Anal canal/rectum WTF??!

[tasar1898]

today is GI day and this is driving me crazy..

Plz someone explain pectinate line and lower upper rectum.. Is anal canal = lower rectum??

Also WHY doesn't inferior rectum drain to IMA nodes if it's supplied by superior rectal
FA says that only superior rectum drains to IMA nodes , inferior rectum to Internal iliac and anal canal to superficial inguinal ...

I thought that you only separate anal canal with rectum with the pectinate line.. Is there another distinction between superior and inferior rectum?

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[Focused1]

Firstly..

Is anal canal = lower rectum??

The rectum is the rectum and the anal canal is the anal canal.. 🙄


Secondly

I thought that you only separate anal canal with rectum with the pectinate line

Incorrect. The line and this entire conversation for that matter is about the anal canal and not the rectum.

The Anal Canal is divided EMBRYOLOGICALY into 2 parts by the pectinate line (aka Hilton's line): The upper part is derived from the endoderm. The lower from the ectoderm. The upper part thus has columnare epithelium, the lower has striated squamous non-keratinized. The rest of the differences are in FA.. the pectinate line is for the anal canal not rectum.

 

[tasar1898]

Firstly..



The rectum is the rectum and the anal canal is the anal canal.. 🙄


Secondly



Incorrect. The line and this entire conversation for that matter is about the anal canal and not the rectum.

The Anal Canal is divided EMBRYOLOGICALY into 2 parts by the pectinate line (aka Hilton's line): The upper part is derived from the endoderm. The lower from the ectoderm. The upper part thus has columnare epithelium, the lower has striated squamous non-keratinized. The rest of the differences are in FA.. the pectinate line is for the anal canal not rectum.

I love you... My anatomy basics are non existent and this was really confusing me since it's not very clear in FA

So is that correct?? --> superior rectum -- superior rectal a.(from IMA) - IMA nodes -- portal system

Inferior rectum + anal canal above pectinate -- superior rectal a. (From IMA) - internal iliac nodes -- portal system

Anal canal below pectinate --- middle and inferior rectal a.(from pudendal a. ) -- superficial inguinal nodes -- caval system


Appreciate your answer

 

[Mad Jack]

I love you... My anatomy basics are non existent and this was really confusing me since it's not very clear in FA

So is that correct?? --> superior rectum -- superior rectal a.(from IMA) - IMA nodes -- portal system

Inferior rectum + anal canal above pectinate -- superior rectal a. (From IMA) - internal iliac nodes -- portal system

Anal canal below pectinate --- middle and inferior rectal a.(from pudendal a. ) -- superficial inguinal nodes -- caval system


Appreciate your answer

Sounds about right. It's important to know because metastases.

 

[tasar1898]

Thanks a lot

 

[Mad Jack]

No problem. Oh, the other big thing to remember is the sensory innervation- above the pectinate line, you have visceral sensory innervation, so hemorrhoids and the like are painless, while below it, hemorrhoids are painful. That'll probably come up once on the boards, they love hemorrhoids.

 

[tasar1898]

@Mad Jack
Cool , at least I know that.. Would you mind clarifying this for me??

External hemorrhoids = thrombosis/inflammation of inferior / middle rectal v. + excruciating pain due to innervation via pudendal n.

Internal hemorrhoids = thrombosis/inflammation ( well that equals thrombophlebitis right?) of superior rectal v. + no pain due to visceral innervation only

Anorectal varices = just dilation and engorgement of both superior and middle/inferior rectal v. and risk of bleeding . Painless

Is the above "classification" correct?

 

[DrPicard]

If I remember correctly, varices and hemorrhoids are both dilations of these veins, with the distinction being the former are asymptomatic. Once symptoms develop (such as prolapsing, bleeding etc), its more apt to use the term hemorrhoids. (Please confirm this).

Internal hemorrhoids cause painless bleeding, yes, due to visceral innervation. But they CAN become painful - if they get thrombosed or inflamed.

