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Digestive System

Digestive System. Chapter 32. The digestive system takes in food (ingests it), breaks it down physically and chemically into nutrient molecules (digests it), and absorbs the nutrients into the bloodstream. Then in rids the body of the indigestible remains (defecates).

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Digestive System

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  1. Digestive System Chapter 32

  2. The digestive system takes in food (ingests it), breaks it down physically and chemically into nutrient molecules (digests it), and absorbs the nutrients into the bloodstream. Then in rids the body of the indigestible remains (defecates). Overview of the Digestive System

  3. Separated into two groups: • Alimentary canal aka gastrointestinal (GI) tract • Performs the whole menu of digestive functions (ingests, digests, absorbs, and defecates) • Ex. Mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus • Accessory digestive organs • Assist the process of digestive breakdown in various ways • Ex. Teeth, tongue, several large digestive glands Organs of Digestive System

  4. The pharynx is subdivided into the nasopharynx(part of respiratory system), the oropharynx, and the laryngopharynx (continues to the esophagus) Parts of the pharynx

  5. The walls of the pharynx contain two skeletal muscle layers • Inner layer runs longitudinally • Outer layer runs circularly • Alternating contractions of these two muscle layers propel food through the pharynx into the esophagus aka peristalsis Pharynx

  6. Runs from pharynx through the diaphragm to the stomach • About 25 cm (10 inches) long • Conducts food to the stomach through peristalsis • The reason why food can get to your stomach even if you are hanging upside down. Esophagus aka gullet

  7. J-shaped, nearly hidden by the liver and diaphragm on the left side of the abdominal cavity Parts of stomach

  8. Stomach collapses when empty into large folds called rugae

  9. Gastric glands secrete acidic gastric juices. • Mixing waves- chyme (processed food that resembles heavy cream) forms and passes to duodenum Parts of stomach

  10. Major digestive organ • Average length of 8-20 feet • Hangs in sausage-like coils in the abdominal cavity, suspended by mesentery Parts of the Small intestine

  11. Mesentery

  12. Larger in diameter than small intestine but shorter in length • About 5 ft long • Major function is the dry out the indigestible food by absorbing water and to eliminate residues as feces • Frames the small intestines on three sides: appendix, colon, rectum and anal canal Parts of the large intestine

  13. Colon

  14. Ingestion-placing food in mouth • Propulsion-swallowing, peristalsis • Mechanical digestion-mixing in mouth, churning in stomach, segmentation in small intestine; physically breaking down into smaller particles • Chemical digestion-food broken down into building blocks by enzymes; water is necessary as dissolving medium and softening agent Functions of Digestive System

  15. Absorption-digested food must enter the mucosal cells by active or passive transport processes; mostly in small intestine • Defecation-elimination of indigestible residues from the GI tract vis the anus in the form of feces Functions of Digestive System

  16. Food physically broken down by chewing • Salivary amylase (enzyme) mixes with food and chemically breaks starch into maltose • More saliva is produced when food enters the mouth • The pharynx and esophagus simply provide a passageway to the stomach • No digestion occurs here Activities of Mouth, Pharynx, Esophagus

  17. Little chemical digestion occurs in the stomach • Only aspirin and alcohol are absorbed in the stomach, very little else • As food enters and fills the stomach, the walls stretch and the muscle layers compress and pummel the food breaking it apart physically and mixing the food with gastric juice to make chyme • It takes about 4 hours for the stomach to empty completely and 6 hours if the meal has a high fat content Activities of the stomach

  18. Carbohydrates and proteins have started digestion in the stomach but fat digestions hasn’t occurred. • By the end of the small intestine, digestion is complete and nearly all food absorption has occurred • Bile and pancreatic juice enter the small intestine together to emulsify fat for absorption and digestion Activities of the Small intestine

  19. All that remains from the small intestine is some water, indigestible food (plant fiber), and large amounts of bacteria. • Residue spends 12-24 hours in the large intestine • Bacteria metabolize remaining nutrients and release methane and hydrogen sulfide gas -> flatus • About 500 mL of gas is produced each day, more when certain foods are eaten Activities of Large intestine

  20. Bacteria also make some vitamins in the large intestine • Ex. E. coli makes vitamin K • Vitamins, some ions, and most of the remaining water are absorbed here • Feces are delivered to the rectum containing undigested food residues, mucus, millions of bacteria, and just enough water for smooth passage Activities of the Large intestine

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