1. Gastrointestinal Anatomy
KAAP 310

2. Alimentary Canal and Accessory Organs
Mouth (oral cavity)
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Anus
Accessory Organs*:
Tongue
Salivary Glands
Liver
Pancreas
Gall bladder

3. Mouth Oral (buccal) cavity Functions
Bounded by lips, cheeks, palate, and tongue
Lined with stratified squamous epithelium
Functions
Ingestion
Mechanical digestion
Chemical digestion
Propulsion

4. Oral Cavity, Pharynx, & Esophagus
Oropharynx
Laryngopharynx
Hyoid Bone

5. 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

6. Figure 23.13 Deglutition (swallowing). Slide 1
Bolus of food
Tongue
Uvula
Pharynx
Bolus
Epiglottis
Epiglottis
Glottis
Trachea
Upper
esophageal
sphincter
Bolus
Esophagus
During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. 1
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. 2
The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters. 3
Relaxed muscles
Peristalsis moves food through the esophagus to the stomach. 4
The gastroesophageal sphincter surrounding the cardial oriface opens, and food enters the stomach. 5
Relaxed
muscles
Circular muscles
contract
Bolus of food
Longitudinal muscles
contract
Circular muscles contract
Gastroesophageal
sphincter closed
Gastroesophageal
sphincter opens
Stomach
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7. Stomach

8. 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

9. Small Intestine

10. 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)

11. Duodenum Curves around head of pancreas; shortest part – 25 cm
Bile duct (from liver) and main pancreatic duct (from pancreas)

12. Jejunum & Illeum Jejunum Ileum Extends from duodenum to ileum
About 2.5 m long
Ileum
Joins large intestine at illeocecal valve
About 3.6 m long

13. 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

14. 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

15. 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

16. Large Intestine
Anus

17. 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

18. Accessory Organs Liver

19. Accessory Organs Pancreas Liver Gallbladder Spleen 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

20. Rectum and Anus Rectum Anal canal Sphincters
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

21. Anal columns Pectinate line Anal sinuses Anus
Figure 23.29b Gross anatomy of the large intestine.
Rectal valve
Rectum
Hemorrhoidal
veins
Levator ani muscle
Anal canal
External anal
sphincter
Internal anal
sphincter
Anal columns
Pectinate line
Anal sinuses
Anus
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22. Digestive Processes Six essential activities Ingestion Propulsion
Mechanical breakdown
Digestion
Absorption
Defecation

23. Digestive Processes Ingestion Propulsion Mechanical breakdown
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
Segmentation mixes food with digestive juices and makes absorption more efficient by repeatedly moving different parts of the food mass over the intestinal wall.

24. Ingestion Mechanical breakdown Digestion Propulsion Absorption
Figure Gastrointestinal tract activities.
Ingestion
Mechanical
breakdown
Digestion
Propulsion
Absorption
Defecation
Food
Pharynx
Esophagus
Chewing (mouth)
• Swallowing
(oropharynx)
• Peristalsis
(esophagus,
stomach,
small intestine,
large intestine)
Stomach
Lymph
vessel
Small
intestine
Large
Blood
Mainly H2O
Feces
Anus
Churning (stomach)
Segmentation
(small intestine)
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25. Functions of Gastrointestinal Organs
Mouth
Ingestion, propulsion, mechanical breakdown, digestion
Pharynx & Esophagus
Propulsion
Stomach
Propulsion, mechanical breakdown, digestion, absorption
Small Intestine & associated accessory organs (liver, gallbladder, pancreas)
Large Intestine
Digestion, absorption, propulsion, defecation

26. Figure 23.3 Peristalsis and segmentation.
From
mouth
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.
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