 

[DrPicard]

Inflammation and ischemia will lead to pain, regardless of the type of innervation (mesenteric ischemia, inflammatory bowel disease etc are painful despite visceral innervation).

 

[tasar1898]

Yeah makes sense.. I read on Wikipedia that both lead to same clinical picture but have different therapies/etiologies...

 

[voicesinmyhead]

@Mad Jack
Cool , at least I know that.. Would you mind clarifying this for me??

External hemorrhoids = thrombosis/inflammation of inferior / middle rectal v. + excruciating pain due to innervation via pudendal n.

Internal hemorrhoids = thrombosis/inflammation ( well that equals thrombophlebitis right?) of superior rectal v. + no pain due to visceral innervation only

Anorectal varices = just dilation and engorgement of both superior and middle/inferior rectal v. and risk of bleeding . Painless

Is the above "classification" correct?

But Uworld says Internal hemorrhoids are from Superior and Middle rectal veins, and external are from Inferior Rectal veins.

Check attachment.

This seems weird, since like @tasar1898 said before, the venous supply above pectinate is SRV, and below are the caval tributaries - MRV and IRV.

 

[zeevee]

@voices
Thats correct both have their own respective venous drainage .The internal haemorrhoids ,from above the dentate line, drain mainly into the portal sys ( IMV) while the external haemorrhoids drain into the systemic venous system ( pudendal vn via inferior reactal vn) and that becomes an important point because in portal HTN due to back pressure from the portal venous system the inferior rectal vein (systemic venous system) might rupture open .

 

[tasar1898]

@voicesinmyhead Yeah dont worry so much about that , because obviously external ''superior'' hemorrhoids will have an middle rectal part , just like internal ''inferior'' hemorrhoids because there is overlap in the venous drainage. Just know that most of the time external drain to caval system , and internal to portal system and also check a couple of pictures so you know what you are looking at if they show you a picture of an ass or smthing

 

[voicesinmyhead]

and that becomes an important point because in portal HTN due to back pressure from the portal venous system the inferior rectal vein (systemic venous system) might rupture open

you mean the SRV (portal) increased pressure will get transmitted to the IRV (IVC) leading to bursting of both? (Variceal rupture?)

 

[voicesinmyhead]

also check a couple of pictures so you know what you are looking at if they show you a picture of an ass or smthing

Yessir. Will do! 🙂

 

[zeevee]

Yes , I believe thats the concept behind portal HTN.In normal individuals portal vein drains to system vein IVC but in portal HTN due to liver destruction there is resistance to forward flow so the portal blood flows backwards .Retrograde blood flow seen by doppler US in the liver is a dxic test for portal HTN .
Similarly at rectal level the portal veins drain backwards to the systemc veins giving rise to varices which are prone to rupture .
The portal shunt TIPS relieves that resistance at the liver level and the the forward flow is maintained .

Portal HTN is like putting your foot on a garden hose , if that hose has a second connection the water will start flowing towards that direction , let it be sideways or backwards but it wont be forwards .

 

[Reperfused]

Since my question is related to the above discussion, I decided to post it here.

Where exactly does the hindgut end?
I know, you'll say at the dentate (pectinate line).

So everything above this line is supplied by the branches of IMA (superior and middle rectal arteries) and everything below is supplied by the branches of internal iliac artery (inferior rectal artery). ok makes sense till here.

BUT THEN,
The inferior rectal artery also supplies the lower third of the rectum. If hindgut is ending at the pectinate line that means everything above it (including the whole of rectum) should be supplied by hindgut's artery (IMA), right?
Then why is this not the case? This will make me doubt that perhaps the hindgut ends at the junction of middle and inferior third of the rectum. But then that can't be cuz IMA branches goes below it to supply the superior part of the anal canal.
Ahhhh so confusing!

If someone can please explain this.

 

[runthiscity]

Since my question is related to the above discussion, I decided to post it here.

Where exactly does the hindgut end?
I know, you'll say at the dentate (pectinate line).

