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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 Humpback whales eat small fishes and crustaceans called krill

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Chapter 21 Nutrition & Digestion

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chapter 21 nutrition digestion

Chapter 21Nutrition & Digestion


Obtaining and processing food

Human Digestive System



getting their fill of krill
Getting Their Fill of Krill
  • Animals obtain and process nutrients in a variety of ways
  • Humpback whales eat small fishes and crustaceans called krill
    • This painting shows how the whales corral their food using “bubble nets”

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
  • Humpback whales strain their food from seawater using large, brushlike plates called baleen

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
  • In a typical day, a humpback whale’s digestive system will process as much as 2 tons of fish and krill
animals ingest their food in a variety of ways


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 other animals


  • Ingest both plants and animals
Some animals are suspension feeders, consuming particles from water
  • Herbivores
  • Feed mainly on plants
the four stages of food processing
The Four Stages of Food Processing
    • Is another word for eating
  • Digestion
    • Is the breakdown of food to small molecules
  • Ingestion
  • 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
Digestion: A Closer Look
  • Begins the process
  • Involves physical processes like chewing
  • Mechanical digestion
  • Chemical digestion
  • Is the breakdown of food by digestive enzymes

Proceeds through hydrolysis reactions

  • Chemical digestion
  • Hydrolases
  • Are enzymes that catalyze digestive hydrolysis reactions
digestive compartments
Digestive Compartments
  • 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

This is called a gastrovascular cavity

  • Example: hydra
  • Relatively simple animals have a sac with a single opening

This is a tube running from mouth to anus

  • This tube is divided into specialized regions that process food sequentially
  • In most animals, the digestive compartment is an alimentary canal
the human digestive system consists of an alimentary canal and accessory glands


The human digestive system consists of an alimentary canal and accessory glands
  • 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
    • Ringlike sphincter muscles regulate the passage of food
digestion begins in the oral cavity
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 pharynx
the pharynx
The Pharynx
  • Connects the mouth to the esophagus
  • Also opens to the trachea
  • The pharynx

The food and breathing passages both open into the pharynx

  • The swallowing reflex moves food from the pharynx into the esophagus
    • At the same time, food is kept out of the trachea
the esophagus
The Esophagus
  • Is a muscular tube
  • Connects the pharynx to the stomach
  • Moves food down by peristalsis
  • The esophagus
  • Peristalsis in the esophagus moves food boluses into the stomach
the stomach
The Stomach
  • Can store food for several hours
  • Churns food
  • Mixes food with gastric juices, which are acidic
  • The stomach
  • The stomach mixes food with gastric juice
    • The gastric juice contains pepsin, which begins the hydrolysis of protein
connection bacterial infections can cause ulcers
Connection: Bacterial infections can cause ulcers
  • New evidence suggests that a spiral-shaped prokaryote causes gastric ulcers
    • Helicobacter pylori growth erodes protective mucus and damages the stomach lining
  • Are erosions of the stomach lining
the small intestine
The Small Intestine
  • Is the longest part of the alimentary canal
  • Is the major organ for chemical digestion and absorption
  • The small intestine

Chemical Digestion in the Small Intestine

  • In the small intestine, hydrolases break down food to monomers
Alkaline pancreatic juice neutralizes stomach acids
    • Its enzymes digest polysaccharides, proteins, nucleic acids, and fats
  • Bile emulsifies fat droplets for attack by pancreatic enzymes
    • It is made in the liver and stored in the gall bladder

The intestinal wall

  • The lining of the small intestine is folded and covered with tiny, fingerlike villi
  • Contains villi and microvilli
  • Has a large surface area for absorption
  • Nutrients pass through the epithelium of the villi and into the blood
    • The blood flows to the liver
    • The liver can store nutrients and convert them to other substances the body can use
absorption of nutrients
Absorption of Nutrients
  • It is not technically “in” the body yet
  • It must be absorbed
  • Although food has been ingested

