Anatomy of digestion and defacation

Flashcards made using the lecture delivered by Dr Emily Hunter

What structures of the digestive system are derived from the embryonic foregut?

The oesophagus, the stomach, the proximal duodenum, the pancreas, the liver and the gallbladder.

What structures of the digestive system are derived from the embryonic midgut?

The distal duodenum, the jejunum, the ileum, caecum, vermiform appendix, the ascending colon and the proximal 2/3rds of the transverse colon.

What structures of the digestive system are derived from the embryonic hindgut?

The distal 1/3rd of the transverse colon, the descending colon, the sigmoid colon, rectum and the proximal anal canal.

Which artery is the foregut supplied by?

The coeliac artery.

Which artery is the midgut supplied by?

The superior mesenteric artery.

Which artery is the hindgut supplied by?

The inferior mesenteric artery.

Underneath the skin of the abdominal wall, there are two layers of fascia, what are the names of the two layers of fascia and what are their characteristics?

The first superficial fascia layer is Camper’s fascia and it is a fatty layer.

The second superficial fascia layer is Scarpa’s fascia and it is a membranous layer.

What are the names of the three muscles of the abdominal wall from the most superficial to the most deep muscle?

The external oblique, the internal oblique and the transversus abdominis muscle.

What are the names of the two fascia layers deep to the abdominal walls?

Transversalis fascia and the extraperitoneal fascia.

What is found deep to the extraperitoneal fascia?

The parietal peritoneum.

What is the origin of the external oblique muscle?

8 digitations from the 8 inferior-most ribs.

What is the fibre orientation of the external oblique muscle?

The external oblique muscle fibres have an inferomedial fibre orientation.

What are the insertions of the external oblique muscle?

The linea alba, the iliac crest and the pubic tubercle.

Where does the linea alba extend to and from?

Extends from the xiphoid process of the sternum to the pubic symphysis.

What is meant by the abdominal muscles becoming aponeurotic?

They form a rectus sheath that covers the rectus abdominis.

Where does the inguinal canal begin and end?

Begins at the superior anterior iliac spine and extends to the pubic tubercle.

What are the origins of the internal oblique muscle?

The lumbar fascia, the iliac crest and the lateral 2/3rds of the inguinal ligament.

What are the insertions of the internal oblique muscle?

The linea alba, the 10th,11th and 12th ribs and the pecten pubis.

What tendon does the internal oblique muscle and transversus abdominis help to form?

The conjoint tendon.

What are the origins of the transversus abdominis?

The transverse fascia, the iliac crest, 7-12th costal cartilages and the lateral 1/3rds of the inguinal ligament.

What is the fibre orientation of the transversus abdominis?

Transverse fibre orientation.

What are the insertions of the transversus abdominis?

The xiphoid process, the linea alba and the pubic crest.

What are the origins of the rectus abdominis?

The pubic crest and the pubic symphysis.

What are the insertions of the rectus abdominis?

The xiphoid process and costal cartilages 5-9.

In the upper abdomen, describe the positions of the aponeuroses of the abdominal muscles over the rectus abdominis.

The aponeurosis of the external oblique passes anteriorly over the rectus abdominis.

The aponeurosis of the internal oblique passes both anteriorly and posteriorly to the rectus abdominis.

The aponeurosis of the transversus abdominis passes posteriorly to the rectus abdominis.

What is the position of the arcuate line?

It is approximately halfway between the umbilicus and the pubic crest.

Describe the positioning of the aponeuroses of the abdominal muscles at the arcuate line.

The external oblique, the internal oblique and the transversus abdominis all pass anteriorly to the rectus sheath.

What makes up the floor of the inguinal canal?

The inguinal ligament.

What is the floor of the inguinal canal thickened medially by?

The lacunar ligament.

What is the anterior wall of the inguinal canal made up from?

The aponeurosis of the external oblique, and the internal oblique laterally.

What makes up the roof of the inguinal canal?

The internal oblique, the transversus abdominis and the transversalis fascia.

What makes up the posterior wall of the inguinal canal?

The transversalis fascia.

What are the functions of the anterolateral abdominal wall?

Move the trunk, increase intraabdominal pressure, depress the ribs and supports the intestines.

What is the parietal peritoneum?

It is a serous membrane that lines the abdominal wall.

What is the visceral peritoneum?

A serous membrane that lines the abdominal viscera.

What is the word for when structures lie within the peritoneum?

Intraperitoneal.

What is the word for when structures lie behind the peritoneum?

Retroperitoneal.

What is the word for when structures lie beneath the peritoneum?

