The Digestive SystemThe Digestive SystemGrade 9 BiologyGrade 9 BiologyMs. Marcos

Moving into human body systems!

What does your digestive What does your digestive system look like?system look like?

The tube starts here:

And although there are a few twists and turns along the way…

It comes out here:

Anything that goes in the top hole (mouth) does not become part of the body until it is broken down then absorbed though a series of specialized structures.

A Tour of the Digestive A Tour of the Digestive SystemSystem Mouth

◦ Tongue, teeth, salivary glands, pharynx

◦ Enzymes

Esophagus◦ Epiglottis and choking

◦ Peristalsis

Stomach◦ Cardiac and pyloric sphincters

and stomach cell types

◦ Enzymes and gastric secretions

Pancreas◦ Digestion enzymes, pH

balance and maintenance of blood sugar

Liver / Gall bladder◦ Roles in digestion and

other body processes Small intestine

◦ Specialization – structure and function three sections and of the villi

◦ Enzyme action Large intestine

◦ Functions and anaerobic bacteria within

Rectum and Anus◦ Expulsion of wastes

What does the digestive What does the digestive system do?system do?DIGESTION:

◦ Mechanical vs. chemical digestion Mechanical is breaking the food into smaller pieces Chemical is using enzymes and chemical reactions

to break apart the moleculeABSORPTION:

◦ Moving the broken down food into the blood or the lymph to be carried around the body

ELIMINATION: ◦ Getting rid of anything that you can’t digest

The parts of the digestive The parts of the digestive system…system…

MouthTongueSalivary glandsOral cavityPharynxEsophagusStomachPyloric sphincterLiverGall-bladderPancreasSmall intestineLarge intestineAnusRectum

Many parts work together and are coordinated by hormones.

A Tour of the Digestive A Tour of the Digestive SystemSystem Mouth

◦ Tongue, teeth, salivary glands, pharynx

◦ Enzymes

Esophagus◦ Epiglottis and choking

◦ Peristalsis

Stomach◦ Cardiac and pyloric sphincters

and stomach cell types

◦ Enzymes and gastric secretions

Pancreas◦ Digestion enzymes, pH

balance and maintenance of blood sugar

Liver / Gall bladder◦ Roles in digestion and

other body processes Small intestine

◦ Specialization – structure and function three sections and of the villi

◦ Enzyme action Large intestine

◦ Functions and anaerobic bacteria within

Rectum and Anus◦ Expulsion of wastes

The Mouth The Mouth – Where digestion begins– Where digestion beginsHard palate (the bony part at

the top)Soft palate composed of muscle

tissue◦The uvula - the thing that hangs

down in the back of your throat It stops liquid or food from coming out

your nose when you swallowTongue – moves around the food

and forms a bolus (a ball of food)

Types of teethTypes of teethThere are different types of teeth for different functions:

Cutting and chopping food

Sharp pointed teeth for cutting and tearing food

Crushing and grinding food

Grinding and mashing food

What’s in saliva and what does it do?

Water Makes food soft

Mucus Helps food slide down the esophagus

Bicarbonate ions neutralize acid produced by bacteria (helps prevent tooth decay)

Salivary amylase breaks down starch in the presence of water

Starch maltose (a disaccharide of glucose)

How much saliva do you produce in a day?About 1-2 litres!

A Tour of the Digestive A Tour of the Digestive SystemSystem Mouth

◦ Tongue, teeth, salivary glands, pharynx

◦ Enzymes

Esophagus◦ Epiglottis and choking

◦ Peristalsis

Stomach◦ Cardiac and pyloric sphincters

and stomach cell types

◦ Enzymes and gastric secretions

Pancreas◦ Digestion enzymes, pH

balance and maintenance of blood sugar

Liver / Gall bladder◦ Roles in digestion and

other body processes Small intestine

◦ Specialization – structure and function three sections and of the villi

◦ Enzyme action Large intestine

◦ Functions and anaerobic bacteria within

Rectum and Anus◦ Expulsion of wastes

Traveling to the Traveling to the stomach…stomach…Esophagus

◦Tube from pharynx to stomach◦It has: Mucus membranes

Helps the food slide down Muscle

Pushes the food down the tubeFood moves down by peristalsis

Peristalsis Peristalsis (and reverse (and reverse peristalsis)peristalsis)

