Majority of chemical digestion (see below) and the first neutralization (via NaHCO 3 ) of acidic chyme occur here. NaHCO 3 provides optimal pH 8-9 for pancreatic amylase, lipase, trypsin, intestinal & pancreatic nuclease, peptidase and maltase.
Up to seven meters in length and 2.5cm in diameter.
Divided into three sections; the first 30 cm is the duodenum .
Walls of the small intestine are covered in villi (small finger-like projections), smooth muscle fibers, pits containing intestinal glands secreting enzymes, goblet cells secreting mucus, epithelial cells contain microvilli , and many folds which increase the surface area for chemical digestion and absorption.
Peristalsis is the alternating contracting and relaxing of smooth muscles . It occurs in the esophagus moving the bolus to the stomach and provides movement of chyme in the small intestine and undigested material in the large intestine .
An accessory organ of digestion (exocrine gland), which produces pancreatic juice (H2O, NaHCO 3 , pancreatic amylase, lipase, trypsin, and pancreatic nuclease) and empties into the duodenum via pancreatic duct.
Also produces a hormone called insulin (from the islets of Langerhans) (endocrine gland) which is secreted into the bloodstream and has the following effects when the concentration of glucose in the blood/blood glucose is high :
i) Stimulates cells permeability to C 6 H 12 O 6 ;
stimulates liver, fat, and muscle cells to metabolize C 6 H 12 O 6 .
ii) Stimulates liver and muscle cells to store excess C 6 H 12 O 6 as glycogen .
Glucose and amino acid monomers move by active transport into epithelial cells , and then diffuse into capillary bed / network .
Glucose and amino acid monomers then enter the bloodstream to the liver via hepatic portal vein , exits liver via hepatic vein to the heart, which then pumps C 6 H 12 O 6 and amino acids throughout the body.
Now the liver can store excess C 6 H 12 O 6 as glycogen and use the amino acids to make proteins.