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BIOS 256 AP 4 BIOS 256 AP 4 Lecture Notes Lecture Notes
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BIOS 256 AP 4Lecture Notes
,Week 2:
Chapter 24: The Digestive System part two
Basic GI Functions
Primary function: movement of nutrient molecules from the external environment to
the internal environment. (Absorption of nutrients)
Food->Digestion->motility and absorption
Pancreas
Gland in the retroperitoneal space behind the stomach
Produces enzymes that digest carbs, proteins, fats, and nucleic acids
Produces the sodium bicarbonate buffer
Empties the contents into duodenum
Relationship of the Pancreas to the Liver, Gallbladder, and Duodenum
Know: Hepatopancreatic ampulla (ampulla of vater) and Sphincter of Oddi
Sphincter of Oddi regulates the passage of bile and pancreatic juices through the
ampulla of vater into the duodenum of the small intestines.
Activation of Pancreatic Proteolytic Enzymes
Pancreas
Exocrine portion secretes pancreatic juices.
o Made up of acini (99% of pancreas)
o Pancreatic juice is made up of
Amylase to digest starch
Trypsin, Chymotrypsin, carboxypeptidase, and elastase to digest protein.
Lipase digests triglyceride
Ribonuclease
Deoxyribose
o Protein Digesting enzymes secreted in inactive form
o NaCO3 buffers acidic gastric juice to allow digestion to begin in small intestines
Endocrine portion secretes hormones like insulin, glucagon
o Made up of pancreatic islet cells
Liver
Split into right and left lobes, separated by the falciform ligament.
Right lobe is larger than the left.
Histology of the Liver
Hepatocytes
, o Functional cell of the liver
o Produce and secrete bile
Bile canaliculi
o Small ducts between hepatocytes that collect bile produced by hepatocytes
o Bile canaliculi-> bile ductules->bile ducts->right and left hepatic ducts->common
hepatic duct->cystic duct=common bile duct
Hepatic sinusoids
o Blood capillaries between hepatocytes
Right and left hepatic ducts merge to form the common bile duct.
Blood Supply of the Liver
Oxygenated blood from hepatic artery and Nutrient rich deoxygenated blood from hepatic
portal vein go to hepatic sinusoids. Then to central vein. Then hepatic vein. The inferior vena
cava. And finally right atrium of the heart
Functions of the Liver and Gallbladder
Carbohydrate, lipid, and protein metabolism
Processing of drugs and hormones (detoxifies)
Bilirubin excretion (derived from Heme and metabolized in small intestine by bacteria
and eliminated feces. )
Bile salt synthesis
Storage of vitamins
Phagocytosis of aged RBCs and WBCs and some bacteria
Vitamin D activation
Liver and Gallbladder
The liver makes bile
o Both and excretory product and a digestive secretion
o Bile= water, bile salts, bile pigments (bilirubin)
o Bile salts play a role in emulsification
Break down of large lipid globules into a suspension of small lipid globules
Enhances role of pancreatic lipase
The gallbladder stores bile until it is needed
Regulation of Bile Production and Secretion
CCK and secretin released into blood when acidic, fatty chime enters intestines
CCK causes
o Gallbladder contraction
o Pancreatic juice secretion
o Relaxation of sphincter of Oddi
Secretin stimulates
o Production of bicarbonate by pancreas and bile by liver
, Anatomy of the Small Intestine
90% of absorption occurs in the small intestine
3 parts
o Duodenum
o Jejunum
o Ileum
Circular folds are permanent ridges of the mucosa and submucosa that enhance
absorption because of the increased surface area and it causes chime to spiral as it
moves through small intestine.
Villi are fingerlike projections of the mucosa that aid in digestion and absorption. The mucosa
contains absorptive cells, goblet cells, enteroendocrine cells (make hormones), and Paneth cells
(help with phagocytosis)… and the villi have their own villi like microvilli.
Mechanical Digestion in the SI
Two types of movements:
Segmentation
o Localized mixing contractions
o Mix chime with digestive juices bringing food into contact with mucosa.
o Do not push food along
Peristalsis
o After most of meal has been absorbed, segmentation stops and peristalsis begins
o Pushes chime down SI
Intestinal Juice and Brush Border Enzymes
Intestinal juice provides a vehicle for absorption of substances from chime as they come
in contact with the villi.
Brush border enzymes, found on the surface of the microvilli of absorptive cells, break
down food products
Chemical Digestion in the SI
Digestion of:
Carbohydrates
Proteins
Lipids
Nucleic acids
Carbohydrate Digestion
Ingested molecules of sucrose, lactose, and maltose are not acted upon until they reach
SI (disaccharides)
Brush border enzymes digest the disaccharides into monosaccharides
Protein Absorption
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