Download Digestive System 2

Periodontal/Gum Disease
• Periodontal/gum diseases are serious infections
that, left untreated, can lead to tooth loss
• The word periodontal literally means "around the
tooth“
• Periodontal disease is a chronic bacterial infection
that affects the gums and bones supporting the teeth
• Periodontal disease can affect one tooth or many
teeth. It begins when the bacteria in plaque causes
the gums to become inflamed
Do you have gum disease???
•
•
•
•
•
•
•
•
•
Do you ever have pain in your mouth?
Do your gums ever bleed when you brush your teeth or
when you eat hard food?
Have you noticed any spaces developing between your
teeth?
Do your gums ever feel swollen or tender?
Have you noticed that your gums are receding (pulling
back from your teeth) or your teeth appear longer than
before?
Do you have persistent bad breath?
Have you noticed pus between your teeth and gums?
Have you noticed any change in the way your teeth fit
together when you bite?
Do you ever develop sores in your mouth?
How to look after your teeth
How to Brush
Place your toothbrush next to the
teeth so that it rests on the gums
forming a 45-degree angle
against the gums.
After brushing,
one by one
tooth, all the
outer teeth
surfaces do the
same for the
inner surfaces.
Move the toothbrush from the gums
towards the edge of teeth to move the
dental plaque away from the gum line.
Brush the chewing
surfaces of the teeth
with horizontal moves.
How to Floss
Human Torso Model
*Please refer to your handout of the human digestive system
Human Digestive System
Alimentary Canal + Associated Glands
Alimentary Canal and Associated Glands
•
•
•
•
•
•
•
Mouth
Pharynx
Oesophagus
Stomach
Small Intestine
Large Intestine
Anus
•
•
•
•
•
Salivary Glands
Gastric Glands
Pancreas
Liver
Intestinal Glands
Digestion
Digestion
• Digestion is the process of breaking down large,
complex substances into smaller, simpler
molecules for absorption
• Carbohydrates -> glucose/fructose/galactose
Proteins -> amino acids
Fats -> fatty acids and glycerol
• Vitamins, minerals and water can be absorbed
directly without digestion
Mechanical Digestion vs. Chemical Digestion
•
•
•
•
Mechanical process
Chewing of teeth
Churning of stomach
Food is changed
physically but
not chemically
• Increase surface area
of food substances
• Chemical process
• Involves action of
digestive enzymes
secreted from glands
• Different types of
enzymes break down
different food types
Protease
Breaks down
protein molecules
A protein molecule is
made of many
different amino acids
Amino acids
Carbohydrase
Breaks down
carbohydrate molecules
A starch molecule is made of
many glucose molecules
Glucose
Lipase
Breaks down
fat molecules
A fat molecule is made
up of fatty acids and
glycerol molecules
Fatty
acids
Glycerol
Example of Carbohydrase: Amylase
• In saliva and pancreatic juice
• Helps break down starch into simple
sugars in mouth and in small intestine
Example of Protease: Pepsin
• In gastric juice
• Helps break down proteins into amino
acids in stomach
Example: Lipase
• In pancreatic juice
• Helps break down oil droplets into fatty
acids and glycerol in small intestine
Saliva
• The taste, smell and sight of food can
stimulate salivary glands to secrete saliva
into the mouth via salivary ducts
• Saliva – contains water, mucus and salivary
amylase. Slightly alkaline
• Water – moistens and softens food
Mucus – lubricate food for swallowing
Salivary amylase – starch -> maltose
Swallowing
1) Food is chewed and mixed with saliva
2) Tongue rolls the food into a bolus
3) Food is swallowed down the oesophagus through
the pharynx
4) Tongue moves upwards and backwards to prevent
food from entering the trachea/nasal cavity
5) The soft palate moves up to block the nasal cavity
6) The larynx moves upwards to so that the glottis (the
opening to the larynx) is covered by the epiglottis to
prevent food from entering the trachea
Movement of Food Along the Alimentary Canal
• Inner surface of alimentary canal is lined
with one to several layers of cells –
epithelium
• Some epithelial cells produce mucus,
which acts as a lubricant
Peristalsis
The small intestine has two muscle layers that
work together in peristalsis and segmentation
Peristalsis
The inner circular muscles contract, tightening the
tube and pushing the food forward in the intestine
Peristalsis
When the circular muscles relax, the outer longitudinal
muscles contract, and the intestinal tube is shortened
Peristalsis
As the circular and longitudinal muscles
tighten and relax, the food moves forward
Stomach
• a muscular, elastic, pear-shaped bag, lying
crosswise in the abdominal cavity
• food enters the stomach from the esophagus. The
connection between the stomach and the
esophagus is called the cardiac sphincter
• The other end of the stomach empties into the
duodenum, the first section of the small intestine.
