GI_anatomy

Report
Gastrointestinal Anatomy
KAAP 310
Alimentary Canal and Accessory Organs
• Alimentary Canal:
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Mouth (oral cavity)
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Anus
• Accessory Organs*:
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Tongue
Salivary Glands
Liver
Pancreas
Gall bladder
http://1.bp.blogspot.com/-JcKROgygeKo/UW4PTqKCiII/AAAAAAAABxg/g0UShGYLiYc/s1600/digestive+system.jpg
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
Hyoid Bone
http://biology-forums.com/index.php?action=gallery;sa=view;id=8468
Laryngopharynx
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
Figure 23.13 Deglutition (swallowing).
Slide 1
Bolus of food
Tongue
Uvula
Pharynx
Bolus
Epiglottis
Epiglottis
Glottis
Trachea
Esophagus
1 During the buccal phase, the upper
esophageal sphincter is contracted.
The tongue presses against the hard
palate, forcing the food bolus into the
oropharynx.
2 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.
4 Peristalsis moves
food through the
esophagus to the
stomach.
Relaxed muscles
Circular muscles
contract
Upper
esophageal
sphincter
3 The constrictor muscles of the
pharynx contract, forcing food into
the esophagus inferiorly. The upper
esophageal sphincter contracts
(closes) after food enters.
Relaxed
muscles
5 The gastroesophageal
sphincter surrounding the
cardial oriface opens, and
food enters the stomach.
Bolus of food
Longitudinal muscles
contract
Circular muscles contract
Gastroesophageal
sphincter closed
Gastroesophageal
sphincter opens
Stomach
© 2013 Pearson Education, Inc.
Bolus
Stomach
http://apbrwww5.apsu.edu/thompsonj/Anatomy%20&%20Physiology/2020/2020%20Exam%20Reviews/Exam%203/stomach%20diagram.jpg
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
http://www.cea1.com/wp-content/uploads/2013/08/Small-Intestine-Duodenum.jpg
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
http://safetyca.info/wp-content/uploads/2013/06/pancreas-accessory-organthe-digestive-system-atxrijk1.jpg
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
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
© 2013 Pearson Education, Inc.
Digestive Processes
• Six essential activities
1.
2.
3.
4.
5.
6.
Ingestion
Propulsion
Mechanical breakdown
Digestion
Absorption
Defecation
Digestive Processes
Ingestion
•
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
http://cnx.org/content/m46502/latest/2405_Digestive_Process.jpg
Figure 23.2 Gastrointestinal tract activities.
Ingestion
Mechanical
breakdown
• Chewing (mouth)
• Churning (stomach)
• Segmentation
(small intestine)
Digestion
Food
Pharynx
Esophagus
Propulsion
• Swallowing
(oropharynx)
• Peristalsis
(esophagus,
stomach,
small intestine,
large intestine)
Stomach
Absorption
Lymph
vessel
Small
intestine
Large
intestine
Blood
vessel
Mainly H2O
Feces
Defecation
© 2013 Pearson Education, Inc.
Anus
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)
– Propulsion, mechanical breakdown, digestion, absorption
Large Intestine
– Digestion, absorption, propulsion, defecation
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.
© 2013 Pearson Education, Inc.
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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