A Digestive Journey: “a trip through the donut hole”

1. A Digestive Journey:“a trip through the donut hole”

2. Some Important Definitions INGESTION – the taking of nutrients. DIGESTION – the breakdown of complex organic molecules into smaller components by enzymes. ABSORPTION – the transport of digested nutrients to tissues of the body. EGESTION – the removal of waste food materials from the body.

3. A series of “stations” along a subway

4. Station #1 – “The Mouth” • Teeth (mechanical) • Tongue (mechanical) • Saliva (chemical)

5. Station #2 – The Esophagus • muscular tube, 2 cm in diameter • connects pharynx to stomach • made up of two main muscle layers: I. circular layer • II. longitudinal layer • there is a flap located at the start of the esophagus called the epiglottis, which protects food from entering the windpipe (trachea). • at the endpoints of the esophagus there are sphincters (esophagealand cardiac sphincter, respectively)

6. Station #2 – The Esophagus • FUNCTIONS OF ESOPHAGUS • Moves bolus through to the stomach, • through a series of rhythmic contractions • called peristalsis • (MECHANICAL BREAKDOWN) • The circular and longitudinal muscles contract and release NOTE: the purpose of sphincters is to prevent food from going in the reverse direction (i.e. reflux from the stomach into the esophagus).

7. Station #3 – The Stomach • - J-shaped stretchable organ • - involves sphinctormuscles (pyloric and esophageal/cardiac) • holds about 2L of food and water • - consists of thick layers of smooth muscle and numerous folds called Rugae. • What’s the purpose of rugae? Enable the stomach to contract & expand.

8. Station #3 – The Stomach • Function(s): • - storage of bolus (1.5-2 L) • - MECHANICAL digestion through “churning” • CHEMICAL digestion with acids and enzymes to • convert bolus to chyme • - cardiac and pyloric sphinctors regulate movement of food through digestive tract  keeps food going ONE way. • Gastric pits - secrete hormones and mucus • (mucus forms protective layer) Enzyme Action: - Hydrochloric acid or HCl(secreted by parietal cells) softens food and activates pepsinogen to pepsin - pepsin breaks down PROTEIN into short chains of AA’s Hormonal Action: - Gastrin induces secretion of more mucus

9. Accessory Organs • Salivary Glands (previously discussed) • Pancreas • Liver • Gallbladder

10. Accessory Organs • THE PANCREAS • - lies behind stomach and extends laterally from the duodenum • - finger shaped organ • -15 cm in length • Function(s): • - secretes digestiveenzymes into the small intestines & hormones into the blood • bicarbonate ions NEUTRALIZE the HCl when entering duodenum • releases amylase into small intestine Enzyme Action:(all released into the small intestine) 1) lipase – digests fat 2) amylase – further breakdown of carbohydrates 3) trypsin – breaks down protein into short chains of amino acids

11. Accessory Organs • THE LIVER • - second largest organ / roughly 1.5 kg • - two main parts: the right and left lobes Functions: - produces bile (emulsifies FAT into little fatty globules) - extracts absorbed nutrients or toxins from blood - decomposes toxins (ie. Alcohol, drugs) - key role in regulating body metabolism (homeostasis) - manufactures many essential body proteins - regulates the balance of hormones - regulates body cholesterol Enzyme Action: - high concentration of catalase enzymes that play key role in decomposing toxins (i.e. Alcohol).

12. Accessory Organs • THE GALLBLADDER • “pear-shaped” muscular sac located under the right lobe of the liver • - connected to liver via hepatic duct Function(s): - collects and concentrates the bile that it receives from liver - releases bile to duodenum Hormonal Action: - gall bladder contracts in reaction to hormone cholecystokinin (CCK) to release bile into the duodenum.

13. Station #4 – Small Intestine 3 Parts  Duodenum, Jejunum, Ileum • 1) DUODENUM • one inch tube • connected to stomach & Ileum • Function(s) • digestion and ABSORPTION of most nutrients • - mixes and propels food forward Enzyme Action: - see pancreas Hormonal Action: - Secretin to reduce acidity from food coming from stomach

14. Station #4 – Small Intestine 2) JEJUNUM & ILEUM Enzyme Action: 1) peptidases- break down short chain of amino acids into individual amino acids 2) disaccharidases- breaks disaccharides into simple sugars Hormonal Action: - synthesis of melatonin= skin pigment

15. Station #5 – Large Intestine (Colon) - about 1.5 m in length - divided into 3 parts: I. ascending II. transverse III. descending • Function(s): • - absorb water and some minerals • vitamin K and some B-complex vitamins are produced by resident bacteria. • - hold and compact the unabsorbed material from small intestine.

16. Station #6 – Rectum & Anus • Rectum = 8 inch chamber connected to anus • Anus - 2 inches long, consists of pelvic muscle and two sphincters, surrounded by sphincter muscles • muscles relax to release stool (feces) • - muscles contract to keep stool in place Functions: Rectum - STORAGE of stool Anus – EXPELS WASTE from the body

17. Reviewing – The Use of Cue Cards Take 10 cue cards (one for each “station” and accessory organ in the digestive system. FRONT of the cue card will represent the structure. - write the name of the organ - draw/sketch or print then glue on a labelled diagram BACK of the cue card will represent the functions. - types of physical & chemical digestion - specific functions - enzyme action - hormonal action QUIZ YOURSELF by: - putting the cue cards in order - having someone read one side of the card and you indicate what is on the other side. FRONT - Structure Station #2 – The Esophagus BACK - Function • Physical – peristalsis • Chemical – none • Functions • Moves bolus from pharynx to stomach • sphincters (esophageal & cardiac) prevent food from moving backwards. • Enzyme action – none • Hormonal action – none