Anaphy-Digestive

Digestive System

Parotid, submandibular, and sublingual glands
Produce saliva containing enzymes to break down food
Parotid glands are serous glands, submandibular glands produce more serous secretions, and sublingual glands produce primarily mucous secretions

Located in the abdomen
Acts as a storage tank for food
Produces mucus, hydrochloric acid, and protein-digesting enzymes
Has three muscular layers and rugae to allow stretching
Chyme is formed when food begins to be broken down
Pyloric opening and pyloric sphincter control the movement of food to the small intestine

Three phases: cephalic, gastric, and intestinal
Sight, smell, taste, or thought of food initiate stomach secretions
Partially digested proteins and stomach distention promote secretion
Acidic chyme stimulates neuronal reflexes and hormones that inhibit gastric secretions

Mixing waves thoroughly mix food to form chyme
Peristaltic waves force chyme toward and through the pyloric sphincter
Hormonal and neural mechanisms stimulate stomach secretions
Stomach empties every 4 hours after a regular meal, and 6 to 8 hours after a high fatty meal

Small intestine has three parts: duodenum, jejunum, and ileum
- Duodenum is the first part, about 25 cm long, receives secretions from the liver and pancreas
- Jejunum is the second part, about 2.5 meters long, absorbs nutrients
- Ileum is the third part, about 3.5 meters long
Mucosa of the small intestine
- Simple columnar epithelium with four major cell types:
  - Absorptive cells: have microvilli, produce digestive enzymes, and absorb digested food
  - Goblet cells: produce protective mucus
  - Granular cells: help protect the intestinal epithelium from bacteria
  - Endocrine cells: produce regulatory hormones
Secretions of the small intestine
- Mainly contain mucus, ions, and water
- Epithelial cells in the walls of the small intestine have enzymes bound to their free surfaces
- Peptidases enzymatically breakdown proteins into amino acids for absorption
- Disaccharidases enzymatically breakdown disaccharides into monosaccharides for absorption
Movement in the small intestine
- Mixing and propulsion of chyme are the primary mechanical events
- Peristaltic contractions move chyme along the small intestine
- Segmental contractions mix intestinal contents
- Ileocecal sphincter allows chyme to move from the small intestine into the cecum
- Ileocecal valve prevents movement from the large intestine back into the ileum

Liver ducts
- Hepatic duct: transports bile out of the liver
- Common hepatic duct: formed from the left and right hepatic duct
- Cystic duct: joins the common hepatic duct, comes from the gallbladder
- Common bile duct: formed from the common hepatic duct and cystic duct
Functions of the liver
- Digestive and excretory functions
- Stores and processes nutrients
- Detoxifies harmful chemicals
- Synthesizes new molecules
- Secretes 700 milliliters of bile each day
- Bile dilutes and neutralizes stomach acid and breaks down fats
Pancreas
- Located posterior to the stomach in the inferior part of the left upper quadrant
- Produces insulin and glucagon (endocrine function)
- Produces digestive enzymes (exocrine function)
Pancreatic secretions
- Major protein-digesting enzymes: trypsin, chymotrypsin, carboxypeptidase
- Pancreatic amylase digests polysaccharides
- Pancreatic lipase digests lipids
- Pancreatic nuclease enzymes degrade DNA and RNA

Large intestine
- Function is to absorb water from indigestible food
- Contains cecum, colon, rectum, anal canal
- Cecum joins small intestine at ileocecal junction, has appendix attached
- Colon is 1.5 meters long, contains ascending, transverse, descending, sigmoid regions
- Rectum is a straight tube that begins at sigmoid and ends at anal canal
- Anal canal is the last 2 to 3 cm of the digestive tract
Digestive process
1. Digestion occurs in the stomach and mouth
2. Propulsion moves food through the digestive tract
3. Absorption primarily occurs in the duodenum and jejunum of the small intestine
4. Defecation is the elimination of waste in the form of feces
Carbohydrate digestion
- Polysaccharides are broken down into disaccharides by salivary and pancreatic amylases
- Disaccharides are broken down into monosaccharides by disaccharidases on the surface of intestinal epithelium
- Glucose is absorbed into the intestinal epithelium and carried to the liver

Lipid digestion
- Lipase breaks down triglycerides into fatty acids and monoglycerides
- Bile salts surround fatty acids and monoglycerides to form micelles
- Micelles attach to the plasma membranes of intestinal epithelial cells and pass into the cells
- Within the cells, fatty acids and monoglycerides are converted to triglycerides and coated with proteins to form chylomicrons
- Chylomicrons enter the lacteals of the intestinal villi and are carried through the lymphatic system to the blood
Lipoproteins
- Lipids are packaged into lipoproteins for transport in the lymph and blood
- Lipoproteins include chylomicrons, low-density lipoproteins (LDL), and high-density lipoproteins (HDL)
Protein digestion
- Pepsin is a protein-digesting enzyme secreted by the stomach
- The pancreas secretes trypsin, chymotrypsin, and carboxypeptidase into the small intestine
- Peptidases on the surface of intestinal epithelium further break down small peptides into tripeptides
- Absorption of tripeptides, dipeptides, or individual amino acids occurs through the intestinal epithelial cells
Water and minerals
- Water can move across the intestinal wall in either direction depending on osmotic pressures
- 99% of water entering the intestine is absorbed
- Minerals are actively transported across the walls of