Download Small intestine

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Lecture 10 Outline (Ch. 41)
I.
Animal Nutrition Overview
II.
Food Intake
III. Digestive Compartments
IV. Adaptations
V.
Energy sources and stores
VI. Preparation for next lecture
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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 (converted to ATP)
• Organic carbon and 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/B7
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: process of breaking food down into molecules small enough to
absorb. In chemical digestion, enzymatic hydrolysis splits bonds in molecules
Small
molecules
Pieces
of food
Mechanical
digestion
Chemical digestion
Nutrient
(enzymatic hydrolysis) molecules
enter body
cells
Undigested
material
Food
1 Ingestion
2 Digestion
Absorption is uptake of
nutrients by body cells
3 Absorption
4 Elimination
Elimination is the passage of undigested
material out of the digestive compartment
Digestive Compartments
• Most animals process food (i.e. hydrolysis) in
specialized compartments
• Reduces risk animal digesting
its own cells/
Tentacles
tissues
Food
Gastrovascular Cavity:
Mouth
Gastrovascular
cavity
For both digestion and
distribution of nutrients
Cells secrete digestive
enzymes
Epidermis
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Gastrodermis
Digestive
Compartments
• More complex animals:
digestive tube with two
openings (mouth, anus)
“Tube within a tube”
Crop Gizzard
Intestine
Esophagus
Pharynx
Anus
Mouth
Typhlosole
Lumen of intestine
(a) Earthworm
Foregut
Midgut
Hindgut
Rectum
Anus
Esophagus
• Called alimentary canal
Crop
• Specialized regions,
carry out digestion and
absorption stepwise
Mouth
Gastric cecae
(b) Grasshopper
Stomach
Gizzard
Intestine
Mouth
Esophagus
Crop
Anus
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(c) Bird
Digestive Compartments
Food moves by peristalsis
Tongue
Sphincter
Salivary
glands
Oral cavity
Salivary glands
Mouth
Pharynx
Esophagus
Esophagus
Sphincter
Liver
Stomach
Ascending
portion of
large intestine
Gallbladder
Gallbladder
Stomach
Duodenum of
small intestine
Pancreas
Small
intestine
Liver
Small
intestine
Small
intestine
Large
intestine
Pancreas
Large
intestine
Rectum
Anus
Rectum
Anus
Appendix
Cecum
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
Tongue
Epiglottis
up
Pharynx
Epiglottis
down
Larynx
Trachea
Esophagus
To To
lungs stomach
Esophageal
sphincter
relaxed
Relaxed
muscles
Contracted
muscles
• Food  bolus,
Relaxed
• Esophagus
muscles
Sphincter
saliva added,
relaxed
conducts food
digestion begins with pharynx to stomach
amylase and mucus
by peristalsis
Stomach
• Pharynx, junction
• Epiglottis blocks
opens to both the
entry to the trachea,
esophagus and the
and larynx.
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trachea (windpipe)
Digestion in the Stomach
• The stomach stores food and secretes gastric
juice, which converts a meal to acid chyme
5 µm
• Highly folded
• Gastric juice hydrochloric acid
(parietal cells) and
the enzyme pepsin
(chief cells)
• Pepsin initially
Gastric gland
secreted as
pepsinogen
Mucus cells
• Mucus protects
the stomach lining
from gastric juice
Esophagus
Sphincter
Stomach
Sphincter
Small
intestine
Folds of
epithelial
tissue
Epithelium
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Pepsinogen
2
HCl
Pepsin
1
Cl–
H+
Chief cell
Parietal cell
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Digestion in the Small Intestine
• The small intestine: longest section of alimentary canal
• Major organ of enzymatic
digestion and absorption
• 1st: duodenum
- acid chyme from
stomach mixes with
digestive juices from
pancreas, liver,
gallbladder, and the
small intestine itself.
