Digestion & Absorption To the small intestines….and beyond….

So far…mechanical and chemical digestion in the mouth and stomach leave us with a “liquidy” substance called CHYME. This continues to the small intestine to be further digested and absorbed…..

Important digestive and absorptive functions –Secretions and buffers provided by pancreas, liver, gall bladder –Most digestion takes place here –7m in length, 2.5cm in diameter Three subdivisions: –Duodenum (most digestion occurs here) –Jejunum –Ileum Small intestine

Regions of the Small Intestine

The chyme coming from the stomach is very acidic….. The small intestine does not have a way to protect itself like the stomach (mucus) Many digestive juices are added at the top of the small intestine through the common bile duct The Pancreas releases biocarbonate (HCO 3 - ) into the top of the small intestine that neutralizes the acid (HCl)

In the small intestine digestion continues…. 1.Carbs are completely broken down into simple sugars by enzymes called disaccaridases that are specific to the carb. Maltase to break down maltose, lactase to break down lactose… 2.Lipids (fats) are emulsified by bile salts, then, broken down by special enzymes called lipidases into molecules of fatty acids and glycerol or phospholipids 3. Proteins are broken down into smaller proteins by trypsin and into individual amino acids by erepsin.

Nutrient absorption: Most nutrient absorption occurs in the small intestine The walls have long finger like tubes called villi which increase surface area for absorption

Chemistry of Digestion: Carbohydrates

Organs that add digestive juices: Through the common bile duct Pancreas Liver/ gall bladder

Pancreas: Secretes bicarbonate to neutralize stomach acid Secretes insuline to keep blood glucose levels in equilibrium (homeostasis) Secretes trysinogen (is converted to trypsin in small intestine) that breaks down proteins Secretes erepsin that finishes the breakdown of proteins into amino acids.

Liver/ Gall Bladder Liver produces bile that speeds up fat digestion. When the stomach is empty, the bile is stored in the gall bladder. Bile emulsifies (physically breaks down) large globules of fats…..same as dish washing detergent does for your dishes…

Main Functions of the liver: 1.Synthesis: produce bile salts 2.Breakdown: removes nitrogen (toxic) from digested food to be excreted in urine 3.Storage: glucose to glycogen (storage molecule) and back to maintain blood sugar levels 4.Detoxification: convert harmful compounds (i.e. alcohol) to less harmful substances to be excreted

On to the large intestine and absorption… By the time food reaches the large intestine, digestion is complete. In the large intestine, water is absorbed (makes feces solid rather than liquid). Vitamins produced by the bacteria such as E. coli, are absorbed. Toxins are eliminated.

The Intestinal Wall

Functions of the large intestine 1. Reabsorb water and compact material into feces 2. Absorb vitamins produced by bacteria 3. Store fecal matter prior to defecation

The Whole Thing…

What goes in must come out…