Download Digestive tract

Digestive Tract
• Digestive tract also called
gastrointestinal (GI) tract
– Is a muscular tube
– Extends from oral cavity to anus:
• Passes through pharynx, esophagus, stomach,
and small and large intestines
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Accessory Organs
Figure 16-1
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Digestive Tract
Figure 16-1
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Functions of the Digestive
System
1. Ingestion
–
Occurs when materials enter digestive tract via the
mouth
2. Mechanical processing
–
–
Crushing and shearing
Makes materials easier to propel along digestive tract
3. Digestion
–
The chemical breakdown of food into small organic
fragments for absorption by digestive epithelium
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The Movement of Digestive Materials
• Peristalsis
– Consists of waves of muscular contractions
– Moves a bolus along the length of the digestive
tract
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The Movement of Digestive Materials
•
Peristaltic Motion
1.
Circular muscles contract behind bolus:
•
While circular muscles ahead of bolus relax
2. Longitudinal muscles ahead of bolus contract:
•
Shortening adjacent segments
3. Wave of contraction in circular muscles:
•
Forces bolus forward
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Peristalsis
Figure 16-3
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Peristalsis
Figure 16-3
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Oral Cavity
Figure 16-4b
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The Tongue
•
Manipulates materials inside mouth
•
Functions of the tongue
–
Mechanical processing some crushing, moving around
–
Manipulation to assist in chewing and to prepare material
for swallowing
–
Sensory analysis by touch, temperature, and taste
receptors
–
Secretion of mucins (slime) and enzymes (lingual lipase)
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Oral Cavity
• Salivary Glands
– Produce 1.0 to 1.5 liters of saliva each day:
• 70% by submandibular glands
• 25% by parotids
• 5% by sublingual glands
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The Salivary Glands
Figure 16-5
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Oral Cavity
• Saliva
– 99.4% water
– 0.6% includes:
• Electrolytes (Na+, Cl–, and HCO3–)
• Buffers
• Antibodies
• Enzymes
• Waste products
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The Teeth
• Tongue movements pass food across
occlusal surfaces of teeth
• Chew (masticate) food
• Tooth structure
– Dentin:
• A mineralized matrix similar to that of bone
• Does not contain cells
– Pulp cavity:
• Receives blood vessels and nerves through the
root canal
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The Teeth
• Tooth Structure
– Root:
• Of each tooth sits in a bony socket (alveolus)
– Crown:
• Exposed portion of tooth
• Projects beyond soft tissue of gingiva
• Dentin covered by layer of enamel
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The Teeth
Figure 16-6a
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Types of Teeth
•
Dental Arcades (Arches)
–
Contain four types of teeth:
1.
2.
3.
4.
Incisors
Cuspids (canines)
Bicuspids (premolars)
Molars
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Dental Succession
• Primary Teeth
– Also called deciduous teeth, milk teeth, or baby
teeth
– 20 temporary teeth of primary dentition
– Five on each side of upper and lower jaws:
• 2 incisors
• 1 cuspid
• 2 deciduous molars
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Primary Teeth
Figure 16-6b
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Dental Succession
• Secondary Dentition
– Also called permanent dentition
– Replaces deciduous teeth
– 32 permanent teeth
– Eight on each side, upper and lower:
• 2 incisors
• 1 cuspid
• 5 molars
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Secondary Teeth
Figure 16-6c
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The Pharynx
• A common passageway for solid food,
liquids, and air
• Regions of the pharynx
– Nasopharynx
– Oropharynx
– Laryngopharynx
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The Esophagus
• A hollow muscular tube
• About 25 cm (10 in.) long and 2 cm (0.80 in.)
wide
• Solid food and liquids to the stomach
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Swallowing
• Also called deglutition
– Can be initiated voluntarily
– Proceeds automatically
– Check out this swallowing xray:
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The Stomach
• Anatomy of the Stomach
– The stomach is shaped like an expanded J:
– Shape and size vary from individual to individual
and from one meal to the next. (supersize me?)
