Anatomy of the Abdomen 3

Question 1

What makes up the small intestine?

Answer 1

• This includes the duodenum, the jejunum and the ileum

Question 2

What is the function of the small intestine?

Answer 2

• It is responsible for the absorption of nutrients into the bloodstream

Question 3

What makes the small intestine efficient at its role in absorption?

Answer 3

• To do this efficiently it has a very large surface area

Question 4

What are the folds in the small intestine called?

Answer 4

Plicae circulares.

Question 5

What is found within the Plicae circulares?

Answer 5

• Down the microscope you can see more folds called villi (grey)
• This SAM image shows the density of the villi
• Coming off villi are more folds called microvilli
• This helps the intestine to do its job very well

Question 6

How long is the jejunum and ileum?

Answer 6

• The jejunum is 2.5m and the ileum is 3.5m in length – food travels a long distance

Question 7

What is the transition from the duodenum to the jejunum called?

What holds this in place?

Answer 7

The 4th part of the duodenum suddenly takes a turn called the duodenojejunal flexure to form the jejunum. This is help in place by the suspensory muscle of the duodenum in close association with the diaphragm (so the start of the duodenum is always located in the same place)

Question 8

What quadrants are the jejunum and ileum in?

Answer 8

• The jejunum coils its way round the abdomen (mostly found in the left lower quadrant), its morphology will change to form the ileum (found in the right lower quadrant).

Question 9

Where does the ileum terminate?

Answer 9

• The ileum then terminates as it enters the cecum (first party of the colon) called the ileocecal junction

Question 10

What is the fat around the small intestines called?

Answer 10

• Fat around intestines is called the mesentery

Question 11

What does the mesentery connect and contain?

Where does the root of the mesentery run from?

Answer 11

• Double fold of peritoneum that connects to the jejunum and ileum
• Coils of intestine are attached to the back wall the mesentery
• The mesentery allows the blood vessels to travel to the small intestine
1. Fan shaped double fold of peritoneum
2. Contains:
a. Superior mesenteric artery
b. Superior mesenteric vein
c. Lymph nodes
d. Fat
e. Autonomic nerves

3. Connected to the posterior abdominal wall via the root of the mesentery (double fold of peritnuem if reflected off the posterior abdominal wall from the duodenaljejumal flexure running
4. The root runs from the duodenojejunal flexure to the sacro-iliac joint

Question 12

Label the root of the mesentery

Answer 12

On image

Question 13

Compare the jejunum to the ileum

Answer 13

On table

Question 14

What are the subdivisions of the large intestine, where does it extend from and how long is it?

Answer 14

• The large intestine is composed of the cecum, the ascending colon (turns at the hapatic flexure), transverse colon across the abdomen at the splenuc flexure, to form the descending colon, to form the sigmoid colon, to form the straight rectum to form the anus
• Extends from ileocecal junction to anus
• 1.5 meters

Question 15

What are the 5 functions of the large intestine?

Answer 15

• Water and salt absorption
• Little or no digestive function
• Temporary storage of faeces
• Secretion of mucus
• Extensive action of microorganisms

Question 16

Label the large intestine

Answer 16

On image

Question 17

What are Taeniae coli?

What are the bunches of the large intestine called?

What is the fat surrounding the large intestine called?

Answer 17

1. Taeniae coli – longitudinal bands of muscle that travel around the large intestine, contraction of this muscle will form the peristalic waves that push the bolus of food through the GI tract.
2. The large intestine is also bunched up into small segments called haustra
3. The colon also has fat pockets called omental appendices (small peritoneal pouches) that hang of the colon

Question 18

What is the caecum?

What is the valve between the caecum and ileum called?

What is the caecum supplied by?

What are folds in the mesentery called?

What attaches to the caecum and supplies it?

Answer 18

The Caecum (retroperitoneal)
• Blind intestinal pouch, here the right iliac fossa has been dissected to reveal the caecum
• We can see the illeo-caecal valve which opens up into the caecum
• The caecum is supplied by the ileocolic artery (a branch of the superior mesenteric artery)
• Hanging from the caecum is the appendix (intraperitoneal), fold of the mesentery is called the mesoappendix and the appendicular artery will travel through the mesentery to reach the appendix
• The appendix can be in a variety of positions e.g post ileal
• Appendicitis is where you get bacteria or faeces build up which becomes infected

Question 19

Label the caecum

Answer 19

On image

Question 20

How long is the ascending colon?

