Download 3.5 the digestive system

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Supporters of marijuana decriminalization claim that:
• Marijuana is not a gateway drug, and only 10% of users become addicted.
• Evidence indicates that cannabis is less harmful than alcohol and should be treated as a public health issue like
alcohol and tobacco consumption, not as a criminal issue like heroin and cocaine use.
• Current penalties are too harsh for possession and use of such a mild drug.
• Convicts do not go to jail but end up with a criminal record that causes them to have difficulty finding jobs, and
makes it more difficult for them to travel abroad.
• 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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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
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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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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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3.6 CASE STUDY: DIGESTIVE DISORDERS
CASE STUDY 3.6 QUESTIONS
(Page 190)
Understanding Concepts
1. Digestive symptoms related to organs:
Symptoms of digestive disorders
Possible digestive organs involved
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
indigestion or heartburn (burning sensation)
discomfort or pain in the abdomen
nausea and vomiting
diarrhea or constipation
bloating after meals
loss of appetite
weakness and fatigue
vomiting blood or blood in the stool
stomach, esophagus, mouth
stomach, small intestine
stomach, esophagus, mouth
small and large intestines
stomach, small intestine
brain
all systems
mouth, esophagus, stomach, small and large intestines
2. Fact Sheet on Crohn’s Disease:
Description
– inflammatory disease (ulcers) of the
small and large intestines, but can affect
digestive system anywhere between
mouth and anus
Symptoms
– many of the common digestive symptoms listed in Section 3.6
– additional symptoms: rectal bleeding, weight loss,
fever, serious and persistent bleeding leading to anemia
– children with Crohn’s Disease may have delayed development
and stunted growth
Cause
– no known cause
– theory: body’s immune system reacts to
a virus or bacterium by causing ongoing
inflammation
Population Data
– affects men and women equally
– about 20% have a blood relative with some form of IBD
– higher incidence in certain ethnic groups, e.g., Jewish descent
Diagnosis
– thorough physical exam required
– additional tests: blood tests to
determine anemia; upper GI examination
(barium X-ray); colonoscopy
Treatment
– goals: control inflammation; correct nutritional deficiencies;
relieve symptoms
– may include drugs, nutritional supplements, surgery, or
combination treatment
– no cure
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Section 3.6
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3. Classification of digestive disorders:
Digestive disorder
Organ on diagram
Stage of digestion
Type of disorder
appendicitis
celiac disease
diverticulitis
dysentery
gallstones
GERD
gingivitis
hiatus hernia
pyloric stenosis
ulcerative colitis
appendix
small intestine
colon
intestine, liver, colon
gallbladder
esophagus
mouth
upper stomach
stomach outlet
large intestine
digestion
absorption
absorption, egestion
absorption, egestion
digestion
digestion
ingestion
digestion
digestion
absorption, egestion
inflammatory
malabsorptive
inflammatory
inflammatory
structural
inflammatory
inflammatory
structural
structural
inflammatory
Making Connections
4. Summary of research on childhood obesity in Canada, from Nelson Science Web links:
Between 1981 and 1996, the incidence of obesity in Canadian children aged 7 to 12 years doubled. In 1996, 35% of
boys were considered to be overweight, and 17% considered obese. In girls, the corresponding numbers were 29% and
15%. Obese children are at risk for a number of problems: Type 2 diabetes; high blood cholesterol levels; high blood
pressure; psychosocial difficulties. Obese children tend to become obese adults, with higher mortality rates.
Uncertainty over the development of obesity remains one of the most important barriers to the development of effective prevention and treatment strategies. Some forms of obesity can be attributed to genetics, but “lifestyle obesities”
are in the majority. Cutting down on high-fat foods and aiming for 30 min exercise a day would be a good policy to
reduce weight or keep excess weight off.
The most effective and least expensive way of reducing weight, and maintaining weight loss, in severely obese
(BMI >35) and very severely obese (BMI >40) people is now considered to involve surgery. A variety of different
methods are available for the treatment of obesity, based on either or both the restriction of energy intake and malabsorption of food. Vertical banded gastroplasty, Roux-en-Y gastric bypass, duodenal switch, and the use of certain
laparoscopic techniques are among the most effective procedures. Intestinal bypass surgery is no longer recommended.
Liposuction of unwanted subcutaneous fat deposits offers no medical benefit and is used extensively for cosmetic
reasons. There are risks to all surgery, especially for the very young and old.
Prevention is the best cure. Students may consider level of physical activity, eating habits (regular meals, avoidance of junk food), family perceptions.
