COMPOSITION OF THE BODY FLUIDS

mirka.rovenska@lfmotol.cuni.cz

Body fluids:

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

Compartment 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 %

- transcellular fluid 1-2 2 2 %

Total 42 60

Note: transcellular fluid includes pleural, peritoneal, and cerebrospinal fluid, fluid in theurinary 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 juiceSaliva

Gastric juice

Pancreatic secretionBile

Secretion of small int.

Feces

Saliva

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

-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)

lysozyme – hydrolyzes the glycosidic bonds in peptidoglycan of bacterial cell walls (and thus helps to fight bacteria)

Gastric juice

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

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

Acid-stable lipase – cleaves triacylglycerols, yielding fatty acids and 1,2-diacylglycerols

Pancreatic secretion

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

Endopeptidases: trypsin, chymotrypsin, elastase; cleave proteins/poly-peptides into oligopeptides

Exopeptidases – carboxypeptidases: cleave off amino acids from the C-terminus of oligopeptides

Endoglycosidases: -amylase

RNAses (ribonucleases),DNAses (deoxyribonucleases)

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

Cholesterol esterase – hydrolysis of cholesteryl esters

Bile

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

glycocholic acid

bilirubin

lecithin = phosphatidylcholin

intestinal bacteria

Secretion of the small intestine

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

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)

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

As the foetus grows, the volume of AF rises (up to ~800 ml around the 35th week)

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

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

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

Increased level of τ-protein indicates the Alzheimer's disease

Function: mechanic protection of CNS, protection against pathogens, removal of waste products, delivery of nutrients

Plasma, blood

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

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