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The Human Digestive System

The Four Stages of Food Processing 1. Ingestion ­ the taking in or eating of food

2. Digestion ­ the breakdown of food by mechanical and chemical processes into molecules small enough for cells of the body to absorb

Mechanical Digestion • chewing, chopping, and grinding of food into smaller pieces, increasing its surface area•done by teeth, beak or other similar structures, and by contractions and churning motions in the stomach

The Digestive System

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Chemical Digestion • the chemical breakdown of nutrient molecules into smaller molecules by enzyme action; called hydrolysis

Carbohydrates simple sugars

Lipids glycerol + fatty acids

Proteins amino acids

3.Absorption ­ the transport of the products of digestion from the digestive system into the circulatory system­ the molecules are transported in the blood to the body cells­ in the cells they are joined to make bigger molecules or broken down to provide energy

4. Elimination ­ the removal of undigested solid waste matter from the body

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• to break up food particles ­ mechanical digestion • to lubricate food particles ­ saliva• begin digestion of complex carbohydrates (starches and glycogen) ­ chemical digestion

Oral Cavity (The Mouth)The primary functions of the oral cavity (mouth) is to ...

The mouth is also used for tasting food (using the tongue) to help determine if it should be ingested or not.

Mechanical Digestion:

Mechanical digestion in the oral cavity (mouth) involves ...

Oral Cavity ﴾The Mouth﴿

Teeth ­ to break up food particles (mastication)Tongue ­ position food particles Salivary Glands ­ lubricate food particles

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Tooth Decay

What do you think causes tooth decay?

­ Saliva is normally slightly alkaline. ­ When we eat, bacteria in our mouth feed on sugar and turn it into acid. ­ The acid starts to attack the enamel and wear it away.

Oral Cavity ﴾The Mouth﴿

Chemical Digestion:

Chemical digestion in the mouth involves the enzyme amylase.

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Oral Cavity ﴾The Mouth﴿

http://health.howstuffworks.com/human­body/systems/nose­throat/adam­200089.htm

The Movement of Food:

Peristalsis is a distinctive pattern of smooth muscle contractions that propels foodstuffs distally through the esophagus and intestines.

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Segmentation contractions are a common type of mixing movement seen especially in the small intestine. Segmental rings of contraction chop and mix the ingested food. Alternating contraction and relaxation of the longitudinal muscle in the wall of the gut also provides effective mixing of its contents.

The Esophagus

Physical description: a muscular tube with a mucus lining

STRUCTURE:

Location: neck / thoracic cavity

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The Esophagus

This is done using a powerful, synchronized set of muscle contractions called Peristalsis.

FUNCTION:The primary function of the esophagus is to transport food from the mouth to the stomach by the process of swallowing.

mouth

stomach

The Esophagus

Between swallows, the esophagus usually does not contract.

There is a sphincter muscle separating the esophagus from the stomach (called the lower esophageal sphincter) which normally stays tightly closed to prevent acid in the stomach from washing up into the esophagus.

However, when we swallow, this sphincter muscle opens up (relaxes) so that the food we swallow can enter the stomach.

sphincter

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The Esophagus

The most common symptom that occurs in the esophagus is heartburn (acid reflux), which is caused when acid washes up into the esophagus repeatedly (gastroesophageal reflux) and irritates the lining of the esophagus.

This happens when the sphincter separating the stomach from the esophagus does not work properly; the function of this sphincter is to prevent reflux from occurring when the stomach contracts.