Download The Digestive System

The Digestive System
The mysterious process uncovered!
The Beginning
• Oral cavity:
– Both physical and chemical digestion takes
place in the mouth.
• Saliva:
– secreted to moisten food,
– protect the mouth from abrasions
– buffer against acids in food, kill some forms of
bacteria
– begin carbohydrate digestion with the enzyme
SALIVARY AMYLASE.
• Tongue:
– is used for taste, manipulates food while
chewing and
– prepares food for swallowing by forming it
into a ball called a bolus.
Down the hatchet (or Pharynx and
esophagus)!
•
Pharynx
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Commonly called the throat.
Intersection of the glottis and
opening to the esophagus is found
here.
Epiglottis is a flap that closes the
glottis when the act of swallowing
occurs.
Esophagus
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Connects the pharynx and the
stomach.
Peristalsis, wave-like contractions of
the smooth muscles push food
down toward the stomach.
Connects with the stomach at the
CARDIAC SPHINCTER.
Into The Stomach
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J shaped expandable organ located on the left side of the abdominal
cavity.
Stores up to 2 liters of food while mixing and digesting it.
The epithelial cells secrete GASTRIC JUICES and HCl making the pH
around 2.
PEPSINOGEN : an enzyme used to partially hydrolyze protein;
pepsinogen reacts with HCL to form pepsin.
The hormone GASTRIN is secreted by the stomach cells to regulate the
production of gastric juices.
Fat Digestion: Bile emulsifies fat. This creates a larger surface area for
the enzyme lipase to digest it.
Carbohydrate Digestion: Disaccharide digestion is under the control of
the enzymes maltase, lactase, sucrase, all of which are mainly found in
saliva.
The stomach is closed at its posterior end by the PYLORIC SPHINCTER
Stomach Photo
Small Intestine and Villi
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Most hydrolysis of macromolecules occur here
It is more than 6 meters in length with smaller diameter than
large intestine.
It is divided into 3 sections: duodenum, jejunum, and ileum
Pancreas, Liver, and Gall Bladder:
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accessory organs, add digestive enzymes, juices and hormones into
the small intestine.
The hormone Cholecystokinin (CCK) is released from the
intestinal cells causing the gall bladder to release bile. It also
causes the pancreas to release its digestive enzymes.
Absorption
•
Absorption and distribution of nutrients:
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Small intestine is lined with small finger-like projections
called Villi
Each villus contains a net of capillaries and a large lymph
vessel called a lacteal
The nutrients except fat are absorbed into the capillaries,
while the fat enters the lacteal.
All the contents of the blood enter the liver via the
Hepatic portal vein.
The liver regulates the contents of the blood.
Large Intestine
•
Colon is connected to the small intestine at a T
junction called the cecum.
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The appendix is found attached to the end of the
cecum.
The main function of the colon is to reabsorb
water from the small intestinal material.
The bacteria Escherichia coli live in this area of
the body. They produce odor, and Vitamin K.
Waste is excreted through the rectum and
out through the anus
Now, who’s hungry?
• Digestion Transit Times:
– Mouth:
• one minute
– Esophagus:
• two to 3 seconds
– Stomach:
• 2-4 hours
– Small Intestine:
• 1-4 hours
– Large Intestine:
• 10 hours to several days!