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Nutrition and Digestion
CHAPTER 22 Nutrition and Digestion
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Biology and Society: Eating Disorders
Millions of Americans suffer from eating disorders Including anorexia and bulimia. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Figure 22.1
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The causes of these diseases are unknown.
Popular culture and the media may promote unhealthy body images.
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Overview of Animal Nutrition
Animals are heterotrophs, organisms that must feed on other organisms.
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Animal Diets Herbivores Feed mainly on plants.
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Figure 22.2a
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Carnivores Mainly eat animals that eat plants. Lobster Mouth Parts
Shark Eating a Seal
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Figure 22.2b
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Omnivores Ingest both plants and animals.
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Figure 22.2c
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The Four Stages of Food Processing
Ingestion Is another word for eating. Digestion Is the breakdown of food to small nutrient molecules.
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Absorption Elimination
Is the uptake of the small nutrient molecules by cells lining the digestive tract. Elimination Is the disposal of undigested materials from the food we eat.
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Digestion: A Closer Look
Mechanical digestion Begins the process. Involves physical processes like chewing.
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Chemical digestion Is the chemical breakdown of food by digestive enzymes.
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Digestion Dismantles food particles for use by the body.
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Figure 22.3
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Chemical digestion proceeds via hydrolysis,
Chemical reactions that break down polymers into monomers using water in the process.
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Figure 22.4a
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Hydrolases Are enzymes that catalyze digestive hydrolysis reactions.
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Figure 22.4b
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Digestive Compartments
In animals, chemical digestion is contained safely within some kind of compartment.
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Food vacuoles Are intracellular organelles filled with digestive enzymes.
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Gastrovascular cavities are compartments with a single opening.
Hydra Eating Daphnia (time lapse)
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Figure 22.5a
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Digestive tubes have two separate openings, a mouth and an anus.
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Figure 22.5b
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A Tour of the Human Digestive System System Map
The human digestive system consists of: A digestive tube, the alimentary canal Accessory organs that secrete digestive chemicals Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Figure 22.6
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The mouth, or oral cavity,
Functions in ingestion and the preliminary steps of digestion.
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Figure 22.7
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The Pharynx The pharynx Connects the mouth to the esophagus.
Also opens to the trachea.
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During swallowing, a reflex tips the epiglottis to close the windpipe entrance.
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Figure 22.8
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The Esophagus The esophagus Is a muscular tube.
Connects the pharynx to the stomach. Moves food down by peristalsis.
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Figure 22.9
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The Stomach The stomach Can store food for several hours.
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Figure 22.10
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The Process of Science: How Does the Stomach Work?
The accidental shooting of a man in 1822 Provided an opportunity for a doctor named William Beaumont to learn about the stomach’s many functions. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Figure 22.11
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Chemical Digestion in the Stomach
Contains gastric juice made of strong acid, digestive enzymes, and mucus. Churns food into a thick soup called acid chyme. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Stomach Ailments Gastric ulcers Are erosions of the stomach lining.
Are often caused by a bacterium named Helicobacter pylori.
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Figure 22.12
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The Small Intestine The small intestine
Is the longest part of the alimentary canal. Is the major organ for chemical digestion and absorption.
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Chemical Digestion in the Small Intestine
In the small intestine, hydrolases break down food to monomers.
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The duodenum Receives digestive agents from several organs.
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Figure 22.13
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The pancreas Secretes juice that neutralizes stomach acids into the duodenum. The liver Secretes bile, which helps digest fats.
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Absorption of Nutrients
Although food has been ingested, It is not technically “in” the body yet. It must be absorbed.
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Figure 22.14
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The jejunum and ileum Are parts of the small intestine specialized for absorption.
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The intestinal wall Contains villi and microvilli, which provide a large surface area for absorption.
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Figure 22.15
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The Large Intestine (and Beyond)
Is shorter, but wider, than the small intestine.
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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.
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The rectum Is the last 15 cm (6 inches) of the large intestine. The anus Regulates the opening of the rectum.
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Food processing takes place along the alimentary canal.
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Figure 22.16
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Human Nutritional Requirements
Proper nutrition helps to maintain homeostasis. A balanced diet provides Fuel energy for cellular work. Building materials to construct needed materials.
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Figure 22.17
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Food as Fuel Cells Break down food molecules in cellular respiration.
Generate many molecules of ATP.
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Figure 22.18
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Calories Calories are A measure of the energy stored in your food.
A measure of the energy you expend in daily activities.
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A calorie is A kilocalorie 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.
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Metabolic Rate The metabolic rate of an organism is the rate of energy consumption per day.
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Table 22.1
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Food as Building Material
The cells of your body Assemble polymers from the monomers found in food. Essential nutrients Are substances needed by the body that it cannot make itself.
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There are eight essential amino acids.
Different foods contain different ones.
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Figure 22.19a
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Figure 22.19b
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Vitamins Vitamins Are organic molecules required in the diet for good health. Function mostly as assistants to enzymes.
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Vitamins and their relationship to body health
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Table 22.2
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Recommended daily allowances (RDAs)
Are the minimal standards established by nutritionists for preventing nutrient deficiencies.
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Minerals Minerals Are inorganic substances required in the diet.
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Essential Fatty Acids Our cells make fats and other lipids by combining fatty acids with other molecules. Essential fatty acids are the fatty acids we cannot make from simpler molecules.
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On food labels, the FDA requires:
Decoding Food Labels On food labels, the FDA requires: The list of ingredients Key nutrition facts
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Figure 22.20
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Nutritional Disorders
Nutritional dysfunction can cause severe problems.
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Malnutrition and Undernutrition
Malnutrition is a dietary deficiency of one or more of the essential nutrients. Protein deficiency is an example.
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Figure 22.21
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Undernutrition Is caused by inadequate intake of nutrients.
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Obesity Obesity Is an inappropriately high ratio of weight to height.
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Figure 22.22
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To some extent, a tendency toward obesity is inherited.
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Figure 22.23
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Evolution Connection: Fat and Sugar Cravings
The majority of Americans consume too many fatty foods. This may be done to satisfy fat cravings. These cravings may have an evolutionary basis. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Figure 22.24
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