1. Distal 1/2 Duodenum 2. Jejunum 3. Ilieum 4. Caecum 5. Appendix 6. Ascending Colon (direction fo travel) 7. Proximal 2/3 Transverse Colon - all common supply of Superior Mesenteric Artery (tells nerve supply and lymphatics)

Lecture 3 Flashcards by sita clark

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

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Spleen

Lymphoid mass

Not part of Gut tube(Foregut region)

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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)

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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

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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))

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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

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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

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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

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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

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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

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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

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What is the relationship between Superior Mesenteric and Yolk stalk

Superior Mesenteric artery goes through the yolk stalk

-maintain connection with umbilical system

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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

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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

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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

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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

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3x stages of Stomach Embryological development

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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?

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2x mesenteries

Forget: Between Dorsal and Ventral Mesogastrium/mesentery

Stomach’s Greater Omentum

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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

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Transverse colon becomes fused with greater omentum. Links stomach with Transverse Colon

Congenital Hypertrophic Pyloric Stenosis

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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

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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

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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

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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

1. 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 2. 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 3. 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

1. Megacolon (Hirschprung's disease) 2. Imperforated Anus 3. Rectal Atresia - generally more common in males (but mostly easily sorted)

Lecture 3 Flashcards

(41 cards)