W3: Vasculature, innervation and reflexes of alimentary tract

Question 1

Level of origin of coeliac

Answer 1

T12

Question 2

Coeliac organs

Answer 2

abdominal oesophagus
stomaCh
duodenum up to ampulla of vater panCreas
spleen
liver

Question 3

What does coeliac trunk split into?

Answer 3

Left gastric
Splenic
Common hepatic

Question 4

Left gastric

Answer 4

It ascends across the diaphragm, giving rise to oesophageal branches, before continuing anteriorly along the lesser curvature of the stomach. Here, it anastomoses with the right gastric artery.

Question 5

Where does splenic come out of coeliac?

Answer 5

Just below left gastric

Question 6

Splenic

Answer 6

Left towards spleen, behind stomach

5 terminal branches supply spleen

In addition to supplying the spleen, the splenic artery also gives rise to several important vessels:

Left gastroepiploic: supplies the greater curvature of the stomach. Anastomoses with the right gastroepiploic artery.

Short gastrics: 5-7 small branches supplying the fundus of the stomach.

Pancreatic branches: supply the body and tail of the pancreas.

Question 7

What is the only branch of the coeliac going right

Answer 7

Common hepatic

Question 8

What does the common hepatic split into?

Answer 8

Proper hepatic and gastroduodenal

Question 9

What does proper hepatic split into?

Answer 9

Right gastric: supplies the pylorus and lesser curvature of the stomach.

Right and left hepatic: divide inferior to the porta hepatis and supply their respective lobes of the liver.

Cystic: branch of the right hepatic artery – supplies the gall bladder.

Question 10

What does gastroduodenal branch into?

Answer 10

Right gastroepiploic: supplies the greater curvature of the stomach. Found between the layers of the greater omentum, which it also supplies.

Superior pancreaticoduodenal: divides into an anterior and posterior branch, which supplies the head of the pancreas. (inf comes from sup mes)

Question 11

Where do midgut structures start and end?

Answer 11

hich spans from the major duodenal papilla (of the duodenum) to the proximal 2/3 of the transverse colon.

Question 12

Which level SMA?

Answer 12

L1

Question 13

What does SMA branch into?

Answer 13

Inferior pancreatoduodenal

Jejunal and ileal

Middle and right colic

Ileocolic

Question 14

Inferior pancreatoduodenal

Answer 14

The inferior pancreaticoduodenal artery is the first branch of the SMA. It forms anterior and posterior vessels, which anastomose with branches of the superior pancreaticoduodenal artery (derived from the coeliac trunk). This network supplies the inferior region of the head of the pancreas, the uncinate process, and the duodenum.

Question 15

Jejunal and Ileal Arteries

Answer 15

The superior mesenteric artery gives rise to numerous arteries that supply the jejunum and ileum.

The arteries pass between the layers of the mesentery and form anastomotic arcades – from which smaller, straight arteries (known as the “vasa recta”) arise to supply the organs (fig 2).

The jejunal blood supply is characterised by a smaller number of arterial arcades, but longer vasa recta. In contrast, the ileal blood supply is marked by more arterial arcades with shorter vasa recta.

Question 16

Middle and Right Colic Arteries

Answer 16

The right and middle colic arteries arise from the right side of the superior mesenteric artery to supply the colon:

Middle colic artery – supplies the transverse colon.

Right colic artery – supplies the ascending colon.

Question 17

Ileocolic Artery

Answer 17

The ileocolic artery is the final major branch of the superior mesenteric artery. It passes inferiorly and to the right, giving rise to branches to the ascending colon, appendix, cecum, and ileum. In cases of appendectomy, the appendicular artery is ligated.

Question 18

What are the organs of the hindgut?

Answer 18

1/3 of the transverse colon, splenic flexure, descending colon, sigmoid colon and rectum.

Question 19

IMA which level?

Answer 19

L3

Question 20

Main branches of IMA?

Answer 20

left colic artery, sigmoid artery and superior rectal artery.

Question 21

Left Colic Artery

Answer 21

The left colic artery is the first branch of the IMA. It supplies the distal 1/3 of the transverse colon and the descending colon. After arising from its parent artery, it travels anteriorly to the psoas major muscle, left ureter and left internal spermatic vessels, before dividing into ascending and descending branches:

Ascending branch – crosses the left kidney anteriorly, before entering the mesentery of the transverse colon, moving superiorly. It supplies the distal 1/3 of the transverse colon, and the upper aspect of the descending colon.

