DIGESTION SYSTEMApril 20-21, 2015

Functions

1. Ingestion (intake of food)

2. Digestion (physical and chemical break down of food)

3. Absorption (passage of chemicals into blood or lymph)

4. Defecation (elimination of indigestible substances as feces)

StructuresDivided into:• Alimentary canal /

gastrointestinal (GI) tract• Mouth• Pharynx• Esophagus• Stomach• Small intestine • Large intestine• Rectum

• Accessory organs• Teeth• Tongue• Gallbladder• Salivary glands• Pancreas• liver

Fun fact: The lumen of the alimentary canal – where the food travels - is considered to be external to the body.

We are essentially an elongated donut!

Digestive Organ Functions1. Mouth

• Teeth mechanically digest food

• Saliva • cleans mouth (contains

many antimicrobial chemicals)

• chemically digests food (the enzyme amylase breaks down starch into sugar)

• Tongue repositions food and helps form a bolus that can be swallowed

Digestive Organ Functions1. Mouth

• Teeth mechanically digest food

• Saliva • cleans mouth (contains

many antimicrobial chemicals)

• chemically digests food (the enzyme amylase breaks down starch into sugar)

• Tongue repositions food and helps form a bolus that can be swallowed

Fun Fact: Mumps is a viral disease of the salivary glands. Painful, but usually not fatal, it can lead to sterility in males. Several college campuses have had outbreaks in recent years.

Digestive Organ Functions2. Pharynx

• Passage for food, water, and air

3. Esophagus• Passage to stomach for

food and water only• Gastroesophageal

sphincter is composed of muscles at the lower end of espophagus that prevent stomach contents and acids from traveling back up the esophagus.

Food is moved through the GI tract by peristalsis – wavelike contraction & relaxation of muscles in the walls of the GI tract click!

Fun Fact: Heart burn occurs when stomach acids go up the esophagus, usually due to

• Over-eating• Pregnancy• Running (runner’s reflux)• Hiated hernia

Long-term, untreated heartburn can cause esophageal ulcers or cancer.

Digestive Organ Functions4. Stomach

• Mechanically digests food by churning and mixing it, to form chyme.

• Chemically digests food by releasing extremely acidic gastric juice which contains HCl and proteases, such as pepsin, that break down proteins into amino acids

• LIMITED absorption (alcohol, aspirin, other drugs)

Fun Fact: Vomiting is regulated by the brain, and is triggered by excessive stomach stretching (as from a very large meal) or by stomach irritants, such as bacterial toxins and some drugs (including excessive alcohol).

During vomiting, the brain signals the diaphragm and other abdominal muscles to contract forcefully, and it signals the gastroesophageal sphincter to relax. The contents of the stomach, and sometimes the upper part of the small intestine, are expelled.

Digestive Organ Functions5. Small Intestine

• Digestion is completed here

• Sm. intestine produces intestinal juice, which is alkaline and contains some digestive enzymes

• Bile is produced by the liver, stored by the gall bladder, and is dumped into the small intestine. It digests fats.

• Pancreas releases pancreatic juice into the small intestine. Include proteases, lipases, amylase, and nucleases.

Fun Fact: Most digestive enzymes only become activated after entering the alimentary canal, which prevents them from self digestion.

For example,

• The stomach produces pepsinogen which is converted to active form – pepsin – by the low pH of the stomach acids

• Most pancreatic enzymes are converted to active form by other chemicals within small intestine.

Digestive Organ Functions5. Small Intestine

• Major site of absorption

• Digested carbohydrates, fats, proteins, nucleic acids, vitamins, electrolytes, and some water absorbed

-- more on this in a bit –

6. Large Intestine (colon)

• Absorption of water, electrolytes, and some vitamins

• Everything not absorbed is expelled by rectum as feces

Fun Fact: Diarrhea and constipation occur when food travels either too quickly (diarrhea) or too slowly (constipation) through the colon.

AbsorptionAbsorption occurs when nutrients pass out of the alimentary canal and into the blood capillaries (water-soluble nutrients) or lymph lacteal (fat-soluble nutrients).

Some nutrients are absorbed through diffusion, but many require active transport.

AbsorptionThe small intestine has many adaptations for absorption:

• Enormous surface area due to: long length (20 ft), folds, and numerous villi & microvilli

• SLOOOW movement of chyme (3-6 hours)

Fun fact: The surface area of the small intestine is about the same as a 2 story house!

Watch me!

ReviewWhat is digestion, and in which structures does it occur?

How does the process of digestion differ for different foods?

What is absorption, and in which structures does it occur?

Closure

1. Which questions did we answer? Which did we not?

2. What was our learner profile trait and how did we demonstrate it?

3. How did what we do today relate to our unit question – how do body systems work together?