Why Do We Need to Digest?Nutrients from food provides us with the energy

and materials we need for work, growth and repair

The problem is that most of the nutrients we need cannot be used in the form they are eaten

Nutrients need to be broken up into their smallest components in order to diffuse into our blood stream

What needs to be broken up?Carbohydrates simple sugarsProteins amino acidsFats Glycerol and fatty acids

Enzymes Type of protein that breaks food molecules

into smaller units.

The Process of Digestion

Divided into 3 stages:1.Physical Digestion

• Taking food in – Cutting and chewing food

2.Chemical Digestion• Enzymes break down food even further

3.Absorption• Wastes are excreted

MouthPhysical digestion starts starch digestion

EsophagusRapid passage of food to stomach

StomachDigestion of proteins

LiverDigestion of proteins

PancreasProduction of many enzymes which digest all

types of food

Small IntestineProduction of more enzymes and absorption of

most end products

Large IntestineReabsorption of water

RectumTemporary storage of undigested waste

EliminationRemoval of undigested wastes

• On your plate with a fork and knife

• Your saliva initiates chemical digestion with an enzyme that breaks carbohydrates down into simple sugars

• Your teeth and tongue break up food into smaller pieces and grind it up

Stage 1

Physical Digestion - TeethAdult humans have 4 different kinds of teeth

(32 total)1.Incisors at the very front (4 on top, 4 on

bottom)2.Canines (cuspids) beside the incisors and are

pointed (4 total)• Used for tearing or shredding

3.Premolars (8 total)4.Molars (12 total incl. wisdom teeth)Premolars + molars – flattened on upper

surface, used for grinding and chewing tough food

Children have deciduous or primary teeth (20 total)

8 Incisors

4 Canines

8 molars

Parts of the TeethCrown - visible part above the gum

Root – Part below the gum line, holds tooth in place

Enamel – protective coating – hardest substance in the body, cannot be replaced.

Parts of the TeethDentine – hard bone that gives teeth shape and

strength. It is sensitive to temperature, sugar, touch, acids, etc.

Pulp Chamber – message center for sensation in the dentine

Gum line – help hold and protect teeth

Parts of the TeethRoot Canal – carries blood and nerve endings

Cementum – connect tooth to the jaw bone

Carnivores – Sharp teeth for grabbing food and ripping it apart

Herbivores – Flat teeth for grinding food

Omnivores – Flat and sharp teeth

What causes tooth decay?Bacteria called plaque live in your mouth

Plaque eats any food that stays on your teeth

Produce acid that eats away the enamel, creating pits called cavities

Build up of a hard crust called tartarNOTE: Sugar does not cause tooth decay, it

feeds the bacteria that do

Brushing and flossing removes plaque and keeps gums healthy

Wear mouth guards in sports

Regular dental checkups (clean away tartar)

Diet: calcium, phosphorus, vitamins A, C & D all help maintain teeth and gums

Some Dental ProblemsSensitivity due to the removal of enamel by

cavities and exposing dentineAbscesses – bacteria get into the root and

infect itPeridontal Disease – Affect the tissue around

the teeth. Includes retreating gum line, sore gums or bleeding. Usually caused by poor diet or hygiene.

Halitosis – bad breath caused by smoking, infections, tooth decay, sinus infections, etc.

Stage 2

Begins In the Mouth

Amylase 1st enzyme to act. Produced by saliva Helps break down starch

into sugar molecules.

SalivaProduced by 3 pairs

of glands inside the mouth

Is slightly acidic

Approx 1000 mL produced per day!

99% is water

Function of SalivaMoistens dry food

Binds the loose crumbs together so bits do not get into the respiratory system

Softens food so rough edges will not scratch the walls

Enzyme amylase begins chemical digestion

Hard Palate Soft Palate

Uvula

The Tongue• Attached to the floor of the mouth

• Helps to move food to the molars

• Mixes food with saliva

The TongueOnce the food is moist and soft, the tongue

rolls it into a ball called a bolus.

This prepares the food to pass into the pharynx to be swallowed.

SwallowingThe tongue moves the bolus of swallowed

food to the back of the mouth

The soft palate moves upward to partially seal off the nasal passage

At the same time, the epiglottis closes the opening into the respiratory passage

• Place cracker in mouth• Chew WITHOUT SWALLOWING! • Note the taste• Leave on tongue until you notice a taste change (can take up to 5 min)• What do you taste?

