6
6.1
Nutrition in humans
The processes of human nutrition (Book 1A, p. 6-3)
food
A
B
C, D
E
Process
Description
A
Ingestion (攝食)
i
The digested food molecules enter the circulatory system.
B
Digestion (消化)
ii
Food is taken in through the mouth.
C
Absorption (吸收)
iii
Food is broken down into soluble and simple molecules.
D
Assimilation (同化)
iv
The undigested materials are removed from the body as
E
Egestion (排遺)
faeces.
v
The absorbed food molecules are taken up by cells for
metabolism.
A: (1) _________ B: (2) _________
Ch. 6 / nutrition in human / P.1
C: (3) _________
D: (4) _________
E: (5) __________
6.2

The human digestive system (Book 1A, p. 6-4)
The human digestive system (消化系統) consists of the (1) _______________
_______________ (消化道) and its associated (2) _______________ (腺).
mouth cavity
tooth
tongue
pharynx (咽)
(3) _______________
_______________
(4) _______________
(食道)
liver (肝)
(5) _______________
(6) _____________
(胃)
_____________ (膽囊)
(7) _______________
(胰)
small intestine (小腸)
(8) _______________
large intestine (大腸)
(十二指腸)
(10) ___________ (結腸)
caecum (盲腸)
appendix (闌尾)
(9) _______________
(迴腸)
(11) ___________ (直腸)
anus (肛門)
 The human digestive system
6.3
Ingestion of food (Book 1A, p. 6-6)

Food is taken into the alimentary canal through the mouth.

The process of chewing food into small pieces in the mouth by the teeth is called
(1) _______________ (咀嚼).
Ch. 6 / nutrition in humans / P.2
A
What types of teeth do we have? (Book 1A, p. 6-6)
D
C
B
A
 The four types of teeth
Type of tooth
A
General feature
Function
(2) _____________
 (3) ______________ (鑿形的)
(5) ______________
(門齒)
 Has flat (4) ___________ edges
and cutting food
 Has one root
B
(6) _____________
 (7) ______________ and curved
(8) ______________
(犬齒)
 Has one root
flesh
 Well developed in carnivores
(9) _____________
C
(前臼齒)
 Broad top with
(10) ______________ (尖突)
 Has one or two roots
(11) _____________
D
(臼齒)
 Similar to (12) ______________
but larger
 Has two or three roots
Ch. 6 / nutrition in humans / P.3
(13) _____________
and grinding food
B
What is the structure of a tooth? (Book 1A, p. 6-7)
(17) ______________ (琺瑯質)
(18) ______________ (牙本質)
(14) ______________
(齒冠)
(19) ______________
(15) ______________
______________ (髓腔)
(齒頸)
gum (齒齦)
cement (牙骨質)
(16) ______________
(20) ______________
(齒根)
______________ (牙周膜)
jawbone (顎骨)
Structure
(21) _____________
(23) _____________
Pulp cavity
Cement and
Feature

The outermost, hardest region of the crown

Non-living and consists mainly of (22) ______________ salt

Protects the tooth from wearing down

The middle region of the tooth

Bone-like substance, but not as hard as enamel

Contains strands (縷) of living cytoplasm

Contains living cells

Contains (24) ______________ ______________ to supply oxygen
and nutrients and remove waste

Contains nerve fibres to detect (25) ______________ and pressure

Fix the tooth to the (26) ______________
periodontal
membrane
C

What is the dentition of humans? (Book 1A, p. 6-8)
Dentition (齒系) describes the (27) _______________ and (28) _______________ of different
types of teeth in a mammal.

Dentition can be represented by a (29) ______________ ______________ (齒式), which shows
the numbers and types of teeth on (30) ______________ side of the upper and lower jaws.

The dental formula of a human adult is (31) _______________.
Ch. 6 / nutrition in humans / P.4
What are milk teeth and permanent teeth? (Book 1A, p. 6-8)
D
Milk teeth
Description

Permanent teeth
Appear during the first two years

of life

Replace the milk teeth between
the ages of 6 and 12
Fall out between the ages of 6

Will not be replaced
and 12
Dental formula (32) _______________
6.4
(33) _______________
Movement of food along the alimentary canal
(Book 1A, p. 6-10)
1
Swallowing (Book 1A, p. 6-10)

After mastication, the food pieces are swallowed down the (1) _______________.

Before swallowing, the tongue mixes the food pieces with (2) _______________ (唾液) and
roll the food into a soft mass called a (3) _______________ (食團).

