2. Large intestine
• extends from the distal end
of the ileum to the anus,
• Measures approximately
1.5 m.
• It absorbs fluids and salts
from the gut contents, thus
forming faeces.
• consists of the caecum,
appendix, colon, rectum,
and anal canal
3. Large intestine ctd
Begins in the right
groin (inguinal) as the
caecum, with its
associated appendix.
It continues upward as
the ascending colon
through the right flank
and into the right
hypochondrium
4. Large intestine ctd
It bends to the left
Just below the liver, to
form the right colic
flexure (hepatic
flexure).
crosses the abdomen
as the transverse colon
to the left
hypochondrium
5. Large intestine ctd
• Just below the spleen, it bends downward,
forming the left colic flexure (splenic
flexure),
• and continues as the descending colon
through the left flank and into the left groin.
• It enters the upper part of the pelvic cavity as
the sigmoid colon.
• continues on the posterior wall of the pelvic
cavity as the rectum, and finally
• terminates as the anal canal.
6. General characteristics
large internal diameter
compared to that of the
small intestine.
peritoneal-covered
accumulations of fat (the
omental appendices) are
associated with the colon;
7. General
characteristics
The segregation of
longitudinal muscle in
its walls into three
narrow bands (the
taeniae coli), which are
primarily observed in
the cecum and colon
and less visible in the
rectum.
the sacculations of the
colon (the haustra of
colon)
8. Caecum and appendix
The caecum is the first
part of the large
intestine.
It is inferior to the
ileocaecal opening and in
the right iliac fossa.
It is an intraperitoneal
structure because of its
mobility not because of
its suspension by a
mesentery
9. Caecum and appendix ctd
• Caecum is continuous with the
ascending colon at the entrance of
the ileum and is usually in contact
with the anterior abdominal wall.
• It may cross the pelvic brim to lie in
the true pelvis.
• The appendix is attached to the
posteromedial wall of the caecum,
just inferior to the end of the
ileum.
10. Caecum and appendix ctd
• The appendix is a narrow,
hollow tube connected to the
cecum.
• It has large aggregations of
lymphoid tissue in its walls
• suspended by the
mesoappendix, which contains
the appendicular vessels
11. Location of the appendix
• Retrocecal - posterior
to the cecum
• Retrocolic - posterior
to the lower ascending
colon
• Subcecal location -
below the cecum
• Preileal position -
anterior to the terminal
ileum
• Postileal position -
posterior to the terminal
ileum
12. • The surface projection of the base of the
appendix is at the junction of the lateral
and middle one-thirds of a line from the
anterior superior iliac spine to the
umbilicus (McBurney's point).
• appendicular problems may present pain
near this location
13. The colon
consists of the
ascending, transverse,
descending, and sigmoid
parts.
Its ascending and
descending segments are
retroperitoneal.
transverse and sigmoid
segments are
intraperitoneal.
14. Colon ctd
Note:
the right colic flexure
(hepatic flexure) just
inferior to right liver lobe.
The left colic flexure
(splenic flexure)
Splenic flexure is
higher and more
posterior and is attached
to the diaphragm by the
phrenicocolic ligament.
15. Colon ctd
Immediately lateral to
the ascending and
descending colons are
the right and left
paracolic gutters
(depressions)
16. Colon ctd
• These depressions are formed between the
lateral margins of the ascending and
descending colon and the posterolateral
abdominal wall.
• Gutters are spaces through which material can
pass from one region of the peritoneal cavity to
another.
17. The sigmoid colon
marks the final
segment of the colon.
begins above the
pelvic inlet and
extends to the level of
vertebra SIII,
it is continuous with
the rectum.
18. sigmoid Colon ctd
• This S-shaped structure is quite mobile
except at its beginning where it continues
from the descending colon, and at its end,
where it continues as the rectum.
• Between these points, it is suspended by the
sigmoid mesocolon.
19. Rectum
• Last part of the large intestine
• Rectum is continuous with the
sigmoid colon at the level of S2 -
S3 or at the end of the sigmoid
mesocolon because the
rectum is a retroperitoneal
structure
• Terminates at the upper end of
the anal canal
• The anorectal junction is 2–3 cm
in front of and slightly below the
tip of the coccyx
20. Rectum: Curvatures
• The rectum also deviates in
three lateral curves: upper,
convex to the right; middle,
convex to the left; lower,
convex to the right
• Anteroposterior curvatures:
sacral and anorectal
curvature
• Variable length (12 to 16 cm
long)
• Initial diameter is similar to
that of the sigmoid colon
21. Rectum
Inferiorly it becomes
dilated as the rectal
ampulla
Rectum is the most
posterior element of the
pelvic viscera, is
immediately anterior to,
concave contour of the
sacrum.
