Gastrointestinal Physiology Overview

Overview of Gastrointestinal Physiology

• The gastrointestinal (GI) tract, also known as the digestive system, is a complex system responsible for breaking down and absorbing nutrients from food.
• The GI tract consists of the mouth, esophagus, stomach, small intestine, and large intestine.

Mouth and Esophagus

• The mouth is responsible for mechanical and chemical digestion of food through chewing and saliva production.
  • Saliva contains enzymes like amylase and lipase that break down carbohydrates and fats.
• The esophagus is a muscular tube that propels food into the stomach through peristalsis.

Stomach

• The stomach is a muscular sac that secretes digestive enzymes and acids to break down proteins and fats.
  • Gastric juice contains pepsin, which breaks down proteins into peptides and amino acids.
  • Hydrochloric acid (HCl) and mucus protect the stomach lining from acid damage.

Small Intestine

• The small intestine is responsible for most of the nutrient absorption in the GI tract.
  • Microvilli on the surface of enterocytes increase the surface area for absorption.
  • Nutrients are absorbed into the bloodstream through facilitated diffusion and active transport.

Large Intestine (Colon)

• The large intestine is responsible for water and electrolyte absorption, as well as the storage and elimination of waste.
  • The colon is home to a diverse microbiome that helps with fermentation and vitamin production.
  • The rectum stores feces until they are eliminated through the anus.

Hormonal Regulation

• Hormones play a crucial role in regulating digestion and absorption in the GI tract.
  • Gastrin stimulates the release of gastric acid and pepsin in the stomach.
  • Secretin stimulates the release of bicarbonate-rich pancreatic juice to neutralize stomach acid.
  • Cholecystokinin (CCK) stimulates the release of bile and pancreatic enzymes.

Gut-Brain Axis

• The GI tract is connected to the central nervous system through the vagus nerve and other pathways.
  • The gut microbiome produces neurotransmitters and hormones that influence mood and cognition.
  • The brain can influence gut function and digestion through the gut-brain axis.