Download 3.5 the digestive system

Unit 03 - Student book
9/25/03
1:00 PM
Page 90
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• Money spent on the criminal justice system could better be spent on drug awareness and prevention programs.
3.5 THE DIGESTIVE SYSTEM
TRY THIS ACTIVITY: BEGINNING DIGESTION
(Page 183)
(a)
Time
Cracker texture
Cracker flavour
First placed in mouth
cracker is crisp
cracker is starch-like
After 1 min
crisp texture of the cracker softens
and becomes mushy
starchy (flour-like) flavour of the
cracker becomes sweet
TRY THIS ACTIVITY: SIMULATING BILE ACTION ON FATS
(Page 185)
(a) The oil forms a globule on the surface of the water; no mixing occurs.
(b) When the tube is shaken, the oil globule breaks up into many small globules, but on standing, the oil again forms a
layer on the surface.
(c) Detergent foam appears on the surface; the water, oil, and detergent mixture appears cloudy and uniform.
(d) The liquid soap emulsified the oil by breaking large drops into smaller ones.
(e) Bile contains bile salts that emulsify dietary fat in a similar way to liquid soap action.
SECTION 3.5 QUESTIONS
(Page 188)
Understanding Concepts
1. The function of the digestive system is to break food down into nutrients that are then absorbed and transported by the
circulatory system. The end products of digestion are glucose, amino acids, fatty acids, and glycerol.
2. In order, food passes through the following digestive structures: mouth (teeth begin mechanical digestion, salivary
glands contribute enzymes); pharynx; esophagus; stomach; small intestine; (pancreas, liver, gallbladder contribute
digestive substances); large intestine; rectum, anus.
3. Comparison of human and bird digestive systems:
Similarities
– both are long tubes, open at each end
– esophagus carries food from intake to storage/digestive site
– intestine absorbs digested food; lower end absorbs water
Differences
Human
– no equivalent of crop
– mechanical and chemical digestion begin in
mouth, with teeth and salivary glands
– one-way passage of food through system
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Unit 3 Student Book Solutions
Bird
– crop stores food internally before digestion
– no teeth; beak breaks up food
– two-part stomach: gizzard for mechanical digestion;
proventriculus for chemical digestion; food passes back
and forth between these organs
NEL
Unit 03 - Student book
9/25/03
1:00 PM
Page 91
4. Function of digestive enzymes:
amylase—breaks down carbohydrates into maltose sugars
pepsin—begins the digestion of protein to long chain polypeptides
trypsin—converts long-chain peptides into short-chain peptides
lipase—breaks down fats into fatty acids and glycerol
5. Bile is a digestive substance secreted continuously by the liver and stored in the gallbladder until it is needed. Bile salts
in the bile act mechanically to break large fat globules into smaller ones. By increasing the surface area of the fat,
digestion can work more efficiently.
6. Three macronutrients are glucose, fatty acids, and amino acids. Glucose is the basic energy source for all cells. Fatty
acids store and provide energy, help the body synthesize hormones, insulate the body, protect organs, provide a protective coating around nerves, and are an essential component of the cell membrane. Amino acids are required by cells
for growth and repair, and to synthesize hormones and enzymes to perform chemical activities.
7. Each villus in the small intestine has blood capillaries and lymph vessels. Amino acids and glucose are absorbed into
the capillary networks; fats are absorbed into the lacteals. Both diffusion and active transport are involved in absorption.
8. Summary table of digestive organs:
Organ
Function
mouth
– chewing of food and digestion of starch
stomach
– storage of food and the initial digestion of proteins
small intestine
– secretion of peptidase and maltase
– final digestion of carbohydrates, proteins, fats
– absorption of glucose, amino acids, fatty acids, and glycerol
liver
– production of bile
gallbladder
– storage and release of bile
pancreas
– production of bicarbonate
– secretion of digestive enzymes (lipase, trypsin, amylase)
large intestine
– reabsorption of water
– production of vitamins K and B
– storage of undigested food
9. Homeostasis is the maintenance of a healthy balance of all chemical reactions in an organism. Smelling, tasting, or
thinking about food stimulate the salivary glands to release saliva, and the stomach to release gastrin. Secretin is
released when acids from the stomach move into the small intestine. This hormone travels in the blood to the pancreas
where it initiates the release of carbonate ions. The rate of digestion is determined by receptors that control stomach
contractions and peristalsis.