The swallowing process:
1
The tongue rises to push the bolus
towards the (4) ______________.
nasal
cavity
2
The soft palate moves up to prevent
the bolus from entering the nasal cavity.
tongue
3
The epiglottis prevents the bolus
from entering the (5) _______________.
trachea (氣管)
4
The bolus enters the
(6) _______________.
2
Peristalsis (Book 1A, p. 6-10)

After swallowing, the bolus moves along the alimentary canal by peristalsis.

The wall of alimentary canal is composed of (7) _______________ muscles and
(8) _______________ muscles.
Ch. 6 / nutrition in humans / P.5
circular muscle (環肌)
longitudinal muscle (縱肌)
connective tissue
lumen (管腔)
 Structure of the wall of alimentary canal

Peristalsis refers to the (9) _______________ action resulting from the rhythmic
(10) _______________ and (11) _______________ of the muscles in the wall of the
alimentary canal.
Behind the bolus
1
Circular muscles (12) _______________.
2
Longitudinal muscles relax.
3
The lumen becomes (13) _____________.
4
The food is squeezed forward.
bolus
In front of the bolus
6.5
A

1
Circular muscles relax.
2
Longitudinal muscles contract.
3
The food slides through the lumen.
direction of movement of bolus
 The process of peristalsis
Digestion of food (Book 1A, p. 6-12)
Why is digestion necessary? (Book 1A, p. 6-12)
The food we take in is too large to pass through the differentially permeable wall of the
alimentary canal.

Digestion breaks down the food into (1) _______________, (2) _______________ and
(3) _______________ form for absorption.
Ch. 6 / nutrition in humans / P.6
B
What is physical and chemical digestion? (Book 1A, p. 6-12)
1
Physical digestion (Book 1A, p. 6-12)

Physical digestion (機械消化) breaks down the food by (4) _______________ actions.

It increases the (5) _______________ _______________ of food for chemical digestion.

Physical digestion is brought about by:
Process
Example
Mechanical actions of the

(6) ______________ by teeth in the mouth cavity
alimentary canal

(7) ______________ (劇烈攪動) in the stomach

(8) ______________ along the alimentary canal

Emulsification of lipids by bile salts in the small
(9) ______________ (乳化)
intestine
2
Chemical digestion (Book 1A, p. 6-12)

Chemical digestion involves chemical reactions catalysed by (10) ______________
______________ (消化酶).

It breaks down large, complex food molecules into small, (11) ______________ form.
Type of enzyme
Reactions it catalyses
Example
Carbohydrases
Breakdown of complex carbohydrates into simpler
amylase,
(碳水化合物酶)
(12) ______________
sucrase,
maltase
(13) ______________
Breakdown of proteins into polypeptides, peptides and
pepsin,
(蛋白酶)
(14) _____________ _____________
trypsin,
peptidases
Lipase (脂肪酶)
Breakdown of lipids into fatty acids and
pancreatic
(15) _____________
lipase
Ch. 6 / nutrition in humans / P.7
C

How is food digested in the mouth cavity? (Book 1A, p. 6-13)
Food is digested by (16) ______________ and the action of digestive juice
(17) ______________ secreted by salivary glands.

Saliva consists of:
Component
(18) ______________
Function

______________
Mucus (黏液)
Catalyses the breakdown of (19) ______________ into
maltose

Binds the food particles together

(20) ______________ the food for easier chewing and
swallowing

Water
D

Dissolves soluble substances in the food
How is food digested in the stomach? (Book 1A, p. 6-14)
Stomach is a muscular bag with two (21) ______________ ______________: cardiac
sphincter and pyloric sphincter.
oesophagus
cardiac sphincter
(賁門括約肌)
pyloric sphincter
(幽門括約肌)
duodenum
 Structure of the stomach

Food is digested by (22) ______________ and the action of gastric juice (胃液) into semi-solid
paste called (23) ______________ (食糜).

Gastric juice is secreted by (24) ______________ ______________. It contains:
Component
(25) ____________
Hydrochloric acid
Mucus
Ch. 6 / nutrition in humans / P.8
Function

Catalyse the breakdown of proteins into (26) ____________

Provides an (27) ______________medium for proteases

Kills most (28) ______________ in the food

Protects the stomach against proteases and hydrochloric acid
E
How is food digested in the small intestine? (Book 1A, p. 6-15)
1
Bile (Book 1A, p. 6-15)

Bile is secreted by the (29) ______________ and stored in the (30) ______________
______________ temporarily. It contains:
Component
Function
Bile salts

(31) _____________ lipids into small droplets
Bile pigments

No function in digestion
Sodium

(32) ____________ the acidic chyme
hydrogencarbonate

Provides an (33) ____________ medium for the enzymes
2
Pancreatic juice (Book 1A, p. 6-16)

