1 2 Think about… 6.1 The process of human nutrition 6.2 The human digestive system 6.3 Ingestion of food 6.4 Movement of food along the alimentary canal

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2

Think about…

6.1 The process of human nutrition

6.2 The human digestive system

6.3 Ingestion of food

6.4 Movement of food along the alimentary canal

6.5 Digestion of food

6.6 Absorption of digested food

6.7 Assimilation of absorbed food

6.8 Egestion

Recall ‘Think about…’

Summary concept map

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Weight loss surgery can help obese people lose weight

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small bag created at the top of stomach

it connects directly to ileum

food bypasses larger stomach and duodenum

ileum

stomach

duodenum

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1 What is the roleof the stomach

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2 How does the surgery help peoplelose weight

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3 What will happenif the food does notpass through the ileum also

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2 digestion (消化 )

1 ingestion (攝食 )

6.1 The processes of human nutrition

complex and insoluble food molecules

food

simple and soluble food molecules

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5 egestion (排遺 )

3 absorption (吸收 )

4 assimilation (同化 )

1 ingestion (攝食 )


digested food

faeces

2 digestion (消化 )

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The five main processes of

and .

nutrition in humans are

absorptiondigestion

ingestion

egestionassimilation

, ,


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What does our digestive system

(消化系統 ) consist of?

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Digestive system

Alimentary canal(消化道 )

Glands(腺 )

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Alimentary canal

1 mouth cavity

2 pharynx (咽 )

3 oesophagus (食道 )

4 stomach


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5 small intestineduodenum

ileum

6 large intestinecolon

rectum7 anus (肛門 )

Alimentary canal6.2 The human digestive system

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Glands

pancreas (胰 )

liver

salivary glands


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its associated .glands

Our digestive system consists of the andalimentary canal

1


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oesophagus

anus

small intestine

stomach

mouth cavity

pharynx

large intestine

start

end

2 Alimentary canal:


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,

liver

pancreassalivary glands3 Associated glands:

,


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mouth cavity• food is taken in through the mouth

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• mastication (咀嚼 ): chewing food into small pieces

teeth


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1 Incisors (門齒 )

• for biting and cutting food

A) Types of teeth

chisel-shaped (鑿形的 )

flat sharp edges

one root


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2 Canine (犬齒 )

• for tearing flesh

• well-developed in carnivores

one root

pointed and curved

A) Types of teeth6.3 Ingestion of food

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3 Premolar (前臼齒 )

• for cutting and grinding food

A) Types of teeth

1 or 2 roots

broad top with cusps


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4 Molar (臼齒 )

• similar to premolar but larger

A) Types of teeth

2 or 3 roots


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B) Structure of a tooth

crown (齒冠 )

neck (齒頸 )

root (齒根 )

• divided into


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1 Enamel (琺瑯質 )

• the outermost, hardest region

• protects teeth from wearing off

• non-living and is made mainly of calcium salt


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1 Enamel (琺瑯質 )

• replaced by cement 　(牙骨質 )

Around the roots…

• fibres from cement form periodontal membrane (牙周膜 )

periodontalmembrane

cement


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2 Dentine (牙本質 )

• the middle region of the tooth

• contains strands of living cytoplasm


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living cells

3 Pulp cavity (髓腔 )

nerve fibres

blood vessels


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blood vessels

• detect temperature and pressure

• supply oxygen and nutrient

nerve fibres

• remove waste

3 Pulp cavity (髓腔 )


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C) Dentition of humans

• represented by a dental formula (齒式 )

• dentition (齒系 ): number and arrangement of different types of teeth


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2 incisors

1 canine

2 premolars

3 molars

• on each side of the upper jaw:


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2 incisors

1 canine

2 premolars

3 molars

• on each side of the lower jaw:


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C) Dentition of humans• dental formula of an adult:

21232123

i , c , pm , m 22

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22

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• appear during the first two years

21022102

• dental formula:

D) Milk teeth and permanent teeth

• first set of teeth:milk teeth (乳齒 )


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• replace milk teeth between the ages of 6 and 12

• second set of teeth:permanent teeth (恆齒 )

• will not be replaced when lost


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milk teeth

permanent teeth


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and cut up by . The proces

s of chewing food into small piece

s is called

1 Food is put into the

mastication

mouth cavity

teeth

.