Infraperitoneal.

What is mesentery?

It is a double fold of peritoneum that attaches structures to the posterior abdominal wall.

What is THE mesentery?

The double fold of peritoneum that attaches the small intestine to the posterior wall of the abdomen.

What other mesentery are there apart from the one that attaches the small intestine to the posterior abdominal wall?

The transverse mesocolon and the sigmoid mesocolon.

What is the omentum?

A fold of peritoneum that attaches the stomach to other abdominal organs.

What nerve innervates the small intestine?

The vagus nerve.

What supplies the small intestine with blood?

The superior mesenteric artery.

What is the comparison in the thickness of the walls of the jejunum and the ileum?

The ileum has thinner walls than the jejunum.

What is the comparison in the fat content of the mesentery between the jejunum and the ileum?

The ileum mesentery has a higher fat content than the jejunum?

What is the comparison in the arterial arcades between the jejunum and the ileum?

There are more arterial arcades in the ileum.

What is the comparison in the vasa recta between the jejunum and the ileum?

The vasa recta in the ileum are shorter than the vasa recta in the jejunum.

Is the ileum or the jejunum the primary site of absorption?

The jejunum is the primary site of absorption.

What is absorbed in the ileum?

Vitamin B12, bile salts, water and lipids.

What is the role of peyer’s patches?

They detect the bacteria that is present in the small intestine and work to regulate it.

What is Meckel’s diverticulum?

It is a vestigial outgrowth of the ileum close to the caecum. It occurs in 2% of the population.

What is absorbed in the large intestine?

Some water, drugs and electrolytes.

Which artery is the large intestine supplied by?

Both the superior and inferior mesenteric artery.

What are the names of the two flexures of the large intestine?

The right colic flexure (hepatic flexure) and the left colic flexure (splenic flexure).

What parts of the large intestine are intraperitoneal?

The appendix, the caecum, the transverse colon and the sigmoid colon.

What parts of the large intestine are retroperitoneal?

The ascending colon and the descending colon.

What parts of the large intestine have their own mesentery?

The appendix (mesoappendix), the transverse colon (transverse mesocolon) and the sigmoid colon (sigmoid mesocolon).

What are the three distinguishing features of the large intestine?

The teniae coli, the haustra and the apendices epiplociae.

What is the teniae coli?

They are longitudinal muscular strands that aid in the movement of waste through the large intestine.

What are the haustra?

The bulges that are observed on the large intestine.

What are the apendices epiplociae?

They are fat deposits along the large intestine.

What is the opening between the ileum and the caecum called?

The ileocaecal valve/orifice.

What is the blood supply of the vermiform appendix?

It is from the appendicular artery which is a branch of the posterior caecal artery.

What is the position of the rectum?

S3.

What is a prominent feature of the rectum?

It has transverse folds which faeces can sit on top of.

Describe how the rectum is covered by the peritoneum.

The proximal part is covered by the peritoneum anteriorly and bilaterally.

The mid part is only covered by the peritoneum anteriorly.

The distal part is not covered by peritoneum at all.

Above the pectinate line, what is the anal canal’s embryological origin?

The endoderm.

What is the type of epithelium of the anal canal above the pectinate line?

Simple columnar epithelium.

Below the pectinate line, what is the anal canal’s embryological origin?

The ectoderm.

What is the type of epithelium of the anal canal below the pectinate line?

Non-keratinised stratified squamous epithelium.

What is the type of epithelium of the anal canal below the anocutaneous line?

Keratinised stratified squamous epithelium.

What is the blood supply to the rectum and the anal canal?

The superior and the inferior rectal arteries and veins.

What kind of muscle makes up the internal anal sphincter?

Smooth muscle.

What kind of muscle makes up the external anal sphincter?

Skeletal muscle.

What is the parasympathetic nerve supply to the smooth muscle of the rectum and anal canal?

From S2, S3 and S4.

What is the sympathetic nervous supply to the smooth muscle of the rectum and the anal canal?

From T11 to L2.

What are the visceral sensory fibres of the smooth muscle in the rectum and anal canal important for?

Triggering reflexes.

What is the nerve that supplies the external anal sphincter?

The inferior anal nerve that is usually a branch from the pudendal nerve but sometimes is from the sacral plexus.

Explain the process of defecation.

The faeces stretch the walls of the rectum.

Sensory stretch receptors detect the stretch and send impulses to the spinal cord.

The spinal cord will organise a spinal response and cause the internal anal sphincter to relax.

However, the faeces cannot be expelled until the voluntary relaxation of the external anal sphincter.