IB Biology Digestion

• Duodenum
• -CCK is produced to stimulate bile release from the galbladder.
• -Secretin stimulates the production of enzymes and bicarbonate from the pancreas
• -Majority of hydrolysis occurs here
• - Peristalsis continues
• -Enzymes in villi continue digestion
• -The villi absorb nutrients and transfer them to capillaries (amino acidsk sugars, and nucleotides) or lacteal (lipids)
• Ileum and Jejunum continue absorption

• -stores and mixes food, begins chemical digestions of protein by secreting gastric juices containing HCl and pepsin.
• -- produces gastrin, when food is present, to stimulate its own production of gastric juices.
• -- secretes mucus to protect itself from self digestion
• -- Stomach undergoes peristalsis to churn and mix food with acid and pepsion to produce chyme.

• Source: Pancreas
• Substrate: Triglycerides (fats)
• Products: glycerol and 3 fatty acids
• optimum pH: 8/basic

• Source: pancreas: trypsin
• Substrate: Protein
• Products: smaller polypeptides
• Optimum pH: 8/basic
• ----or----
• Source: Stomach, Pepsin
• Substrate: Proteins
• Products: polypeptides
• Optimum pH:2

• Source: Salivary glands/pancreas
• Substrate: Polysaccharides
• Products: Smaller polysaccharides and maltose
• Optimum pH: 7/basic

• - the human body temperature is optimal for human enzymes, and speeds up digestive reactions, such as hydrolysis. Elevated temperature alone is insufficient to speed up reactions.
• - Enzymes accelerate the process of hydrolysis, which allows for more frequent eating

• -Breakdown macromolecules in food to monomers that are able to be absorbed by the body
• - Allows for the consumption of large food items, which increases efficiency
• -Nutrients must enter the cells lining the digestive tract to be carried by the blood stream
• - Macromolecules in food are different that those in human cells
• - Monomers must be reassembled to make the correct human proteins and other macromolecules

• -absorption of water
• -flora of bacteria produce vitamins
• -compaction of feces

Absorption is the uptake of small nutrient molecules such as nucleotides, amino acids and simple sugars into the epithelial cells lining the small intestine. Assimilation is the incorporation of absorbed nutrients into the structure of cells.

• -Villi are finger like projections of the epithelium of the small intestine which increase surface area for membrane pumps which transport nutrients into the cells of the epithelium.
• -The cells of the villus are covered in microvilli which increase surface area, therefore increasing absorption.
• -There are capillaries in the interior of the villus that absorb nutrients directly into the blood stream.
• -Central capillary-like structure called the lacteal absorbs fat and connects directly to the lymphatic system.
• -The epithelial cells of the brush border have enzymes embedded in the membrane, which complete digestion

salivary, gastric

The exocrine portion of the pancreas comprises rings of acinar cells surrounding small branches of the pancreatic duct. The acinar cells secrete pancreatic juice via the pancreatic duct to the duodenum. In order to make these enzymes there would need to be alot of rough Er to support ribosomes and Golgi apparatus to process the products and secrete them by vesicles.

• -Saliva contains amylase which digests polysaccharides, buffers which nuetralize acids, anti bacterial compounds, and mucin.
• -Gastric Juices- HCl, pepsin(ogen), mucus, resulting in a paste called chymee when mixed with food.
• - Pancreatic Juice- contains many hydrolytic enzymes (nucleases, proteases, lipase, amylase) bicarbonate (nuetralizes acid in chyme)
• - Both saliva and pancreatic juice contain amylase
• -Gastric Juice and Pancreatic Juice contain proteases (pepsin and trypsin)
• - Saliva pH 7, gastric jucice pH 2, pancreatic juice 7.5-8.2

• Secreted by the epithelial lining
• Parasympathetic stimulation of the stomach through the vagus nerve increases secretion
• Stretch receptiors in the stomach stimulate the release of gastrin from cells in the mucous of the stomach (simple reflex)
• Gastrin released into the blood stream, acting back on the stomach, causing peristalsis to increase
• Gastrin also causes secretion of more gastric juice by the stomach

• Enzymes embedded in the cell membrane of epithelial cells hydrolyze many different molecules
• -Dissaccharides (sucrase cleaves sucrose into glucose and fructose), dipeptidases, amino peptidases (small polypeptides into single amino acids), nucleotidases->nucleosidases (break nucleotides into sugar, phosphate, and nitrogenous base components)
• -Ensure that digestion is completed (polymers converted to monomers) so material can be absorbed

• The alimentary canal is the digestive tract
• Enzymes that digest starch by hydrolyzing its alpha linkages are unable to hydrolyze the beta linkages of cellulose because of the distinctly different shapes of these two molecules.

• They are secreted as inactive precursors so they don't hydrolyze the cells that are secreting them (damage teh lining and we get an ulcer)
• Pepsinogen is converted to Pepsin by HCl in the lumen of the stomach, and pepsin then converts more pepsinogen.
• Trypsinogen is converted to trypsin by enteropeptidase which is embedded in the membrane of the epithelial cells of the duodenum

• Helicobacter pylori attacks the mucus lining of the stomach, causing inflammation
• Gastric Juice attacks the stomach tissue
• If damage is severe and long term, ulcers and cancers can occur

Lipid molecules tend to coalesce and are only accessible to lipase at the lipid-water interface. Bile molecules have a hydrophilic end and a hydrophobic end, and thus prevent lipid droplets coalescing. The maximum surface is exposed to lipases. There is a need for lipase to be water soluble and to have an active site to which a hydrophobic substrate binds

• microvilli: small fingerlike projections of the plasma membrance of epithelial cells on the villus, they increase surface area for 2 things: embedded enzymes and absorption of digested food)
• Mitochondria are numerous- membrance pumps and pinocytosis require atp
• Pinocytotic vesicles are used to take in droplets of nutrient containing fluid
• Tight Junctions- cement cells of epithelium together to prevent leakage of material in the lumen into the rest of the body

• Facilitated diffusion: move through channels down concentration gradient (fructose)
• Active transport: membrane pumps move amino acids, glucose, peptides, and vitamins against their concentration gradients (require ATP) into cells
• Endocytosis: intake of larger materials/fluid through a vesicle.

• Cellulose: wrong linkages
• Lignin: presentin woody materials
• Bile pigments: waste product from red blood cell breakdown in liver
• Bacteria feed on and multiply in the material in the colon
• Intestinal cells shed from lining