Biolove chapter 1 digestive system

BIOLOVE 2013

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BIOLOVE DIGESTIVE SYSTEM

BIOLOVE 2013


Ways of ingesting

• Substrate feeders – caterpillar

- Live in or on the food source

- Ingest the food source and also eliminate on the

food source.

• 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

- Extract food particles suspended in the surrounding water.

Food processing

• Ingestion – the act of eating

• Digestion – the break down food into smaller

molecules

• Absorption – cells lining in the digestive tract take

up the products of digestion

• Elimination/defecation – undigested material passes out of the digestive tract

Figure 1: Digestion Division

Digestion

mechanical

breakdown of food into

pieces

using teeth

chemical

hydrolysis

digestive enzyme

Photo 2 : Aphid sucking nutrient from phloem

Photo 1 : caterpillar (substrate feeder)

Photo 3 : whale (suspension feeder)

Baleen

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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

Nutrient travel to body cells

Combine together become macromolecules

Macromolecules will break to

supply energy

Excess nutrients stored as fats

Absorption process occurred

mainly in the small intestine

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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

elimination

Separate part for ingestion and elimination – has

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)

Other organisms’ teeth

Carnivores have pointed teeth for cutting

and shearing

Herbivores have large flat teeth for

grinding cellulose

Humans have

Incisors

Canines (Cuspids)

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

Palate

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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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Biolove chapter 1 digestive system