QS Study

Gross anatomy of the rectum

It is the distal part of the large gut, placed between the sigmoid colon above and the anal canal below. It is the last part of the large intestine and connects the sigmoid colon to the anal canal. It has an important role as a temporary store of faeces.

Situation – In the posterior part of the lesser pelvis, in front of the lower three pieces of the sacrum and the coccyx. It is situated in the posterior part of the lesser pelvis in front of the lower 3 sections of the sacrum and the coccyx and behind the urinary bladder in the male and uterus in the female.

Length – 13 cm. It is about 12 to 16 cm long and may be subdivided into three parts: The upper third lies intraperitoneally, the middle third retroperitoneally and the lower third under the pelvic diaphragm and therefore extraperitoneally.

Extension:

  • Begins – as a continuation of the sigmoid colon at the level of the S3 vertebra.
  • Ends – by becoming continuous with the anal canal at the anorectal junction.

Rectal ampulla – Lower part of the rectum is dilated to form the rectal ampulla.

Curvatures

(i) Two anteroposterior curvatures.

(ii) Three side to side curvatures.

Course

The rectum runs –

(i) 1st downwards and backward.

(ii) Then downwards.

(iii) Finally downwards and forwards.

Relations

(A) Peritoneal relations:

(a) Upper 1/3 rd – Peritoneum covers in front and both sides.

(b) Middle 1/3 rd – peritoneum covers only in front.

(c) Lower 1/3rd – Devoid of the peritoneum.

(B) Visceral relations:

Fig: Sagittal section of the rectum in (a) female and (b) male

(1) Anterior relations: (Anteriorly in male – bladder, ureter, prostate, seminal vesicle)

  • The upper 2/3 of the rectum- Rectovesical pouch containing coils of intestine.
  • The lower 1/3 of the rectum- Urinary bladder.

Terminal parts of ureters, Seminal vesicles, and Ductus deference and prostate.

In females (bladder, ureter, vagina, rectovaginal septum), upper 2/3 of the rectum – Rectouterine pouch containing the coil of the intestine.

Lower 1/3 of the rectum – lower 1/3 of the vagina.

Fig: Posterior relations of the rectum

(2) Posterior relation:

The relations are the same in the male and female –

  • Lower 3 pieces of sacrum, coccyx, and anorectal ligament.
  • Piriformis and levator ani.
  • The medial sacral, sup. Rectal and lower lateral sacral vessels.
  • Sympathetic chain with the ganglion impar, anterior primary rami of S 3,4,5, Co1, the pelvic splanchnic nerves.
  • Lymph nodes and lymphatic vessels.
  • Fat.

Mucosal folds

(i) Longitudinal fold &

(ii) Transverse folds – Upper, middle and lower.