Digestive System Physiology

Stomach Control

• Stomach endocrine cells release gastrin upon neural stimulation
• Gastrin stimulates gastric juice secretion (HCl, mucus, water, pepsin activation)
• Positive feedback loops prepare the stomach for food intake

Chyme and Duodenum Control

• When chyme enters the duodenum, endocrine cells release CCK (cholecystokinin)
• CCK triggers gallbladder bile release for lipid emulsification
• CCK levels directly correlate with chyme levels in the duodenum
• Secretin is released by duodenum endocrine cells in response to chyme
• Secretin increases pancreatic enzyme formation and bicarbonate production
• Secretin stimulates pancreatic secretions to mix with chyme
• Secretin levels in blood are proportional to chyme levels in the duodenum

Liver Bile Secretion

• Liver bile production and secretion are not hormonally controlled

Blood Glucose Homeostasis

• Normal blood glucose levels in adults are 3-4.5 mmol/dL
• Hyperglycemia (high blood glucose) can cause tissue damage, glaucoma, swelling, and neural diseases
• Hypoglycemia (low blood glucose) can cause temperature issues, hypotension, and bradycardia
• Post-meal blood glucose rises to ~5.0 mmol/dL (trigger level)
• Between meals, blood glucose levels fall to ~3.5 mmol/dL (trigger level)