The Digestive System Part 2

The Digestive System Cont’d… Learning Goal: To continue exploring the digestive system of humans. Success Criteria: I know I am succeeding when I can… explain that most digestion takes place in the duodenum in the small intestine through the action of bile, hormones, and many pancreatic and liver enzyme explain that villi and microvilli greatly increase the surface area of the small intestine for absorption explain the roles of the jejunum, ileum and colon, rectum, and anus

The Small Intestine most digestion and absorption of nutrients takes place in the small intestine can be up to 7 m in length lipids and carbohydrates, as well as any remaining proteins, are digested in the small intestine

The Small Intestine Cont’d… three sections of the small intestine: duodenum  where most enzymes are added and digestion takes place jejunum  digestion continues and some nutrients are absorbed Ileum majority of nutrients are absorbed

The Small Intestine Cont’d… the inner surface of the small intestine is adapted to provide the maximum surface area for efficient nutrient absorption the inner layer of the small intestine is folded into ridges and has many small finger-like projections called villi (singular: villus) each of the epithelial cells that make up the villi has even smaller, microscopic projections of the cell membrane called microvilli

The Small Intestine Cont’d… within each villus is a network of tiny blood vessels called capillaries all nutrients, except digested fats, enter the bloodstream through the capillaries digested fats are transported through small vessels called lacteals, lymphatic system, and from there into the bloodstream

The Small Intestine Cont’d… the pyloric sphincter periodically relaxes to release small portions of chyme into the duodenum slow and steady release of chyme into the small intestine prevents overloading and allows time for thorough digestion most of the enzymes required for digestion are added in the duodenum and require the accessory organs

The Pancreas the pancreas is a long, flat gland between the stomach and the duodenum secretes: digestive enzymes hormones that regulate the absorption and storage of glucose from the blood

The Pancreas Cont’d… digestion of carbohydrates (i.e. starch) continues in the duodenum the enzyme amylase (found in saliva) is also secreted by the pancreas

The Pancreas Cont’d… a hormone called cholecystokinin (CCK) is secreted by duodenum and released into the bloodstream signals the pancreas to secrete a variety of substances, including ones that control the pH of the intestine and enzymes that are needed for lipid, carbohydrate, and protein digestion these secretions enter the duodenum through the pancreatic duct CCK also signals the stomach to slow down the speed of digestion so that the small intestine can effectively digest the fats

The Pancreas Cont’d… chyme is acidic (pH of about 2.5) when chyme enters the small intestine, it converts prosecretin into its active form, secretin Sercretin stimulates …. the liver to make more bile the pancreas to secrete lipid and protein enzymes the pancreas to release bicarbonate ions (HCO3-) to neutralize the chyme (pepsin is inactivated which protects the small intestine from stomach acids) secretin also prevents more food from entering the duodenum

The Pancreas Cont’d… pancreas releases trypsinogen and when it reaches the duodenum, an enzyme called enterokinase converts it into active trypsin trypsin breaks down any partially digested proteins that remain other protein-digesting enzymes help break the short protein chains into single amino acid molecules

The Pancreas Cont’d… the pancreas also secretes lipases which is a group of enzymes secreted by the pancreas that digest lipids (fats) in the small intestine lipases break the lipid chains into shorter chains and into individual fatty acid molecules BUT fats in chyme are present as large globules and for lipases to work they need the fat to be in small globules

The Liver the liver is the largest internal organ of the body, located just underneath the diaphragm

The Liver Cont’d… functions produces and secretes bile (emulsifies fats, breaking them into tiny droplets called micelles) produces and stores various nutrients (i.e. glycogen and fat soluble vitamins) removes and breakdowns toxins in our blood, such as alcohol, that have been absorbed by the digestive system

The Gall bladder bile is stored in the gall bladder until food enters the duodenum lipids entering the duodenum stimulate the gall bladder to contract, which causes bile to be squeezed out from the gall bladder into the duodenum through the bile duct

Absorption in the Small Intestine once proteins, carbohydrates, and lipids are broken down, they are absorbed in the jejunum and ileum vitamins, minerals, and water are also absorbed in the small intestine nutrients pass through into the bloodstream, where they are then transported by capillaries to the tissues of the body

The Large Intestine undigested food (the waste) is passed through the large intestine and water, vitamins and ions are absorbed the large intestine is only 1.5 m in length but is two to three times larger in diameter than the small intestine

The Large Intestine Cont’d… the large intestine consists of the following: cecum: pouch that receives processed material from the small intestine colon: the longest part of the large intestine and has four segments (the ascending colon, the transverse colon, the descending colon, and the sigmoid colon) rectum: holds the waste products of digestion anus: external opening that eliminates waste The small intestine does not simply continue on and become the large intestine.

Egestion the absorption of water in the large intestine changes the liquid material in the colon into a soft solid called feces nerves in the wall of the large intestine detect the movement of feces into the rectum which initiates the defecation reflex the anus is surrounded by two sphincter muscles one of which is under voluntary control feces are eliminated through the anus when both sphincters are relaxed The small intestine does not simply continue on and become the large intestine.

The Digestive System Cont’d… Learning Goal: To continue exploring the digestive system of humans. Success Criteria: I know I am succeeding when I can… explain that most digestion takes place in the duodenum in the small intestine through the action of bile, hormones, and many pancreatic and liver enzyme explain that villi and microvilli greatly increase the surface area of the small intestine for absorption explain the roles of the jejunum, ileum and colon, rectum, and anus

Homework Finish Worksheet