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