Rectum And Anal Canal

Question 1

Rectum characteristics

Answer 1

Retroperitoneal
Smooth walled
Starts at s2
Very curvy (transversus plicae)

Question 2

Rectal pouches and peritoneum

Answer 2

Upper third: peritoneum on front and back
Middle third: front only
Lower third: none

Question 3

urogenital + Anal triangle location, parts, attachments

Answer 3

Urogenital: 2 ischial tuberosities-> pubis
Anal: 2 ischial tuberosities-> coccyx
Both below pelvic floor

Question 4

True pelvis vs false pelvis

Answer 4

True: inlet to outlet
False: crest to inlet

Question 5

Ischioanal fossa

Answer 5

Between pelvic floor muscle and obturator internus

Filled with fat -> compression when anus expands during pooping

Question 6

Pudendal canal contents and location

Answer 6

Between ischioanal fossa and obturator internus

Internal pudendal artery / internal pudendal vein/ pudendal nerve

Question 7

Pelvic floor muscles

Pelvic wall muscles

Answer 7

Floor: levator ani (puborectalis/pubococcygeus/ iliococcygeus) + coccygeus

Wall: obturator internus + piriformis

Question 8

Puborectalis and defaecation

Answer 8

Puborectalis contracted: anal canal pulled towards pubis -> small anorectal angle
Puborectalis relaxed: anorectal angle large-> pelvic floor lowers -> shit out

Question 9

Pelvic floor location

Answer 9

At anorectal junction

Question 10

Transversus plicae function

Answer 10

Slows passage of faeces

Question 11

What’s the region of rectum right before anus

Answer 11

Rectal ampulla

Question 12

Significance of pectinate line

Answer 12

Splits upper and lower half of anal canal
Upper formed from hindgut
Lower from proctodeum
Upper has venous plexus
Upper has anal columns that end in anal valves

Question 13

What’s pecten

Answer 13

Thin mucosal wall In between pectinate line and white line of hilton (location of transition from epithelium to skin)

Question 14

External anal sphincter constituents

Answer 14

Puborectalis + deep + superficial + subcutaneous

Question 15

Conjoined longitudinal muscle

Answer 15

Innermost muscle
Maintains continence
Continues down and joins skin of anus-> puckering

Question 16

Arterial supply of rectum and anus

Answer 16

Aorta->
IMA: superior rectal artery (rectum + upper anal canal)
Common iliac->
External iliac
Internal iliac: middle rectal (rectum) + internal pudendal-> inferior rectal

Question 17

Location of haemorrhoids and rationale behind position

Answer 17

3/7/11

Location of plexuses

Question 18

Lymphatic drainage of rectum and anus

Answer 18

Superior rectal nodes -> IMN
Middle rectal -> internal iliac -> common iliac -> para-aortic
Inferior rectal-> superficial inguinal -> external iliac

Question 19

somatic + SNS + PNS innervation

Answer 19

SNS : least splanchnic nerve (T12-L2)
PNS: pelvic splanchnic nerves (S2-4)
Somatic: pudendal nerve

Question 20

Neural control of defaecation

Answer 20

Stretch receptors in rectum stimulate pelvic splanchnic nerve (PSN)
-> impulses sent to brain-> urge to shit
-> impulses sent to brain -> SNS inhibited
-> PNS reflex via psn -> contraction of rectum/colon/anus; relaxation of internal anal sphincter
Conscious contraction of external anal sphincter via pudendal nerve keeps Shit off the floor