Digestive System Notes
January 27, 2016
*Record Notes in your Body Systems Booklet*
Digestive System
• Functions:
1. Breaks down food into
molecules the body can
use.
2. Molecules are absorbed
into the blood & carried
throughout the body (by
the circulatory system).
3. Wastes are eliminated
from the body (by the
excretory system)
BrainPop Video – Digestive System
Roles of Organs
• Mouth – mechanical & chemical digestion starts here
– Mechanical – physically breaking down food (teeth)
– Chemical – breakdown of molecules of food (saliva)
• Esophagus – muscular tube connecting the mouth to
the stomach
– Peristalsis (muscle contraction) moves the food
Roles of Organs
• Stomach
– Most mechanical digestion takes place
– Some chemical with the help of digestive juices (enzymes & acids)
• Small Intestine
– Most of the chemical digestion takes place
– Absorption of nutrients from digested food into the bloodstream
Roles of Organs
• Large Intestine
– Water is absorbed into the bloodstream
– Remaining material is readied for elimination from the body
• Rectum
– Waste material is compressed into solid form
Process of digestion (simplified)
• 1. Ingestion: The MOUTH Food enters the gastrointestinal tract
through the mouth.
• 2. Digestion: A) MOUTH – both physical (mechanical) and
chemical digestion begins here v Physical - Two main structures
involved: teeth and tongue
• i) TEETH - four types (normal adult has 32 teeth on average)
Digestion
• ii) TONGUE - both tongue and teeth help to physically break apart
food
– Chemical digestion: using ENZYMES to break up food In the mouth,
– SALIVARY glands produce SALIVA which contains the enzyme AMYLASE which
acts on starch, breaking it into maltose.
– BOLUS: the resulting ball of food in the mouth made by the actions of the
teeth, tongue, and saliva
– PERISTALSIS: the rhythmic muscular contractions that push digested food in
one direction through the gastrointestinal tract
The bolus is swallowed and travels down the esophagus into the stomach. It
moves down the esophagus by peristalsis.
Digestion
• B. STOMACH: physical and chemical digestion
• The bolus passes through the CARDIAC SPHINCTER, the top opening in the stomach.
• Sphincter: a muscle that controls the opening
• i) cardiac: esophagus & stomach ii) pyloric: stomach and duodenum v
• Physical: the stomach is a muscular storage organ that churns the food
• Chemical: GASTRIC juice mixes with bolus - stomach contents now called CHYME
• GASTRIC juice contains: a) HCl – hydrochloric acid b) pepsin – enzyme that breaks down PROTEIN
• HCl: - helps breakdown fibrous tissue - kills bacteria - helps pepsin work properly (ph = 2 optimal pH for
pepsin)
• PEPSIN: - enzyme begins to break down PROTEIN into smaller polypeptides
• MUCUS: - also made by stomach to protect itself from STRONG ACID
• Chyme stays in stomach until adequate protein digestion has occurred. This is why you feel less hungry
between meals if you have eaten some protein. The chyme is kept in the stomach by the pyloric
sphincter.
Digestion
• Chemical: GASTRIC juice mixes with bolus - stomach contents now
called CHYME
• GASTRIC juice contains: a) HCl – hydrochloric acid b) pepsin – enzyme
that breaks down PROTEIN
• HCl: - helps breakdown fibrous tissue - kills bacteria - helps pepsin work
properly (ph = 2 optimal pH for pepsin)
• PEPSIN: - enzyme begins to break down PROTEIN into smaller
polypeptides
• MUCUS: - also made by stomach to protect itself from STRONG ACID
• Chyme stays in stomach until adequate protein digestion has occurred.
This is why you feel less hungry between meals if you have eaten some
protein. The chyme is kept in the stomach by the pyloric sphincter.
Digestion
• C. SMALL INTESTINE Final area where MOST digestion occurs and
ABSORPTION begins. ·
• Physical – villi and microvilli help separate food particles ·
• Chemical – where many enzymes complete the digestive process many enzymes from accessory glands (liver, gall bladder,
pancreas) are dumped into the SI to help with digestion
• The small intestine is a long tube (7 m) in length and 2.5 cm in
diameter with a total inner surface area of 30 m2 (due to the villi
and microvilli). The SI is also divided into three sections: a)
duodenum b) jejunum c) ileum
Digestion
• 3. ABSORPTION OF NUTRIENTS
• Stomach: - small amounts of water - alcohol - some medicines, e.g.
aspirin
• Small intestine: jejunum - where most of the absorption takes place
• ileum: where the remaining nutrients are absorbed Absorption is greatly
aided by the folded interior structure of the intestine, particularly due to
the presence of the villi and microvilli.
• Structure of Villi: - tiny finger like projections lining the interior of the
intestines
• Small molecules like vitamins, minerals, natural glucose and amino
acids do not need to be digested and are easily absorbed by the small
intestine.
Digestion
• The COLON – the LARGE INTESTINE (the BOWEL)
• Structure: - 1.5 m in length, 5 cm in diameter (twice the diameter
of SI) - made up of four sections: ascending transverse
descending sigmoid process -the colon ends with the rectum
• Function: - main job is to reabsorb water - bacteria here produce
vitamins K and some B
Digestion
• 4. EGESTION OF WASTE
• CELLULOSE: main component of feces, along with living and dead
bacteria and water –
• FIBRE, found in plant cell walls, cannot be digested by humans
• FECES: - waste is stored in rectum - removed by body removing
possible toxic materials v
• Egestion controlled by anal sphincter which allows feces to leave
rectum through the anus. Toilet training is learning how to control
the anal sphincter.
Path of food through Digestive System
mouth
esophagus
stomach
small intestine
large intestine
rectum
eliminated from body
Summary
• How does the digestive system work with the respiratory system to
provide energy for the body?
Procedures for Today’s Activity
•
1. Build your model.
•
2. “Eat” (place in the mouth/sandwich bag) cracker. Slowly “drink” ( add the water to the bag).
•
3. Close your “mouth” (you should not chew with your mouth open!) by zipping the bag shut, and then “chew” (smash all
the ingredients until no more clumps are present) in your snack.
•
4. Move the food to one side of the bag, toward the opening, and down the esophagus.
•
5. Swallow your food by squeezing the esophagus in rhythmic waves to move the food along.
•
6. Keep squeezing the esophagus until all of the food makes it way into the stomach.
•
7. From the stomach, the snack needs to pass into the small intestine. Squeeze the contents of the “stomach” into the
small intestine. Place toe end of the panty hose inside the cup labeled “nutrients”. To simulate the removal of nutrients
from the food, squeeze the liquid from the contents in the panty hose [Note: Removal of the liquid actually occurs in the
large intestine.] into the cup.
•
8. Once most of the liquid has been squeezed from the food, take the panty hose out of the cup. Squeeze the food from
the small intestine into the large intestine.
•
9. Once in the “large intestine” things should really be squeezed hard with a paper towel to remove the water.
•
10.Cut the toe end of the nylon (“the colon” – the end part of the large intestines) and squeeze the remaining solids out of
the “rectum” (opening at the bottom of the panty hose) into the paper cup (the toilet).