Descending branch – moves inferiorly to supply the lower part of the descending colon. It anastomoses with the superior sigmoid artery.

Question 22

Sigmoid Arteries

Answer 22

descending colon and the sigmoid colon.

Question 23

Superior Rectal Artery

Answer 23

Rectum

*Supplies all rectal mucosa

Question 24

Mneumonic for branches of abdominal aorta

Answer 24

Prostitutes cause super super red testicles lumbering into my cock

Inferior phrenic

Coeliac

Superior mesenteric

Middle suprarenal (adrenal)

Renal

Testicular (gonadal)

Lumbar

Inferior mesenteric

Middle sacral

Common iliac

Question 25

Discuss levels at which branches from the abdominal aorta exit

Answer 25

T12

Inferior phrenic

Coeliac

L1

Middle adrenal

1st lumbar

Renal

Superior mesenteric

L2

Gonadal

2nd lumbar

L3

3rd lumbar

Inferior mesenteric

L4

4th lumbar

Question 26

Where does abdominal aorta bifurcate?

Answer 26

L4

Question 27

Discuss anterior trunk of internal iliac

Answer 27

Will go on to supply pelvic viscera:

Obturator - supplies adductors of thigh, iliac, iliacus, bladder (obturator foramen)

Umbilical (has a pelvic and distal which becomes obliterated in adults) - main branch is superior vesicle which goes on to supply superior bladder

Inferior vesical – supplies bladder

Middle rectal – supplies the distal rectum above pectinate line

Internal pudendal – supplies perineum (leaves via greater sciatic foramen) and external genitalia

Inferior gluteal – supplies gluteus medius & minimus and the acetabulofemoral joint.

Oxford university is more interesting inebriated

Question 28

Difference between internal iliac in males and females

Answer 28

Females:

uterine artery - uterine cervix and vaginal branches to vagina

arises just below to obturator

This forms anastomosis with ovarian artery

Males:

The inferior vesicle also supplies prostate and seminal vesicles

Superior vesicle (proximal part of umbilical) gives direct branch to ductus deferens

Question 29

Discuss posterior trunk of internal iliac

Answer 29

Iliolumbar – quadratus lumborum, psoas major, iliacus, cauda equina

Lateral sacral – erector spinae, piriformis, skin of lower back

Superior gluteal – piriformis, gluteus maximus, obturator internus

Question 30

What drains into the hepatic portal vein?

Answer 30

The superior mesenteric vein, the inferior mesenteric vein, and the splenic vein

Question 31

Rectal venous plexus

Answer 31

a venous plexus resting on the posterior and lateral walls of the rectum; it drains into the superior rectal vein to the portal, the middle rectal to the internal iliac, and the inferior rectal to the internal pudendal.

Question 32

Discuss abdominal lymph nodes

Answer 32

Converge around the aorta

3 main types:

Preaortic. - in front - coeliac, superior and inferior mesenteric

Para-aortic/lumbar - lateral to aorta - iliacnodes, gonads and other pelvic organs

Retro-aortic - behind - general

Question 33

Discuss pelvic lymphatics (draw)

Answer 33

Deep inguinal -> external (clitoris, penis, labia minora)

Superficial inguinal -> internal iliac (scrotum/labia majora)

Because of this connection with abdominal lympathics = easy spread of cancer

Question 34

Internal vs internal haemorrhoids

Answer 34

There are two kinds of hemorrhoids: internal hemorrhoids, which occur in the lower rectum, and external hemorrhoids, which develop under the skin around the anus. External hemorrhoids are the most uncomfortable, because the overlying skin becomes irritated and erodes.

