Transcript Chapter 3: Digestion, Absorption, and Transport

Chapter 3: Digestion,
Absorption, and
Transport
What Are…?
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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
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Gastrointestinal Tract
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A 23-foot-long muscular tube comprised of the organs of
the digestive tract
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Extends from the mouth through the esophagus, stomach,
and small and large intestines to the anus
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Sphincters allow food to pass from one organ to the next
Saliva
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Dissolves small food particles
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Contains the enzyme amylase, which begins to break down
carbohydrate
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Journey through the GI Tract: Ingestion
Figure 3.1
Sphincters at Work
Figure 3.3
Journey through the GI Tract: Digestion
and Absorption
Figure 3.1
Anatomy of the Stomach
Figure 3.4
Small Intestine
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Most digestion occurs in the small intestines
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Extends from the pyloric sphincter to the ileocecal valve
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Contains three sections
• Duodenum
• Jejunum
• Ileum
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Takes 3 to 10 hours for food to traverse the small intestine
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Anatomy of the Small Intestine
Villi require proper nutrients or will
deteriorate and flatten causing
malabsorption
Figure 3.5
Anatomy of the Large Intestine
Figure 3.6
Large Intestine
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Site of water, sodium, potassium, and chloride absorption
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Bacteria produces vitamin K, thiamin, riboflavin, biotin,
and vitamin B12
• Only biotin and vitamin K can be absorbed
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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
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Journey through the GI Tract:
Elimination
Final stage of
defecation is
influenced by age,
diet, prescription
medications, health,
and abdominal
muscle tone
Figure 3.1
The Accessory Organs
Figure 3.7
The Accessory Organs
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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
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The Accessory Organs
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Gallbladder
• Receives bile from the liver via common hepatic duct
• Releases bile into small intestine via common bile duct
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Pancreas
• Endocrine function – releases hormones to maintain
blood glucose levels
• Exocrine function – secretes digestive enzymes into the
small intestine
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Quick Review
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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.
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Propelling Food through the GI Tract
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Food is propelled through the GI tract by synchronized
contractions of the diagonal, circular, and longitudinal
muscles
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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
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Peristalsis and Segmentation
Figure 3.8
Quick Review
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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
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Chemical Digestion of Food
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Aided by digestive enzymes and other substances
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Regulated by hormones
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Completed by the time the food reaches the large intestine
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Chemical Digestion of Food
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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
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pH
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Concentration of
hydrogen ions in a
solution
The more hydrogen ions
(H–) the more acidic
The more hydroxide
ions (OH–) the more
basic
Quick Review
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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
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Nutrient Absorption
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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
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Nutrient Absorption
Figure 3.10
Nutrient Absorption
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Some absorption takes place in the stomach and large
intestine
• Water and salt are absorbed in the large intestine
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Quick Review
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Brush border of the small intestine is the major site of
nutrient absorption
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Water and salt not absorbed in the small intestine are
absorbed in the large intestine
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Nutrients are absorbed by
• Passive diffusion
• Facilitated diffusion
• Active transport
• Endocytosis
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Hormones Affect Digestion
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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
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Hormones Affect Digestion
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Hormones
• Regulate digestion by controlling
- The release of gastric and pancreatic secretions
- Peristalsis
- Enzyme activity
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How Does the Nervous System Affect
Digestion?
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Lets you know when you need to eat and drink
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Extrinsic nerves originate in the brain and spinal cord
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Intrinsic nerves are woven into the lining of the esophagus,
stomach, and small and large intestine
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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
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Quick Review
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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
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Transportation of Nutrients Throughout
the Body
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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
Hepatic
Portal Vein
Water-soluble
nutrients
GI tract
Capillaries
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• Watersoluble
nutrients
• Watersoluble
nutrients
Liver
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
• Fatsoluble
nutrients
Lymph
Capillaries
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Lymphatic
vessels
• Fatsoluble
nutrients
• Fatsoluble
nutrients
Thoracic
Duct
Quick Review
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The circulatory and lymph system transport absorbed
nutrients throughout the body and deliver them to the cells
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Water-soluble nutrients are transported via the circulatory
system
• Carbohydrates, proteins, and water-soluble vitamins
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Fat-soluble nutrients are transported via the lymph system
• Fat-soluble vitamins and long-chain fatty acids
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Common Digestive Disorders
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Digestive disorders can range from annoying to serious in
nature
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The esophagus, stomach, gallbladder, and large and small
intestines can all be affected by problems ranging from
ulcers to cancer
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Disorders Affecting the Esophagus
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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
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Disorders Affecting the Esophagus
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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
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Disorders Affecting the Stomach
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Belching
• Generally caused by swallowing amounts of air
• It usually happens as a result of eating too fast, drinking
carbonated beverages, or anxiety
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Disorders Affecting the Stomach
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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
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Disorders Affecting the Stomach
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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
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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
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Disorders Affecting the Gallbladder
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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
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An Ulcer and a Large Gallstone
Disorders Affecting the Intestines
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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
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Disorders Affecting the Intestines
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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
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Disorders Affecting the Intestines
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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
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Disorders Affecting the Intestines
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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
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Disorders Affecting the Intestines
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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
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Disorders Affecting the Intestines
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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
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Disorders Affecting the Intestines
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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
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Celiac disease
• Consuming foods containing gluten leads to damage of
the small intestine
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Sample
Celiac
Disease
Serum Test
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Disorders Affecting the Intestines
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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
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Quick Review
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Putting It All Together
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The digestive process
Absorb
into
circulation
Eat food
Digest to food to
nutrients in the GI
tract
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Deliver
nutrients
to the cells