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2 Match the functions of different types of teeth:

incisors canine

premolars

molars

biting and cutting

tearing flesh

crushing and grinding


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root

neck

crown

3a Label the structure of the tooth.


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pulp cavity

dentine

enamel

3b Label the structure of the tooth.


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4a refers to the number and arrangement of different types of teeth in a mammal.

Dentition

It can be represented by a

.dental formula


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4b Humans have two sets of teeth

in a lifetime:

i)

ii) permanent teeth

milk teeth


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What will happen to us after

mastication?

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1 Swallowing

Food is chewed

The tongue shapes the food into a

bolus

• before swallowing:

teeth

bolus (食團 )

tongue

Animation


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• during swallowing:

1 Swallowing

1 The tongue pushes the bolus towards pharynx


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• during swallowing:

1 Swallowing

2 The soft palate (軟腭 ) moves up to prevent the bolus from entering the nasal cavity


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1 Swallowing• during swallowing:

3 The epiglottis (會厭 ) covers the trachea

4 The bolus enters the oesophagus


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2 Peristalsis (蠕動 )

circular

muscle

(環肌 )

longitudinal muscle (縱肌 )

lumen (管腔 )

• rhythmic contraction and relaxation of the muscles

alimentary canal


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circular muscles relax, longitudinal muscles contract

circular muscles contract, longitudinal muscles relax

food

food moved forward

2 Peristalsis (蠕動 )


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1 Food is moved from the mouth cavity down the oesophagus by

the oesophagus towards the anus by .peristalsis

swallowing and down from


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of the and

muscles in the wall of alimentary

canal. It causes the food to move

forward along the canal.

2 Peristalsis is the rhythmic

circular

contraction and relaxation

longitudinal


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undigested food molecules

alimentary canal

blood

6.5 Digestion of food• undigested food is too large to pass

through the wallwall of alimentary canal

(differentially permeable)

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digested food molecules

6.5 Digestion of food• digestion makes the food smaller,

simpler and soluble for absorption

alimentary canal

blood

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Physical digestion (機械消化 )

smaller surface area larger surface area

• increases surface area for action of digestive juices (消化酶 )

physical action

• breaks down food into smaller pieces

food


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• examples:

1 Chewing by teeth

2 Churning (劇烈攪動 ) in the stomach

Physical digestion (機械消化 )


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4 Emulsification (乳化 ) by bile salts

lipidssmall droplets

3 Peristalsis along alimentary canal

Physical digestion (機械消化 )• examples:


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Chemical digestion (化學消化 )

digestive enzymes (消化酶 )

large, complex small, simple

• chemical reactions in which large, complex food molecules are broken down


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• three types of digestive enzymes

1 Carbohydrases (碳水化合酶 )

complex carbohydrates simpler sugars

e.g. amylase, sucrase and maltase


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2 Proteases (蛋白酶 )e.g. pepsin, trypsin and peptidases

protein

polypeptides

peptides amino acids



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3 Lipase (脂肪酶 )e.g. pancreatic lipase

fat fatty acids glycerol



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Digestion in mouth cavity• food is chewed into small pieces

and mixed with salivaAnimation


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salivary glands

Digestion in mouth cavity

• secreted by salivary glands

Saliva

• slightly alkaline


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i) salivary amylase

starch maltose

• consists ofSaliva

ii) mucus (黏液 )

