© 2015 Pearson Education, Inc. PowerPoint Lectures Campbell Biology: Concepts & Connections, Eighth...

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Campbell Biology: Concepts & Connections, Eighth EditionREECE • TAYLOR • SIMON • DICKEY • HOGAN

Chapter 21

Lecture by Edward J. Zalisko

Nutrition and Digestion


Introduction

• More than a third of American adults are obese.

• The obesity epidemic, combined with increasingly sedentary jobs and inactive lifestyles, has contributed to higher incidences of

• heart disease, • diabetes, • cancer, and • other weight-related health problems.

• More than 300,000 deaths per year in the United States are attributed to weight-related issues.


Introduction

• Despite the need for reliable methods to shed pounds, only about 5% of dieters are able to

• reach their goal weight and• maintain it for the long term.

• With a wealth of fad diets, it can be difficult to evaluate their soundness.

• As you think about your own diet, you should begin with a clear understanding of the structure and function of your digestive system.


OBTAINING AND PROCESSING FOOD


21.1 Animals obtain and ingest their food in a variety of stages

• Most animals have one of three kinds of diets.1. Herbivores eat plants and include cattle, gorillas,

sea urchins, and snails.2. Carnivores eat meat and include lions, owls,

whales, and spiders.3. Omnivores eat plants and other animals and

include humans, roaches, raccoons, and crows.


21.1 Animals obtain and ingest their food in a variety of stages

• Animals obtain and ingest their food in different ways.

• Filter feeders sift small organisms or food particles from water.

• Substrate feeders live in or on their food source and eat their way through it.

• Fluid feeders suck nutrient-rich fluids from a living host.

• Bulk feeders ingest large pieces of food.


Figure 21.1a


Figure 21.1b

Caterpillar

Feces


Figure 21.1c


Figure 21.1d


21.2 Overview: Food processing occurs in four stages

• Food is processed in four stages.1. Ingestion is the act of eating.2. Digestion is the breaking down of food into

molecules small enough for the body to absorb.3. Absorption is the take-up of the products of

digestion, usually by the cells lining the digestive tract.

4. Elimination is the removal of undigested materials from the digestive tract.


Figure 21.2a

Ingestion1 2 3 4Digestion Absorption Elimination

Mechanicaldigestion

Piecesof food

Chemicaldigestion(hydrolysis)

Smallmolecules

Nutrientmoleculesenter bodycells

Undigestedmaterial


21.2 Overview: Food processing occurs in four stages

• Chemical digestion is necessary because animals cannot directly use the proteins, carbohydrates, fats, and nucleic acids in food.

• Although all organisms use the same building blocks to make their macromolecules, food is disassembled into the individual building blocks, which are then reassembled into the body’s own molecules (a protein, for example).


21.3 Digestion occurs in specialized compartments

• Sponges and protists digest food in vacuoles.

• Most animals digest food in compartments.• Cnidarians and flatworms have a gastrovascular

cavity with a single opening, the mouth.• Food enters the mouth.• Enzymes from cells lining the gastrovascular cavity

break down the food.• Other cells engulf these small food particles.• Undigested materials are expelled back out the

mouth.



• Most animals have an alimentary canal with• a mouth at one end,• an anus at the other end, and• specialized regions associated with one-way flow of

food.



• The normal one-way flow moves food• into the pharynx, or throat,• down the esophagus to

• perhaps a crop, where food is softened and stored,• perhaps a gizzard, where food is ground and stored, and/or • more commonly a stomach, where food is ground and

stored,

• to the intestines, where chemical digestion and nutrient absorption occur.

• Undigested materials are expelled through the anus.



• Figure 21.3B illustrates three examples of alimentary canals.