The Sense of TasteHumans detect taste with taste receptor cellsThese are clustered into taste buds Taste buds are clustered into bumps called papillaeThere are 5 primary taste sensations

salty sour sweet bitter Umami (Savory)

The movement of food from the tongue down into the pharynx is under voluntary control

The second stage, involving the epiglottis and the movement of the food into the esophagus, is involuntary

The EsophagusFlexible tube – approx. 25 cm long

Leads from the pharynx to the stomach

Walls have 2 layers of muscle

The inner lining covered with mucus – helps food pass through easily

PeristalsisBolus is moved through peristaltic actionPeristalsis - the rhythmic contractions of muscles –

like squeezing a tube of tooth paste

Cardiac sphincter:Ring of muscle that controls the passage of

bolus into stomach – like pulling a drawstring

The StomachLarge muscular bag that stretches as it fills

with food

Can hold 1.5 L

Made up of many layers, including 3 layers of muscle

Gastric glands produce gastric juice.Pepsin (an enzyme) – Breaks down proteinHydrochloric Acid

The muscular walls of the stomach contract to mix food with gastric juice, producing a mixture called chyme.

Hydrochloric Acid (HCL)Lowers the pH of the stomach to allow enzymes

to work efficiently

Helps kill bacteria

Mucus secretions protect the stomach walls from HCl

BUT sometime mucus is not enough and HCL and digestive enzymes eat away at the lining, resulting in a peptic ulcer.

Heart BurnPresence of stomach acid in the esophagus

Cardiac sphincter is not working properly – opens allowing acidic stomach contents into the esophagus

http://videos.howstuffworks.com/hsw/17648-food-into-fuel-the-process-of-digestion-video.htm

The pyloric sphincter is located at the lower end of the stomachControls the flow of partially digested food

(Chyme) out of the stomach

The Small Intestine2.5 cm in diameter, and is about 7m in length

Esophagus

Stomach Small Intestine

Small IntestineA long coiled and looped tube

Fills most of the abdomen Held in place by a membrane called

mesentery

4 functions of the Small Intestine1. Keeps the food moving by peristalsis2. Secretes enzymes which continue the

digestive process3. The site where digestion by chemicals from

the pancreas and liver take place4. Nutrients are absorbed into the bloodstream

Digestive processes…3 basic food substances in the small intestine:

• Carbohydrates• Fats• Proteins

They are broken down into molecules that are small enough to pass through the wall and enter the circulatory system

The PancreasProduce pancreatic juice – which contain

about 28 enzymes and sodium bicarbonateLipase – breaks down fatAmylase – completes carbohydrate digestionTrypsin and peptidase – complete protein

digestion

Sodium bicarbonate neutralizes the acidic chyme as it comes out of the stomach

How are our bodies built to handle the acid in our stomach?

The Liver• Produces bile that is stored in the gall

bladder

• Bile emulsifies fat – which means that it helps fat dissolve in water so it can be digested and absorbed

Absorption Stage 3

Absorption of Nutrients

Villi:Increase surface

area for absorption Collect the nutrients

and transport them to where they are needed in the body

o Surface of the small intestine is foldedo Covering the surface are projections called villi

Reabsorption and Elimination: The Large Intestine

The Large Intestine consists of:Cecum

Appendix

Colon

Rectum

The Large IntestineApprox. 1.5 m in

length

7.6 cm in diameter

Functions mainly to reabsorb water

Appendix Believed to have

no function

Can become infected –called appendicitis

Cecum – Where the small intestine empties into the large intestine

Large Intestine functionReabsorbs water and maintains the fluid

balance of the body Absorbs certain vitamins

Undigested food is dried into suitable consistency for defecation

Stores waste before it is eliminated

The RectumLast section of the digestive tract

Ends with the anal sphincter (like a drawstring)

When full there is a mild feeling of discomfort, which tells us that the feces is ready to be eliminated

What Your Feces Can tell you…

Feces are 75% water and 25% solids

Diet lacking fiber = drier, compacted feces which can result in constipation

Sufficient fiber = Holds more water and is much softer which allows it to pass through easily

Quick Recap…Small Intestine:

Breaks down food and absorbs nutrientsVilli increase’s surface area = more absorption Moves the rest to the large intestine (through

peristalsis)

Quick RecapLarge Intestine:

Removes waterMoves undigested food (peristalsis) to be

released as waste

http://videos.howstuffworks.com/hsw/26494-managing-your-health-the-digestive-system-video.htm