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Nutrition and Digestion An overview of animal nutrition
A tour of the human digestive system
Human nutritional requirements
Nutritional disorders
Figure 22.0
OVERVIEW OF ANIMAL NUTRITION
• Food provides the raw materials that animals, including people, need to
– build tissue and
– fuel cellular work.
© 2013 Pearson Education, Inc.
Figure 22.UN02
O2
Carnivores eat animalsHerbivores eat plantsand/or algae
Omnivoreseat both
Figure 22.UN03
Digestion
Food
Ingestion
Mechanicaldigestion
Chemicaldigestion
via enzymesFood
in mouth
Smallmolecules
Undigestedmaterials
Insidebody
Absorption
Elimination
1
2
3
4
Figure 22.UN04
Mouth(oral cavity)
DigestionAbsorption
ChemicalMechanical
Alimentarycanal
Accessoryorgans
Pharynx andesophagus
Stomach
Smallintestine
Largeintestine
Anus
Salivary glands
Liver,gallbladder,pancreas
Chewing
Churning
Salivaryamylase
Acid andpepsin (ingastric juice)
Otherenzymes
Nutrientsand water
Water
Animal Diets
• Herbivores mainly feed on plants or algae.
• Carnivores mainly eat other animals.
• Omnivores eat
– animals and
– plants or algae.
© 2013 Pearson Education, Inc.
Figure 22.1
Herbivore(mainly eats plants
or algae)
Carnivore(mainly eats animals)
Omnivore(regularly eats animals as
well as plants or algae)
ANIMAL DIETS
The Four Stages of Food Processing
• Ingestion is another word for eating.
• Digestion is the breakdown of food into molecules small enough for the body to absorb.
• Absorption is the uptake of the small nutrient molecules by cells lining the digestive tract.
• Elimination is the disposal of undigested materials left over from food.
© 2013 Pearson Education, Inc.
Digestion: A Closer Look
• The dismantling of food molecules is necessary because food molecules are
– too large to cross the membranes of animal cells and
– different from molecules that make up an animal’s body.
© 2013 Pearson Education, Inc.
• Mechanical digestion
– begins the process and
– involves physical processes like chewing.
• Chemical digestion is the chemical breakdown of food by digestive enzymes.
Digestion: A Closer Look
© 2013 Pearson Education, Inc.
Figure 22.2
Cheese protein(a polymer ofamino acids ina specific sequence)
Amino acidmonomer
Amino acids
Human protein
Breakdown of proteinby human digestivesystem
Absorption of amino acids by cells lining thesmall intestine; transport via bloodstream toother cells
Cells use amino acidsfrom the cheese andother foods to producenew human proteins
1
2
3
Figure 22.2c
• Chemical digestion proceeds via hydrolysis, chemical reactions that break down polymers into monomers using water in the process.
• Like most biological reactions, digestion also requires enzymes.
Digestion: A Closer Look
© 2013 Pearson Education, Inc.
Figure 22.3
Enzyme (pepsin)
Enzyme (amylase)
Enzyme (lipase)
Protein
Carbohydrate
Fat
Amino acid
Fatty acidGlycerol
Sugar
H2O
H2O
H2O
H2O
H2O
HOH
OHH
H
H
OH
OH
HOH
Digestive Compartments
• How do animals digest their food without digesting themselves?
• In animals, chemical digestion is contained safely within some kind of compartment.
© 2013 Pearson Education, Inc.
• As a cell engulfs food by phagocytosis,
– a food vacuole forms,
– which then fuses with a lysosome filled with digestive enzymes, and
– as food is digested, small food molecules pass through the vacuole membrane into the cytoplasm, which nourishes the cell.
Digestive Compartments
© 2013 Pearson Education, Inc.
• Food vacuoles are the simplest of all digestive compartments.
• Sponges are the only animals that digest food solely within their cells.
• Gastrovascular cavities
– are digestive compartments surrounded by cells and
– have only a single opening.
Digestive Compartments
© 2013 Pearson Education, Inc.
