Development of the Midgut and Hindgut Flashcards
(125 cards)
1
Q
What does the midgut give rise to?
A
- Small intestine, including most of the duodenum post bile duct entry
- Caecum and appendix
- Ascending colon
- Proximal 2/3 or transverse colon
2
Q
Draw a diagram illustrating the position of the midgut in an embryo
A
3
Q
What causes the midgut to make a loop?
A
It elongates enormously, and quickly runs out of space due to the large size of the developing liver
4
Q
What does the loop made by the midgut have at its axis?
A
The superior mesenteric artery
5
Q
What is the loop made by the midgut connected to?
A
The yolk sac
6
Q
How is the midgut loop connected to the yolk sac?
A
By the vitelline duct
7
Q
What are the limbs of the midgut loop called?
A
Cranial and caudal limbs
8
Q
Label this diagram
A
- A - Cranial limb
- B - Superior mesenteric artery at axis
- C - Caudal limb
- D - Vitelline duct to yolk sac
- SMA
- Cranial
- Caudal
9
Q
What are the derivatives of the cranial limb?
A
- Distal duodenum
- Jejunum
- Proximal ileum
10
Q
What are the derivates of the caudal limb?
A
- Distal ileum
- Cecum
- Appendix
- Ascending colon
- Proximal 2/3 of transverse colon
11
Q
What happens to the primary loop during the 6th week of development?
A
It elongates very rapidly
12
Q
What happens to the liver during the 6th week of development?
A
It grows very rapidly
13
Q
What is the problem with the rapid growth of both the liver and the primary loop?
A
The abdominal cavity is too small to accomodate both
14
Q
What is the result of the abdominal cavity being too small too accomodate the primary loop and the liver?
A
Physiological herniation
15
Q
What is physiological herniation?
A
Where the intestines herniate into the proximal umbilical cord, alongside the umbilical vessels
16
Q
What are the stages in rotation of the midgut loop?
A
- First rotation
- Second rotation
17
Q
By how much is the first rotation of the midgut loop?
A
90 degrees
18
Q
By how much is the second rotation of the midgut loop?
A
180 degrees
19
Q
What happens in the first rotation of the midgut loop?
A
During herniation into the umbilical cord, the midgut rotates around the axis formed by the SMA in a counter clockwise direction (cranial limb moves to back, caudal to the front)
20
Q
Draw a diagram illustrating what happens in the first rotation of the midgut loop?
A
21
Q
Does elongation of the small intestinal lumen continue during rotation?
A
Yes
22
Q
What is the result of the elongation of the small intestinal loop continuing during rotation?
A
The jejunum and ileum form a number of coiled loops
23
Q
What happens to the large intestine during rotation?
A
It lengthens, but does not participate in the coiling phenomenon
24
Q
When does the second rotation of the midgut loop occur?
A
When it returns into the abdominal cavity, around week 10
25
In what direction does the second rotation of the midgut loop occur?
Turns 90 degrees counter-clockwise twice
26
Draw a diagram illustrating the second rotation of the midgut loop
27
In total, by how much does the midgut loop rotate?
270 degrees counter-clockwise
28
Which limb returns to the abdomen first?
The cranial limb
29
In what direction does the cranial limb move on return to the abdomen?
To the left hand side
30
What returns to the abdomen last following rotation?
The cecal bud
31
What happens once the cecal bud has returned to the abdomen?
It descends, moving the ceacum to the right lower quadrant
32
What does the rotation of the midgut loop account for?
The positions of the small and large intestines, and the twisted apperances of the mesentery of the small intestine
33
Are abnormalities of rotation common?
Yes
34
What do abnormalities of rotation cause?
Abnormal positioning of the midgut derivatives, *e.g. the appendix on the left*
35
What happens in incomplete rotation?
The midgut only makes one 90 degree rotation
36
What is the consequence of incomplete rotation?
Left sided colon
37
Draw a diagram showing the consequence of incomplete rotation
38
What happens in reversed rotation?
The midgut makes one 90 degree rotation clockwise
39
What is the consequence of reversed rotation?
The transverse colon passes posterior to the duodenum, and can wrap arround and occlude
40
Draw a diagram showing the consequences of reversed rotation
41
What does incomplete or reversed rotation lead to?
