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The Mouth
38–2 The Process of Digestion
42. What are the organs of the digestive system?
The mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
Other structures add secretions to the digestive system, and aid in digestion. These include the salivary glands, pancreas, and liver.
43. What is the function of the digestive system?
The function is to help convert foods into simpler molecules that can be absorbed and used by cells.
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The Mouth
44. What is mechanical digestion?
Chewing, the physical breakdown of large pieces of food into smaller pieces. As the teeth cut and grind the food, salivary glands secrete saliva, which moistens food and makes it easier to chew.
45. What’s the purpose of saliva?
It helps ease the passage of food through the digestive system and also begins the process of chemical digestion. Saliva contains amylase - an enzyme that breaks the chemical bonds in starches and releases sugars; and also contains lysozyme - an enzyme that fights infection.
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The Esophagus
46. Where does the food go next?
The chewed food passes through the esophagus, or food tube, into the stomach. Food is moved along by contractions of smooth muscle. These contractions, known as peristalsis, squeeze the food through the esophagus into the stomach.
47. Where next?
Food from the esophagus empties into the stomach. The stomach continues mechanical and chemical digestion.
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4. What type(s) of digestion take place in the stomach?
The function of the digestive system is to help ___________ into simpler molecules that can be ________ and used by ______.
What are the two types of digestion? Circle the one which one involves chewing the food.
What type(s) of digestion take place in the stomach?
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The Stomach
48. How does chemical digestion occur?
The stomach lining has millions of gastric glands that release substances into the stomach.
Some glands produce mucus, which lubricates and protects the stomach wall.
Other glands produce hydrochloric acid (HCl), which makes the stomach contents very acidic.
Other glands produce pepsin, an enzyme that digests protein.
49. What do pepsin and HCl do?
They begin protein digestion.
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The Stomach
50. What happens with mechanical digestion in the stomach?
The stomach contracts to churn fluids and food, gradually producing a mixture known as chyme.
51. Where does the food go after the stomach?
After 1–2 hours, the pyloric valve between the stomach and small intestine opens and chyme flows into the small intestine.
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The Small Intestine
52. Where does the majority of chemical digestion occur?
Most chemical digestion and absorption of food occurs in the small intestine.
53. How is the pancreas involved?
It produces enzymes that break down carbohydrates, proteins, lipids, and nucleic acids. It also produces sodium bicarbonate, a base that neutralizes stomach acid so that these enzymes can be effective in a lower pH.
54. What does the liver do?
Assisting the pancreas, it produces bile, which dissolves and disperses droplets of fat in fatty foods.
Bile is stored in the gallbladder.
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Some glands produce _________, which makes the environment in the stomach very acidic.
Most ________ digestion and ________ of food takes place in the small intestine.
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9. Absorption in the Small Intestine
55. What is the small intestine designed to do?
The small intestine is adapted for the absorption of nutrients.
56. How does it absorb the nutrients?
The folded surfaces of the small intestine are covered with fingerlike projections called villi. Cell surfaces of villi have more projections called microvilli. These provide an enormous surface area for the absorption of nutrient molecules.
57. What do capillaries in the villi absorb?
Most products of carbohydrate and protein digestion are
absorbed into the capillaries in the villi.
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10. Absorption in the Small Intestine
Villus
Small intestine
Circular folds
Epithelial cells
Villi
Capillaries
Lymph vessel
The lining of the small intestine consists of folds that are covered with tiny projections called villi. Within each villus there is a network of blood capillaries and lymph vessels that absorb and carry away nutrients. 
Vein
Artery
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The Large Intestine
58. When the chyme leaves the small intestine, what’s next?
It enters the large intestine, or colon.
59. What does the large intestine do?
The large intestine removes water from the chyme. Water is absorbed quickly, leaving undigested materials behind.Concentrated waste material passes through the rectum and is eliminated from the body.
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12. The small intestine is adapted for the _______ ___ _________.
The small intestine has many fingerlike projections in order to increase surface area and absorption. These small projections are called __________.
The large intestine _____ ________ from the chyme.
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38–2
Food is moved through the esophagus into the stomach by
air pressure.
muscle contractions.
gravity.
swallowing.
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38–2
The enzyme in saliva that begins the digestion of starch is
amylase.
pepsin.
lysozyme.
peptidase.
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38–2
Stomach muscles contract to churn and mix stomach fluids and food, producing a mixture known as
chyme.
amylase.
bile.
acid.
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38–2
Absorption of vitamins, minerals, and digested food molecules takes place in the
stomach.
small intestine.
large intestine.
duodenum.
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