Session 2 Flashcards
Describe embryonic folding
In the 4th week the embryo folds
Laterally: •
Creates ventral body wall
• Primitive gut becomes tubular
Craniocaudally:
• Creates cranial and caudal pockets from yolk sac endoderm (beginning primitive gut development)
What is the gut tube?
- Endoderm lined tube
- Runs the length of the body
- Blind pouches at the head and tail ends
- Opening at the umbilicus
- Splanchnic mesoderm covering
Describe the embryonic divisions of the gut
- Foregut and hindgut begin as blind diverticula
- Midgut has an opening at first and is continuous with the yolk sac
- These embryonic divisions have implications for blood supply and lymphatic drainage in the adult
What are the derivatives of the foregut?
Oesophagus
Stomach
Pancreas, liver and gall bladder
Duodenum (proximal to entrance of bile duct)
What are the derivatives of the midgut?
Duodenum (distal to entrance of bile duct)
Jejunum
Ileum
Cecum
Ascending colon
Proximal 2/3 transverse colon
What are the derivatives of the hindgut?
Distal 1/3 transverse colon
Descending colon
Sigmoid colon
Rectum
Upper anal canal
Internal lining (epithelium) of bladder and urethra
Describe the implications on blood supply of having different embryonic sections of the gut tube
- Arterial supply reflects embryonic development
- Each embryonic segment receives blood supply from a distinct branch of the abdominal aorta:
Foregut - Celiac trunk
Midgut - Superior mesenteric artery
Hindgut - Inferior mesenteric artery
Describe areas of the gut that will have mixed blood supply
• Those structures that develop close to the junction between foregut and midgut will have mixed blood supply
Duodenum:
• Proximal to entry of bile duct: Gastroduodenal artery and superior pancreaticoduodenal artery (CT)
AND
• Distal to entry of bile duct: Inferior pancreaticoduodenal artery (SMA)
Pancreas:
- Head
- superior pancreaticoduodenal artery (CT)
AND
• inferior pancreaticoduodenal artery (SMA)
What is the intraembryonic coelom?
- Formed as the embryo folds
- Begins as one large cavity
- Later subdivided by the future diaphragm into abdominal and thoracic cavities
Intraembryonic coelom and its membrane: Somatic mesoderm lines the body wall portion of coelom, wrapping the gut tube is splanchnic mesoderm which separates gut tube from coelom. Atop this splanchnic mesoderm sits a serous membrane which secretes small amounts of lubricating fluid allowing structures within the abdomen can move without friction or adhesions.
- One membrane lining the whole intraembryonic cavity
- Specialises as the cavities specialise to become pericardium, pleural membrane and peritoneum and peritoneal cavity
- the peritoneal membrane lines the abdominal cavity and invests the viscera - during development it grows, changes shape and specialises
- the peritoneal “cavity” is a potential space only - under normal conditions it should contain except tiny amounts of serous lubricant.
Describe the what, why, how and where of the mesenteries
- What?
- Double layer of peritoneum suspending the gut tube from the abdominal wall
- Why?
- allow a conduit for blood and nerve supply • allow mobility where needed
- How?
- The new primitive gut is suspended within the intraembryonic coelom • Splanchnic mesoderm surrounds new gut • Mesentery formed from a condensation of this mesoderm
- Where?
- Dorsal mesentery suspends the entire gut tube from the dorsal body wall • Ventral mesentery ONLY in the region of the foregut
What are the greater and lesser peritoneal sacs?
- Dorsal and ventral mesenteries in the region of the foregut divide the cavity into left and right sacs in this region only
- the left sac contributes to the greater sac
- the right sac becomes the lesser sac - comes to lie behind the stomach Lesser sac allows for distension of GI tract e.g. stomach during feeding.
What are the greater and lesser omenta?
- Omenta are specialised regions of the mesenteries of the peritoneum
- Greater omentum
Suspended from the greater curvature of the stomach
Contains epiploic fat.
Formed from the dorsal mesentery
First structure seen when the abdominal cavity is opened anteriorly
• Lesser omentum
Reflects off the lesser curvature of the stomach
Formed from the ventral mesentery
Free edge conducts the portal triad
What influences the position of the greater and lesser sacs? How are the omenta formed?
Rotation of the stomach during development Stomach begins to rotate, vagus nerves switch from left/right to anterior/posterior. One side of the channel is pushed behind the stomach which forms lesser sac (other channel goes in front to form greater sac). Stomach changes shape so starts to enlarge then tips on its axis. As it tilts, because the dorsal mesentery is attached to the dorsal wall and stomach, it’s going to drag and fold this membrane over so dorsal mesentery has been elongated and folded over to become the greater omentum. Ventral mesentery goes on to become lesser omentum
What are the consequences of rotation of the stomach?
- Puts the vagus nerves anterior and posterior to the stomach (instead of left and right)
- Shifts cardia and pylorus from the midline
- Stomach comes to lie obliquely
- Contributes to moving the lesser sac behind the stomach
- Creates the greater omentum
What is a peritoneal reflection? Give examples
• A change in direction, where membrane reflects off one surface onto another. E.g. from parietal peritoneum to mesentery E.g. From mesentery to visceral peritoneum
What happens to structures in the abdomen where there is no mesentery?
