Introduction to Gastrointestinal Physiology

The function of gastrointestinal (GI) system is to digest food and absorb nutrients, salts and water

Digestion is the process of breaking down food into components that can be absorbed

Absorption is the movement of nutrients, salts and water across the GI epithelium into blood or lymph

Introduction to Gastrointestinal Physiology

Digestion requires the secretions of the GI system and motility, the activity of the muscle of the GI tract that mix and propel its content

Chemical factors and hormones some from the GI tract act on the hypothalamus, the CNS, regulate the caloric intake by stimulation or suppressing appetite

Functions of the GI Tract

Motility: Movement of food through the GI tract.

Ingestion: Taking food into the mouth.

Mastication: Chewing the food and mixing it with saliva.

Deglutition: Swallowing the food.

Peristalsis: Rhythmic wave-like contractions that move

food through GI tract.

Functions of the GI Tract

Secretion: Includes both exocrine and endocrine

secretions. Exocrine:

HCl, HC03-, bile, lipase, pepsin, amylase, and

trypsin are secreted into the lumen of the GI tract.

Endocrine: Stomach and small intestine secrete hormones

to help regulate the GI system. Gastrin, secretin, and somatostatin.

Functions of the GI Tract

Digestion: Breakdown of food particles into

subunits (chemical structure change). Absorption:

Process of the passage of digestion (chemical subunits) into the blood or lymph.

Storage and elimination: Temporary storage and elimination of

indigestible food.

Digestive System (GI)

GI tract divided into: Alimentary

canal. Accessory

digestive organs.

GI tract is 30 ft long and extends from mouth to anus.

Insert fig. 18.2

The wall of GI Tract has four layers

Composed of 4 parts: Mucosa. Submucosa.

Muscularis. Serosa.

Mucosa

Lines the lumen of GI tract. Consists of simple columnar epithelium.

Forms the inner or luminal boundary Lamina propria:

Thin layer of connective tissue carries blood and lymph vessels

Muscularis mucosae: Thin layer of smooth muscle responsible

moving the mucosal surface Goblet cells:

Secrete mucus.

Submucosa

Thick, highly vascular layer of connective tissue.

Absorbed molecules enter the blood and lymphatic vessels.

Submucosal plexus Provide autonomic nerve supply to the

muscularis mucosae.

Muscularis

Responsible for segmental contractions and peristaltic movement through the GI tract. Inner circular layer of smooth muscle. Outer longitudinal layer of smooth muscle.

Contractions of these layers move food through the tract;

Myenteric plexus located between the 2 muscle layers. Major nerve supply to GI tract.

Fibers and ganglia from both sympathetic and parasympathetic nervous systems.

Serosa

Binding and protective outer layer. Consists of connective tissue

1. Describe the features of red muscle fiber

2. Describe in steps the contraction and relaxation mechanism of smooth muscle cells