5. If a gallbladder is removed, there is no capacity to store bile. The liver releases it as it is synthesized. In this case, it
would be wise to avoid high-fat meals as they could overload the capacity of bile produced to emulsify the fat. Eating
more frequently, in smaller quantities, is also good advice.
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Exploring
6. Comparison of IBDs, from Nelson Science Web links:
Crohn’s Disease
– chronic condition that causes inflammation in the lining of the small intestine, usually in the last part of the
small intestine called the terminal ileum and cecum
– symptoms include diarrhea, abdominal pain, weight loss, and rectal bleeding
– roughly 500 000 Americans suffer from Crohn’s disease; about 20% have a direct relative with some form of IBD
– men and women are equally affected
– although cause is unknown, theory is that the immune system is reacting to a virus or bacterium that causes
inflammation
– an upper gastrointestinal series and colonoscopy are used for diagnosis
– depending on severity, treatment options include nutritional supplements, drugs, and surgery
– there is currently no cure for the disease
Ulcerative Colitis
– causes inflammation and ulcers in the lining of the rectum and lower part of the colon but can affect the entire
colon
– symptoms are similar to Crohn’s disease (diarrhea, weight loss, and rectal bleeding)
– an estimated 500 000 people in the U.S. have ulcerative colitis, typically in the 15 to 40 age range; it appears
to be hereditary
– the cause is unknown, but like Crohn’s Disease, the immune system is suspected of reacting to a virus or
bacterium that causes inflammation in the intestinal wall
– about 5% of people with ulcerative colitis develop colon cancer
– diagnostic methods include barium enema, colonoscopy, MRI, and CT scan
– depending on the severity, treatments include diet modification, medication, and surgery
– surgery to remove the diseased colon is the only cure
Irritable Bowel Syndrome
– affects about 20% of the Western population and is one of the most common functional gastrointestinal disorders
– symptoms of IBS may appear similar to ulcerative colitis and Crohn’s disease, but it does not cause
inflammation, intestinal bleeding, or lead to cancer
– characterized by chronic abdominal pain, bloating, and altered bowel function such as diarrhea and
constipation, or an alternating pattern between the two
– most often affects people in their late teens to early 40s and may run in families
– diagnosis via X-rays and endoscopy
– no cure; symptoms may be controlled with diet modification, medication, and stress management
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Section 3.6
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(e) The spleen helps to produce and maintain blood cells and is an essential organ in both the digestive and circulatory
systems. Healthy blood cells are required to carry digested nutrients to body cells.
Synthesis
(f) Perch are carnivores. They disable smaller fish by the tail with their sharp teeth, and then swallow the prey headfirst.
The long, straight stomach of the perch allows it to swallow a fish almost the same size as itself. Because a perch has
a diet higher in proteins and fats than carbohydrates, it requires a shorter intestine than an herbivorous fish.
(g) Comparison of perch and human digestive systems:
Components
of digestion
Perch
Human
ingestion
– disables prey with teeth; uses teeth
to position prey for swallowing whole
– uses teeth to break food into pieces for
swallowing
digestion
– mechanical and chemical;
begins in stomach
– relatively large stomach
– pyloric caeca have important secretion
and absorption function, which continue
in intestine
– intestine not differentiated
– liver, gallbladder, and pancreas involved
– mechanical and chemical begins in mouth,
continues in stomach
– relatively smaller stomach
– no pyloric caeca; major portion of
digestion occurs in upper part of
small intestine
– liver, gallbladder, and pancreas involved
– relatively large liver
absorption
– can occur from pyloric caeca to anus
– relatively short intestine
– nutrient absorption from small intestine;
water reabsorption from large intestine
– relatively long small intestine
egestion
– through the anus
– through the rectum and anus
CAREER CONNECTION
Aquaculture managers and operators manage the operation of facilities that cultivate and harvest fish, shellfish, or marine
plants for enhancing wildlife stocks or for commercial sale. This career usually requires a one- or two-year program in
aquaculture, plus several years experience in fishing or aquaculture. Self-employed aquaculture operators must have a
commercial aquaculture or fish hatchery licence, permit, or lease. A listing of Aquaculture Education and Training in
Canada is found on the Nelson Science Web site, along with specific programs. In Ontario, courses are available at
Sir Sandford Fleming College and at the University of Guelph. The Canadian Aquaculture Institute works worldwide to
develop and deliver customized training programs and workshops in the field of aquaculture and related industries. Online
programs are available.
