Development of the Digestive System Flashcards
1
Q
Digestive Tract organs
A
- Mouth, pharynx, esophagus, stomach, small and large intestine, rectum and anus
2
Q
Accessory digestive organs
A
- Liver
- Gall bladder
- Pancreas
3
Q
What are the contents of the primitive gut
A
- the foregut (pharynx and from the esophagus to the liver), midgut (2/3 of the transverse colon of the large intestine) and hindgut (1/3 of the transverse colon to the rectum)
4
Q
What is the relation between the digestive tract and the germ layers
A
- The endoderm gives rise to the epithelium and glands
- The intra-embryonic splanchnic mesoderm gives rises to the connective tissue and muscles of the wall
5
Q
What is the function of retinoic acid in the gut tube?
A
- Retinoic acid is a morphogen that specifies the cranial to caudal end of the primitive gut at a graded rate
- RA is also a transcription factor so once it binds to its receptor, the regulation of several genes (SOX2, PDX1, CDXC and CDXA) are ensured through out the gut tube
6
Q
What organs in the gut tube are regulated by SOX2
A
The pharynx, esophagus and stomach (foregut derivatives)
7
Q
What organs in the gut tube are regulated by PDX1
A
The pancreas and duodenum of the small intestine
8
Q
What organs in the gut tube are regulated by CDXC
A
The small intestine
9
Q
What organs in the gut tube are regulated by CDXA
A
The large intestine and rectum
10
Q
what divides the esophagus from the trachea
A
- The tracheoesophageal septum
11
Q
What is esophageal atresia
A
- This is the complete blockage of the esophagus by the improper division on the trachea and esophagus (two organs that are close together)
- This is typically with a tracheoesophagal fistula which is an abnormal connection between the trachea and fistula
- OR when the esophagus fails to reopen after being closed (recanalization typically happens in week 8-10)
12
Q
The __________ _________ connects the stomach to the dorsal body wall
A
- Dorsal mesogastrium
13
Q
what supplies blood to the foregut?
A
celiac artery
14
Q
what connects the duodenum to the dorsal body wall
A
Dorsal mesoduodenum
15
Q
What is the function of the lesser omentum
A
This is a double layer of peritoneum that extends from the liver to the stomach
16
Q
The _____ supplies blood to the midgut
A
Superior mesenteric artery
17
Q
What is the mesentery proper?
A
This is a peritoneal connective tissue that suspends the intestines in the peritoneal cavity
18
Q
What supplies blood to the hindgut
A
Inferior mesenteric artery
19
Q
What happens to the stomach in the 4th week?
A
- A dilation happens that makes it bigger
- A rotation happens 90º clockwise on the longitudinal axis making the original left side the ventral surface and the original right side the dorsal surface
- A rotation occurs on the anteroposterior axis as well making the greater curvature end on the caudal end and the lesser curvature end on the cranial end
20
Q
Visual image to understand longitudinal stomach rotation
A
- Put a tube (or something lol i used chapstick with a pencil sticking out) in front of you
- Bump (pencil) is away from you (this is 12 o’ clock)
- Your right is 3 o’ clock
- Clockwise would be towards 3 o’ clock making the bump where 3 o’ clock used to be
- Pencil (greater curvature) is on YOUR right and back of chapstick (lesser curvature) is on YOUR left
- Original left side of chapstick is away from you (ventral) and original right side of chapstick is towards you (dorsal)
21
Q
Visual image to understand anterioposterior stomach rotation
A
- Keep in mind pencil (bump) is going to be on your right and the back of the chapstick is on your left
- This bump (greater curvature) is going to tilt DOWNWARDS making the back of the chapstick (lesser curvature) face the ceiling ish
- Think of more of a 45º angle than a 90º this time
22
Q
What is congenital pyloric stenosis
A
- The pyloric sphincter is the tube of the pylorus and this condition is the narrowing of this tube
- This will restrict the movement of materials from the stomach to the small intestine
- The stomach gets bigger and projectile vomiting happens
23
Q
Explain the formation of the omental bursa
A
- A hollow space formed from the greater and lesser omenta
- The dorsal mesogastrium is formed from these clefts that fuse to become the omental bursa (tube)
- When the stomach gets bigger, this tube gets longer and it makes a loop at the bottom called the greater omentum
24
Q
What makes up the lesser omentum
A
- Formed from the ventral mesogastrium
- the hepatoduodenal ligament: the caudal end holding the duodenum to the liver
- the hepatogastric ligament : the cranial end holding the stomach to the proximal part of the liver
25
Explain the formation of the duodenum?
- The duodenum developed from the caudal part of the **fore**gut in the **fourth** week
- When it grows, it forms a C-shaped loop that projects ventrally.