The pyloric sphincter separates the stomach
from the duodenum
Sphincter Opened
Sphincter Closed
Functions of Stomach
• Storage
• Mechanical digestion – turns food into
chyme
• Chemical digestion
• The lining of the stomach
contains deep collections of cells
organized into gastric glands
• The openings of the gastric
glands into the surface of the
stomach are called gastric pits
• The mucous cells in the gastric
pits secrete mucus
• In the deeper part of the gland,
the parietal cells secrete
hydrochloric acid
• The chief cells secrete
pepsinogen (an inactive form of
the protein-digesting enzyme
pepsin)
Rennin
• In young children, the gastric juice also contains
a type of protease called rennin
• Rennin coagulates milk – allow the proteins to
stay in stomach longer for digestion
* Rennin can be used to curdle milk to make
cheese!
Ulcer/Peptic Ulcer
• A small erosion in the gastrointestinal tract
• A weakening of the mucus coating – acid
erodes the wall of the GI tract
• Stomach – gastric ulcer
• Small intestine – duodenal ulcer
• Main cause – bacterial infection
• Can be treated with antibiotics
Small Intestine
The small intestine is divided into 3
sections:
• Duodenum
• Jejunum
• Ileum
* In the small intestine, both digestion and
absorption occur
Bile
• Bile is a dark green fluid containing:
1) bile salts
2) sodium hydrogen carbonate
3) bile pigments
• Bile does NOT contain digestive enzymes
• Made by the liver
• Stored in the gall bladder
• The gall
bladder
contracts to
release bile
into the
duodenum via
the bile duct
• Stimulated by
the arrival of
chyme in the
duodenum
Bile
1) Bile salts – EMULSIFICATION
- Bile salts break up (emulsify) lipids into
small oil droplets
- This allows enzymes to have a larger
surface area to break down the fat
molecules
Lipids
droplets
Small oil
Bile
2) Sodium Hydrogen Carbonate – NEUTRALIZATION
- It neutralizes stomach acid to provide the
necessary alkaline condition (pH 8) for the
pancreatic and intestinal enzymes to work
The pH Scale
Alkaline
Acidic
1
2
3
4
5
6
Neutra
More acidic l
7
8
9
10
More basic
11
The Need for Different pH Levels
•
•
The stomach releases hydrochloric acid to
provide an acidic condition (pH1 - 2) for
stomach proteases (e.g. pepsin) to work.
Acid also kills germs
The activity of salivary amylase is stopped in
the stomach since it cannot work in acidic
conditions. Pancreatic amylase also
requires an alkaline condition to work
The Need for Different pH Levels
3) The gall bladder releases bile into the
small intestine to provide an alkaline
condition (pH 8) for the pancreatic and
intestinal enzymes to work
Bile
3) Bile pigments
- Waste products formed from the breakdown of
old red blood cells in the liver
Investigation #1:
Investigating the
effect of bile salts on oil
Pancreas
• A yellowish organ found beneath the
stomach and is connected to the small
intestine at the duodenum
• Produces pancreatic juice that flows into
the duodenum through the pancreatic duct
Pancreas
Pancreatic juice contains 3 types of digestive
enzymes:
• Tryptase
• Amylase
• Lipase
*Pancreas also produces the hormones glucagon
and insulin to regulate the level of blood glucose
Intestinal Juice
• Alkaline solution containing digestive
enzymes, hormones, mucus, neutralizing
substances, etc.
• Secreted by intestinal glands in the wall of
the duodenum
• e.g. carbohydrases catalyze the breakdown
of double sugars into simple sugars
Carbohydrase
•
Maltase: Maltose ->
Glucose + Glucose
2) Sucrase: Sucrose ->
Glucose + Fructose
3) Lactase: Lactose ->
Glucose + Galactose
Lactose Intolerance
• Inability to digest significant
amount of lactose, the
predominant sugar of milk,
due to a shortage of the
enzyme lactase
• Common symptoms include
nausea, cramps, bloating,
gas, and diarrhoea
• The undigested lactose will
serve as food for bacteria
found in the large intestine
Digestion in Ileum
• Completion of digestion
• Food is churned by peristaltic movement
and is mixed with digestive juices
• Food becomes watery fluid called chyle
• Food is now present in simplest form
Absorption
Absorption
• Absorption is the uptake of simple and
small food molecules from the alimentary
canal into the blood stream
• Food molecules can be absorbed into blood
by diffusion or active transport
• Absorption occurs in the stomach, the
small intestine and the large intestine
Absorption in Stomach
Food substances that are absorbed in the
stomach:
• Water
• Minerals
• Alcohol
• Simple sugars
• Water-soluble vitamins
Absorption in Small Intestine
• Most of the digested food is absorbed in the
small intestine
• The inner lining of the small intestine is
folded to provide a large surface area
• The inner surface of the small intestine is
made up of a large number of finger-like
projections called villi (singular: villus)
• Peristalsis in the small intestine allows the
digested food to come into contact with the
villi for absorption
Structure of Villi
• Epithelium lining
• Blood capillaries (transportation of simple
sugars, amino acids and minerals)
• Lacteal (lymph vessel)
Lacteal
• fatty acids and glycerol recombine in the
epithelium of the villus to form fat which
then enters the lacteal as fine fat droplets
• the lymphatic system converges with the
circulatory system at a duct located in the
neck area
Feature
Adaptation
1. It is very long (6 m)
Food can stay long enough
for absorption to occur
2. Its inner surface is
covered with numerous
finger-like projections
called villi
3. The wall of villi is thin
(one-cell thick)
These villi can increase the
total surface area for
absorption
4. Each villus contains a
dense network of blood
capillaries
They take up the absorbed
food and transport them
away
This allows the food to cross
the membrane rapidly
Absorption in Large Intestine
• Much of the remaining water and minerals
is absorbed in the colon
• The appendix, which has no known
functions, is joined to the caecum
• Appendicitis – food materials trapped in
the appendix causing bacterial infection
Caecum in Herbivores
• Do not have digestive
enzymes to break
down cellulose
• Rely on bacteria
residing in the long
caecum to provide the
enzyme cellulase
• Cellulose -> Glucose
Investigation #2:
A Model Gut
• What does the content inside the dialysis
tubing represent?