Is the first part of the small intestine

  • Receives digestive agents from several organs
  • The duodenum
  • The pancreas
    • Secretes juice that neutralizes stomach acids
  • The liver
    • Secretes bile, which helps digest fats

Are parts of the small intestine

  • Are specialized for absorption
  • The jejunum and ileum
the large intestine and beyond
The Large Intestine (and Beyond)
  • Is shorter, but wider, than the small intestine
  • The large intestine
  • The colon
  • Makes up most of the length of the large intestine
  • Absorbs water from the alimentary canal
  • Produces feces, the waste product of food
  • The rectum
    • Is the last 15 cm (6 inches) of the large intestine
  • The anus
    • Regulates the opening of the rectum
the large intestine reclaims water
The large intestine reclaims water
  • Undigested material passes to the large intestine, or colon
    • Water is absorbed
    • Feces are produced
adaptations of vertebrate digestive systems reflect diet


Adaptations of vertebrate digestive systems reflect diet
  • Herbivores and omnivores generally have longer alimentary canals than carnivores
    • Plant matter is more difficult to digest than meat
    • Nutrients in vegetation are less concentrated than in meat

The cecum is a pouch where the large and small intestines connect

    • Examples: horses and elephants
  • Other mammals re-ingest their feces to recover nutrients
    • Examples: rabbits and some rodents
  • Some mammals house cellulose-digesting microbes in the colon or cecum
overview a healthful diet satisfies three needs


Overview: A healthful diet satisfies three needs
  • An animal’s diet provides
    • fuel for its activities
    • raw materials for making the body’s own molecules
    • essential nutrients that the body cannot make
chemical energy powers the body
Chemical energy powers the body
  • Once nutrients are inside cells, they can be oxidized by cellular metabolism to generate energy
    • This energy is in the form of ATP
  • A measure of the energy stored in your food
  • A measure of the energy you expend in daily activities
  • Calories are
  • A calorie is
    • The amount of energy required to raise the temperature of a gram of water by 1ºC
  • A kilocalorie is
    • One thousand calories
    • The unit listed on food labels
metabolic rate
Metabolic Rate
  • The metabolic rate of an organism is the rate of energy consumption per day
More energy is required for an active life
  • Excess energy is stored as glycogen or fat
connection body fat and fad diets
Connection: Body fat and fad diets
  • The human body tends to store excess fat molecules instead of using them for fuel
  • A balanced diet includes adequate amounts of all nutrients
connection vegetarians must be sure to obtain all eight essential amino acids
Connection: Vegetarians must be sure to obtain all eight essential amino acids
  • The eight essential amino acids that adults require must be obtained from food
    • They are easily obtained from animal protein
    • They can also be obtained from the proper combination of plant foods
connection a healthful diet includes 13 vitamins
Connection: A healthful diet includes 13 vitamins
  • Most of these vitamins function as coenzymes
  • Vitamins
  • Are organic molecules required in the diet for good health
  • Mostly function as assistants to enzymes
connection essential minerals are required for many body functions
Connection: Essential minerals are required for many body functions
  • Minerals are elements other than carbon, hydrogen, oxygen, and nitrogen
    • They play a variety of roles in the body
  • Are inorganic substances required in the diet
connection what do food labels tell us
Connection: What do food labels tell us?
  • Food labels provide important nutritional information about packaged foods
nutritional disorders
  • Nutritional dysfunction can cause severe problems
  • Malnutrition is a dietary deficiency of one or more of the essential nutrients
  • Protein deficiency is an example
  • Undernutrition
  • Is caused by inadequate intake of nutrients
  • Is an inappropriately high ratio of weight to height
  • Obesity
connection diet can influence cardiovascular disease and cancer
Connection: Diet can influence cardiovascular disease and cancer
  • Choice of diet may reduce the risk of cardiovascular disease and cancer

enough raw materials to make all the macromolecules we need

  • the proper amounts of prefabricated essential nutrients
  • enough kilocalories to satisfy our energy needs
  • A sound diet supplies