1. Chapter 21 Nutrition & Digestion
Overview:
Obtaining and processing food
Human Digestive System
Diets
Nutrition

2. 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”

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

4. In a typical day, a humpback whale’s digestive system will process as much as 2 tons of fish and krill
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

5. Animals ingest their food in a variety of ways
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 other animals

6. Omnivores
Ingest both plants and animals

7. Some animals are suspension feeders, consuming particles from water
Herbivores
Feed mainly on plants

8. Carnivores
Mainly eat animals that eat plants

9. Some are fluid feeders, sucking liquids

10. The Four Stages of Food Processing
Ingestion
Is another word for eating
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

11. Digestion: A Closer Look
Mechanical digestion
Begins the process
Involves physical processes like chewing
Chemical digestion
Is the breakdown of food by digestive enzymes

12. Chemical digestion Hydrolases Proceeds through hydrolysis reactions
Are enzymes that catalyze digestive hydrolysis reactions

13. 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

14. Relatively simple animals have a sac with a single opening
This is called a gastrovascular cavity
Example: hydra

15. In most animals, the digestive compartment is an alimentary canal
This is a tube running from mouth to anus
This tube is divided into specialized regions that process food sequentially

16. HUMAN DIGESTIVE SYSTEM
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

17. 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

18. The food and breathing passages both open into the pharynx
Connects the mouth to the esophagus
Also opens to the trachea
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

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

20. 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

21. 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
The gastric juice contains pepsin, which begins the hydrolysis of protein

22. 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

23. Chemical Digestion in 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

24. 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

25. Enzymes from the walls of the small intestine complete the digestion of many nutrients

26. Nutrients pass through the epithelium of the villi and into the blood
The lining of the small intestine is folded and covered with tiny, fingerlike villi
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
The blood flows to the liver
The liver can store nutrients and convert them to other substances the body can use

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

28. The duodenum The pancreas The liver
Is the first part of the small intestine
Receives digestive agents from several organs
The pancreas
Secretes juice that neutralizes stomach acids
The liver
Secretes bile, which helps digest fats

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

30. 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

31. The large intestine reclaims water
Undigested material passes to the large intestine, or colon
Water is absorbed
Feces are produced

32. Adaptations of vertebrate digestive systems reflect diet
DIETS AND DIGESTIVE ADAPTATIONS
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

33. Some mammals house cellulose-digesting microbes in the colon or cecum
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

34. Overview: A healthful diet satisfies three needs
NUTRITION
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

35. 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

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

37. The energy a resting animal requires each day to stay alive is its basal metabolic rate (BMR)

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

39. More energy is required for an active life
Excess energy is stored as glycogen or fat

40. 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

41. Fad diets are often ineffective and can be harmful

42. 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

43. 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

44. 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

45. Connection: What do food labels tell us?
Food labels provide important nutritional information about packaged foods

46. NUTRITIONAL DISORDERS
Nutritional dysfunction can cause severe problems

47. Malnutrition
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

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

49. To some extent, a tendency toward obesity is inherited

50. Connection: Diet can influence cardiovascular disease and cancer
Choice of diet may reduce the risk of cardiovascular disease and cancer

51. A sound diet supplies
enough raw materials to make all the macromolecules we need
the proper amounts of prefabricated essential nutrients
enough kilocalories to satisfy our energy needs