Nutrition & Digestion

How do we get from this…

…to this.

Digestive System Parts  Mouth – chewing, lubrication, digestion  Pharynx and Esophagus - swallowing  Stomach - some digestion  Small intestine – most digestion and absorption (of water and nutrients)  Large intestine – some absorption  Colon and Rectum - packaging  Liver and Gall Bladder - produces bile - aids in fat digestion  Pancreas - produces many digestive enzymes

Food Processing

 Most food consists of what macromolecules? Carbohydrates, lipids, and proteins  Why is food chemically broken down? The macromolecules are too large to pass through cell membranes They must be broken down into monomers, so that the organism can make their own polymers

Human Digestion System

Human Digestion: Mouth  At sight or smell of food, salivary glands secrete saliva Glycoprotein protects & lubricates lining of mouth Antibacterial agents Amylase to hydrolyze starch  Why do you chew your food? Easier to swallow Expose more surface area to enzymes  Tongue pushes mass of food (bolus) to back of oral cavity & into pharynx

Human Digestion: the epiglottis How does the epiglottis prevent food from moving into the trachea?

Human Digestion: into the esophagus

Human Digestion: stomach

Human Digestion: the stomach  Why don’t we need to eat constantly? Besides breaking down food, the stomach stores food – enough to satisfy our body for many hours  What prevents gastric juice from digesting away the stomach lining? Pepsin, an enzyme which begins the chemical digestion of protein, is secreted in the inactive form pepsinogen  Protects the gastric gland cells Mucus helps protect the stomach lining from both pepsin and acid However, the stomach lining must be replaced about every 3 days

Human Digestion: small intestine

 Nutrients are absorbed into the blood from the small intestine  All 4 types of macromolecules (carbohydrates, lipids, proteins, & nucleic acids) are digested in the small intestine  Carbohydrate digestion completed in rest of the small intestine Enzymes break down polymers into monomers

Human Digestion: small intestine  Protein digestion Pancreas and small intestine secretes enzymes that break polymer into monomers (amino acids)  Nucleic acid digestion Pancreas and small intestine secrete enzymes which breakdown DNA & RNA polymers into  Nitrogenous bases, sugars, phosphates

Human Digestion: small intestine  Lipid digestion Lipids reach stomach almost completely undigested  Why?  Fats are hydrophobic Bile salts from gallbladder coat tiny fat droplets that keep them separated from each other  Why is the separation of fats into small droplets beneficial for digestion?  More surface area is exposed, which allows the enzyme to breakdown the fats quickly

Human Digestion: small intestine

 Capillaries that drain away from the small intestine converge into larger blood vessels and eventually into a main vessel that leads directly to liver Converts many of nutrients into new substances the body needs Liver removes excess glucose and stores it as?  Glycogen in liver cells  Blood is then transported to heart, which pumps blood and nutrients to all parts of the body

Human Digestion: large intestine

 Colon absorbs water –approximately 90% of the 7 liters of fluid that enters the canal a day are reclaimed (most in small intestine)  Remains of undigested food become more solid as water is absorbed Feces  Consists mainly of plant fibers and bacteria  Diarrhea occurs when the colon is irritated and is less effective at reclaiming water  Constipation occurs when muscle contractions move the feces too slowly  Colon reabsorbs too much water and feces becomes too compacted  Diet low in plant fiber or lack of exercise

Nutrition  There are 3 needs which demand a healthy diet Fuel to power our bodies Organic raw materials needed to make our own molecules Essential nutrients that we cannot make ourselves and must obtain in a prefabricated form

Nutrition: why we need chemical energy  The chemical processes of our bodies are fueled by? ATP  Cellular metabolism produces ATP by oxidizing small molecules that are digested from food  Usually use carbohydrates and fats, but when required, will use proteins too

So, what happens when something harmful gets past all the acids and enzymes?? You would think with a pH of 0 and nasty enzymes floating around, your stomach would kill anything you swallow. This is not the case. Some bacteria and protists can survive your stomach’s defenses and cause you misery or worse!! Ex: Salmonella, E.coli, Giardia, campylobacter, amoebic dysentery, botulism, and listeria are a few.

So what does that food label mean?  First look at the serving size. Many pre-packaged items are for more than 1 serving.  Calories = the amount of available energy from that food.  % Daily Value = how much of that nutrient you are getting as a percentage of what you need in a day