- moistens and lubricates (潤滑 ) food


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• consists of

iii) water

- dissolves soluble substances in food

Saliva


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Digestion in stomach

oesophagus

Structure of the stomach

duodenum

muscle bag


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cardiac sphincter (賁門括約肌 )- closes the entrance

pyloric sphincter (幽門括約肌 )

- regulates the release of food into duodenum

Digestion in stomachStructure of the stomach


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stomach wall (450)

gastric glands inside pits

• gastric glands secrete gastric juice (胃液 )

Digestion in stomachStructure of the stomach


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Gastric juice

i) proteases• contains

protein peptides

Digestion in stomach6.5 Digestion of food

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Digestion in stomachGastric juice

ii) hydrochloric acid- provides an acidic medium

for the action of proteases- kills most bacteria in food

• contains

HCl

bacteria


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Digestion in stomachGastric juice

iii) mucus- protects stomach from

being damaged by proteases and hydrochloric acid

• contains

proteases & HCl

mucus


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Digestion in stomach

churning & chemical digestion

food

called chyme (食糜 )

semi-solid paste


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• released to duodenum through bile duct (膽管 )

Digestion in small intestine

1 Bile• three digestive juices

• secreted by liver

• stored in gall bladder


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• released to duodenum through bile duct (膽管 )

• stored in gall bladder

• secreted by liver


1 Bile• three digestive juices


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Digestion in small intestine1 Bile• has no enzymes but containsi) bile salts

- emulsify lipids into small droplets

lipidslarger surface

areasmaller surface area

emulsification


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Digestion in small intestine1 Bile

iii) sodium hydrogencarbonate

ii) bile pigments

- neutralizes the acidic chyme

- give green colour to bile

- provides an alkaline medium for the actions of enzymes in duodenum


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Bile is produced by the gall bladder.



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Bile is produced by the liver and temporarily stored in the gall bladder.



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6.3

Investigation of the effect of bile salts on oil

1 Add 10 drops of bile salt solution to 1 cm3 of peanut oil.

peanut oil

bile salt solution

Animation


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6.3

2 Stopper the test tube and shake for 30 seconds. Observe the mixture and note any changes. shake

Results and discussion

An emulsion (乳狀物 ) is formed. This shows that bile salts can break down lipids into tiny droplets.


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• released to duodenum through pancreatic duct

Digestion in small intestine2 Pancreatic juice

• secreted by pancreas


pancreas

pancreatic duct


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• contains:

i) pancreatic amylase

starch maltose


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• contains:

ii) protease

protein peptides


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• contains:


ii) protease


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• contains:

iii) lipase

lipid fatty acids glycerol


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• contains:

iv) sodium hydrogencarbonate- neutralizes the acidic chyme

- provides an alkaline medium for the actions of enzymes in duodenum


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Digestion in small intestine3 Intestinal juice

• secreted by the glands on the wall of the small intestine

ileum

duodenum


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Digestion in small intestine3 Intestinal juice

• contains mucus


ileum

duodenum

• no enzymes


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Digestion in small intestine• some specialized cells on the wall also

involved in digestion

ileum

duodenum

specialized cells


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Digestion in small intestine• enzymes present on their cell membrane

enzymeshere

ileum

duodenum


specialized cells

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Digestion in small intestine• The enzymes include:

i) carbohydrases

disaccharides monosaccharides


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ii) proteases



• The enzymes include:


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• Digestion completed at the end of ileum

monosaccharides

amino acids

fatty acids

glycerol

ready for

absorption


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makes the food ,

and for absorption.

1 The food we take in is tooto pass through the wall of the

alimentary canal, which is

differentially permeable. Digestion

large

smaller simpler

soluble


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Physical digestion is mainly brought about by action of the teeth, in the stomach, along the alimentary canal, and

of lipids by bile salts.

peristalsis

churning

chewing2a

emulsification


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Physical digestion increases the of food for chemical digestion.

surface area

2b


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involves chemical reactions in which large, complex food molecules are broken down into smaller, simpler forms. The reactions are catalysed by .digestive enzymes

Chemical digestion3a


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Some digestive enzymes are

present in the

secreted by the .