- 2nd: jejunum
- 3rd: ileum
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Digestion in the Small Intestine
liver/gallbladder
pancreas
bile aids digestion
and absorption
of fats
proteases trypsin
& chymotrypsin
amylase & lipase
bicarbonate
neutralizes the
acidic chyme
small intestine
lining of duodenum
(brush border)
produces several
digestive enzymes
jejunum and ileum
mainly absorb17
water & nutrients
Carbohydrate digestion
Oral cavity,
pharynx,
esophagus
Polysaccharides Disaccharides
Salivary amylase
Smaller
Maltose
polysaccharides
Protein digestion
Proteins
Stomach
Pepsin
Small polypeptides
Small
intestine Pancreatic amylases
(enzymes Disaccharides
from
pancreas)
Pancreatic trypsin and
chymotrypsin
Smaller
polypeptides
Nucleic acid digestion
Fat digestion
DNA, RNA
Fat (triglycerides)
Pancreatic
nucleases
Nucleotides
Pancreatic lipase
Pancreatic carboxypeptidase
Glycerol, fatty acids,
monoglycerides
Small peptides
Small
intestine
(enzymes
from
epithelium)
Disaccharidases
Dipeptidases, carboxypeptidase, and
aminopeptidase
Nucleotidases
Nucleosides
Nucleosidases
and
phosphatases
Monosaccharides
Amino acids
Nitrogenous bases,
sugars, phosphates
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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
extension (appendix),
-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
– Internal smooth
muscle sphincter
(involuntary)
– External striated
muscle sphincter
(voluntary)
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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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Abomasum
3
Omasum
Adaptations
• Herbivores
generally
longer
alimentary
canals than
carnivores;
longer time
needed to
digest
vegetation
Small intestine
Stomach
Small
intestine
Cecum
Enzymes for
digesting
plant matter
• Coprophagy –
method to
recover more
nutrients by
ingesting feces
Colon
(large
intestine)
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Carnivore
Herbivore
Energy Sources and Stores
Pancreas
releases insulin
– cells uptake
sugars
Stimulus:
Blood glucose
level rises
after eating.
Homeostasis:
90 mg glucose/
100 mL blood
Pancreas releases
glucagon – liver
releases sugars
Stimulus:
Blood glucose
level drops
below set point.
Energy Sources and Stores
• Animals store excess calories as glycogen in the
liver and muscles
• Energy secondarily stored as adipose, or fat, cells
• Fewer calories taken in than expended 
fuel is taken from storage and oxidized
• Excessive intake of food energy,
excess stored as fat
Fat cells
• Obesity contributes to
diabetes (type 2), colon
and breast cancer, heart
attacks, and strokes
100 µm
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Energy Sources and Stores
• The complexity of weight
control in humans is wellstudied
• Mice that inherit a defect
in the gene for leptin
become very obese
Ghrelin – secreted by stomach,
stimulates appetite
Insulin – secreted by pancreas,
suppresses appetite
Leptin – released by fat cells,
suppresses appetite
PYY – secreted by Sm. Intestine,
suppresses appetite
hypothalamus
Ghrelin
Insulin
Leptin
PYY
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Obese mouse with mutant ob gene (left) – mutant
for leptin production – next to wild-type sibling mouse.
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Things To Do After Lecture 10…
Reading and Preparation:
1.
Re-read today’s lecture, highlight all vocabulary you do not
understand, and look up terms.
2.
Ch. 41 Self-Quiz: #2, 3, 4, 5, 6 (correct answers in back of book)
3.
Read chapter 41, focus on material covered in lecture (terms,
concepts, and figures!)
4.
Skim next lecture.
“HOMEWORK” (NOT COLLECTED – but things to think about for studying):
1.
Describe the pathway that food molecules take from ingestion through
elimination – where appropriate, indicate which digestive enzymes are
secreted and what biomolecules are broken down.
2.
Define, and then list: necessary vitamins and minerals.
3.
Explain the difference between a substrate feeder and a bulk feeder.
4.
Compare the function of leptin and ghrelin – where and when are each
secreted/released?