Nutrition and Digestion CHAPTER 22 Nutrition and Digestion

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

Figure 22.1

The causes of these diseases are unknown. Popular culture and the media may promote unhealthy body images.

Overview of Animal Nutrition Animals are heterotrophs, organisms that must feed on other organisms.

Animal Diets Herbivores Feed mainly on plants.

Figure 22.2a

Carnivores Mainly eat animals that eat plants. Lobster Mouth Parts Shark Eating a Seal

Figure 22.2b

Omnivores Ingest both plants and animals.

Figure 22.2c

The Four Stages of Food Processing Ingestion Is another word for eating. Digestion Is the breakdown of food to small nutrient molecules.

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.

Digestion: A Closer Look Mechanical digestion Begins the process. Involves physical processes like chewing.

Chemical digestion Is the chemical breakdown of food by digestive enzymes.

Digestion Dismantles food particles for use by the body.

Figure 22.3

Chemical digestion proceeds via hydrolysis, Chemical reactions that break down polymers into monomers using water in the process.

Figure 22.4a

Hydrolases Are enzymes that catalyze digestive hydrolysis reactions.

Figure 22.4b

Digestive Compartments In animals, chemical digestion is contained safely within some kind of compartment.

Food vacuoles Are intracellular organelles filled with digestive enzymes.

Gastrovascular cavities are compartments with a single opening. Hydra Eating Daphnia (time lapse)

Figure 22.5a

Digestive tubes have two separate openings, a mouth and an anus.

Figure 22.5b

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

Figure 22.6

The mouth, or oral cavity, Functions in ingestion and the preliminary steps of digestion.

Figure 22.7

The Pharynx The pharynx Connects the mouth to the esophagus. Also opens to the trachea.

During swallowing, a reflex tips the epiglottis to close the windpipe entrance.

Figure 22.8

The Esophagus The esophagus Is a muscular tube. Connects the pharynx to the stomach. Moves food down by peristalsis.

Figure 22.9

The Stomach The stomach Can store food for several hours.

Figure 22.10

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

Figure 22.11

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

Stomach Ailments Gastric ulcers Are erosions of the stomach lining. Are often caused by a bacterium named Helicobacter pylori.

Figure 22.12

The Small Intestine The small intestine 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.

The duodenum Receives digestive agents from several organs.

Figure 22.13

The pancreas Secretes juice that neutralizes stomach acids into the duodenum. The liver Secretes bile, which helps digest fats.

Absorption of Nutrients Although food has been ingested, It is not technically “in” the body yet. It must be absorbed.

Figure 22.14

The jejunum and ileum Are parts of the small intestine specialized for absorption.

The intestinal wall Contains villi and microvilli, which provide a large surface area for absorption.

Figure 22.15

The Large Intestine (and Beyond) Is shorter, but wider, than the small 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.

Food processing takes place along the alimentary canal.

Figure 22.16

Human Nutritional Requirements Proper nutrition helps to maintain homeostasis. A balanced diet provides Fuel energy for cellular work. Building materials to construct needed materials.

Figure 22.17

Food as Fuel Cells Break down food molecules in cellular respiration. Generate many molecules of ATP.

Figure 22.18

Calories Calories are A measure of the energy stored in your food. A measure of the energy you expend in daily activities.

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.

Metabolic Rate The metabolic rate of an organism is the rate of energy consumption per day.

Table 22.1

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.

There are eight essential amino acids. Different foods contain different ones.

Figure 22.19a

Figure 22.19b

Vitamins Vitamins Are organic molecules required in the diet for good health. Function mostly as assistants to enzymes.

Vitamins and their relationship to body health

Table 22.2

Recommended daily allowances (RDAs) Are the minimal standards established by nutritionists for preventing nutrient deficiencies.

Minerals Minerals Are inorganic substances required in the diet.

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.

On food labels, the FDA requires: Decoding Food Labels On food labels, the FDA requires: The list of ingredients Key nutrition facts

Figure 22.20

Nutritional Disorders Nutritional dysfunction can cause severe problems.

Malnutrition and Undernutrition Malnutrition is a dietary deficiency of one or more of the essential nutrients. Protein deficiency is an example.

Figure 22.21

Undernutrition Is caused by inadequate intake of nutrients.

Obesity Obesity Is an inappropriately high ratio of weight to height.

Figure 22.22

To some extent, a tendency toward obesity is inherited.

Figure 22.23

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

Figure 22.24