DIGESTION by liaoqinmei


									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 sugars
 Proteins  amino acids
 Fats  Glycerol and fatty acids

 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
Physical digestion starts starch digestion

Rapid passage of food to stomach
 Digestion of proteins

 Digestion of proteins
Production of many enzymes which digest all types of

Small Intestine
 Production of more enzymes and absorption of most
   end products
Large Intestine
Reabsorption of water

 Temporary storage of undigested waste
Removal 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 - Teeth
Adult 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 Teeth
Crown - 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 Teeth
Dentine – 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

Gum line – help hold and protect teeth
Parts of the Teeth
Root 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 tartar
NOTE: Sugar does not cause tooth decay, it feeds the
 bacteria that do
Brushing and flossing removes plaque and keeps gums

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 Problems
 Sensitivity due to the removal of enamel by cavities
  and exposing dentine
 Abscesses – bacteria get into the root and infect it
 Peridontal 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

 1st enzyme to act.
 Produced by saliva
 Helps break down starch into
  sugar molecules.
 Produced by 3 pairs of
  glands inside the mouth

 Is slightly acidic

 Approx 1000 mL
  produced per day!

 99% is water
Function of Saliva
 Moistens 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

The Tongue
• Attached to the floor of the mouth

• Helps to move food to the molars

• Mixes food with saliva
The Tongue
Once 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
The 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
• 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 Taste
Humans detect taste with taste receptor cells
These are clustered into taste buds
Taste buds are clustered into bumps called papillae
There 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 Esophagus
 Flexible 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
Bolus is moved through peristaltic action
Peristalsis - the rhythmic contractions of muscles – like
  squeezing a tube of tooth paste
Cardiac sphincter:
   Ring of muscle that controls the passage of bolus into
   – like pulling a drawstring
The Stomach
 Large 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 protein
    Hydrochloric Acid

 The muscular walls of the stomach contract to mix
 food with gastric juice, producing a mixture called
Hydrochloric Acid (HCL)
  Lowers the pH of the stomach to allow enzymes to work

  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 Burn
Presence of stomach acid in the esophagus

Cardiac sphincter is not working properly – opens
 allowing acidic stomach contents into the esophagus
The pyloric sphincter is located at the lower end of the
   Controls the flow of partially digested food (Chyme) out
    of the stomach
                  The Small Intestine
   2.5 cm in diameter, and is about 7m in length

Small Intestine                                Stomach
Small Intestine
 A long coiled and looped tube

 Fills most of the abdomen

 Held in place by a membrane called mesentery
4 functions of the Small
1. Keeps the food moving by peristalsis
2. Secretes enzymes which continue the digestive
3. The site where digestion by chemicals from the
   pancreas and liver take place
4. 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 Pancreas
 Produce pancreatic juice – which contain about 28
 enzymes and sodium bicarbonate
   Lipase – breaks down fat
   Amylase – completes carbohydrate digestion
   Trypsin 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
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
   o Surface of the small intestine is folded
   o Covering the surface are projections called villi
 Increase surface area for
 Collect the nutrients and
  transport them to where
  they are needed in the
Reabsorption and Elimination: The Large
The Large Intestine consists of:
 Cecum

 Appendix

 Colon

 Rectum
The Large Intestine
 Approx. 1.5 m in length

 7.6 cm in diameter

 Functions mainly to
 reabsorb water
Cecum – Where the small intestine empties into the
large intestine

 Appendix
    Believed to have no

   Can become infected
    –called appendicitis
Large Intestine function
 Reabsorbs water and maintains the fluid balance of
  the body

 Absorbs certain vitamins

 Undigested food is dried into suitable consistency for

 Stores waste before it is eliminated
The Rectum
 Last 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 nutrients
   Villi increase’s surface area = more absorption
   Moves the rest to the large intestine (through peristalsis)
Quick Recap
Large Intestine:

   Removes water
   Moves undigested food (peristalsis) to be released as
 http://videos.howstuffworks.com/hsw/26494-

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