The Digestive System

Chapter 3Nutrition and Wellness

HS 340

Introduction

• Your genes, in the form of DNA, direct your body’s development and basic functions

• Many of your genes are ancient in origin and have not changed for thousands of centuries.

• There is no guarantee that a diet haphazardly chosen from today’s foods will meet the needs of your “ancient” body.

• You need to learn how your body works, what it needs, and how to select foods to meet its needs.

The Body’s Cells

The human body is made up of trillions of cells

The Body’s Cells

• All living things are single cells or organisms made up of many cells

• Cells need energy

oxygen

water

Nutrients

• Cells die and must replenish themselves

Cells, Tissues, Organs, Systems

• Cells are organized into tissues to perform specialized tasks (i.e. muscles, nerves, blood, bone)

• Tissues are grouped together to form organsto perform specific tasks (i.e. heart, liver, brain)

• Related organs work together as part of a body system to perform a function (i.e. circulatory system, respiratory system, nervous system)

The Digestive System

• Humans have an innate preference for sweet, salty and fatty foods.

Sugar provides the body with energy and fuels the brain

Fats provide concentrated energy and essential nutrients

Salt provides the body with sodium and chloride

This inborn preference can lead to over-consumption of these foods

The Digestive Tract

• The digestive system is comprised of many organs to digest and absorb foods eaten

A flexible, muscular tube extending from the mouth, throat, esophagus, stomach, small intestine large intestine, rectum and anus

A total of about 26 feet long!

The digestive tract is separate from the rest of the body

Nutrients and substances must pass through the wall of the digestive tract to enter the body’s tissues

Mechanical Aspect of Digestion

• Mechanical digestion begins in the mouth

▫ Food is chewed into smaller pieces

▫ Saliva moistens food so it can pass easily into the esophagus

• The stomach liquefies foods by mashing and squeezing which turns them into Chyme

▫ peristalsis, (squeezing waves), which also pushes food through the digestive tract

The Stomach

Mechanical Aspects of Digestion

• A sphincter muscle at the base of the esophagus prevents foods from moving back up the esophagus

• The pyloric valve controls the exit of chyme from the stomach into the small intestine for nutrient absorption

• The chyme then travels to the colon for water resorption▫ The remaining fiber and undigested materials are

called feces which are stored in the rectum and excreted in intervals

The Chemical Aspects of Digestion

• Several organs in the digestive system secrete digestive juices containing enzymes that break down nutrients into their component parts

salivary glands stomach pancreas liver small intestine

• Enzymes in saliva break down starch and a little fat (especially milk fat)

The Chemical Aspects of Digestion

• The stomach releases gastric juice containing water

enzymes

hydrochloric acid

• Initiates the digestion of protein

• Gastric juice is very acidic (pH 2) Mucus protects the digestive tract lining

The Chemical Aspects of Digestion

• The small intestine finishes what the mouth and stomach started

The gallbladder squirts bile (an emulsifier which combines fats and water) into the intestine

The pancreas releases pancreatic juice containing bicarbonate to neutralize stomach acid and enzymesto digest carbohydrates, fats and proteins

Absorption of most nutrients occurs

Water, Fiber and Minerals remain in the small intestine and are transported to the colon

The Chemical Aspects of Digestion

• In large intestine (colon)

▫ some fiber is broken down by resident bacteria

▫ small fat fragments released from the fiber provide a tiny bit of energy

Are some food combinations more

easily digested than others?

• The digestive system adjusts to whatever mixture of foods is presented to it

• All foods, regardless of identity, are broken down by enzymes into the basic molecules that make them up

If “I am what I eat” then how does a

sandwich become me?

