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Chapter 3: Digestion, Absorption, and Transport. What Are…?. Digestion : The process of breaking down food into individual molecules small enough to be absorbed through the intestinal wall Absorption : The process of moving nutrients from the gastrointestinal (GI) tract into the bloodstream - PowerPoint PPT Presentation
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Chapter 3: Digestion, Absorption, and Transport
© 2010 Pearson Education, Inc.
What Are…?
Digestion: The process of breaking down food into individual molecules small enough to be absorbed through the intestinal wall
Absorption: The process of moving nutrients from the gastrointestinal (GI) tract into the bloodstream
Transport: The process of moving absorbed nutrients throughout the body through the circulatory and lymph systems
Elimination: The excretion of undigested and unabsorbed food through the feces
© 2010 Pearson Education, Inc.
Gastrointestinal Tract
A 23-foot-long muscular tube comprised of the organs of the digestive tract
Extends from the mouth through the esophagus, stomach, and small and large intestines to the anus
Sphincters allow food to pass from one organ to the next
Saliva Dissolves small food particles Contains the enzyme amylase, which begins to break down
carbohydrate
Figure 3.1
Journey through the GI Tract: Ingestion
Figure 3.3
Sphincters at Work
Figure 3.1
Journey through the GI Tract: Digestion and Absorption
Figure 3.4
Anatomy of the Stomach
© 2010 Pearson Education, Inc.
Small Intestine
Most digestion occurs in the small intestines Extends from the pyloric sphincter to the ileocecal valve Contains three sections
• Duodenum
• Jejunum
• Ileum Takes 3 to 10 hours for food to traverse the small intestine
Villi require proper nutrients or will deteriorate and flatten causing malabsorption
Figure 3.5
Anatomy of the Small Intestine
Figure 3.6
Anatomy of the Large Intestine
© 2010 Pearson Education, Inc.
Large Intestine
Site of water, sodium, potassium, and chloride absorption Bacteria produces vitamin K, thiamin, riboflavin, biotin,
and vitamin B12
• Only biotin and vitamin K can be absorbed In the large intestine, 1 liter of fluid material is gradually
reduced to 200 grams of brown fecal material
• Brown color is due to unabsorbed iron mixed with yellowish-orange substance called bilirubin
• Greater the iron content, the darker the feces
Figure 3.1
Journey through the GI Tract: Elimination
Final stage of defecation is influenced by age, diet, prescription medications, health, and abdominal muscle tone
Figure 3.7
The Accessory Organs
© 2010 Pearson Education, Inc.
The Accessory Organs
Liver
• Is the first organ to receive absorbed nutrients from the portal vein
• Is essential in carbohydrate metabolism
• Produces proteins
• Manufactures bile salts that are used to digest fats
• Is the site of alcohol metabolism
• Removes and degrades toxins and excess hormones
© 2010 Pearson Education, Inc.
The Accessory Organs
Gallbladder
• Receives bile from the liver via common hepatic duct
• Releases bile into small intestine via common bile duct Pancreas
• Endocrine function – releases hormones to maintain blood glucose levels
• Exocrine function – secretes digestive enzymes into the small intestine
© 2010 Pearson Education, Inc.
Quick Review
In the mouth, saliva mixes with and moistens food Bolus of food mixes with gastric juices in the stomach,
becoming chyme The majority of digestion and absorption occur in the small
intestine Undigested residue enters the large intestine, where water
is removed from the chyme The remnants of digestion reach the anus and exit the body
in the feces Accessory organs include the liver, which produces bile,
the gallbladder, which concentrates and stores it, and the pancreas, which produces enzymes and hormones.
© 2010 Pearson Education, Inc.
Propelling Food through the GI Tract
Food is propelled through the GI tract by synchronized contractions of the diagonal, circular, and longitudinal muscles
Two primary contractions are
• Peristalsis – Squeezes food through the GI tract
• Segmentation – Shifts food back and forth along the GI tract
- Allows contact with surface of small and large intestine and increase absorption
• Dependent on coordination between muscles, nerves, and hormones
Figure 3.8
Peristalsis and Segmentation
© 2010 Pearson Education, Inc.
Quick Review
Food is propelled through GI tract by strong muscular contractions
• Peristalsis squeezes food and propels it forward
• Segmentation shifts food back and forth along intestinal walls
© 2010 Pearson Education, Inc.
Chemical Digestion of Food
Aided by digestive enzymes and other substances Regulated by hormones Completed by the time the food reaches the large intestine
© 2010 Pearson Education, Inc.
Chemical Digestion of Food
Enzymes Proteins Catalyze hydrolysis
• Compatible with a specific compound or nutrient• Optimal pH range for enzyme function• Optimal temperature for enzyme function
Reactions do not change them Named by type of substrate plus suffix –ase
• Example: sucrase and maltase• Exception: pepsin
Secreted along the GI tract Majority produced by the pancreas
Concentration of hydrogen ions in a solution
The more hydrogen ions (H–) the more acidic
The more hydroxide ions (OH–) the more basic
pH
© 2010 Pearson Education, Inc.
