Lecture 3 Flashcards
9x Foregut structures
- (Pharynx)
- (Lower Respiratory Tract- tracheobronchial diverticulum)
- (Proximal Oesophagus)
- foregut starts at mouth/oropharynx. Have different blood supply
- general digestive system foregut starts below diaphragm - Distal Oesophagus
- Stomach
- Liver
- Biliary Apparatus
- Pancreas
- Proximal 1/2 Duodenum
- 4-9 supplied by ciliac axis artery
-Spleen not part of gut tube- Lymphoid Mass
Spleen
Lymphoid mass
Not part of Gut tube(Foregut region)
7x Midgut Structures
- Distal 1/2 Duodenum
- Jejunum
- Ilieum
- Caecum
- Appendix
- Ascending Colon (direction fo travel)
- Proximal 2/3 Transverse Colon
- all common supply of Superior Mesenteric Artery (tells nerve supply and lymphatics)
5x Hindgut Structures
- Distal 1/2 Transverse Colon
- Descending Colon
- Sigmoid colon
- Rectum
- Proximal 2/3 Anal Canal
- all common supply of Inferior Mesenteric Artery
Initial Development of Gut
Start as Bi-lamina Disc. Epiblast + Hypoblast. amnion + yolk sac on either side. Oropharyngeal membrane/mouth (present early on in development)
Quickly after bi-laminar disc formation= Cell Migration through Primitive streak, invading between 2x layers, forms Tri-laminar disc.
Epiblast= Ectoderm (skin/outerbody wall)
Mesoderm (muscles, BV, nerves)
Hypoblast = Endoderm (yolk sac/gut tube/anything mucosal(gut/lungs))
Growth within Womb
Limited space, start folding around to form 3D shape
Simultaneous Longitudinal and Transverse Folding
a) Longitudinal Folding = sides extend/elongate down and curl on themselves
b) Transverse Folding = sides fold to form tube
Lateral/Transverse Folding
Ectoderm + Mesoderm fold Laterally and Ventrally
Pinches off yock sac and Closes of Endoderm - separated gut tube structure
Endoderm: Epithelial lining of tube
Mesoderm: supporting structures + smooth muscle
Outer Mesenchymal: outer tissue layer (undifferentiated stem cells)
Space b/w mesoderm= body cavity
Longitudinal Folding
Cradial and Caudal ends
Tissue Proliferation
~17-18 days = opening to gut tube/yolk sac drawn shut (like a purse string) (narrows neck)
-a) divides into Anterior and Posterior Intestinal portions (Foregut and Hindgut)
-b) Midgut remains open to Yolk sac (still a connection)
Further folding = communication with yolk sac gets smaller
Fore/mid/hindgut regions become more refined
28days/4weeks: begin to get lung buds, liver buds- Endodermal Bud off from gut tube
Extremities of the Tube
Beginning Week 4: 2 membranes closing off tube
Cranial end: Oropharyngeal membrane -Ectoderm of the Stomodeum
Caudal end: Anal membrane. -Ectoderm of the Anal Pit
-both are Transitional regions between Endoderm and Ectoderm (Mucosal Tissue and Skin) (Lips wet as secrete mucus)
Week4: Oropharyngeal membrane ruptures
Week8: Anal membrane ruptures
Lumen of the Tube
Initially the gut tube is Patent/Open
the Proliferation of epithelium plugs up the lumen of the gut tube
~week 8= End of embryonic period = Recanalization occurs
Aterial supply and Gut Differentation
Fore: Celiac Trunk T12
Mid: Superior Mesenteric L1 (goes through the yolk stalk and therefore maintains connection with umbilical system)
Hind: Inferior Mesenteric L3
-Define regions by their arterial supply
-vertebral levels dictate where lymph drains to
What is the relationship between Superior Mesenteric and Yolk stalk
Superior Mesenteric artery goes through the yolk stalk
-maintain connection with umbilical system
Oesophagus
Foregut
Immediately caudal to pharynx
Initially Oesophagus is Short
-then rapidly elongates (to reach mouth and diaphragm as grow. Majority of oesophagus in Thorax) - if doesnt elongate (fast enough) (w. growth) = Displace stomach cranially/Oesophagus congenital Malformations
Partitions from Trachea(ventral) to form oesophagus (dorsal)
-Everything that secretes mucous is Endodermal origin- Respiratory Diverticulum. Lung buds originate from (fore)gut tube. Creating Trache-oesophageal ridge.
