<< Chapter < Page Chapter >> Page >

Digestive system organs

The easiest way to understand the digestive system is to divide its organs into two main categories. The first group is the organs that make up the alimentary canal. These organs are part of the "tube" our food travels through from the mouth to the anus. Accessory digestive organs comprise the second group. Food never enters or passes through these organs, but they are critical for orchestrating the breakdown of food. Accessory digestive organs, despite their name, are critical to the function of the digestive system.

Alimentary canal organs

Also called the gastrointestinal (GI) tract or gut, the alimentary canal    (aliment- = “to nourish”) is a one-way tube about 25 feet in length The main function of the organs of the alimentary canal is to nourish the body. This tube begins at the mouth and terminates at the anus. Between those two points, the canal is modified as the pharynx (throat), esophagus, stomach, and small and large intestines to fit the functional needs of the body. Both the mouth and anus are open to the external environment; thus, food and wastes within the alimentary canal are technically considered to be outside the body. Only through the process of absorption do the nutrients in food enter into and nourish the body’s “inner space.”

Accessory structures

Each accessory digestive organ    aids in the breakdown of food ( [link] ). The salivary glands, in the mouth, begin the chemical digestion of food. Once food products enter the small intestine, the gallbladder, liver, and pancreas release secretions—such as bile and enzymes—essential for digestion to continue. Together, these are called accessory organs because although they are important, food does not pass through them. You could not live without their vital contributions, and many significant diseases result from their malfunction.

Tissues of the alimentary canal

Throughout its length, the alimentary tract is composed of the same four tissue layers; the details of their structural arrangements vary to fit their specific functions. Starting from the lumen and moving outwards, these layers are the mucosa, submucosa, muscularis, and serosa, which is continuous with the mesentery (see [link] ).

Layers of the alimentary canal

This image shows the cross section of the alimentary canal. The different layers of the alimentary canal are shown as concentric cylinders with major muscles and veins labeled.
The wall of the alimentary canal has four basic tissue layers: the mucosa, submucosa, muscularis, and serosa.

The mucosa    is referred to as a mucous membrane, because mucus production is a characteristic feature of this layer. The membrane consists of epithelium, which is in direct contact with ingested food. Epithelium —is a type of tissue, found in the mouth, stomach, intestines, pharynx, esophagus,and anal canal, The beginning and end of tube is lined with of a type of epithelium called stratified squamous epithelium . The stomach and intestines are lined simple columnar epithelium . Notice that the epithelium is in direct contact with the space inside the alimentary canal called the lumen .

As its name implies, the submucosa    lies immediately beneath the mucosa. It is composed of another tissue known as dense connective tissue . The mucosa    is referred to as a mucous membrane, because mucus production is a characteristic feature of this layer. It includes blood and lymphatic vessels (which transport absorbed nutrients).

The third layer of the alimentary canal is the muscularis    . The muscularis in the small intestine is made up of a double layer of smooth muscle. The contractions of these layers promote mechanical digestion, expose more of the food to digestive chemicals, and move the food along the canal.

The serosa    is the outermost layer of the alimentary canal, superficial to the muscularis. Instead of serosa, the mouth, pharynx, and esophagus have a dense sheath of collagen fibers called the adventitia. These tissues serve to hold the alimentary canal in place near the ventral surface of the vertebral column.

Nerve supply

As soon as food enters the mouth, it is detected by receptors that send impulses along the sensory neurons of cranial nerves. Without these nerves, not only would your food be without taste, but you would also be unable to feel either the food or the structures of your mouth, and you would be unable to avoid biting yourself as you chew, an action enabled by the motor branches of cranial nerves. In addition the nervous system controls the movement of food through the alimentary tube and controls the release of enzymes and hormones that are important in the digestion and absorption of food

Blood supply

The blood vessels serving the digestive system have two functions. They transport the protein and carbohydrate nutrients absorbed by cells after food is digested in the lumen. Lipids are absorbed via lacteals , tiny structures of the lymphatic system. The blood vessels’ second function is to supply the organs of the alimentary canal with the nutrients and oxygen needed to drive their cellular processes.

The veins that collect nutrient-rich blood from the small intestine (where most absorption occurs) empty into the hepatic portal system . This network takes the blood into the liver where the nutrients are either processed or stored for later use. Only then does the blood circulate back to the heart.

Chapter review

The digestive system includes the organs of the alimentary canal and accessory structures. The alimentary canal forms a continuous tube that is open to the outside environment at both ends. The organs of the alimentary canal are the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The accessory digestive structures include the teeth, tongue, salivary glands, liver, pancreas, and gallbladder. The wall of the alimentary canal is composed of four basic tissue layers: mucosa, submucosa, muscularis, and serosa. The enteric nervous system provides intrinsic innervation, and the autonomic nervous system provides extrinsic innervation.

Questions & Answers

do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Berger describes sociologists as concerned with
Mueller Reply
Got questions? Join the online conversation and get instant answers!
QuizOver.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Digestive system. OpenStax CNX. Feb 23, 2015 Download for free at http://legacy.cnx.org/content/col11761/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Digestive system' conversation and receive update notifications?

Ask