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Alimentary Digestion

  • Definition: The process whereby complex biomolecules in food are broken down into simpler substances useful to the body.

  • Role of Digestive Enzymes: The breakdown of food is facilitated by hydrolytic enzymes, which catalyze the hydrolysis of:

    • Proteins → Amino Acids

    • Starches → Monosaccharides

    • Fats → Acyl Glycerols

Saliva

  • Overview: A watery secretion produced by three pairs of large salivary glands and numerous minor buccal glands in the mouth.

  • Functions:

    • Speeds up chemical changes in carbohydrates of ingested materials.

    • Has no chemical effect on proteins and fats.

  • Composition:

    1. Water: Over 99% of saliva.

    2. Salivary Amylase/Ptyalin: Hydrolyzes starch to maltose.

    3. Mineral Salts: Help maintain saliva pH of 6.5 - 7.5, optimum for amylase activity (approx. pH 8).

    4. Mucin: A sticky glycoprotein that binds food particles and lubricates them for swallowing.

    5. pH and Enzyme Activity: Salivary amylase effective at 6.5 - 7.5, inactive in the acidic stomach (pH 1.0 - 3.5).

Mucin

  • Characteristics: Sticky glycoprotein, increases saliva viscosity.

  • Test for Mucin: Precipitated from saliva using dilute acetic acid.

Proteins (Biuret Test)

  • Positive result indicated by violet coloration when reacted with alkaline CuSO4.

  • Formation of Biuret complex with two CONH bonds.

Inorganic Matter

Calcium in Saliva

  • Importance: Stabilizes the conformation of salivary amylase, maintaining its enzymatically active state.

Thiocyanate

  • Definition: Metabolite of cyanide detoxification, produced via rhodanase.

  • Test (FeCl Test): Everyone has thiocyanates in saliva.

  • Sources: Smoking, foods containing cyanide.

Digestion of Starch

  • Overview: Starch forms a violet complex with iodine due to helical structure of amylose or amylopectin.

  • Salivary digestion breaks starch into smaller saccharides, preventing further violet complex formation.

Achromic Point

  • Definition: Point where the reaction no longer changes color with iodine, indicating starch breakdown into dextrins and monosaccharides.

  • Chloride ion enhances salivary amylase activity.

Salivary Amylase

  • Function: Cleaves α-1,4 linkages in starch.

  • Color reactions with iodine:

    1. Amylodextrin: Purple

    2. Erythrodextrin: Red

    3. Achroodextrin: Colorless

    4. Maltose: Colorless

Phenylhydrazine Reaction

  • Produce Osazone crystals from monosaccharides after starch digestion.

Benedict's Test

  • Function: Tests for reducing sugars; positive test shows color change from green to red ppt.

  • Negative result for sucrose.

Intestinal Digestion

Small Intestine

  • Key Area: Duodenum, where pancreatic juice, intestinal juice, and bile enter.

Trypsin

  • Function: Hydrolyzes peptide linkages involving arginine and lysine; optimal between pH 7 to 9.

  • Active form: Trypsinogen, activated by enteropeptidase.

Effect of Temperature on Trypsin

  • Optimal temperature: 40°C; higher temperatures lead to denaturation, lower temperatures decrease activity.

Lipase

  • Function: Catalyzes hydrolysis of fats, including triglycerides, cholesterol, and phospholipids.

  • Optimal temperature: 37°C; similar temperature effects as trypsin.

Pancreatin

  • Definition: Commercial enzyme mixture (amylase, lipase, protease); used for digestive issues.

Bile Salt

  • Role: Emulsifies lipids, increasing surface area for hydrolysis and enhancing lipase efficiency.

  • Activity is temperature dependent; lower temperatures reduce lipase activity.

Urine Color and Constituents

  • Normal color: Yellow to amber, due to urobilin; abnormal colors indicate health issues or conditions.

  • Transparency: Cloudy urine signals possible infection or metabolites.

Urine Specific Gravity

  • Less than 1.015: Indicates excessive fluid intake or kidney issues.

  • More than 1.025: Suggests water retention or dehydration.

  • Normal volume: 0.5 - 1.5 L/day; affected by lipid intake and water loss.

Uric Acid

  • End product of purine metabolism; elevated levels indicate gout.

  • Normal excretion: 0.5 - 1.0 g/hr.

Creatinine

  • Normal excretion: 1.2 - 1.7 g/hr.; depends on muscle development and diet.

Nitroprusside/Weyl's Test (Creatinine)

  • Indication of presence of cystine in urine; contraindicated in renal failure.

Picric Acid Test

  • Positive test indicated by deep orange red solution; assesses presence of sugar/creatinine.

Indican

  • Potassium indoxyl sulfate; oxidized to indigo blue.

  • Obermeyer’s Test: Tests for intestinal putrefaction, positive result shows greenish-blue chloroform layer.

Pathological Organic Constituents

  • Albumin: Albuminuria indicates kidney damage; checked by protein precipitation with HNO3.

  • Sugar: Glycosuria indicates glucose presence; occurs in high sugar intake or diabetes.

  • Bile Pigments: Urobilinogen and bilirubin in urine used for liver function assessment.

Gmelin's Test

  • Qualitative test for bilirubin; colored rings indicate the presence of bile pigments, revealing liver conditions.

Ketone Bodies

  • Produced from fat metabolism; ketonuria indicates excessive ketone excretion, correlated with incomplete fat oxidation.