Biology in Focus - Chapter 33

CAMPBELL BIOLOGY IN FOCUS

© 2014 Pearson Education, Inc.

Urry • Cain • Wasserman • Minorsky • Jackson • Reece

Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge

33Animal Nutrition


Food is taken in, taken apart, and taken up in the process of animal nutrition

In general, animals fall into three categories

Herbivores eat mainly plants and algae

Carnivores eat other animals

Omnivores regularly consume animals as well as plants or algae

Most animals are also opportunistic feeders

Overview: The Need to Feed


Figure 33.1


Concept 33.1: An animal’s diet must supply chemical energy, organic molecules, and essential nutrients

An animal’s diet provides

Chemical energy, which is converted into ATP to power cellular processes

Organic building blocks, such as organic carbon and organic nitrogen, to synthesize a variety of organic molecules

Essential nutrients, which are required by cells and must be obtained from dietary sources


Essential Nutrients

Essential nutrients must be obtained from an animal’s diet

There are four classes of essential nutrients

Essential amino acids

Essential fatty acids

Vitamins

Minerals


Figure 33.2

Iron cofactor

Essentialaminoacids

NADH coenzyme(vitamin B3)

NADH

Fatty acid desaturase

γ-Linoleic acid

Phospholipids

Prostaglandins

Gly

Ile

Leu

Phe

Phe

Tyr

Glu

Linoleic acid


In animals, fatty acids are converted into a variety of cellular components, such as membrane phospholipids, signaling molecules, and storage fats

Essential fatty acids can be synthesized by plants

Deficiencies of essential fatty acids are rare

Essential Fatty Acids and Amino Acids


Animals require 20 amino acids and can synthesize about half from molecules in their diet

The remaining amino acids, the essential amino acids, must be obtained from food in preassembled form

Meat, eggs, and cheese provide all the essential amino acids and are thus “complete” proteins


Most plant proteins are incomplete in amino acid composition

Individuals who eat only plant proteins need to eat specific plant combinations to get all the essential amino acids


Vitamins

Vitamins are organic molecules required in the diet in small amounts

Thirteen vitamins are essential for humans

Vitamins are grouped into two categories: fat-soluble and water-soluble


Minerals

Minerals are simple inorganic nutrients, usually required in small amounts

Ingesting large amounts of some minerals can upset homeostatic balance


Dietary Deficiencies

Malnutrition results from the long-term absence from the diet of one or more essential nutrients


Deficiencies in Essential Nutrients

Deficiencies in essential nutrients can cause deformities, disease, and death

Animals may consume salt, minerals, shells, or stones to prevent mineral deficiencies


Figure 33.3


A diet with insufficient amounts of one or more amino acids is the most common type of malnutrition among humans

Individuals subsisting on simple rice diets are often deficient in vitamin A

To overcome this, scientists have engineered a strain of rice that synthesizes beta-carotene, which is converted to vitamin A in the body


Undernutrition results when a diet does not provide enough chemical energy

An undernourished individual will

Use up stored fat and carbohydrates

Break down its own proteins

Lose muscle mass

Suffer protein deficiency of the brain

Die or suffer irreversible damage

Undernutrition


Assessing Nutritional Needs

Genetic defects that disrupt food uptake provide information about human nutrition

For example, hemochromatosis causes iron buildup without excessive iron intake

Insights into human nutrition have come from epidemiology, the study of human health and disease in populations

Neural tube defects were found to be the result of a deficiency in folic acid in pregnant mothers


Concept 33.2: The main stages of food processing are ingestion, digestion, absorption, and elimination

Food processing can be divided into four distinct stages


Figure 33.4

Mechanicaldigestion

Nutrient moleculesenter body cells

Chemicaldigestion(enzymatichydrolysis)

Undigestedmaterial

EliminationAbsorptionDigestionIngestion1 2 3 4


Ingestion is the act of eating or feeding

Strategies for extracting resources from food differ widely among animals

Video: Shark Eating a Seal


Figure 33.5

Filter feeders Substrate feeders Fluid feeders

Bulk feeders

Caterpillar Feces

Baleen


Figure 33.5a

Filter feeders

Baleen


Figure 33.5b

Substrate feeders

Caterpillar Feces


Figure 33.5c

Fluid feeders


Figure 33.5d

Bulk feeders


Digestion is the process of breaking food down into molecules small enough to absorb

Mechanical digestion, including chewing, increases the surface area of food

Chemical digestion splits food into small molecules that can pass through membranes

In chemical digestion, the process of enzymatic hydrolysis splits bonds in molecules with the addition of water


