The Anal Canal

Question 1

where is the anal canal found within the GI tract?

Answer 1

The anal canal is the final segment of the gastrointestinal tract

Question 2

where does the anal canal extend between?

Answer 2

extending between the rectum and the anus

Question 3

what is the role of the anal canal?

Answer 3

It has an important role in defecation and maintaining faecal continence

Question 4

where is the anal canal located?

Answer 4

The anal canal is located within the anal triangle of the perineum

Question 5

what does the anal canal lie in close proximity to?

Answer 5

It lies in close proximity to several other important structures in the pelvis and perineum

Question 6

what is anterior to the anal canal in males?

Answer 6

Perineal body
Urogenital diaphragm
Urethra
Bulb of the penis

Question 7

what lies anterior to the anal canal in females?

Answer 7

Perineal body
Urogenital diaphragm
Vagina

Question 8

what lies posterior to the anal canal?

Answer 8

Anococcygeal ligament

Coccyx and sacrum

Question 9

what lies laterally to the anal canal?

Answer 9

Ischioanal fossae

Question 10

about how long is the anal canal in length?

Answer 10

4cm

Question 11

where does the anal canal begin?

Answer 11

It begins as a continuation of the rectum

Question 12

which direction does the anal canal passes?

Answer 12

passes in an infero-posterior direction

Question 13

where does the anal canal terminate?

Answer 13

at the anus

Question 14

when is the anal canal collapsed?

Answer 14

during defecation

Question 15

what is the anal canal collapsed by?

Answer 15

internal and external anal sphincters

Question 16

why does the anal canal need to collapse during defecation?

Answer 16

to prevent the passage of faecal material

Question 17

what is the anal canal surrounded by?

Answer 17

The anal canal is surrounded by internal and external anal sphincters

Question 18

what is the function of the internal and external anal sphincters?

Answer 18

play a crucial role in the maintenance of faecal continence

Question 19

what does the internal anal sphincter surround?

Answer 19

surrounds the upper 2/3 of the anal canal.

Question 20

what forms the internal anal sphincter?

Answer 20

It is formed from a thickening of the involuntary circular smooth muscle in the bowel wall

Question 21

what type of muscle is the external anal sphincter?

Answer 21

voluntary muscle

Question 22

what does the external anal sphincter surround?

Answer 22

surrounds the lower 2/3 of the anal canal

Question 23

what does the external anal sphincter blend in with superiorly?

Answer 23

It blends superiorly with the puborectalis muscle of the pelvic floor

Question 24

what is the anorectal ring?

Answer 24

a muscular ring

Question 25

where is the anorectal ring?

Answer 25

at the junction of the rectum and the anal canal

Question 26

what is the anorectal ring formed by?

Answer 26

It is formed by the fusion of the internal anal sphincter, external anal sphincter and puborectalis muscle

Question 27

when can the anorectal ring be palpated?

Answer 27

on digital rectal examination

Question 28

what lines the superior aspect of the anal canal? which structure is the same lining as?

Answer 28

The superior aspect of the anal canal has the same epithelial lining as the rectum (columnar epithelium)

Question 29

how is the mucosa organised in the anal canal? what is it known as?

Answer 29

organised into longitudinal folds, known as anal columns

Question 30

where are the anal columns joined? what are they joined by?

Answer 30

joined together at their inferior ends by anal valves

Question 31

what is situated above the anal valves?

Answer 31

anal sinuses

Question 32

what are anal sinuses?

Answer 32

small pouches above the anal valves which are referred to as anal sinuses

Question 33

what do anal sinuses contain?

Answer 33

contain glands that secret mucus

Question 34

what do anal valves collectively form? what is it known as?

Answer 34

an irregular circle – known as the pectinate line (or dentate line)

Question 35

what does the pectinate line divide?

Answer 35

This line divides the anal canal into upper and lower parts

Question 36

what is different in the upper and lower parts of the anal canal?

Answer 36

differ in both structure and neurovascular supply

Question 37

why do the upper and lower parts of the anal canal differ in both structure and neurovascular supply?

Answer 37

result of their different embryological origins

Question 38

what is the embryonic origin of structures above the pectinate line?

Answer 38

derived from the embryonic hindgut

Question 39

what is the embryonic origin of structures below the pectinate line?

Answer 39

derived from the ectoderm of the proctodeum

Question 40

what is the anal canal lined by inferior to the pectinate line? what is it known as?

Answer 40

Inferior to the pectinate line, the anal canal is lined by non keratinised stratified squamous epithelium (known as the anal pecten)

Question 41

how does anal pecten look like?

Answer 41

pale and smooth surface

Question 42

when does anal pecten transit into skin?

Answer 42

anal pecten transitions at the level of the inter-sphinteric groove to true skin

Question 43

what type of epithelium is true skin?

Answer 43

keratinised stratified squamous