22. Rectum
• Rectum differs from the sigmoid
colon in having no sacculations
or appendices epiploicae
• Rectum lacks distinct taeniae
coli muscles
• Rectum is encircled by layer of
longitudinal muscle, which
invests the entire length
Function
• Water absorption (stool is
thickened)
• Absorption of eletrolytes from
the stool
23. Rectum
• Rectum also plays an
important part in defecation
• When stool enters the rectal
ampulla which is usually
empty, it stimulates stretch
receptors
• The information is conveyed
to the CNS, giving the person
the urge to defecate
• The person can now decide
either to initiate or delay
defecation by relaxing or
tensing the levator ani
muscles and the EAS
24. Rectum
• Rectum has three
permanent semi-lunar
transverse folds or valves
of Houston
• Superior fold is at the
beginning of the rectum
may be either on the left
or right
• The middle fold is largest
projecting from the
anterior and right wall
• inferior fold is found on the
left
25. Rectum
• Rectum is subdivided into
3 parts;
• Upper third lies
intraperitoneally
• Middle third lies
retroperitoneally
• Lower third lies
extraperitoneally
26. Rectum
• The upper third of the
rectum is covered by
peritoneum on its anterior
and lateral aspects
• The peritoneum is reflected
superiorly onto the urinary
bladder in males to form the
rectovesical pouch
• In females, onto the
posterior vaginal wall to
form the recto-uterine
pouch (pouch of Douglas)
27. Mesorectum
• mesorectum is enclosed by
mesorectal fascia
• It contains the superior
rectal artery and its
branches, the superior
rectal vein and its
tributaries, the lymphatic
vessels and nodes that lie
along the superior rectal
artery
32. Applied Anatomy
Digital Rectal Examination
-Prostate gland can be
palpated
-- Rectal tumor below
the middle rectal
transverse fold can be
palpated
33. Anal Canal
• The anal canal begins at the terminal end
of the rectal ampulla where it narrows at
the pelvic floor.
• It terminates as the anus after passing
through the perineum.
• As it passes through the pelvic floor, the
anal canal is surrounded along its entire
length by the internal and external anal
sphincters, which normally keep it closed.
34.
35. Anal Canal
• Rectal mucosa lines
the upper part of the
anal canal.
• Anal region
distinguished by a
number of
longitudinally oriented
folds known as anal
columns, which are
united inferiorly by
crescentic folds
termed anal valves.
36. • Superior to each valve is a depression termed
an anal sinus.
• The anal valves together form a circle around
the anal canal at a location known as the
pectinate line,
• Inferior to the pectinate line is a transition zone
known as the anal pecten, which is lined by
nonkeratinized stratified squamous epithelium.
• The anal pecten ends inferiorly at the
anocutaneous line ('white line'), or where the
lining of the anal canal becomes true skin.
38. Anal cushions
Infolding of anal mucosa
Three anal cushions located at
the 3 o'clock, 7 o'clock and 11
o'clock in lithotomy position
Two are located on the right
and one on the left side
These cushions play an
important role for air and
water tight closure of the anal
canal and promote continence
39. Function of Anal cushions
• Internal anal sphincter
alone cannot completely
close the anal canal
• The anal cushions
physiologically contributes
as well to the complete
closure of the anal canal
• When they become
pathological, they are
referred as haemorrhoids
40. Internal anal sphincter
• is a well-defined ring of
obliquely orientated
smooth muscle fibres
continuous with the
circular muscle of the
rectum.
• terminates at the
junction of the
superficial and
subcutaneous
components of the
external sphincter.
• It is usually thinner in
females and becomes
thicker with age.
41. External anal sphincter
• is an oval tube-shaped of
slow twitch skeletal
muscle fibres surrounding
the anal canal
• Consists of 3 parts: deep,
superficial and
subcutaneous
• They are well suited to
prolonged contraction
• Innervated by the inferior
rectal nerve a branch of
pudendal nerve
(voluntary control)
• Function: controls
defecation
51. Reference Books
1. Standring, Susan and Standring (2015).Gray's anatomy.
41st International edition, Elsevier Health Sciences.
ISBN 9780702052309.
2. Keith L. Moore, Arthur F. Dalley, Anne M. R. Agur
(2017). Moore's Clinically Oriented Anatomy, 8th
edition, Walter Kluwer. ISBN 9781496347213.
3. Alan J. Detton (2020). Grant’s Dissector. 17th edition,
Lippincott Williams & Wilkins. ISBN 9781975134600.
4. Adrian Kendal Dixon, David J. Bowden, Bari M. Logan
and Harold Ellis (2017). Human Sectional Anatomy -
Pocket atlas of body sections, CT and MRI images, 4th
edition, CRC Press. ISBN 9781498708548.
