Transcript Nutrition and Digestion

Chapter 21
NUTRITION AND DIGESTION
Stages of Food Processing
1. Ingestion: The act of eating. Usually involves
placing food in mouth or oral cavity.
2. Digestion: Macromolecules in food (fats, proteins,
polysaccharides, etc.) are too large to be absorbed
by digestive system.
Must be broken down into small molecules
(amino acids, simple sugars, etc.) so they can be
absorbed and utilized by the body.
Involves two processes:
Mechanical: Chewing and churning.
Chemical: Enzymatic breakdown of food.
Stages of Food Processing
Stages of Food Processing
3. Absorption: Cells lining the digestive cavity take
up building blocks (simple sugars, amino acids,
etc.), which then enter the bloodstream.
Circulatory system distributes nutrients in blood
to cells throughout the body.
4. Elimination: Undigested food materials are
discharged from body.
Parts of the Human Digestive System
Alimentary canal: Long tube like structure.
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Mouth
Tongue
Pharynx (throat)
Esophagus
Stomach
Small intestine
Large intestine
Rectum
Anus
Digestive glands: Produce enzymes, bile, and other
substances important for digestion.
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Salivary glands
Pancreas
Liver and gallbladder
Human Digestive System
Human Digestive System
Mouth:
 Ingest
and mechanically break down food.
 Digestion:
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Saliva lubricates and starts to digest food.
Starch is digested by salivary amylase
 Other
enzymes in saliva kill bacteria.
Mouth: Ingestion, Mechanical
Breakdown, and Early Digestion of Food
Part of the Human Digestive System
Pharynx (Throat):
 Throat
opens into both the trachea (respiratory
system) and esophagus (digestive system).
 As food enters pharynx, swallowing reflex is triggered:
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Esophageal sphincter relaxes
Epiglottis blocks tracheal opening
Food is directed towards esophagus
Esophagus:
 Muscular
tube that conveys food to stomach.
 Peristalsis: Wavelike involuntary muscle contractions
squeeze food through alimentary canal (towards the
stomach).
Swallowing Reflex and Esophageal Peristalsis
Smooth Muscle Peristalsis Moves
Food Along Alimentary Canal
Part of the Human Digestive System
Stomach:
 Located
on left side of abdominal cavity, right below
diaphragm.
 Stores food (can stretch to accommodate up to 2 liters
of food and water), and breaks it down with acids and
enzymes.
 Gastric juice is secreted by stomach. Contains
hydrochloric acid (HCl), enzymes (pepsin), and mucus.
 Protein digestion starts in stomach with pepsin.
 Food is churned in stomach with gastric juice to form
chyme.
 Food remains in stomach from 2 to 6 hours, after
which it is released into the small intestine.
Stomach: Food Storage and Digestion
Part of the Human Digestive System
Gastric ulcers:
 Open
lesions in stomach wall.
 Until recently believed to be caused by stress or diet.
 Now we know that most are caused by a bacterium
Helicobacter pylori.
 Up to 50% people worldwide are infected.
 Initially causes gastritis, inflammation of stomach
lining, which may worsen with time.
 About 10% of infected individuals develop ulcers,
which may cause internal bleeding or infection.
 A small percentage of infected individuals will
develop stomach cancer.
 Can be treated and cured with antibiotics.
Helicobacter pylori causes Gastric Ulcers
Part of the Human Digestive System
Small Intestine:
 Huge
surface area, about 300 square meters.
 Most digestion and absorption occurs here.
 Pancreas and liver empty digestive enzymes and bile
into the small intestine.
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Pancreatic amylase: Breaks down starch
Trypsin and Chymotrypsin: Break down proteins
Lipases: Break down fats
Peptidases: Break down proteins
Nucleases: Break down DNA and RNA
Bile: Helps fat digestion by emulsifying fats.
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large surface area for absorption due to:
Large circular folds (villi)
Tiny cell surface projections (microvilli).
 Capillaries
drain nutrients from small intestine and
then sends them to first to liver and then rest of body.
Small Intestine: Site of Digestion and Absorption
Small Intestine is Site Most Enzymatic
Digestion
Human Digestive System
Large Intestine (Colon):
 1.5
m long and 5 cm wide (diameter)
 Most water absorption occurs here (up to 90%).
 Undigested remainder of food is converted into feces.
 Site of bacterial synthesis
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Vitamin K
Folic acid
Biotin
Several B vitamins
 Appendix:
Small fingerlike projection. Involved in
immunity.
Rectum:
 Stores
feces until ready to eliminate
Large Intestine: Water Absorption
and Formation of Feces
Human Digestive System
Digestive Glands:
Liver:
 Produces
bile which is stored in gallbladder.
 Bile is released into the small intestine after a meal.
 Bile contains no enzymes, but helps solubilize fat
particles.
 Has many other functions.
Pancreas:
 Produces
several digestive enzymes which are emptied
into small intestine.
 Enzymes digest starch, protein, fats, and nucleic acids.
Digestive Glands: Liver and Pancreas
Empty Contents into Small Intestine
Nutritional Needs of Animals
The diet of animals provides:
1. Fuel (chemical energy) to power body activities.
2. Organic raw materials to make animal’s own
macromolecules.
3. Essential nutrients or substances that the animal
cannot make for itself and must obtain
prefabricated from food:
 Essential
 Vitamins
 Minerals
amino acids
Nine Amino Acids are Essential Nutrients
 Essential
nutrients are substances that the animal
cannot make for itself from raw materials.
 Adult
humans cannot make nine of the 20 amino
acids needed to make proteins.
 Complete
proteins: All essential amino acids are
present (Example: Meat, milk, eggs, and cheese).
 Incomplete
proteins: Deficient in one or more amino
acid. Most plants are incomplete sources of amino
acids (Example: Rice, corn, and wheat).
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Vegetarian diets must carefully balance protein sources.
Essential Amino Acids Are Not Synthesized by Humans
Most Vegetables are Incomplete Protein Sources
Humans Require 13 Vitamins in Their Diets
Animals can be classified based on their diet:
I. Omnivores: Ingest both plants and animals.
II. Herbivores: Only eat plants.
III. Carnivores: Eat other animals.
Adaptations of vertebrate digestive systems reflect
their diet:
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Teeth
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Special chambers
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Digestive tract length
Adaptations of Vertebrate Digestive System Reflect Diet
Animal Digestive Systems Are Adapted to Their Diets
Ruminant Digestive System: Reticulum and Rumen Harbor Microbes
that Digest Cellulose
Diet Can Influence Cardiovascular Disease and Cancer