• Structures that are not suspended within the abdominal cavity are retroperitoneal
Retroperitoneal:
• were never in the peritoneal cavity and never had a mesentery
Secondarily retroperitoneal:
• began development invested by peritoneum, had a mesentery BUT, with successive growth and development, the mesentery is lost through fusion at posterior abdominal wall
Retroperitoneal can’t be mobilised but secondary retroperitoneal can.
Describe separation of the developing GI and respiratory tracts and formation of the lung bud
Foregut extends from the lung bud to the liver bud • Formation of the lung bud - In the 4th week, a respiratory diverticulum forms in the ventral wall of the foregut at the junction with the pharyngeal gut. Diverticulum is then separated from the GI tract by the tracheooesophageal septum which is a dividing wall between the GI tract and the respiratory tract
Goes onto form:
- Respiratory primordium (ventrally)
- Oesophagus (dorsally)
What are the consequences of abnormal positioning of the tracheoesophageal septum?
If there’s misplacement of the tracheooesophageal septum you can get blind-ending oesophagus, abnormal connections between the GI tract and respiratory tract e.g oesophagus draining into respiratory tract, and tracheooesophageal fistula
Describe the development of the foregut-derived glands
- Liver and biliary system develops within ventral mesentery
- Pancreas - Components develop in both ventral and dorsal mesentery:
- Uncinate process and inferior head = ventral • Superior head, neck, body and tail = dorsal
Describe the peritoneal reflections of the liver
Falciform ligament - runs from anterior abdominal wall and wraps around ligament. Liver develops close to the diaphragm and this area that is borderline touching it is the ‘bare area’ and is restricted to its limits by the coronal ligament which then becomes left and right triangular ligaments. Bare area is slightly duller and rougher to touch.
Describe development of the duodenum
- Develops from caudal foregut and cranial midgut
- Its C shape is determined by rotation of the stomach
- Growth and rotation of the stomach pushes duodenum to the right, then against posterior abdominal wall.
- Therefore it loses its mesentery and becomes secondarily retroperitoneal
Describe nervous sympathetic outflow
T5-L2 (preganglionic) Preganglionic fibres pass through (paravertebral) sympathetic trunk without synapsing and go onto form (abdominopelvic) presynaptic splanchnic nerves (preganglionic)
◦ Greater (T5-9) supply foregut structures
◦ Lesser (T10-11) - supply midgut structures
◦ Least (T12) - supply hindgut structure
These splanchnic nerves synapse with prevertebral ganglia
Coeliac, superior mesenteric, inferior mesenteric ganglia.
Extend from prevertebral ganglia to viscera (postganglionic)
Mainly innervate blood vessels
Describe the parts of a hernia
The sac
o Is a pouch of peritoneum
Contents of the sac
o Any structure found within the abdominal cavity
o Commonly: Loops of bowel or Omentum
Coverings of the sac:
o Consist of the layers of the abdominal wall through with the hernia has passed
What is the Inguinal canal?
Oblique passage through lower part of the abdominal wall
In males
◦ Structures pass through from abdomen-testis
In Females
◦ Round ligament goes from Uterus to labium majus
What are the boundaries of the inguinal canal?
Floor - inguinal ligament (formed from aponeurosis of external oblique rolling itself inferiorly) and lacunar ligament (medially)
Roof - Arching fibres of Internal oblique/transverse abdominis (muscular arches and aponeurosis)
Posterior wall - Transversalis fascia (conjoint tendon medially (conjoint tendon formed by fusion of arching fibres of internal oblique and rectus abdominis))
Anterior wall - Aponeurosis of external oblique
Describe the borders of Hesselbachs triangle
Inferior epigastric artery, Rectus abdominis muscle, Inguinal and lacunar ligament
Describe an indirect inguinal hernia
Passes through the deep Inguinal ring through the inguinal canal and then out through the superficial Inguinal ring
Then depending on where the Processus Vaginalis was obliterated can potentially descend into the scrotum
Describe a direct inguinal hernia
Bulges through Hesselbach’s triangle Generally in the vicinity of the superficial Inguinal ring
Does not traverse the inguinal canal.
What is the anatomical difference between direct and indirect inguinal hernias
Indirect Inguinal hernia
◦ Lateral to the Inferior Epigastric vessels as deep ring is lateral to these vessels.
Direct Inguinal Hernia
◦ Medial to Inferior Epigastric vessels as deep ring is medial to these vessels
What is a femoral hernia, what are common complications?
Empty space between femoral vein (lateral) and lymphatics is the femoral canal and the femoral canal has an inferior opening called the femoral ring. Femoral ring boundaries are, laterally the femoral vein and medially the lacunar ligament. Femoral hernia will try and get into the femoral ring via femoral canal. More common in Females as their pelvic anatomy different so femoral ring is slightly wider
◦ Can easily get stuck (incarcerated) as canal is quite narrow. Easily become irreducible.
◦ Can strangulate
What is the processus vaginalis and tunica vaginalis? What happen if processus vaginalis doesn’t close? Link to repro
In the male, an outpouching of the future peritoneum of the coelomic cavity protrudes into the labioscrotal swellings, into the space created by the gubernaculum. This outpouching is known as the processus vaginalis, and it precedes the future testis into the scrotum. After descent of the testis this close and is obliterated and leaves behind the tunica vaginalis. Can leave a connection to the inguinal canal if doesn’t obliterate fully.
