Download small intestine

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Lecture 13 Outline (Ch. 48)
I.
Animal Nutrition Overview
II.
Essential Parts of Animal Diet
III. Food Intake
IV. Digestive Compartments
V.
Adaptations
VI. Obesity
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Overview: The Need to Feed
• 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 autotrophs (plants, algae)
– Carnivores eat other animals
– Omnivores regularly consume animals as well as plants
or algal matter
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Essential Parts of Diet
• Chemical energy, which is converted into
ATP and powers processes in the body
• Organic carbon and organic nitrogen
• Essential nutrients must be obtained
from dietary sources
–Essential amino acids
–Essential fatty acids
–Vitamins
–Minerals
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Essential Parts of Diet
• Meat, eggs, cheese - provide all nine essential
amino acids ( “complete” proteins)
• Individuals eating only plant proteins need specific
plant combinations for all essential amino acids
Essential amino acids for adults
Methionine
Valine
Beans and
other legumes
Threonine
Phenylalanine
Leucine
Corn (maize)
and other grains
Isoleucine
Tryptophan
Lysine
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Essential Parts of Diet
• Animals can synthesize most fatty acids they need
• The essential fatty acids are certain unsaturated fatty
acids that must be obtained from the diet
• Vitamins: organic molecules
needed in small amounts
• 13 essential vitamins for humans
• Fat-soluble & water-soluble
Vitamin A
B-complex
Vitamin D
Biotin
Vitamin E
Vitamin C
(ascorbic acid)
Vitamin K
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Minerals
• Minerals: inorganic nutrients, small amounts needed
Calcium
Phosphorus
Potassium
Sulfur
Chlorine
Sodium
Magnesium
Iron
A diet missing a certain essential part or not enough calories
overall leads to malnourishment or undernourishment
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Food Intake
Ingestion: the act of eating
• Suspension feeders - many aquatic animals,
which sift small food particles from the water
• Substrate feeders are animals that live in or on
their food source
• Fluid feeders suck nutrient-rich fluid from a living
host
• Bulk feeders eat relatively large pieces of food
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Leaf miner caterpillar, substrate feeder
Baleen
Humpback whale, a suspension feeder
Caterpillar
Mosquito, a fluid feeder
Feces
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Rock python, a bulk feeder
Food Intake
• Digestion is the process of breaking food
down into molecules small enough to
absorb
– 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 compartment10
Food Intake
Small
molecules
Pieces
of food
Mechanical
digestion
Chemical digestion
Nutrient
(enzymatic hydrolysis) molecules
enter body
cells
Undigested
material
Food
1 Ingestion
2 Digestion
3 Absorption
4 Elimination
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Digestive Compartments
• Most animals process food in specialized
compartments
• Reduces risk animal digesting
its own cells/
Tentacles
tissues
Food
Mouth
Gastrovascular
cavity
Epidermis
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Gastrodermis
Digestive
Compartments
Crop Gizzard
Intestine
Esophagus
Pharynx
Anus
Mouth
• More complex animals:
digestive tube with two
openings (mouth, anus)
• Tube called a complete
digestive tract or an
alimentary canal
• Can have specialized
regions, carry out
digestion and
absorption stepwise
Typhlosole
Lumen of intestine
(a) Earthworm
Foregut
Midgut
Hindgut
Rectum
Anus
Esophagus
Crop
Mouth
Gastric cecae
(b) Grasshopper
Stomach
Gizzard
Intestine
Mouth
Esophagus
Crop
Anus
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(c) Bird
Digestive Compartments
Tongue
Sphincter
Salivary
glands
Oral cavity
Salivary glands
Mouth
Pharynx
Esophagus
Esophagus
Sphincter
Liver
Stomach
Ascending
portion of
large intestine
Gallbladder
Gallbladder
Duodenum of
small intestine
Pancreas
Liver
Small
intestine
Small
intestine
Pancreas
Large
intestine
Anus
Cecum
Small
intestine
Large
intestine
Rectum
Anus
Rectum
Appendix
Stomach
A schematic diagram of the
human digestive system
• Mammalian alimentary canal and accessory
glands that secrete digestive juices through ducts
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Oral Cavity, Pharynx, Esophagus
Food
Epiglottis
up
Tongue
Epiglottis
up
Pharynx
Esophageal
sphincter
contracted
Glottis
Larynx
Trachea
Epiglottis
down
Esophagus
To To
lungs stomach
• Food shaped into a
bolus, lubricated by
saliva, digestion begins
with amylase.
• Pharynx, a junction that
opens to both the
esophagus and the
trachea (windpipe)
Glottis up
and closed
Glottis
down
and open
Esophageal
sphincter
relaxed
• The esophagus
conducts food from the
pharynx down to the
stomach by peristalsis
• Epiglottis blocks entry
to the trachea, and
larynx.
