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COMPOSITION OF THE BODY FLUIDS

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.

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COMPOSITION OF THE BODY FLUIDS

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  1. COMPOSITION OF THE BODY FLUIDS mirka.rovenska@lfmotol.cuni.cz

  2. Body fluids: • Digestive juices (saliva, gastric juice, pancreatic secretions, bile, secretions of the small intestine) • Plasma • Cerebrospinal fluid • Urine • Sweat • Tears • Amniotic fluid

  3. Compartmentalization of the body water 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...).

  4. Extra- versus intracellular fluid Important for homeostasis! Deviations of the levels are dangerous!!!

  5. Digestive juice Saliva Gastric juice Pancreatic secretion Bile Secretion of small int. Feces Composition of digestive juices

  6. 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

  7. 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)

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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)

  13. bilirubin glycine cholic acid intestinal bacteria glycocholic acid lecithin = phosphatidylcholin

  14. 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

  15. 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.

  16. 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)

  17. 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 (lactatedehydrogenase) • 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

  18. 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

  19. Plasma composition

  20. 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

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