Hypermobile guts
42
What is a volvulus?
A bowel obstruction where a loop of bowel has abnormally twisted in on itself
43
What makes a volvulus more likely?
Hypermobile guts
44
What can a volvulus lead to?
* Strangulation
* Ischaemia
45
What does the hindgut give rise to?
* The distal 1/3 transverse colon
* Descending colon
* Rectum
* Superior part of anal canal
* Epithelium of the urinary bladder
46
Draw a diagram illustrating the position of the hindgut
47
What happens to the hindgut at 6 weeks?
It ends in the cloaca
48
What separates the cloaca from the outside?
The cloacal membrane
49
What does the cloaca undergo after formation?
An anteroposterior division
50
What happens in cloacal partitioning?
A wedge of mesoderm grows down into the cloaca
51
What is the cloaca divided into in partitioning?
* The urogenial sinus anteriorly
* The anorectal canal posteriorly
52
Draw a labelled diagram illustrating the progression of cloacal partitioning
53
What is the anal canal derived from?
* The superior part is derived from the hindgut
* The inferior part is derived from the endoderm
54
What is the pectinate line?
The line at which the two parts fo the anal canal meet
55
Draw a diagram illustrating the formation of the anal canal
56
Label this diagram
* A - Rectum
* B - Pectinate line
* C - 'White' line
* D - Anal pecten
* E - Anal aperture
57
What is the blood supply for the anal canal above the pectinate line?
Inferior mesenteric artery
58
What is the blood supply for the anal canal below the pectinate line?
Pudendal artery
59
What is the innervation of the anal canal above the pectinate line?
S2/3/4 pelvic parasympathetic
60
What is the epithelia in the anal canal above the pectinate line?
Columnar
61
What is the lymph drainage of the anal canal above the pectinate line?
Internal iliac nodes
62
What is the blood supply of the anal canal below the pectinate line?
Pudendal A.
63
What is the innervation of the anal canal below the pectinate line?
S2/3/4 Pudendal N.
64
What is the epithelia of the anal canal below the pectinate line?
Stratified squamous *(non-keratinised)*
65
What is the lymph drainage of the anal canal below the pectinate line?
Superficial inguinal nodes
66
Why do the two different parts of the anal canal vary in several ways?
Because they have different origins
67
What sensation is possible above the pectinate line?
Stretch
68
What sensation is possible below the pectinate line?
* Temperature
* Touch
* Pain
69
Why is the tissue below the pectinate line sensitive to temperature, touch, and pain?
Due to its somatic innervation by the Pudendal nerve *(S2/3/4)*
70
What are some common congital defects of the GI tract?
* Vitelline duct
* Meckel's Diverticlum
* Vitelline cyst
* Vitelline fistula
* Recanalisation problems
* Pyloric stenosis
71
What is the most common GI abnormality?
Meckel's Diverticulum
72
What is the problem with a vitelline duct?
It can persist, resulting in a number of different abnormalities
73
What is Meckel's Diverticulum also known as?
Ilieal diverticulum
74
What does Meckel's Diverticulum follow?
A rule of 2's
75
What is the rule of 2's followed by Meckel's diverticulum?
* 2% of population affected
* 2 feet from ileocecal valve
* 2 inches long
* Usually detected in under 2's
* 2:1 male:female
76
Can Meckel's Diverticulum be asymptomatic?
Yes
77
What does Meckel's Diverticulum cause?
Ulceration
78
Why does Meckel's Diverticulum cause ulceration?
Because the diverticulum can contain ectopic gastric or pancreatic tissue. The ectopic tissue will secrete enzymes and acids into the tissue not protected from them, causing ulceration
79
Draw a diagram illustrating Meckel's diverticulum
80
What is a vitelline cyst?
When the vitelline duct forms fibrous strands at either end
81
Draw a diagram illustrating a vitelline cyst?
82
What is a vitelline fistula?
When there is direct communication between the umbilicus and the intestinal tract
83
What is the result of a vitelline fistula?
Faecal matter coming out of the umbilicus
84
Draw a diagram illustrating a vitelline fistula
85
Why is recanalisation required in the embryo?