Pancreatic juice is secreted by the (34) ______________ into the duodenum. It contains:
Component
Pancreatic amylase
Function

Catalyses the breakdown of starch into (35) _____________

Catalyse the breakdown of some proteins into
Proteases
Lipase
(36) _____________, and some peptides into amino acids

Catalyses the breakdown of lipids into (37) _____________
and (38) _____________ _____________
Sodium

Neutralizes the acidic chyme
hydrogencarbonate

Provides an alkaline medium for the enzymes
3
Intestinal juice (Book 1A, p. 6-16)

Intestinal juice is secreted by the glands in the wall of the (39) _____________
_____________. It is a slightly alkaline liquid containing mucus, but no (40) _____________.

Some enzymes present on the cell membrane of the specialized cells on the wall of the small
intestine are also involved in digestion. These enzymes include:
Function
(41) ____________

Catalyse the breakdown of disaccharides into monosaccharides
Proteases

Catalyse the breakdown (42) _____________ into amino acids
Ch. 6 / nutrition in humans / P.9
Misconception
Some students wrongly think that bile is produced by the gall bladder. In fact, bile is produced by
the liver and temporarily stored in the gall bladder.
6.6

A

Absorption of digested food (Book 1A, p. 6-18)
Absorption of food mainly takes place in the (1) _______________.
How is the small intestine adapted for food absorption? (Book 1A, p. 6-18)
The small intestine is very long, which
allows (2) _______________
epithelium
_______________ for complete
blood capillaries
digestion and absorption.

lacteal
Its wall is highly folded and has many
finger-like projections called
(3) _______________.
 A villus

Adaptation of villi for food absorption:
Adaptation
Significance
(4) _______________ the surface area for absorption
Finger-like
Thin epithelium of one cell thick Shorten diffusion distance, thus allow rapid absorption
With (5) _______________and
Allow the absorbed food molecules to be carried away
blood capillaries
rapidly
Movement caused by
Allow the surface of the villi to be in contact with the food,
(6) _______________
keeping a steep concentration gradient for rapid diffusion
B
How is digested food absorbed? (Book 1A, p. 6-19)
Into the blood
Food substance
Into the lymph
(7) _______________, amino acids,
Fatty acids and
minerals and water-soluble vitamins
(8) _______________
Ch. 6 / nutrition in humans / P.10
Process
Food substances absorbed by
Fatty acids and glycerol diffuse into
(9) _______________ and active
the epithelium and recombine into
transport into the blood capillaries.
lipids. Lipids then enter the lacteals.
Transport
Villi → hepatic portal vein →
Villi → main lymph vessels → blood
pathway
(10) _____________ → hepatic vein
vessel → (11) _______________→
→ heart → all parts of the body
all parts of the body
hepatic vein
(肝靜脈)
heart
liver
hepatic
portal vein
(肝門靜脈)
monosaccharides, amino
acids, minerals and
water-soluble vitamins
lymph
vessel
all parts of
the body
lipid molecules
villus
 Transport of digested food from the villi to different parts of the body

Over 90% of water is absorbed in the stomach and the small intestine by (12) _____________,
and the remaining water is absorbed in the (13) ______________ ______________.
6.7

A
Assimilation of absorbed food (Book 1A, p. 6-22)
Assimilation is the uptake and use of absorbed food molecules by cells for (1) ____________.
What are the fates of the absorbed food? (Book 1A, p. 6-22)
Fate
Glucose
Amino acids

Releases energy by (2) ______________ in the body cells

Converted into (3) ______________ or lipids in the liver if in excess

Make different types of proteins for growth and repair

Make (4) ______________, antibodies and some hormones

(5) ______________ in the liver if in excess
Ch. 6 / nutrition in humans / P.11
Lipids

Act as the energy (6) ______________ of our body

Make (7) ______________ ______________

Deposited around the internal organs or build up in (8) ______________
______________ under the skin if in excess
B
What are the roles of the liver? (Book 1A, p. 6-23)
The liver has the following functions:

Regulates the blood glucose level by conversion between glucose and glycogen

Stores glycogen, iron and (9) ______________ vitamins

Produces bile, vitamin A and (10) ______________

Removes excess amino acids and converts the amino groups into urea, i.e. (11) ____________

Changes mild toxins into harmless substances, i.e. (12) ______________ (解毒)
6.8

Egestion (Book 1A, p. 6-25)
After absorption, the remaining materials are called (1) ______________ (糞便). Faeces mainly
consist of indigestible food such as (2) ______________ ______________, secretions from
the alimentary canal, bacteria, dead cells from the intestinal wall and a small amount of water.

