A Why is digestion necessary? (Book
Ø The wall of the
alimentary canal is (1) differentially permeable. Large, complex food
molecules
must be broken down into small, (2) soluble molecules so
that they can pass through the wall and enter the blood.
Ø The process of
breaking down food into small molecules is called (3) digestion.
B Physical digestion and chemical digestion (Book
|
(4)Physical / Mechanical digestion
(機械消化)
|
(10)Chemical digestion (化學消化)
|
Principle
|
breaking down
of food into smaller pieces by physical
actions
|
involves (11) chemical reactions
|
Purpose
/ action
|
increases the (5)
surface area of food in contact with the digestive juices.
|
Break down large,
complex food molecules into small, simpler forms
|
brought about by:
|
n Mechanical
actions of alimentary canal:
l Chewing in the mouth cavity, i.e.
(6) mastication
l
(7) chuning (劇烈攪動) in the stomach
l
(8) peristalsis along the alimentary
canal
n (9) Emulsification (乳化) of lipids by bile salts (膽鹽)
|
Chemical reactions are catalysed by
(12) digestive
enzymes
(消化酶)
|
Ø Three main types
of digestive enzymes in our digestive system:
Type
|
Function
|
Example
|
(13)
Carbohydrases
(碳水化合物酶)
|
Break down complex
carbohydrates into
simpler (14) sugars
|
Amylase (澱粉酶), sucrase (蔗糖酶), maltase (麥芽糖酶)
|
(15)
Proteases
(蛋白酶)
|
Break down proteins into polypeptides,
peptides and (16) amino acids
|
Pepsin (胃蛋白酶), pancreatic proteases
(胰蛋白酶), peptidase (肽酶)
|
(17) Lipase
(脂肪酶)
|
Break down lipids into fatty acids and
(18) glycerol
|
Pancreatic lipase (胰脂肪酶)
|
C Digestion in the mouth cavity (Book
Ø In the mouth
cavity, food is chewed into smaller pieces by the teeth and mixed with (19) saliva (唾液) produced by salivary glands. Saliva contains:
Component
|
Function
|
(20) Salivary amylase (唾液澱粉酶)
|
Catalyses the breakdown of starch into (21) maltose
|
(22) Mucus
(黏液)
|
l
Helps bind
food particles together
l Moistens and (23) lubricates the food
|
Water (>95%)
|
l
Moistens and lubricates food
l
(24) Dissolves soluble substances
|
Inorganic ions: Na+,
Cl- & HCO3- etc
|
Maintain optimum pH
(6.5 – 7.5) for amylase
|
Ø After chewing, the tongue rolls the food into a (25) food bolus (食團), which is then
swallowed down the oesophagus (食道) through the (26) pharynx (咽)
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