Where does it run from?

What is found lateral to the ascending colon?

Label the ascending colon and name its flexure

Answer 20

15-20cm

On image

hepatic flexure

Question 21

Label the transverse colon

Where does it run to and from?

Describe its peritoneum

Answer 21

• 50 cm
• Runs from hepatic flexure to splenic flexure
• Intraperitoneal: Transverse mesocolon

Question 22

What is the transverse mesocolon and what does it attach to?

What does this then form?

Answer 22

• Double fold of peritoneum that connects transverse colon to the posterior abdominal wall.
• Anterior layer of transverse mesocolon is attached to the posterior layer of greater omentum.
• Divides abdominal cavity into supracolic and infracolic compartments.

Question 23

Have a look at the boundary between the mid and hindgut

Answer 23

• Here the greater omentum has been lifted up, and the transverse colon also moves upwards.
• We can see the transverse mesocolon and an artery called the middle colic artery that runs through the double fold of mesocolon to reach the transverse colon
• The transverse colon also marks the boundary between mid gut and the hindgut, which is around 2/3rds distally along the transverse colon. At this point the blood and nerves supply change because the midgut and hindgut have a distinct embryological development

Question 24

Describe the arterial and venous supply of the midgut and hindgut

Answer 24

On table

Question 25

Does the descending colon have a mesentery and why?

What is lateral to the descending colon?

What attaches to the descending colon and what attaches it to the wall?

Answer 25

• The descending colon is retroperitoneal but it can have a mesentery
• They are described as secondary retroperitoneal because it starts its embryological development wrapped in the mesentery (intraperitoneal structures) and migrate posteriorly to become retroperitoneal. However, in some people this migration does not occur
• Lateral to the descending colon is the left paracolic gutter (another peritoneal resses where there is peritoneal fluid)
• The descending colon then becomes the sigmoid colon (attracted by a mesentery called the sigmoid mesocolon)

Question 26

Describe the peritoneum of the sigmoid colon

What level does it terminate to form the rectum?

Answer 26

• The sigmoid colon has a root where the mesentery is reflected off the posterior abdominal wall. There is an inverted V structure that gives the sigmoid colon its S shaped appearance
• The sigmoid colon is always intraperitoneal and terminates at the level of S3 where the sigmoid colon then becomes the rectum
• 40 cm
• Continuous with descending colon superiorly and rectum inferiorly
• S-Shaped

Question 27

Why is the sigmoid colon an S shape?

Answer 27

• The sigmoid colon has a root where the mesentery is reflected off the posterior abdominal wall. There is an inverted V structure that gives the sigmoid colon its S shaped appearance

Question 28

Describe the peritoneum of the sigmoid colon and describe its level

What is it continuous with superiorly and inferiorly?

Answer 28

• The sigmoid colon is always intraperitoneal and terminates at the level of S3 where the sigmoid colon then becomes the rectum
• Continuous with descending colon superiorly and rectum inferiorly

Question 29

Label the rectum

Answer 29

On image

Question 30

What does the rectum follow the curve off?

What happens during defecation?

Describe the internal and external anal sphincter

Answer 30

• Anatomy is adapted to allow for continence.
• Rectum follows curve of sacrum and coccyx
• The anorectal flexure bends posteriorly at an 80 degree angle as it pierces through the pelvic floor (levator ani muscle, the puborectalis muscle wraps around this which constricts during peristaltic waves to maintain continence)
• During defecation, the anorectal junction straightens
• Internal anal sphincter (autonomic control), so naturally constricted
• The external anal sphincter wraps around the anal canal, which has 3 parts: deep part, middle part and subcutaneous part. Under somatic innervation so you can control it. Innvervated by the inferior rectal branch

Question 31

Label the anal canal

Answer 31

On image

Question 32

What is the anal column?

Answer 32

The anal columns is where the rectum becomes the anal canal – where the rectum pierces the rectal diaphragm

Question 33

What is between the anal columns?

What does the inferior portion secrete?

Answer 33

Between the anal columns are anal sinuses that secrete mucus. The inferior portion of the sinuses are called anal valves and collectively form the pectinate line which demarcates the terminal end of the embryonic hind gut. Everything below has a different embryonic origin. So at the pectinate line the neurovascular changes

Question 34

What does the anocutaneous line mark?