Absorption is uptake of nutrients by body cells

Elimination is the passage of undigested material out of the digestive system


Digestive Compartments

Most animals process food in specialized compartments

These compartments reduce the risk of an animal digesting its own cells and tissues


Intracellular Digestion

In intracellular digestion, food particles are engulfed by phagocytosis

Food vacuoles, containing food, fuse with lysosomes containing hydrolytic enzymes


Extracellular Digestion

Extracellular digestion is the breakdown of food particles outside of cells

It occurs in compartments that are continuous with the outside of the animal’s body

Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients

Video: Hydra Eating


Figure 33.6

Mouth

Tentacles

Digestive enzymesreleased

Food particlesbroken down

Food particlesengulfed and digested

GastrodermisEpidermis

Food

1

2

3


More complex animals have a complete digestive tract or an alimentary canal with a mouth and an anus

The alimentary canal can have specialized regions that carry out digestion and absorption in a stepwise fashion


Figure 33.7

Crop

Gizzard

Intestine

Anus

Esophagus

Pharynx

Mouth

(a) Earthworm

EsophagusCrop

StomachGizzard

Intestine

Anus

Mouth

(c) Bird(b) Grasshopper

MouthCrop Gastric

cecae

AnusRectumEsophagus

Foregut Midgut Hindgut


Concept 33.3: Organs specialized for sequential stages of food processing form the mammalian digestive system

The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts

Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder


Figure 33.8

Tongue

Salivaryglands

Liver

Gall-bladder

Pancreas

SmallintestineLargeintestine

Rectum

Anus

Oral cavity

Pharynx

Esophagus

Sphincter

Sphincter

Stomach

Liver

Pancreas

Gallbladder

Duodenum ofsmall intestine

Stomach

Smallintestine

Largeintestine

RectumAnus

Salivaryglands

Esophagus

Mouth


Figure 33.8a

Liver

Pancreas

GallbladderStomach

Smallintestine

Largeintestine

RectumAnus

SalivaryglandsEsophagus

Mouth


Food is pushed along by peristalsis, rhythmic contractions of muscles in the wall of the canal

Valves called sphincters regulate the movement of material between compartments


The Oral Cavity, Pharynx, and Esophagus

The first stage of digestion is mechanical and takes place in the oral cavity

Salivary glands deliver saliva to the oral cavity through ducts

Teeth chew food into smaller particles that are exposed to salivary amylase, initiating breakdown of glucose polymers

Saliva also contains mucus, a viscous mixture of water, salts, cells, and glycoproteins


The tongue shapes food into a bolus and provides help with swallowing

The throat, or pharynx, is the junction that opens to both the esophagus and the trachea

The esophagus connects to the stomach

The trachea (windpipe) leads to the lungs


Swallowing must be carefully choreographed to avoid choking

The esophagus conducts food from the pharynx down to the stomach through rhythmic cycles of contraction

The form of the esophagus fits its function and varies among species


Digestion in the Stomach

The stomach stores food and secretes gastric juice, which converts a meal to a mixture of food and digestive juice called chyme


Figure 33.9

Esophagus

Sphincter

Sphincter

Stomach

Folds ofepithelialtissue

Smallintestine

Epithelium

Production of gastricjuice

Pepsinogen andHCI secreted intolumen

HCI convertspepsinogen topepsin.

Pepsin activatesmore pepsinogen,starting a chainreaction.

Parietalcell

Pepsin(activeenzyme)

Chiefcell

Pepsinogen1

2

3

1

2

3

Gastric gland

Mucous cell

Chief cell

Parietal cell

Gastric piton the interiorsurface ofstomach

10 µ

m

HCI

H+

Cl−


Figure 33.9a

Gastric gland

Mucous cell

Chief cell

Parietal cell

Gastric piton the interiorsurface ofstomach Epithelium

Parietalcell


Chiefcell

HCI

H+

Cl−

Pepsinogen

1

2

3


Figure 33.9b-1



Parietalcell

Chiefcell

HCI

H+

Cl−

Pepsinogen1

1


Figure 33.9b-2




Parietalcell


Chiefcell

HCI

H+

Pepsinogen

2

1

1

2

Cl−


Figure 33.9b-3




Pepsin activatesmore pepsinogen,starting a chainreaction.