Quick Review
Foods are chemically digested by hydrolysis Enzymes catalyze hydrolysis when
• Correct substrate is available
• pH is optimal
• Temperature is optimal Secretions of the GI tract help optimize the environment for
digestion
• Saliva
• Gastric juices
• Bile
• Bicarbonate
© 2010 Pearson Education, Inc.
Nutrient Absorption
Majority of absorption takes place in the small intestine
• Nutrients are absorbed via
- Passive diffusion – nutrients move from high concentration to low concentration; no energy is required
- Facilitated diffusion – nutrients move from high concentration to low concentration with the help of a carrier protein; no energy is required
- Active transport – nutrients move from low concentration to high concentration with the help of a carrier protein, energy is required
- Endocytosis – cell forms a vesicle to surround and engulf a nutrient
Figure 3.10
Nutrient Absorption
© 2010 Pearson Education, Inc.
Nutrient Absorption
Some absorption takes place in the stomach and large intestine
• Water and salt are absorbed in the large intestine
© 2010 Pearson Education, Inc.
Quick Review
Brush border of the small intestine is the major site of nutrient absorption
Water and salt not absorbed in the small intestine are absorbed in the large intestine
Nutrients are absorbed by
• Passive diffusion
• Facilitated diffusion
• Active transport
• Endocytosis
© 2010 Pearson Education, Inc.
Hormones Affect Digestion
The GI tract releases hormones
• Enterogastrones
- Are produced and secreted by the cells lining the stomach and small intestine
- Gastrin, secretin, cholesystokinin (CCK), and gastric inhibitory peptide (GIP)
- Influence GI motility, stomach emptying, gallbladder contraction, intestinal absorption, and hunger
• Release is stimulated by the types of food passing through the digestive tract
© 2010 Pearson Education, Inc.
Hormones Affect Digestion
Hormones
• Regulate digestion by controlling
- The release of gastric and pancreatic secretions
- Peristalsis
- Enzyme activity
© 2010 Pearson Education, Inc.
How Does the Nervous System Affect Digestion?
Lets you know when you need to eat and drink Extrinsic nerves originate in the brain and spinal cord Intrinsic nerves are woven into the lining of the esophagus,
stomach, and small and large intestine Hormones work with nerves to communicate feelings of
hunger and fullness
• Ghrelin – hormone of hunger
• Peptide YY – signals that you have eaten or are full
© 2010 Pearson Education, Inc.
Quick Review
Enterogastrones regulate digestion by stimulating or inhibiting the release of stomach, small intestine, pancreas, and gallbladder secretions, and influencing GI motility
• Gastrin, secretin, cholecystokinin, and gastric inhibitor peptide
Extrinsic and intrinsic nerves communicate and interpret changes in the GI tract
• Affect gastric motility, release or inhibition of digestive juices, and hunger
• Ghrelin and peptide YY communicate with the nervous system
- Help decide when to eat and when to stop eating
© 2010 Pearson Education, Inc.
• Water-soluble nutrients
GI tract Capillaries
• Water-soluble nutrients
Hepatic Portal Vein • Water-
soluble nutrients
Liver
Transportation of Nutrients Throughout the Body Nutrients are absorbed into the circulatory or lymphatic
system
• Water-soluble nutrients are absorbed into the circulatory system
- Carbohydrates, amino acids, and water-soluble vitamins
© 2010 Pearson Education, Inc.
• Fat-soluble nutrients
Lymph Capillaries
• Fat-soluble nutrients
Lymphatic vessels • Fat-
soluble nutrients
Thoracic Duct
Transportation of Nutrients Throughout the Body
• Fat-soluble nutrients are absorbed into the lymphatic system
- Fat-soluble vitamins, long-chain fatty acids, and proteins too large to be transported via the capillaries
© 2010 Pearson Education, Inc.
Quick Review
The circulatory and lymph system transport absorbed nutrients throughout the body and deliver them to the cells
Water-soluble nutrients are transported via the circulatory system
• Carbohydrates, proteins, and water-soluble vitamins Fat-soluble nutrients are transported via the lymph system
• Fat-soluble vitamins and long-chain fatty acids
© 2010 Pearson Education, Inc.
Common Digestive Disorders
Digestive disorders can range from annoying to serious in nature
The esophagus, stomach, gallbladder, and large and small intestines can all be affected by problems ranging from ulcers to cancer
© 2010 Pearson Education, Inc.
Disorders Affecting the Esophagus
Heartburn, also known as indigestion or acid reflux
• The lower esophageal sphincter doesn’t close properly, allowing HCl from the stomach to flow into the esophagus
• Chronic heartburn and stomach acid reflux are typical of gastroesophageal reflux disease (GERD)
- Certain foods and lifestyle factors are generally associated with GERD
• Dietary changes, behavior modification, antacids, prescription drugs, or surgery may help
© 2010 Pearson Education, Inc.