• A digestive tube, or alimentary canal, has two separate openings:
– a mouth and
– an anus.
Digestive Compartments
© 2013 Pearson Education, Inc.
• Food moves through specialized regions of a digestive tube that
– digest and
– absorb nutrients in a stepwise fashion.
Digestive Compartments
© 2013 Pearson Education, Inc.
Figure 22.4
Food(water flea)
Gastrovascular Cavity(compartment with single opening)
MAIN TYPES OF DIGESTIVE COMPARTMENTS
Interior ofintestineNewly
engulfedfood particle
Singleopening
Gastrovascularcavity
Earthworm
Intestine
Mouth
Hydra
Anus
Alimentary Canal (Digestive Tract)(tube from mouth to anus)
Digestedfoodparticle
A TOUR OF THE HUMAN DIGESTIVE SYSTEM System Map Bozeman Digestive
• The human digestive system consists of
– a digestive tube, the alimentary canal (or gut), and
– accessory organs that secrete digestive chemicals.
© 2013 Pearson Education, Inc.
Figure 22.5
Oral cavity (mouth)
Pharynx
Esophagus
Stomach
Small intestineColon of large intestineAppendixRectumAnus
Salivary glands
LiverGallbladderPancreas
Tongue
ALIMENTARY CANALACCESSORY ORGANS
The Mouth
• The mouth, or oral cavity, functions in
– ingestion and
– the preliminary steps of digestion.
• Chemical digestion begins in the mouth with the secretion of saliva from salivary glands.
• The muscular tongue
– tastes,
– shapes food into a ball, and
– pushes the food to the back of the mouth for swallowing.© 2013 Pearson Education, Inc.
Figure 22.6
Incisors
Canine
Premolars
Molars
“Wisdom”tooth
Tongue
Opening of asalivary gland duct
Teeth
• The pharynx
– connects the mouth to the esophagus and
– opens to the trachea, which leads to the lungs.
• During swallowing, a reflex
– moves the opening of the trachea upward and
– tips the epiglottis to close the trachea entrance.
The Pharynx
© 2013 Pearson Education, Inc.
Figure 22.7
Epiglottisdown
Air flowinginto opentrachea(windpipe)
Esophagusclosed
Epiglottisup
Pharynx
BREATHING SWALLOWING
Food flowinginto openesophagus
Adam’sapple
Tracheaclosed
The Esophagus
• The esophagus
– is a muscular tube,
– connects the pharynx to the stomach, and
– moves food down by peristalsis, alternating waves of muscular contraction and relaxation.
© 2013 Pearson Education, Inc.
Figure 22.8
Esophageal sphincter(contracted)
Contracted muscles
Relaxed muscles
Relaxed muscles
Food ball
Stomach
The Stomach
• The stomach
– can store food for several hours and
– churns food into a thick soup called chyme.
• Fluid in the stomach contains gastric juice, made of
– strong acid,
– digestive enzymes,
– mucus, and
– the enzyme pepsin, which digests proteins.© 2013 Pearson Education, Inc.
Figure 22.9
Stomach lining secretes gastric juice (acid, enzymemolecules, and mucus)
Sphincters controlthe flow into andout of the stomach
Accordion-likefolds allow thestomach to expand.
Food particleSmall intestine
Esophagus
Stomach Ailments
• Heartburn is caused by backflow of chyme into the esophagus.
• Gastric ulcers are
– erosions of the stomach lining and
– often caused by the bacterium Helicobacter pylori.
© 2013 Pearson Education, Inc.
Weight Loss Surgeries
• The most common weight loss surgery in the United States is gastric bypass.
– Staples are used to reduce the stomach to about the size of a chicken egg.
– The first 18 inches of the small intestine are bypassed by attaching the downstream intestine directly to the reduced stomach pouch.
• As a result,
– patients quickly feel full when eating and
– the body’s ability to absorb food is reduced.
© 2013 Pearson Education, Inc.
Figure 22.10
Esophagus Small stomach pouch
Staples
New attachment
Bypassed portionof stomach
Tube through whichfood is bypassed
Small intestine
The Small Intestine
• The small intestine is
– the longest part of the alimentary canal and
– the major organ for chemical digestion and absorption of nutrients into the bloodstream.
