The Digestive System

Why do you eat food?

Why do you eat food?

• Because your cells need energy to function

• Because your cells need raw materials to keep

building your body

• Proteins• Proteins

• Carbohydrates

• Lipids

• Nucleic Acids

What happens to the food when

you eat it?

• It is processed in 4 steps:

1. Ingestion

2. Digestion

3. Absorption3. Absorption

4. Elimination

Ingestion: the art of eating!

• Ingestion is the process of the food entering

the mouth.

• (Ingestion is eating.)

Digestion

• Digestion is the process of breaking food into

small molecules that can be absorbed into the

blood stream later.

• Enzymes are a type of protein that speed up • Enzymes are a type of protein that speed up

chemical reactions. Enzymes are found in the

stomach to speed up the rate of digestion.

– Amylase breaks carbohydrates into simpler sugars

– Pepsin helps break proteins into amino acids

– Lipase breaks lipids down

Digestion

• Digestion is the process of breaking food into

small molecules that can be absorbed into the

blood stream later.

• Digestion happens via 2 processes

– Mechanical digestion– Mechanical digestion

– Chemical digestion

Digestion

happens in

the mouth

and

stomach

Digestion happens via 2 processes:

• Mechanical

– Using crushing force to break apart the

food into small molecules

– EXAMPLES: CHEWING &

STOMACH CRUSHING THE FOODSTOMACH CRUSHING THE FOOD

• Chemical

– Using chemicals to break apart the

food into small molecules

– EXAMPLES: SALIVA IN THE MOUTH AND

HYDROCHLORIC ACID IN THE STOMACH

HCl

Absorption

• Absorption is the process of the food

molecules being absorbed into the blood

stream from the small intestines

small intestines

Elimination

• Elimination is the discarding of waste from

the body.

– Solid is called feces

– Liquid is called urine– Liquid is called urine

Let’s walk through the steps one

more time:

Ingestion � Digestion

• Food is ingested through the mouth where it

is chewed (mechanical digestion) and coated

in saliva (chemical digestion).

• When the food is swallowed, it goes through

the esophagus to the stomach so it can be

further digested.

Digestion � Absorption

• The food is crushed by muscles in the

stomach (mechanical digestion) and coated in

HCl and enzymes (chemical digestion) until it

is a soupy mixture.

• Then the soupy mixture is pushed into the • Then the soupy mixture is pushed into the

small intestine where the food is absorbed

into the blood stream.

Small Intestine

Stomach

Absorption� Elimination• The rest of the mixture is pushed to the large

intestines where the water in the soupy

mixture is absorbed back into the body,

leaving only solid waste.

• The solid waste is pushed through the large • The solid waste is pushed through the large

intestines until it is eliminated from the body

through the anus as feces.

Small Intestine

Large Intestines

1. What are the 2 types of

digestion. Gives examples of each.

1. What are the 2 types of

digestion. Gives examples of each.

• Mechanical

– Examples: chewing or the stomach muscles

crushing the foodcrushing the food

• Chemical

– Examples: the enzymes in saliva breaking the food

down or the HCl and enzymes in the stomach

breaking down the food.

2. What is pushing the food

through the digestive system?

2. What is pushing the food

through the digestive system?

• Smooth muscles in the digestive organs

contract and relax pushing the food through

the digestive system.the digestive system.

3. Where does digestion start?

3. Where does digestion start?

• Digestion starts in the mouth

– Food is mechanically broken down by teeth

– Food is chemically broken down by enzymes in – Food is chemically broken down by enzymes in

saliva

4. Where does absorption take

place?

4. Where does absorption of

nutrients take place?

• Absorption of nutrients into the blood stream

takes place in the small intestine.

5. Why does the body need to re-

absorb water in the large

intestines?

5. Why does the body need to re-

absorb water in the large

intestines?

• So that the body will not become easily

dehydrated.dehydrated.

6. Where do the enzymes involved

in digestion come from?

6. Where do the enzymes involved

in digestion come from?

• Amylase comes from salivary glands in the

mouth

• Pepsin and lipase come from the pancreas and • Pepsin and lipase come from the pancreas and

are fed into the stomach through ducts

7. What is the correct sequence of

organs in the digestive tract?

7. What is the correct sequence of

organs in the digestive tract?

�mouth

� esophagus

� stomach � stomach

� small intestine

� large intestine

8. Label the parts of the digestive

system.

8. Label the parts of the digestive

system.

esophagus

stomachliver

gall bladder

pancreas

large intestine

small intestine