The Digestive System

VIDEO

Food Processing

• Ingestion – eating or drinking

• Digestion – break down molecules to absorb– Hydrolysis: the process of breaking bonds in food

molecules by adding water to them in the presence of specific enzymes

• Absorption – small intestine

• Elimination – removal of wastes

What is digestion?

• Chemical and mechanical breakdown of Chemical and mechanical breakdown of organic molecules into units small enough organic molecules into units small enough for the body to absorbfor the body to absorb

• These molecules provide:These molecules provide:1.1. Energy resourcesEnergy resources

2.2. Raw materials to build materials for the cellRaw materials to build materials for the cell

THE MOUTHCanines - Used for tearing

Molars – Used for crushing

Pre-molars – Used for grinding

Incisors – Used for cutting

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• Physical digestion – chewing and teeth break food into smaller pieces

• Saliva moistens food (produced by salivary glands)

•Chemical digestion of starch by enzyme amylase, which is dissolved in saliva

THE TONGUE• Has taste buds that are

groups of cells located on the tongue that enable one to recognize different tastes

• Assists with moving food around mouth while chewing

Check this Out!

• http://www.youtube.com/watch?v=2Fhc0t_QNhs

ESOPHAGUSFood going down the esophagus has a new name, bolus.

What is this called?

The cardiac sphincter opens to allow the bolus of food to enter the stomach

Peristalsis - contraction and relaxation of the smooth muscle down the esophagus moves bolus down to the stomach

Peristalsis

VIDEO

THE STOMACH

The pyloric sphincter, regulates the movement of chyme to the small intestine. VIDEO

• Along with HCl (hydrochloric) acid, enzymes, and muscle contractions, the bolus is churned and broken down further into a solution called chyme

• Chemical digestion of protein occurs here by the enzyme pepsin

How does it work?

• The pH of your stomach is about 1-2 (facilitates breakdown of protein)

• Stomach cells secrete hydrochloric acid (gastric juices) which helps to break down the food and kills pathogens

• A layer of mucous secreted by cells lining the stomach protects the stomach from damage

SMALL INTESTINE

• 3 sections: duodenum, jejunum, ileum

• Digestion is completed here

• Undigested food (waste) passes on to the large intestine

SMALL INTESTINE

• 1st section - duodenum - majority of digestion (fats)

• 2nd section - jejunum -absorption of nutrients such as carbohydrates and proteins occur here

• 3rd section – ileum - longest section; fats and bile salts are absorbed here

SMALL INTESTINE

• Contains little finger-like projections called villi which increase the surface area

• Why is this advantageous?

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.16a

Regions of the Small Intestine

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.17b, c

The Intestinal Wall

THE COLON (LARGE

INTESTINE)• Undigested food is not needed by the body

• Waste is stored and eliminated

•Absorption of water, vitamins, minerals, and inorganic salts

• Most of the water from food is reabsorbed here

• Bacteria that reside in the colon produce vitamin B12

THE RECTUM• “Warehouse for feces”

• Waste (feces) is stored here until it is ready to be excreted

THE ANUS• Opening at the far end of the digestive tract through where stool leaves the body

• A muscular ring (anal sphincter) keeps the anus closed until a person has a bowel movement.

The Pancreas• HCl enters the duodenum triggers the production of digestive enzymes

• Produces chemicals (bicarbonate) that neutralize stomach acids that pass from the stomach into the small intestine

The Liver

Gallbladder

• The liver produces bile salts which are stored in the Gallbladder

• Bile salts aid in the physical breakdown, emulsification, and absorption of fats •Bile is secreted into the small intestine (duodenum)

Gallbladder

• The bile salts produced by the liver, are stored in the gallbladder

• A hormone, CCK, triggers their release into the small intestine

Sm

all Intestine

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.21a, b

Figure 24.21 The Gallbladder

ReviewThe mouth contains different teeth, used for different purposes.

Food moves down the esophagus using muscle contractions, called peristalsis. The stomach breaks

down the food, and passes it on to the small intestineThe liver produces

bile salts that break down fats. Bile salts are stored in the gall bladder.

The gall bladder, stores the bile salts, and releases them when CCK is present.

The pancreas produces enzymes to digest the food

The small intestine has three parts. The majority of digestion, and some absorption happens here.

The colon absorbs the remaining moisture

Common Disorders

Ulcer

• Stomach lining is broken down and irritated by gastric acid

• Peptic Ulcers: Sores found in stomach lining, esophagus or upper small intestine

Inflammatory Bowel Disorder

• IBD

• Intestines become irritated and inflamed

• Develop many ulcers causing abdominal pain and diarrhea

• Crohn’s and colitis

Constipation

• Two reasons:– Peristalsis moves feces along too slowly– colon absorbs too much water so feces

becomes too compacted

• Temporary condition – eat fibre, exercise and drink lots of H2O

• Sometimes results from surgery, pregnancy, medication, air travel

Diarrhea

• Lining of colon irritated (bacterial or viral infection)

• Less effective in reclaiming water

• Can cause dehydration

Nausea and Vomiting

• Nausea: feeling associated with urge to vomit

• Vomiting: expulsion of stomach contents through esophagus and mouth

• Safety mechanism for eliminating toxic or foreign contents

• Causes: inner ear, drugs, infections, brain, injury, diseases

Please Complete

1. What happens during hydrolysis?

2. Compare and contrast the terms “mechanical digestion” and “chemical digestion”

a) In the mouth b) in the stomach

3. What is bile? What is its role in digestion?

4. As the end result of digestion:Carbohydrates are broken down to form ____, which provide your cells

with _______.

Proteins are broken down to form ____, which provide your cells with _______.

Fats are broken down to form ____, which provide your cells with _______.

5. What is the major function of the large intestine?