NEM 10V Lecture 48: Digestive System

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6 May 2018
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Department
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Nematology
Digestive System:
Primary functions of the digestive system are the breakdown of food, called digestion,
and absorption of nutrients.
Digestion begins in the mouth where the teeth break food into smaller particles during
mastication.
Salivary glands located near the oral cavity secrete saliva that begins chemical digestion
and keeps the food moist.
As food is swallowed the soft pallet blocks the upper pharynx to prevent food from
entering the:
1. nasal cavity,
2. and multiple voluntary muscles in the face,
3. neck
4. tongue contract pushing food particles through the pharynx.
The one-way movement of the food mass now called a bolus is controlled by wavelike
involuntary muscle contractions.
This movement is known as peristalsis.
Muscular contractions in the stomach churn its contents to further break down the bolus
and mix it with stomach secretions to form a thick liquid called chyme.
Chyme exits the stomach thru the pyloric sphincter and enters the small intestine where
most digestion and absorption occurs.
The small intestine is the longest segment of the gut and consists of three parts, the
duodenum, jejunum, and ileum.
Bile from the liver and digestive enzymes from the pancreas empty into the duodenum to
aid in digestion.
Absorbed nutrients pass from the lumen of the small intestine into blood and lymph.
Chyme not absorbed in the small intestine enters the large intestine.
As it passes through the cecum and ascending, transverse, and descending sigmoid
colon, water and salts are absorbed and chyme is converted into feces.
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