Digestive System

Standards:

4a. Describe the chemical and physical mechanisms of digestion, elimination, transportation, and absorption within the body to change food and derive energy.

Big idea(s):

Changing food to get energy involves—• Physical and chemical changes• Basic processes of digestion,

elimination, transportation & absorption

A. Diet:5 basic types of nutrients

1. carbohydrates

2. proteins

3. fats4. vitamins5. minerals

OLD

1. Carbohydrates – major energy source for cells

• cells break down carbohydrates (glucose) to make energy (ATP)

• each gram of carbohydrates you consume yields 4 Calories (the unit we use to measure energy)

The largest of carbs are the polysaccharides (starches, fiber, grains) which are good for energy and digestive health

The smallest are the mono- and disaccharides (sweet tasting foods) which are good for short-term energy

Carbohydrate-rich food categories:

breads

pasta1. Grains like:

http://www.choosemyplate.gov/food-groups/grains.html

Make at least half of your grains whole grains.

Key consumer message:

Subgroups (click):

Carbohydrate-rich food categories:

2. Fruits, like…

http://www.choosemyplate.gov/food-groups/fruits.html

Make half your plate fruits & vegetables.

Key consumer message:

3. Vegetables: can be organized into 5 subgroups (click)—

a. Dark green, like…

b. Starchy, like…

c. Red & orange, like…

d. Beans & peas, like…

e. other, like…

Make half your plate fruits & vegetables.

Key consumer message:

2. Protein rich foods include:

fisheggsbeansnutsmeatmilkcheese

• when you ingest proteins, your digestive system breaks them down into smaller polypeptides or dipeptides, then into units called amino acids

• your cells need these amino acids to produce muscles, bones, enzymes, and hormones

Your body requires 20 different amino acids

• 8 of these amino acids must be obtained in your diet

• as long as you have these 8 amino acids, your body can manufacture the other 12

Since these 8 amino acids are so vital they have become known as the essential amino acids

Fish, meat, milk, and eggs are called complete proteins because they contain all 8 essential amino acids

Proteins, such as beans, are called incomplete (they lack 1 or more of the 8 essential amino acids)

• your cells can break down proteins to produce energy (ATP), but only if they run out of carbohydrates

• 1 gram of protein yields 4 Calories

• avg person needs 6 oz. per day

Select a variety of protein foods to improve nutrient intake and health benefits, including at least 8 ounces of cooked seafood per week

Key consumer message (click):

** Dairy ** (click)

Key consumer message:

Switch to fat-free or low-fat (1%) milk.

Calcium-fortified foods and beverages such as cereals, orange juice, or rice or almond beverages may provide calcium, but may not provide the other nutrients found in dairy products.

3. Fats are required by your body to build cell membranes, to insulate nerve cells and to allow your body to absorb fat-soluble vitamins (A, D, E, and K) from the foods you eat

• fats can also be used by your cells to produce energy (ATP), but only if you run out of carbohydrates

• fats yield the greatest amount of energy – 9 Calories/gram

• ** if you burn the calories!**

• fats are digested into triglycerides, fatty acids, cholesterol

• LDLs transport of lipids from liver to body cells

• HDLs transport of lipids from body cells to liver

Fat rich foods include (click): whole milk, meat, butter, oils, fried foods, and chips

Oils are NOT a food group, but they provide essential nutrients.

What are my allowances? (click)

Key consumer message:

Substitute oils for solid fats; be aware of the oils & fats in the foods you already eat.

4. Vitamins are essential organic substances that are required in small amounts for normal growth and activity

There are 2 major types of vitamins:

a. Fat-soluble

b. Water-soluble

Fat-soluble vitamins include vitamins A, D, E, and K

Vitamin A is needed for good vision

too little vitamin A:

•night blindness

•infections of the urinary and digestive tracts

Vitamin D:

•For strong bones and teeth

Too little vitamin D:

•bone deformities,

•bad teeth;

•poor muscle tone

Vitamin E is needed to protect cell membranes from damage

too little vitamin E:

•Anemia

•nerve tissue damage (infants)

Vitamin K is needed for blood to clot

too little vitamin K:

•increases the time it takes for blood to clot

Excess intake of any of the fat-soluble vitamins can be harmful because you store excesses of these of these vitamins in your body rather than excrete them

Overdoses of vitamin A:

•enlargement of your liver & spleen

•blurred vision

•hair loss

Overdoses of vitamin D:

•calcium deposited in your soft tissues (kidney stones)

•high blood pressure

b. Water-soluble vitamins include vitamin C and the B vitamins (B1, B2, B3, and B12)

Vitamin C is needed for:

•proper wound healing

•healthy teeth and gums

too little C:

•bleeding gums

•loose teeth

•slow wound healing

Vitamin B1 (thiamine) is needed for:

•proper nerve & heart function

•carbohydrates to be broken down

too little B1:

•digestive problems (beriberi)

•impairs sense of touch

Vitamin B2 (riboflavin) is needed for:

