SNC4M The Digestive System

What is digestion?

• Chemical and mechanical breakdown of

organic molecules into units small enough

for the body to absorb

• These molecules provide:

1. Energy resources

2. Essential chemical elements

3. Raw materials to build materials for the cell

Your task�should you accept

it�

• Make a chart and fill it in as you go along:

Organ Properties Function

Organs to Include

• Mouth

• Tongue

• Esophagus

• Stomach

• Small intestine

• Large intestine

• Rectum

• Anus

• Liver

• Gall bladder

• Pancreas

THE MOUTHTHE MOUTHTHE MOUTHTHE MOUTH

Canines - Used

for tearing

Molars – Used for

crushing

Pre-molars –

Used for grinding

Incisors – Used for

cutting

1

2

3

4

• Physical digestion –

chewing and teeth break

food into smaller pieces

• Saliva moistens food

(produced by salivary

glands)

•Chemical digestion of

starch by enzyme

amylase, which is

dissolved in saliva

THE TONGUETHE TONGUETHE TONGUETHE TONGUE

• Has taste buds that are groups of cells located on the tongue that enable one to recognize different tastes

• Assists with moving food around mouth while chewing

ESOPHAGUSESOPHAGUSESOPHAGUSESOPHAGUS

Food going down the

esophagus has a new

name, bolus.

What is this called?

The cardiac sphincter opens to

allow the bolus of food to enter the

stomach

Peristalsis - contraction and

relaxation of the smooth muscle

down the esophagus moves

bolus down to the stomach

THE STOMACHTHE STOMACHTHE STOMACHTHE STOMACH

The pyloric sphincter, regulates

the movement of chyme to the

small intestine.

• Along with HCl

(hydrochloric) acid,

enzymes, and muscle

contractions, the bolus

is churned and broken

down further into a

solution called chyme

• Chemical digestion of

protein occurs here by

the enzyme pepsin

How does it work?

• The pH of your stomach

is about 1-2 (facilitates

breakdown of protein)

• Stomach cells secrete

hydrochloric acid (gastric

juices) which helps to

break down the food and

kills pathogens

• A layer of mucous

secreted by cells lining

the stomach protects the

stomach from damage

Cows have how many stomachs?

• Cows do not have 4 stomachs; they have one

stomach with 4 digestive compartments

• They rely on micro-organisms (a large amount) to help

digest cellulose (which comes from nutrient-poor

grass)

SMALL INTESTINESMALL INTESTINESMALL INTESTINESMALL INTESTINE

• 3 sections: duodenum,

jejunum, ileum

• Digestion is completed

here

• Undigested food (waste)

passes on to the large

intestine

SMALL INTESTINESMALL INTESTINESMALL INTESTINESMALL INTESTINE

• 1st section - duodenum -

majority of digestion

• 2nd section - jejunum -

absorption of nutrients such as

carbohydrates and proteins

occur here

• 3rd section – ileum - longest

section; fats and bile salts are

absorbed here

SMALL INTESTINESMALL INTESTINESMALL INTESTINESMALL INTESTINE

• Contains little finger-like

projections called villi which

increase the surface area

• Why is this advantageous?

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.16a

Regions of the Small Intestine

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.17b, c

The Intestinal Wall

THE COLON THE COLON THE COLON THE COLON

(LARGE INTESTINE)(LARGE INTESTINE)(LARGE INTESTINE)(LARGE INTESTINE)

• Undigested food is not

needed by the body

• Waste is stored and

eliminated

•Absorption of water, vitamins,

minerals, and inorganic salts

• Most of the water from food is

reabsorbed here

• Bacteria that reside in the

colon produce vitamin B12

THE RECTUMTHE RECTUMTHE RECTUMTHE RECTUM

• “Warehouse for poop”

• Waste (feces) is stored

here until it is ready to be

excreted

THE ANUSTHE ANUSTHE ANUSTHE ANUS

• Opening at the far end of

the digestive tract through

where stool leaves the

body

• A muscular ring (anal

sphincter) keeps the anus

closed until a person has a

bowel movement.

The PancreasThe PancreasThe PancreasThe Pancreas

• HCl enters the duodenum triggers the

production of digestive enzymes

• Produces chemicals (bicarbonate) that

neutralize stomach acids that pass from

the stomach into the small intestine

The LiverThe LiverThe LiverThe Liver

Gallb

ladder

• The liver produces bile

salts which are stored in

the Gallbladder

• Bile salts aid in the

physical breakdown,

emulsification, and

absorption of fats

•Bile is secreted into the

small intestine

(duodenum)

Gallbladder

• The bile salts

produced by the liver,

are stored in the

gallbladder

• A hormone, CCK,

triggers their release

into the small intestine

Sm

all In

testin

e

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.21a, b

Figure 24.21 The Gallbladder

ReviewReviewReviewReviewThe mouth contains

different teeth, used

for different purposes.

Food moves down

the esophagus

using muscle

contractions, called

peristalsis. The stomach breaks

down the food, and

passes it on to the

small intestineThe liver produces

bile salts that break

down fats. Bile salts

are stored in the gall

bladder.

The gall bladder, stores

the bile salts, and

releases them when

CCK is present.

The pancreas

produces enzymes

to digest the food

The small intestine

has three parts. The

majority of digestion,

and some absorption

happens here.The colon absorbs the remaining moisture

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Peristalsis

Peristalsis (contd.)

Peristalsis (contd.)

Intestinal Bacteria – good?

• Scientists estimate that a healthy woman’s body is inhabited by 750 trillion bacteria, yeast, and other microorganisms, mostly colonizing the GI tract

• ~3-5 lbs. of your total body weight!

• We’ve evolved a mutually beneficial, symbiotic relationship with some bacteria

Beneficial Bacteria

• Many species manufacture B vitamins and vitamin K

and help digest foods

• Good intestinal bacteria helps prevent bloating, gas,

and yeast overgrowth by controlling the pH level, or

acidity, of the intestines

• Fermented foods such as miso, tempeh, soy sauce, and

yogurt introduce active probiotic cultures that help

wedge out unfriendly bacteria

How long does it take?

• Digestion time varies depending

on the individual

• For healthy adults, it's usually

between 24 and 72 hours

• After you eat, it takes about six to

eight hours for food to pass

through your stomach and small

intestine

• Elimination of undigested food

residue through the large

intestine usually begins after 24

hours