Nutrients and Digestion

• Essential nutrients are crucial for survival, including oxygen, carbon, hydrogen, and nitrogen.
• Non-essential nutrients are not vital for survival.

Fat and Water Soluble Vitamins

• Fat-soluble vitamins include A, D, E, and K.
• Water-soluble vitamins are the B vitamins and vitamin C, which are eliminated through urine and sweat.

Macronutrients vs. Micronutrients

• Macronutrients (carbohydrates, proteins, fats) are needed in large quantities for energy and structure.
• Micronutrients (vitamins, minerals) are required in small amounts for physiological processes.

Dietary Categories

• Herbivores consume plants.
• Carnivores consume meat.
• Omnivores consume both plants and meat.
• Fortified foods have added nutrients.
• Digestion involves ingestion, digestion, absorption, and elimination.

Chemical vs. Mechanical Digestion

• Chemical digestion uses enzymes and chemical processes like amylase, bile, and HCl.
• Mechanical digestion physically breaks down food through chewing, etc.

Pathway of Food Through the Digestive Tract

• Begins in the mouth, moves through the oral cavity, pharynx, and esophagus, and into the stomach.
• In the stomach, food mixes with gastric juice and becomes chyme.
• Chyme then enters the small intestine (duodenum, jejunum, ileum) for chemical digestion and nutrient absorption.
• It proceeds to the large intestine (cecum, ascending, transverse, descending, sigmoid colon, rectum, anus) for water reabsorption and waste elimination.

Parts of the Digestive System

• Two categories: alimentary canal and accessory organs/glands.

Alimentary Canal

• Mouth/Oral Cavity: Functions in ingestion and initial chemical (salivary amylase) and mechanical digestion (chewing).
• Pharynx & Esophagus: Transports food via peristalsis.
• Stomach: Secretes gastric juice (mucus, HCl, pepsinogen) and churns food into chyme and has rugae and sphincters.
• Small Intestine: Duodenum (receives pancreatic enzymes and bile), jejunum, ileum, functions in most digestion and absorption through blood vessels and lacteals in villi.
• Large Intestine: Functions in reabsorption of water, houses bacteria (producing vitamin K), and stores feces.

Accessory Organs/Glands

• Liver: Produces bile for emulsifying fats, regulates nutrient distribution, and stores glycogen.
• Gallbladder: Stores and releases bile into the duodenum.
• Pancreas: Secretes digestive enzymes (amylase, lipase, proteases) and hormones (insulin and glucagon).

Feeding Mechanisms

• Examples include herbivory, omnivory, carnivory, and specialized ruminant digestion (as in cows).

Production of Gastric Juice

• Gastric glands produce mucus, HCl, pepsinogen, and pepsin.
• Mucus lubricates and protects the stomach lining.
• HCl creates a low pH (around 2) to denature proteins and activate pepsinogen.
• Pepsinogen is an inactive enzyme precursor converted into pepsin.
• Pepsin is a protease that digests proteins into polypeptides.

Stomach Secretions and Cell Types

• Mucus Cells: Secrete protective mucus.
• Chief Cells: Secrete pepsinogen and gastric lipase.
• Parietal Cells: Secrete HCl and intrinsic factor.
• Other cells include mucous neck cells (mucus and bicarbonate), enterochromaffin-like cells (histamine), D cells (somatostatin), and G cells (gastric hormone).

Enzyme Release and Breakdown

• Salivary Amylase: Converts starch into maltose.
• Pepsin: Breaks down proteins into smaller polypeptides in the stomach.
• Pancreatic Enzymes: Function in the small intestine and include amylase (carbohydrates), lipase (lipids), and proteases (proteins).
• Disaccharidases (maltase, lactase, sucrase) further digest sugars.

Structures

• Villi: Increase the small intestine’s surface area for nutrient absorption, containing blood vessels and lacteals.
• Rugae: Folds in the stomach mucosa that allow expansion and increase surface area.
• Sphincters: Muscular valves (e.g., esophageal/cardiac and pyloric sphincters) that control the passage of food between sections.

Digestion and Absorption of Fats

• Fats are emulsified into micelles by bile.
• Fatty acids are absorbed by epithelial cells and reassembled into triglycerides.
• They are then packaged with proteins in the Golgi to form chylomicrons.
• Chylomicrons enter lacteals and the lymphatic system.

Dentition and Diet

• Dentition: Refers to the structure and arrangement of teeth (incisors, canines, premolars, molars; with components like the crown, enamel, root, cementum, and dentin).
• Diet: Dentition corresponds with dietary needs (cutting, grinding) based on what is consumed.

