gastrointestinal system -...
TRANSCRIPT
Gastrointestinal system
Xiang-Yao LI, PhD Department of Physiology Zhejiang University School of Medicine Email: [email protected]
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
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!!
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
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: