Gastrointestinal Anatomy
KAAP 310
Alimentary Canal and Accessory Organs
• Alimentary Canal:– Mouth (oral cavity)– Pharynx– Esophagus– Stomach– Small intestine– Large intestine– Anus
• Accessory Organs*:– Tongue– Salivary Glands– Liver– Pancreas– Gall bladder
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Mouth
• Oral (buccal) cavity– Bounded by lips, cheeks, palate, and tongue – Lined with stratified squamous epithelium
• Functions– Ingestion– Mechanical digestion– Chemical digestion– Propulsion
Oral Cavity, Pharynx, & Esophagus
Oropharynx
LaryngopharynxHyoid Bone
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Pharynx • Throat, passes air and food via sequential
contraction of muscles
Esophagus• Carries food from throat to stomach,
collapsed when empty• Diaphragm and esophageal sphincter (and
gravity) keep food in stomach
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Figure 23.13 Deglutition (swallowing).Bolus of food
Tongue
Pharynx
Epiglottis
Glottis
Trachea
During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx.
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Uvula
Bolus
Epiglottis
Esophagus
The pharyngeal-esophageal phase begins as the uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus.
The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters.
Peristalsis moves food through the esophagus to the stomach.
The gastroesophageal sphincter surrounding the cardial oriface opens, and food enters the stomach.
Relaxed muscles
Circular musclescontract
Bolus of food
Longitudinal musclescontract
Gastroesophagealsphincter closed
Relaxedmuscles
Circular muscles contract
Gastroesophagealsphincter opens
Upperesophagealsphincter
Bolus
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Stomach
Slide 1
Stomach
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Stomach
• Mechanical breakdown• Denaturation of proteins by HCl• Enzymatic digestion of proteins by pepsin (and milk
protein by rennin in infants)• Delivers chyme to small intestine• Lipid-soluble alcohol and aspirin absorbed into blood• Secretion of intrinsic factor for vitamin B12 absorption
• Only stomach function essential for life• B12 needed mature red blood cells
Small Intestine
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Small Intestine
• Major organ of digestion and absorption• 2-4 m long; from pyloric sphincter to illeocecal
valve • Subdivisions
– Duodenum (retroperitoneal)– Jejunum (attached posteriorly by mesentery)– Ileum (attached posteriorly by mesentery)
Duodenum
• Curves around head of pancreas; shortest part – 25 cm
• Bile duct (from liver) and main pancreatic duct (from pancreas)
Jejunum & Illeum
• Jejunum– Extends from duodenum to ileum– About 2.5 m long
• Ileum– Joins large intestine at illeocecal valve– About 3.6 m long
Digestion in Small Intestines
• Chyme from stomach contains– Partially digested carbohydrates and proteins – Undigested fats
• 3–6 hours in small intestine– Most water absorbed– ~ All nutrients absorbed
• Small intestine, like stomach, no role in ingestion or defecation
Large Intestine
• Cecum – first part of large intestine• Appendix – masses of lymphoid tissue
– Part of MALT of immune system– Bacterial storehouse recolonizes gut when
necessary– Twisted enteric bacteria accumulate and
multiply
Large Intestine
• Retroperitoneal except for transverse and sigmoid regions
• Ascending colon (right side – to level of right kidney) right colic (hepatic) flexure
• Transverse colon left colic (splenic) flexure
• Descending colon (left side) • Sigmoid colon in pelvis rectum
Large Intestine
Anus
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Digestion in Large Intestine
• Residue remains in large intestine 12–24 hours• No food breakdown except by enteric bacteria• Vitamins (made by bacterial flora), water, and
electrolytes (especially Na+ and Cl–) reclaimed• Major functions - propulsion of feces to anus;
defecation• Colon not essential for life
Accessory Organs
Liver
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Accessory Organs
• Pancreas– Endocrine function
• Pancreatic islets secrete insulin and glucagon
– Exocrine function• Acini (clusters of secretory cells) secrete pancreatic juice
– To duodenum via main pancreatic duct
• Liver– Many functions; only digestive function bile production
• Bile – fat emulsifier
• Gallbladder– Chief function bile storage
• Spleen
Rectum and Anus
• Rectum– Three rectal valves stop feces from being passed
with gas (flatus)• Anal canal
– Last segment of large intestine– Opens to body exterior at anus
• Sphincters– Internal anal sphincter—smooth muscle– External anal sphincter—skeletal muscle
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Figure 23.29b Gross anatomy of the large intestine.
Rectal valveRectumHemorrhoidalveinsLevator ani muscle
Anal canal
External analsphincterInternal analsphincterAnal columns
Pectinate lineAnal sinuses
Anus
Digestive Processes
• Six essential activities1. Ingestion2. Propulsion3. Mechanical breakdown4. Digestion5. Absorption6. Defecation
Digestive ProcessesIngestion• Bringing food in via the mouth
Propulsion• Swallowing – voluntary• Peristalsis – involuntary contraction and relaxation of muscles in organ walls
Mechanical breakdown• Chewing, mixing food with saliva, churning food in stomach, and segmentation – rhythmic local
constrictions of the small intestine
Digestion• Enzymes break down complex food molecules to their chemical building blocks
Absorption• Passage of digested end products from the lumen of the GI tract into the blood or lymph
Defecation• Elimination of indigestible substances from the body via the anus
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© 2013 Pearson Education, Inc.
Figure 23.2 Gastrointestinal tract activities.
Ingestion
Mechanicalbreakdown
Digestion
Propulsion
Absorption
Defecation
Food
PharynxEsophagus• Chewing (mouth)
• Swallowing (oropharynx)• Peristalsis (esophagus, stomach, small intestine, large intestine)
Stomach
Lymphvessel
Small intestineLargeintestine
Bloodvessel
Mainly H2OFeces
Anus
• Churning (stomach)• Segmentation (small intestine)
Functions of Gastrointestinal OrgansMouth
– Ingestion, propulsion, mechanical breakdown, digestion
Pharynx & Esophagus– Propulsion
Stomach– Propulsion, mechanical breakdown, digestion, absorption
Small Intestine & associated accessory organs (liver, gallbladder, pancreas)– Propulsion, mechanical breakdown, digestion, absorption
Large Intestine– Digestion, absorption, propulsion, defecation
© 2013 Pearson Education, Inc.
Figure 23.3 Peristalsis and segmentation.
Frommouth
Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, moving food along the tract distally.
Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving food forward then backward.Food mixing and slow food propulsion occur.