May 7th, 2012

Today in class we took some practice quizzes and discussed the calorimetry lab.

Homework

• finish calorimetry lab, due tomorrow
• design a quiz, due tomorrow
• study for Tissues, Excretion and Digestion test, Thursday
• make sure you've read the chapters (21 and 22)

NEXT SCRIBE: Emma

Digestion Notes

There are 4 stages of digestion.

• Ingestion: eating food
• Digestion: breaking down the food you eat into small molecules that your body can use
• Absorption: the cells in the lining of the digestive tract take in the molecules and transport them throughout the body using the bloodstream
• Elimination: getting rid of undigested wastes

There are 2 types of digestion.

• Mechanical Digestion: physical processes like chewing and stomach churning
• Chemical Digestion: breaking down food with enzymes
• Hydrolysis: breaking down of polymers into monomers using the atoms from water
• Hydrolases: digestive enzymes that catalyze hydrolysis
• Enzymes: specific molecules that start chemical reactions

The alimentary canal is a fancy name for the digestive tract. It has hollow cativities where food passes through to be digested and absorbed (in red), accessory organs (in blue) and enzymes (in purple). The process of digestion starts in the mouth...

Mouth (oral cavity)

• chewing, lubricates food, swallowing into the pharynx (first part of the throat, before the split between the trachea and esophagus
• attached to the mouth are 3 pairs of salivary glands: release saliva (1 liter a day) and salivary amylase
• salivary amylase: breaks starches into sugars (maltose)

Esophagus

• muscular tube, uses muscle contractions called peristalsis to push food into the stomach
• no enzymes

Stomach

• stores food for 2 to 6 hours, can hold 2 liters of food and water
• muscular, churns food and gastric acid into a mixture called acid chyme
• contains gastric juice: pH of .8 to 2 (VERY acidic), hydrochloric acid (HCl) that kills bacteria and activates pepsin, pepsin: breaks proteins into amino acids, rennin: breaks down milk proteins
• stomach lining coated in mucus to protect itself from gastric juice, replaced every 2 to 3 days
• top of the stomach is closed off by the cardiac sphincter (esophageal sphincter in the picture) and the end of the stomach is closed off by the pyloric sphincter
• sphincter: muscular ring that contricts a part of the body until materials need to exit or enter

Liver

• produces bile: emulsifies fats, breaking big fat droplets into little fat droplets so they are accessible to enzymes
• bile is stored, concentrated and released by the neighboring gall bladder
• bile is secreted into the duodenum

Pancreas

• pancreatic juice: contains trypsin, lipase and amylase, neutralizes stomach acids in the duodenum
• trypsin: breaks down proteins into amino acids
• lipase: breaks down fats (lipids) into glycerol and fructose
• pancreatic amylase: breaks down starches into sugars (maltose)
• pancreatice juice is secreted into the duodenum

Small Intestine

• 2.5 centimeters wide, 6 meters long
• duodenum: first part of the small intestine, mixes pancreatic juice, bile and intestinal juice, 90% of digestion
• peptidase: breaks down proteins into amino acids
• maltase: breaks down maltose (disaccharide) into 2 glucose molecules (monosaccharide)
• sucrase: breaks down sucrose (disaccharide) into glucose (monosaccharide) and fructose (monosaccharide)
• lactase: breaks down lactose (disaccharide) into glucose (monosaccharide) and galacatose (monosaccharide)
• small intestine completes digestion and does most of the aborption
• villi: tiny projections on the lining of the intestine, increase surface area for absorption, absorbs nutrients and passes them into the sorrounding capillaries

Large Intestine

• 5 centimeters wide
• colon: majority of large intestine, absorbs water and excess salts
• appendix: small projection where the small and large intestines meet, no purpose in humans, possible function: to store extra "good" bacteria that the digestive system needs?
• rectum: end of the large intestine, stores wastes (feces)
• anus: final sphincter fo the digestive system

Pictures
http://science.howstuffworks.com/environmental/life/cellular-microscopic/cell2.htm
http://en.wikipedia.org/wiki/Mouth
http://www.umm.edu/patiented/articles/stomach_000329.htm
http://www.emedicinehealth.com/pancreatitis/article_em.htm
http://missinglink.ucsf.edu/lm/IDS_106_LowerGI/Lower%20GI/mainpages/smallintestine.htm