Figure 21.3b-0

Anus

Earthworm

Mouth

PharynxEsophagus

CropGizzard

Intestine

Grasshopper

Esophagus

Mouth

Crop

Gastric pouches Hindgut

Midgut

Anus

Bird

MouthEsophagus

Crop

Stomach

Gizzard

Intestine

Anus


THE HUMAN DIGESTIVESYSTEM


21.4 The human digestive system consists of an alimentary canal and accessory glands

• In humans, food is• ingested and chewed in the mouth, or oral cavity,• pushed by the tongue into the pharynx,• moved along by alternating waves of contraction

and relaxation by smooth muscle in the walls of the canal in a process called peristalsis, and

• moved into and out of the stomach by sphincters.


21.4 The human digestive system consists of an alimentary canal and accessory glands

• The final steps of digestion and nutrient absorption in humans occur in the small intestine.

• Undigested materials move through the large intestine, and feces are stored in the rectum and then expelled out the anus.


Figure 21.4-0

Stomach

Alimentary canal

Oral cavity(mouth)

Tongue

Pharynx

Esophagus

Smallintestine

Esophagus

Largeintestine

Rectum

Anus

Sphincters

Smallintestine

Accessory organs

Salivary glands

Liver

Gallbladder

Pancreas


21.5 Digestion begins in the oral cavity

• Mechanical digestion and chemical digestion begin in the mouth.

• Chewing cuts, smashes, and grinds food, making it easier to swallow.

• The tongue• tastes the food,• shapes the food into a ball called a bolus, and • moves it toward the pharynx.


21.5 Digestion begins in the oral cavity

• Salivary glands release• a slippery glycoprotein that moistens and lubricates

food for easier swallowing, • buffers that neutralize acids,• the salivary enzyme amylase that begins the

hydrolysis of starch, and• antibacterial agents that kill some bacteria ingested

with food.


Figure 21.5

Incisors

Canine

Premolars

Molars

“Wisdom”tooth

Tongue

Opening ofa salivarygland duct

Teeth


21.6 After swallowing, peristalsis moves food through the esophagus to the stomach

• Swallowed food and drink move from the pharynx into the esophagus (a muscular tube that conveys food from the pharynx to the stomach) and then into the stomach.

• During swallowing, the tip of the larynx, a door-like flap of cartilage called the epiglottis, moves upward, preventing the food from entering the trachea.


Figure 21.6a-0

Tongue

Epiglottis up

Larynx down

Trachea(windpipe)

Starting to swallow(sphincter contracted)

Bolus of food

Pharynx

Esophagealsphincter

Esophagus

EpiglottisdownLarynx up

Swallowing reflex(sphincter relaxed)

Epiglottisup

Larynxdown

Swallowing completed(sphincter contracted)


Figure 21.6b

Stomach

Esophageal sphincter(contracted)

Bolus offood

Muscles contract,squeezing the bolusthrough the esophagus.

Muscles relax,allowing thepassagewayto open.

Bolus offood


Figure 21.6c


21.7 CONNECTION: The Heimlich maneuver can save lives

• The Heimlich maneuver• involves a forceful elevation of the diaphragm,• pushes air into the trachea, and• can dislodge food from the pharynx or trachea

during choking.

• Brain damage or death will occur within minutes if no airway is open.


Figure 21.7


21.8 The stomach stores food and breaks it down with acid and enzymes

• The stomach can stretch and store up to 2 liters of food and drink.

• Some chemical digestion occurs in the stomach.

• The stomach secretes gastric juice, made up of• mucus,• a protein-digesting enzyme, and• strong acid with a pH of about 2 that

• kills ingested bacteria,• breaks apart cells in food, and• denatures proteins.



• Pepsinogen and HCl produce active pepsin.• Pepsinogen, H+, and Cl– are secreted into the

lumen of the stomach.• HCl converts some pepsinogen to pepsin.• Pepsin helps activate more pepsinogen, starting a

chain reaction.• Pepsin begins the chemical digestion of proteins.



• What prevents the gastric juices from digesting the walls of the stomach?

