Superior Mesenteric Artery (and inferior....)

Last time I promised a piece on the superior mesenteric artery - a major trunk from the abdominal aorta, and one other topic I have really grappled with in the past: especially in dissection! SO without further ado, let's introduce....

The Superior Mesenteric Artery
It comes from L1. and hides behind the stomach, splenic vein and neck of the pancreas. P(pancreas)posterior to the two Ss (stomach and splenic vein)

- It sits in front of the left renal vein, inferior duodenum and uncinate process of the pancreas.


- The uncinate process hooks around the back of the superior mesenteric artery.

Supplies: Can you remember how the coeliac trunk supplied the foregut? Well guess what the superior mesenteric supplies, if not the foregut? The midgut! That's right, the superior mesenteric artery supplies the major duodenal papilla and the first 2/3 of the transverse colon

•SO without further ado - let us begin...

•The superior mesenteric artery comes from the front of the abdominal aorta and divides into six branches

•1. Middle colic

•2. Jejunal

•3. Ileal

•4. Ileocolic

•5. Middle colic

•6. Inferior pancreaticoduodenal: we have already met this artery before in the previous post on the coeliac trunk, and provides a link between the arterial supply of the midgut and foregut.  

--> You can remember these with the mnemonic: In My Room I'm In Jail. (I = ileocolic, m = middle colic, r = ?, I = ill, i = inferior pancreaticoduodenal, j = jejunal) <--

a. •The Middle Colic artery: supplies the transverse colon. ("In the middle")

•This divides into the left and right colic arteries.

•- The left colic anastomoses with the inferior mesenteric artery which supplies the hind gut. 

- The right colic - well see below... :)

b. The Right Colic artery – supplies the ascending colon: ("right up"). 

•Yes - this is the artery mentioned above: the right colic and middle colic arteries anastomose after branching off from the superior mesenteric artery. 

•- The right colic artery also anastomoses with the ileocolic branch from the superior mesenteric artery.

c. •Ileocolic artery – supplies the ileum, caecum and appendix (in the name)

•The ileocolic artery divides into:

•- Ascending colic artery

•- Anterior caecal

•- Posterior caecal

•- Appendicular

d•Ileal and Jejunal - these form anastomotic arcades – basically intricate connections between layers of mesentery. They form the marginal artery of Drummond - this is basically the arterial connections around the inner border of the colon made up of the branches of the ileocolic, right colic and middle colic from the superior mesenteric artery. It is also made up of branches from the inferior mesenteric artery (another branch of the abdominal aorta), namely the left colic artery and sigmoid branches. This is named after the English surgeon: Hamilton Drummond. 

  From these anastamotic arcades, there are smaller straight arteries – the vaa recta (literally straight vessels) which supply the organs. 

Important clinical note: The superior mesenteric artery stops supplying the gut at the splenic flexure - where the inferior mesenteric artery supply begins. Because the splenic flexure is the junction between the superior mesenteric artery and inferior mesenteric artery and is known as Griffith's point. This is vulnerable to ischaemia because the arterial connections in this area are particularly weak. 

•- SO what’s the difference between arcades in the ileum and jejunum? Well the ileum has more arterial arcades with short vasa recta, as opposed to the jejunum which has small arterial arcades and long vasa recta.

The Arc of Riolan...? (Mesenteric meandering artery of Moskowitz). What is it and why is it important? 
So if you have ever looked at the arteries of the midgut and handgun before, I bet you've heard of the Arc of Riolan. But what exactly is it?

Basically it is a connection between the inferior mesenteric artery and the superior mesenteric artery. When the arteries of the gut are occluded, this connection provides collateral flow to some of the organs. 

Quick review before moving on
Before you go any further why not test your understanding with a few quick questions? Try these and see how you do :)

Problem 1:

a. Inferior pancreaticoduodenal
b. middle colic
c. right colic
d. ileocolic
e.appendicular artery
f. ileal artery
g. jejunal artery
h. superior mesenteric

Problem 2: 

a. Ileal
b. Jejunal
c. RCA
d. MCA

Problem 3: a bit easier this time

a. = middle colic
b. = right colic
c = marginal artery of drummon
d = ileocolic
e. superior rectal
f = middle sacral
g = superior mesenteric artery

•The Inferior Mesenteric

•Yep – that’s right, we are doing two branches of the abdominal aorta today (the superior AND inferior mesenteric artery) to make up for my short hiatus from this blog, and also – well it just makes sense to combine the two doesn’t it? I know you want to :)

So here are the branches - just remember Inferior is LESS! :)

•1. Left colic – divides into ascending and descending branches. The ascending branch passes to the left kidney, transverse mesocolon, the dexcending colon and distal transverse colon. Meanwhile the descending branch supplies the descending colon and anastmoses with the first sigmoid artery (another branch of the inferior mesenteric artery.

•2. E- (doesn't stand for anything - this is a filler letter)

3. Sigmoid arteries - these are two to four branches off the inferior mesenteric artery which supply the sigmoid colon. They make connections with two other arteries:

- The left colic artery 

4.  superior rectal artery: this is an interesting artery, also known as the superior haemorrhoidal artery and is found in the anus as the continuation of the inferior mesenteric artery. 

3. Superior rectal artery (haemorrhoidal artery) - this divides into two on either side of the anus - the left and right superior rectal artery which then divide further.

Adapted from https://courses.lumenlearning.com/ap2/chapter/circulatory-pathways/

Clinical relevance:
The superior rectal artery is also known as the haemorrhoidal artery because when a part of it becomes swollen, the patient may suffer from haemorrhoids. 

So that's it for today folks - see you next time :) Probably for veins of the gut or the venous sinuses, we are just going to have to wait and see. . . 

One final summary review section....
Problem 1: 

1= superior mesenteric artery

2 = jejunal branches

3 = ill branches

4 = superior mesenteric artery

5 = ileocolic artery

7 = right colic artery

8 = middle colic artery

Case courtesy of Dr Donna D'Souza, <a href="https://radiopaedia.org/">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/36188">rID: 36188</a>

2. 

a = inferior mesenteric artery
b. = left colic artery
c. = sigmoid arteries
d = marginal artery of drummond
e = middle colic artery
f = right colic
g = ileoclic
h = ileal
i = appendicular

References:

Teach me Anatomy

Radiopaedia

http://knowmedge.com/medical_mnemonics/Anatomy_mnemonics/Superior-Mesenteric-Artery-Branches/368
NIDDK
Elesvier 2005 (Gray's Anatomy) - all pictures unless said otherwise

• McGraw-Hill 2005