•healthy skin

•tissue repair

•carbohydrates to be broken down

too little B2:

•blurred vision

•cataracts

•cracking of the skin

Vitamin B3 (niacin) is needed for:

•healthy skin

•carbohydrates to be broken down

too little B3:

•mental disorders

•diarrhea

•dermatitis of eyes, nose, and mouth

Vitamin B12 is needed for:

•production of RBCs

too little B12:

• anemia

Massive doses of water-soluble vitamins can be hazardous to your health

Excess vitamin C can cause:

•kidney stones

•blood clots

Excess niacin (B3):

•liver damage

•gout

(uric acid crystals deposited in joints – extremely painful)

5. Minerals are trace elements required by your body

Some of the most important minerals you require are:

iodinecobaltzincmanganese

Iodine is needed for you to make thyroid hormone

• too little iodine causes hypothyroidism which causes stunted growth and retardation in children

• in adults, hypothyroidism causes lack of energy, dry skin, and weight gain

Cobalt is needed for production of vitamin B12

• too little B12 causes anemia

Anemic

Zinc is needed for the production of proteases (enzymes that break down proteins into amino acids)

• too little zinc causes you to be unable to digest proteins

Manganese is needed to make hemoglobin

• too little manganese – RBCs will not be able to transport enough oxygen to your cells and you feel tired

Empty calories are everywhere:

candies

soft drinks

http://www.choosemyplate.gov/weight-management-calories/calories/empty-calories.html

desserts

cheesepizza

sausages/bacon/hot dogs

Intro to obesity:

• unfortunately, if you consume more Calories of any kind per day than your body uses, it will convert these extra Calories to fat and store it

About 80% of the fat in your body is found just beneath your skin

• functions to protect and insulate

• will also serve as an energy source if you fail to consume enough carbohydrates

Obesity is a big problem in developed countries, where food is abundant

Click map for CDC data for the US, 1980-2010

More stats from the CDC:http://www.cdc.gov/obesity/data/adult.html

•More than ____________ of U.S. adults (______%) are obese.

•Approximately ______% (or ______million) of children and adolescents aged ______ years are obese.

one-third35.7

• In 2010, ____________ state had a prevalence of obesity less than ______%.

• In 2010, it was reported that Georgia’s population was composed of approximately ______% obese people.

no

20

29.6

Obesity-related conditions include heart disease (atherosclerosis),

stroke, type 2 diabetes and certain types of cancer, some of the leading

causes of preventable death.

• a person is considered to be obese if they are 20% heavier than the average person of the same sex and height

BMI from 17 up to 24 refers to healthy weight.

BMI from 25 up to 30 refers to overweight

BMI 30 or higher refers to obesity

Waist Circumference:

Measuring waist circumference helps screen for possible health risks that come with overweight and obesity.

If most of your fat is around your waist rather than at your hips, you’re at a higher risk for heart disease and type 2 diabetes.

For more information, click here for info from the National Institute of Health.

B. Digestion

This is the process your body uses to break down nutrients into products your cells can use

(sugars, fatty acids, glycerol,and amino acids)

1. Enzymes

• proteins that help your digestive system break down nutrients

• classified as carbohydrases, lipases, or proteases

Click here for a quick review of how enzymes work

a. Carbohydrases – are enzymes that function to break down carbohydrates into simpler sugars

3 major carbohydrases:

1. Salivary amylase – produced by salivary glands

• released into mouth and functions to break down starch molecules into maltose

amylose(a polysaccharide)

many molecules of maltose(a disaccharide)

enzyme action of amylase

2. Pancreatic amylase – produced by pancreas

• released into small intestine and functions to break down starch into maltose

3. Maltase – produced by small intestine

• functions to break down maltose into glucose

many molecules of glucose(a monosaccharide)

enzyme action of maltase

many molecules of maltose(a disaccharide)

b. Lipases are enzymes that are produced by your pancreas

They are released into your small intestine where they function to break down fat molecules into fatty acids and glycerol

enzyme action of lipase

a fat

glycerol 3 fatty acids

c. Proteases are enzymes that function to break down proteins into amino acids

3 major proteases:

1. pepsin – produced by your stomach, where it functions to break down proteins into polypeptides

2. trypsin – produced by your pancreas. It is released into your small intestine where it functions to break down different proteins into polypeptides

3. peptidase – produced by your small intestine. It functions to break down polypeptides into amino acids

part of a protein (a large polypeptide)

How would these enzymes work on this protein molecule?

