The Digestive System

Digestion

• Nutritionists classify foods into six groups.

– These six groups are: meat, milk, fruits, vegetables, breads/cereals, and fats/oils/sweets.

• Nutrients provide energy for powering cellular processes.

Food Pyramid

Nutrients Needed

• The three nutrients needed by the body in the greatest amounts are carbohydrates, proteins, and lipids.

• An example of a carbohydrate is pasta; an example of a protein is chicken; and an example of lipids is olive oil.

Organic Molecule Review

• What are the four organic molecules?

• Carbohydrates

• Lipids

• Proteins

• Nucleic Acids

Carbohydrates

•Small sugar moleculesSmall sugar molecules to large sugar moleculeslarge sugar molecules.

•Examples:Examples:A.A. monosaccharidemonosaccharideB.B. disaccharidedisaccharideC.C. polysaccharidepolysaccharide

Monosaccharide: one sugar Monosaccharide: one sugar unitunit

Examples:Examples: glucose (glucose (C6H12O6)deoxyribosedeoxyriboseriboseriboseFructoseFructoseGalactoseGalactose

Disaccharide: two sugar unitDisaccharide: two sugar unit

Examples: Examples: –Sucrose (glucose+fructose)Sucrose (glucose+fructose)–Lactose (glucose+galactose)Lactose (glucose+galactose)–Maltose (glucose+glucose)Maltose (glucose+glucose)

Polysaccharide: many Polysaccharide: many sugar unitssugar units

Examples:Examples:starch (bread, potatoes)starch (bread, potatoes)glycogen (beef muscle)glycogen (beef muscle)cellulose (lettuce, corn)cellulose (lettuce, corn)

Lipids

• General term for compounds which are not not soluble in watersoluble in water.

• Lipids are soluble in hydrophobic solventsare soluble in hydrophobic solvents.• Remember:Remember: “stores the most energy”“stores the most energy”• Examples:Examples: 1. Fats1. Fats

2. Phospholipids2. Phospholipids3. Oils3. Oils4. Waxes4. Waxes5. Steroid hormones5. Steroid hormones6. Triglycerides6. Triglycerides

• LipidsLipids

Six functions of lipids:Six functions of lipids:1.1. Long term Long term energy storageenergy storage2.2. Protection against heat loss Protection against heat loss (insulation)(insulation)3.3. Protection against physical shockProtection against physical shock4.4. Protection against water lossProtection against water loss5.5. Chemical messengers (hormones)Chemical messengers (hormones)6.6. Major component of membranes Major component of membranes

(phospholipids)(phospholipids)

Lipids

One glycerolThree fatty acids

H

H-C----O

H-C----O

H-C----O

H

glycerol

=

fatty acids

O

C-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

=

C-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

=

fatty acids

O

C-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

=

• Fatty AcidsFatty Acids

There are two kinds of fatty acidsfatty acids you may see these on food labels:

1.1. Saturated fatty acids:Saturated fatty acids: no double no double bonds (bad)bonds (bad)

2.2. Unsaturated fatty acids:Unsaturated fatty acids: double double bonds (good)bonds (good)

=

O

C-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

=

saturatedsaturated

O

C-CH2-CH2-CH2-CH=CH-CH

2 -CH2 -CH

2 -CH2 -CH

3

=unsaturated

Proteins=Polypeptides

• Amino acids (20 different kinds of aa) bonded together by peptide bondspeptide bonds (polypeptidespolypeptides).

• Six functions of proteins:Six functions of proteins:1.1. Storage:Storage: albumin (egg white)albumin (egg white)2.2. Transport: Transport: hemoglobinhemoglobin3.3. Regulatory:Regulatory: hormoneshormones4.4. Movement:Movement: musclesmuscles5.5. Structural:Structural: membranes, hair, nailsmembranes, hair, nails6.6. Enzymes:Enzymes: cellular reactionscellular reactions

Dehydration Synthesis

Protein

• Vitamins, minerals, and water are nutrients that do not provide energy but are required for proper functioning of the body.

• Vitamins are organic compounds that participate in chemical reactions by helping to build various molecules in the body.

• Minerals are nutrients that are inorganic compounds and are necessary for certain body processes.

Importance of Vitamins

• Vitamins

– Vitamins work as coenzymes to enhance enzyme activity.

– A diet should include vitamins because they cannot usually be made in the body. An exception to this is vitamin D.

– Vitamins can dissolve in water or fat.

Importance of Minerals

• Minerals

– Minerals are used to make certain body structures, to carry out normal nerve and muscle function, and to maintain osmotic balance.

– Minerals can come from plants we eat directly or the plants other animals eat.

– Minerals are released out of the body through urine and by perspiration.

Importance of Water

• Water

– Water, which is a main component in blood, helps to transport gases, nutrients, and wastes throughout the body.

– Water also is a reagent in some of the body’s chemical reactions.

– Water also helps regulate body temperature by absorbing and distributing the heat released in cellular reactions.

Digestive Process

The First Stages of Digestion

The Gastrointestinal Tract

• The process of breaking down food into molecules the body can use is called digestion.

• Digestion occurs in the gastrointestinal tract, or digestive tract, which is a long tube which begins at the mouth and winds through the body to the anus.