Applying Inquiry Skills
10. If undigested wastes pass very quickly through the large intestine, little water is absorbed and diarrhea results. At the
other extreme, if wastes are held longer than normal in the large intestine, a greater proportion of water is absorbed,
the feces are hard, and constipation results. Rate of water absorption is compared. The person with diarrhea has a lower
rate of absorption; the person with constipation has a higher rate of water absorption. Normal intestinal absorption rate
would be somewhere between 10 mL/4 h and 100 mL/4 h—about 55 mL/4 h.
11. The glucose in Juan’s drink is already in the form of energy recognized by cells. It requires no further digestion, and
passes quickly through the digestive tract and into the bloodstream. Juan’s blood glucose levels peak about 30 min
after ingestion, giving him a burst of energy. It is quickly metabolized, as indicated by the drop in blood glucose level
at 60 min. The sucrose in Jeff’s drink must be broken down by pancreatic analyses into glucose. This process takes
longer; the release of glucose into the blood stream is slower and there is a less dramatic effect on blood glucose levels.
After about 100 min, Jeff and Juan’s blood glucose levels are identical.
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Section 3.5
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Unit 03 - Student book
9/25/03
1:00 PM
Page 92
Making Connections
12. Summary of ulcer research, from Nelson Science Web links:
Kinds of ulcers:
– an ulcer is an open sore usually found on the skin or mucous membranes of the body
– three types of digestive ulcers: peptic (lining of the stomach or duodenum, where hydrochloric acid and pepsin
are present); gastric (stomach lining); and duodenal (lining of duodenum)
– can develop at any age; rare among teenagers and even more uncommon in children
– about 1 in 10 North Americans develops at least one ulcer during his or her lifetime
Causes:
– in the past it was believed stomach acids and lifestyle factors, such as stress and diet, caused ulcers
– today, research shows that 80–90% of ulcers develop as a result of infection with Helicobacter pylori (H. pylori)
bacteria
– in addition, it appears that the body’s own immune system reacts strongly to the infection; the reaction is
ineffective and can make the ulcer worse
Environmental risk factors:
– cigarette smoking increases the chances of getting an ulcer, slows the healing of existing ulcers, and contributes
to ulcer recurrence
– coffee, tea, colas, and foods that contain caffeine seem to stimulate acid secretion in the stomach, aggravating
the pain of an existing ulcer
– ulcers are more common in people who have cirrhosis of the liver, a disease associated with heavy alcohol
consumption
– although emotional stress is no longer thought to be a cause of ulcers, anecdotal evidence suggests that
emotional stress increases ulcer pain
– physical stress (e.g., severe burns, major surgery) increases the risk of developing ulcers, particularly in
the stomach
– nonsteroidal anti-inflammatory drugs such as aspirin and ibuprofen make the stomach vulnerable to the harmful
effects of acid and pepsin; they interfere with the stomach’s ability to produce mucus and bicarbonate and affect
blood flow to the stomach and cell repair, resulting in an increased chance of developing stomach ulcers
Symptoms:
– ulcers do not always cause symptoms
– most common ulcer symptom is pain in the abdomen between the breastbone and the navel, often occurring
between meals and in the early hours of the morning; it may last for minutes or hours; pain may be relieved
by eating food or taking antacids
– less common ulcer symptoms: belching, nausea, vomiting, and poor appetite; weight loss; lethargy and
weakness; symptoms may last for minutes or hours and may be relieved by eating food or by taking antacids
– bleeding ulcers may lead to anemia with weakness and fatigue; blood may appear in vomit or bowel
movements, changing colour to dark red or black
Treatment:
– medications such as H2-blockers (to reduce the amount of acid the stomach produces by blocking histamine);
acid pump inhibitors (to more completely block stomach acid production); mucosal protective agents (to shield
the stomach’s mucous lining from the damage)
– H. pylori is effectively treated with a combination of antibiotics; there is little chance of recurrence
– people who do not respond to medication or those who develop complications may require laparoscopic surgery
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Unit 3 Student Book Solutions
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