Embryology

Question 1

What part of the mesoderm does the kidney system form from?

Answer 1

Intermediate mesoderm at the urogenital ridge

Question 2

What are the 3 systems that develop sequentially to eventually form the kidney?

Answer 2

1) pronephros
2) mesonephros
3) metanephros

Question 3

What is the function of the pronephros?

Answer 3

No function in humans

Forms propnephric duct to drive development of the next stage

Question 4

What is the function of the mesonephros?

Answer 4

Mesonephric duct sprouts ureteric bud to induce development of definite kidney
Mesonephric duct has role in development of male reproductive system (vas deferens)

Question 5

What is the function of the metanephros?

Answer 5

Signal released from ureteric bud drive development of definite kidney in caudal region of embryo

Question 6

What is the derivative in the male urethra of the lower part of the urogenital sinus?

Answer 6

Pre-prostatic urethra, prostatic urethra and membranous urethra

Question 7

What is the derivative in the male urethra of the phallic part of the urogenital sinus?

Answer 7

Spongy urethra

Question 8

How does the urinary tract separate from the GI tract?

Answer 8

By the urogenital sinus which forms from the urorectal septum which moves causally to the cloaca to separate the tracts

Question 9

Which duct regresses in female but not males?

Answer 9

Mesonephric ducts
(Don't regress in males as they form the vas deferens)

Question 10

Where do they ureteric buds sprout from?

Answer 10

The mesonephric ducts
(Both then make independent openings in the urogenital sinus in males, but only the UBs make openings in the UGS in females as the MDs regress)

Question 11

A failure of interaction between which structures can lead to renal agenesis?

Answer 11

Between the ureteric bud and metanephros

would present as abnormally low amniotic fluid of pregnant woman

Question 12

How does a horseshoe kidney form?

Answer 12

When the two developing kidneys are too close together and fuse as they undergo lateral rotation
The fused kidneys get caught on the inferior mesenteric artery

Question 13

What are the adult derivatives of the foregut?

Answer 13

Oesophagus
Stomach
Pancreas
Liver gallbladder 
First part of duodenum (proximal to entrance of bile duct)

Question 14

What are the adult derivatives of the midgut?

Answer 14

Part of the duodenum distal to bile duct entry
Jejenum
Ileum
Caecum 
Ascending colon
Proximal 2/3rds transverse colon

Question 15

What are the adult derivatives of the hindgut?

Answer 15

Distal 1/3rd transverse colon
Descending colon
Sigmoid colon
Rectum
Upper anal canal
Inner lining of bladder and urethra

Question 16

How does the blood supply differ for the foregut, midgut and hindgut?

Answer 16

Foregut = celiac trunk
Midgut = superior mesenteric artery
Hindgut = inferior mesenteric artery

BUT structures that develop close to junction b/n foregut and midgut have mixed blood supply
Proximal duodenum = CT (superior pancreaticoduodenal)
Distal duodenum = SMA (inferior pancreaticoduodenal)
Head of pancreas = CT and SMA (superior and inferior pancreaticoduodenal)

Question 17

How do mesenteries form?

Answer 17

When the new primitive gut tube is suspended in the intra embryonic coelom and surrounded by splanchnic mesoderm, part of it forms a double layer that suspends the gut tube from the abdominal wall = mesentery

Question 18

Where are the dorsal and ventral mesenteries?

Answer 18

Ventral mesentery only within the foregut region (so has a free edge)

The dorsal mesentery suspends the entire gut tube from the dorsal body wall

Question 19

How do the dorsal and ventral mesentery contribute to the greater and lesser sacs?

Answer 19

In the region of the foregut, cavity is divided into right and left sacs due to having both ventral and dorsal mesentery

The left sac contributes to the greater sac
The right sac contributes to the lesser sac and comes to lie behind the stomach

Question 20

What does the free edge of the ventral mesentery conduct?

Answer 20

The portal triad

Question 21

How do the ventral and dorsal mesentery contribute to the greater and lesser omenta?

Answer 21

Lesser omentum formed by ventral mesentery

Great omentum formed by dorsal mesentery

Question 22

How do the omenta and greater and lesser sacs form?

Answer 22

Rotation of the stomach, firstly around longitudinal axis then around the anteroposterior axis

Question 23

What does rotation of the stomach achieve?

