Digestive SystemObtaining nutrients

Nutrition

Energy

• Body cells need energy to run cell processes.

• Animals obtain chemical energy from food. Energy is derived from breaking chemical bonds.

• Food energy is measured in units called calories.

Food labeling• A typical label for

packaged food lists calories and major nutrients.

• While the information is incomplete, it does help people make some important choices.

Lipids• Lipids are fats, oils,

and waxes.

• Lipids are energy dense, containing 9 calories per gram.

• Lipids are used for storing energy, making cell membranes, and synthesizing steroid hormones.

Many lipids are made up of fatty acids and

glycerine.

Carbohydrates

• Sugars and starch are the carbohydrates that humans can digest. “Fiber” is indigestible carbohydrates, such as cellulose and inulin.

• Glucose is needed by all body cells as energy. Nerve cells must have glucose to operate.

Starch is made up of glucose.

• Sometimes my students describe sugars or starch as “fatty,” or tell me that sugar has lots of fat in it. Look at the diagrams of starch, sugar, and fat in your notes. Are they right or not?

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Proteins• Amino acids from

digested proteins are used by cells to build all the proteins that our body needs.

• Humans need a balance of the 20 amino acids, which can be obtained from animal proteins, or by blending plant protein sources.

Proteins are made up of amino acids.

• Since there are 20 different amino acids, and hundreds or thousands of amino acids in a single protein, there are billions of possible combinations and therefore many, many different, distinctive proteins. We’ve learned about some already. Name some proteins we’ve learned about. (Hint: “Meat” is a source, not a protein.)

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Macromolecule summary

Polymers Monomers Roles

Complex Carbohydrates

(i.e. starch)

Glucose and other simple sugars

Broken apart to get energy to make ATP.

Proteins Amino acidsUsed to make our own

enzymes and other body proteins.

Lipids (Fats, waxes, oils, and

steroids)

Fatty acid chains, glycerine (except

steroids)

Used for cellular energy and energy storage; used to make

cell membranes, steroid hormones.

Minerals

• Sodium, potassium, zinc, iron, calcium, copper, and selenium are among the minerals that humans need.

• Most minerals can be found in whole grains, fruits, vegetables, nuts, and meats. Highly processed foods may be deficient.

Major MineralsMineral Major roles Natural sources

Calcium Bone and tooth formation; muscle and nerve function.

Dairy products, leafy greens, dry beans.

Iron Used to make hemoglobin and myoglobin.

Red meats, eggs, nuts, whole grains, leafy greens.

Zinc Component of certain enzymes, required for growth.

Meats, whole grains, nuts, legumes.

Phosphorous Bone and tooth formation; pH of body fluids, phospholipids.

Dairy products, grains.

Potassium Maintains pH of body fluids; used in action potentials.

Many fruits and vegetables, meats, milk.

Sodium Maintains pH of body fluids; used in action potentials.

Table salt, meats.

Selenium Used by the immune system. Nuts, esp. Brazil nuts; many fruits and vegetables.

Vitamins

• Vitamins play many different roles in metabolism.

• We do not obtain energy from vitamins; however, some vitamins are necessary to run energy-related processes in cells.

Major VitaminsVitamins Major roles Natural sources

Vitamin A (fat soluble

Used to make visual pigments; maintains epithelial tissues; needed for normal growth.

Orange and yellow fruits and vegetables, egg yolk, dairy products.

B complex vitamins (water soluble)

Used in cellular respiration to metabolize sugars and other carbon compounds.

Whole grains, legumes, many fruits and vegetables. B12 comes from animal sources.

Vitamin C (water soluble)

Used in collagen synthesis, possible role in immune function.

Fresh fruits and vegetables.

Vitamin D (fat soluble)

Bone growth, calcium absorption, possible role in immune function.

Eggs, dairy products. Sunlight on skin oils creates Vitamin D.

Vitamin E (fat soluble)

Antioxidant, reduces cellular damage.

Nuts, whole grains, leafy vegetables.

Vitamin K Plays a role in blood clotting. Produced by intestinal bacteria.

Antioxidants• Free-radicals are

released by cell damage and many cell processes.

• Anti-oxidants, such as Vitamins C and E, and many plant pigments, combine with free radicals and reduce their effects, which slows cell aging.

Moral of the story: eat colorful food

No, Skittles don’t count as “colorful food!”

