Digestion
Grade 9
Video Demo
http://videos.howstuffworks.com/hsw/5822-digestive-system-stomach-video.htm
Bill Nye
Jelly Bean Digestion
What biochemical compound makes up this jelly bean?Eg. lipids, carbohydrates, proteins or
nucleic acids What happens when you put the jelly
bean into your mouth? Than what happens? …
Teeth
Tear, rip and chew food to physically break it into smaller pieces.
(Mechanical Digestion).
Let’s look at the internal structure of teeth.
TeethThe crown is the part of the tooth above the gum line
The root is the part of the tooth below the gum line
•The enamel is the white part you can see covering the crown.•Enamel is the hardest substance in the human body•It covers the dentine and stops bacteria getting inside the tooth
TeethThe crown is the part of the tooth above the gum line
The root is the part of the tooth below the gum line
•The dentine is the major component within the tooth. •It is made from softer material than enamel so is easier to decay.
TeethThe crown is the part of the tooth above the gum line
The root is the part of the tooth below the gum line
•The pulp contains the nerves and blood vessels of the tooth. •It is underneath the dentine.•This is the part that hurts when you have a toothache!
TeethThe crown is the part of the tooth above the gum line
The root is the part of the tooth below the gum line
•The cementum is found outside the dentine in the root.•It cements (holds) the tooth into the jaw bone.
Bacteria
Our mouths are busy places, full of friendly bacteria that coat our teeth
Sometimes unfriendly bacteria, including one called Porphymonas gingivalis, will overgrow the friendly bacteria and cause damage to the gums and the jawbone. This bacterium is one of the main causes of gum disease.
Porphymonas gingivalis
To fend off the attack, the body will send immune cells to kill the bacteria. The bacteria are difficult to kill so the immune cells can cause even more damage to your gums.
Mouth: What happens
Food is crushed and ground up by teeth The salivary glands secrete saliva which
makes the food moist and easy to swallow (Semi-solid lump now called Bolus).
Amylase enzyme (in saliva) breaks the carbohydrate starch down into glucose.
EnzymesRemember : Large particles cannot be absorbed
in the small intestine
starchstarch
starch
starch G
G
G
GUT INSIDE THE BODY (BLOOD)
Large particles (e.g. starch) are left in the gut and small particles (e.g. glucose) pass into the bloodstream.G
G
G
BUT large particles can be broken down into small particles. This is called DIGESTION
Enzymes
Large particles need to be broken down chemically by ENZYMES.
Enzymes are biological catalysts. They speed up chemical reactions in the body.
Digestive enzymes cleave (cut) the larger molecules into smaller ones.
Digestive Enzymes
Mouth:Amylase breaks starch down into glucose.
Stomach:Protease (Pepsin) breaks protein down
into peptides.
Digestive Enzymes
Amylase
StarchGlucose
Protease
ProteinPeptides
Enzymes and pH
Enzymes work best at one pH. This pH is different for each different enzyme.
If the pH goes too low (more acidic) or too high (more alkaline), the enzyme will not work as effectively.
However, changes to pH will NOT denature enzymes.
Epiglottis
Is the flap of cartilage lying behind the tongue and in front of the entrance to the larynx (voice box).
At rest, the epiglottis is upright, allowing air to pass into the trachea (for breathing).
At Rest
During Swallowing
The tongue pushes the bolus toward the pharynx (throat).
The epiglottis folds back to cover the entrance to the trachea, protecting the larynx.
This allows food to enter into the esophagus.
*The epiglottis acts as a lid*
Swallowing
Esophagus A muscular tube that leads from the throat
to the stomach.
The smooth muscle of the esophagus pushes the bolus toward the stomach using wave-like contractions.
This is called Peristalsis.
Peristalsis
Entering the Stomach
From the esophagus, the bolus enters the stomach through the Cardiac sphincter (muscular ring).
-Sphincters help move digested material in one direction.
Entering the Stomach
The Stomach
A hollow, sac-like organ that stores, mixes, sterilizes and continues the digestive process.
Storage: walls have folds called Rugae which allow the stomach to expand.Food spends 3-4 hours in here!
The Stomach
Mixes: The stomach walls contain three layers of
smooth muscle arranged in longitudinal, circular, and oblique (diagonal) rows.
These muscles allow the stomach to squeeze and churn the food (mechanical digestion).
Muscles and Rugae
The Stomach
Sterilizes and Chemically Digests: Secretes gastric juice & hydrochloric acid
The acid kills germs in the food (pH 2)The gastric juice contains the protease
enzyme PEPSIN to digest protein into peptides
Protease
ProteinPeptides
Mucus
A thick mucus layer lines the stomach walls to prevent the stomach from digesting itself.
Mucus
Mucus
What do you think may happen when mucus is limited?
Ulcer Peptic ulcer disease occurs when
the protective mucus layer wears away in certain areas, allowing damage to occur from the natural acids of the stomach.
Ulcer- 60% to 80% of gastric ulcers caused by bacteria
Helicobacter pylori is a spiral shaped bacterium that lives in the stomach and duodenum (section of intestine just below stomach)
The stomach is protected from its own gastric juice by a thick layer of mucus that covers the stomach lining. Helicobacter pylori takes advantage of this protection by living in the mucus lining.
Helicobacter pylori
Once H. pylori is safely ensconced in the mucus, it is able to fight the stomach acid that does reach it with an enzyme it possesses called urease
However, the immune system will respond to an H. pylori infection
It may not be H. pylori itself which causes peptic ulcer, but the inflammation of the stomach lining; i.e. the immune response to H. pylori.
Continuation of Digestion
The chyme is slowly transported from the stomach through the pyloric sphincter and into the small intestine where further digestion and nutrient absorption occurs.
DIGESTION
DefinitionsGland: an organ or group of cells
which secretes enzymes or hormones
Peristalsis: muscle contractions that push food through a tube
Bolus: chewed food
Definitions continuedChyme: nutrients in semi-liquid
form Uvula: component that stops
food from entering nasal cavityEpiglottis: component that
stops food from entering the trachea
Digestive Tract and Functions
1) Mouth2) Pharynx3) Esophagus4) Stomach5) Small intestine6) Large intestine7) Rectum8) Anus
Decomposition of foodAbsorption of nutrientsElimination of waste
Digestive Glands and Functions
Salivary glands In mouth
Gastric glandsIn walls of
stomach Pancreas Liver Intestinal glands
In small intestine
Secretion of: salivaGastric enzymesDigestive juicesBile
Physical/Mechanical Breakdown Food DOES NOT change its molecular
makeup, just its shape and size, looks different1. Mouth- chewing and swallowing2. Esophagus- peristalsis3. Stomach- churning, grinding and
peristalsis4. Small intestine- peristalsis and churning5. Large intestine- peristalsis and churning
Chemical Breakdown
Food changes its molecular makeup, looks and is different
See handout*
Absorption
Through folds called villi by diffusion Small intestine – amino acids,
glucose, glycerol and fatty acids Large intestine – vitamins, minerals
and water
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