• What does the dialysis tubing represent?
• What does the water in the beaker/boiling
tube represent?
Assimilation
Assimilation
• the process by which absorbed food
molecules in the blood are transported to
cells for the use of growth, tissue repair
and other metabolic activities. The actual
destiny of each food molecule depends not
only on its type but also on the body
requirements at that time (e.g. use
immediately or put into storage)
Liver
• Largest organ of the body
• Reddish brown in color
• Lies on the right side of the abdominal
cavity beneath the diaphragm
• Blood is carried to the liver via two large
vessels called the hepatic artery and the
hepatic portal vein
• After processing in the liver, blood leaves
the liver through the hepatic vein
Functions of Liver
•
•
Carbohydrate metabolism - the liver
converts excess glucose into glycogen as
a temporary way of storing the glucose.
Glycogen can also be converted back to
glucose when needed
Fat metabolism - the liver converts
excess protein and carbohydrate into fat.
Excess glycogen is stored as fat for long
term storage
Functions of Liver
3) Protein metabolism – the liver can
synthesize new proteins/ amino acids and
deaminate excess amino acids
Deamination
• Amino group (~NH2)
removed
• Ammonia (NH3)
produced (toxic)
• Ammonia converted to
urea – excreted in urine
• Carbon skeleton –
converted to
carbohydrates
Functions of Liver
3) Protein metabolism – the liver can synthesize
new proteins/amino acids and deaminate
excess amino acids
4) Vitamin storage - the liver stores mainly
vitamins A, D and B12
5) Iron storage - the liver stores iron which is
obtained from the breakdown of red blood
cells. The iron salts can be used in the
formation of new RBC
Functions of Liver
6) Bile production – emulsification and
neutralization
7) Drug/Alcohol metabolism – the liver
changes the drug into an excretable and
harmless form (detoxification)
8) Disposal of bacteria - The liver filters many
bacteria, viruses, and other
microorganisms from the blood
Egestion
Egestion
• Faeces – semi-solid, greenish brown mass
containing undigested and unabsorbed
food substances. Also contains bile
pigment (hence the color of faeces), dead
RBC, cells from intestinal wall, bacteria, etc.
• Temporarily stored in rectum
• Anal sphincter – relaxes to allow a person
to defaecate
Constipation and Diarrhoea
• Peristalsis too slow
• Too much water absorbed
• Some common causes
include lack of fibre in
diet, not enough liquids,
lack of exercise, etc.
• Lead to dry, hard faeces
• Difficulty in defaecation
• May damage wall of
rectum and cause
bleeding or form piles
• Peristalsis too fast
• Too little water absorbed
• Some common causes
include bacterial / viral /
parasitic infections, food
intolerance, etc.
• Lead to loose, watery
stools
• More frequent egestion
• May cause dehydration
Haemorrhoids
• Also referred to as piles
• Haemorrhoids are enlarged veins just under
the surface tissue of the rectum or the anus
• Haemorrhoids in the rectum are called
internal haemorrhoids; those that occur
around the anus are called external
haemorrhoids
• May cause bleeding, pain, itching and a sense
of pressure
Haemorrhoids
•
•
•
•
•
•
Increased pressure in the veins around the anus is
thought to be the cause of haemorrhoids:
straining to pass a bowel motion because of hard,
dry stools (as in constipation)
diarrhoea
heavy lifting
being very overweight
sitting or standing for long periods
pregnancy