So everything above this line is supplied by the branches of IMA (superior and middle rectal arteries) and everything below is supplied by the branches of internal iliac artery (inferior rectal artery). ok makes sense till here.

BUT THEN,
The inferior rectal artery also supplies the lower third of the rectum. If hindgut is ending at the pectinate line that means everything above it (including the whole of rectum) should be supplied by hindgut's artery (IMA), right?
Then why is this not the case? This will make me doubt that perhaps the hindgut ends at the junction of middle and inferior third of the rectum. But then that can't be cuz IMA branches goes below it to supply the superior part of the anal canal.
Ahhhh so confusing!

If someone can please explain this.

If I'm reading your post correctly, I think you got a little messed up somewhere along the line (completely understandable, there's a butt load of crap we're supposed to know!) I think you're making the assumption that the pectinate line separates the rectum from the sigmoid colon? However, the pectinate line separates the superior 2/3 and inferior 1/3 of the rectum (think of it like the esophagus... top 2/3 follow one rule, bottom 1/3 follow another; also kinda similar to the tongue!) Here's the simplest way I can put things:

(main artery) --> (branch(es)) --> (supply)
IMA --> superior rectal a. --> anal canal above pectinate line (still part of hindgut, follows the "hindgut = IMA" rule)
internal iliac a.--> middle rectal a. --> anal canal below pectinate line
internal iliac a. --> internal pudendal a. --> inferior rectal a. --> anal canal below pectinate line

So, above pectinate line = branch of IMA; below pectinate line = branches of internal iliac.
Remember, the superior/upper 2/3 of the anal canal is above the pectinate line = hindgut derivative. The inferior/lower 1/3 of the anal canal is below the pectinate line = ectoderm derivative.

Hope that helps! (And if I'm incorrect... Ignore everything I said that confuses you further!)

Edit: my bad; I changed the wording so hopefully it is correct now should anyone stumble upon this in the future.

 

[Pholston]

So everything above this line is supplied by the branches of IMA (superior and middle rectal arteries) and everything below is supplied by the branches of internal iliac artery (inferior rectal artery). ok makes sense till here.

BUT THEN,
The inferior rectal artery also supplies the lower third of the rectum. If hindgut is ending at the pectinate line that means everything above it (including the whole of rectum) should be supplied by hindgut's artery (IMA), right?
Then why is this not the case? This will make me doubt that perhaps the hindgut ends at the junction of middle and inferior third of the rectum. But then that can't be cuz IMA branches goes below it to supply the superior part of the anal canal.
Ahhhh so confusing!

If someone can please explain this.

Pectinate line divides the upper two thirds and lower third of the anal canal.
The anal canal above the pectinate line is supplied by the superior rectal artery, which is the terminal branch of the inferior mesenteric artery. The middle rectal artery (a branch of the internal iliac artery) and the inferior rectal artery (a branch of the internal pudendal artery which is a branch of the internal iliac artery) supply the lower anal canal below the pectinate line.

The inferior rectal artery supplies blood to the lower anal canal NOT the rectum.

 

[Reperfused]

I know very well that pectinate line divides the anal canal.

Sorry if my wordings have been unclear. But what I'm trying to ask is, how can a branch of internal iliac artery ( internal pudendal artery)--> inferior rectal artery goes on to supply the lower third of the rectum? When it's supposed to supply below pectinate structures only.
If hindgut ends at the pectinate line, it means superior portion of the anal canal as well the whole of rectum (upper, middle and inferior parts) should be supplied by IMA. Rectum comes before anal canal, no?

