Anatomy of the Digestive System The importance of sphincters!

Major Functions of the Digestive System Excretion

Structure of the Gastrointestinal Tract Wall Aka Enteroendocrine cells Extramural glands

Liver, Gallbladder, and Associated Ducts Main secretions of Liver: bile salts for emulsification of fats and bicarbonate

How are these exocrine secretions regulated?

Recall Components of a Reflex Arc Stimulus Receptors Afferent Pathway Integrator Efferent Pathway Effectors Response Enteroendocrine cells Hormones Glands, Smooth Muscles, Sphincters

Basic Principles of Control Luminal stimuli: Neural regulation comes through the CNS and ENS: distension of the wall by the volume of luminal contents Enteric nervous system Chyme osmolarity Submucosal plexus Chyme acidity Myenteric plexus Chyme concentration of specific digestion products CNS contributions to neural control of the GI system through regulation of the SNS and PSNS. Hormonal regulation

Cholecystokinin

Stomach AKA Cardiac Sphincter

Gastric Gland pH

Regulation of HCl Secretion

Pepsin Secretion Why has natural selection resulted in the conversion of pepsinogen to pepsin in the lumen of the stomach?

Pancreas Exocrine cells here secrete ZYMOGENS (which require modification to become enzymes!) Why zymogens?

Trypsin Secretion Zymogens What controls secretion of bicarbonate and zymogens from the pancreas?

Control of Pancreatic HCO3- Secretion

Control of Pancreatic Zymogen Secretion What else does CCK do?

Regulation of Bile Flow

Large Intestine