The primitive gut tube is a simple tube. In some gut stuctures, cell growth becomes so rapid that the lumen is partially or completely obliterated. Recanalisation occurs to restore the lumen
86
What structures can cause the obliteration of the lumen in the primitive gut tube?
* Oesophagus
* Bile duct
* Small intestine
87
What happens if recanalisation is wholly or partially unsuccessful?
Atresia or stenosis of the stucture can occur
88
When does atresia of the gut tube structure occur?
When there is a complete loss of the lumen
89
When does stenosis of the gut tube structures occur?
When there is a narrowing of the lumen
90
Where does most atresia/stenosis occur?
In the duodenum
91
What is the most likely cause of atresia/stenosis in the duodenum?
Incomplete canalisation, *but 'vascular accidents' can also contribute*
92
What is meant by a 'vascular accident'?
Where there is a loss of blood supply and that part of the gut dies
93
Where does atresia occur more, the duodenum or the jejenum?
Duodenum
94
Where does atresia/stenosis occur more, the jejenum or the ileum?
The same
95
Where does atresia/stenesis occur more, the ileum or the colon?
Ileum
96
What are atresias most often due to in the upper duodenum?
Recanalisation failure
97
What are atresias most commonly due to in the lower duodenum?
A vascular accident
98
What can cause a vascular accident in the lower duodenum?
* Malrotation
* Volvulus
* Body wall defects
99
What is pyloric stenosis?
A narrowing of the exit from the stomach
100
Where is pyloric stenosis common?
In infants
101
What does pyloric stenosis result in?
Characteristic projectile vomiting
102
What causes pyloric stenosis?
Hypertrophy of the circular muscle in the region of the pyloric sphincter
103
What are some defects of the abdominal wall?
* Gastroschisis
* Omphalocoele
104
What is gastroschisis?
The failure of closure of the abdominal wall during folding of the embryo, leaving the gut tube and its derivatives outside the body cavity
105
What happensto the gut tube/derivates in gastroschisis?
There is no covering over them as they herniate through the abdominal wall directly into the amniotic cavity
106
What is omphalocoele?
The persistance of physiological herniation
107
What physiological herniation persists in omphalocoele?
A part of the gut tube fails to return to the abdominal cavity following normal herniation into the umbilical cord
108
Is there a covering in omphalocoele?
Yes
109
Why is there a covering in omphalocoele?
Since the umbilical cord is covered by a reflection of the amnion, this epithelial layer covers the defect
110
What are some hindgut abnormalities?
* Imperforate anus
* Anal/anorectal agenesis
* Hindgut fistulae
111
What is an imperforate anus?
Failure of the anal membrane to rupture
112
Draw a diagram of an imperforate anus
113
What is anal/anorectal agenesis?
Failure of development
114
Draw a diagram illustrating anal/anorectal agenesis?
115
What is a hindgut fistulae?
An abnormal connection within the hindgut
116
Draw a diagram illustrating hindgut fistulae
117
What are the mesenteries retained by?
* Jejenum
* Ileum
* Appendix
* Transverse colon
Sigmoid colon
118
What structures of the midgut/hindgut are fused with mesenteries?
* Duodenum
* Ascending colon
* Descending colon
* Rectum *(no peritoneal covering in distal 1/3)*
119
What happens, regarding gut development, in week 3?
Tubular gut begins to form
120
What happens, regarding gut development, in week 4?
* Primordia of liver, pancreas, and trachea
* Buccopharyngeal membrane ruptures
121
What happens, regarding gut development, in week 5?
* Expansion and early rotation of the stomach
* First intestinal loop appears
* Caecum and bile duct develop
122
What happens, regarding gut development, in week 6?
* Increased liver growth
* Herniation of intestinal loop
* Appendix develops
* Cloacal partioning begins - urorectal septum appears
123
What happens, regarding gut development, in week 7?
* Pancreatic buds fuse
* Clocal partioning complete
* Rupture of clocal membrane
124
What happens, regarding gut development, in week 8?
* Counterclockwise rotation of herniated loop
* Recanalisation
125
What happens, regarding gut development, in week 10?
* Return of herniated loop
* Adult disposition achieved
