Overview
This lecture covers the structure, types, and functions of animal digestive systems, emphasizing processes of digestion and absorption across various species and organ systems.
Types of Diets and Digestive Systems
- Animals are classified as herbivores (plant-eaters), carnivores (meat-eaters), or omnivores (eat both).
- Herbivores may be frugivores, granivores, nectivores, or folivores, based on plant parts they eat.
- Carnivores include obligate (strict meat-eaters) and facultative (mainly eat meat, but can eat other foods).
- Omnivores consume both animal and plant-based foods.
Invertebrate Digestive Systems
- Gastrovascular cavity has one opening for ingestion and excretion (found in flatworms, jellyfish, etc.).
- Alimentary canals have two openings (mouth and anus) and facilitate stepwise digestion (e.g., earthworms).
Vertebrate Digestive Systems
- Monogastric systems have one stomach chamber (e.g., humans, rabbits).
- Birds have a two-chambered stomach: proventriculus (chemical digestion) and gizzard (mechanical grinding).
- Ruminants (e.g., cows, goats) have four-chambered stomachs (rumen, reticulum, omasum, abomasum) for cellulose digestion.
- Pseudo-ruminants (e.g., camels) have three-chambered stomachs and a large cecum for fermenting roughage.
Digestion and Absorption Process
- Mouth initiates mechanical (chewing) and chemical (saliva enzymes) breakdown of food.
- Esophagus moves food to stomach via peristalsis (wave-like muscle contractions).
- Stomach uses acid and enzymes (e.g., pepsin) to digest proteins and churns food into chyme.
- Small intestine completes digestion and absorbs nutrients via villi and microvilli, with help from liver and pancreas.
- Large intestine reabsorbs water and forms feces.
- Rectum stores feces; anus expels waste with sphincter control.
Accessory Organs
- Salivary glands secrete saliva for initial digestion.
- Liver produces bile for fat digestion and detoxifies blood.
- Pancreas secretes digestive enzymes and bicarbonate to neutralize acids.
- Gallbladder stores and releases bile into the small intestine.
Key Terms & Definitions
- Gastrovascular cavity — Digestive cavity with one opening for both ingestion and excretion.
- Alimentary canal — Digestive tract with separate mouth and anus.
- Monogastric — Having a single-chambered stomach.
- Ruminant — Animal with a four-chambered stomach for digesting cellulose.
- Pseudo-ruminant — Animal with a three-chambered stomach and large cecum for fermenting plant material.
- Peristalsis — Involuntary, wave-like muscle contractions moving food through the digestive tract.
- Chyme — Semi-liquid mixture of food and digestive juices in the stomach.
- Villi/microvilli — Fingerlike intestinal projections increasing surface area for nutrient absorption.
- Bile — Digestive fluid from the liver that emulsifies fats.
Action Items / Next Steps
- Review digestive system diagrams for animal types.
- Study enzyme roles and organ functions in digestion.
- Complete assigned textbook readings on digestive system processes.