Answer 23

• puts vagus nerves anterior and posterior to stomach (instead of left and right)
• moves cardia and pylorus away from the midline (as stomach lies obliquely)
• contributes to moving lesser sac behind the stomach
• creates the greater omentum

Question 24

What is a peritoneal reflection?

Answer 24

Reflection from parietal peritoneum to mesentery
From mesentery to visceral peritoneum
Etc…

Question 25

What happens to structures without mesentery that are not suspended within the abdominal wall?

Answer 25

These structure are retroperitoneal

Question 26

What is the 'bare area of the liver'?

Answer 26

Part of the liver attached to the diaphragm and so is not covered by visceral peritoneum like the rest of the liver (that has a shiny surface).

Question 27

What is meant by secondary retroperitoneal organs?

Answer 27

Organs that developed intra peritoneal but lost their mesentery due to fusion with the posterior abdominal wall parietal peritoneum Eg duodenum and pancreas

Question 28

How does the midgut connect to the yolk sac?

Answer 28

Vitelline duct

Question 29

What happens when the abdominal cavity is too small to accommodate both rapidly growing liver and intestines?

Answer 29

The intestines temporarily herniate out into the umbilical cord

Question 30

How does the midgut rotate?

Answer 30

Three 90 degree rotation so what was initially cranial now returns to the abdominal cavity first, on the left hand side. The caecum then drops down,mcreating the ascending colon.

Question 31

What is derived from the cranial limb of the midgut?

Answer 31

Distal duodenum, jejenum, proximal ileum

Question 32

What is derived from the caudal limb of the duodenum?

Answer 32

Distal ileum, caecum, appendix, ascending colon, proximal 2/3rds transverse colon

Question 33

What are some complications arising from midgut rotations?

Answer 33

- Volvulus (when part of the intestine twist around itself and its supporting mesentery, resulting in bowel obstruction) - malrotation (may have left sided colon, or transverse colon could pass posterior to duodenum) - if caecum doesn't drop, will have very short ascending colon

Question 34

When do atresia and stenosis form?

Answer 34

Failure of recanalisation (sometimes cell growth is so rapid that lumen may be partially or completely obliterated, so recanalisation must occur to restore the lumen in oesophagus, bile duct and small intestines) Atresia is when lumen is obliterated Stenosis is when lumen is narrowed Common in duodenum, but may also be due to vascular accidents (ie Volvulus, malrotation)

Question 35

Is pyloric stenosis a recanalisation failure?

Answer 35

No It is hypertrophy of the circular muscle of the pyloric sphincter Results in projectile vomiting in infants

Question 36

What is gastroschisis?

Answer 36

Failure of closing of abdominal wall during embryonic folding, so leaves gut tube and viscera outside of the body WITHOUT a peritoneal covering Abdominal wall defect is to the right of the umbilicus

Question 37

What is exampholos?

Answer 37

Abdominal contents herniate into umbilical cord. Viscera are covered by peritoneum and amnion. * differs from umbilical hernia because hernias have covering of skin and subcutaneous tissue *

Question 38

When a wedge of mesoderm grows down into the cloaca, what does it divide it into anteriorly and posteriorly?

Answer 38

Anteriorly is the urogenital sinus | Posteriorly is the anorectal canal

Question 39

How does the blood supply of the anal canal differ above and below the Pectinate line?

Answer 39

Above: inferior mesenteric artery (as its hindgut derivative) Below: pudendal artery

Question 40

What is the innervation of the anal canal?

Answer 40

Above Pectinate line: S2,3,4 pelvic parasympathetic Below Pectinate line: S2,3,4 pudendal nerve

Question 41

How does the epithelium of the anal canal differ above and below the Pectinate line?

Answer 41

Above: columnar Below: stratified squamous (Above is only sensitive to stretch, below is sensitive to temperature, touch and pain)

Question 42

Where does visceral pain of the foregut, midgut and hindgut localise to?

Answer 42

Visceral pain is poorly localised. Foregut pain localises to epigastric region Midgut pain localises to periumbilical region (eg appendicitis) Hindgut pain localises to suprapubic area Parietal pain is more localised as it has somatic innervation

Question 43

What does the ventral mesentery become?

Answer 43

``` Lesser omentum (lesser curvature of stomach to liver) Falciform ligament (liver to ventral body wall) ```

Question 44

What is Meckel's diverticulum?

Answer 44

Congenital bulge of the ileum due to incomplete obliteration of the Vitelline duct.