Question

MCAT Tutorial: The Digestive System

Answer 1

\({\bf{Basic~Path:}}\) ingestion -> mouth -> pharynx -> esophagus -> gastroesophogeal sphincter -> start of digestion -> stomach -> pyloric sphincter -> small intestines -> large intestines -> colon -> rectum - > "butthole" [can't use the proper scientific word b/c of the filter ;_;]

\({\bf{Ingestion~(Mouth):}}\)
- begins in mouth
- chewing (mastication) physically breaks down food and increases surface area --> bolus
- salivary amylase: enzyme for hydrolysis of starch
- salivary lipase: enzyme for hydrolysis of lipids
- epiglottis: covers the trachaea (the sensation of "food going down the wrong pipe" is food entering the trachae by mistake)
- peristalsis: involuntary muscle contraction that moves food through the digestive system

\({\bf{The~Stomach:}}\)
- where digestion starts
- churning: contractions of the stomach wall --> turns bolus to chyme
- rugae: folds of the stomach
- parietal cells: secrete HCl
- chief cells: secrete pepsinogen
- mucous cells: secrete mucous (duh)
- enteroendocrine cells: secrete enzymes

\({\bf{The~Liver:}}\)
- produces bile
- bile breaks down fats
- bile goes to the duodenum or to the gallbladder for storage
- regulates glucose
- glycogenolysis: breakdown of glycogen into blood
- glycogenesis: formation of glycogen from glucose
- glucuneogenesis: formation of glucose from non-carbs
- ketosis: use of lipids for energy instead of carbohydates, produces ketone bodies and may result in ketoacidosis (lowering of pH)
- lipogenesis: synthesis of fats from carbohydrates and proteins

Answer 2

\({\bf{Pancreas:}}\)
- produce trypsinogen and chymotrypsinogen (digestive proteases) and secrete them into the small intestine
- produce sodium bicarbonate (neutralizes chyme)

\({\bf{Small~Intestines:}}\)
- three components: duodenum, jejunum, ileum
- contains microvilli/villi

- duodenum: connected to stomach
> uses trypsinogen and chymotrypsinogen to break polypeptides apart for digestion
> emulsifies lipids using bile salts
> products of lipase digestion form chylomicrons (lipoproteins that transport lipids through bloodstream)

- jejunum and ileum: water absorption

\({\bf{Large~Intestines:}}\)
- colon, cecum, appendix, rectum
- absorbs water and electrolyes
- saccharides broken down by bacteria
- forms feces
- stores feces (rectum), excretion controlled by the a. sphincter

Answer 3

Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is the 2nd Edition Barron's Prep book for the new MCAT