Download The Digestive System

Chapter 16
The Digestive System
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16-1: The Digestive System
• Consists of digestive tract & accessory
organs
• Functions of digestive system
– Ingestion—food enters digestive tract
– Mechanical processing—moving food
– Digestion—chemical breakdown of food
– Secretion—release enzymes, acids
– Absorption—move nutrients
– Excretion—remove waste products
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Organization of Digestive Tract
• Digestive tract has four layers:
– Mucosa—inner lining; has folds to increase
surface area for absorption
– Submucosa—blood vessels, nerves
– Muscularis externa—smooth muscle cells;
push materials along digestive tract
– Serosa—outer layer
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Movement of Digestive Materials
• Muscle cells in digestive tract trigger waves
of contraction
• Peristalsis
– Waves of contractions propels materials from
one part of digestive tract to another
• Segmentation
– Movements that churn & fragment digested
materials
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16-1 Checkpoint
1. Identify the organs of the digestive system.
2. List and define the six primary functions of
the digestive system.
3. Name the layers of the digestive tract from
superficial to deep.
4. Which is more efficient in propelling
intestinal contents: peristalsis or
segmentation?
16-2: The Oral Cavity
• Mouth opens into the oral cavity
– Senses & analyzes food, begins digestion of
carbs & lipids
• Cheeks, lips, vestibule, gingivae form
boundaries of oral cavity
• Hard & soft palate form roof of oral
cavity; tongue forms floor
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The Tongue
• Manipulates materials inside the mouth
– Also senses temperature, taste
Salivary Glands
• Parotid, sublingual, submandibular
glands
• Produce saliva containing water, mucins,
enzymes
– Begins digestion of carbs
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Teeth
• Perform mastication (chewing)
• Parts of tooth:
– Root anchors tooth; crown is top of tooth
– Enamel covers surface of tooth
– Dentin composes tooth
– Pulp cavity contains blood vessels & nerves
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• Types of teeth:
– Incisors—used in biting/cutting
– Canines—used in tearing
– Bicuspids & molars—used in
crushing/grinding
• First teeth—deciduous teeth (baby
teeth)
– Replaced by permanent teeth
– Wisdom teeth may emerge later
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16-2 Checkpoint
1. Name the structures associated with the
oral cavity.
2. The digestion of which nutrient would be
affected by damage to the salivary
glands?
3. Which type of tooth is most useful for
chopping off bits of raw vegetables?
16-3: Pharynx, Esophagus
The Pharynx
• Passageway for air, food, liquid
The Esophagus
• Moves substances from mouth to stomach
• Meets stomach at lower esophageal
sphincter (cardiac sphincter)
Swallowing
• Food compacted into a bolus
• Phases of swallowing:
– Buccal—moves bolus to back
of mouth, triggers swallowing
reflex
– Pharyngeal—pushes bolus
through pharynx into
esophagus
– Esophageal—peristalsis pushes
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16-3 Checkpoint
1. Describe the function of the pharynx.
2. Name the structure connecting the
pharynx to the stomach.
3. What process is occurring when the soft
palate and larynx elevate, the glottis
closes, and the food bolus moves past the
structures?
16-4: The Stomach
• Stores & breaks down food
– Food bolus becomes chyme
• Regions of stomach
– Cardia—by esophagus
– Fundus—upper bulge of stomach
– Body—majority of stomach
– Pylorus—connects stomach to small intestine;
ends in pyloric sphincter
– Rugae—folds to expand stomach
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The Gastric Wall
• Gastric pits in stomach wall contain
gastric glands
– Release gastric juice containing acid &
enzymes
• Stomach protected from gastric juice by
mucosal barrier
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Regulation of Gastric Activity
• Cephalic phase
– Begins with sight/thought of food
– Prepares stomach for digestion
• Gastric phase
– Food arrives at stomach
– Gastric juices released, contents mixed
• Intestinal phase
– Chyme enters small intestine
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Digestion in the Stomach
• Proteins & carbohydrate digestion
continues in stomach
• Most nutrient absorption does not take
place in stomach
– Nutrients are broken down; some absorption
occurs
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16-4 Checkpoint
1. Name the four main regions of the
stomach.
2. Discuss the significance of the low pH in
the stomach.
16-5: The Small Intestine
• Digests & absorbs 90% of nutrients
• Segments of small intestine
– Duodenum—closest to stomach
– Jejunum—middle segment
– Ileum—last, longest segment; connects to
large intestine at ileocecal sphincter
The Intestinal Wall
• Intestinal lining has folds
– Each fold covered with fingerlike villi to
increase surface area for absorption
Intestinal Movements
• Chyme is pushed along intestine by
peristalsis (takes about 5 hrs)
• Intestinal juice & hormones assist in
digestion & absorption
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16-5 Checkpoint
1. What purpose do the folds and the villi of
the small intestine serve?
2. Name the three segments of the small
intestine from proximal to distal.
16-6: Pancreas, Liver,
Gallbladder
The Pancreas
• Lies behind stomach
• Produces pancreatic juice that contains
enzymes
– Carbohydrases—break down carbs
– Lipases—break down lipids
– Nucleases—break down nucleic acids
– Proteases—break down proteins
The Liver
• Liver divided into lobes
– Gallbladder contained in liver
• Lobes contain liver lobules composed of
hepatocytes
– Hepatocytes release bile to break down fat &
aid in fat digestion
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• Liver functions
– Metabolic regulation—monitor glucose &
nutrients levels
– Blood regulation—detoxifies & filters blood
– Bile production
The Gallbladder
• Stores & concentrates bile before its
release into small intestine
– Concentrated bile forms gallstones
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16-6 Checkpoint
1. Does a high-fat meal raise or lower the
level of bile released into the small
intestine?
2. What is the purpose of the pancreas in
the digestive system? In the endocrine
system?
16-7: The Large Intestine
• Reabsorbs water & vitamins, stores feces
• Segments of large intestine
– Cecum—first segment; location of appendix
– Colon segments—ascending colon,
transverse colon, descending colon,
sigmoid colon
– Rectum—stores feces; ends in anal canal
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Functions of the Large Intestine
• Reabsorption water, bile salts, vitamins, &
organic wastes
• Movements of the large intestine
– Mass movements push materials along
intestine
– Diarrhea results from rapid movements
• Defecation
– Distention of rectal wall triggers defecation
reflex
16-7 Checkpoint
1. Identify the four segments of the colon.
2. What are some structural differences
between the large intestine and the small
intestine?
3. A narrowing of the ileocecal sphincter
would cause problems with movement
between what two organs?
16-8: Digestion & Absorption
• Carbohydrates break down into di- &
monosaccharides
• Lipids break down into fatty acids &
glycerol
• Proteins break down into amino acids
• Fat-soluble & water-soluble vitamins
absorbed during digestion
16-8 Checkpoint
1. An increase in which component of a
meal would increase the number of fatty
acids and glycerol in the small intestine?
2. Why is diarrhea potentially life
threatening but mild constipation is not?