23-01-23 – Jejunum, Ileum and Large Intestine Flashcards
Learning outcomes
- Describe the anatomy (position, function, relations, neurovascular supply) of the jejunum and ileum
- Describe the anatomy (position, function, relations, neurovascular supply) of the caecum and appendix
- Describe the anatomy (position, function, relations, neurovascular supply) of the colon (ascending, transverse, descending and sigmoid)
- Explain the anatomical bases of the clinical conditions related to the small and large intestines, and appendix
- Identify major features of small and large intestines on medical images
- Identify branches of superior and inferior mesenteric arteries on angiograms
What are the 4 layers of the wall of the small intestine from lumen outwards?
Where are the 2 nerve plexuses of the GIT found?
What are they each involved in?
What is the lamina propria?
What does it divide?
What is the difference between in situ and invasive lesions?
Which is more deadly?
What are Peyers patches?
- 4 layers of the wall of the small intestine from lumen outwards:
1) Mucosa
2) Submucosa
3) Muscular layer
4) Serosa - The 2 nerves plexuses are the submucosal and myenteric plexuses
- The submucosal plexus is located between the mucosa and submucosa and is involved in secretion
- The myenteric plexus is located between the circular and longitudinal muscle layers in the muscular layer
- The myenteric plexus is involved in peristaltic activity and supplies sphincters
- The lamina propria is the basement membrane
- It serves as the dividing line between in situ and invasive lesions
- If the lesion is above the lamina propria, it is in situ, meaning the prognosis is a lot better
- If the lesion has entered the submucosa, it is an invasive lesion
- In the submucosa we have lymph vessels and veins, meaning cancerous cells can spread, making the prognosis for this lesion worse
- Peyer’s patches are lymphatic aggregates located within the lamina propria
What are the jejunum and ileum part of?
Where are they located?
Where do the jejunum and ileum extend between?
What takes places in the jejunum and ileum?
How is absorption facilitated?
- The jejunum and ileum form part of the small intestine, and are the longest part of the GI tract
- The jejunum and ileum fill the space between the colon
- The jejunum lies in the upper left abdomen while the ileum tends to be in the lower right & partly in the pelvis
- The jejunum and ileum form a convoluted tube that runs from the duodenojejunal junction to the ileocecal valve/junction, with there being a gradual change from jejunum to ileum (Proximal 40% jejunum is jejunum, remaining 60% is ileum)
- Almost all absorption takes place in the jejunum and ileum
- Absorption is facilitated by the contents in the small intestine being shuffled back and forth while peristaltic waves push them chyme distally
What do the jejunum and ileum hang from?
What is the mesentery?
What 5 structures does the base of the mesentery cross?
What 4 important structures are within the mesentery?
- The jejunum and ileum hang from the posterior abdominal wall by the mesentery, which consists of 2 layers of peritoneum
- The mesentery is a fold of membrane that attaches the intestine to the abdominal wall and holds it in place
- 5 structures the base of the mesentery crosses:
1) 3rd part of the duodenum
2) Aorta
3) IVC
4) Right gonadal vessels
5) Right ureter - 4 important structures are within the mesentery:
1) Branches of the superior mesenteric artery, forming anastomotic arcades
2) Branches of the superior mesenteric vein
* Will feature tributaries of the superior mesenteric vein
* Tributaries - a vein that empties into a larger vein.
3) Lymph vessels
* Accompany blood vessels, also includes some lymph nodes
4) Nerves
* Autonomic nerves reach the organs rapped around the arteries that supply them
What are 4 morphological differences between the Jejunum and ileum?
- 4 morphological differences between the Jejunum and ileum
- Jejunum
1) Wide
2) More plica circulares (aka Valvulae conniventes, valves of Kerckring)
* Permanent transverse ridges
* Slow down the passage of contents to allow more time for absorption
3) Contains MALT (Mucosa associated lymphoid tissue)
4) No Peyer’s patches
- Ileum
1) Narrow
2) Fewer plica circulares
3) Contains MALT (Mucosa associated lymphoid tissue)
4) Numerous Peyer’s patches (Along the anti-mesenteric side)
* MALT aggregate here to form Peyer’s patches
Jejunum and Ileum barium x-ray
Where is the ileocecal valve found?