• The secretion of pepsin in the inactive form of pepsinogen helps protect the cells of the gastric glands.

• Mucus helps protect the stomach lining against acid and pepsin.

• New cells lining the stomach are produced by mitosis about every three days to replace those that have been damaged.



• Another protection for the stomach is that gastric glands do not secrete acidic gastric juice constantly.

• Their activity is regulated by a combination of nerve signals and hormones.

• When you see, smell, or taste food, a signal from your brain stimulates your gastric glands.

• As food arrives in your stomach, it stretches the stomach walls and triggers the release of the hormone gastrin.

• When the stomach contents become too acidic, this inhibits the release of gastrin, an example of a negative feedback mechanism.



• About every 20 seconds, your stomach muscles contract, which churns and mixes your stomach contents.

• These contractions mix food with enzymes to form an acidic, nutrient-rich broth known as chyme.


21.9 CONNECTION: Digestive ailments include acid reflux and gastric ulcers

• Acid reflux of chyme from the stomach back into the esophagus causes the feeling of heartburn.

• Gastroesophageal reflux disease (GERD) results from frequent and severe acid reflux that harms the lining of the esophagus.

• Open sores in the lining of the stomach, called gastric ulcers, may form.

• Bacterial infections (Helicobacter pylori) in the stomach and duodenum can produce ulcers.


Figure 21.9

Bacteria

Mucouslayer ofstomach


21.9 CONNECTION: Digestive ailments include acid reflux and gastric ulcers

• How can a bacteria cause ulcers?

• The low pH of the stomach kills most microbes, but not H. pylori.

• Growth of H. pylori seems to result in a localized loss of protective mucus and damage to the cells lining the stomach, which can lead to a life-threatening infection.

• Gastric ulcers usually respond to a combination of antibiotics and bismuth.


21.10 The small intestine is the major organ of chemical digestion and nutrient absorption

• The small intestine is• named for its smaller diameter,• about 6 meters long,• the site of much chemical digestion, and• where most nutrients are absorbed.



• The first 25 cm of the small intestine is the duodenum, where chyme squirted from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and gland cells in the intestinal wall.

• The pancreas produces pancreatic juice containing a mixture of digestive enzymes and an alkaline solution rich in bicarbonate that neutralizes the acidity of chyme.

• The liver produces bile, which is stored in the gallbladder until it is needed. Bile breaks up fats into small droplets that are more susceptible to attack by digestive enzymes.

• The intestinal wall produces digestive enzymes.


Figure 21.10a

Liver

Gall-bladder

Intestinalenzymes

Duodenum ofsmall intestine

Pancreas

Chyme

StomachBile

Bile



• The surface area for absorption in the small intestine is greatly increased by

• folds of the intestinal lining,• fingerlike projections called villi, and• tiny projections of the surface of intestinal cells

called microvilli.


Figure 21.10b-0

Musclelayers

Largecircular foldsVilli

Intestinal wall

Nutrientabsorption

Vein carryingblood to the liver

Lumen

Lumen of intestine

Epithelialcells

Bloodcapillaries

Lymphvessel

Villi

Nutrientabsorption

Microvilli

Aminoacidsand

sugars

Fattyacidsand

glycerol

Fats

Blood

Lymph

Epithelial cells ofa villus



• Nutrients pass into epithelial cells by• diffusion and• against concentration gradients.

• Fatty acids and glycerol are• absorbed by intestinal cells,• recombined into fats,• coated with proteins, and• transported into lymph vessels.



• Other absorbed nutrients such as amino acids and sugars pass out of the intestinal epithelium, across the thin walls of the capillaries into blood, and finally to the liver.


21.11 The liver processes and detoxifies blood from the intestines

• The liver performs many functions. The liver• converts glucose in blood to glycogen,• stores glycogen and releases sugars back into the

blood as needed,• synthesizes many proteins, including blood-clotting

proteins and lipoproteins that transport fats and cholesterol to body cells,

• modifies substances absorbed in the digestive tract into less toxic forms, and

• produces bile.


