Chapter 33

Overview of Animal Nutrition

• Food is processed in animals through three stages:
  • Ingestion (taking in food)
  • Digestion (breaking down food)
  • Absorption (uptake of nutrients)
  • Elimination (waste disposal)

Types of Animals Based on Diet

• Animals can be categorized into three main dietary groups:
  • Herbivores: Primarily consume plants and algae.
  • Carnivores: Primarily consume other animals.
  • Omnivores: Consume both animals and plants.
  • Many animals are opportunistic feeders, taking advantage of a variety of food sources.

Essential Nutrients

• Essential nutrients must be obtained through diet. Four main classes:
  1. Essential Amino Acids: Out of 20 amino acids, 9 are essential and must be obtained from food.
  2. Essential Fatty Acids: Cannot be synthesized by animals; typically obtained from dietary sources.
  3. Vitamins: Organic molecules required in small amounts; 13 essential vitamins for humans, categorized into fat-soluble and water-soluble.
  4. Minerals: Inorganic nutrients, often acting as cofactors in biological reactions, required in small amounts; excessive intake can harm health.

Digestion Process

• Stages of Food Processing:
  1. Ingestion: Intake of food via various feeding strategies.
  2. Digestion: Process of breaking down food, which includes:
  • Mechanical Digestion: Involves physical breakdown (e.g., chewing).
  • Chemical Digestion: Involves enzymatic reactions that break food into small molecules (e.g., hydrolysis).
  1. Absorption: Uptake of nutrients into body cells from the intestinal lumen.
  2. Elimination: Removal of undigested materials from the body.

Digestive Compartment Types

• Intracellular Digestion: Food particles engulfed by cells and broken down internally (phagocytosis).
• Extracellular Digestion: Occurs outside cells in digestive compartments; includes:
  • Gastrovascular Cavity: Simple organisms digest and distribute nutrients.
  • Alimentary Canal: More complex animals have a complete digestive tract (mouth to anus) with specialized regions.

The Mammalian Digestive System

• Consists of an alimentary canal and accessory glands (e.g., salivary glands, pancreas).
• Mechanical and Chemical Digestion begin in the oral cavity:
  • Salivary amylase initiates carbohydrate breakdown.

Stomach Functionality

• The stomach secretes gastric juice containing enzymes and hydrochloric acid (HCl), converting food into chyme.
• Pepsin: An active enzyme that breaks down proteins; initially secreted as pepsinogen.
• Stomach muscles churn contents and sphincters regulate passage into the small intestine after several hours.

Small Intestine Role

• Major organ for digestion and nutrient absorption:
  • Duodenum: First segment where chyme mixes with digestive juices.
  • Pancreas produces enzymes (proteases) and alkaline solution to neutralize chyme.
  • Bile aids in fat digestion, produced by the liver, stored in the gallbladder.

Nutrient Absorption

• The small intestine’s surface is increased by villi and microvilli, greatly enhancing absorption capacity.
• Nutrients absorbed enter the bloodstream via the hepatic portal vein to the liver for processing.

Large Intestine Function

• Major functions include:
  • Water recovery from undigested food.
  • Housing of bacteria that aid in digestion, producing vitamins.
  • Feces formation as water is absorbed.

Adaptations in Digestion

• Dental Adaptations: Teeth structure is varied based on dietary needs, reflecting an animal's diet.
• Digestive System Length: Carnivores tend to have shorter digestive tracts compared to herbivores, who require longer canals for digesting plant material.
• Mutualistic Relationships: Herbivores often have fermentation chambers inhabited by microorganisms that digest cellulose.

Energy Regulation

• Metabolic rate: the energy an animal uses over time; depends on activity levels and physiological states.
• Storage of excess energy mainly in the form of glycogen and fat; mobilized when needed.
• Insulin and glucagon regulate blood glucose levels, maintaining homeostasis.

Diabetes Mellitus

• Caused by insulin deficiency or resistance, affecting glucose uptake in cells.
• Type 1 diabetes: Autoimmune destruction of insulin-producing cells.
• Type 2 diabetes: Insulin resistance, often associated with obesity.