© 2013 Pearson Education, Inc.
Chemical Digestion in the Small Intestine
• Most chemical digestion occurs in the duodenum, the first part of the small intestine.
• In the duodenum, chyme from the stomach mixes with
– pancreatic juice,
– bile, and
– a digestive juice secreted by the intestinal lining.
© 2013 Pearson Education, Inc.
Figure 22.11
Liver
Gallbladder
Bile
Bile
Chyme
Stomach
Pancreas
Pancreatic juice
Duodenum ofsmall intestine
Intestinal enzymes
• The pancreas secretes juice that
– neutralizes stomach acids in the duodenum and
– aids in digestion.
• The liver secretes bile, which
– is stored in the gallbladder and
– helps digest fats.
Chemical Digestion in the Small Intestine
© 2013 Pearson Education, Inc.
Absorption of Nutrients
• In the duodenum, nutrients are
– completely digested and
– ready to be absorbed.
• Nutrients only enter the body if they are absorbed into the walls of the digestive tract.
© 2013 Pearson Education, Inc.
Figure 22.12
Food through the alimentary canalA finger through a hole
Alimentarycanal
Mouth
Anus
• Villi and microvilli on the surface of the small intestine increase
– the surface area and
– capacity for absorption.
Absorption of Nutrients
© 2013 Pearson Education, Inc.
Figure 22.13
Blood vessels
Interior ofintestine
Interior ofintestine
Musclelayers
Nutrientabsorption
Nutrientabsorption
Nutrientabsorption
Epithelialcells
Bloodcapillaries
LymphaticvesselEpithelial cells and
blood capillary
Intestinal wall
Microvilli
Villi
Blood
Villi
The Large Intestine
• The large intestine is
– shorter, but wider, than the small intestine and
– about 1.5 meters in length.
• At the junction of the small and large intestine is a small, finger-like extension called the appendix.
– The appendix contains white blood cells that make minor contributions to the immune system.
– Appendicitis is a bacterial infection of the appendix.
© 2013 Pearson Education, Inc.
• The colon
– forms the main portion of the large intestine,
– absorbs water from the alimentary canal, and
– produces feces, the waste product of food.
– The colon is composed of the cecum(receiving chamber for food from ileum), the ascending colon, the transverse colon, the descending colon, the sigmoid colon, the rectum and anus
The Large Intestine
© 2013 Pearson Education, Inc.
• The rectum
– forms the last 15 cm (6 inches) of the large intestine and
– stores feces until elimination.
• The anus
– consists of two sphincters and
– regulates the opening of the rectum.
The Large Intestine
© 2013 Pearson Education, Inc.
Figure 22.14
Colon oflargeintestine
Endof smallintestine
Smallintestine
Nutrientflow
Sphincter
Appendix
Rectum
Anus
Figure 22.14b
Endof smallintestine
Nutrientflow
Sphincter
Appendix
Figure 22.15-4
Smallintestine
Largeintestine
Stomach
Mouth
Anus
Food
Feces
Digestion Mechanical digestion Chewing in mouth Churning in stomach
Ingestion Food into mouth
Chemical digestion Saliva in mouth Acid and pepsin in stomach Enzymes in small intestine
Absorption Nutrients and water in small intestine
Water in large intestine
Elimination Feces formed in large intestine
Elimination from anus
HUMAN NUTRITIONAL REQUIREMENTS
• Proper nutrition provides
– fuel for cellular work,
– materials for building molecules, and
– essential nutrients for health.
© 2013 Pearson Education, Inc.
Food as Fuel
• Cells use cellular respiration to
– extract energy stored in food molecules and
– generate molecules of ATP to do work.
© 2013 Pearson Education, Inc.
Figure 22.16“Fuel”
(organic moleculessuch as glucose)
Cellularrespiration
Mitochondrion
Cell
O2C6H12O6
“Exhaust”
andCO2H2O
ATP
(energy forcellular work)
Calories
• Calories are a measure of the energy
– stored in your food and
– used in daily activitiesA calorie is the amount of energy required to raise the temperature of one gram of water by 1°C.
