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The Digestive System. The Mouth. Lips : grasping, speaking Teeth: chopping, tearing, ripping, crushing of food. (Mechanical digestion) Salivary glands : secrete digestive enzymes (break carbohydrates down to sugar) Makes saliva. Tongue: mixing food with saliva (mech. digest.) , speaking

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The Digestive System

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the mouth
The Mouth

Lips: grasping, speaking

Teeth: chopping, tearing, ripping, crushing of food. (Mechanical digestion)

Salivary glands: secrete digestive enzymes (break carbohydrates down to sugar)

Makes saliva.

Tongue: mixing food with saliva (mech. digest.) , speaking

Uvula: Blocks off nose when swallowing , making uvular sounds, snoring , gag reflex

Hard palate (roof of mouth, food pushes up here.

Soft palate can expand so chewed food (bolus) can enter



The opening after the mouth. It is the place where the digestive and the respiratory systems meet. Why????

Epiglottis is a flap that folds over the trachea and prevents food or water from going down it. I.e. choking "went down the wrong way."


Esophagus: A passageway to the stomach

Rhythmic contractions of smooth muscle force food and water down. Called peristalsis.

Glug glugglug


Temporary storage, mechanical and chemical digestion

Glands release stomach acid and digestive enzymes.

Upper and lower sphincters close and three layers of muscle contract causing the stomach to churn the food.


The first part of the intestine. Many secretions happen here.

Digestive enzymes from the pancreas will break down protein. NaHCO3 neutralizes stomach acid. Bile is made in the liver and stored in the gall bladder. It is an emulsifier (physical change) and breaks fat up into small goblets.

Food leaving the stomach is called chyme (liquidy, soupy mixture)


Note the liver and the gall bladder and the pancreas are accessory organs.

  • The are attached to the digestive system, but are not a part of the alimentary canal.

The pancreas is a digestive gland and also an endocrine gland (insulin controls blood sugar)

The liver and the gall bladder.


Seen via an endoscope. Fibre optics.

small intestine
Small intestine

6 m long 2.5 – 3 cm in diameter

Duodenum is the first part.

Jejunum is the second and the ileum is the last.

In the first part chemical digestion takes place.

Food is broken down into it molecular form. i.e. protein amino acids, carbohydrates  sugar and fats  lipids

In the latter part of the small intestine more and more absorption of nutrients into the blood occurs.

The small intestine is lined with blood vessels.

The surface area of the small intestine is HUGE

surface area of the small intestine
Surface area of the small intestine
  • As a pipe 6 m X 3 cm surface area = 0.5 m2
  • But the inside of the pipe is folded which increase the surface area
  • These folds are covered in finger like projections called villi. These graetly increase surface area. (30 X increase)
  • Each villi is covered with more projections called micro villi. (60 X increase)
  • This results in an interior surface area of 250 m2 (size of a tennis court)
cross section of small intestine
Cross section of small intestine

Outer layer smooth muscle for peristalsis.

Yellow is smooth muscle used to mix food.

The inner lumen is folded to increases surface area.

The red villi further increase surface area.

Micro villi can not be seen here.

villi and microvilli
Villi and Microvilli

Villi covered in microvilli

blood vessels in villi
Blood Vessels in villi

Why is the surface area so important?

large intestine colon
Large Intestine (colon)

Three parts, ascending (up), transverse (across), descending (down)

Main function is to absorb water and minerals from the chyme.

This makes it more solid feces.

rectum and anus
Rectum and anus

The rectum is for storage of feces before elimination.

The anus is the connection with the external environment.

When you can consciously control your external anal sphincter you are

………………. Trained.