Parietalcell


Chiefcell

HCI

H+

Pepsinogen

3

2

1

1

2

3

Cl−


Figure 33.9c

Gastric pit on the interiorsurface of stomach

10 µ

m


Chemical Digestion in the Stomach

Gastric juice has a low pH of about 2, which kills bacteria and denatures proteins

Gastric juice is made up of hydrochloric acid (HCl) and pepsin

Pepsin is a protease, or protein-digesting enzyme, that cleaves proteins into smaller peptides


Figure 33.10

Fat digestion

Fat(triglycerides)

Glycerol,fatty acids,monoglycerides

Pancreaticlipase

Pancreaticnucleases

Nucleotidases

Pepsin

Pancreatic trypsinand chymotrypsin

Pancreaticcarboxypeptidase

Dipeptidases,carboxypeptidase,and aminopeptidaseDisaccharidases

Pancreatic amylases

Disaccharides

Monosaccharides Amino acids

Small peptides

Smallerpolypeptides

Small polypeptides

Nucleotides

Nucleosides

Nitrogenous bases,sugars, phosphates

Nucleosidasesandphosphatases

DNA, RNA

Nucleic aciddigestion

Protein digestion

Proteins

MaltoseSmallerpolysaccharides

Polysaccharides(starch, glycogen)

Disaccharides(sucrose,

lactose)

Carbohydrate digestionOral cavity,pharynx,esophagus

Smallintestine(enzymesfrompancreas)

Stomach

Smallintestine(enzymesfromepithelium)

Salivary amylase


Figure 33.10a

MaltoseSmallerpolysaccharides

Polysaccharides

Carbohydrate digestion

Oral cavity, pharynx, esophagus

Salivary amylase

Disaccharides


Figure 33.10b

Pepsin

Small polypeptides

Protein digestion

Proteins

Stomach


DisaccharidesMaltoseSmallerpolysaccharides


Figure 33.10c

Fat digestion

Fat(triglycerides)

Glycerol,fatty acids,monoglycerides

Pancreaticlipase

Pancreaticnucleases

Pancreatic trypsinand chymotrypsin

Pancreaticcarboxypeptidase

Pancreatic amylases

Disaccharides

Smallpeptides

Smallerpolypeptides

Small polypeptides

Nucleotides

DNA, RNA

Small intestine (enzymes from pancreas)


Protein digestion

Polysaccharides Disaccha-rides


Aminoacids


Figure 33.10d

NucleotidasesDipeptidases,carboxypeptidase,and aminopeptidase

Disaccharidases

Monosaccharides Amino acids

Nucleosides

Nitrogenous bases,sugars, phosphates

Nucleosidasesandphosphatases

Small intestine (enzymes from epithelium)


Protein digestionCarbohydrate digestion

Disaccharides Amino acidsSmallpeptides

Nucleotides


Mucus protects the stomach lining from gastric juice

Also, cell division adds a new epithelial layer every three days, to replace any cells damaged by digestive juices

Gastric ulcers, lesions in the stomach lining, are caused mainly by the bacterium Helicobacter pylori


Stomach Dynamics

Coordinated contraction and relaxation of stomach muscle churn the stomach’s contents

Sphincters prevent chyme from entering the esophagus and regulate its entry into the small intestine

Stomach contents typically pass into the small intestine 2–6 hours after a meal


Digestion in the Small Intestine

The small intestine is the longest section of the alimentary canal

It is the major organ of digestion and absorption

The first portion of the small intestine is the duodenum

Here, chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the intestinal wall


Pancreatic Secretions

The pancreas produces proteases trypsin and chymotrypsin, which are activated in the lumen of the duodenum

Its solution is alkaline and neutralizes the acidic chyme


Bile Production by the Liver

In the small intestine, bile aids in digestion and absorption of fats

Bile is made in the liver and stored in the gallbladder

Bile also destroys nonfunctional red blood cells


Secretions of the Small Intestine

The epithelial lining of the duodenum produces several digestive enzymes

Enzymatic digestion is completed as peristalsis moves the chyme and digestive juices along the small intestine

Most digestion occurs in the duodenum; the jejunum and ileum function mainly in absorption of nutrients and water


Figure 33.11

Vein carryingblood to liver

Microvilli (brushborder) at apical(lumenal) surface

Villi

Lumen

Basalsurface

Lymphvessel

Capillary

Epithelialcells

(towardcapillary)

Bloodcapillaries

Epithelialcells

Largecircularfolds

Muscle layers

VilliIntestinalwall

Nutrientabsorption

Lacteal


Figure 33.11a

Vein carryingblood to liver

Largecircularfolds

Muscle layers

VilliIntestinalwall

Nutrientabsorption


Figure 33.11b

Microvilli (brushborder) at apical(lumenal) surface

Villi

Lumen

Basalsurface

Lymphvessel

Capillary

Epithelialcells

(towardcapillary)

Bloodcapillaries

Epithelialcells

Lacteal

Nutrientabsorption


Absorption in the Small Intestine

The small intestine has a huge surface area, due to villi and microvilli that project into the intestinal lumen

The enormous microvillar surface creates a brush border that greatly increases the rate of nutrient absorption

Transport across the epithelial cells can be passive or active depending on the nutrient

Animation: Membrane Transport


Figure 33.12

Triglyceridesare broken downto fatty acids andmonoglyceridesby lipase.

