Digestive Systems Quiz

Animal Digestion

• Animal digestion encompasses three dietary categories: herbivores, carnivores, and omnivores.
• Nutritional needs include fuel for all animals' requirements, biosynthesis to create new molecules, and essential nutrients that cannot be synthesized (10 amino acids, some fatty acids, vitamins, and minerals).
• The four stages of food processing are ingestion, digestion (chemical and mechanical), absorption, and elimination.
• Digestion can be intracellular (within a cell, e.g., food vacuoles + lysosomes) or extracellular (in a specific compartment, e.g., cnidarians have a gastrovascular cavity).
• Animals avoid self-digestion by processing food in compartments.

Intracellular Digestion

• Intracellular digestion (endocytosis) involves taking in food through pseudopodia and digesting it within individual cells.
• Stages of intracellular digestion include ingestion, digestion, assimilation, and egestion.

Animals with Simple Body Plans

• Gastrovascular cavity: digests and distributes food, begins digestion in the cavity (gastrodermis secretes enzymes), and is completed intracellularly (nutritive muscular cells engulf food).

Simple vs Complex Systems

• Porifera (sponges) and Cnidaria (jellyfish) have one opening that functions as both mouth and anus.
• Most animals have a digestive tube with two openings (mouth and anus) – a complete digestive tract (extracellular digestion).
• Food moves in one direction, allowing specialized compartments.

Revision Questions

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

Alimentary Canal - Complete Digestive Tract

• Diagrams depict the alimentary canal of various animals (rabbit, snake, dolphin).
• Structures like stomach, intestines (small and large), esophagus, salivary glands, pancreas, liver, and gallbladder are included.
• Examples of variations like crop and gizzard (in some animals) are also shown.

Human Digestive System

• Diagram illustrates the human digestive system, marking key organs and timed processes (e.g., salivary glands, stomach, small intestine, etc.).
• Peristalsis, the involuntary movement of food, and sphincters control food passage.
• Time estimates for different stages of digestion are also noted (e.g., 5-6 seconds in esophagus, 2-6 hours in stomach).

Carbohydrate, Protein, and Fat Digestion Summary

• Details of enzymatic digestion of carbohydrates, proteins, and fats in the oral cavity, stomach, and small intestine are laid out.
• Specific enzymes (e.g., salivary amylase, pancreatic amylases, pepsin, pancreatic trypsin, etc.) and their roles in breaking down different macromolecules are illustrated.

Initial Movement of Food

• Oral cavity : salivary amylase and mucin process food.
• Saliva (1 L/day) helps hydrolyze starch and glycogen.
• Esophagus: food moves by peristalsis to the stomach.
• Epiglottis covers the glottis during swallowing, preventing food from entering the trachea.

From Mouth to Stomach

• Swallowing mechanism and the role of the epiglottis, esophageal sphincter, and peristalsis is illustrated.
• Diagram clarifies the digestive process's steps.

Microbiome: Current and Future Research

• Human gut contains 500-1000 microbial species.
• Commensal bacteria convert dietary fiber to short-chain fatty acids.
• Microbiome-gut-brain axis is a current area of research.

The Cecum

• Most mammalian herbivores have a relatively large cecum that contains bacteria to help break down plant materials (cellulose).
• Obligatory carnivores have a reduced or less developed cecum.

The Large Intestine (Colon)

• The Colon is 1.5 m long.
• Reabsorption of water occurs in the large intestine
• The colon contains a rich microflora of bacteria (e.g., E. coli), which produce vitamins.
• Production of feces is another notable function of the large intestine.

Liver

• The liver produces bile, which is stored in the gallbladder.
• Bile components: bile salts (for fat digestion) and pigments (from red blood cell destruction, eliminated in feces).

Hormonal Control of Digestion

• Hormones like gastrin, secretin, and cholecystokinin (CCK) regulate digestion via the bloodstream.
• Cholecystokinin stimulates pancreas enzyme & bile release; secretin triggers bicarbonate release to neutralize chyme.
• Enterogastrone inhibits peristalsis and acid secretion in the stomach when chyme enters the duodenum.

Absorption of Nutrients in Small Intestine

• Absorption of nutrients occurs primarily in the small intestine via epithelial cells in the villi & microvilli (brush border).
• Nutrients are absorbed into blood capillaries (for water-soluble) and lymphatic vessels (lymphatics, for fat-soluble).

The Pancreas: Endocrine/Exocrine Functions

• The pancreas is both endocrine (releasing insulin/glucagon via the circulatory system) and exocrine (releasing digestive enzymes into ducts of the duodenum).
• Different enzymes (proteases, amylases, lipases, nucleases) are produced by the pancreas.
• Secretin and other hormones regulate pancreas activity.