Question 35

Bowel cancer

Answer 35

Large bowel - colon and rectum

Question 36

Sympathetic innervation of the GI tract

Answer 36

Sympathetic innervation is derived from the abdominal pre-vertebral ganglia: the coeliac, superior mes- enteric and inferior mesenteric ganglia. These ganglia are innervated by T5-L2 levels of the sympathetic chain, via the greater, lesser and least splanchnic nerves. The coeliac ganglia, together known as the coeliac plexus, produce post-ganglionic fibres that innervate the stomach, liver, gallbladder, kidney, spleen, ascending and trans- verse colon. The superior mesenteric ganglion innervates the jejunum, ileum, ascending and transverse colon. The inferior mesenteric ganglion supplies the descending and sigmoid colon, as well as the rectum. Sympathetic innervation is responsible for control of blood flow, epithelial transport and reduces glandular secretions.

Question 37

Parasympathetic innervation of the GI tract

Answer 37

Parasympathetic innervation is provided by the Vagus nerve and pelvic splanchnic nerves (S2-S4). Para- sympathetic fibres travelling with the Vagus nerve innervate the more proximal parts of the GI tract, including the oesophagus, stomach, small intestine and ascending colon, whilst the pelvic splanchnic nerves innervate the transverse, descending and sigmoid colons, rectum and anal canal. The parasympathetic ganglia are located within the walls of the GI tract, close to their terminal organs. Parasympathetic innervation increases motility and absorption, controls peristalsis, promotes glandular secretion and relaxes sphincter muscles.

Question 38

What does the pudendal nerve supply?

Answer 38

Anal canal and external voluntary anal sphincter, a voluntary striated muscle sphincter.

Question 39

Enteric nervous system

Answer 39

one of the main divisions of the autonomic nervous system

capable of acting independently of sympathetic and parasympathetic

The myenteric plexus, located between the inner circular and outer longitudinal muscle layers of the GI tract, and the submucous plexus, located within the submucosa, together make up the enteric nervous system. The myenteric plexus is responsible for the generation of peristaltic movements, whilst the submucous plexus con- trols glandular secretion and electrolyte transport across the mucosa.

Question 40

Discuss innervation of the visceral and parietal peritoneum

Answer 40

Visceral afferent fibres travel with the autonomic fibres to diffusely terminate within the spinal cord. As such, sensation within the GI tract is poorly localised until the parietal peritoneum becomes involved.

In general, visceral sensory information is referred to the epigastric region for foregut structures, the umbilical region for midgut structures and the hypogastric region for hindgut structures.

When the parietal peritoneum becomes involved, due to its innervation by the somatic nervous system, sensation becomes well-localised.

Question 41

Vomiting reflex

Answer 41

Vomiting may be triggered by a range of stimuli, including gastric irritation, motion sickness, opioid medications, chemotherapy, severe pain and fear. Afferent fibres are transmitted to the vomition centres of the medulla reticular formation. From here, a predictable set of reflexes are triggered to expel potentially noxious substances from the GI tract:

1. Deep breath taken to avoid aspiration of vomit (phrenic nerve).
2. Increased salivation to reduce damage to teeth caused by stomach acid (parasympathetic innervation)
3. Glottis closed, soft palate elevated and larynx raised, opening the upper oesophageal sphincter and closing off the nasopharynx.
4. Sharp contraction of the diaphragm inferiorly to create negative pressure within thorax, causing the oesophagus and lower oesophageal sphincter to open.
5. Abdominal wall muscle contraction to raise intra-abdominal pressure and expel stomach contents into the oesophagus and ultimately into the external environment.

Therefore, sympathetic, lower intercostal, phrenic and vagus nerves are all involved

Question 42

Defaecation reflex

Answer 42

Coordinated contraction and relaxation of the rectum and associated sphincters are required to expel faeces during the defaecation reflex. This reflex is triggered on mass movement of faeces towards the rectum, initiated by high intensity contractions of the colon. Sufficient distension of the rectum, detected by visceral afferents travelling with the parasympathetic pelvic splanchnic nerves (S2-4)(from pelvic plexus), stimulates:

1. Contraction of the sigmoid colon and rectum
2. Relaxation of the internal anal sphincter (triggered by parasympathetic fibres of pelvic splanchnic nerves)
3. Contraction of the external anal sphincter (triggered by inferior rectal nerve, branch of the pudendal nerve)

This combination of events triggers an urge to defaecate, which is permitted on voluntary relaxation of the external anal sphincter. Expulsion is aided by the Valsalva manoeuvre, which raises the intra-abdominal pressure.