Figure 21.11

Heart

Liver

Intestines

Hepaticportalvein


21.12 The large intestine reclaims water and compacts the feces

• The large intestine, or colon,• is about 1.5 m long and 5 cm in diameter,• has a pouch called the cecum near its junction with

the small intestine, which bears a small, finger-like extension, the appendix,

• contains large populations of E. coli, which produce important vitamins,

• absorbs these vitamins and water into the bloodstream, and

• helps form firm feces, which are stored in the rectum until elimination.


21.12 The large intestine reclaims water and compacts the feces

• Diarrhea occurs when too little water is reclaimed from the contents of the large intestine.

• Constipation occurs when too much water is reclaimed.


Figure 21.12

Cecum

Appendix

End ofsmallintestine

Largeintestine(colon)

Unabsorbedfood material

Smallintestine

Rectum

Anus


21.13 EVOLUTION CONNECTION: Evolutionary adaptations of vertebrate digestive systems relate to diet

• The length of the digestive tract often correlates with diet. In general, the alimentary canals (relative to their body size) are

• longer in herbivores and omnivores and• shorter in carnivores.


Figure 21.13-0

Stomach

Small intestine

Cecum

Colon(largeintestine)

Carnivore Herbivore


21.13 EVOLUTION CONNECTION: Evolutionary adaptations of vertebrate digestive systems relate to diet

• Many herbivores have specializations of the gut that promote the growth of cellulose-digesting bacteria and protists because these animals lack the enzymes needed to digest cellulose in plants.

• These mutualistic organisms may be housed in• the cecum, for example, in a coyote or koala,• the large intestine and the cecum in rabbits and

some rodents, or• the stomach of ruminants such as cattle, sheep,

and deer.


NUTRITION

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21.14 An animal’s diet must provide sufficient energy

• All animals have the same basic nutritional needs. Animals must obtain

1. organic building blocks for macromolecules,2. chemical energy to power cellular work, and3. essential nutrients to maintain health.



• Cellular respiration produces the body’s energy currency, ATP, by oxidizing organic molecules digested from food, usually using carbohydrates or fats as fuel.

• The oxidation of a gram of fat liberates more than twice the energy than is contained in a gram of carbohydrate or protein.



• The energy content of food is measured in calories.

• One calorie is the amount of energy required to raise the temperature of a gram of water by 1°C.

• When discussing human diet and activity, we usually refer to kilocalories (1 kcal = 1,000 calories).

• The calories listed on food labels or referred to in regard to nutrition are actually kilocalories and are often written as Calories (capital C).



• The rate of energy consumption by an animal is called its metabolic rate, the sum of all the energy-requiring biochemical reactions over a given interval of time.

• The basal metabolic rate (BMR) is the energy a resting animal requires each day.

• The metabolic rate is the BMR plus the energy needed for physical activity.

• Excess energy is stored as glycogen and fat.


Table 21.14


21.15 An animal’s diet must supply essential nutrients

• Essential nutrients cannot be made from any raw material.

• There are four classes of essential nutrients.1. Essential fatty acids, such as linoleic acid, are

• used to make phospholipids of cell membranes and• found in seeds, grains, and vegetables.

2. Essential amino acids are• used to make proteins and• found in meats, eggs, milk, and cheese.


Figure 21.15a

Corn

Essential amino acids

Methionine

Valine

(Histidine)

Threonine

Phenylalanine

Leucine

Isoleucine

Tryptophan

LysineBeans

and other legumes


Figure 21.15b


21.16 A proper human diet must include sufficient vitamins and minerals

• Essential vitamins and minerals are• required in minute amounts and• absolutely essential to good health.

• Vitamins are organic nutrients that may be• water-soluble, such as vitamins B and C, or• fat-soluble, such as vitamins A, D, E, and K.