What does it consist of?
What is the functional of the ileocecal valve?
- The ileocecal valve is found at the end of the small intestines, situated at the junction of the small intestine (ileum) & the large intestine (caecum)
- Consists of 2 horizontal folds of mucous membrane that project around the orifice of the ileum
- The functional of the ileocecal valve is to limit the reflux of colonic contents into the ileum & possibly control the flow of ileal contents into the caecum (colon)
What occurs in the condition intussusception?
What are these parts referred to as?
What is the most common site of intussusception?
What does this affect the functioning of the small intestine?
- Intussusception is a serious condition in which part of the intestines enters into the adjacent part
- Intussusceptum (proximal part) / Intussuscipiens (distal part)
- The most common site of intussusception is the ileocaecal valve, where the ileum is connected to the cecum of the colon
- Intisussusceptum blocks food or fluid from passing through, cuts off the blood supply to the affected part, which can lead to necrosis and perforation
- The artery that supplies the ileum enters from one side only
- When the proximal part of the ileum enters into the distal part, it will be disrupted
Where is the abdominal aorta located?
What are the 3 midline branches of the abdominal aorta?
What do they each supply?
What are the 3 lateral branches of the abdominal aorta?
What do they each supply?
- The abdominal aorta is a midline, retroperitoneal structure that Lies anterior to vertebral bodies and to left of IVC
- 3 midline branches of the abdominal aorta (unpaired):
1) Celiac trunk (foregut organs)
2) Superior mesenteric artery (midgut organs)
3) Inferior mesenteric artery (hindgut organs)
- 3 lateral branches of the abdominal aorta (paired):
1) Kidneys/adrenal glands (aka suprarenal) branches
2) Gonadal (Testes/Ovaries)
3) Body wall (Posterolateral)
* 4 pairs of lumbar arteries
What is the arterial supply to the jejunum and ileum?
What are these arteries branches of?
Where does the superior mesenteric artery arise?
What does it supply?
What is the ampulla of Vater?
What travels through it?
What do jejunal and ileal arteries form?
- The jejunum and ileum are supplied by Jejunal and ileal arteries, which are branches of superior mesenteric artery
- The superior mesenteric artery arises from aorta at the lower border of L1
- Supplies the midgut (from ampulla of Vater in duodenum to 2/3 along the transverse colon)
- The ampulla of Vater is a small opening that enters into the first portion of the small intestine, known as the duodenum.
- The ampulla of Vater is the spot where the pancreatic and bile ducts release their secretions into the intestines
- Jejunal and ileal arteries form a series of vascular anastomotic arcades within the mesentery, from which vasa recta arise
- Vasa recta are straight capillaries coming off from arcades
- Arteries of the jejunum form one or two arcades with long vasa recta in the mesentery of the jejunum
- Arteries of the ileum form many arcades with short vasa recta in the mesentery of the ileum
Where do jejunal and ileal veins drain?
Where does the hepatic portal vein drain blood form?
- Jejunal and ileal veins drain into the superior mesenteric vein that will eventually join with the splenic vein and form the portal vein
- The hepatic portal vein drains blood from foregut, midgut and hindgut structures to the liver for first pass metabolism
Describe the flow chart for lymphatic drainage of the small intestine (in picture).
What are Peyer’s patches formed from?
Where will lymph pass to in the small intestine?
Why are there 2 different paths?
- Flow chart for lymphatic drainage of the small intestine (in picture)
- There two pathways for lymph drainage in the small intestine: Peyer’s patches and Lacteals
- Peyer’s patches are located in the mucosa and extend into the submucosa and are formed from aggregations of MALT (Mucosa associated lymphoid tissue/lymphocytes)
- In the small intestine, the lymph will pass to the nodes in the organs, into the nodes of the mesentery, then into the nodes around the artery that supplies the organ (superior mesenteric nodes around superior mesenteric artery
- There is another lymph drainage system in the small intestine.
- This system is for absorbed nutrients within the villi of the mucosa
- There is a lacteal in the centre of each villus, and these lacteals are for the absorption ff digested fats and lipids (chyle)
- This alternative system is needed due to the size of the fats and lipids
- They are too large for lymph nodes, and so bypass them to reach the lymph vessels, and then converge on the cisterna chyli that lies in the upper abdomen & passes through the diaphragm as the thoracic duct (the absorbed lipid molecules are too big for the lymph node “filters”)
Describe the 3 steps in the formation of the myenteric and submucosal plexuses.
