus grows, the volume of AF rises (up to ~800 ml around the 35th
week)
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Conc. of cations (Na+, K+, Mg2+) is slightly lower than in maternal serum,
conc. of Cl- is similar, conc. of glucose, triacylglycerols, and total protein is
significantly lower. On the other hand, conc. of urea, creatinine, and uric
acid is higher than in maternal serum. As a result, osmolality of AF is lower.
Proteins of the amniotic fluid
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Mainly those of low molecular weight
Albumin
Cytokines, growth factors (?regulation of foetal development?)
Foetus itself produces -fetoprotein (AFP): its conc. rises until the 15th
week, then drops down (in AF). AFP level (determined in maternal
serum) is increased in neural tube defects; decreased levels may indicate
the Down's syndrome
Immunoglobulins (IgA, IgG, IgM)
Surfactants
Enzymes (acetylcholinesterase, -glutamyltransferase) – determination of
activity in AChE can be used in diagnosis of developmental defects
(e.g.: AChE activity rises in neural tube defects but not in the Down's
syndrome)
Cerebrospinal fluid
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Isosmotic, but concentrations of particular ions differ from that found in
plasma (lower conc. of Na+,K+, Ca2+, HCO3- x higher conc. of Mg2+, Cl-)
Total protein conc. is ~200-fold lower than in plasma; low amount of cells
pH = 7,35-7,40
Metabolites: glucose (lower than in serum), lactate (higher), urea
Proteins: albumin, immunoglobulins, enzymes (lactate dehydrogenase)
The levels of these compounds change under pathological conditions:
 total protein conc. changes in bacterial meningitis, brain tumours
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Increased level of τ-protein indicates the Alzheimer's disease
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Function: mechanic protection of CNS, protection against pathogens,
removal of waste products, delivery of nutrients
Plasma, blood
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Plasma = liquid medium for blood cells
Serum, despite plasma, lacks the clotting factors
pH of plasma = 7,40, pH of the blood = 7,36 – 7,44
Composition of plasma:
 water (90-92%)
 electrolytes – compared to cytoplasm of cells, plasma contains higher
conc. of Na+, Ca2+, and Cl- and lower conc. of K+, Mg2+, phosphates,
and proteins
 metabolites, nutrients, hormones, vitamins
 plasma proteins
Plasma composition
Functions of blood/plasma
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Respiration – transport of O2 and CO2
Nutrition – transport of absorbed food materials
Excretion – transport of metabolic waste to the kidneys, lungs, skin,
intestines
Maintenance of acid-base balance
Regulation of water balance
Regulation of body temperature
Defense against infection (white blood cells, circulating antibodies)
Transport of hormones and regulation of metabolism
Transport of metabolites
Coagulation