Parts of the digestive system
- mouth
- salivary glands
- esophagus
- stomach
- small intestine
- accessory organs: pancreas, liver, gall bladder
- large intestine
- rectum and anus
Mouth (role in digestion)
- breaks food down mechanically
- voluntary
Salivary glands (role in digestion)
- secrete saliva
- saliva breaks down food chemically (specifically starches: contains amylose)
- helps make bolus
Esophagus (role in digestion)
- pathway for food to travel to the stomach
- movement of food by peristalsis (waves of muscle contractions)
Stomach (role in digestion)
- further breaks down food
- contains HCl (stomach acid), helps break food down chemically: low pH breaks bonds, and kills foreign bacteria
- muscle contraction breaks down food mechanically
- enzyme pepsin helps break down protein (chemically)
small intestine: duodenum (role in digestion)
- upper half of SI
- liver and gall bladder secrete bile which neutralizes the HCl and emulsifies fats
- contains amylases and lipase which digest carbohydrates and fats (pancreatic)
- trypsin digests polypeptides
Small intestine: ileum (role in digestion)
- lower part of the SI
- nutrients absorbed into the blood through villi and microvilli
Pancreas (accessory organ) (role in digestion)
- secretes enzymes such as lipase, amylase and protease into the SI
- neutralizes acidic chyme (food when it is btwn the stomach and SI) thru the use of sodium bicarbonate
Liver (accessory organ) (role in digestion)
- secretes bile to break up lipid droplets
- bile is stored in gall bladder
Gall bladder (accessory organ) (role in digestion)
- stores bile from liver
Large intestine (role in digestion)
- absorbs water from food
- formation of feces
Rectum and anus
- rectum stores feces
- anus releases feces
Role of peristalsis in digestion
- peristalsis = series of muscle contractions which move food along the alimentary canal
- in SI, mixed enzymes and forces food to come into contact with the wall of the intestine
- food is moved very slowly in the intestines
Main types of enzymes synthesized in the pancreas (and in pancreatic juice)
- amylase: digests starches
- lipase: digests lipids
- protease: digestes proteins and polylpeptides
What controls the release of enzymes?
- hormones created and secreted by he stomach
How are enzymes created?
- enzymes synthesized by the pancreas by the ribosomes on rER and processed by Golgi apparatus and secretes through exocytosis
Specific enzymes (used for digestion) you should know (all destined for the SI and produced in the pancreas)
Made in pancreas:
- amylase: breaks down starch, produces maltose
- lipase: breaks down triglycerides, produces fatty acids and glycerols
- phospholipase: breaks down phospholipids, produces fatty acids, glycerol and phosphate (PO4 (-3))
- protease: (an example is pepsin) breaks down proteins, polypeptides, produces shorter peptides
What kind of reaction breaks down/digestion of food molecules
hydrolysis, catabolic rxns
Specific enzymes (used for digestion) you should know (all destined for the SI and produced in the small intestine)
- nuclease: breaks down DNA and RNA, produces nucleotides
- maltase: breaks down maltose, produces glucose
- lactase: breaks down lactose, produces galactose and glucose
- sucrase: breaks down sucrose, produces fructose and glucose
- exopeptidase: breaks down peptides, produces dipeptides
- dipetidase: breaks down dipeptides, produces amino acids
Layers of small intestine
(Outer layers to inner layers)
- serosa: protective outer layer
- muscle layers (muscularis externa): inner circular and outer longitudinal muscle which perform peristalsis
- sub-mucosa: connective tissue (between mucosa and muscle)
- mucosa: inner lining, includes villi
- epithelial cells: single outer layer of cells on each villus
Goblet cell in small intestine
- specialized cells on villi
- absorbs nutrients
- secrete mucus
Lacteal in small intestine
- branch of lymphatic system
- allow rapid absorption and transport of lipids
Membrane transport in SL: fatty acids/monoglycerides
- simple diffusion
- fatty acid only: facilitated diffusion via transmembrane proteins
- once inside epithelium cells, fatty acids and monoglycerides combine so that they cannot diffuse back into the lumen of SL
Membrane transport: glucose
- facilitated diffusion via glucose channels
- large polar molecules: simple diffusion cannot occur
