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Nutrition
• Autotrophs
– plants, some protists & bacteria
– producers
Nutrition
• Heterotrophs
– animals, fungi, some protists & bacteria
– consumers
Animal Nutrition
• Most obtain food by ingestion
– take in their food whole or piece by piece
Animal Nutrition
• Classify based on what they eat:
– Herbivores (primary consumers)
• eat autotrophs
– Carnivores (secondary or higher consumers)
• eat heterotrophs
– Omnivores
• eat both
Stages of Food Processing
• Ingestion
– eating
• Digestion
– breaking down food into small molecules
– mechanical and chemical (enzymatic hydrolysis)
• Absorption
– body takes in small molecules
• Elimination
– undigested material exits the body
Digestion
• Must take place in specialized
compartments
• to avoid damage to body cells
Food vacuoles
• food enters by endocytosis & then vacuole
merges with lysosome
• Some protists
• Sponges
– only animal with only intracellular digestion
Figure 41.10 Intracellular digestion in Paramecium
Gastrovascular Cavities
•
•
•
•
single opening
serve to both digest & transport nutrients
extracellular digestion, then intracellular
Platyhelminthes (planaria) & Cnidarians
(hydra)
What is the advantage of
extracellular digestion?
Eat larger food
Extracellular digestion in a gastrovascular cavity
Alimentary canals
or Complete Digestive Tracts
• two openings: mouth & anus
• food passes in one direction
• Found in all other animals
What is the advantage of oneway movement of food?
• Allows for specialization of different
regions of the digestive tract
Figure 41.12 Alimentary canals
Types of Digestive Systems
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Earthworm
Nematode
Salamander
Anus
Pharynx
Intestine
Mouth
Stomach Intestine
Cloaca
Intestine
Pharynx
Mouth
Mouth
Anus
Crop
Gizzard
Liver
Anus
Esophagus
Pancreas
Mammalian Digestive System
• Four-layered wall surrounds the lumen
–
–
–
–
Mucosa (epithelial tissue)
Submuscosa (connective tissue)
Muscularis (muscle)
Serosa (connective tissue)
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Oral cavity
Salivary
glands
Liver
Gallbladder
Salivary gland
Pharynx
Esophagus
Stomach
Pancreas
Small intestine
Colon
Cecum
Appendix
Rectum
Anus
Human Digestive System
• Mouth
– teeth mechanically break down food
• Similar in function to the gizzard of birds and
worms
– saliva is secreted from salivary glands
•
•
•
•
mucous protects mouth
antibacterial agents
buffer to neutralize acidity
salivary amylase – hydrolyzes glucose polymers
Human Digestive System
• Pharynx (throat)
– swallowing
• Esophagus
– peristalsis
Swallowing
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Pharynx
Air
1. As food moves to
Larynx
Trachea
Esophagus
Hard palate
Tongue
Soft palate
Epiglottis
the back of the
mouth, the soft
palate seals off
the nasal cavity.
2. During swallowing, the larynx rises
and is sealed off by the epiglottis.
This forces the bolus into the
esophagus and prevents entry into
the trachea. As the bolus moves
into the esophagus the larynx relaxes.
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Peristalic
movement
Esophagus
Relaxation
Contraction
Food Bolus
Relaxation
Human Digestive System
• Stomach
• stores food (as does the crop in other organisms)
• lining secretes gastric juice
• Pepsinogen (inactive) becomes pepsin (active) in
low pH
• smooth muscles churn the food
• Acid chyme
The Stomach
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Stomach
Gastric pit
Gastric pit
Esophagus
Serosa
Duodenum
Pyloric
sphincter
Muscularis
Mucous
cell
Longitudinal
Circular Mucosa
Oblique
Chief
cell
Mucosa
Parietal
cell
Submucosa
Oblique
Muscularis Circular
Longitudinal
Serosa
Gastric glands
Human Digestive System
• Small Intestine
• Longest part of the canal (6 m in humans)
• Duodenum (first 25 cm) – most digestion takes
place
• Jejunum and ileum – mainly absorption
• Very large surface area (300 m2) – folds, villi &
microvilli
– Similar to mycelium in fungi & roots in plants
The Small Intestine
Small intestine
Villus
Epithelial
cell
Capillary
Lacteal
Villi
Mucosa
Submucosa
Muscularis
Serosa
Lymphatic
duct
Vein
Artery
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Pancreatic islet
(of Langerhans)
 cell
From liver
 cell
Common Pancreas
bile duct
Gallbladder
Pancreatic
duct
Duodenum
Human Digestive System
• Accessory Glands:
– Pancreas
• digestive enzymes
– Lipase-lipids; pancreatic amylase-starch; trypsin - proteins
• Bicarbonate- buffer
Human Digestive System
• Accessory Glands:
– Liver
• produces bile salts which are stored in the
gallbladder until needed
• aid in the digestion of fats by emulsification
– Gallbladder
Human Digestive System
• Large Intestine or Colon
– main function is concentration & storage of
wastes
• absorption of water, sodium, vitamin K
– Feces are moved along by peristalsis and exit
the body through the anus
Hormonal Control of Digestion
• Gastrin
– released by the stomach
– feeds back to cause the secretion of gastric
juices
– Low pH inhibits its production – negative
feedback
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Stomach
Liver
pH
Proteins
Gastrin
(+)
(+)
( – ) Chief cells Parietal cells
GIP
Pepsin
(+)
Bile
Pancreas Enzymes
Bicarbonate
Gallbladder
(+)
CCK
Secretin
Duodenum
Acinar
cells
(+)
HCl
Hormonal Control of Digestion
• Enterogastrones
– Released by duodenum of small intestine
– inhibit peristalsis & secretions in the stomach
– Secretin
• Stimulated by low pH
• causes pancreas to release bicarbonate
– CCK (cholecystokinin)
• Stimulated by high fat content
• Stimulates gall bladder to release bile
– GIP (gastric inhibitory peptide)
• Inhibits emptying of the stomach
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Stomach
Liver
pH
Proteins
Gastrin
(+)
(+)
( – ) Chief cells Parietal cells
GIP
Pepsin
(+)
Bile
Pancreas Enzymes
Bicarbonate
Gallbladder
(+)
CCK
Secretin
Duodenum
Acinar
cells
(+)
HCl
Evolutionary Adaptations to Diet
• Teeth
– pointed in carnivores, flat in herbivores
Mouth and Teeth
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Herbivore
Carnivore
Omnivore
Horse
Lion
Human
Incisors
Canines
Premolars
Molars
Evolutionary Adaptations to Diet
• Length of gut
– longer in herbivores than carnivores
• Cecum
– houses bacteria that aid in digestion
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Nonruminant Herbivore
Ruminant Herbivore
Simple stomach, large cecum
Four-chambered stomach with large rumen;
long small and large intestine
Esophagus
Esophagus
Stomach
Small
intestine
Rumen
Abomasum
Reticulum
Omasum
Cecum
Small
intestine
Large
intestine
Anus
Cecum
Spiral
loop
Large
intestine
Anus
Insectivore
Carnivore
Short intestine, no cecum
Short intestine and
colon, small cecum
Esophagus
Small
intestine
Stomach
Esophagus
Stomach
Small
intestine
Large
intestine
Anus
Anus
Cecum
Large
intestine
Evolutionary Adaptations to Diet
• Ruminant Stomach- cows, deer
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Rumen
Small intestine
Esophagus
Reticulum
Abomasum Omasum
Evolutionary Adaptations to Diet
• Coprophagy – rodents, rabbits