Digestion and Absorption: Overview of Food Processing

1. Topic 6.1~ Digestion and Absorption

2. Overview of food processing • 1-Ingestion: act of eating • 2-Digestion: process of food breakdown into monomers • enzymatic hydrolysis of macromolecules • Ex. Proteins, lipids, nucleic acids, carbs (starch and glycogen) broken down to respective monomers (review) • extracellular: breakdown outside cells (in digestive tract) • 3-Absorption: when food molecules pass through a layer of cells such as passing through the villi. • 4- Assimilation:when food actually becomes part of the body's tissue. • 5- Elimination: removal of undigested material Important note: Cellulose remains undigested. Why?

3. Mouth through Stomach • Oral cavity •salivary amylase: begins starch breakdown • Pharynx-- throat •epiglottis– cartilage flap • Esophagus (moves food via peristalsis) to… • Stomach • Primary function = protein digestion • pepsin/pepsinogen • gastric juice (HCl) • acid chyme- • pyloric sphincter– regulates passage of chyme into small intestine

4. Accessory glands • Accessory Glands– secrete substances into the lumen (interior space) of the small intestine • Liver– secretes bile into gall bladder • Gall bladder– Stores bile • Bile emulsifies fat (evenly distributes to prevent clumping) • Think-- why is clumping a problem? • Pancreas • Secretes digestive enzymes into small intestine. http://www.daviddarling.info/images/small_intestine.jpg

5. Important enzymes of the pancreas • Amylase • Lipase • an Endopeptidase • Trypsin is the specific name but you don’t need to know this… • What molecules do each of these help digest respectively?

6. Accesory Gland ducts (note general connections)

7. Small intestine • Small intestine • Primary functions: • Further breakdown of food (enzymatic hydrolysis) • Absorption of nutrients • Essential idea: The structure of the wall of the small intestine allows it to move, digest and absorb food. •duodenum (first 25 cm)– site where chyme mixes with digestive juices from pancreas, liver, gall bladder, and gland cells of the intestine.

8. Small intestine • Contraction of circular and longitudinal muscles mixes the food with enzymes and moves it along the gut.

9. Small intestine • Enzymes digest most macromolecules in food into monomers in the small intestine.

10. Enzymes: Why important?

11. Small intestine • Villi / microvilli (Be able to relate structure to function) • Function: • Villi increase the surface area of epithelium over which absorption is carried out. • Villi absorb monomers formed by digestion as well as mineral ions and vitamins. • Different methods of membrane transport are required to absorb different nutrients.

12. Small intestine • Villi / microvilli (Be able to relate structure to function) Structure: • Each villus has: • Microvilli with protein channels and pumps for nutrient absorption. • a net of capillaries • leads to Hepatic portal vessel– carries blood to liver • Lacteal (lymphatic)= a lymph vessel • Transports fats mixed with cholesterol

13. Draw and Label a villus

14. Skill: Transverse (cross) sections of the small intestine (know tissue layers) • Serosa - the outermost layer consisting of connective tissue which is in contact with body cavities. • Longitudinal muscles - responsible for peristalsis. • Circular muscles - reponsible for peristalsis. • Submucosa - connective tissue that supports the mucosa and that contains large veins and arteries which give rise to the capillary bed of the mucosa. • Mucosa - innermost layer with epithelium for absorption (villi form part of this layer).

15. Think and make a hypothesis! • State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase. note: not part of syllabus anymore but still valuable exercise. Doesn’t need to be written down.

16. Large intestine • Large intestine (colon)- absorption of water, electrolytes, vitamins (B and K) • Cecum (start of large intestine) • Appendix (extension of cecum) • Feces • Rectum/anus • (story: Jesus Alberto) • Digestion video! • http://www.teachertube.com/video/the-journey-of-digestion-329947

17. Draw and Label! (be sure to clearly show connections) Skill: Production of an annotated diagram of the digestive system.

18. Draw and Label

19. Application: Use of dialysis tubing to model absorption of digested food in the intestine. • Discuss: What are some limitations to this model?

20. Utilization: • Some hydrolytic enzymes have economic importance, for example amylase in production of sugars from starch and in the brewing of beer.