Mutualistic Adaptations

• Humans have adaptations in dentition and enzyme secretion for an omnivorous diet.
• Herbivores often feature longer digestive tracts and mutualistic bacteria to break down plant material.

Ruminant Digestion in the Cow

• Cows have a four-chambered stomach
• They use rumination (regurgitating and re-chewing food) to ferment and digest tough plant fibers.

Appetite-Regulating Hormones

• Ghrelin: Secreted by the stomach, triggers hunger.
• Leptin: Produced by adipose tissue; suppresses appetite.
• Leptin levels fall with decreased body fat.
• PYY: Secreted by the small intestine after meals; suppresses appetite and counters ghrelin.
• Insulin helps reduce hunger by promoting glucose uptake.

Glucose Homeostasis

• Maintained through insulin and glucagon balance.
• Insulin lowers blood glucose by moving it into cells.
• Glucagon raises blood glucose by releasing it from glycogen.

Diabetes Mellitus

• Type I is insulin-dependent, with the pancreas producing little to no insulin.
• Type II is often lifestyle-related, with insulin resistance.
• Gestational diabetes occurs during pregnancy.

Macromolecules

• Carbohydrates: Monosaccharides (glucose, fructose, galactose), disaccharides (sucrose, maltose, lactose), and polysaccharides (starch, glycogen, cellulose) provide energy and structure.
• Lipids: Include fats, oils, triglycerides, phospholipids, and steroids; store energy and build cell membranes.
• Proteins: Made of amino acids that act as enzymes, structural elements, antibodies, and transporters.
• Nucleic Acids: DNA and RNA store and transmit genetic information.

Carbohydrates

• Provide quick energy and are made of carbon and water.
• Simple carbohydrates: Single sugars (monosaccharides).
• Complex carbohydrates: Multiple sugar units (polysaccharides).

Monosaccharide vs. Disaccharide

• Monosaccharide: One sugar unit (e.g., glucose, fructose, galactose).
• Disaccharide: Two monosaccharides joined together (e.g., sucrose, maltose, lactose).

Dehydration Synthesis vs. Hydrolysis

• Dehydration Synthesis: Joins two monosaccharides by removing a water molecule to create a disaccharide.
• Hydrolysis: Breaks disaccharides into monosaccharides by adding water.

Counting Carbon Atoms for Glycosidic Linkages

• 1-2 Glycosidic Linkage: Involves the 1st carbon of one sugar and the 2nd carbon of another (example: sucrose formation from glucose and fructose).
• 1-4 Glycosidic Linkage: Involves the 1st carbon of one sugar and the 4th carbon of another (example: lactose formation from galactose and glucose or maltose formation from two glucose units).

Identifying the Sugar Molecules

• Fructose: C₆H₁₂O₆, pentagon-shaped; carbons counted counter-clockwise starting at the top left.
• Glucose: C₆H₁₂O₆, hexagon-shaped; the 4th carbon has an OH on the bottom.
• Galactose: C₆H₁₂O₆, hexagon-shaped; the 4th carbon has an OH on the top.
• Maltose: Formed from two glucose molecules; enzyme: maltase.
• Sucrose: Formed from glucose and fructose; enzyme: sucrase.
• Lactose: Formed from glucose and galactose; enzyme: lactase.

Fats (Lipids)

• Composition: Glycerol molecule + 3 fatty acids yields triglycerides.
• Formation Reaction: Dehydration synthesis (removes 3 water molecules, one per fatty acid) vs. hydrolysis (adds water to break bonds).
• Fatty Acid Types:
• Saturated Fat: All carbons in the chain have only single bonds.
• Unsaturated Fat: Contains one or more double bonds.
• Trans Fatty Acids: Produced via hydrogenation, which changes the structure of the hydrocarbon chains.
• Functional Groups:
• Glycerol: Contains hydroxyl (OH) groups.
• Fatty Acids: Contain carboxyl groups.

Proteins

• Proteins are built from amino acids, joined by peptide bonds.
• Peptide bonds are formed via dehydration synthesis between the amino and carboxyl groups.
• Dipeptide: Two amino acids linked together.
• Polypeptide: Three or more amino acids linked together.
• R Group (Side Chain): The variable R group distinguishes each amino acid and determines its properties.
• Essential Amino Acids: Must be obtained from food because they can not be synthesized by the body.
• Non-Essential Amino Acids: Can be synthesized by the body.
• Main Structure + R Group: Each amino acid has a common backbone (amino group, carboxyl group, and hydrogen attached to a central carbon) plus its unique R group.
• Complete Proteins: Contain all essential amino acids (often found in animal products).
• Incomplete Proteins: Lack one or more essential amino acids (commonly found in individual vegan sources such as nuts, seeds, legumes, or grains).