Animal Digestion and Nutrition Quiz

Animal Digestion

• Animal digestion involves three dietary categories: herbivores, carnivores, and omnivores.
• All animals require fuel for energy and biosynthesis (making new molecules).
• Animals also need essential nutrients (like amino acids, fatty acids, vitamins, and minerals) that cannot be synthesized by their bodies.

Stages of Food Processing

• Food processing involves four stages: ingestion, digestion, absorption, and elimination.
• Ingestion is the initial intake of food.
• Digestion breaks down complex food molecules to absorbable sizes.
• Absorption of nutrients occurs, transferring them into the body cells.
• Elimination is the expulsion of undigested material.

Types of Digestion

• Digestion can be intracellular (within cells, using vacuoles and lysosomes) or extracellular (outside cells in specific compartments like a gastrovascular cavity).
• Intracellular digestion is common in single-celled organisms and some animals.
• Extracellular digestion occurs in more complex animals which may have gastrovascular cavities.

Gastrovascular Cavity

• The gastrovascular cavity is a digestive compartment, found in some invertebrates (e.g., cnidarians)
• Digestion begins in the cavity with enzymes from the gastrodermis.
• Digestion is completed within cells of the lining, using intracellular processes.

Simple vs. Complex Digestive Systems

• Some animals (e.g., sponges and jellyfish) have a simple digestive system with one opening for both ingestion and elimination.
• Most animals have a complete digestive system (a tube with two openings: mouth and anus), allowing for specialized digestion compartments.

Human Digestive System Review Questions

• What are intracellular and extracellular digestion?
• What are the two functions of the gastrovascular cavity?
• What is the difference between a complete and an incomplete digestive system?

Alimentary Canal

• In the alimentary canal, food moves in one direction, facilitating specialized compartments for different digestive steps.
• The human alimentary canal includes the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine. Accessory organs like the liver, pancreas, and gallbladder play vital roles in digestion.

Enzymatic Digestion

• Digestion of carbohydrates, proteins, nucleic acids and fats occur by a variety of enzymes at different stages in the digestive tract. These enzymes break these complex molecules into their smaller components for absorption. Specific enzymes for each class of molecule are found at different locations, like the mouth, stomach or the small intestine. Examples include amylase and lipase.
• The epithelium of the small intestine has brush border enzymes to further digest the components.

Initial Movement of Food

• Food enters as a bolus in the mouth.
• Salivary amylase in saliva begins starch digestion.
• Food is moved to the stomach via peristalsis.
• Epiglottis covers/protects the airway during swallowing.

From Mouth to Stomach

• Mechanical and enzymatic actions and movements (peristalsis) move food to the stomach. The epiglottis protects the airway when swallowing.

Stomach

• Mechanical churning mixes food with gastric juices.
• Pepsinogen is activated by hydrochloric acid (HCl) to form pepsin, initiating protein digestion.
• Mucus protects the stomach lining from the acid.
• Chyme, a partially digested mixture, forms in the stomach and is emptied progressively into the small intestine.

Stomach in Detail

• The interior surface of the stomach wall is highly folded.
• Three types of cells in the gastric glands secrete components of gastric juice: mucus cells, chief cells, and parietal cells.
• Gastric juice contains hydrochloric acid (HCl), pepsinogen, and mucus.
• Pepsinogen is converted into pepsin by HCl, which activates more pepsinogen in a chain reaction.
• HCI converts pepsinogen into pepsin, resulting in protein digestion.
• Pepsinogen and HCI into the lumen of the stomach. HCI converts pepsinogen into pepsin. Pepsin then activates more pepsinogen, in a chain reaction.

Small Intestine in Detail

• Enzymes from the pancreas and liver, along with intestinal enzymes, complete digestion in the small intestine.
• The nutrients are absorbed into the blood or lymph.

Accessory Glands

• Pancreas produces enzymes (amylases, proteases, lipases, nucleases) that aid digestion. It also secretes bicarbonate to neutralize stomach acid.
• Liver produces bile that is stored in the gallbladder. Bile aids fat digestion by emulsifying fats. It also removes waste products.

Hormonal Control of Digestion

• Hormones like gastrin, secretin, and cholecystokinin regulate digestive processes through feedback loops, influencing various digestive organs and their secretions.
• Hormones like cholecystokinin and secretin regulate digestive processes.

Absorption of Nutrients in the Small Intestine

• The inner surface of the small intestine is highly folded and contains villi and microvilli which greatly increases surface area for absorption of nutrients into the blood or lymph. These folded structures are important for maximizing absorption rates.

Large Intestine

• The large intestine absorbs water and electrolytes. It houses gut microflora, which aid in vitamin synthesis. Produces faeces for expulsion.
• Appendix has a role in defense, and plays a role in immune function.

Microbiome and Gut Microflora

• The microbial community (microbiome) in the digestive tract includes bacteria, fungi, and viruses.
• These microbes participate in digestion, vitamin synthesis, and maintaining gut health.
• The microbiome plays an important role in digestion and health.

Revision

• Where does absorption of nutrients occur?
• Where does protein digestion commence?
• What food group does amylase break down?
• What is the inactive form of pepsin?
• What are three functions of the colon?
• What are three functions of the colon?

Cecum

• Most mammalian herbivores have a relatively large caecum.
• The caecum contains bacteria aiding in plant material breakdown (e.g. cellulose).
• In contrast, carnivores have decreased cecum size, often being replaced by an appendix.

Microbiome Research

• The human gut contains 500-1000 microbial species.
• Commensal bacteria in the gut can convert dietary fibre to short-chain fatty acids and vitamin K.
• Microbiome research examines the gut-brain axis impact on anxiety, obesity, and memory.
• Studies involve examining the effects of factors such as diet, antibiotics, probiotics and faecal transplants on the gut microbiome.