Table 21.16a-0


Table 21.16a-1


Table 21.16a-2



• Minerals are simple inorganic nutrients.• Calcium and phosphorus are required in larger

amounts to construct and maintain our skeleton.• Iron is needed to make hemoglobin and as a

component of thyroid hormones.• Iodine is required to make thyroid hormones.• Sodium, potassium, and chlorine are important in

nerve function and help maintain the osmotic balance of your cells.

• Most people ingest more salt than they need.


Table 21.16b



• The Recommended Dietary Allowances (RDAs) are

• the minimum amounts of nutrients that are needed each day and

• determined by a national scientific panel.

• Overdoses of vitamins can be harmful.• In general, excess water-soluble vitamins will be

eliminated in urine.• However, excess fat-soluble vitamins can

accumulate to toxic levels in body fat.


21.17 CONNECTION: Food labels provide nutritional information

• Food labels indicate• serving size,• calories per serving,• amounts of selected nutrients per serving and as a

percentage of daily value, and• recommendations for daily limits of selected

nutrients.


Figure 21.17

Ingredients: whole wheat flour,water, high fructose corn syrup,wheat gluten, soybean or canola oil,molasses, yeast, salt, cultured whey,vinegar, soy flour, calcium sulfate(source of calcium).

Nutrition FactsServing Size 1 slice (43g)Servings Per Container 16

Calories 100 Calories from Fat 10

Total Fat 1.5g

Saturated Fat 0g

Trans Fat 0g

Cholesterol 0mg

Sodium 190mg

Total Carbohydrate 19g

Dietary Fiber 3g

Sugars 3g

Protein 4g

Vitamin A 0% • Vitamin C 0%

Calories per gram:Fat 9 • Carbohydrate 4 • Protein 4

2%

0%

0%

0%

8%

6%

12%

Amount Per Serving

% Daily Value*

Calcium 2% • Iron 4%

Thiamine 6% • Riboflavin 2%

Niacin 6% • Folic Acid 6%

* Percent Daily Values are based on a 2,000calorie diet. Your daily values may be higheror lower depending on your calorie needs:

Calories: 2,0002,500

Total Fat Less than 65g80g

Sat. Fat Less than 20g25g

Cholesterol Less than 300mg300mg

Sodium Less than 2,400mg2,400mg

Total Carbohydrate 300g375g

Dietary Fiber 25g 30g


21.18 Dietary deficiencies can have a number of causes

• Malnutrition • is a health problem caused by an improper or

insufficient diet and• may be caused by inadequate intake or by disease,

such as metabolic or digestive abnormalities.

• More than 800 million people in the world must cope with hunger.

• About 14,000 children under the age of 5 starve to death each day.


21.18 Dietary deficiencies can have a number of causes

• The most common type of human malnutrition is protein deficiency, insufficient intake of one or more essential amino acids.

• Sometimes undernutrition is self-inflicted.• Anorexia nervosa is an eating disorder characterized by

self-starvation due to an intense fear of gaining weight, even when the person is actually underweight.

• Bulimia is a behavioral pattern of binge eating followed by purging through induced vomiting, abuse of laxatives, or excessive exercise.

• Both disorders can result in serious health problems and often death.


Figure 21.18


21.19 EVOLUTION CONNECTION: The human health problem of obesity may reflect our evolutionary past

• In the United States and many other industrialized countries, overnourishment is the nutritional disorder of greatest concern.

• Obesity is defined as a too-high body mass index (BMI), a ratio of weight to height.


Figure 21.19a

ObeseBMI 30–39

Extremelyobese

BMI >39

Nor

mal

BM

I 18.