• A kilocalorie (kcal) is
– 1,000 calories,
– the unit listed on food labels, and
– often called Calories with an uppercase C.© 2013 Pearson Education, Inc.
Metabolic Rate
• The rate of energy consumption by the body is the metabolic rate.
• A person’s metabolic rate consists of
– the basal metabolic rate (BMR), the amount of energy it takes to maintain body functions, and
– energy needed for activities.
© 2013 Pearson Education, Inc.
Table 22.1
Food as Building Material
• Building blocks from the breakdown of organic molecules are used to
– repair tissues and
– maintain tissues.
• Essential nutrients
– are substances needed by the body but
– cannot be made in the body from other molecules.
© 2013 Pearson Education, Inc.
Essential Amino Acids
• In humans, eight essential amino acids
– must be obtained from the diet and
– are in different proportions in different foods.
• All eight essential amino acids can be consumed by eating
– meat, eggs, or milk or
– a variety of plants, typically grains and legumes such as beans, peanuts, and peas.
© 2013 Pearson Education, Inc.
Figure 22.17
Complete mealsBread and peanut butterRice and beans Rice and tofu
Beans and otherlegumes
Methionine
Valine
Threonine
Phenylalanine
Leucine
Isoleucine
Tryptophan
Lysine
Vitamins
• Vitamins
– are organic molecules,
– are required in the diet in very small amounts, and
– usually assist enzymes in catalyzing metabolic reactions. “coenzymes”
• Too much or too little of most vitamins can cause harm.
© 2013 Pearson Education, Inc.
Table 22.2
Figure 22.UN01
Minerals
• Minerals are inorganic substances required in the diet.
• Too much or too little of most minerals can cause harm.
• Iodine is used by the thyroid gland
• Iron is used in hemoglobin
• Calcium is used to make bone
© 2013 Pearson Education, Inc.
Essential Fatty Acids
• Our cells make fats and other lipids by combining fatty acids and other molecules.
• Essential fatty acids must be obtained in the diet.
© 2013 Pearson Education, Inc.
Decoding Food Labels
• On food labels, the FDA requires
– the list of ingredients and
– key nutrition facts.
© 2013 Pearson Education, Inc.
Figure 22.18
NUTRITIONAL DISORDERS
• Dietary problems can cause severe health problems.
© 2013 Pearson Education, Inc.
Malnutrition
• Malnutrition refers to health problems caused by an
– improper or
– insufficient diet.
• Protein deficiency
– causes the most human suffering and
– is concentrated where there is a great gap between food supply and population size.
© 2013 Pearson Education, Inc.
Figure 22.19
Eating Disorders
• Eating disorders
– affect millions of Americans,
– are more common in women than men, and
– result in malnutrition.
• Anorexia nervosa is self-starvation, even when a person is underweight.
• Bulimia involves
– binge eating,
– purging through induced vomiting,
– abuse of laxatives, and/or
– excessive exercise.© 2013 Pearson Education, Inc.
Obesity
• Obesity
– is a too-high body mass index (BMI),
– is the nutritional disorder of greatest concern,
– affects about one-third of all Americans, and
– increases the risk of heart attack, diabetes, and other diseases.
© 2013 Pearson Education, Inc.
Figure 22.20
Weight (pounds)
Hei
gh
t
Und
erw
eigh
t
Nor
mal
Ove
rwei
ght
Obe
se
Ext
rem
ely
obes
e
6’4”
6’3”
6’2”
6’1”
6’0”
5’11”
5’10”
5’9”
5’8”
5’7”
5’6”
5’5”
5’4”
5’3”
5’2”
5’1”
5’0”
4’11”
4’10”100 110
BM
I <18
.5
BM
I 18.
5–24
BM
I 25–
29
BM
I 30–
39
BM
I >39
120 130 140 150 160 170 180 190 200 210 220 230 240 250 260