 

[Pholston]

If I'm reading your post correctly, I think you got a little messed up somewhere along the line (completely understandable, there's a butt load of crap we're supposed to know!) I think you're making the assumption that the pectinate line separates the rectum from the sigmoid colon? However, the pectinate line separates the superior 2/3 and inferior 1/3 of the rectum (think of it like the esophagus... top 2/3 follow one rule, bottom 1/3 follow another; also kinda similar to the tongue!) Here's the simplest way I can put things:

(main artery) --> (branch(es)) --> (supply)
IMA --> superior rectal a. --> rectum above pectinate line (still part of hindgut, follows the "hindgut = IMA" rule)
internal iliac a.--> middle rectal a. --> rectum below pectinate line
internal iliac a. --> internal pudendal a. --> inferior rectal a. --> rectum below pectinate line

So, above pectinate line = branch of IMA; below pectinate line = branches of internal iliac.
Remember, the superior/upper 2/3 of the rectum is above the pectinate line = hindgut derivative. The inferior/lower 1/3 of the rectum is below the pectinate line = ectoderm derivative.

Hope that helps! (And if I'm incorrect... Ignore everything I said that confuses you further!)

Pectinate line divides the upper two thirds and lower third of the anal canal.

Just replace "rectum" with "anal canal" and everything will be fine!

 

[Pholston]

I know very well that pectinate line divides the anal canal.

Sorry if my wordings have been unclear. But what I'm trying to ask is, how can a branch of internal iliac artery ( internal pudendal artery)--> inferior rectal artery goes on to supply the lower third of the rectum? When it's supposed to supply below pectinate structures only.

Inferior rectal artery does NOT supply the lower third of the rectum. It supplies the lower anal canal (below the pectinate line). Upper half of anal canal (below the pectinate line) is supplied by middle rectal artery which is a branch of the internal iliac artery NOT inferior mesenteric artery (IMA).

If hindgut ends at the pectinate line, it means superior portion of the anal canal as well the whole of rectum (upper, middle and inferior parts) should be supplied by IMA. Rectum comes before anal canal, no?

Yes it does.
The anal canal above the pectinate line is supplied by the terminal branches of the superior rectal artery, which is the terminal branch of the inferior mesenteric artery.

 

[Reperfused]

Inferior rectal artery does NOT supply the lower third of the rectum. It supplies the lower anal canal (below the pectinate line). Upper half of anal canal (below the pectinate line) is supplied by middle rectal artery which is a branch of the internal iliac artery NOT inferior mesenteric artery (IMA).

Yes it does.
The anal canal above the pectinate line is supplied by the terminal branches of the superior rectal artery, which is the terminal branch of the inferior mesenteric artery.

Okay so this is what I was looking for. Thanks!!
The way it's written in some books it implies as if inferior rectal artery supplies the lower third part of the rectum! Then which artery does?

Everything else I understand. But thanks a billion for pointing out where exactly I was making a wrong connection.

 

[Pholston]

Okay so this is what I was looking for. Thanks!!
The way it's written in some books it implies as if inferior rectal artery supplies the lower third part of the rectum! Then which artery does?

Everything else I understand. But thanks a billion for pointing out where exactly I was making a wrong connection.

For Step 1 purposes superior rectal artery supplies the rectum and part of the anal canal above pectinate line.
Yes, some books do mention that middle and inferior rectal artery supply the lower part of the rectum.
However, what they should be saying that middle and inferior rectal arteries are capable of supplying the lower part of the rectum due to their rich anastomotic connections with the superior rectal artery (which is the anatomical basis of anorectal varices in portal hypertension as venous drainage mirrors arteries).

 

[Reperfused]

ok got it, finally. Thanks a lot!

 

[runthiscity]

I know very well that pectinate line divides the anal canal.

Sorry if my wordings have been unclear. But what I'm trying to ask is, how can a branch of internal iliac artery ( internal pudendal artery)--> inferior rectal artery goes on to supply the lower third of the rectum? When it's supposed to supply below pectinate structures only.
If hindgut ends at the pectinate line, it means superior portion of the anal canal as well the whole of rectum (upper, middle and inferior parts) should be supplied by IMA. Rectum comes before anal canal, no?

Sorry about that- I apparently got confused while reading your original post, I didn't mean to make false assumptions about your knowledge. Good thing @Pholston cleared everything up as I was just making things worse 😕