Packet 13 Notes
**Be sure to read your textbook and review book.**
Aim: The Digestive System
(A)
NUTRIENTS
 Humans are heterotrophs--which means we eat other organisms for food and energy
 Food contains nutrients: molecules that provide energy and material for growth and repair
 Nutrients are chemical substances needed by the body for growth, repair and maintenance
 All the different foods contain at least one of the six kinds of nutrients:

Carbohydrates

Proteins

Lipids

Vitamins

Minerals

Water
 The large molecules in food must be broken down in order to be absorbed into the blood and
carried to the cells throughout the body
 The process of breaking down food into molecules the body can use is DIGESTION
 Your cells than break the chemical bonds of the digested food molecules and use the energy
that is released to make ATP during the process of cellular respiration
1. CARBOHYDRATES
 Carbohydrates that exist as single sugar molecules are called monosaccharides or simple
sugars
 Carbohydrates made of two or many sugar molecules linked together by chemical bonds are
called complex carbohydrates
 Complex carbs must be broken down—digested—into simple sugars before cells can use their
energy
 Carbohydrates are the body’s main source of energy
2.
PROTEINS
 Growth and repair require the materials contained in proteins
 Our cells need proteins to make other proteins, such as enzymes
 Proteins are made up of smaller units called amino acids
 Most amino acids are made in the body, but there are eight essential amino acids which can
only be obtained in the food we eat
3. LIPIDS
 AKA fat
 Although too much fat is not healthy, your body does need some fat
 Fat is important for:

Another source of energy

Protect our organs

Make up cell membranes

Help to insulate the body against changes in environmental temperature
4. VITAMINS
 Organic molecules that are needed by the body in very small amounts that serve as
coenzymes
 They do not contain energy
 Most vitamins are enzyme helpers and play a role in cellular reactions
5. MINERALS
 Inorganic substances required the normal functioning of the body
 Many bodily functions rely on minerals
 We obtain minerals from the food we eat
6. WATER
 The most important nutrient
 Animals will die from lack of water long before they will starve from lack of food
(B) BREAKING DOWN FOOD
 Before your body can use the nutrients in the food you eat, the large molecules must be
broken down physically and chemically
 Digestion: the process of breaking down food into molecules the body can use
 The digestive system is the body system that is involved in the taking in and processing of
food for use by your body cells
 The digestive system is made up of a long, winding tube, the digestive tract, that begins at the
mouth and winds through your body to the anus
 The digestive tract includes the mouth, pharynx, esophagus, stomach, small intestine, large
intestine, and rectum
(C) STARTING DIGESTION
 three activities are involved in the digestive process:

mechanical digestion—to break down food into tiny pieces without changing the
chemical structure of the food

chemical digestion—breaking down the food into smaller and smaller pieces so
that the molecules can be absorbed into the bloodstream

absorption—when the molecules are picked up by the blood and distributed to
the rest of the body
 The digestion of food goes through the following path:
1.
2.
3.
Mouth—digestion begins here


some mechanical digestion—chewing
some chemical—saliva—saliva contains salivary amylases which are
enzymes that help break up the food
Pharynx: where the food triggers a swallowing response—this moves the
epiglottis over the trachea so the food does not enter the trachea
Esophagus: a long narrow tube that connects the mouth to the stomach—no
digestion occurs here—food is pushed down the esophagus by peristalsis:
muscular contractions in the esophagus
4.
5.
6.
7.
Stomach: saclike organ located just beneath the diaphragm—temporarily
stores food and mechanically and chemically digests proteins
 Gastric juice—a combination of hydrochloric acid and pepsin—is
located in the stomach
 Protected by a coating of mucus
Small Intestine: coiled tubular organ that functions mainly in digestion and
absorption—most of the absorption occurs here
 Fat is broken down here by a process called emulsification—bile
breaks up fat globules into tiny droplets
 The lining of the small intestine is covered with fingerlike projections
called villi which have cells called microvilli on their surface—this
greatly increases the surface area available for absorption
Large Intestine: wastes—component of food that aren’t used for energy—
move into the large intestine
 Also known as the colon
 No digestion occurs here
 Most of the colon’s contents are dead cells, mucus, digestive secretions,
bacteria, and yeast—also bacteria that make many compounds needed
by the body
Rectum: last part of the large intestine—wastes remain here until they are
released though the anus
(D) LIVER
 Secretes bile, which aids in the emulsification of fats
 Stabilizes blood sugar by converting extra sugar to glycogen for storage
 Breaks down the glycogen when needed for energy
 Can be damaged by viral infections, drug use, alcohol and traumatic injury
(E) DISORDERS
 Diarrhea—watery feces—occurs when wastes are rushed through the large intestine
before the remaining water is absorbed
 Constipation—hard feces—occurs when food remains in the colon for long periods
of time, which causes too much water to be absorbed
 Ulcers—holes in the lining of the stomach—causes the acids to leak through