Flashcards in Lecture 3 Deck (78):
What are the foregut structures?
- (Lower respiratory tract - tracheobronchial diverticulum)
- (Proximal oesophagus)
- Distal oesophagus
- Biliary apparatus
- Proximal 1/2 Duodenum
What artery is the foregut supplied by?
Coeliac axis at T12
Is the spleen a part of the gut tube? Why?
No, it is a lymphoid mass
What are the midgut structures?
Distal 1/2 duodenum
Proximal 2/3 transverse colon
What artery is the midgut supplied by?
Superior mesenteric artery at L1
What are the hindgut structures?
- Distal 1/3 transverse colon
- Descending colon
- Sigmoid colon
- Proximal 2/3 anal canal
What artery is the hindgut supplied by?
Inferior mesenteric artery at L3
What does the epiblast become?
What does the hypoblast become?
What does the mesoderm create?
3rd layer between ectoderm and endoderm
What does the ectoderm go on to form?
Skin and outer body wall
What does the endoderm eventually form?
Gut tube and anything mucosal
What does the mesoderm eventually form?
Forms muscles, blood vessels, nerves
What does the oropharyngeal membrane ultimately form?
Describe the process of transverse folding in the development of the gut
- Ectoderm and mesoderm fold laterally and ventrally
- Closes off endoderm, forming a separated gut-tube structure
- Endoderm formed epithelial lining of tube
- Mesoderm gives rise to supporting structures and smooth muscle
- Outer mesenchymal layer gives rise to outer tissue layer
- Space between mesodermal layers gives rise to body cavity
What is mesenchyme?
Undifferentiated stem cells
Describe the process of longtudinal folding in the development of the gut
- Starts to draw opening of gut tube to yolk sac closed
- Divides into anterior intestinal portion (foregut) and posterior intestinal portion (hindgut)
- Midgut remains open to yolk sac
- Further folding - communication with yolk sac gets smaller
- Fore/mid/hindgut regions become more refined
What is at the extremities of the gut tube?
Cranial end: oropharyngeal membrane (ectoderm of the stomodeum)
Caudal end: anal membrane (ectoderm of the anal pit)
What eventually happens to the oropharyngeal and anal membrane?
What is the composition of the oropharyngeal and anal membrane?
Both transitional regions between endoderm and ectoderm. Between mucosal tissue and skin. Inside of mouth is endoderm origin and outside dry skin is ectoderm.
Where is the oesophagus found?
Immediately caudal to pharynx
What does the oesophagus partition from?
Partitions from the trachea, forming the respiratory diverticulum
What are the positions of the trachea and oesophagus respective to each other?
Trachea is ventral
Oesophagus is dorsal
Is the oesophagus initially short or long?
Initially short but rapidly elongates
What happens if the oesophagus doesn't elongate?
It can displace the stomach cranially
What is an atresia?
A blockage of a tube
What is a fistula?
Connection between tubes
What do atresia and fistula occur as a result of?
When does atresia present?
Soon after birth because infant will suckle milk and vomit it up. This is because milk will gather in the sack and have nowhere to go.
Describe congenital hiatal hernia
- displaces stomach cranially
- herniates into thorax (through oesophageal hiatus)
- issues with reflux and food getting lodged
What is another word for mesentery?
Between which mesenteries does the stomach sit?
Dorsal and ventral
What is stage 1 of stomach formation?
Gut tube starts to dilate
What is stage 2 of stomach formation?
- Dilation continues
- Rotation on long axis 90 degrees clockwise
- Anterior mesogastrium moves to the right and posterior moves to the left
What is stage 3 of stomach formation?
- Dilation continues
- Rotation on coronal axis 90 degrees clockwise
- Right boundary becomes superior to form lesser curvature
- Left boundary becomes inferior to form greater curvature
Why are the ascending and descending colon secondary intraperitoneal structures?
They start off intraperitoneally. They get pushed up against the wall and the peritoneum gets obliterated.
Describe the formation of the greater omentum
Dorsal mesogatrium dragged around by rotation of stomach. It begins to hang down under the weight of gravity. Both sides of the hanging fold fuse together making a 4 layered peritoneal structure.
What is the greater omentum?
A quadruple fold of peritoneum. Migrates to areas of trauma. Has many WBC's so wraps itself around and helps contain things.
