Digestive System Notes
Functions of the Digestive System:
Digestion is the process that breaks down food into
small molecules so that they can be absorbed and
moved into the blood. Once in the blood, food
molecules are transported across the cell membrane so
they can be used by the cell.
Digestion is mechanical and chemical. Mechanical
digestion takes place when food is chewed, mixed, and
churned.
Chemical Digestion occurs when chemical reactions
occur that break down large molecules of food into
smaller ones.
Enzymes:
Chemical digestion is possible only because of enzymes.
An Enzyme is a type of protein that speeds up the rate
of chemical reaction in your body. One way enzymes
speed up reactions is by reducing the amount of energy
need for a chemical reaction to begin.
Many enzymes help you digest carbohydrates, proteins,
and fats. Amylase is an enzyme produced by glands
near the mouth that helps speed up the breakdown of
complex carbohydrates, such as starch, into simpler
carbohydrates like sugars.
In your stomach pepsin is an enzyme that aids chemical
reactions that break down complex proteins into less
complex proteins. In your small intestine there are
many other enzymes that further break down proteins
into amino acids. The pancreas also has enzymes that
turn sugar into glucose that can be used by the body’s
cells.
Organs of the Digestive System:
Your digestive system is made up of two parts—the
digestive tract and the accessory organs.
The major organs of your digestive tracts are: mouth,
esophagus, stomach, small intestine, large intestine,
rectum, and anus. These are considered part of the
digestive tract because food passes through them.
Major accessory organs are: the tongue, teeth, salivary
glands, liver, gallbladder, and pancreas. Although food
doesn’t pass through them, they are important for
mechanical and chemical digestion.
The Mouth:
Mechanical and chemical digestions begin in your
mouth. Mechanical digestion happens when you chew
your food with your teeth and mix it with your tongue.
Chemical digestion begins with the addition of a watery
substance called saliva.
Saliva is produced by three sets of glands near your
mouth. Saliva is mostly water, it also contains mucus
and an enzyme that aids in the breakdown of starch
into sugar.
The Esophagus:
Food moving into the esophagus passes the epiglottis.
This structure automatically covers the opening in the
windpipe to prevent food from entering it and stopping
you from choking.
Your esophagus is a muscular tube about 25 cm long. It
takes about 4 to 10 seconds for food to move down the
esophagus to the stomach. No digestion actually takes
place in the esophagus. Smooth muscles in the wall
move food downward by using a wave of muscle
contractions called peristalsis.
The Stomach:
The stomach is a muscular bag. When empty, it is
somewhat sausage shaped with folds on the inside. As
food enters from the esophagus, the stomach expands
and the folds smooth out. Mechanical and Chemical
digestions take place inside the stomach. Mechanically
food is mixed in the stomach through peristalsis.
Chemically food is mixed with enzymes and digestive
solutions to help break down food.
Specialized cells in the walls of the stomach release
about 2 liters of hydrochloric acid per day. The acidic
solution works with the enzyme pepsin to digest
Digestive System Notes
protein. The acidic solution also destroys bacteria that
are present in the food. The stomach also produces a
mucus that makes food more slippery and lines the
walls of the stomach to protect it from its own digestive
solutions. Food moves through your stomach in 2 to 4
hours and is changed into a thin watery liquid called
chime.
Small Intestines:
Your small intestine is small in diameter, but can be 4
to 7 meters in length. As chime leaves the stomach it
enters the first part of the small intestine called the
duodenum. In the duodenum a greenish fluid from the
liver called bile is added and helps break up large fat
particles.
Chemical digestion of carbohydrates, proteins, and fats
occurs when a digestive solution from the pancreas is
mixed in. This solution contains bicarbonate ions and
enzymes that help neutralize stomach acid. Your
pancreas also makes insulin, a hormone that allows
glucose to pass from the bloodstream into your cells.
Absorption of food takes place in the small intestine.
The wall of the small intestine has ridges and folds that
are covered with finger like projections called villi. Villi
increase surface area so that more nutrients can be
absorbed.
Large Intestine:
When the chime enters the large intestine it is still a
thin, watery mixture. The main job of the large
intestine is to absorb water from your undigested mass.
This keeps large amounts of water in your body and
helps maintain homeostasis. Peristalsis usually slows
down in the large intestine to give excess water more
time to be absorbed. The remaining undigested
materials become more solid. Muscles in the rectum
which is in the last section of the large intestine, and
the anus control the release of semisolid wastes from
the body in the form of feces.
Bacteria:
Many types of bacteria actually live in your body.
Bacteria live in many of the organs in your digestive
tract including your mouth and large intestine. Some of
these bacterial help your body. The bacteria in your
large intestine feed on undigested material like
cellulose. In turn, bacteria make vitamins you need like
Vitamin K and two B Vitamins. Vitamin K is needed for
blood clotting. The two B vitamins niacin and thiamine,
are important for your nervous system and for other
body functions.