• Organs next to the digestive tract also aid in the digestion of food through the secretions that they produce.

Digestive System of the Human Body

• Mouth

– Mechanical digestion begins when the teeth cut and grind food.

– The tongue also aids in mechanical digestion by keeping the food between the chewing surfaces of the teeth.

• Mouth, continued

– Saliva is produced by the salivary glands to begin chemical digestion of food.

• Saliva is a mixture of water, mucus, and a digestive enzyme called salivary amylase.

• Salivary amylase is the chemical in saliva that begins the chemical digestion of carbohydrates by breaking down certain starches into maltose.

• Esophagus

– The ball of food is then forced by swallowing action into the pharynx.

– The pharynx is an open area that begins at the back of the mouth, and serves as a passageway for both air and food.

– The ball of food is then forced from the pharynx into the esophagus.

Stomach

• The stomach is an organ involved in both mechanical and chemical digestion.

• It is located in the upper left side of the abdominal cavity, just below the diaphragm.

• Mechanical Digestion, continued

– The inner lining of the stomach is a mucous membrane that is composed of epithelial cells and openings called gastric pits.

– Gastric pits are the open ends of gastric glands that release secretions into the stomach.

– These secretions form the acidic digestive fluid that digests food in the stomach.

– Hydrochloric acid and pepsin (breaks down protein)

• Chemical Digestion

– Gastric fluid carries out chemical digestion in the stomach.

• Gastric fluid is a liquid that is secreted by the gastric glands in the stomach.

– Hydrochloric acid within the gastric fluid helps dissolve food and minerals and keep bacteria at bay.

• Chemical Digestion, continued

– Mucus secreted in the stomach forms a coating that protects the lining of the stomach from hydrochloric acid and other digestive enzymes.

– An ulcer will result if the mucous layer is absent from the stomach lining.

• An ulcer is a lesion of the surface of the skin or a mucous membrane of the stomach.

• Formation of Chyme

– After food enters the stomach, it closes by way of the cardiac sphincter.

• The cardiac sphincter is a circular muscle located between the esophagus and the stomach.

– While closed, the stomach churns to break up the food and mixes it with the gastric fluid. This process forms a mixture called chyme

• The other organs that help digestion are the liver, gallbladder, and pancreas.

• Liver

– The liver performs numerous function in the body including storing glucose, making proteins, and breaking down toxic substances.

– The liver produces bile, which is vital to digesting fats.

• Gallbladder

– After the liver produces bile it travels through a Y-shaped duct to the gallbladder.

– The gallbladder is a saclike organ that stores and concentrates bile.

– The gallbladder releases the bile through a common bile duct into the small intestine.

• Pancreas

– The pancreas is an organ that lies behind the stomach. The pancreas serves two roles in its part in the digestive system.

• The first role it plays is to increase the pH of the stomach acid by producing sodium bicarbonate.

• The second role it plays is to secrete enzymes such as trypsin to break down protein, lipase to break down fats and more amylase to finish the break down of carbohydrates.

Small Intestine

Small Intestine

• The small intestine includes three sections—the duodenum, the jejunum, and the ileum.

• The chyme from the stomach will further break down in the small intestine.

• Absorption

– Absorption occurs mostly in the small intestine. Absorption occurs when the end products of digestion are transferred into the circulatory system through the blood and lymph vessels.

• Absorption, continued

– The surface area of the small intestine is large due to the presence of many folds within the lining of the small intestine and the millions of villi that are also present.

– The surface area is further increased by the presence of microvilli.

• Microvilli are extensions of the cell membranes present on the villi.

• Absorption, continued

– Nutrients are sent to the correct place by the lacteals.

• The lacteals are capillaries and tiny lymph vessels within the villi.

– The lacteals will take the nutrients to either the liver or the lymph vessels, and then the blood will take over delivery of the nutrients to the cells.

Large Intestine

Large Intestine

• Once absorption is complete in the small intestine, peristalsis will move the remaining contents into the colon or large intestine.

• The colon has various sections, and all of these sections work together to finish the absorption of nutrients and water.

• The colon initiates contractions that move the material out of the body. Bacteria produces vitamin K-used in blood clotting.

• As nutrients and water are absorbed from the matter in the colon, the matter solidifies into feces.

• Feces leave the body by passing through the rectum and the anal canal.

The Final Stages of Digestion

1. What is the primary function of carbohydrates?

A. to aid in digestion

B. to break down molecules

C. to regulate the flow of chyme

D. to supply the body with energy

• Answer

• D. To supply the body with energy

2. How can dehydration best be prevented?

F. by perspiring

G. by inhaling water

H. by drinking water

J. by not drinking water

• Answer

• H. By drinking water

3. Why is the epiglottis important?

A. It regulates the flow of chyme.

B. It prevents food from going down the trachea.

C. It separates the pharynx from the nasal cavity.

D. It is the passage through which food travels to the stomach.

• Answer

• B. It prevents food from going down the trachea

4. Bile breaks up large fat droplets. Approximately how long is the food in the digestive tract before it comes into contact with bile?

F. 4 hours

G. 7 hours

H. 11 hours

J. 13 hours

• Answer

• F. 4 hours

Ulcers