Where the myenteric and submucosal plexuses located?
What is their function?
- 3 steps in the formation of the myenteric and submucosal plexuses:
1) Sympathetics from the lesser splanchnic nerve (T10-T11) and parasympathetics from the vagus nerve come together at the origin of the superior mesenteric artery, where they will rap around it to form the superior mesenteric plexus
2) The superior mesenteric plexus reaches the small intestine round the branches of the super mesenteric arteries (jejunal and ileal arteries)
3) Here, the superior mesenteric plexus will form 2 plexuses: The myenteric plexus and the submucosal plexus.
- The submucosal plexus is located between the mucosa and submucosa and is involved in secretion
- The myenteric plexus is located between the circular and longitudinal muscle layers in the muscular layer
- The myenteric plexus is involved in peristaltic activity and supplies sphincters
Formation of myenteric and submucosal plexus diagram
What is the mesentery?
What is the difference between retroperitoneal and intraperitoneal?
What are 5 examples of intraperitoneal organs?
What are 4 examples of primary retroperitoneal organs?
What does secondary retroperitoneal mean?
What are 3 examples of secondary retroperitoneal organs?
- The mesentery is a fold of membrane that attaches the intestine to the abdominal wall and holds it in place (suspends it)
- Intraperitoneal: peritonealized organs having a mesentery
- 5 examples of intraperitoneal organs:
1) Stomach
2) Small intestine (jejunum and ileum)
3) Transverse and sigmoid colon
4) Liver
5) Gallbladder. - Primary Retroperitoneal: organs without a mesentery and associated with posterior body wall
- 4 examples of Primary retroperitoneal organs:
1) Aorta
2) Inferior vena cava
3) Kidneys
4) Suprarenal glands. - Secondarily retroperitoneal: organs which had a mesentery once and lost it during development, resulting in them migrating to behind the peritoneum
- 3 examples of secondary retroperitoneal organs:
1) Pancreas
2) Duodenum
3) Ascending and descending colons
Name the parts of the large intestine
Where does the large intestine extend between?
How long is the large intestine?
Which parts of the large intestine are intraperitoneal?
What are the 2 functions of the large intestine?
- Different parts of the large intestine on the diagram
- The large intestine extends from the caecum to the rectum & anal canal
- The large intestine is approximately 1.5 meters long
- The transverse & sigmoid colon have their mesenteries/mesos, making them intraperitoneal
- The ascending & descending colon are secondarily retroperitoneal
- 2 functions of the large intestine:
1) Fluid-electrolyte balance −Absorbs fluid & salts
2) Dries out the chyme to form faeces
What is the size of the large intestine in comparison to the small intestine?
What are taenia coli?
How are taenia coli formed?
What is the name of the 3 types?
How long are taenia coli?
What does this cause to form?
What are epiploic/omental appendices?
What can happen if they’re inflamed?
What structure does the large intestine lack?
- The large intestine is larger in diameter than the small intestine unless contracted by a wave of peristalsis
- Teniae coli are 3 bands of longitudinal smooth muscle on the colon surface
- Longitudinal smooth muscle fibres thicken to form 3x taenia coli
- 3 types of taenia coli:
1) Free taenia
* Visible
2) Mesenteric taenia
* Where the mesentery of the colon is attached
* Need to remove mesentery to be able to see this
3) Omental taenia
* Where the greater omentum is attached
* Need to exercise greater omentum to see this structure
- Taenia coli are shorter than the large intestine, which causes mobile sacculations/pouches called haustra to form
- Epiploic/omental appendices are small fat filled pouches of peritoneum found on the large intestine (most commonly in distal colon)
- If the Epiploic/omental appendices become inflamed, this can cause appendicitis
- The large intestine lacks Peyer’s patches
What structure is the cecum?
Where can it be found?
What it the cecum continuous with?
What is it covered with?
How is the iloececal orifice formed?
What stuctures can be found around the cecum?
What can be found within one of these structures?
