Digestive System

1
Digestive System

• Obtaining nutrients

2
Nutrition
3
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.

4
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.

5
Lipids
Many lipids are made up of fatty acids and
glycerine.

• 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.

6
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.
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Thinking Question

• Sometimes my students describe sugars or starch
  as fatty, or tell me that sugar has lots of fat
  in it. Are they right or not?

8
Proteins
Proteins are made up of amino acids.

• 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.

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Thinking question

• 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. See if you can name some.
  (Hint Meat is a source, not a protein. What
  proteins are in the muscle fibers that meat is
  composed of?)

10
Macromolecule summary
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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.

12
Vitamins

• Vitamins play many different roles in metabolism.
• We do not obtain energy from vitamins however,
  many vitamins are necessary to run energy-related
  processes in cells.

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Antioxidants
Moral of the story eat colorful food

• 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.

No, Skittles dont count as colorful food!
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Thinking question

• Trick question what ingredient in energy
  drinks actually gives you energy?
• What would be incorrect about a label that said,
  calorie-free energy drink?

15
Digestion
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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.

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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.

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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.

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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.

20
Duodenum

• Alkaline digestion takes place in the upper small
  intestine, the duodenum.
• Enzymes from the pancreas require an alkaline
  environment to be active.

21
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.

22
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.

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Villi and microvilli
24
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.

25
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.

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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 dont realize theyre full.

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Hormones

• NOVA Science Now video Hormones and Obesity