Describe the parts of the small and large intestine of human:

Introduction to small intestine:

  The part of the gastrointestinal tract,which extends from the pylorus to the ileocecal valve and opens into the large intestine is known as small intestine .

The diameter of the small intestine is relatively small than that of large intestine , that's why it is known as small intestine.

But on the other hand the length of the small intestine is greater than that of large intestine. The length of the small intestine is about 6meter .

Parts of small intestine:

   Small intestine consists of three parts namely duodenum(proximal part), jejunum (Middle part), ileum(Distal part ).

SmallIntestine Anatomy Image by-BruceBlaus ,Source , License- CC BY 3.0

Duodenum:

  The first part of the small intestine which is also the shortest part is known as is known ad duodenum. The duodenum is also the widest and most fixed part.

The fixation of duodenum is essential because mobile duodenum will cause twisting ,and kinking of common bile duct and pancreatic ducts which open into it.

The length of the small intestine is about 10inches (25cm). The duodenum is C shaped and for descriptive purposes is divided into four parts: superior(1st)part , descending(2nd)part, horizontal (3rd),and ascending (4th) part.

Superior part of the duodenum is also known as duodenul cap or bulb.

Jejunum and ileum:

  Jejunum and ileum form respectively,the proximal 2/5th and distal 3/5th of the remaining part of small intestine. Jejunum and ileum are not properly separated.

The inner mucosal surfaces of jejunum and ileum ,however,can be differentiated,from each other .The duodenum and jejunum are principally concerned with the digestion and absorption of digested food ,hence these two parts together form the small intestinal proper .

The jejunum is more vascular than the ileum the jejunum is also slightly wider in diameter than the ileum. There are present large number of aggregated lymphatic follicles(Peyer's patches) in the wall of the ileum than the jejunum.

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Large intestine:

The large intestine is a tube like structure which is about 6cm in diameter. The length of the small intestine is about 100cm . The large intestine extends from the caecum in the right iliac fossa to the anus in the perineum.

Apart from the transverse colon and sigmoid colon it is more fixed in position than the small intestine.

Parts of large intestine: 

LargeIntestine ,Image by-BruceBlaus,Source, License-CC BY3.0

  Large intestine is made up of the following parts:

 Caecum:

  The caecum(L. caecum=blind) is the large dilated blind sac at the commencement (proximal end ) of the large intestine. Caecum is situated in the right iliac fossa above the lateral half of the inguinal ligament.

Caecum communicates superiorly with the ascending colon and medially at the ileocaecal junction with ileum and posteromedially with appendix.

Generally the caecum appears as a dilated pendulous  sac inferior to the ileocaecal junction. Caecum is one of those organs in the body which have greater width than length.

Appendix:

From the medial side of the caecum a worm shaped tube like structure arises ,which is known as appendix. In humans appendix is a vestigial organ.

The length of the appendix varies from 2-20cm(average 9cm). And the average width of the caecum is about 5mm. The appendix consists of three parts base,body,and tip.

Colon:

  For descriptive purposes the colon is divided into four parts namely : ascending colon , transverse colon ,descending colon,sigmoid colon.

 Ascending colon:

  The characteristics of ascending colon is ,it is an upward continuation of the caecum. It extend upward from the caecum along the right side of abdomen up to the inferior surface of the right lobe of the liver where it bends to the left to form the hepatic flexure . The length of the ascending colon is about 12.5cm .

Transverse colon:

  The longest (50cm)and the most mobile part of the large intestine is transverse colon. Transverse colon extends from the right hepatic flexure to the left splenic flexure. It forms a wide U shaped curve.

Descending colon:

  The characteristics of descending colon is ,it is longer(25cm), narrower and more deeply located than the ascending colon. Descending colon extends from the left splenic  flexure to the pelvic inlet below.

Sigmoid colon:

Sigmoid colon:

 The length of the sigmoid colon is about 37.5cm . Sigmoid colon help in the joining of descending colon with the rectum. It is S shaped and hence the name sigmoid colon .

Sigmoid colon begins at the pelvic inlet as continuation of the descending colon and joins the rectum in front of the sacrum.

Rectum:

The distal part of the large intestine which is present between the sigmoid colon and anal canal is known as rectum. Rectum descends in front of the sacrum to leave the pelvis by piercing the pelvic floor.

Here it becomes continuous with anal canal in the perineum. The rectum is about 12cm long . The diameter of the rectum is not uniform throughout.

Anal canal:

 The terminal part of the large intestine is anal canal. Through the anus anal canal opens to the exterior. The anal canal is situated in the perineum below the pelvic diaphragm.

The length of the anal canal is about 3.8cm. Anal canal is surrounded by an inner involuntary sphincter and an outer voluntary sphincter. The anal canal is located in the anal triangle of the perineum , between the right and left fat filled ischiorectal fossa.

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