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Anatomy of the Stomach
Figure 16-8a
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Anatomy of the Stomach
Figure 16-8b
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The Gastric Wall
• Histology of the Stomach
– Simple columnar epithelium lines all portions of
stomach. (Oh I remember those)
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Digestion in the Stomach
• Stomach performs preliminary digestion of
proteins.
– Some digestion of carbohydrates and lipids.
• Stomach contents
–
–
–
–
Become more fluid
pH approaches 2.0
Pepsin activity increases
Protein disassembly begins
• Although digestion occurs in the stomach,
nutrients are not absorbed there
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The Small Intestine
• Plays key role in digestion and
absorption of nutrients
• 90% of nutrient absorption occurs in
the small intestine
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The Small Intestine
• The Duodenum
– The segment of small intestine closest to the
stomach
– “Mixing bowl” that receives chyme from stomach
and digestive secretions from pancreas and liver
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The Small Intestine
• The Jejunum
– Is the middle segment of the small intestine
– 2.5 meters (8.2 ft) long
– Is the location of most:
• Chemical digestion
• Nutrient absorption
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The Small Intestine
• The Ileum
– The final segment of the small intestine
– 3.5 meters (11.48 ft) long
– Ends a sphincter that controls flow of
material from the ileum into the large
intestine
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Segments of the Intestine
Figure 16-10
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The Intestinal Wall
Figure 16-11a
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The Intestinal Wall
Figure 16-11b
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The Intestinal Wall
Figure 16-11c
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Intestinal Movements
• Chyme arrives in duodenum
– Weak peristaltic contractions move it
slowly toward jejunum:
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Intestinal Secretions
• Watery intestinal juice
– 1.8 liters per day enter intestinal lumen
– Moisten chyme
– Assist in buffering acids
– Keep digestive enzymes and products of
digestion in solution
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The Pancreas
• Lies posterior to the stomach
– From duodenum toward spleen
• Pancreatic Secretions
– 1000 mL (1 qt) pancreatic juice per day
– Contain pancreatic enzymes
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The Pancreas
Figure 16-13a
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The Pancreas
• Pancreatic Enzymes
• Break down starches
• Break down complex lipids
• Break certain proteins apart
• Release products (e.g., fatty acids) that are easily
absorbed
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The Liver
• Is the largest visceral organ
– (1.5 kg; 3.3 lb)
– (hepa means liver…..hepatitis?)
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The Surface Anatomy of the
Liver
Figure 16-14a
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The Surface Anatomy of the
Liver
Figure 16-14b
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The Gallbladder
• Is a pear-shaped, muscular sac
• Stores and concentrates bile prior to
excretion into small intestine
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The Gallbladder
• Functions of the Gallbladder
– Stores bile
– Releases bile into duodenum when triggered by
body. (when it is kind of full but not really)
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The Gallbladder
• Physiology of the Gallbladder
– Full gallbladder contains 40–70 mL bile
– Bile composition gradually changes in
gallbladder:
• Water is absorbed
• Bile salts and solutes become concentrated
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The Large Intestine
• Is horseshoe shaped
• Extends from end of ileum to anus
• Also called large bowel
• Is about 1.5 meters (4.9 ft) long and 7.5 cm (3
in.) wide
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The Large Intestine
• Functions of the Large Intestine
– Reabsorption of water
– Compaction of intestinal contents into
feces
– Absorption of important vitamins produced
by bacteria
– Storage of fecal material prior to
defecation
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The Large Intestine
Parts of the Large Intestine
1. Cecum:
•
The pouchlike first portion
2. Colon:
•
The largest portion
3. Rectum:
•
The last 15 cm (6 in.) of digestive tract
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The Large Intestine
• The Cecum
– Is an expanded pouch
– Receives material arriving from the ileum
– Stores materials and begins compaction
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The Large Intestine
• Appendix
– Is a slender, hollow appendage about 9 cm (3.6
in.) long. Doesn’t do anything.
