23-03-23 - Rectum and Anal Canal Flashcards
Learning outcomes
- Describe the anatomy (position, structure, function, blood, nerve supply and lymph drainage) of the rectum and anal canal
- Describe the anatomical basis of defecation
- Discuss the clinical implications of the rectum and the structures within the anal triangle
Which part of the digestive tract is the rectum?
What is it continuous with?
At what level does it begin?
What structures does it follow the curvature of?
Where does the rectum end?
- The rectum is the pelvic part of digestive tract
- It is continuous with sigmoid colon
- It begins in front of the 3rd sacral vertebra
- The rectum follows the curve of the sacrum & coccyx
- It ends in front of the tip of the coccyx by piercing the pelvic diaphragm & becoming continuous with the anal canal
Which parts of the rectum are covered in peritoneum?
What boundary corresponds to the rectovesical/rectouterine pouch?
- The upper 1/3rd of the rectum is completely covered in peritoneum (all 3 surfaces)
- The middle 1/3rd of the rectum has peritoneum on the anterior surface only
- The lower 3rd of the rectum is extraperitoneal
- The boundary between the middle and lower 1/3rd of the peritoneal reflection corresponds to the rectovesical/rectouterine pouch
Where does the rectum have lateral curvatures?
How is the rectal ampulla formed?
Where are the pararectal fossa located?
What 3 structures are present in the large intestine that aren’t present in the rectum?
What is the role of the rectum?
- The rectum has lateral curvatures, coinciding with rectal folds or valves internally – follows the shape of the sacrum
- The lower part of the rectum is expanded to form the rectal ampulla
- Pararectal fossa are located on both sides (similar to paracolic gutters)
- 3 structures are present in the large intestine that aren’t present in the rectum:
1) Taenia
2) Haustra
3) Epiploic appendices - The role of the rectum is the storage of faeces prior to defecation
Rectum misnomers.
What is the name rectum a misnomer?
Does the rectum have mesentery?
What is the mesorectum?
- The name rectum is a misnomer, as “Rectum” from Latin “rectus” meaning straight despite the rectum having a number of flexures
- The rectum does not have a mesentery but surgeons often refer to a mesorectum
- The mesorectum is the perirectal fat that surrounds the rectum and is not an anatomical term recognized by the Terminologia Anatomica
How many transmucosal folds are there?
What is the purpose of these folds?
What do these rectal folds result in the formation of?
- Inside the rectum there are 3 transverse mucosal folds which do not disappear when rectum is distended
- These folds slow down the descent of the stool
- The rectal folds result in the formation of 3 lateral flexures:
1) Superior and inferior on left side
2) Intermediate on right side
What is the anorectal flexure (anorectal junction/angle, perineal flexure)?
How is it caused? What does the puborectalis muscle do during defecation?
- The anorectal flexure (anorectal junction/angle, perineal flexure) is the unction between the rectum and anal canal
- It is caused by the anterior pull of the rectum by puborectalis muscle (part of the levator ani muscle)
- During defecation, the puborectalis muscle relaxes, making the rectum and anal canal more straight
What are the 8 anatomical relations to the rectum in males?
- 8 Anatomical relations to the rectum in males:
1) Bladder
2) Rectovesical pouch (7.5 cm above)
3) Rectoprostatic fascia (Denonvillier’s fascia)
4) Prostate (palpable per rectum)
5) Pelvic plexus (at risk in rectal surgery)
6) Seminal vesicles
7) Ductus deferens
8) Ureter
Rectum in males diagram
What are the 8 anatomical relations to the rectum in females?
- 8 anatomical relations to the rectum in females
1) Rectouterine pouch (of Douglas) (7.5 cm above)
2) Rectovaginal fascia
3) Pubic symphysis
4) Bladder
5) Upper part of vagina
6) Rectum
7) Puborectalis
8) Anococcygeal body
What does the anal canal function as?
How long is it?
What structures does it extend between?
What structure is the anal canal related to laterally?
- The anal canal functions as the conduit to outside world
- It is approximately 4cm long
- The anal canal runs from the pelvic diaphragm to the anus
- It is related to ischioanal fossa laterally
What 3 structures surround the anal canal?
What is the anorectal ring?
What happens if the anorectal ring is damaged?
How can this occur?
What structures are included in the anorectal ring?
- 3 structures surround the anal canal:
1) Levator ani
2) External anal sphincter
3) Internal anal sphincter - The anorectal ring is a muscular structure at the junction of the anal canal and the rectum
- If the anorectal ring is damaged, it can cause bowl incontinence
- This can occur during uncontrolled vaginal delivery
- The anorectal ring includes the puborectalis sling and upper portions of the internal and external sphincters
What is the internal anal sphincter made from?
How is it controlled?
What is it derived from?
What is the external anal sphincter made from?
What are the 3 parts of the external anal sphincter?
What does the external anal sphincter fuse with?
- The internal anal sphincter is made from smooth muscle, meaning it is autonomic controlled
- It is delivered from the circular muscle layer
- The external anal sphincter is made from striated muscle
- 3 parts of the external anal sphincter:
1) Deep
2) Superficial
3) Subcutaneous - The external anal sphincter fuses with the puborectalis to form the anorectal ring
Anal canal neurovascular diagram
What are anal columns?