- The cecum is the First and widest part of large intestine
- The caecum can be found below the junction of the ileum with the large intestine in the right iliac fossa, below the level of the ileocecal valve
- The cecum is continuous with the ascending colon
- The cecum is covered with periotoneum, but not on a mesentery
- The ilecocecal orifice is formed by the Ileum entering the caecum obliquely and partly invaginating into it
- Around the cecum, there are perioteoneal recesses, with the vermiform appendixe being found in one of these recesses
What does the term ‘diverticula’ mean?
How can the vermiform appendix be described?
Where can it be found?
Why is the appendix easy to find?
What is the surface projection of this point?
What is the submucosa of the vermiform appendix full of?
What is the appendix suspended on?
What are 5 potential anatomical positions the appendix can be found in?
Why is this?
Why can this be bad?
- “Diverticula” is the medical term used to describe the small bulges that stick out of the side of the large intestine (colon)
- Diverticula are common and associated with ageing.
- The vermiform appendix is a blind intestinal diverticulum found at the posteromedial aspect of the caecum
- The appendix is easy to find due to the fact 3 taeniae coli converge at the root of the vermiform appendix
- The root of the vermiform appendix is at McBurney’s point, which is the surface projection
- The submucosa of the vermiform appendix is full of lymphoid tissue
- The appendix is suspended on a short but highly variable mesoappendix that transmits the appendicular vessels
- 5 potential anatomical positions the appendix can be found in:
1) Retrocaecal (65%)
2) Pelvic (30%)
3) Subcaecal
4) Retroileal
5) Preileal - This is because the appendix is highly mobile
- This can be a bad thing, as it can be difficult to locate during surgery
Where is the base of the appendix most often found?
Where is McBurney’s point?
When can pain be felt at this point?
- The base (root) of the appendix most often lies deep to McBurney’s point
- McBurney’s point is a point that is one third of the way along the oblique line joining the ASIS to the umbilicus
- In advanced appendicitis, pain can be felt around this point, and the surgical incision is made at this point
What is appendicitis?
Where is pain referred to?
- Appendicitis is Inflammation of the vermiform appendix
- Initially, pain is referred to the periumbilical pain
- Later, pain is referred to the right lower quadrant, which is where the appendix is located
- This occurs if the inflammation spreads to the parietal peritoneum
Where is the ascending colon found?
Does the ascending colon have its own mesentery?
What is the right paracolic gutter formed by?
Why is the ascending colon drained by 2 different venous systems?
What does this lead to the formation of?
- The ascending colon is found in the right lumbar region between the caecum and hepatic flexure
- The ascending colon is secondarily retroperitoneal, so it lost its mesentery during development
- Right paracolic gutter is a relatively wide space formed between the right side of the ascending colon and posterior abdominal wall
- The ascending colon is drained by 2 different venous systems because it is part of the digestive system, but also attached to the posterior abdominal wall
- Structures in the digestive system are usually drained by tributaries of the hepatic portal vein
- Since the ascending colon is attached to the posterior abdominal wall, it is also drained by systemic veins (lumbar veins)
- This leads to the formation of portocaval anastomoses posteriorly between these 2 venous systems
Where does the transverse colon extend between?
What is the transverse colon suspended by?
Is it intraperitoneal?
What are the left and right colic flexure related to?
What are some of the anatomical positions of the transverse colon (in picture)?
- The transverse colon extends between hepatic and splenic flexures
- The transverse colon is suspended by the transverse mesocolon
- This makes the transverse colon intraperitoneal
- The hepatic (right colic) flexure is related to the liver
- The splenic (left colic) flexure is related to the spleen
- Some of the anatomical positions of the transverse colon (in picture)
What is the role of the transverse mesocolon?
Why do we say meso instead of mesentery?
What 3 structures does the root of the transverse mesocolon cross?
- The role of the transverse mesocolon is to attach the transverse colon to the posterior abdominal wall
- It is a type of mesentery, but to differentiate it from the small intestines mesentery, we call it meso
- 3 structures the root of the transverse mesocolon crosses:
1) inferior edge of the pancreas
2) Aorta
3) 2nd part of duodenum (descending part)
Transverse mescolon diagram
Where is the descending colon located?
What is it hidden by?