Disorders Affecting the Esophagus
Esophageal cancer
• This is one of the most common cancers of the digestive tract
• Sufferers are typically males over age 50 who smoke and drink heavily, living in urban areas
• Treatment can include surgery, radiation, and chemotherapy
© 2010 Pearson Education, Inc.
Disorders Affecting the Stomach
Belching
• Generally caused by swallowing amounts of air
• It usually happens as a result of eating too fast, drinking carbonated beverages, or anxiety
© 2010 Pearson Education, Inc.
Disorders Affecting the Stomach
Stomachache can occur for a number of reasons
• Gastroenteritis (stomach flu) is the inflammation of the stomach or intestines
- It can be caused by a variety of viruses
- Symptoms can include nausea, vomiting, diarrhea, and abdominal cramping
- Treat symptoms through rest, rehydration, and eating soft foods
• Consuming food or drink fluid contaminated with a pathogenic microbe can cause vomiting, abdominal cramps, diarrhea, and fever
© 2010 Pearson Education, Inc.
Disorders Affecting the Stomach
Ulcers
• Helicobacter pylori, a bacterium, is often involved in the creation of ulcers
• Common symptoms are vomiting, fatigue, bleeding, general weakness, and burning pain
• Treatment can include prescription drugs, dietary recommendations, and/or surgery
An untreated ulcer can result in peritonitis, scar tissue that can obstruct food and cause vomiting and weight loss, and greater risk for stomach cancer
© 2010 Pearson Education, Inc.
Disorders Affecting the Gallbladder
Gallbladder disease
• Diagnosed most frequently in women, older Americans
• Obesity and rapid weight loss are contributing factors
• An unhealthy gallbladder can create gallstones
- Treatment includes surgery for gallbladder removal, prescription medication, shock-wave therapy, or a combination of therapies
- The body eventually adapts to the removal of the gallbladder by secreting bile directly into the duodenum
An Ulcer and a Large Gallstone
© 2010 Pearson Education, Inc.
Disorders Affecting the Intestines
Flatulence
• Intestinal gas, which needs to be released 10 to 20 times a day
• Caused by:
- foods high in fiber and starch
- eating quickly
- drinking carbonated beverages
- lack of exercise
- smoking
© 2010 Pearson Education, Inc.
Disorders Affecting the Intestines
Diarrhea: the passage of watery, loose stools more than three times a day
• Generally the result of bacterial, viral, or parasitic infections that cause food and fluids to pass too quickly through the colon
- Chronic diarrhea may be the sign of a more serious problem
- Untreated diarrhea can lead to malnutrition
• Diarrhea can lead to dehydration and potentially death, particularly in children and the elderly
© 2010 Pearson Education, Inc.
Disorders Affecting the Intestines
Constipation: infrequent passage of dry, hardened stools
• Often due to insufficient fiber or water intake.
- Exercise, normal eating patterns, and proper rest can help resolve constipation
- Laxatives should be used sparingly as they can cause dehydration, salt imbalances, and laxative dependency
• Colon cleansing (enema) is not recommended as a treatment
© 2010 Pearson Education, Inc.
Disorders Affecting the Intestines
Hemorrhoids: swelling of the veins of the rectum and anus
• Can lead to bleeding, itching, and/or pain
• Caused by a variety of factors, including diarrhea and constipation
• Treatment includes increased dietary fiber and fluid intake
- Some symptoms (itching and pain) can be relieved through use of creams, ice packs, and soaking in a warm bath
- Severe cases may require surgery
© 2010 Pearson Education, Inc.
Disorders Affecting the Intestines
Irritable bowel syndrome (IBS): changes in colon rhythm
• Those with IBS experience an overresponse to colon stimuli, resulting in alternating patterns of diarrhea, constipation, and abdominal pain
• The exact cause is not known
• Treatment includes increased dietary fiber, stress management, and prescription drugs
© 2010 Pearson Education, Inc.
Disorders Affecting the Intestines
Ulcerative colitis: a chronic inflammation of the large intestine, resulting in ulcers in the lining of the colon
• Tends to run in families
• Afflicts both men and women, beginning between the ages of 15 and 30
• There is no known cause or cure
• Treatment includes drug therapy and surgery
© 2010 Pearson Education, Inc.
Disorders Affecting the Intestines
Crohn’s disease
• Similar to ulcerative colitis, but ulcers can occur throughout the GI tract
• There is no known cause or cure
• Treatment includes drug therapy and possibly surgery Celiac disease
• Consuming foods containing gluten leads to damage of the small intestine
© 2010 Pearson Education, Inc.
Sample Celiac Disease
Serum Test
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Disorders Affecting the Intestines
Colon cancer
• The third-leading cause of cancer death
- One of the most curable cancers if detected early
• It begins with polyps on the lining of the colon that are often small, benign, and can be surgically removed
- Polyps can develop into cancerous tumors if not detected early
• Treatment includes radiation, chemotherapy, or surgery
• Survival rates vary depending on age, treatment response, stage of cancer diagnosis
© 2010 Pearson Education, Inc.
Quick Review
© 2010 Pearson Education, Inc.
Putting It All Together
The digestive process