Food Processing in Animals (copy)

Food Processing in Animals

Chapter Overview

  • Four Phases:

    1. Ingestion

    2. Digestion

    3. Absorption

    4. Egestion

Definitions of Phases

  1. Ingestion: Food consumption via alimentary canal and blood.

  2. Digestion: Nutrient breakdown into smaller molecules in the alimentary canal.

  3. Absorption: Ions, water, and small molecules move from alimentary canal to body fluids.

  4. Egestion: Elimination of undigested waste.

Animal Nutrition

Nutritional Requirements

  • Animals need organic (carbon-containing) and inorganic nutrients.

  • Organic Nutrients (5 categories):

    • Carbohydrates

    • Proteins

    • Lipids

    • Nucleic Acids

    • Vitamins

  • Inorganic Nutrients:

    • Water

    • Minerals

Digestive Systems Adaptation

  • Digestive systems adapt to diet:

    • Herbivores: Microorganisms aid cellulose digestion.

    • Carnivores: Consume animal flesh or fluids.

    • Omnivores: Eat both plant and animal material.

Fundamentals of Nutrients

Key Organic Molecules Required by Animals

  • Carbohydrates: Supply energy and carbon.

  • Proteins: Supply amino acids and energy.

  • Lipids: Supply membrane components, thermal insulation, and energy.

  • Nucleic Acids: Supply components for DNA, RNA, and ATP synthesis.

Essential Nutrients

Basics of Essential Nutrients

  • Compounds not synthesized by the body must be obtained through diet.

Essential Amino Acids

  • 9 Essential Amino Acids (e.g., Isoleucine, Leucine, Lysine) are needed for protein building but not synthesized by animals.

    • Sources: Meat has all 20; most plants lack sufficient amounts of all essential amino acids.

Essential Fatty Acids

  • Unsaturated fatty acids (e.g., linoleic acid) cannot be synthesized by animals, mainly found in plants. Carnivores get them from fish or adipose tissues.

Vitamins

  • Organic nutrients acting as coenzymes.

    • Water-Soluble Vitamins: (e.g., Vitamin C) not stored.

    • Fat-Soluble Vitamins: (e.g., Vitamin A) stored in adipose tissue.

  • Not all animals need the same vitamins; only primates and guinea pigs can't synthesize vitamin C.

Minerals

Function of Minerals

  • Inorganic ions vital for cell function.

  • Examples of Important Minerals:

    • Fe (Iron): Cofactor, part of hemoglobin; essential for red blood cells.

    • Zn (Zinc): Required for many enzyme functions.

    • Ca (Calcium): Bone formation, muscle, nerve signaling.

    • Na (Sodium) & K (Potassium): Maintain electrical gradients for heart, muscle, and neuronal activity.

Digestion Process

Overview of Digestion

  • Mostly extracellular.

  • Steps:

    1. Food trapped, delivered to gastrovascular cavity.

    2. Digestive enzymes break down food.

    3. Nutrients absorbed by phagocytosis into cells.

    4. Undigested waste excreted.

Vertebrate Digestive Systems

Structure of Alimentary Canal

  • Human GI tract includes: Mouth, Pharynx, Esophagus, Stomach, Intestines, Anus.

  • Accessory Structures: Salivary glands, liver, gallbladder, pancreas (not in all vertebrates).

Functional Regions of the GI

  1. Anterior End: Mouth, pharynx, esophagus (Ingestion).

  2. Middle Section: Stomach, upper small intestine (Storage, initial digestion).

  3. Posterior Section: Remainder of small intestine, large intestine (Final digestion, absorption, elimination).

Digestive Mechanisms

Mouth Functionality

  • Terrestrial vertebrates secrete saliva.

Functions of Saliva:

  • Moisten/lubricate food, dissolve for taste.

  • Kill bacteria.

  • Initiate carbohydrate digestion (amylase).

Pharynx & Esophagus

  • Pathways to storage; no digestion/absorption.

  • Swallowing: voluntary in pharynx, involuntary peristalsis in esophagus.

Crop

  • Food storage; softens food.

  • Enables regurgitation for young birds.

Stomach

  • Muscular, sac-like organ for food storage.

  • Muscular contraction breaks down food, partially digests proteins.

  • Glands secrete HCl and pepsinogen.

  • HCl converts pepsinogen to pepsin, initiating protein digestion, kills microbes, dissolves particulates.

  • Stomach epithelium protected by alkaline mucus.

  • Note: No lipid or carbohydrate digestion here; food reduced to chyme.

Ruminants Stomach

  • Multiple compartments: Rumen, Reticulum, Omasum, Abomasum (true stomach).

Small Intestine

  • Main site for food/water digestion and absorption.

  • Hydrolytic enzymes break macromolecules.

  • Digestion products absorbed into bloodstream.

  • Specializations: Villi increase surface area for absorption.

Accessory Organs

Functions and Contributions

  • As chyme enters small intestine, three organs secrete into duodenum:

    • Pancreas: Secretes digestive enzymes (lipase) and bicarbonate to neutralize chyme.

    • Liver: Produces bile (bicarbonate, cholesterol, phospholipids, bile salts) to emulsify fats.

    • Gallbladder: Stores and releases bile.

Large Intestine

  • Stores and concentrates fecal matter, absorbs remaining ions and water.

  • Defecation through muscular contractions via anus.

  • Bacteria produce vital vitamins and flatus.

Digestion Processes

Digestion of Carbohydrates

  • Polysaccharides (starch, cellulose) broken into maltose, then monosaccharides (fructose, glucose, galactose) for blood absorption.

Digestion of Proteins

  1. Trypsinogen (pancreas) converted to trypsin by enterokinase.

  2. Trypsin/other proteases cleave proteins into small polypeptides.

  3. Proteases on epithelial cells cleave polypeptides into amino acids.

  4. Amino acids absorbed via secondary active transport/facilitated diffusion into bloodstream.

Digestion of Lipids

  • Triglycerides break into 2 free fatty acids and 1 monoglyceride, forming micelles. Reconstituted into triglycerides, packaged into chylomicrons for blood absorption.

Vitamins, Minerals, and Water Absorption

  • Absorbed in complete forms, not digested.

  • Absorption Mechanisms:

    • Water-soluble vitamins: diffusion/active transport.

    • Fat-soluble vitamins (A, D, E, K): follow lipid absorption.

    • Most water absorbed in small intestine.

    • Mineral absorption (K⁺, Mg²⁺, Ca²⁺): specific transport proteins.

Neural and Endocrine Control of Digestion

Nervous System Contributions

  • Controls muscular/glandular activities locally (alimentary canal neurons); long-distance regulation by brain.

Hormonal Contributions

  • Hormones from stomach/small intestine epithelial cells:

    • Gastrin: Stimulates stomach contractions and acid production in response to chyme.

    • Cholecystokinin (CCK) and Secretin: From small intestine in response to chyme; stimulate pancreas (enzymes, bicarbonate) and gallbladder (bile) release.