The Digestive System

The Digestive System

4 steps for processing nutrients from food1. Ingestion2. Digestion3. Absorption4. Elimination

Ingestion & DigestionIngestion: Eating or drinking

Digestion: the breaking down of food into molecules that are small enough to be absorbed by the body

Mechanical digestion: Chewing and grinding food into smaller pieces, increasing the surface area

Chemical digestion: Breaking chemical bonds of macromolecules (carbs, proteins and lipids) into monomers (sugars, amino acids, glycerol & fatty acids)

• Hydrolysis reactions that are carried out by enzymes

Absorption & EliminationAbsorption:• Cells absorb small molecules (monomers)

allowing them to enter into the circulatory system for immediate use or be transported to storage organs for later use

Elimination: • Removing undigested waste (feces)

Digestive SystemDigestive Tract

– A.k.a. an alimentary canal (2 openings)

– The mouth, pharynx, esophagus, stomach, small intestine, and large intestine

Accessory Glands & Organs– Aid in digestion, but not a part of

the digestive tract– Salivary glands, pancreas, liver,

gallbladder. – Secrete digestive juices and

enzymes into the digestive tract

What’s Your Size?Predicted Length

(m)Actual Length

(m)Mouth 0.15Pharynx 0.05Esophagus 0.25Stomach 0.25Duodenum 0.2Jejunum 2.8Ileum 4.2Large Intestine 1.5Total ~9

Mouth• Plays a role in ingestion and

digestion• Teeth, tongue, hard palate aid in

mechanical digestion• Tongue moves food down to the

esophagus• Salivary glands aid in chemical

digestion– Release saliva (~1L/day), a watery liquid

containing digestive enzymes– Salivary amylase begins to break down

starch into smaller carbohydrates– Lubrication Chewed up food is now

called a bolus

Esophagus• Located behind the trachea• As you swallow, the epiglottis

closes over the trachea and the food bolus passes through pharynx into the esophagus

• The bolus is pushed through the esophagus by a series of muscle contractions called peristalsis

Heart Burn

• After food passes into the stomach, the cardiac sphincter closes the esophagus

• If the sphincter opens at an inappropriate time, stomach acid can flow back into the esophagus

• Esophagus does not have the same protective lining as the stomach

Stomach• Elastic, muscular sac with

a protective lining that contains millions of gastric glands

• Can ~ 2 L• Mechanical and chemical

digestion

I ate too much…I’m STUFFED!

StomachChemical Digestion:• The hormone, gastrin, stimulates gastric glands to

release gastric juice – Hydrochloric acid breaks apart cells and kills bacteria– Enzymes e.g. pepsin– Mucus lubrication and protection

Mechanical Digestion:• Stomach muscles churn• Bolus becomes an acidic,

nutrient-rich liquid called chyme

Small Intestine• Chyme passes through the pyloric sphincter

and enters the small intestine (peristalsis)• Long, narrow tube where digestion is

completed and absorption begins• 3 parts:

– Duodenum– Jejunum– Ileum

Duodenum• Bile from the liver and gallbladder are

secreted into the duodenum to help with lipid digestion

• Pancreas secretes pancreatic juice into the duodenum– Neutralizes acidic chyme– Pancreatic amylase – Trypsin & chymotrypsin (protein digestion)– Pancreatic lipase

• Small intestine releases enzymes too

Jejunum & IleumJejunum• Contains more villi, therefore

more absorption• Breakdown of remaining

polypeptides and carbohydrates

Ileum• Absorption• Push remaining undigested

material into the large intestine

Large Intestine• Undigested material passes through the sphincter

between the ileum and the cecum• Absorption of water and dissolved minerals• Intestinal bacteria produce vitamins• Indigestible material (feces) passes through the

rectum to the anus– Anal sphincters help control timing of elimination

Increased Surface Area• The small and large

intestine are folded to surface area and therefore absorption

• Within the folds, there are finger-like projections called villi– Lacteal absorbs fats and fat-

soluble vitamins– Capillaries absorb glucose,

amino acids, minerals and water-soluble vitamins

Regulation of Digestive Processes

• http://www.neok12.com/php/watch.php?v=zX680f4e7e6e7c420f746402&t=Digestive-System

• http://www.neok12.com/quiz/DIGSYS04• http://www.neok12.com/quiz/DIGSYS01• http://www.neok12.com/diagram/Digesti

ve-System-01.htm