Summarizing Digestive Systems

Summary

Different animals have evolved different types of digestive systems specialized to meet their dietary needs. Humans and many other animals have monogastric digestive systems with a single-chambered stomach. Birds have evolved a digestive system that includes a gizzard where the food is crushed into smaller pieces. This compensates for their inability to masticate. Ruminants that consume large amounts of plant material have a multi-chambered stomach that digests roughage. Pseudo-ruminants have similar digestive processes as ruminants but do not have the four-compartment stomach. Processing food involves ingestion (eating), digestion (mechanical and enzymatic breakdown of large molecules), absorption (cellular uptake of nutrients), and elimination (removal of undigested waste as feces).

Many organs work together to digest food and absorb nutrients. The mouth is the point of ingestion and the location where both mechanical and chemical breakdown of food begins. Saliva contains an enzyme called amylase that breaks down carbohydrates. The food bolus travels through the esophagus by peristaltic movements to the stomach. The stomach has an extremely acidic environment. An enzyme called pepsin digests protein in the stomach. Further digestion and absorption take place in the small intestine. The large intestine reabsorbs water from the undigested food and stores waste until elimination.

Glossary

alimentary canal

tubular digestive system with a mouth and anus

anus

exit point for waste material

bile

digestive juice produced by the liver; important for digestion of lipids

bolus

mass of food resulting from chewing action and wetting by saliva

carnivore

animal that consumes animal flesh

chyme

mixture of partially digested food and stomach juices

duodenum

first part of the small intestine where a large part of digestion of carbohydrates and fats occurs

esophagus

tubular organ that connects the mouth to the stomach

gallbladder

organ that stores and concentrates bile

gastrovascular cavity

digestive system consisting of a single opening

gizzard

muscular organ that grinds food

herbivore

animal that consumes strictly plant diet

ileum

last part of the small intestine; connects the small intestine to the large intestine; important for absorption of B-12

jejunum

second part of the small intestine

large intestine

digestive system organ that reabsorbs water from undigested material and processes waste matter

lipase

enzyme that chemically breaks down lipids

liver

organ that produces bile for digestion and processes vitamins and lipids

monogastric

digestive system that consists of a single-chambered stomach

omnivore

animal that consumes both plants and animals

pancreas

gland that secretes digestive juices

pepsin

enzyme found in the stomach whose main role is protein digestion

pepsinogen

inactive form of pepsin

peristalsis

wave-like movements of muscle tissue

proventriculus

glandular part of a bird’s stomach

rectum

area of the body where feces is stored until elimination

roughage

component of food that is low in energy and high in fiber

ruminant

animal with a stomach divided into four compartments

salivary amylase

enzyme found in saliva, which converts carbohydrates to maltose

small intestine

organ where digestion of protein, fats, and carbohydrates is completed

sphincter

band of muscle that controls movement of materials throughout the digestive tract

stomach

saclike organ containing acidic digestive juices

villi

folds on the inner surface of the small intestine whose role is to increase absorption area