Large Intestine

LARGE INTESTINE

Length: About 1.5 m long.

Extension: From the caecum in the right iliac fossa to the anus in the perineum.

Lining Epithelium of Large gut
Simple columnar epithelium with intersperse goblet cells

Parts: It has four parts:

  1. Caecum and appendix
  2. Colon
  3. Rectum
  4. Anal canal

The colon is further divided into four parts:

  • Ascending colon
  • Transverse colon
  • Descending colon and
  • Sigmoid colon

Cardinal Feature of Large Intestine:

a) Teniae coli

These are three ribbon-like bands of the longitudinal muscle coat.

Location: In the caecum, ascending colon & descending colon. Absent in appendix, rectum, & anal canal.

Positions of teniae in ascending colon are

  • Anterior (Teniae libera),
  • Posteromedial (Teniae mesocolica), and
  • Posterolateral (Teniae omentalis),

But in the transverse colon, the corresponding positions are inferior, posterior, and superior, respectively.


b) Appendices Epiploicae:

These are small bags of visceral peritoneum filled with fat attached to the teniae of the large intestine. Thus, they are absent in the appendix, rectum, and anal canal.


c) Sacculation (or Haustrations):

These are a series of pouches/dilatations in the wall of the caecum and colon between the teniae.

The sacculations are responsible for the characteristic puckered appearance of the large intestine.

 

CAECUM

The caecum is the large dilated blind sac at the commencement (proximal end) of the large intestine.

It communicates:

  • Superiorly with the ascending colon.
  • Medially at the ileocaecal junction with ileum.
  • Posteromedially with appendix.


Ascending Colon

The ascending colon is an upward continuation of the caecum.

Extension: From the caecum, at the level of the ileocaecal orifice, to the hepatic (right colic) flexure.


Transverse Colon

The most mobile part of the large intestine.

Extension: From the right colic flexure (in right lumbar region) to the left colic flexure (in the left hypochondriac region).


Descending Colon

Extension: From the left colic flexure to the front of the left external iliac artery at the level of pelvic brim where it becomes continuous with the sigmoid colon.


Sigmoid Colon

Extension: From the lower end of descending colon at the left pelvic inlet to the pelvic surface of the third sacral vertebra where it becomes continuous with the rectum.

 

Rectum:
It is the continuation of the sigmoid colon at the level of sacral 3 vertebrae.

Length: 12 cm

It has 2 types of curvature

Antero-posterior curvature
1. Sacral curve
2. Perineal curve
Lateral curvature
1. Upper
2. Middle
3. Lower


Peritoneal relation of Rectum:

Upper 1/3rd: Covered with peritoneum in front & on both side
Middle 1/3rd: Covered only in the front
Lower 1/3rd: Devoid of peritoneum


Visceral relations of Rectum:

Anteriorly in males:

Rectovesical pouch (upper 2/3rd)
Base of the urinary bladder
Terminal parts of ureters
Seminal vesicles
Prostate


Anteriorly in females

Rectouterine pouch (Upper 2/3rd)
Lower part of the vagina (lower 1/3rd)


Posteriorly: Same in males and females

Lower 3 pieces of the sacrum, coccyx
Piriformis, Coccygeus, Lecator ani muscles
Sympathetic chain
Lymph nodes, Lymphatics
Fat


Interior of the rectum:

Two types of fold

Temporary (longitudinal type, disappear when distended)
Permanent: Known as Houston's Valve, 4 in number


Nerve supply:

Sympathetic: By superior Hypogastric Plexus (L1, L2) vasomotor

Parasympathetic: Pelvic splanchnic nerves, secretomotor to glands


Importance of Rectal vein:

They are the site of portosystemic anastomosis

They're devoid of valves. In portal obstruction, veins became distended and form primary internal piles

 

Anal canal:

The terminal portion of the large intestine below the pelvic diaphragm

Length: 3.8 cm

Extension: Anorectal junction to the anal orifice

 

Interior of Anal Canal:

Divided into upper, intermediate, and lower parts by a pectinate line & Hilton's line respectively

1. Upper part: 1.5 cm in length

Area above the pectinate line
Lined by Simple columnar epithelium
Internal rectal venous plexus lies outside, gives the "plum red" appearance
Feature:
Anal columns
Anal valves
Anal papillae
Anal Sinuses
Anal glands


2. Intermediate Part

Area between Pectinate to Hilton's line
Lined by Non-Keratinized stratified squamous epithelium,
Internal rectal venous plexus gives a bluish pink appearance.


3. Lower Part (8 mm)

Area below Hilton's Line
Lined by true skin (Keratinized stratified squamous epithelium)
Sweat, sebaceous gland presents


Nerve supply :

Above the pectinate line: (like rectum)

Sympathetic:
By superior Hypogastric Plexus (L1, L2) vasomotor

Parasympathetic:
Pelvic splanchnic nerves, secretomotor to glands

Below the pectinate line:
Somatic spinal nerve via inferior rectal nerves

Somatic means pain, temperature, touch pressure sensation occur here.


Difference between Male & Female Anal Canal

Male has hair follicle in the lower part of the anal canal but in female no hair follicle.


Anal Fissure:

When hard, large feces passage during bowel movement, then a small tear may occur in the mucosa of the anal canal resulting in a painful condition called Anal Fissure.

Infected glands act as a source of anal fissure.


What is a hemorrhoid (Piles)?

Dilatation, elongation, and tortuosity of anorectal venous plexus formed by radicals of superior middle and inferior rectal veins. In portal obstruction of superior rectal veins, veins are distended and form primary internal hemorrhoids

Types: 

Internal or true piles:
Piles that appear above the pectinate line.
Painless, bright red blood,
External or false piles:
Piles that appear below the pectinate line.
Very painful, don't bleed.


Peritoneal Relations of Large Gut:

All the parts of the large intestine are retroperitoneal & fixed except the appendix, transverse colon & sigmoid colon which are intraperitoneal and possess mesenteries.

Part of Large gut Name of mesentery
Appendix Mesoappendix
Transerve colon  Transverse mesocolon
Sigmoid colon Sigmoid mesocolon

 

Functions of the large intestine

Absorption of water from fluid contents in it to help form the feces.
Storage, lubrication, and expulsion of feces.
Synthesis of vitamin B complex by normal bacterial flora presents its lumen.
Protection from invasion by microorganisms by its mucoid secretion which is rich in IgA group of antibodies.


Difference between Right colic Flexure & Left colic Flexure

Right colic Flexure Left colic Flexure
Also called Hepatic flexure Also called Splenic Flexure
Located in the Right lumber region Located in the Left hypochondrium region
Lining epithelium developed from the endoderm of the midgut Lining epithelium developed from the endoderm of the hindgut

 

Difference between the Rectum with the rest of the Large Intestine.

Cardinal features of Large Intestine like Teniae coli, Appendices Epiploicae, Sacculation is absent in Appendix.