Monoglyceridesand fatty acids diffuseinto epithelial cellsand are re-formed intotriglycerides.

Triglycerides areincorporated intochylomicrons.

Chylomicrons enterlacteals and are carriedaway by lymph.

4

3

2

1

Triglycerides

Chylomicron

Lacteal

Phospholipids,cholesterol,and proteins

Triglycerides

Fatty acidsMono-

glycerides

Epithelialcell

LUMENOF SMALLINTESTINE


Figure 33.12a

Triglyceridesare broken downto fatty acids andmonoglyceridesby lipase.

Monoglyceridesand fatty acids diffuseinto epithelial cellsand are re-formed intotriglycerides.

1

Triglycerides

Fatty acidsMono-

glycerides

Epithelialcell

LUMENOF SMALLINTESTINE

Triglycerides

2


Figure 33.12b

Triglycerides areincorporated intochylomicrons.

Chylomicrons enterlacteals and are carriedaway by lymph.

Chylomicron

Lacteal

Phospholipids,cholesterol,and proteins

Triglycerides

3

4


The hepatic portal vein carries nutrient-rich blood from the capillaries of the villi to the liver, then to the heart

The liver regulates nutrient distribution, interconverts many organic molecules, and detoxifies many organic molecules


Epithelial cells absorb fatty acids and monoglycerides and recombine them into triglycerides

These fats are coated with phospholipids, cholesterol, and proteins to form water-soluble chylomicrons

Chylomicrons are transported into a lacteal, a lymphatic vessel in each villus

Lymphatic vessels deliver chylomicron-containing lymph to large veins that return blood to the heart


Absorption in the Large Intestine

The colon of the large intestine is connected to the small intestine

The cecum aids in the fermentation of plant material and connects where the small and large intestines meet

The human cecum has an extension called the appendix, which plays a very minor role in immunity


Figure 33.13

Ascendingportionof colon

Smallintestine

Appendix

Cecum

Junction of the small andlarge intestines


A major function of the colon is to recover water that has entered the alimentary canal

The colon houses bacteria (e.g., Escherichia coli) that live on unabsorbed organic material; some produce vitamins

Feces, including undigested material and bacteria, become more solid as they move through the colon


Feces are stored in the rectum until they can be eliminated through the anus

Two sphincters between the rectum and anus control bowel movements


Concept 33.4: Evolutionary adaptations of vertebrate digestive systems correlate with diet

Digestive systems of vertebrates are variations on a common plan

However, there are intriguing adaptations, often related to diet


Dental Adaptations

Dentition, an animal’s assortment of teeth, is one example of structural variation reflecting diet

The success of mammals is due in part to their dentition, which is specialized for different diets

Nonmammalian vertebrates have less specialized teeth, though exceptions exist

For example, the teeth of poisonous snakes are modified as fangs for injecting venom


Figure 33.14

Carnivore Herbivore

Omnivore

Incisors Canines Premolars Molars


Mutualistic Adaptations

Many herbivores have fermentation chambers in their alimentary canals, where mutualistic microorganisms digest cellulose

Rabbits and some rodents harbor mutualistic bacteria in their large intestines and ceca

The most elaborate adaptations for an herbivorous diet have evolved in the animals called ruminants, including deer, sheep, and cattle


Figure 33.15

Rumen Reticulum

Esophagus

OmasumAbomasum

Intestine


Stomach and Intestinal Adaptations

Many carnivores have large, expandable stomachs

Herbivores and omnivores generally have longer alimentary canals than carnivores, reflecting the longer time needed to digest vegetation


Figure 33.16

Smallintestine

Small intestine

Stomach

Cecum

Colon(largeIntestine)Carnivore

Herbivore


Figure 33.16a


Figure 33.16b


Concept 33.5: Feedback circuits regulate digestion, energy allocation, and appetite

An animal’s intake of food and use of nutrients are matched to circumstance and need


Regulation of Digestion

Each step in the digestive system is activated as needed

The enteric division of the nervous system helps to regulate the digestive process

The endocrine system also regulates digestion through the release and transport of hormones