3.8 EXPLORE AN ISSUE: DIET AND THE MEDIA
Understanding the Issue
(Page 194)
1. Body Mass Index (BMI) is used to define normal body weight. This calculation is obtained by dividing weight in
kilograms by height in metres squared. This is an easy calculation, and a more standardized way of assessing ideal
body weight than the use of height-weight charts. Its disadvantage is that it does not take into account the proportion
of muscle mass to fat mass, so a high BMI does not necessarily indicate obesity.
2. The cost of treating obesity and obesity-related diseases is a drain on Canada’s health care system. Conditions such as
coronary artery disease, stroke, osteoarthritis, cancers, diabetes, respiratory diseases, gastrointestinal abnormalities,
and psychosocial difficulties are all related to obesity (e.g., obesity is a risk factor in each disorder).
3. The success rate of losing weight is low: 95% of people who diet gain the weight back within two years. Cycles of
dieting and gaining may be more dangerous to health than maintaining a stable body mass. The use of appetite
suppressants such as amphetamines or laxatives is a dangerous practice.
4. Significant muscular development follows height growth, and many teens desiring to bulk up have not reached height
potential. Protein supplements promote muscle development by increasing food intake beyond the body’s needs.
Bulking up through the use of anabolic steroids is a dangerous practice; negative side effects include mood swings and
prematurely halted growth.
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Section 3.8
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5. Like other systems in the body, the digestive system thrives in homeostasis. Fluctuations in type and quantity of food
ingested trigger changes in digestive processes: amount of digestive enzymes released, muscular contractions, absorption rate, levels of nutrients in the bloodstream, etc. Constant changes cause stress to the system as the body struggles
to react.
TAKE A STAND: WHAT IS HEALTHY?
Answers will vary according to the definition of the issue, individual circumstances and experiences. Connections between
the medical professions, diet industry, media portrayals, and the pursuit of ideal body shapes can be explored on the Nelson
Science Web site at the Student Centre. The following is a sample answer; other ways to define the issue are outlined in
the Teacher’s Resource.
The Issue:
Media pressures to be thin are the cause of eating disorders.
Pro
Con
Anorexia nervosa is characterized as drastic
weight loss from dieting, leading to emaciation,
compromised physical and psychological health,
and sometimes death.
The cause of eating disorders such as anorexia nervosa
and bulimia is unknown.
The social pressure to be thin is the most commonly
known cause of eating disorders.
Anorexia nervosa is not a new disease; it was first identified in 1669, and most commonly after 1873. In neither
period was thinness seen as desirable. Bulimia was
identified in the ancient Greeks.
The most common feature of all eating disorder
victims is that dieting has triggered their condition.
Eating is controlled by many factors, including appetite,
food availability, family, peers, and cultural practices.
Dieting to a body weight leaner than needed for
health is highly promoted by current fashion trends,
the diet industry, and in some sports.
Low self-esteem, feelings of helplessness, and the need
to exert control over some aspect of life may all play as
large a role in eating disorders as desire for thinness.
Professional models have a severe negative
impact on eating disorders.
If an eating disorder runs in the family that may also be
a main cause.
The average American model is 5’11” and weighs
only 117 pounds; the average American woman is 5’4”
and weighs 140 pounds, showing that models are
thinner than 98% of American women.
Several family and twin studies suggest a high inheritability of anorexia and bulimia. Researchers suspect
that multiple genes may interact with environmental and
other factors to increase the risk of developing these
disorders.
In one study, 42% of Grades 1, 2, and 3 girls want to be
thinner, 81% of ten-year-olds are afraid of becoming fat,
and 51% of nine- and ten-year-old girls feel better if they
are on a diet.
The weight loss industry is worth $30 billion a year in
North America.
Gonadal steroids may play a role in eating disorders,
considering their emergence at puberty or soon after,
and the increased risk for eating disorders among girls
with early onset of menstruation.
3.9 THE CIRCULATORY SYSTEM
SECTION 3.9 QUESTIONS
(Page 202)
Understanding Concepts
1. The circulatory system brings oxygen and nutrients to cells; takes wastes away from cells; relays chemical messages
throughout the body; and helps maintain acceptable levels of fluids. The circulatory system is also important in the
body’s immune system and permits the transport of immune cells throughout the body.
2. The circulatory system includes the heart, blood vessels, and the blood. The cardiovascular system (cardio referring
to the heart, and vascular referring to vessels) includes only the heart and blood vessels.
3. Assuming that the average human lifespan is 76 years and assuming an average heart rate of 72 beats per min, the heart
beats approximately 2 876 083 200 times in a lifetime.
72 beats/min 60 min/h 24 h/d 365 d/y 76 y/lifetime 2 876 083 200 beats/lifetime
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