What does the transverse colon become fused with?
The greater omentum
What is congenital hypertrophic pyloric stenosis?
Marked thickening of the muscular wall of the pylorus.
Blocks exit of stomach into first part of duodenum.
How does congenital hypertrophic pyloric stenosis cause vomiting?
When you are trying to empty the contents from the stomach to the duodenum, you end up with a spasming of muscles, which causes non-bilious vomiting.
Why is there no bile in vomit due to congenital hypertrophic pyloric stenosis?
Bile enters into the duodenum so blockage occurs before the duodenum where bile is not present.
How can adults get hypertrophic pyloric stenosis?
Due to chronic peptic ulceration, which is less common
What structure eventually forms the liver and biliary tree?
What happens to the hepatic diverticulum as it grows?
Divides into 2:
- Larger, cranial = liver
- Smaller, caudal = biliary apparatus
Which other bud also comes from the hepatic diverticulum?
Describe the initial position of the bile duct and after the duodenum grows and rotates.
Bile duct starts attached to ventral duodenum
As duodenum grows and rotates, bile duct position becomes dorsal
What are the gall bladder, cystic duct and ventral pancreatic bud in?
In the ventral mesentery
What does the pancreas develop between?
Between both layers of mesogastrium
What part of the foregut is the pancreas a part of?
What are the two buds of the pancreas?
Dorsal and ventral bud
What is the majority of the pancreas made up of?
Describe the development of the ventral bud of the pancreas
Ventral bud carried round as duodenum rotates. Ventral fuses with dorsal - ducts anastamose
What does the main pancreatic duct flow through? What happens to the other portion of the pancreas?
The smaller ventral portion of the pancreas (head). Main portion becomes accessory. Most people lose this duct as it is unnecessary.
In what percentage of people does the accessory duct remain in?
Where does the spleen develop?
Not part of the foregut but does develop in the dorsal mesogastrium
What is the ventral mesogastrium split into 2 by? What are the two divisions?
Liver sits in the ventral mesogastrium, dividing it into:
- Falciform ligament between the liver and body wall
- Lesser omentum between the liver and stomach.
What shape is the developing midgut?
What does the developing midgut loop around?
The superior mesenteric artery still connected to the umbilical system
What are the limbs of the developing midgut and what are they named after?
Cranial and caudal limbs named after relation to SMA
Is herniation a normal process in the formation of the midgut?
Yes, the loop migrates through into the umbilical cord
Which way does the midgut rotate?
What happens after the midgut has rotated through 270 degrees?
Herniation retracts. Midgut loop returns to abdominal cavity. Caecum and appendix rotate down to lower abdomen.
What happens in an umbilical herniation/fistula?
Failure of the umbilical cord to close properly. Gut herniates through weakened region in body wall.
What is Meckel's diverticulum?
Ileal diverticulum. Remnant of the yolk sac (Vitelline duct).
What is a diverticulum?
An extra bit that did not pinch off properly
How common is Meckel's diverticulum?
Very common - 2% of population
What is the cloaca?
Expanded distal part of the hindgut. Divided into dorsal and ventral parts by the mesenchymal urorectal septum. Urogenital system is from the same precursor as the distal gut tube. As septum grows, separates rectum from urogenital sinus.
What is the anal canal a boundary between? What denotes the boundary?
Outer ectoderm and inner endoderm. Pectinate line
What is the blood supply of the upper 2/3 of the anal canal?
Where do the anal columns terminate?
At the site of the anal membrane
What is meant by portal systemic anastomosis? What is it important for?
Venous drainage goes to 2 different systems. Important to cases of hepatic hypertension.
Where do the lymphatics change? in the hindgut?
Anocutaneous line (white line)
Below: superficial inguinal nodes
Inside proximal 2/3 = inferior mesenteric nodes in aorta
What is the blood supply of the lower 1/3 of the anal canal?
Systemic veins (internal iliac, peroneal veins)
What is Megacolon?
Segment of colon dilated due to absence of ANS ganglion cells in wall of gut distal to it. Failure of peristalsis in aganglionic part means that it cannot relax. Prevents movement of intestinal contents. Normally located around region of gut close to anus.
What is another name for Megacolon?
What is the name for a disease where the anal membrane fails to perforate?