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Science For Forth Primary - Term Two - Human digestive system
The human body :
- The human body is made up of a number of "systems".
- Each system performs "a certain function".

For example :
- Digestive system: Digests and absorbs food.
- Respiratory system: Carries out the process of breathing.
- Circulatory system: Distributes the digested food and oxygen all over the body.
- Urinary system: Helps the body to get rid of harmful substances.
- Nervous system: Lets us have the ability to feel, hear, smell and taste.
- Reproductive system: Makes us give birth for new individuals.

The human digestive system:
Digestion:
Changing the food from a complex form into a simple one to let the body get benefit.
The digestive system:
Is the system which is responsible for digesting food.

The digestive system consists of two main parts which are:
A- Alimentary canal:
A set of organs which contact with each other in a shape of along pipe (duct) known as the digestive canal. (9-10) meters.
It consists of:
1. Mouth
2. Pharynx
3. Oesophagus
4. Stomach
5. Small intestine
6. Large intestine
7. Anus
B- Alimentary canal accessories (associates):
They secrete juices and enzymes, which help in the digestion process.
They include:
1. Salivary glands
2. Liver
3. Pancreas
The human digestive system:


(1): Mouth:
Is a cavity in where teeth and tongue are exited and the salivary glands open to it as well.
: It is the first organ of the digestive system it contains
1- Tongue:
It upturns food inside the mouth cavity and mixes it up with saliva assisting the process of good swallowing and taste.
2- Teeth:
- Chew the food.
- They are 32 in an adult, each jaw has 16 teeth divided into (4 incisors, 2 canines and 10 molars):
I- Incisors and canines: cut and tear food into small pieces.
II-Molars: grind the food to ease its swallowing process.

3- Salivary glands:
They are three pairs of glands secrete a liquid known as the saliva which digest starches then convert them into sugar.

(2): Pharynx:
- It is a common cavity extending leads to the oesophagus and trachea.
- It permits food to pass from the mouth to the oesophagus.

(3): Oesophagus:
- It is a muscular tube that the food travels thought from the mouth to the stomach.
- It allows food to pass from the pharynx to the stomach.

(4): Stomach:
- It is a sac-like muscular organ.
- "1" it works on "mixing food up" by its digestive juices (food changes into semi-liquid substances)
- "2" it secrets "gastric juice" that digests "proteins" into simple water "soluble substances".

(5): Small intestine (ileum):
- Its length is about 7 "meters".
- It coils (lies) inside the "abdominal cavity".
- It starts with a part known as "duodenum".
- "Duodenum" is followed by a part of the small intestine called (ileum) because it is a long convoluted tube.
- It digests food completely.
- Absorption process takes place in the small intestine walls then it delivers the blood which distributes it all over the body organs.
Food is completely digested in the small intestine by the help of:
1- Intestinal Juice:
- From the small intestine.
- Poured in the (ileum).
2- Bile Juice:
- From the liver and it is stored in gall bladder.
- Poured in the duodenum.
3- Pancreatic Juice:
- From the pancreas.
- Poured in the duodenum.

(6): Large intestine:
- It is an inverted U-shaped tube.
- It starts from the end of small intestine ending in the anus which is located at the end of the rectum.
- "1" Water is absorbed in rectum from food remains, then these wastes are rejected outside the body through anus.
Keeping the digestive system healthy:
"To keep your digestive system healthy you have to follow the following instructions":
1. Chew the food well.
2. Don't eat much food that contains large amounts of fats such as fast meals.
3. Skip having food containing the additive compounds and flavorings.
4. Skip purchasing food from streets to avoid infectious diseases.
5. Practice sports regularly.

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