- In the **5th to 6th** week, the epithelial cells are proliferating rapidly making the lumen inside smaller until it is **temporarily** obliterated
- At the end of the embryonic period the duodenum is recanalized as the epithelial cells degenerate making vacuolation occur
26
What is duodenal stenosis
- This is the narrowing or **partial closing** of the lumen in the duodenum
- When the duodenum doesn’t completely recanalize a defective vacuolization happens
- because the **bile duct** is connected to the duodenum, when projectile vomiting occurs, there’s typically **bile** contents found
27
What is the difference between duodenal and pyloric stenosis?
- The presence of **bile** in the vomit indicates it is **duodenal** stenosis as the pylorus is not connected to the bile duct
28
What is duodenal atresia?
- This is when recanalization of the lumen doesn’t happen which makes the lumen completely occlude
- The block always happens where the bile and pancreatic duct connect
29
How are the **liver** and **gallbladder** developed?
- the liver develops within the **ventral mesogastrium** in the 4th week
- A liver bud from the endoderm projects into the splanchnic mesoderm and divides into cranial (liver) and caudal parts (gallbladder and cystic ducts)
- The endoderm gives rise to hepatocytes, and the mesoderm gives rise to other cell types. (hemopoietic and fibrous tissue)
30
when does hemopoiesis and bile formation begin?
Hemopoeisis: week **6**
Bile formation: week **12**
31
Explain the induction of the liver in the foregut
- all of the foregut can initially form the liver, but is inhibited everywhere by the non-cardiac mesoderm, ectoderm and the notochord
- The liver bud growth is induced by the secretion of **FGF8** from the cardiac mesoderm which inhibits those inhibitory factors
32
describe the development of the pancreas
- At the caudal end of the foregut, dorsal and ventral pancreatic buds are formed by endoderm cells
- Dorsal has its own bud and ventral come from the same duct as the gallbladder (future bile duct)
- when the duodenum rotates, the **ventral** bud is carried dorsal to lie posterior to the dorsal bud
- With the two ducts being on top of one another, the papillae holding them (**minor** for ventral and **major** for dorsal) will fuse to form the **major pancreatic duct**
33
What are the derivatives of the midgut
- The small intestine
- The proximal part of the large intestine (caecum, appendix, ascending colon and 2/3 of transverse colon)
- The midgut elongates to form a **U-shaped loop** that projects into the extra embryonic coelom
34
What happens to the midgut in the **6th week**?
- Physiological herniation; when the midgut protrudes into the yolk sac
- This happens due to lack of space in the abdominal cavity because of the liver and kidneys
- The **cranial** limb of the midgut that’s growing gives rise to the **small** intestine
- The **caudal** limb gives rise to parts of the large intestine
35
Explain the development of the **midgut**
- during herniation, the loop rotates 90º **counterclockwise**
and the herniation is rectified in the **10th** week causing the midgut to return to the abdomen because the abdominal cavity becomes bigger and the liver and kidneys decrease in size
- Then it undergoes **2** more 90º rotations
- In total the midgut undergoes **three** 90º rotations = 270º
- When the midgut returns. the intestines becomes fixed in position when the mesenteries fuse with the abdominal wall
36
Visual image to understand midgut rotation
- put two pencils on top of one another on your chest with the erasers pointing away from you (these are your cranial and caudal limbs)
- the top pencil (cranial) moves to **YOUR** right on your chest and the bottom pencil moves to **YOUR** left (90º)
- Then as the limbs are growing another rotation occurs, your two pencils are now **side to side**,
- They’re going to rotate in the **SAME** direction again where your top pencil is now your **bottom** pencil and your previously bottom pencil is now on **TOP** (180º)
- Then another rotation occurs in the same direction making your **NOW** bottom (originally top) pencil on **YOUR** left your top (originally bottom) pencil on **YOUR** right (270º)
37
What are the two gut rotation abnormalities
- When the transverse colon is **dorsal** instead of ventral to the duodenum
- When the rotations don’t occur and the tubes aren’t tightly wound up
38
What is congenital omphalocele
This is when the midgut hernia is not reduced and it remains in the proximal part of the umbilical cord after birth
- “The protrusion of something through the navel - omphalocele”
39
What are the derivatives of the **hindgut**
- The **distal** (1/3) portion of the transverse colon. the descending and sigmoid colon
- The rectum
- The superior anal canal
40
What is the cloaca?
- It is the end part of the hindgut gut, in contact with the surface ectoderm at the cloacal membrane
- The cloacal membrane is composed of the **endoderm** of the cloaca and the **ectoderm** of the anal pit
41
How does the cloaca partition
- when the mesoderm invaginates into the hind-gut it gives rise to the urorectal septum
in the **7th** week, this septum invaginates into the cloaca, dividing it into **vental** urogenital sinus and **dorsal** GI parts
- At the end of the **8th** week, the anal membrane ruptures bringing the digestive tract in contact with the amniotic cavity
42
The adult anal canal derives from the ___________
-Hindgut