How long does peristalsis take?◦ About 9 seconds from pharynx to stomach (rate of 2-4cm/s)

Swallowing Animation

Swallowing…Swallowing…The bolus enters the PHARYNX1.Uvula moves back to cover

openings to nose2.Trachea (to the lungs) moves up

3. Epiglottis covers the trachea (so that you don`t choke!)

4.Food goes down by peristalsis

Swallowing in action…Swallowing in action…

Reaching the stomach…Reaching the stomach…Bolus arrives at the cardiac sphincter

◦ This is the “door” at the top of the stomach◦ Made of muscle

What is heartburn and what causes it? Opening of the cardiac sphincter allowing food

(soaked in stomach acid) to enter the esophagus.

http://www.youtube.com/watch?v=1ZIK6Ua20JA

A Tour of the Digestive A Tour of the Digestive SystemSystem Mouth

◦ Tongue, teeth, salivary glands, pharynx

◦ Enzymes

Esophagus◦ Epiglottis and choking

◦ Peristalsis

Stomach◦ Cardiac and pyloric sphincters

and stomach cell types

◦ Enzymes and gastric secretions

Pancreas◦ Digestion enzymes, pH

balance and maintenance of blood sugar

Liver / Gall bladder◦ Roles in digestion and

other body processes Small intestine

◦ Specialization – structure and function three sections and of the villi

◦ Enzyme action Large intestine

◦ Functions and anaerobic bacteria within

Rectum and Anus◦ Expulsion of wastes

The StomachThe StomachHow big is your stomach?

◦ About 1.5 to 2L in an adult human (300L in a cow!)

This is a rabbit stomach

The StomachThe Stomach J-shaped organThree layers of muscle

◦ Mix up and break up the foodGastric glands make gastric juiceGastric juice has:

◦ Pepsinogen + Hydrochloric acid Pepsin

PEPSIN an enzyme it breaks down proteins into

peptides (small protein sections)

Within the walls of the Within the walls of the stomach…stomach…

Parietal Cell Peptic cell

Mucus cell (shown in red)

HCl

Pepsinogen Pepsin(Activates more

Pepsinogen)

Gastric gland

3 types of cells in the stomach:◦Mucus cells

Mucus protects the stomach

◦Parietal cells Secrete acid (HCl at pH 3) kills bacteria and helps break food down

◦Peptic cells Secrete pepsinogen to make pepsin

Why doesn’t the stomach digest Why doesn’t the stomach digest itself?itself?

HCl could eat through the stomach

Stopped by the mucus layer

Pepsin could digest protein in the stomach cells

Pepsin is only made when pepsinogen mixes with HCl

Stopped by the mucus layer

When things go wrong…When things go wrong…Bacterial infections

◦Cells can’t make mucus◦Can cause ulcers and stomach

cancer

http://www.youtube.com/watch?v=1ZIK6Ua20JA&feature=channel_page

How long does food stay in your stomach?◦2 - 6 hours

Chyme = liquid food that leaves your stomach

Enters the small intestinecontrolled by the PYLORIC

SPHINCTER “Door” of muscle at the bottom of the

stomach

Digestion Questions #1:Digestion Questions #1:1. Explain the step by step process that occurs when

a. someone chokes on a piece of food. What goes wrong? (1)

b. you are drinking water and accidentally laugh, causing the water to come out of your nose. What goes wrong? (1)

2. Explain all the types of digestion that occur in the mouth. (2)

3. What possible problem could lead to an esophageal ulcer? Explain what would happen to cause this. (2)

4. Explain all the types of digestion that occur in the stomach. (2)

5. If someone had a severe ulcer, would it be possible to remove his or her stomach and replace it with a bag? What properties would this bag need to have in order to function? How would that person’s diet need to change? (3)