21. Option H stuff for rest of slides

22. Digestion (some general vocab) • Peristalsis: rhythmic waves of contraction by smooth muscle • Sphincters: ring-like valves that regulate passage of material • Accessory glands: salivary glands; pancreas; liver; gall bladder

23. Ex: Gastric Juice: Nervous system: gastric juice release due to sight/smell of food Hormonal Action: Gastrin– produced by stomach in response to food causes stomach wall to produce gastric juice Negative feedback– low pH Option H: Control of digestive juice secretion

24. Option H: Small intestine (more) • Membrane bound enzymes in surface cells (ex. Maltase) help with digestion • Jejunum and ileum– parts of small intestine involved in absorption of nutrients and water. Be able to draw ileum! (mucosa and layers of longitudinal and circular muscle) http://science.nhmccd.edu/biol/digestive/ileum.htm

25. Option H • Be able to draw ileum! (mucosa and layers of longitudinal and circular muscle) http://science.nhmccd.edu/biol/digestive/ileum.htm lumen circular muscle layer villi longitudinal muscle layer mucosa transverse section drawing

26. Exocrine Glands and Digestion (Option H) • Exocrine glands- secrete substances through ducts • Secrete enzymes (why important to digestion?) • Acini- the berry-shaped ends of exocrine glands, (where the secretion is produced.) • Duct = the tube the substance travels through • Examples: • Salivary glands • Glands in the stomach wall • Pancreatic glands • Glands in the small intestine

27. Option H: The LIVER… • H.4.1 Outline the circulation of blood through the liver tissue including hepatic artery, hepatic portal vein, sinusoids and hepatic vein. • Hepatic Portal Vein = brings blood with nutrients from small intestine to liver. • Hepatic Artery = brings oxygenated blood to liver. • Sinusoids = vessels that branch off of the Hepatic Portal Vein. • This allows for very close contact of blood with the surrounding tissue.  The cells are capable of removing substances, such as excess nutrients or toxins.   • Hepatic vein--  returns blood back towards the heart. 

28. H.4.2 Explain the need for the liver to regulate levels of nutrients in the blood. • Remove toxic substances.  • Blood homeostasis (of glucose for example)  • H.4.3 Outline the role of the liver in the storage of nutrients including carbohydrate, iron, the vitamins retinol and calciferol. • carbohydrates (conversion of glucose to glycogen), • Iron • vitamin A (retinol) • vitamin D (calciferol).  • The liver cells store these nutrients so they are not excreted. Thus, they are accessible when needed.

29. H.4.4 Describe the process of bile secretion. • Bile secreted by the liver.  • Some components of bile: • bile pigments formed from the breakdown of haemoglobin from worn-out red blood cells. • bile salts produced by liver, are reclaimed by the liver from the blood.    • Bile is secreted into the bile canaliculi which flow to the bile duct.  • bile duct transports the bile to the gall bladder, where it is released by muscular contractions into the duodenum. 

30. H.4.5 Describe the process of erythrocyte and haemoglobin breakdown in the liver including phagocytosis, digestion of globin, and bile pigment formation. • Phagocytosis of old Red blood cells by Kupffer cells which line the sinusoids.  • These cells break down the haemoglobin.  • The protein part (the globin) is converted back into the amino acids which make it up, and these amino acids are then released into the bloodstream.  • The non-protein part (the haem residue) has the iron removed and stored.  • The rest of it is converted into bile pigments. 

31. H.4.6 Outline the synthesis of plasma proteins by the liver.  • Liver makes 90% of the proteins in blood plasma.  • blood-clotting agents prothrombin and fibrin • plasma albumin • globulin (including immunoglobulins) • The liver cells break down amino acids and other nutrients which then are used to make the blood proteins. 

32. Note: not sure where this comes from! Outline the action of endopeptidases and exopeptidases. • Endopeptidases • break down peptides by acting on amino acids toward middle of chain • Ex. Trypsin, chymotrypsin, pepsin • Exopeptidases • Break down peptides by acting on amino acids on end of chain • Ex. Carboxypeptidase, (pancreatic enzyme that cleaves a single amino acid from the carboxylic end of the peptide.)