Faeces is temporarily stored in (3) _____________ and egested through the (4) ____________.

The process of expelling faeces from body is called egestion or (5) ______________ (排糞).
 Go to …
Quick check
(Book 1A, p. 6-25)
Ch. 6 / nutrition in humans / P.12
Exercise
The diagram on the right shows the human
alimentary canal.
A
B
C
D
E
a
The table shows the percentage of
undigested food substances in three
different parts of the alimentary canal.
P
Q
R
Protein
100
0
60
Starch
85
0
85
Lipid
100
0
100
Which part (P, Q or R) corresponds to the structures A and B respectively? Explain your
answer.
(4 marks)
____________________________________________________________________________
____________________________________________________________________________
b
What will happen if digestive juice secreted by structure C is mixed with oil?
(2 marks)
____________________________________________________________________________
____________________________________________________________________________
c
The duct leading from structure D to duodenum is blocked in a patient. Explain why the faeces
of this patient contains large amounts of lipids.
(2 marks)
____________________________________________________________________________
____________________________________________________________________________
d
With reference to the diagram, state one feature that facilitates the absorption of food in
structure E.
(2 marks)
____________________________________________________________________________
____________________________________________________________________________
－ END －
Ch. 6 / nutrition in humans / P.13
Answers
Ch 6
Nutrition in humans
6.1
1
ii
2
iii
3
i
4
v
5
iv
1
alimentary canal
2
glands
3
salivary gland
4
oesophagus
5
stomach
6
gall bladder
7
pancreas
8
duodenum
9
ileum
10
colon
11
rectum
6.2
6.3
1
mastication
2
Incisor
3
Chisel-shaped
4
sharp
5
Biting
6
Canine
7
Pointed
8
Tearing
9
Premolar
10
cusps
11
Molar
12
premolar
13
Crushing
14
crown
15
neck
16
root
17
enamel
18
dentine
19
pulp cavity
20
periodontal membrane
21
Enamel
22
calcium
23
Dentine
24
blood vessels
25
temperature
26
jawbone
27
number
28
arrangement
29
dental formula
30
each
31
2123/2123
32
2102/2102
33
2123/2123
1
oesophagus
2
saliva
3
bolus
4
pharynx
5
trachea
6
oesophagus
7
circular
8
longitudinal
9
wave-like
10
contraction
11
relaxation
12
contract
13
smaller
1
smaller
2
soluble
3
simpler
4
physical
5
surface area
6
Chewing
7
Churning
8
Peristalsis
9
Emulsification
10
digestive enzymes
11
simpler
12
sugars
13
Proteases
14
amino acids
15
glycerol
16
chewing
17
saliva
18
Salivary amylase
19
starch
20
Lubricates
21
muscular rings
22
churning
23
chyme
24
gastric glands
25
Proteases
26
peptides
27
acidic
28
bacteria
29
liver
30
gall bladder
31
Emulsify
32
Neutralizes
33
alkaline
34
pancreas
35
maltose
36
peptides
37
glycerol
38
fatty acids
39
small intestine
40
enzymes
41
Carbohydrases
42
peptides
6.4
6.5
Ch. 6 / nutrition in humans / P.14
6.6
1
ileum
2
sufficient time
3
villi
4
Increase
5
lacteals
6
peristalsis
7
Monosaccharides
8
glycerol
9
diffusion
10
liver
11
heart
12
osmosis
13
large intestine
1
metabolism
2
respiration
3
glycogen
4
enzymes
5
6
reserve
7
cell membranes
8
adipose tissue
9
fat-soluble
10
heat
11
deamination
12
detoxification
faeces
2
dietary fibre
3
rectum
4
anus
5
defaecation
6.7
Deaminated
6.8
1
Exercise
a
A: Part P
1m
B: Part R
1m
It is because saliva is present in A (mouth cavity). It contains salivary amylase which catalyses
the breakdown of starch into maltose. However, it does not contains enzymes for the
breakdown of proteins and lipids.
1m
B (stomach) secretes gastric juice which contains proteases. Proteases catalyse the breakdown
b
c
d
of proteins into peptides. Lipids are not digested in B.
1m
The oil will be emulsified
1m
into oil droplets.
1m
Due to the blockage of the pancreatic duct, pancreatic lipase cannot reach the duodenum.
1m
Lipids cannot be digested and is egested in the faeces.
1m
Structure E is very long.
1m
This allows sufficient time for complete absorption.
1m
Ch. 6 / nutrition in humans / P.15