What does each anal column have?
- In the upper part of the anal canal, there are 8-10 longitudinal folds called anal columns
- Each anal column has their own branches of:
1) Superior rectal vein
2) Superior rectal artery
3) Anal valve connections
4) Lymphatics
5) Nerves
How does each anal column unite with each other?
What is behind each anal valve?
What does each anal sinus contain the openings to?
- Anal columns unite with each other inferiorly and form anal valves.
- Superior/behind to each valve is a crypt termed an anal sinus (crypt)
- The anal sinuses contain the openings of mucous glands, which allow for the lubrication of the faeces
What forms the pectinate (dentate) line?
What 2 structures are located at the pectinate line?
What structures is inferior to the pectinate line?
What is the anal pecten innervated by?
What 4 senses does this allow for?
Where does the anal pecten end?
- All anal valves form pectinate (dentate) line
- 2 structures are located at the pectinate line:
1) Where cloacal (anal) membrane was
2) Endoderm-ectoderm (proctodeum)
* Boundary between the endoderm of the hindgut and the ectoderm of the skin
- Inferior to the pectinate line is a transition zone known as the anal pecten/intermediate zone
- The anal pecten is Supplied by inferior rectal nerve
- 4 senses the inferior rectal nerve allows for:
1) Pain
2) Temperature
3) Touch
4) Pressure - The anal pecten ends inferiorly at the anocutaneous line (“white line”), or where the lining of the anal canal becomes true skin (keratinized squamous epithelium
Anal canal labelled diagram
Rectum and anal canal arterial supply.
What is the arterial supply to the superior, middle and below the anorectal line parts of the rectum and anal canal?
What artery can cause bleeding during surgery?
- Rectum and anal canal arterial supply:
1) Superior 1/3
* Inferior mesenteric artery to Superior rectal artery
2) Middle 1/3:
* Internal iliac to Middle rectal artery
3) Below anorectal line:
* Internal pudendal to Inferior rectal artery
* Inferior mesenteric artery to Superior rectal artery
* A contribution from the median sacral artery may cause bleeding during surgery
What are the 2 venous plexuses of the rectum and anal canal?
Where is the internal rectal plexus located?
What structures does it drain to?
What anal cushions does it form?
What is the role of these anal cushions?
- 2 venous plexuses of the rectum and anal canal:
1) Internal rectal plexus
2) External venous plexus - The internal rectal plexus is located in the submucosa
- It drains to the superior and inferior rectal vein
- Forms anal cushions (larger anal columns) seen at 3, 7, 11 o’clock in the lithotomy position (position when giving birth
- These anal cushions close the anal sphincters and make it gas and water tight
Where is the external venous plexus located?
What is the venous drainage for the superior, middle, and inferior rectum and anal canal?
- The external venous plexus is located within and outside of the muscle layer (sphincter)
- Venous drainage for the superior, middle, and inferior rectum and anal canal:
1) Superior 1/3
* Superior rectal to inferior mesenteric to Hepatic portal vein
2) Middle 1/3
* Middle rectal to internal iliac + internal pudendal vein to IVC
3) Inferior 1/3
* Inferior rectal to internal iliac + internal pudendal vein to IVC
What happens if the hepatic portal systems become blocked?
- If the hepatic portal systems become blocked, the venous plexuses will get bigger, forming piles (haemorrhoids)
Where do epicolic lymph nodes in the wall of the rectum and anal canal drain?
What is the lymphatic drainage for the following structures:
1) Superior rectum
2) Inferior rectum & proximal anal canal
3) Distal anal canal
- Lymphatic drainage of rectum and anal canal:
1) Epicolic lymph nodes (along the wall of rectum and anal canal)
2) to paracolic (along the vessels)
3) to intermediate (in meso)
4) to principal lymph nodes (around origin of artery) - Lymphatic drainage for the following structures:
1) Superior rectum
* Inferior mesenteric nodes
2) Inferior rectum & proximal anal canal
* Internal iliac nodes
3) Distal anal canal
* Superficial inguinal nodes
What is the parasympathetic supply to the rectum and anal canal?
What are 3 functions of the parasympathetics in the rectum and anal canal?
Where do sympathetics from the rectum and anal canal come from?
- Parasympathetic supply to the rectum and anal canal is from S2-4 via pelvic splanchnic nerves, which forms the pelvic (inferior hypogastric) plexus
- 3 functions of the parasympathetics in the rectum and anal canal:
1) Increase peristaltism
2) Relax anal sphincter
3) Visceral senses (follow parasympathetics, as they are below the pelvic pain line) - Sympathetics for the rectum and anal canal come from L1-2(3) via lumbar splanchnic nerves
- The sympathetics contract the internal anal sphincter
Where do somatic nerves for the rectum and anal canal come from?
What 2 structures do the somatic nerves supply in the rectum and anal canal?
What is the Somatic afferent below the dentate line of the anal canal?
- Somatic nerves for the rectum and anal canal come from S2-4, which forms the pudendal nerve
- 2 structures the somatic nerves supply in the rectum and anal canal:
1) External anal sphincter
2) Adjacent pelvic floor muscles (puborectalis) - The somatic afferent below the dentate line of the anal canal is pudendal nerve
