Digestion
What is digestion?
• Before our bodies can use the
(Biomolecules)food that we eat it must first
be digested.
How does it work?
• Along the pathway through our body our
food is broken down into very small
molecules by digestive juices and
enzymes
Can you label the main parts of
your digestive system?
Beginning (mechanical and chemical)
The chewing, softening and breaking up food is called mechanical
digestion. Which makes it have a larger surface area, then and
enzyme in your saliva called amylase starts breaking the
carbohydrate into sugar. Salivary amylase begins the chemical
digestion of starch into maltose.
Once chewed the food is now called a bolus
The bolus then moves
through the pharynx and
into esophagus and then
pushed down the
oesophagus to the
stomach by
PERISTALSIS.
What is peristalsis?
Peristalsis is the contraction and
relaxation of the circular muscles in
the wall of the gut.
When the muscle relaxes
the food drops down and
when it contracts at the
top the food at the bottom is pushed
down
Purpose of the muscular stomach: to
temporarily store ingested food,
partially digest, and kill bacteria.
The food is then in the stomach, the
food is churned around by more
waves of peristalsis to make it into
mush, and it mixes with gastric juice.
In the stomach gastric juices contain an
enzyme called pepsin which breaks down,
yup you guessed it, protein, into smaller
peptides (amino acids). pH2
It also contains hydrochloric acid which kill
bacteria and makes the optimum PH for this
enzyme, meaning it will work at its best at a
lower PH. HCL also kills bacteria.
The partially digested food, now called, chyme is ready to
enter the small intestine through the pyloric sphincter.
About 23 feet for the ave. person.
The pancreas secretes a number of
enzymes into the small intestine: trypsin,
chymotrypsin, pancreatic lipase, and
pancreatic amylase via the pancreatic duct.
What do each of these enzymes do?
Bile is another enzyme secreted into the
small intestine, it is not a digestive enzyme
but an emulsifier: it mechanically breaks up
fats into smaller fat droplets.
Bile is made in the liver and stored in the
gall bladder
These enzymes complete the digestion of
fats to fatty acids, glycerol, (carbohydrate)
to simple sugars and protein to amino
acids.
Oh I see, what then?
The ileum is specially adapted for
absorption, passing digested food into the
blood. It is very long to allow time for
digestion
It has a very large surface area due to the
presence of villi (finger like projections) and
microvilli
This allows rapid diffusion
of the products of digestion.
Aren’t villi walls only one cell thick?
Yes, this helps speed up the diffusion.
Within each villus there are lymph vessels,
called lacteals that absorb fatty acids.
Hormones involved in digestion:
Gastrin: which stimulates stomach
cells to produce gastric juice.
Secretin: stimulates pancreas to
produce bicarbonate and digestive
enzymes.
Cholecystokinin: stimulates the
secretion of pancreatic enzymes and
release bile.
The food will then move to the large
intestine and reabsorb water and salt.
It harbours harmless bacteria that
break down undigested food and in
the process provide essential
vitamins, Vitamin K. The left over
undigested food, called feces, then
moves out into the rectum.
Review
•
•
•
•
Molars (tear food apart-break plastic bag).
Saliva (use spray bottle to squirt on food).
Pancreatic juices (spray on food).
Small intestines (absorb food, find plastic bags
of candy and pass to blood).
• Blood (transports food, distribute the food to
every cell/participant).
• Large intestine (reabsorbs moisture, sponge up
water on the floor).
• Rectum (puts the waste papers in the trash can).
How much did you remember?
What enzyme is in saliva?
What does that help break down?
What type of food is broken down in
the stomach?
What happens to food that can’t be
digested?
What is the function of bile?
Well here’s what I got!
1)Amylase
2) That starts to break down carbohydrates
3) Proteins, by an enzyme called protease
4) It is passed out of the body through the anus
5) It neutralises the acid that was added in the
stomach. This helps the small intestine work
more effectively.
Well done 5/5!
Each part of your digestive system
has a special job!
http://dsc.discovery.com/tv-shows/othershows/videos/assignment-discovery-shorts06-07-07-08-human-digestion.htm
• Lets put it all together!
– Digestion animation
– http://www.medtropolis.com/VBody.asp
Why does your stomach growl?
•
•
The digestive system is, in essence, a long tube that starts at the mouth and
ends at the anus. This tube connects with the various organs and passages
that play important roles in digestion. One of the most important things to
know about the digestive system is the manner in which it propels food.
Waves of muscle contractions move and push the contents continually
downward in a process called peristalsis. In addition to moving your meal
along its digestive path, these contractions also help churn food, liquid and
different digestive juices together, rendering them into a gooey mix known
as chyme.
Stomach growling is the result of this process. Moving with those solid and
liquid chyme ingredients are gasses and air. As all these ingredients get
pushed around and broken down into easy-to-absorb bits, pockets of air
and gas also get squeezed and create the noises we hear. Stomach
growling can happen at any time -- not just when you're hungry -- but if
there's food in your stomach or small intestine, the growling becomes
quieter. It's like putting a pair of sneakers in the dryer by themselves versus
with a load of towels. The towels muffle the noise of the shoes as they
bounce around