5–24

Ove

rwei

ght

BM

I 25–

29

Und

erw

eigh

t

BM

I <18

.5

Hei

gh

t

Weight (pounds)100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260

6′4″

6′3″

6′2″

6′1″

6′0″

5′11″

5′10″

5′9″

5′8″

5′7″

5′6″

5′3″

5′2″

5′5″

5′4″

5′1″

5′0″

4′11″

4′10″



• The obesity epidemic has stimulated an increase in scientific research on the causes and possible treatments for weight-control problems.

• Scientists are studying the signaling pathways that regulate appetite and the body’s storage of fat.

• Dozens of genes have been identified that code for weight-regulating hormones.

• The complexity of the body’s system for weight regulation has made it difficult to develop effective drug treatments.



• One well-studied component of human weight control is the hormone leptin, which is produced by adipose (fat) cells and suppresses appetite.

• Obese children who have an inherited mutant form of the leptin gene lose weight after leptin treatments.

• However, high levels in otherwise healthy people do not suppress appetite.


Figure 21.19b



• Some of our current struggles with obesity may be a consequence of our evolutionary history.

• Though fat hoarding can be a health liability today, it may actually have been an advantage in our evolutionary past.

• In a feast-and-famine existence, natural selection may have favored those individuals with a physiology that induced them to gorge on fatty foods on those rare occasions when such treats were available.


21.20 SCIENTIFIC THINKING: Scientists use a variety of methods to test weight-loss claims

• We are all bombarded with a great variety of weight loss claims, some of which contradict each other.

• The field of nutrition uses scientific approaches to investigate such questions.

• Epidemiological research often looks for links between health and diet.



• A study published in 2011• measured the body mass index of 4,451 healthy

Canadian adults and • tracked their diet through daily self-reporting.

• The results indicated that the more carbohydrates consumed, the lower the risk of obesity.


Table 21.20



• One important fact about epidemiological studies is that scientists must differentiate correlation from causation.

• Low carbohydrate intake correlates with greater risk of obesity versus low-carb diets cause weight gain.

• Just because two factors seem to affect one another does not mean they actually do.

• One way to eliminate such confusion is to perform controlled trials in which researchers determine the conditions for their research participants.



• A 2009 study by researchers at the Harvard School of Public Health assigned 811 overweight (BMI > 25) adults to one of four diets.

• All of the diet plans averaged the same number of total calories per day.

• But where those calories came from (fats versus protein versus carbohydrates) varied among the four groups.

• After two years, the total weight lost was recorded and comparisons between the diets were made.


Figure 21.20

Dietary component

We

igh

t lo

ss a

fter

2 y

ea

rs (

lbs

.)

High fat Low fat High carb Low carbHighprotein

Lowprotein

4.5

4

3.5

3

2.5

2

1.5

1

0.5

0


21.20 SCIENTIFIC THINKING: Scientists use a variety of methods to test weight loss claims

• The data table reveals two interesting facts.• First, members of every group lost a moderate

amount of weight over the two-year trial.• Second, every group lost a similar amount of

weight.• These data suggest that cutting calories is what

results in weight loss, not cutting carbs.


21.21 CONNECTION: Diet can influence risk of cardiovascular disease and cancer

• Diet also plays an important role in a person’s risk of developing serious illnesses, including

• cardiovascular disease and• cancer.



• Two main types of cholesterol occur in the blood.1. Low-density lipoproteins (LDLs) generally

correlate with a tendency to develop• blocked blood vessels,• high blood pressure, and • consequent heart attacks.

2. High-density lipoproteins (HDLs) may decrease the risk of vessel blockage, perhaps because HDLs convey excess cholesterol to the liver, where it is broken down.



• You can decrease your levels of “bad” cholesterol by avoiding a diet high in

• saturated fats and• hydrogenated oils.

• You can increase your levels of “good” cholesterol by

• eating mainly unsaturated fats and• avoiding hydrogenated oils.



• The relationship between food and health is complex.

• The American Cancer Society recommends• regular exercise and• a diverse diet of healthy foods with an emphasis on

plant sources.


Table 21.21

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