Is it intraperitoneal or retroperitoneal?
Is it attached to the posterior abdominal wall?
What forms the left paracolic gutter?
What is the venous drainage of the descending colon?
What does this lead to the formation of?
- The descending colon is located in in the left lumbar region, hidden anteriorly by small intestine (jejunum primarily)
- The descending colon is secondarily retroperitoneal and is attached to the posterior abdominal wall (like the ascending colon)
- Left paracolic gutter is a widened space formed between the left side of the descending colon and posterior abdominal wall
- The venous drainage of the descending colon consists of both the hepatic portal vein and the systemic veins (lumbar veins)
- This leads to the formation of portocaval anastomoses posteriorly
How do Double Contrast Barium Enema x-rays work?
- In Double Contrast Barium Enema x-rays, 2 forms of contrast are used: barium and then air/CO2 is pumped into the rectum/colon
- Example in picture
Why is the sigmoid colon given this name?
What is it a continuation of?
Is it intraperitoneal or retroperitoneal?
What is it suspended by?
What is more common in sigmoid colon?
Why is this?
Where is the sigmoid colon continuous with the rectum?
- The sigmoid colon is given this name because it is S shaped
- The sigmoid colon is a continuation of the descending colon in front of the pelvic inlet
- The sigmoid colon is intraperitoneal
- It is suspended by the sigmoid mesocolon and attached to the posterior abdominal wall
- Volvulus is more common in the sigmoid colon due to it being long
- The sigmoid colon is continuous with the rectum in front of the 3rd sacral vertebra
Sigmid colon x-ray (Double Contrast Barium Enema x-rays)
What is volvulus?
What are the most commonly affected parts in adults and children?
How does volvulus disrupt the function of the intestines?
What are 5 symptoms of volvulus?
- Volvulus is the twisting of a loop of intestine around itself and the mesentery that supplies it
- In adults, the sigmoid colon and caecum are commonly affected parts
- In children, the stomach and small intestines are the most commonly affected parts
- Volvulus obstructs the flow of bowel contents and can cause ischemia
- 5 symptoms of volvulus:
1) Abdominal distension
2) Pain
3) Vomiting
4) Constipation
5) Bloody stools
Describe diverticulosis.
Why does it most commonly affect the sigmoid colon?
What age groups does it commonly affect?
What side does it affect?
What condition can diverticulosis develop into?
- Diverticulosis is when saclike pouches of colonic mucosa and submucosa (diverticula) protrudes through the muscular layer of the colon
- Diverticulosis commonly affects the sigmoid colon because its lumen is the narrowest, making the pressure higher than other points, resulting in the inner later of the intestine pushing through the weak spot of the muscular layer
- Most common with people over 60 years of age and nearly everyone by the age of 80
- Diverticulosis affects and causes discomfort in the left side most of the time, which is opposite to appendicitis, which affects the right side
- Diverticulosis can develop into diverticulitis if the saclike pouches of colonic mucosa and submucosa become inflamed
Is the rectum retroperitoneal or intraperitoneal?
Where does the rectum begin?
What does it follow?
Where does the rectum end?
What 3 structures are absent in the rectum?
What is the role of the rectum?
- The rectum is ‘almost’ retroperitoneal
- The upper 1/3rd is intraperitoneal while the lower 2/3rds are retroperitoneal
- The rectum begins in front of the 3rd sacral vertebra
- It follows the curve of the sacrum & coccyx
- The rectum ends in front of the tip of the coccyx by piercing the pelvic diaphragm & becoming continuous with the anal canal
- 3 structures are absent in the rectum:
1) Taenia
2) Haustra
3) Appendices epiploica - This means when longitudinal muscle bands reach the rectum, they disperse
- The role of the rectum is to store faeces until the appropriate time
How long is the anal canal?
Where does it extend from?
What does it serve as?
- The anal canal is Approximately 4cm long
- The anal canal extends from the pelvic diaphragm to the anus
- The anal canal serves as the conduit to the outside world
Mid gut colon arterial supply.
Where does the superior mesenteric artery originate?
What does the superior mesenteric artery supply with its branches?
Where are there anastomosis present in the superior mesenteric artery?
What are 3 branches of the superior mesenteric artery that supply the colon?
What do they each supply?
