GI_anatomy

Transcript GI_anatomy

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 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 Laryngopharynx Hyoid Bone http://biology-forums.com/index.php?action=gallery;sa=view;id=8468

• 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).

Bolus of food Slide 1 Tongue Pharynx Epiglottis Glottis Trachea Uvula Bolus Epiglottis 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.

Relaxed muscles Circular muscles contract Bolus of food Longitudinal muscles contract Esophagus 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.

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 Bolus The gastroesophageal sphincter surrounding the cardial oriface opens, and food enters the stomach.

Circular muscles contract Gastroesophageal sphincter closed

Stomach

Gastroesophageal sphincter opens

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 B 12 absorption • Only stomach function essential for life • B 12 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  necessary recolonizes gut when – Twisted  multiply enteric bacteria accumulate and

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 http://test.classconnection.s3.amazonaws.com/232/flashcards/464232/png/large_intestine.png

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

Liver

Accessory Organs

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 – fat emulsifier bile production

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

Digestive Processes

• Six essential activities 1. Ingestion 2. Propulsion 3. Mechanical breakdown 4. Digestion 5. Absorption 6. 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

Small intestine Large intestine Defecation Food Pharynx Esophagus Propulsion • Swallowing (oropharynx) • Peristalsis (esophagus, stomach, small intestine, large intestine) Stomach Absorption Lymph vessel Mainly H 2 O Feces Blood vessel 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.

Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving food forward then backward.

Food mixing and slow food propulsion occur.