Esophageal
sphincter
contracted
Relaxed
muscles
Relaxed
muscles
Contracted
muscles
Sphincter
relaxed
Stomach
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Digestion in the Stomach
• The stomach stores food and secretes gastric
juice, which converts a meal to acid chyme
Esophagus
5 µm
• Gastric juice hydrochloric
acid (parietal
cells) and the
enzyme pepsin
(chief cells)
Interior surface
• Mucus protects of stomach
the stomach
Gastric gland
lining from
gastric juice
Mucus cells
Sphincter
Stomach
Sphincter
Small
intestine
Folds of
epithelial
tissue
Epithelium
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Pepsinogen
2
HCl
Pepsin
1
Cl–
H+
Chief cells
Chief cell
Parietal cells
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Parietal cell
Digestion in the Small Intestine
• The small intestine: longest section of alimentary canal
• Major organ of digestion and absorption
• First is the duodenum - acid chyme from the stomach
mixes with digestive juices from the pancreas, liver,
gallbladder, and the small intestine itself.
pancreas
proteases trypsin &
chymotrypsin
amylase & lipase
neutralizes the
acidic chyme
liver/gallbladder
bile aids digestion
and absorption
of fats
small intestine
lining of duodenum
(brush border)
produces several
digestive enzymes
jejunum and ileum
mainly absorb water
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& nutrients
Digestion in the Small Intestine
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Carbohydrate digestion
Oral cavity,
pharynx,
esophagus
Polysaccharides
Disaccharides
(starch, glycogen)
(sucrose, lactose)
Protein digestion
Nucleic acid digestion
Fat digestion
Salivary amylase
Smaller polysaccharides,
maltose
Stomach
Proteins
Pepsin
Small polypeptides
Lumen of
small intestine
Polysaccharides
Pancreatic amylases
Polypeptides
Pancreatic trypsin and
chymotrypsin
DNA, RNA
Fat globules
Pancreatic
nucleases
Bile salts
Maltose and other
disaccharides
Nucleotides
Fat droplets
Smaller
polypeptides
Pancreatic lipase
Pancreatic carboxypeptidase
Glycerol, fatty
acids, monoglycerides
Amino acids
Epithelium
of small
intestine
(brush
border)
Small peptides
Disaccharidases
Monosaccharides
Nucleotidases
Nucleosides
Dipeptidases, carboxypeptidase,
and aminopeptidase
Amino acids
Nucleosidases
and
phosphatases
Nitrogenous bases,
sugars, phosphates
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Absorption in the Small Intestine
• small intestine has huge surface area, from villi and
microvilli exposed to the intestinal lumen
• enormous microvillar surface greatly increases rate
of nutrient absorption
Microvilli (brush
border) at apical
(lumenal) surface Lumen
Vein carrying blood
to hepatic portal vein
Blood
capillaries
Muscle layers
Epithelial
cells
Basal
surface
Large
circular
folds
Villi
Epithelial cells
Lacteal
Key
Nutrient
absorption
Intestinal wall
Villi
Lymph
vessel
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Absorption in the Small Intestine
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Absorption in the Large Intestine
• The colon of the large intestine is
connected to the small intestine
• The cecum aids
in fermentation
of plant material,
connects where the
small and large
intestines meet
• Human cecum has
extension (appendix),
plays a minor role in
immunity
Feces stored in rectum
until eliminated
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Absorption in the Large Intestine
• The colon houses strains of the
bacterium Escherichia coli, some of
which produce vitamins
• Two sphincters between the rectum and
anus control bowel movements
– Smooth muscle sphincter (involuntary)
– Striated muscle sphincter (voluntary)
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Adaptations
• Herbivores
generally have
longer
alimentary
canals than
carnivores,
reflecting the
longer time
needed to
digest
vegetation
Small intestine
Stomach
Small
intestine
Cecum
Colon
(large
intestine)
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Carnivore
Herbivore
Mutualistic Adaptations
• Many herbivores have symbiotic microorganisms
that digest cellulose
• The most elaborate adaptations in ruminants
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Rumen
2
Reticulum
Intestine
Esophagus
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4
Abomasum
3
Omasum
Energy Sources and Stores
• Animals store excess calories as glycogen in the
liver and muscles
• Energy secondarily stored as adipose, or fat, cells
• When fewer calories are taken in than are
expended, fuel is taken from storage and oxidized
• Obesity is due to excessive
intake of food energy,
excess stored as fat
• Obesity contributes to
diabetes (type 2), cancer
of the colon and breasts,
heart attacks, and strokes
100 µm
Fat cells
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Energy Sources and Stores
Stimulus:
Blood glucose
level rises
after eating.
Homeostasis:
90 mg glucose/
100 mL blood
Stimulus:
Blood glucose
level drops
below set point.
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Energy Sources and Stores
• The complexity of
weight control in
humans is evident
from studies of the
hormone leptin
• Mice that inherit a
defect in the gene
for leptin become
very obese
Ghrelin
Insulin
Leptin
PYY
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Obese mouse with mutant ob gene (left) next to
wild-type sibling mouse.
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Obesity and Evolution
• The problem of maintaining weight partly
stems from our evolutionary past, when
fat hoarding was a means of survival
• A species of birds called petrels become
obese as chicks; in order to consume
enough protein from high-fat food, chicks
need to consume more calories than they
burn
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A plump petrel
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Lecture 13 Summary
1. Essential Nutrients (Ch. 48)
Amino acids, fatty acids, vitamins, minerals
2. Types of Food Intake and Digestive Tracts (Ch. 48)
Suspension, substrate, fluid, bulk feeders
Gastrovascular, simple, complex digestive cavities
3. Digestive Tract and Enzymes/Secretions (Ch. 48)
Mouth
Stomach
Auxiliary Organs
Small Intestine
Large Intestine
4. Adaptations and Control (Ch. 48)
Diet and digestive tract
Mutualisms
Obesity and Energy Stores