1. BIOLOVE 2013
BIOLOVE
DIGESTIVE SYSTEM
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Ways of ingesting
• Substrate feeders – caterpillar
- Live in or on the food source
- Ingest the food source and also eliminate on the
food source.
Photo 1 : caterpillar (substrate feeder)
• Bulk feeders – humans, snake, tiger
- Ingest large pieces of foods.
• Fluid feeder – mosquito
- Sucking nutrient from a living host
• Suspension feeder – tube worm, whale, oyster, clam Photo 2 : Aphid sucking nutrient from phloem
- Extract food particles suspended in the surrounding water.
Food processing
Baleen
• Ingestion – the act of eating
• Digestion – the break down food into smaller
molecules
• Absorption – cells lining in the digestive tract take Photo 3 : whale (suspension feeder)
up the products of digestion
• Elimination/defecation – undigested material passes out of the digestive tract
Digestion
mechanical chemical
breakdown of
food into hydrolysis
pieces
digestive
using teeth
enzyme
Figure 1: Digestion Division
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Nutrient travel to
body cells
Absorption process occurred
Excess nutrients
Combine mainly in the small intestine
together become
stored as fats
macromolecules
Macromolecules
will break to
supply energy
Figure 2: Absorption
QUESTION
Question 1 (OCT 2010)
a) Describe in detail four (4) types of feeding mechanisms used by animals. (8marks)
ANSWER:
-
ADAPTATION!
- Organisms have special compartment where the food is digested without digesting their
own cells
Intracellular digestion
 Hydrolysis of food inside vacuoles.
 After cells engulf food by phagocytosis or liquid food by pinocytosis.
 Newly formed food vacuoles fuses with lysosome, an organelle containing hydrolytic
enzymes.
 Example : sponges
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Intracellular digestion in Paramecium sp.
Extracellular digestion
- Breakdown of food in compartments that are continuous with the outside of the
animal’s body
- Advantage of having more extracellular
compartments – enables an animal to
devour much larger sources of food than can
be ingested by phagocytosis.
Example : Hydra
Gastrovascular cavity
• Animals with simple body plans
• A digestive compartment with single opening.
• Functions : Digestion & distribution of nutrient
Example: flatworm
Alimentary canal
 Digestive tube extending between two openings – mouth and anus
 A complete digestive tract.
 Advantage: can ingest food while earlier meals are being digested.
Question [Part A]
1. Which of these animals has a gastrovascular cavity?
A. Bird
B. Hydra
C. Mammal
D. Insect
E. Annelid
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Question:
Difference between gastrovascular cavity and alimentary canal
Answer:
Gastro vascular cavity Alimentary canal
Single opening for both ingestion and Separate part for ingestion and elimination – has
elimination opposite ends
Structure Functions
Pharynx Sucks food in through mouth
Crop Store and moisten food
Gizzard Mechanical digestion
Intestine Digestion and absorption
Typhlosole/Dorsal fold Increase TSA for nutrient absorption
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• Three main regions: foregut, midgut, hindgut.
• Foregut consist of esophagus and crop
• Food stored and moistened in crop.
• Digestion occur in midgut
• Gastric cecae functions in digestion and absorption
• Three separate chambers – crop, stomach, gizzard
• Gizzard and crop has the same function as earthworm.
• Digestion and absorption occur in intestine
Human Digestive System
• Consist of alimentary canal and accessory glands.
• Accessory glands – salivary glands, pancreas, liver and gallbladder.
• Accessory gland secrete digestive juices through duct into the canal
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Three types of salivary gland
1. Submandibular gland
2. Sublingual gland
3. Parotid gland
Every gland has duct to conduct saliva
• The presence of food stimulates
nervous reflex – salivary gland – secrete
saliva
Saliva –
 Initiates chemical digestion
 Protecting oral cavity
 Lubricates food for easier swallowing (has slippery glycoprotein, Mucin)
 Aids bolus formation
 Neutralize food acid – prevent tooth decay
 Antibacterial agents
 Contain digestive enzymes
Peristalsis
 Food pushed down by peristalsis
 Peristalsis – alternating wave of contraction and relaxation of smooth muscle of
esophagus
 Peristalsis enable food to be pushed down even when we are lying down… sleeping
Sphincter
 Muscular layer forms ring-like valves.
 To close off the alimentary canal.
 Regulate the passage of material between
compartments.
Cardiac sphincter (lower esophageal sphincter)
- Limit upward movement of food from
stomach
Pyloric sphincter
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- Control movement of food from stomach to the small intestine
Question:
Why organisms have different shapes of teeth?
Dental Adaptation
- Teeth help to increase Total surface area of food to be hydrolyse by enzymes
(salivary amylase)
Humans have
 Incisors
 Canines (Cuspids)
Palate
 2 Premolars
 3 molars
Used to chew, grind, smash, crush, crack food!
Palate
- bone reinforced structure
- provide hard surface for tongue
- to press food to be mixed with saliva
Other organisms’ teeth
Carnivores have pointed teeth for cutting
and shearing
Herbivores have large flat teeth for
grinding cellulose
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Tongue
- Has taste bud (help to taste food)
- Shape food into bolus
- Move bolus into pharynx
Swallowing food
Question: Explain the mechanism of swallowing food into the stomach
Answer:
- The pharynx opens to the trachea and esophagus.
- Normally, esophagus opening closes due to contraction of esophageal sphincter.
- Air enters the larynx (opening of the trachea)
- During swallowing:
1: Tongue pushes bolos to the back of oral cavity
2: Larynx moves up, epiglottis moves down; opening of trachea closes
3: Esophageal sphincter relaxes; opening of esophagus opens
- After swallowing:
- Epiglottis moves up
- Larynx moves down
- Esophageal sphincter contact
- Opening of trachea opens, opening of
esophagus closes
Esophagus layers
1. mucosa,
2. submucosa,
3. mascularis externa
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4. serosa.
Sphincter between Rectum and anus
Internal sphincter – involuntary
External sphincter - voluntary
Feces are stored temporarily at the rectum
These sphincter control movement of bowel
Digestion stomach
Stomach
Can stretch – accommodate 2L food and fluid
Secrete gastric juice – mixed with food – form chime
Chemical digestion in stomach
Carried out by gastric juice
Gastric juice has two components
1. HCl
2. Pepsin
What HCl do?
- Disrupts extracellular matrix that bind cells together in meat and plant material
- pH is 2 (so high)
- unfolds protein in food (increase exposure to peptide bond)
After HCl done its action, followed by pepsin
- pepsin is a protease
- work best in strong acidic environment
- Protein  small polypeptides
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- Polypeptides is further digested in the small intestine
Why doesn’t gastric juice destroy stomach cells that make it?
- The ‘ingredients’ of gastric juice are kept inactive until released to the lumen of
stomach
- Gastric juice
produced by gastric glands
Gastric glands
Parietal cells
- Secrete hydrogen and
chloride ions
- H+ and Cl- then form
HCl
Chief cells
- Secrete pepsinogen
- Pepsinogen is inactive
form of pepsin
- Pepsinogen converted
to pepsin by HCl
- HCl clip off small portion of the molecule and exposing its active site
- HCl and pepsin form in the lumen, not within the cells of the gastric glands
Production of pepsin will stimulate the release of more pepsinogen. Pepsinogen then
activated to pepsin. (Positive feedback mechanism)
Wall of stomach is vulnerable to gastric juice and acid tolerant pathogen in food.
Stomach lining secrete mucus to prevent self digestion
Stomach cell also divide every three days to replace cells
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