–Successive stages in development of the Respiratory Diverticulum:
1. Tracheo-oesophageal ridges
2. Formation of Septum
3. splitting foregut into Oesophagus
4. Trachea with Lung buds
Oesophagus Congenital Malformations
Initially Oesophagus is Short
-then rapidly elongates (to reach mouth and diaphragm as grow. Majority of oesophagus in Thorax) - if doesnt elongate (fast enough) (w. growth) = Displace stomach cranially/Oesophagus congenital Malformations
1. Tracheoesophageal Fistula/Atresia
Atresia: Blockage - blind ended tube - presented soon after birth, sucking mums milk, gather, the immediately puke up. Cure: connect tube
Fistula: Connection - remnant connection - punching somewhere not meant to be
-both due to incomplete partitioning
-lots of divisions and partitions occuring therefore lots of scope for things to go wrong
2. Congenital Hiatal Hernia
Short oesophagus (does elongate fast enough with growth)
-displaces stomach cranially
-herniates through oesophageal hiatus into thoracic cavity (pushes up through diaphragm)
-issues with reflux and food loging
Atresia
Blockage
Oesophagus e.g. - blind ended tube - presented soon after birth, sucking mums milk, gather, the immediately puke up. Cure: connect tube
-lots of divisions and partitions occuring therefore lots of scope for things to go wrong
Fistula
Connection
Oesophagus e.g. - remnant connection - punching somewhere not meant to be
-both due to incomplete partitioning
-lots of divisions and partitions occuring therefore lots of scope for things to go wrong
3x stages of Stomach Embryological development
Stage 1: Gut tube starts to dilate
Stage 2: Dilation continues. Rotation on long axis ~90 degrees Clockwise. Anterior/Ventral Mesogastrium move to right. Posterior/Dorsal moves to left
Stage 3: Dilation continues. Rotation on coronal axis ~90 degrees clockwise.
-Ventral –> Right boundary –> Superior Lesser curvature
-Posterior –>Left boundary –> Inferior Greater curvature
What does your gut tube sit between?
2x mesenteries
Forget: Between Dorsal and Ventral Mesogastrium/mesentery
Stomach’s Greater Omentum
Quadruple fold of peritoneum
“policemen” of stomach, continuing lots of WBC, migrating to areas of trauma/pathology, wrapping itself around to help contain things
Dorsal mesogastrium dragged round by rotation of stomach
Begins to hang down under weight of gravity
Both sides of the hanging fold fuse together (making a 4 layered peritoneal structure)
The Greater Omentum is formed
Ascending+Descending colon start as Intraperitoneal –> get pushed up against body wall and other layer is obliterated to become Retroperitoneal (Secondary Retroperitoneal as didnt start off life there)
Gastro-Colic Ligament= Transverse colon becomes fused with greater omentum. Links stomach with Transverse Colon
Gastro-Colic Ligament
Transverse colon becomes fused with greater omentum. Links stomach with Transverse Colon
Congenital Hypertrophic Pyloric Stenosis
Marked thickening of the muscular Wall of the pylorus
-trying to empty stomach, spasm of muscle, causing non-bilius vomitting (as blockage is before the duodenum where bile enters-identifying feature)
-Can get in adult due to chronic peptic ulceration
Blocks exit of stomach into 1st part of the Duodenum
Liver and Biliary Tree
Week4: Ventral Outgrowth (Hepatic Diverticulum)-bud offs endodermal gut tube
Divides in 2 as it grows:
-Larger, cranial = Liver. rapid growth to become 9wks is 10% of embryo body mass
-Smaller, caudal = Biliary Apparatus-gall bladder
-Gall bladder and liver are both intimately linked via biliary system, coming from same precursor origin
Pancreatic bud- also from hepatic diverticulum
Bile duct starts attached to ventral duodenum
As duodenum grows and rotates (as does stomach) - bile duct position becomes dorsal
Pancreas
Develops between both layers of mesogastrium
Caudal part of foregut
2 buds - Majority = Dorsal bud
Ventral bud carried round as duodenum rotates
Ventral fuses with Dorsal -ducts anastomose
-want to mix pancreatic fluid with bile fluid therefore enter duodenum together
(main) Pancreatic duct = Ventral duct + distal dorsal duct
-main pancreatic duct flows through smaller ventral portion of pancreas (Main pancreatic bud goes through head of pancreas and Uncinate process)
(accessory duct remains in only 9% of population, more likely to lose as no longer necessary)
-main part running through ventral portion. Ventral part spins to join caudal part and then fuses
Spleen
Not part of the foregut
does develop in dorsal mesogastrium
Falciform Ligament
Between Liver and Body Wall
Mesogastrium
Within contains BV
-where umbilical veins gets into embryo
Lesser Omentum
Anterior Boundary of lesser sac
Free border on bottom/Free edge which is flicked back around itself after rotation
Gastrolienal/Gastrosplenal Ligament
Between stomach and Spleen
-contain BV supplying gut
Lienorenal Ligament
Between spleen and Kidneys
-contain BV suppling gut
Where is the greatest embryological development?
