Transcript 38-2 The Digestive System

38-2 The Digestive System
Digestive Tract
• Alimentary canal
– one way passage through the body
• Function:
– to convert food into simple molecules that can
be absorbed and used by the cells of the body
The Mouth
• Start of digestion
• Chewing of teeth tear/ crush moistened
food into a fine paste
• Teeth
– anchored in the bones of jaw and connected
to a network of blood vessels and nerves
– Coated with mineralized enamel
The Mouth
• Types of teeth
– Incisors – sharp to cut thru meat
– Cuspids and bicuspids – grasp and tear food
– Molars – large flat surface for grinding food
• Herbivores – molars are most common
• Carnivores – incisors are common
The Mouth
Salivary glands
• 3 pairs –moistens food and make it easier to chew
• controlled by nervous system (triggered by smell)
• Amylase
– enzyme to break down starches releasing sugars
– Results in sweet taste (rxn of amylase on start)
• Lysozyme
– fights infection by digesting the cell walls of many
bacteria
– result: chewed clump of food called the bolus
• Last – food is swallowed and safely passes the
epiglottis closed over the trachea
The Esophagus
• 25 centimeters long
• Receive bolus from the mouth after
swallowed and carries it to the stomach.
• Peristalsis
– the contractions of smooth muscle that occur
throughout the alimentary canal the squeezes
the food through the esophagus
The Stomach
• Cardiac sphincter
– thick ring of muscles the close the esophagus after the food has passed into
the stomach preventing back flow.
• Functions
– has the ability to store food
– Produce enzymes and strong acids, hydrochloric acid
– Churn the food through muscle contractions
• Gastric glands
– line the stomach
– Produce mucus – lubricates and protects stomach wall
– Produce pepsin – digests proteins
• (combination of pepsin and hydrochloric acid allows for proteins to
be broken down into polypeptide fragments)
• End product of stomach – chyme