Gastrointestinal system

Xiang-Yao LI, PhD Department of Physiology Zhejiang University School of Medicine Email: lixiangy@zju.edu.cn

Alimentary Canal Continuous, muscular digestive tube winding throughout the body Digests and absorbs food particles Contains the following organs:

Mouth, Pharynx, Esophagus, Stomach, Small Intestine Large Intestine

Accessory Digestive Organs Contains the following organs:

Teeth, Tongue, Gallbladder, Salivary Glands, Liver, Pancreas

The four processes carried out by the GI tract: digestion,

secretion, absorption, and motility.

Many functions in the

gut are found in

specific locations

along its length.

Most of the

absorption of

nutrients occurs in

the small intestine, so

most of digestion is

accomplished there

or upstream.

Functions of the digestive system

Movement: propels food through the digestive system

Secretion: release of digestive juices in response to a specific

stimulus

Digestion: breakdown of food into molecular components small

enough to cross the plasma membrane

◦ Mechanical (physical): Chew,Tear,Grind,Mash,Mix

◦ Chemical: Enzymatic reactions to improve digestion of

Carbohydrates,Proteins,Lipids

Absorption: passage of the molecules into the body's interior

and their passage throughout the body

Elimination: removal of undigested food and wastes

Fun Facts

• HOW LONG ARE YOUR INTESTINES? At least 25 feet in

an adult. Be glad you're not a full-grown horse -- their coiled-

up intestines are 89 feet long!

• Food drying up and hanging out in the large intestine can

last 18 hours to 2 days!

• In your lifetime, your digestive system may handle about 50

tons!!

Histology of the GI Tract

Microscopic Anatomy of the

Esophagus

Microscopic Anatomy of the stomach

Microscopic Anatomy of the Small

Intestine

Microscopic Anatomy of the Large

Intestine

General properties of gastrointestinal

smooth muscle

Low excitability

High distensibility

Tonic contraction

Autorhythmicity

High sensitivity to temperature, stretch

and chemical stimulation

Electrophysiological properties of

gastrointestinal smooth muscle

Resting membrane potential

◦ -40~-80 mV

◦ Ionic basis

Em (selective membrane permeability to K+, Na+,

Cl- and Ca2+)

Electrogenic Na+-K+ pump

Slow wave (basic electrical rhythm)

◦ The spontaneous rhythmic, subthreshold

depolarizations of the cell membrane (slow wave) of

the gastrointestinal tract that characterizes the

underlying electrical activity of the bowel

◦ Initiated in the interstitial cells of Cajal (ICC)

(pacemaker cell)

Santiago Ramon Y Cajal

He and Camillo Golgi

received the Nobel

Prize in 1906 for

introduction of the

silver-chromate stain

Calcium imaging in ICC-MY from the guinea-pig antrum. A colocalization procedure was used to identify the Rhod-2 signal from ACK2-Alexa 488 labelled ICC-MY. Panel A shows a stack of 30 sequential optical sections made in the Z optical axis of the ACK2-Alexa 488 signal and the Rhod-2 signal; panels B and C show each signal independently. Panel D shows the stack after the colocalization algorithm was used on each confocal slice, showing that most ICC-MY were well labelled with Rhod-2. It was evident from this experiment that some, but not all, ICC-MY were well-labelled with Rhod-2 (see text for more details). The scale bar in panel D is 40 um and it applies to all images

Intracellularly recorded electrical activity from a guinea-pig antral ICC-

MY identified with ACK2-Alexa 488. Panel A shows a network of ICC-MY

labelled with ACK2-Alexa 488 visualized using fluorescence microscopy,

and a single ICC-MY impaled with a LY-filled microelectrode. Panel B

shows changes in membrane potential recorded intracellularly from an

ICC-MY. One slow wave, marked with the horizontal line in Panel B, is

shown in Panel C at an expanded time scale. The scale bar is 15 um.

Cyclic changes in intracellular calcium in ICC-MY in the murine jejunum. Panel A shows a

single confocal image with ACK2-Alexa 488 immunore-activity (green) and Rhod-2

labelling (red) taken from a time series. ICC-MY were distinctly labelled with Rhod-2 as

shown in panel B. The average fluorescence intensity delineated by the white circled

region was measured from images recorded every second, shown in panel C

Slow wave (basic electrical rhythm)

◦ Intensity: 10~15 mV

◦ Frequency: 3~12 cpm

◦ Ionic mechanism

spontaneous rhythmic changes in Na+-K+ pump activity

Normal BER frequencies in the

gastrointestinal system

Spike potential (Action potential)

◦ Duration: 10~20 ms

◦ Ionic mechanism:

Depolarization: Ca2+ influx

Repolarization: K+ efflux

Summary

Gastrointestinal system Alimentary Canal:

Mouth, Pharynx, Esophagus, Stomach, Small Intestine, Large Intestine

Accessory Digestive Organs:

Teeth, Tongue, Gallbladder, Salivary Glands, Liver,

Pancreas

Functions of the digestive system

Movement, Secretion, Digestion: Mechanical (physical),

Chemical, Absorption, Elimination

The structure of the GI tract wall

Mucosa, Submucosa, Muscularis externa, Serosa

General properties of gastrointestinal smooth muscle

Low excitability, High distensibility, Tonic contraction,

Autorhythmicity, High sensitivity to temperature, stretch

and chemical stimulation

On a sheet of paper, write the name of

each colored organ:

Green:

Red:

Pink:

Brown:

Purple:

Green:

Yellow:

How’d you do?

Great Job!