Download THE HUMAN DIGESTIVE SYSTEM

THE HUMAN DIGESTIVE
SYSTEM
Objectives
At the end of the lesson, students will be able to:
 Identify
the parts of the Human Digestive System
 Describe
the role of the parts Human Digestive System
 Work
cooperatively with others in a group (Valuing other
people’s opinions /experiences).
 The
Human Digestive System is made up of a
tube called the alimentary canal (gut).
 Food
travels through the body along the
alimentary canal beginning at the mouth and
ending at the anus.
 Digestion
 The
Mouth
of food starts in the mouth.
food that we eat is broken down
mechanically into smaller pieces by the action
of the teeth.
 The
food is then mixed with saliva and its enzyme,
salivary amylase.
 Salivary
amylase breaks down large starch molecules
into smaller maltose molecules (Complex Molecule).
starch→ 𝑚𝑎𝑙𝑡𝑜𝑠𝑒
The
tongue rolls the partially digested food
into small balls called bolus which is then
swallowed into the oesophagus or gullet.
Oesophagus (Gullet)
The
oesophagus pushes down food from the
mouth into the stomach, by contracting and
relaxing its muscular walls a process called
peristalsis.
No
chemical digestion takes place here.
Stomach
 The
 Its
stomach is a muscular bag.
walls secrete a liquid called gastric juices
which is made up of hydrochloric acid, two
proteases ( pepsin and rennin) and water.
The
proteases in the stomach digest
long chains of protein molecules into
shorter chains.
 The
hydrochloric acid in the gastric juices kills
bacteria and activates proteases.
 Muscular
contractions of the stomach
walls(Peristalsis) churn the food inside the stomach
and mix it with the gastric juices.
When
food leaves the stomach, it has
become a semi-liquid mass called chyme,
which is released in small amounts at
different intervals of time into the small
intestine.
Small Intestine
As
the food from the stomach enters the
duodenum (the first part of the small
intestine) a little at a time, bile produced
by the liver is squirted onto it.
Bile
emulsifies fats, that is, it breaks
up large fat droplets into smaller fat
droplets which suspend in water to
form a stable emulsion.
The
reason for breaking large fat
droplet into smaller fat droplets is, it
increases the surface area of the fat
droplet for lipase ( digestive enzyme)
to work on.
Pancreatic juice and intestinal juice in the
small intestine contain different digestive
enzymes to digest different nutrients:
Lipase
breaks down fats into simple units
of fatty acids and glycerol.
𝒇𝒂𝒕𝒔 → 𝒇𝒂𝒕𝒕𝒚 𝒂𝒄𝒊𝒅𝒔 + 𝒈𝒍𝒚𝒄𝒆𝒓𝒐𝒍
Proteases break down shortened protein chains of the
partially digested food from the stomach into small
units of amino acids.
𝑷𝒓𝒐𝒕𝒆𝒊𝒏 → 𝒂𝒎𝒊𝒏𝒐 𝒂𝒄𝒊𝒅𝒔
Carbohydrates
Breaks down carbohydrates which have not been fully
digested in the mouth into simple sugars. These
include :
 Pancreatic
amylase which breaks down starch into
maltose
𝒔𝒕𝒂𝒓𝒄𝒉 → 𝒎𝒂𝒍𝒕𝒐𝒔𝒆
 Maltase
which breaks down maltose (complex
sugar) into glucose
𝒎𝒂𝒍𝒕𝒐𝒔𝒆 → 𝒈𝒍𝒖𝒄𝒐𝒔𝒆
 Lactase
which breaks down lactose (complex sugar)
into glucose and galactose (simple sugars)
𝒍𝒂𝒄𝒕𝒐𝒔𝒆 → 𝒈𝒍𝒖𝒄𝒐𝒔𝒆 + 𝒈𝒂𝒍𝒂𝒄𝒕𝒐𝒔𝒆
 Sucrase
which breaks sown sucrose into glucose
and fructose (simple sugars)
𝒔𝒖𝒄𝒓𝒐𝒔𝒆 → 𝒈𝒍𝒖𝒄𝒐𝒔𝒆 + 𝒇𝒓𝒖𝒄𝒕𝒐𝒔𝒆
 Digestion
ends in the ileum, the coiled and last section
of the small intestine.
 The
final products of digestion are glucose, amino
acids, fatty acids and glycerol.
 The
digested food molecules are absorbed by tiny
finger-like projections called villi on the inner walls
of the small intestine.
The
villi increase the surface area
for absorption of the digested food.
 Digested
food, which are absorbed, are then
transported away from the small intestine by blood
vessels and lymphatic vessels, which surround the
villi.
 Undigested
food such as fibre, excess water and
mineral salts pass on into the large intestine (Colon)
by peristalsis.
Large intestine
 Water,
mineral salts and undigested food (such as fibre)
pass into the large intestine where the water and mineral
salts are absorbed into the blood stream.
 The
undigested food contents move into the colon
and is stored in the rectum and passed out as
faeces through the anus when the sphincters in
the rectum relax.
 The
removal of undigested matter from the body is
called defecation or egestion ( not excretion).
Summary video
https://www.youtube.com/watch?v=bFczvJp0bpU