Figure 33.17

Food

Stomach

GastrinGastricjuices

Pancreas

Liver

Gallbladder

Stimulation

Inhibition

1


Bile

Chyme

HCO3−, enzymes

32

CCK

CCK

Secretinand CCK

Secretin

Gastricjuices


Figure 33.17a

Food

Stomach

GastrinGastricjuices

Pancreas

Liver

Gallbladder

Stimulation

Inhibition

1



Figure 33.17b

Bile

Chyme

HCO3−, enzymes

CCK

CCKSecretinStimulation

Inhibition

2


Figure 33.17c

Secretinand CCK

Gastricjuices

3

Stimulation

Inhibition


Energy Allocation

The flow and transformation of energy in an animal—its bioenergetics—determine nutritional needs

An animal’s energy use per unit of time is called its metabolic rate

Metabolic rate can be determined by monitoring an animal’s rate of heat loss, the amount of O2 consumed, or the amount of CO2 produced


Figure 33.18-1

Organic moleculesin food

Animalbody

Externalenvironment


Figure 33.18-2


Heat

Energylost infeces

Digestion andabsorption

Nutrient moleculesin body cells

Animalbody

Externalenvironment


Figure 33.18-3


Heat

Energylost infeces

Energylost innitrogenouswaste

HeatCellular

respiration



Animalbody

Externalenvironment

Carbonskeletons

ATP


Figure 33.18-4


Heat

Energylost infeces

Energylost innitrogenouswaste

HeatCellular

respiration



Animalbody

Externalenvironment

Carbonskeletons

ATP

Bio-synthesis

Cellularwork

Heat

Heat


Minimum Metabolic Rate

Animals must maintain a minimum metabolic rate for basic cell functions

Basal metabolic rate, BMR, is the minimum metabolic rate of a nongrowing endotherm that is at rest, has an empty stomach, and is not experiencing stress

The metabolic rate of a fasting, nonstressed ectotherm at a particular temperature is called standard metabolic rate, SMR


Endothermy is more energetically costly than ectothermy

For ectotherms and endotherms, activity greatly affects metabolic rate


Regulation of Energy Storage

When an animal takes in more energy than is needed for metabolism and activity, excess energy is stored

In humans, the liver and muscle cells are used first; energy is stored as glycogen

When glycogen depots are full, additional excess energy is stored as fat in adipose cells

When fewer calories are taken in than expended, the body expends liver glycogen, muscle glycogen, and then fat, in that order


Glucose Homeostasis

Insulin and glucagon together maintain glucose levels

Insulin levels rise after a carbohydrate-rich meal, and glucose entering the liver through the hepatic portal vein is used to synthesize glycogen

When glucose concentration is low in the hepatic portal vein, glucagon stimulates the liver to break down glycogen and release glucose into the blood

Insulin and glucagon are produced in the pancreas in beta cells and alpha cells, respectively

Animation: Homeostasis


Figure 33.19

Transport ofglucose intobody cellsand storageof glucoseas glycogen

Breakdown ofglycogen andrelease ofglucose intoblood

Secretionof insulin bypancreas

Secretionof glucagonby pancreas

Stimulus:Blood glucose

level dropsbelow set point.

Stimulus:Blood glucose

level risesafter eating.

Homeostasis:70–110 mg glucose/100 mL blood


Diabetes Mellitus

Diabetes mellitus is a disease caused by a deficiency of insulin or a decreased response to insulin in target tissues

Cells are unable to take up glucose to meet their metabolic needs

Fat becomes the main substrate for cellular respiration


Type 1 diabetes is an autoimmune disorder in which the immune system destroys the pancreatic beta cells

Type 2 diabetes is characterized by a failure of target cells to respond normally to insulin

Heredity is a factor in type 2 diabetes

Excess body weight and lack of exercise increase the risk


Regulation of Appetite and Consumption

Overnourishment causes obesity, which results from excessive intake of food energy with the excess stored as fat

Obesity contributes to diabetes (type 2), cancer of the colon and breasts, heart attacks, and strokes

Researchers have discovered several of the mechanisms that help regulate body weight


Ghrelin, a hormone secreted by the stomach wall, triggers a feeling of hunger before meals

Insulin and PYY, a hormone secreted by the small intestine after eating, both suppress appetite

Leptin, a hormone produced by adipose (fat) tissue, also suppresses appetite and may regulate body fat levels


Figure 33.UN01a


Figure 33.UN01b


Figure 33.UN02

Veins to heart

Lymphatic system

StomachLipids

Mouth

Esophagus

Small intestine

Hepatic portal vein

Liver

Absorbedwater

Absorbed food(except lipids)

Anus

RectumLargeintestine

Secretions from liver

Secretions from pancreas

Secretionsfrom gastricglands

Secretionsfrom salivaryglands

Science

Biology in Focus - Chapter 33