• Digestion and absorption are remarkably efficient

• Within about 24 to 48 hours of eating, a healthy body digests and absorbs about 90% of the energy nutrients in meal

• Video on the digestive process:

http://www.youtube.com/watch?v=s06XzaKqELk

• Let’s follow a peanut butter and banana sandwich on whole-wheat, sesame bread through the tract:

In the mouth:▫ Teeth/tongue crush

and mash food

▫ Digestion begins of starch to sugar from the

bread

banana

peanut butter

In the stomach▫ Food is collected in upper

storage area

▫ Starch digestion stops in presence of gastric juices

▫ Food enters digesting area of stomach

▫ Proteins in bread, Peanut butter, and seeds are unwound

▫ Enzymes clip proteins

▫ Contents become Chyme

In the small intestine▫ Sugars from banana cross

lining of small intestine (absorption)

▫ Bile from liver arrives to blend with fat from Peanut Butter and seeds (emulsification)

▫ Pancreas and intestinal cells send digestive enzymes

▫ Small units from energy nutrients absorbed

▫ Vitamins and minerals absorbed

In the large intestine▫ Fiber fragments, fluid,

and some minerals are absorbed

▫ Fiber in seeds, bread, PB, and banana is partly digested by bacteria

▫ Most fiber excreted as feces

Absorption and Transportation of

Nutrients• Once food is broken down into nutrient

components, the nutrients must cross the cells of the intestinal lining

• The cells of the small intestine are arranged into millions of finger like projections called villi

Every cell on the villi contain tiny hair-like projections called microvilli which expand the surface area available to trap nutrient particles

The surface area of the small intestine is 200m2 roughly the size of a tennis court

Absorption and Transportation of

Nutrients• After the nutrients pass through the cells of the

villi, blood and lymph transport them to the body’s cells

Lymph primarily transports products of fatdigestion

Blood carries products of carbohydrate and protein digestion, most vitamins and the minerals from the digestive tract to the liver and from there to the rest of the cells of the body

Digestive tract

• Hiccups – spasms of the vocal cords and diaphragm (eating and drinking too fast)

• Heartburn – backflow of stomach acid into the esophagus (eating or drinking too much)

• Antacid – medication that reduce stomach acid• Stomach Ulcer – an erosion in the lining of the digestive

tract• Hiatal Hernia – Protrusion of the stomach through the

diaphragm into the chest cavity• GERD (Gastroesophageal reflux disease) – Severe and

chronic invasion of stomach acid and enzymes into the throat • Irritable Bowel Syndrome (IBS) intermittent

disturbance of bowel function with alternating diarrhea and constipation

Foods and Intestinal Gas

• Milk Causes gas in people who cannot digest the milk sugar lactose

(lactose intolerant)

• Beans Some carbohydrates in beans are not digestible by enzymes,

but they are broken down by bacteria in the colon

Rinse canned beans, use enzyme drops (beano)

• Air Swallowing air while eating or drinking can cause gas

Slow down while eating and drinking, avoid chewing gum

• Vegetables May cause gas in some people

Try small amounts of cooked vegetables

Alcohol and Nutrition: Do the risks

outweigh the benefits?• Total daily energy

intake as alcohol▫ U.S. average of 6 to

10 percent

• Ethanol - Alcoholic beverages

• MODERATE alcohol consumption:▫ 1 drink/day women▫ 2 drinks/day men

Breakdown of Alcohol

• Stomach produces ADH (alcohol dehydrogenase)

An enzyme that breaks down alcohol

Men produce more than women

• Liver also produces ADH and clears the majority of alcohol from the system

• Liver can clear about 1 drink per hour

• Only time restores sobriety Caffeine only acts as a stimulant

Alcohol and the liver

• Alcohol metabolism generates damaging free radicals

▫ Leads to inflammation, diabetes, cancer

• Fatty liver – alcohol speeds up liver production of fat

• Liver fibrosis

▫ Cirrhosis – scar tissue forms on the liver

• Reproductive and other organs

Alcohol’s effects on the liver

• Left: Normal, Middle Fatty Liver, Right: Cirrhosis

Alcohol’s effect on nutrition

• Causes disturbances in nutrition

• All discretionary calories – No nutritional value

• Fattening power of alcohol “Beer belly” – prmotes fat gain around abdomen

• Effects on vitamins Malnutrition – reduces absorption

Wernicke-Korsakoff syndrome – Thiamin Deficiency

Folate

Does Moderate Alcohol Use Benefit

Health?• Middle aged people (over 35 only)

Reduced risk of heart disease, stroke, dementia, diabetes and lower mortality

• Among young drinkers, (Under 35) mortality risk higher among drinkers

• Amounts more than 1-2 drinks/day significantly increase risk of cardiovascular disease.

• Risk for alcoholism

• Adversely affects fetus