3bdigestive juices

digestive glands


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4a Digestion of carbohydrates:Mouth cavity

starch maltosein

Duodenum

starch maltosepancreatic amylase

pancreatic juice

salivasalivary amylase

in


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carbohydrases

4a Digestion of carbohydrates:Small intestine

disaccharides monosaccharides

on the cell membranes of the specialized cells in the intestinal wall


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proteasesgastric juicein

pancreatic juiceproteases

in

4b Digestion of proteins:Stomach

protein

Duodenumprotein, peptides,

amino acidspeptides

peptides


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Small intestine

peptides amino acidson the cell membrane

of the specialized cells in the intestinal wall

proteases


4b Digestion of proteins:

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in

bile salt

bile

4c Digestion of lipids:Duodenum

lipidssmall droplets

lipidsfatty acids,glycerolpancreatic juice

lipasein


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mainly takes place in ileum

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• allows sufficient time for absorption

1 Long intestine

It’s 7m long!

Adaptation of small intestine for food absorption


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cross-section of small intestine

2 Highly-folded intestinal wall and numerous villi (絨毛 )

epithelium covered with villi



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inner surface of ileum

epithelium covered with villi


2 Highly-folded intestinal wall and numerous villi (絨毛 )


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Adaptive features of villi

• increases surface area for absorption

1 Finger-like projections


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• reduces the distance for diffusion of food molecules


2 Thin epithelium


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3 Presence of lacteal and a network of blood capillaries

• carry away the absorbed food molecules rapidly


blood capillary

lacteal


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4 Movement of villi caused by peristalsis

• keeps a steep concentration gradient of food molecules

Adaptive features of villi6.6 Absorption of digested food

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monosaccharides

amino acids

water-soluble vitamins

active transport

diffusion

Absorption of digested foodInto the blood

minerals

Animation


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hepatic vein

hepatic portal vein all parts of

the body

Absorption of digested foodInto the blood

liver


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Absorption of digested foodInto the lymph

lumen epithelium lacteal

fatty acid

glycerol

fatty acid

glycerollipid lipid


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all parts of the body

lymph vessel

Absorption of digested foodInto the lymph


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Absorption of water

water

osmosis

blood capillary

• most water is absorbed in stomach and small intestine


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6.4

Simulation of digestion and absorption in the small intestine using dialysis tubing

1 Tie a knot at one end of a dialysis tubing. Fill the tubing with equal volumes of starch solution and amylase solution.


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6.4

2 Tie the other end of the tubing.

3 Immerse the tubing in water at 37°C.

dialysis tubing

water at 37oC

starch and amylase


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6.4

4 Test the water outside the tubing immediately for starch and reducing sugars using iodine solution and Benedict’s solution respectively. Perform the same tests after one hour.


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6.4


• At the beginning of the experiment, neither starch nor reducing sugars are present in the water. However, reducing sugars are detected after one hour.


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6.4


• These results show that amylase helps break down starch into reducing sugars and only the reducing sugar molecules are small enough to pass through the dialysis tubing.


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Absorption1 is the movement of

food molecules from the

alimentary canal into the

circulatory system. It takes place

mainly in the ileum.


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2a

Adaptation Significance

Increase surface area for

absorption

Highly-folded wall and nume

rous villi

How is the small intestine adapted for food absorption?


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Reduces the distance for

diffusion of food molecules

Thin epithelium

2b How is the small intestine adapted for food absorption?


125


Carry away the absorbed food

molecules rapidly

2c

Presence of lacteal and a network of blood capillaries

How is the small intestine adapted for food absorption?


126


Keeps a steep concentration

gradient of food molecules

Movement of villi caused by peristalsi

s

2d How is the small intestine adapted for food absorption?


127

diffusion and active transport. They are carried to the liver via the .