Mid gut
Midgut
Shape and elongation: U-shape “Midgut Loop”. ( as limited space) Cranial & Caudal limbs - named after relation to SMA (still connected to umbilical system) - important relationship w. yolk sac
Herniation: Normal process - loop migrates through the umbilical cord - Physiological Herniates into yolk stalk/Omphaloenteric duct
Rotation: Midgut loop begins to rotate counter-clockwise (anticlockwise)
Rotation continues through 270 degrees
Return: eventually herniation retracts (pulls itself back into gut)
Midgut loop returns to abdominal cavity
Caecum & Appendix: rotate down to lower abdomen
Non-rotation events can occur
Migration of the Midgut
- During 6th week, mid gut loop is situated in the Proximal part of the Umbilical cord
a) Transverse section through the midgut loop, showing the initial relationship of the limbs the midgut loop to the superior mesenteric artery - A later stage, showing the beginning of the midgut rotation
a) Illustration of the 90 degree counter-clockwise rotation that carrier the cranial limb of the midgut to the right - A approx 10 weeks the intestines return to the abdomen
a) further rotation of 90 degrees
4) by approx 11 Weeks, all of the intestines return to the abdomen
a) a further 90 degree rotation of the gut, for a total of 270 degrees
5) The later total period, showing the caecum rotating so its normal position in the lower right quadrant of the abdomen
Umbilical Herniation/Fistula
Failure of umbilical cord to close properly
-can lead to Omphalacere - gut on outside - can be corrected
Gut herniates through weakened region in body wall
Meckel’s Diverticulum
Ileal diverticulum (non-pinched off part on diverticulum)
Very common (~2% of population)
Remnant of the yolk sac (Vitelline Duct)
-may end up with inflammation
Hindgut-Cloaca
Starting of Hindgut:
Expanded distal part of the hind gut
Divided into Dorsal and Ventral parts
- via Mesenchymal (undifferentiated cells) Urorectal Septum
As Septum grows- separates rectum(distal digestive sys) from urogenital sinus
-6wks - coming towards Proctodeum (primitive anus). Eventually reaches outer body wall and splits off two systems
-Will be skin/Ectoderm
Hind Gut - Rectum/Anal Canal
Boundary between outer ectoderm(skin) and inner endoderm (mucousal lining)
-Pectinate Line denotes boundary
Blood Supply to upper 2/3 =IMA (inferior mesenteric artery)
Portal Systemic anastomosis
Anal columns terminate at site of anal membrane
Lymphatics change at Anocutaneous Line (White Line)
Inside prox 2/3 go to inferior mesenteric nodes around aorta.
-Below = Superficial inguinal nodes
(helps to differentiate where source of trouble is based on the lymphatics)
Superior 2/3 supplied by SMA
Inferior 1/3 supplied by systemic veins (internal iliac and peroneal veins)
Veinous drainage is to 2x systems – Portal-systemic system/anastomosis (important for hepatic hypertension leading to issues in this region)
Mesenchyme
Undifferentiated cells
Venous drainage of Rectum/Anus
Veinous drainage is to 2x systems – Portal-systemic system/anastomosis (important for hepatic hypertension leading to issues in this region)
Hypertension causes peoblems at portal/systemic anastomosis
Megacolon (Hirschprung’s Disease)
Segment of colon = Dilate
-due to absence of ANS ganglion cells in wall of gut distal to it (no sympathetic innervation)
Failure of peristalsis in aganglionic part - cannot relax
-prevents movement of intestinal contents
-creates blockage of food proximal to it - creating dilation
-closer to distal end of hindgut
Normally located around region of gut close to anus
-Generally more common in males (but mostly easily sorted)
Imperforated Anus
Failure of anal membrane to perforate
- not connected to outer body wall
- caught quickly and surgically fixed
- Generally more common in males (but mostly easily sorted)
Rectal Atresia
Anal canal and rectum = separated
Fistulas may present
- connect L Intestine to Urethra, bladder or vagina ( digestive system join to urigenital system)
-Generally more common in males (but mostly easily sorted)
Hindgut Congenital Malformations
- Megacolon (Hirschprung’s disease)
- Imperforated Anus
- Rectal Atresia
- generally more common in males (but mostly easily sorted)