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The Large Intestine
• The Colon
– Has a larger diameter and thinner wall than
small intestine
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The Large Intestine
• The Rectum
– Forms last 15 cm (6 in.) of digestive tract
– Is an expandable organ for temporary storage of
feces
– Movement of fecal material into rectum triggers
urge to defecate
• The anal canal is the last portion of the
rectum
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The Large Intestine
• Anus
– Also called anal orifice
– Is exit of the anal canal
– Has keratinized epidermis like skin
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The Large Intestine
• Anal Sphincters
– Internal anal sphincter:
• Circular muscle layer of muscularis externa
• Has smooth muscle cells, not under voluntary control
– External anal sphincter:
• Encircles distal portion of anal canal
• A ring of skeletal muscle fibers, under voluntary control
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Figure 16-17a
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The Large Intestine
Figure 16-17b
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The Functions of the Large Intestine
• Physiology of the Large Intestine
– Less than 10% of nutrient absorption
occurs in large intestine
– Prepares fecal material for ejection from
the body (doesn’t that sound nice?)
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The Functions of the Large Intestine
• Absorption in the Large Intestine
– Reabsorption of water
– Reabsorption of bile salts:
– Absorption of vitamins produced by
bacteria
– Absorption of organic wastes
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The Functions of the Large Intestine
• Vitamins
– Are organic molecules
– Are important as cofactors or coenzymes in
metabolism
– Normal bacteria in colon make three
vitamins that supplement diet
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The Functions of the Large Intestine
Three Vitamins Produced in the Large Intestine
1.
Vitamin K (fat soluble):
•
Required by liver for synthesizing four clotting factors,
including prothrombin
2. Biotin (water soluble):
•
Important in glucose metabolism
3. Pantothenic acid: B5 (water soluble):
•
Required in manufacture of steroid hormones and some
neurotransmitters
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The Functions of the Large Intestine
• Toxins
– Bacteria break down peptides in feces and
generate:
• Ammonia:
– as soluble ammonium ions
• Indole and skatole:
– nitrogen compounds responsible for odor of feces
• Hydrogen sulfide:
– gas that produces “rotten egg” odor
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The Functions of the Large Intestine
• Toxins
– Bacteria feed on indigestible
carbohydrates (complex polysaccharides):
• Produce flatus, or intestinal gas, in large
intestine
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The Functions of the Large Intestine
• Movements of the Large Intestine
– Distension of the rectal wall triggers defecation reflex
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The Functions of the Large Intestine
• Elimination of Feces
– Requires relaxation of internal and external
anal sphincters
– Reflexes open internal sphincter and close
external sphincter
– Opening external sphincter requires
conscious effort
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Digestion
• Essential Nutrients
– A typical meal contains:
• Carbohydrates
• Proteins
• Lipids
• Water
• Electrolytes
• Vitamins
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Digestion
• Digestive Enzymes
– Are secreted by:
•
•
•
•
Salivary glands
Tongue
Stomach
Pancreas
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Homestatic Imbalances
• Heartburn: (Gastric reflux) when gastric juices are
forced back into your esophagus. Hurts like a heart
attack hence the name.
• Ulcer: Any open sore in the lining of the GI tract.
caused by stress, smoking, diet, bacteria.
• Gallstones: If bile (in gall bladder) stays too long
cholesterol crystals form and block the duct.
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Homestatic Imbalances
• Cirrhosis: Chronic inflammatory condition that
hardens/scars tissue. Caused by alcohol and/or drug
abuse
• Jaundice: When bile pigments accumulate through
body (you look yellow)
•
Hepatitis: Swelling of the liver usually due to a virus.
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Homestatic Imbalances
• Constipation: Large intestine holds contents too long
and absorbs too much water. Caused by lack of
exercise, fiber, and/or fluids.
• Diarrhea: When contents pass through before water
is absorbed (gastroenteritis). Usually caused by
microorganisms.
• Hemorrhoids: Blood vessels in the rectum and anus
swell and rupture. Itches and hurts.
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Homestatic Imbalances
• Diverticulitis: When your diet lacks fiber, colon works
too hard and increases pressure on its walls. Can be
life threatening if the mucosa ruptures.
• Appendicitis: Swelling of the appendix. Life
threatening if it ruptures. Lower right abdomin pain.
• Dental plaque: Masses of bacteria and other particles
clinging to your teeth.
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Digestion
• The end
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