3a Monosaccharides, amino acids, minerals and water-soluble vitamins are absorbed into the

hepatic portal vein

blood capillaries of the villi by


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before entering the

.

3b Fatty acids and glycerol diffuse

into the epithelium of the villi.

Here they recombine to form

lacteals

lipids


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• the uptake and use of absorbed food molecules for metabolism

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energyglucose

i) for releasing energy

The fate of absorbed food1 Glucose

respiration


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ii) excess glucose is converted into glycogen or lipid in liver

glycogen

lipid

stored in

stored

liver / muscle

under skin / around internal organs

The fate of absorbed food1 Glucose


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The fate of absorbed food2 Amino acidsi) for making proteins

ii) excess amino acids are deaminated in liver

proteins for growth

proteins for repair

enzymes

antibodies

hormones


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The fate of absorbed food3 Lipidsi) as energy reserve

ii) for making cell membrane

iii) for protecting internal organs or reducing heat loss

subcutaneous fat


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The roles of the liver

• blood glucose level > normal

glucoseliver

• blood glucose level < normal

glucoseliver

glycogen

glycogen

1 Regulate blood glucose level


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• main site for storing glycogen

glycogen

2 Storage of glycogen, iron and fat-soluble vitamins

The roles of the liver6.7 Assimilation of absorbed food

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• stores fat-soluble vitamins

vitamin A

vitamin D

2 Storage of glycogen, iron and fat-soluble vitamins


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• for storing iron from the breakdown of red blood cells

iron

2 Storage of glycogens, iron and fat-soluble vitamins


red blood cells


138

• secretes bile

• changes carotene to vitamin A

• produces heat

3 Production of bile, vitamin A and heat


metabolic activities

heat


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4 Deamination

excess amino acids

ureaamino group

carbohydrates

lipids

remaining parts


140

toxins

(e.g. alcohol,

drugs)

harmless

substances

The roles of the liver5 Detoxification (解毒 )


141

Assimilation1 is the uptake and

use of absorbed food molecules by cells for metabolism.


142

for making cell membrane

as energy reserve

for releasing energy

for making proteins

2 How are the absorbed food molecules assimilated inside cells? glucose

amino acids

lipids


143

• stores , and iron

blood glucose level

glycogen

fat-soluble vitamins

bile vitamin A

heat

• produces , and

• regulates3 The roles of the liver include:


144

• deaminates excess

• detoxifies mild toxins

amino acids

3 The roles of the liver include:


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6.8 Egestion

• the process of expelling faeces (糞便 ) from the body

• faeces consist of

dietary fibre secretions from alimentary canal

bacteria dead cells

• also called defaecation (排糞 )

146

faeces stored in rectum temporarily

anal sphincter muscle relaxes and rectum muscle contracts to push the faeces out

6.8 Egestion

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is the process of expelling Egestion

faeces from the body.

6.8 Egestion

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1 What is the role of the stomach?• The stomach churns to break down

food into smaller pieces physically.

• It secretes proteases to chemically digest proteins.

• It also releases hydrochloric acid which kills most bacteria in food.

149

2 How does the surgery help people lose weight?

Without passing through the stomach and duodenum, the food cannot be fully digested. Therefore, fewer food molecules are absorbed by the body.

150

3 What will happen if the food does not pass through the ileum also?

It may result in malnutrition as most consumed food is undigested and the body cannot get enough nutrients for healthy growth.

151

Nutrition

ingestion

digestion

consists of

absorption

assimilation

egestion

occurs mainly in

villi

occurs in

body cells

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involves

digestion

physical digestion

chemical digestion

brought about by

enzymes

153

physical digestion

brought about by

chewing by teeth

churning in stomach

emulsification of lipids by bile salts

peristalsis

Documents

1 2 Think about… 6.1 The process of human nutrition 6.2 The human digestive system 6.3 Ingestion of food 6.4 Movement of food along the alimentary canal