Digestive Tract and Tooth Structure

Digestive Tract

• Also called the alimentary canal
• Submucosa: Thick layer of loose connective tissue containing glands, blood vessels, lymphatic vessels, and nerves.
• Mechanical Digestion: Physical breakdown of large food pieces into smaller pieces, starting with chewing (the first phase of digestion).
• Mesenteries: Layers of visceral peritoneum that suspend digestive organs in the abdominal cavity while anchoring them loosely to the abdominal wall.
• Mouth (Buccal Cavity): Where digestion begins.
• Soft Palate: Primarily composed of skeletal muscle.
• Salivary Glands: Secrete saliva (mostly water).
• Mastication: Digestion begins when food enters the mouth and is chewed.

Tooth Structure

• Dentin: Firm, yellowish tissue forming the bulk of teeth. Dentin and cementum can be regenerated.
• Enamel: Cannot be regenerated.

Stomach

• Muscular and elastic sac, primarily for storing food.
• Chyme: Semifluid mixture leaving the stomach and entering the duodenum.
• Intrinsic Factor: Necessary for vitamin B12 absorption.
• Cephalic Phase: Stomach secretes gastric juices and gastrin in response to sight, smell, taste, or thought of food.
• Liver: Body's largest gland.
• Portal Vein: Carries nutrient-rich blood from digestive organs and spleen to the liver.

Liver and Gallbladder

• Sinusoids: Filter blood, allowing cells to remove nutrients, hormones, toxins, and drugs.
• Gallbladder: Stores and concentrates bile.
• Bilirubin: Main bile pigment resulting from hemoglobin breakdown.
• Acinar Cells: Secrete digestive enzymes in an inactive form.

Small Intestine

• Duodenum: Site of most digestive processes.
• Trypsin: Chymo breaks down into individual amino acids that are absorbed into the bloodstream
• Small Intestine: Location of most digestion and absorption.
• Amylase: Enzyme initiating carbohydrate digestion in the mouth.
• Pepsin: Enzyme initiating protein digestion in the stomach.
• Jejunum: Large folds and projections maximizing nutrient absorption surface area.
• Peyer's Patches: Clusters of lymphatic tissue throughout the ileum.

Pancreas

• Pancreatic Lipase: Main fat-digesting enzyme.

Large Intestine

• Processes remaining food and absorbs water.
• Waste material (feces) is eliminated.

Metabolism

• Nutrients transform into energy or materials usable by the body.
• Body size and composition affect calorie burning efficiency.
• Males generally burn more calories than females; muscle mass is a factor.
• Age affects metabolic rate; muscle mass declines with age.
• Leptin suppresses appetite with stored energy levels.
• Ghrelin produces hunger.

Macronutrients

• Carbohydrates: Primary energy source; complex carbohydrates are desirable.
• Disaccharides: Broken down into monosaccharides (e.g., sucrose, lactose, maltose).
• Fats: Enable vitamin absorption, contribute to structure, and insulate.
• Fat-Soluble Vitamins: Stored in the liver and fat tissues.

Micronutrients

• Vitamins and minerals are obtained by combining foods.

Protein

• Proteins are broken down into amino acids for absorption then recombined to form new proteins.
• Complete proteins contain all essential amino acids.
• Incomplete proteins lack one or more essential amino acids.

Metabolism

• Carbohydrate Metabolism: Glucose, primarily for energy, converted to glycogen or fat.
• Anaerobic Fermentation: Occurs when oxygen is low, converts pyruvic acid to lactic acid.
• Aerobic Respiration: Most efficient energy production process using oxygen.
• Protein Metabolism: Proteins may be converted to glucose, fat, or used directly as fuel.
• Negative Nitrogen Balance: Occurs when protein breakdown exceeds protein creation (e.g., during starvation).

Thermoregulation

• Heat produced by chemical reactions within cells helps regulate body temperature.

Digestion

• Emulsification: Breakdown of large fats into smaller droplets aiding digestion.
• Peptidases: Enzymes that break down peptides into individual amino acids for absorption.