• The intestinal wall
– Contains villi and microvilli – Has a large surface area for absorption
• Nutrients pass through the epithelium of the villi and into the blood
• Humpback whales eat small fishes and crustaceans called krill
– This painting shows how the whales corral their food using “bubble nets”
• Humpback whales strain their food from seawater using large, brushlike plates called baleen
• The swallowing reflex moves food from the pharynx into the esophagus
– At the same time, food is kept out of the trachea
• During swallowing a reflex tips the epiglottis to close the windpipe entrance
– When they feed, they take in large amounts of seawater in which the fish and krill live
– They must filter out the water in order to get a meal
• In a typical day, a humpback whale’s digestive system will process as much as 2 tons of fish and krill
• When food is swallowed, it is moved through the alimentary canal by peristalsis
– Peristalsis is rhythmic muscle contraction in the walls of the digestive tract
OBTAINING AND PROCESSING FOOD
Animals ingest their food in a variety of ways
• Animal diets are highly varied
– Herbivores are plant-eaters – Carnivores are meat-eaters – Omnivores eat both plants and
– Helicobacter pylori growth erodes protective mucus and damages the stomach lining
– Are erosions of the stomach lining
The Small Intestine
• The small intestine
– It is not technically “in” the body yet
– It must be absorbed
• The duodenum
• Carnivores
– Mainly eat animals that eat plants
– Some are fluid feeders, sucking liquids
The Four Stages of Food Processing
• Ingestion
– Is another word for eating
Chapter 21 Nutrition & Digestion
Overview: Obtaining and processing food Human Digestive System Diets Nutrition
Getting Their Fill of Krill
• Animals obtain and process nutrients in a variety of ways
• In animals, chemical digestion is contained safely within some kind of compartment
• Food is digested in compartments housing hydrolytic enzymes
• Most animals have a specialized digestive tract
other animals
• Omnivores
– Ingest both plants and animals
– Some animals are suspension feeders, consuming particles from water
• Herbivores
– Feed mainly on plants
The Esophagus
• The esophagus
– Is a muscular tube – Connects the pharynx
to the stomach – Moves food down by
peristalsis
• Peristalsis in the esophagus moves food boluses into the stomach
– They store the excess energy they harvest in the form of blubber
– In about 4 months, a humpback whale eats, digests, and stores as fat enough food for an entire year
– Is the longest part of the alimentary canal – Is the major organ for chemical digestion and
absorption
Chemical Digestion in the Small Intestine
• In the small intestine, hydrolases break down food to monomers
– Ringlike sphincter muscles regulate the passage of food
Digestion begins in the oral cavity
• The teeth break up food • Saliva moistens it • Salivary enzymes begin the hydrolysis of starch • The tongue pushes the chewed food into the
• Digestion
– Is the breakdown of food to small molecules
• Absorption
– Is the uptake of the small nutrient molecules by the body’s cells
• Elimination
– Is the disposal of undigested materials from the food we eat
Digestion: A Closer Look
• Mechanical digess – Involves physical processes like chewing
• Chemical digestion
– Is the breakdown of food by digestive enzymes
The Stomach
• The stomach
– Can store food for several hours
– Churns food
– Mixes food with gastric juices, which are acidic
• The stomach mixes food with gastric juice
– It is made in the liver and stored in the gall bladder
• Enzymes from the walls of the small intestine complete the digestion of many nutrients
• The lining of the small intestine is folded and covered with tiny, fingerlike villi
pharynx
The Pharynx
• The pharynx
– Connects the mouth to the esophagus – Also opens to the trachea
The food and breathing passages both open into the pharynx
• Relatively simple animals have a sac with a single opening
– This is called a gastrovascular cavity – Example: hydra
• In most animals, the digestive compartment is an alimentary canal