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/other-

shows/videos/assignment-discovery-shorts-

06-07-07-08-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