1.pepsin

2.trypsin

3.peptidase

Notice that the different types of nutrients are digested in different areas of the digestive tract

Carbohydrate digestion begins in the mouth, but also occurs in the small intestine

Lipid digestion occurs only in the small intestine

Protein digestion begins in the stomach but ends in the small intestine

The activity of all enzymes is greatly affected by pH and temperature

Ex: pepsin breaks down proteins in the stomach, where the pH = 2

Pepsin will not break proteins down in the small intestine, where the pH = 8.5

All enzymes found in the body function best at body temperature (98.6°F or 37°C)

• this is why there is concern if your temperature rises much above 105°F

• enzymes are permanently denatured at high temperatures

2. The Digestive Tract

The digestive tract snakes through the body from the mouth to the anus

• it is about 21 feet in length

Pathway of digestive tract from mouth to anus:

mouth – food entering the mouth is:

1. broken down by your teeth (incisors, canines, premolars, and molars) into small enough pieces to swallow

Chewing also increases the surface area of food

This aids in chemical digestion

2. mixed with saliva, which is produced by the 3 pairs of salivary glands that empty into your mouth

• saliva has 2 functions

1. Moisten and lubricate food so that it can be swallowed more easily

2. to begin the digestion of starch

b. Pharynx – food leaving the mouth enters the region at the back of the mouth called the pharynx

• remember, both food and air pass through the pharynx

• food is prevented from entering the respiratory tract by the small flap of tissue called the epiglottis

• when you swallow, the epiglottis closes and forces food into the esophagus

c. Esophagus – this is a tube that connects the pharynx to the stomach

• the esophagus functions to transport food to the stomach by peristaltic contraction (waves of contraction)

• peristaltic contraction is so effective you can even swallow while standing on your head

Food leaving the esophagus passes through a ring of muscle called the cardiac sphincter into the stomach

• function of the cardiac sphincter is to prevent food in the stomach from reentering the esophagus

• if the cardiac sphincter doesn’t function well you suffer from heartburn (acids from the stomach burn the lower end of the esophagus

d. Stomach – a J-shaped organ found just below the diaphragm

The stomach functions to:

1. begin the digestion of proteins. Your stomach is able to digest proteins because it produces HCl and pepsin. HCl functions to unfold large proteins

Pepsin functions to break the large unfolded proteins down into smaller segments called polypeptides

2. Produce the hormone gastrin.

Gastrin functions to regulate the production of HCl.

When pH of stomach is greater than 1.5 then gastrin is released.

Gastrin causes more HCl to be produced, which keeps the pH of the stomach a 2.0

3. transform food into a soupy mixture, called chyme, which is able to enter the small intestine

• chyme leaving the stomach passes through a 2nd circular muscle called the pyloric sphincter

Click here for a youtube clip

showing inside of stomach

• the function of the pyloric sphincter is to allow very small amounts of chyme to enter the small intestine

e. small intestine – this is a long, highly folded tube that connects the stomach to the large intestine

Small intestine

Click here & here for youtube clips

showing intestinal

peristalsis

The first portion of the small intestine is called the duodenum

• this is where most digestion and absorption of nutrients occurs (not in the stomach, as most people believe)

• in fact, the duodenum is the only portion of the digestive tract in which all 3 classes of nutrients are digested

• the duodenum produces 2 digestive enzymes: peptidase (breaks polypeptides down into amino acids) and maltase

Two organs, the liver and pancreas, produce products that they release into the duodenum

The liver produces bile, which it stores in the gall bladder

• the gall bladder releases bile into the duodenum when it is needed

Bile is not an enzyme.

It is a thick greenish fluid that functions to emulsify lipids.

• this means that it breaks large globs of fat into smaller droplets so that they can then be broken down by lipases

The pancreas produces 2 enzymes:

pancreatic lipase (breaks lipids down into glycerol and fatty acids and

trypsin (breaks proteins down into polypeptides

The end products of digestion (glucose, amino acids, fatty acids, and glycerol) are absorbed in the small intestine.

Small intestine

The length of the small intestine maximizes absorption

Also, the small intestine is lined with tiny, fingerlike projections called villi

These increase surface area and further maximize absorption

• this means that they pass through the wall of the small intestine and enter into your bloodstream

• materials that are not absorbed will enter the large intestine

f. Large intestine ( = colon ) – a short tube that is about 3 times larger in diameter than the small intestine

Large intestine

The large intestine functions to:

1. house bacteria which produce vitamin K

2. absorb water, salts, and vitamin K

3. Act as a trash compactor, forming feces (undigested materials)

Feces enter the rectum (last portion of the large intestine) and finally pass out of the body through the anus

3. Digestive System Abnormalities

a. ulcer – hole in the wall of the stomach or small intestine

• caused by excessive acid production

• Also related to presence of H. pylori

b. gastritis – irritation of the stomach

• can be caused by excessive alcohol consumption

c. appendicitis – inflammation of the appendix (= a finger-like projection from the large intestine)

d. mumps – viral infection of the salivary glands

e. Anorexia nervosa – eating disorder which the person starves themselves

f. diarrhea – food rushes through the intestines too rapidly.

Thus, very little water is absorbed.

g. Colon cancer – polyps of abnormal cells form inside the colon; can metastasize

-often spreads to liver

(blood leaving the colon proceeds to the liver in the systemic loop of circulation)

- Caused by a dominant gene

- 50% chance of passing to kids

- Testing recommended 10 years younger than parent’s age at diagnosis

constipation

http://www.youtube.com/watch?v=cdijh32NiLs