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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