Answer 34

The anconaeus line demarcates a change in the mucus epithelium

Transition from non-keratinised squamous epithelium to keratinised squamous epithelium

Question 35

Where does the foregut, midgut and hindgut run?

Where do they get there blood supply from and label this

Answer 35

• The main gut tube develops in 3 sections: foregut, midgut and hindgut
• The foregut runs from the lower respiratory tract (pharynx down to the oesophagus), stomach, first part of the duodenum to the major duodenal papilla where it becomes the midgut. Foregut gets there blood supply via the coeliac trunk (arises from aorta at T12)
• The mid cut that arises from the major duodenal papilla forms the jejunum, ileum, caecum, appendix, colon, proximal 2/3rds of transverse colon. The midgut gets its blood supply from the superior mesenteric artery (L1).
• The hindgut is supplied by the inferior mesenteric artery at the level of L3 and includes the distal 2/3rds of the transverse colon, the descending colon, sigmoid colon, rectum up to the pectinate line

Question 36

Describe the arterial supply to the midgut - the branches of the SMA supply the large and small intestine

Answer 36

• Superior mesenteric artery runs within the mesentery of the small intestine that will give of jejunal branches which form small arterial archades. There are also long vaso recta going towards the jejunum.
• Ileal branches supply the ileum from the superior mesenteric artery via small vaso recta
• The ileocolic artery will form the appendicular artery which runs in the mesoappendix to supply the appendix
• The superior mesenteric artery also gives off the right colic artery supplies the ascending colon
• The superior mesenteric artery also gives off a middle colic artery that supplies the proximal 2/3rds of the transverse colon

Question 37

Describe the arterial supply to the hindgut - descending colon, sigmoid colon and superior rectum

Answer 37

Arterial Supply to Hindgut
• The inferior mesenteric comes of at L3, this gives of the left colic artery and supplies the descending colon.
• Sigmoid arteries running in the sigmoid mesocolon supplies the sigmoid colon
• The inferior mesenteric artery takes an inferior route and continues as the superior rectal artery supplying the superior rectum

Question 38

What is the Marginal Artery (of Drummond)?

Answer 38

• We can see the branches of the superior mesenteric artery and descending (jejunum and ileum have been removed), mesentery has also been removed
• The marginal artery acts as an anastomoses to the midgut and the blood supply to the hindgut. So if an artery becomes blocked the marginal artery can compensate

Question 39

Go over venous drainage system of the GIT

Answer 39

• Blood is directed from alimentary canal, spleen, pancreas and gallbladder via the portal vein into the liver
• Hepatic veins (from liver) drain directly into inferior vena cava
• The portal vein is formed posterior to the neck of the panaceas close to the level of L1 and the transpyloric plane
• In one third of people inferior mesenteric vein also meets at portal vein

Question 40

Describe the arterial supply to the rectum and anal canal

Answer 40

The superior rectal artery will supply above the pectinate line

Distal to the pectinate line the anal canal is supplied by the middle rectal artery (branch from left internal iliac artery) and the inferior rectal artery (branch of internal pudendal artery

Question 41

Describe the venous drainage of the anal canal

Answer 41

• Everything above the pectinate line is drained by the superior rectal vein that enters the hepatic portal system.
• The superior rectal vein will join the inferior mesenteric vein which joins the splenic vein forming the portal vein
• The middle and inferior rectal veins will drain into the caval system, which will drain into the internal iliac veins and then enter the inferior vena cava
• Rectum and anal canal is a system for portal anastomoses

Question 42

What does the pectinate line mark

Answer 42

On image

Question 43

Describe innervation to the GIT

Answer 43

• The enteric nervous system is located between the muscular layers of the GIT.
o Myenteric plexus
o Submucosal plexus
• The activity of the enteric nervous system is modulated by the autonomic nervous system.

Question 44

What is the parasympathetic, sympathetic supply of the foregut, midgut and hindgut?

Where is the referred pain felt?

Answer 44

On table

Question 45

Why do we get referred abdominal pain?

Answer 45

• Pain from the abdominal region is often poorly localised.
• Sensory input (pain) from visceral organs is interpreted by the brain as originating from one of the midline dermatomes.
• Dermatomes share a convergent spinal root with the autonomic nerve which supplied that that particular organ. As Visceral afferent fibres (form the organ) also travel in the nerve.