The Digestive System

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MACRONUTRIENTS

•These are our direct sources of energy for daily life, physical exercise and work

• There are 3 types:

1. Protein 2. Carbohydrate 3. Fat

PROTEIN

•Made up of hundreds of amino acids joined together by peptide bonds into one or more chains

• when ingested:-broken down into 20 amino acids

- 9 essential amino acids attained through food (body produces 11 others)

• Complete protein – food that contains all 9 amino acids- meat, eggs, cheese and milk

• Incomplete protein –foods containing one but not all essential amino acids- vegetables and fruits

•necessary for growth and repair of all tissues, and a critical component of hormones, enzymes and the immune system

Lipids• One important property = insoluble in water

• Structure = glycerol (alcohol) which is 3 carbon atoms each attached to a fatty acid chain (an acid with a long tail of carbon and hydrogen atoms)

• Stores 2.25X more energy per gram than other molecules

• Functions as energy storage molecules

• Ex of lipids: butter, lard, olive oil

Carbohydrates• Always contain carbon, hydrogen, oxygen

• 2 main types– Simple sugars (monosaccharides)

• 3-7 carbon atoms• Ex: glucose, fructose• Disaccharides are made up of 2 simple sugars• Ex: sucrose, maltose, lactose

– Polysaccharides• Ex: starch, cellulose, glycogen

• Complex (starch)

-takes body longer to absorb-80 % of total carb intake-cereals, fruits, vegetables, legumes and pasta

• Simple (sugars)

-absorb MUCH faster- refined white sugar, pop, candy, etc

. . .but why is it important that we ingest carbohydrates?

ATP (Adenosine Triphosphate)

- 3 phosphates attached to adenosine

MICRONUTRIENTS-needed in smaller quantities- there are 3 types:

Vitamins Minerals Water

Vitamins and Minerals•Vitamins:•A: good vision, healthy skin and bones•B1: metabolizing carbs, growth and muscle tone•C: healthy bones, teeth, gums, blood vessels, and boosting immune system•D: absorbing calcium, forming bone•E: strengthening red blood cell membranes

•Minerals:•Calcium: forming bone, contracting muscle, clotting blood•Iron: producing hemoglobin•Magnesium: supporting enzyme functions•Potassium: contracting muscle•Sodium: conducting nerve signals, balancing body fluid

Water

• sufficient water is needed to help:-aid in digestion, carry nutrients and eliminate waste products

Breading down Macromolecules• Macromolecules must be chemically broken down into small

molecules to be absorbed by the cells lining the small intestine

• Hydrolysis = a chemical reaction in which water breaks apart macromolecules into smaller molecules, by breaking chemical bonds

• The breakdown of chemical bonds involves a protein known as an enzyme

• Enzymes are catalysts, which increase the rate of chemical reactions without being used up in the reactions

Type of Enzyme Macromolecule it breaks down

Product of breakdown

Example of enzyme and where it functions

Carbohydrase Carbohydrate Simple sugars Amylase: produced in the salivary glands and functions in the mouth

Lipase Lipid Glycerol, fatty acids Pancreatic lipase: produced in the pancreas and functions in the small intestine

Protease protein Amino acids Pepsin: produced by the stomach glands and functions in the stomach

Nuclease Nucleic acid Nucleotides Pancreatic nuclease: produced in the pancreas and functions in the small intestine

4 stages of food processing1. ingestion: the taking in or eating food

2. Digestion: the breakdown of food by mechanical and chemical processes into molecules small enough for cells of the body to absorb

3. Absorption: the transport of the products of digestion from the digestive system into the circulatory system, which distributes them to the rest of the body

4. Elimination: the removal of undigested solid waste matter from the body

Alimentary Canal• Alimentary canal: long open tube (from mouth to anus)

• Mechanical digestion: physical breakdown of large pieces of food into smaller pieces in the mouth by the action of teeth, beak or other similar structures and by contractions and churning motions in the stomach

• Chemical Digestion: chemical breakdown of nutrient molecules into smaller molecules by enzyme action

Length of digestive track• Varies according to the feeding

habits of species

• Herbivores and omnivores have longer digestive tracts relative to body size than carnivores

• Why? Cellulose walls in plant tissues are more difficult to digest than animal tissues. Allows extra time needed for digestion

• teeth break down food (mechanical digestion) Increase the SURFACE AREA

(INGESTION)

• Incisors and canines grabbing and cutting food• Premolars and molars grinding and crushing food

Different teeth for different types of eaters

Mouth• Teeth breakdown food into smaller pieces• Saliva: contains amylase that breaks food into

small pieces– mixes with food to make a bolus

• Tongue: places food on appropriate teeth

3 salivary glands

1. Parotid Gland2. Sublingual Gland3. Submandibular Gland

Sight and smell of food willcause an increase in production

• Tongue pushes food to back of mouth• Swallowing into pharynx

• Soft palate rises no food to nasal• Larynx rises epiglottis closes no food to trachea

• Bolus into esophagus (muscular tube)• Peristalsis

Esophagus• To prevent food from going down the trachea (for breathing), the

epiglottis closes the opening

• Behind trachea

• To get food to stomach, wave-like muscular contractions called peristalsis

• Entrance of the stomach is controlled by the esophageal sphincter – It is closed to prevent acidic contents of stomach going into esophagus

Stomach• J shaped organ, can expand to 2L

• Stomach is lined with gastric glands that secrete gastric juices

• Gastric juices mix with food to create chyme: a thick liquid made up of digested food combined with gastric juices

• Pepsin: enzyme in gastric juice that helps break down proteins

• At the end of the stomach is the pyloric sphincter, keeps food in stomach

Small intestine

• Long coiled tube (7m long)• 3 sections– Duodenum– Jujenum– Ileum

MAXIMIZE SURFACE AREA

• folded (ridges)• villi fingerlike projections increases SA 10x’s

• microvilli increase SA 500x’s• contain blood vessels nutrients enter

Duodenum

• U shaped• To speed up absorption, lined by folds that

increase surface area• Folds are covered by tiny finger-like

projections called villi• As food passes through, gets secretions from

pancreas and gall bladder

CHEMICAL DIGESTION IN THE DUODENUM

Jejunum and Ileum• Jejunum contains more folds than duodenum– Breaks down the remaining proteins and carbs to

be absorbed into bloodstream• Ileum contains fewer and small villi. Absorbs

nutrients and push undigested material into large intestine