What branch of the superior mesenteric artery gives off the appendicular artery?
Why is this an important artery?
- Mid gut colon arterial supply
- The superior mesenteric artery originates at the lower border of the L1 vertebra
- With its branches, The superior mesenteric artery supplies part of the large intestine, from vermiform appendix to proximal 2/3 of the transverse colon
- There are anastomoses between branches of superior mesenteric artery
- 3 branches of the superior mesenteric artery that supply the colon:
1) Middle colic artery
* First branch
* Primarily supplies the transverse colon
* Also supplies the hepatic flexure and a small part of the ascending colon
2) Right colic artery
* Ascending colon
3) Ileocolic artery
* Supplies the cecum
* Gives off the appendicular artery, which is a terminal artery
* This means there is no anastomosis to this artery, so if it becomes blocked, the appendix will become necrotic and die
Superior mesenteric artery diagram
Superior mesenteric artery digital subtraction angiography
Label these branches
Hindgut colon arterial supply.
Where does the inferior mesenteric artery arise from?
What structures do branches of the inferior mesenteric artery supply?
What are 2 branches of the inferior mesenteric artery?
What do they each supply?
What does the inferior mesenteric artery end as?
What does this supply?
- Hindgut colon arterial supply.
- The Inferior mesenteric artery arises from aorta at L3
- Branches of Inferior mesenteric artery supply distal 1/3 of the transverse colon, the splenic flexure, descending colon, sigmoid colon and part of the rectum
- 2 branches of the inferior mesenteric artery:
1) Left colic artery
* Supplies the distal 1/3rd of transverse colon, Splenic flexure and descending colon
2) Sigmoid artery
* Supplies the sigmoid colon
- The inferior mesenteric artery ends as the superior rectal artery, supplying the rectum & anal canal
Inferior mesenteric artery digital subtraction angiography
Label these branches
What is the marginal artery?
Why is this artery important?
- The marginal artery (of Drummond) is an anastomosis between inferior and superior mesenteric arteries
- This artery is important as it forms a collateral circulation should the inferior mesenteric artery becomes obstructed e.g blood can go from superior mesenteric through marginal artery
Marginal artery collateral supply
What do veins of the colon run with?
Describe the venous drainage of the colon.
Describe the lymphatic drainage of the colon
- Veins of the colon run with arteries & drain into the portal vein
- The area of the colon supplied by the inferior mesenteric artery will be drained by the inferior mesenteric vein (same for superior mesenteric artery)
- The inferior mesenteric vein joins with the splenic with, which will join with the superior mesenteric vein to form the hepatic portal vein
- Lymphatic drainage of the colon is into the nodes in the organ, then into nodes in the mesentery, then into nodes around the origins of the superior & inferior mesenteric arteries
What structure do autonomic fibres to the GIT run alongside?
Describe the nerve supply to the foregut, midgut, and hindgut
- Autonomic nerves run with the 3 arteries:
1) Coeliac trunk to foregut
* Sympathetics from T5-9 (greater splanchnic)
* Parasympathetics from vagus
2) Superior mesenteric to midgut
* Sympathetic from T10-11 (lesser splanchnic)
* Parasympathetics from vagus
3) Inferior mesenteric to hindgut
* Sympathetics from T12-L2 (least splanchnic and 1st and 2nd lumbar splanchnic nerves)
* Parasympathetics from S2-4
Digestive system referred pain.
What structures do visceral sensory afferents from abdominal viscera run with?
When will pain localisation occur?
Where will pain from areas supplied by the celiac trunk, superior mesenteric, and inferior mesenteric arteries be referred to?
Where will pain from appendicitis be referred to in the first 6-8 hours?
- Digestive system referred pain:
- Visceral sensory afferents from abdominal viscera run with the sympathetics
- Brain cannot localise visceral pain
- Pain localisation occurs when the overlying parietal peritoneum is involved
- Pain from areas supplied by Celiac trunk refers to lower thorax and epigastric region (T6-T9)
- Pain from areas supplied by Superior mesenteric refers to Periumbilical region (T10-11) - Appendicitis pain in the first 6-8h
- Pain from areas supplied by Inferior mesenteric refers to Suprapubic region (T12), lateral and anterior thighs and groin
