Lesson#1:
Quarter 4
DIGESTIVE SYSTEM
Key Concepts:
● The digestive system is used for breaking down food into nutrients which then pass into the circulatory system and are
taken to where they are needed in the body. It consists primarily of the alimentary canal (digestive tract) and accessory
organs.
● Digestion is the complex process of turning food that you eat into nutrients, which the body uses for energy, growth, and
cell repair needed to survive. The digestion process also involves creating waste to be eliminated.
.Types of Digestion
● Mechanical Digestion - the physical breakdown of chunks of food into smaller pieces. This type of digestion takes place
mainly in the mouth and stomach.
● Chemical Digestion - the chemical breakdown of large, complex food molecules into smaller, simpler nutrient molecules
that can be absorbed by the blood.
Functions of the Digestive System
● Digestion of foods - Digestion is the process of breaking down food into components the body can absorb.
● Absorption of foods - Absorption is the process in which substances pass into the bloodstream, where they can circulate
throughout the body. Absorption of nutrients occurs mainly in the small intestine.
● Elimination of solid food waste - Any remaining matter from food that cannot be digested and absorbed passes into the
large intestine as waste. The waste later passes out of the body through the anus in the process of elimination.
Parts of the Digestive System
Alimentary Canal
● Mouth - It breaks down the food by your teeth as a means of mechanical digestion. Sharp teeth in the front of the mouth
cut or tear food when you bite into it (see Figure below). Broad teeth in the back of the mouth grind food when you chew.
● Esophagus - A muscular tube through which food passes from the mouth into the stomach. The wavelike contraction of
the food tube is called peristalsis.
● Stomach - A big muscular pouch where digestion begins. It is made up of muscles that churn and help mix the food with
gastric juices and acids and break it into even smaller pieces. Other enzymes such as lipase and protease help break
down proteins in the stomach and fats in the small intestine.
● Small Intestine - Absorption of food particles takes place here. The walls contain many folds that are lined up with tiny
fingerlike protrusions called villi and microvilli where nutrients pass through.
● Large Intestine - known as colon which absorbs water, secretes mucus, and eliminates undigested materials
● Rectum - stores feces
● Anus - an opening where the feces is eliminated through the process of defecation
Accessory Organs
● Salivary Organs - The main salivary gland function is saliva production. Saliva also keeps the mouth and other parts of
the digestive system moist. The main function of saliva are: To help in digestion; to help chewing and to swallow.
● Liver - secretes bile, a greenish fluid that emulsifies fats and neutralizes stomach acid, and increases the efficiency of
digestion and absorption
● Gallbladder - where bile is stored.
● Pancreas - creates natural juices called pancreatic enzymes to break down foods. These juices travel through your
pancreas via ducts.
Digestive Processes
● Ingestion - The process where food is taken in through the mouth and broken down by teeth and saliva.
● Digestion - The breaking down of food into small pieces
● Absorption - The process by which food molecules move into the bloodstream to be carried to the cells of the body.
● Assimilation - Incorporation of food molecules into the cells of the body to be used as energy, structural materials or
storage products.
● Defecation - The process of eliminating undigested food from the body
How does the Digestive System work?
● Mastication or chewing is the process by which food is mashed and crushed
by teeth. Food is physically broken down by the teeth and chemically broken
down by amylase, an enzyme in saliva that break down carbohydrates.
● Food leaves the mouth when the tongue and pharyngeal muscles propel it
into the esophagus
● The bolus (chewed food) passes down to the esophagus by peristalsis.
Peristalsis is a wave of muscular contractions that push the bolus down
toward the stomach.
● To enter the stomach, the bolus must pass through the lower esophageal
sphincter. The lower esophageal sphincter is a tight muscle that keeps
stomach acid out of the esophagus.
● The stomach churns the bolus and mixes it with gastric juice, a mixture of
stomach acid, mucus, and enzymes. The acid kills off any invading bacteria
and viruses. The enzymes help break down proteins (protease) and lipids
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(lipase). The mucus protects the lining of the stomach from being eaten away by the acid.
The stomach does do some absorption too. Some medicines, water, and alcohol are all absorbed through the stomach.
The digested bolus is now called chyme and it leaves the stomach by
passing through the pyloric sphincter.
Chyme is now in the small intestine. The majority of absorption occurs here.
The small intestine is broken down into three parts: Duodenum, Jejunum,
and Ileum.
The liver and pancreas help the small intestine to maximize absorption.
Bile, produced in the liver but stored in the gallbladder, enters through the
bile duct. It breaks down fats.
The pancreas secretes pancreatic juice to reduce the acidity of the chyme.
The jejunum is where the majority of absorption takes place. It has tiny
fingerlike projections called villi lining it, which increase the absorbing
nutrients. Each villi itself has tiny fingerlike projections called microvilli,
which further increase the surface area for absorption.
The last portion of the small intestine is the ileum, which has fewer villi and
basically compacts the leftovers to pass through the caecum into the large
intestine.
The large intestine (or colon) is used to absorb water from the waste
material left over. It produces vitamin K and some B vitamins using helpful
bacteria that live here.
All leftover waste is compacted and stored at the end of the large intestine
called the rectum.
When full, the anal sphincter loosens and the waste, called feces, passes
out to the body through the anus.
Defecation is the process of eliminating undigested food from the body.
Diseases of the Digestive System
In the Philippines, the leading causes of death are related to the digestive tract, which includes among others, liver cancer,
colorectal cancer, peptic ulcer disease, diarrhea, and stomach cancer.
● Liver Cancer - It is a disease in which malignant (cancer) cells form in the tissues of the liver.
Treatments:
Surgery,
Radiation Therapy
Localized treatment
Supportive Care
Targeted Drug Therapy
Liver Transplant
Chemotherapy
Radiation
Preventions:
Limit alcohol consumption
Maintain a healthy body weight
Hepatitis B Vaccination
Treat underlying conditions
Limit tobacco use
● Colorectal Cancer - It is a type of cancer that starts in the large intestine or colon, which is the tail end of the digestive
tract.
Treatments:
Surgery,
Targeted Therapy
Chemotherapy
Immunotherapy
Radiation Therapy
Preventions:
Healthy lifestyle
Exercise
Avoid smoking and drinking alcohol
● Peptic Ulcer Disease - It involves the formation of open lesions on the areas of the gastrointestinal tract exposed to gastric
juice.
Treatments:
Lifestyle change
Surgery
Medications
Preventions:
Avoid smoking
Don’t use aspirin and/or NSAIDs.
Avoid alcohol
● Diarrhea - is very common, happening in most people a few times each year. When you have diarrhea, your stool will be
loose and watery.
Treatment:
Rehydrate
Preventions:
Wash foods properly
Prepare foods properly
Wash your hands
Drink water from safe sources
● Stomach Cancer - is also referred to as gastric cancer. It is just one form of cancer that affects a digestive organ inside
your abdomen.
Treatments:
Surgery,
Targeted Therapy
Chemotherapy
Immunotherapy
Radiation Therapy
Preventions:
Eat plenty of fruits and vegetables
Stop smoking
Reduce the amount of salty and smoked foods you eat.
Tell your healthcare provider if stomach cancer runs in your family