The monomers of proteins:

1 2 3 4

25% 25%25%25%

1. Simple sugars2. Lipids3. Amino acids4. Depends on the

protein

Humans obtain energy from:

1 2 3 4 5

20% 20% 20%20%20%

1. Carbohydrates2. Vitamins3. Minerals4. Antioxidants5. All of these

Mom says carrots make you see better. Any reason why this might be

true?

1 2 3

33% 33%33%1. No, but they do

contain antioxidants.

2. Yes. Beta carotenes in carrots are converted to Vitamin A.

3. No, it’s just an old folk belief.

Which nutrients are “anti-aging” because they prevent free-radical

damage?

1 2 3 4

25% 25%25%25%

1. Lipids2. Minerals3. Antioxidants4. B-vitamins

Which vitamin can you overdose on?

1 2 3 4

25% 25%25%25%

1. B vitamins2. Vitamin C3. Vitamin A4. None – you can’t

overdose on vitamins.

• Trick question: what ingredient in “energy drinks” actually gives you energy?

• What would be incorrect about a label that said, “calorie-free energy drink”?

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Digestion

Two-way digestion• Simple animals have

a single digestive pouch with a single opening.

• Food enters through the opening, waste leaves through the same opening.

• These organisms must finish digesting before eating again.

One-way digestion

• More complex animals have one-way digestion.

• Food enters one opening and waste leaves from another.

• Animals with one-way systems can eat any time, which is an advantage.

Mechanical digestion• In humans, mechanical

digestion takes place in the mouth.

• Human incisors and canines are adapted for tearing food, while molars are adapted for grinding food.

• Saliva, which contains enzymes, mixes with food.

Stomach• Acid digestion

occurs in the stomach.

• Gastrin, a hormone, stimulates acid release.

• Pepsin, an enzyme that breaks up proteins, requires an acidic environment to become active.

Stomach problems• Stomach ulcers

cause pain when the stomach is empty. These are bacterial infections that create ulcerations.

• Acid reflux is often due to weakness in the sphincter muscle at the top of the stomach.

Duodenum

• Alkaline digestion takes place in the upper small intestine, the duodenum.

• Enzymes from the pancreas require an alkaline environment to be active.

Pancreas and Liver• Pancreas releases

pancreatic juice, containing bicarbonate, lipases, proteases, and amylase.

• The liver makes bile, which emulsifies fats. Bile is made from cholesterol, which is made in the liver.

Small intestine• The walls of the

small intestine are lined with millions of microvilli. This is the site of nutrient absorption.

• Small intestines also produce many digestive enzymes to break large polymers completely down into monomers.

Villi and microvilli

Digestion and pHLocation pH Enzymes Molecules

digested

Mouth neutral Amylase Starch

Stomach acidic Pepsin (a peptidase)

Initial protein digestion

Small intestine Basic to neutral Mixture of amylase, peptidases, lipases

Digestion of starches, final breakdown of proteins, digestion of lipids.

Large intestine• Water from digested

food is absorbed in the large intestine.

• Bacteria present in the large intestine feed on unabsorbed nutrients, and produce several vitamins.

• Fecal material is formed from fiber and other undigested material.

Most digestion occurs in:

1 2 3 4

25% 25%25%25%

1. The mouth2. The stomach3. The small

intestines4. The large

intestines

Digestion of starches begins in the:

1 2 3 4

25% 25%25%25%

1. Mouth2. Stomach3. Small intestine4. Large intestine

Why do we have microvilli?

1 2 3

33% 33%33%1. To protect the intestinal lining.

2. To vastly increase the intestine’s surface area.

3. To block acids coming from the stomach.

Does a colon need cleaned?

• Products like these raise worry in people who believe their colon is “dirty.” These are laxatives that are unnecessary, or even harmful.

• “Cleansing” products can disrupt bowel function and do not cure any real illnesses. A diet high in fiber is a healthier option.

Hormones and digestion• Many hormones produced by the digestive

system itself are responsible for appetite and digestion.

• Gastrin in the stomach, produced when food is present, signals release of acid.

• Secretin signals the release of sodium bicarbonate by the pancreas.

• Ghrelin and Leptin, recently discovered, control appetite. Changes in these hormones cause overeating, because people with too little of these hormones don’t realize they’re full.

Hormones

• NOVA Science Now video: Hormones and Obesity