embryology

Question 1

What do Hox genes do?

Answer 1

Hox genes regulate the pattern of development in embryos
Their sequence on the DNA is the same order as they are used (head to tail)
Overlapping or changes of hox genes = valve/sphincter/change in diameter/change in function

Question 2

How does the gut tube form?

Answer 2

Develops from ventral invaginations at either end of the embryo
they elongate and fuse along the ventral midline to form a straight tube

Question 3

What happens to the mesoderm, ectoderm and endoderm outside of the embryonic disc?

Answer 3

They becomes placenta and membranes

Question 4

Describe the formation of the buccopharyngeal and cloacal membranes

Answer 4

2 small areas at head and tail of embryo have no mesoderm
Here the ectoderm and endoderm are in direct contact
this forms the buccopharyngeal and cloacal membranes

Question 5

How are the thoracic, cardiac and abdominal cavities form?

Answer 5

• splitting of the mesoderm to create a space
• Split forms extra-embryonic coelum, somatic mesoderm and splanchnic mesoderm
• Splitting continues until it reaches embryo and stalk becomes umbilical cord
• GIT is pinched off yolk sac

Question 6

How does the yolk sac form?

Answer 6

from blastocoele as embryo rolls up:
- links to midgut
- becomes the choriovitelline placenta

Question 7

How does the allantoic sac form?

Answer 7

forms as an outgrowth of the hindgut:
- the root with gut becomes divided by the urorectal septum to create the hindgut and the bladder
- becomes the choriaallantoic placenta

Question 8

Where does the abdominal cavity come from?

Answer 8

Extra-embryonic space (coelom)

Question 9

How does the bladder and rectum form?

Answer 9

Growth of urorectal septum divides the cloaca into the bladder and rectum

Question 10

What is a mesentery?

Answer 10

A fold or membrane that conveys blood vessels, nerves and lymphatics to a visceral structure

Question 11

How does the tongue develop?

Answer 11

as an outgrowth from the mesoderm of the lower jaw

Question 12

How does the small intestine develop?

Answer 12

• jejunum grows lengthwise - herniates from abdomen as gut initially grows faster than embryo
• gradually coils on itself as it is drawn back into abdomen as fetus grows to accomodate jejunum
• rotation draws duodenum and large colon anticlockwise

Question 13

What is an umbilical hernia?

Answer 13

faulty closure of abdominal wall leaves a large opening:
- herniation of fat, then SI through umbilicus
- hereditary
- important to check for in neonates

Question 14

What are clefts and give some examples

Answer 14

persistance of embryonic/fetal clefts due to abnormal growth processes

Question 15

What is agenesis?

Answer 15

failure of organ formation

Question 16

What is aplasia?

Answer 16

absence of part of all of an organ

Question 17

What is hypoplasia?

Answer 17

reduced development of an organ

Question 18

What is dysplasia?

Answer 18

failure of formation of normal structure

Question 19

What is metaplasia?

Answer 19

change of differentiation

Question 20

What is neoplasia?

Answer 20

uncontrolled proliferatio

Question 21

What is ectopia?

Answer 21

abnormal position

Question 22

How is the liver formed?

Answer 22

• The liver bud grows from the gut and fuses with the diaphragm
• The final liver is made from glandular tissue from the gut and connective tissue from mesenchyme

Question 23

How is the diaphragm formed?

Answer 23

• Formed from the septum transversum
• As the embryo rolls up the diaphragm end up in the middle of the embryo, next to the gut

Question 24

How is the pancreas formed?

Answer 24

• The pancreas buds grows from the gut
• The final pancreas is made from glandular tissue from the gut and connective tissue from mesenchyme
• Acinar and islet cells both arise from foregut endoderm

Question 25

how does the spleen develop?

Answer 25

• develops in the dorsal mesentary
• Serosal surfaces are covered by mesothelium (simple squamous epithelium derived from mesoderm)

Question 26

What is the vitelline artery?

Answer 26

• initially supplies the yolk sac and forms a plexus around the gut
• vitelline plexus forms the arterial blood supply to the gut (coeliac artery, cranial and caudal mesenteric arteries)

Question 27

What organs do the coeliac artery supply?

Answer 27

• stomach
• duodenum
• pancreas
• liver and spleen

Question 28

What organs do the cranial mesenteric artery supply?

Answer 28

• stomach/duodenum
• pancreas
• jejunum
• ileum
• large intestine (part)

Question 29

What organ does the caudal mesenteric artery supply?

Answer 29

rest of large intestine

Question 30

Describe the blood supply from the stomach

Answer 30

• Left and right gastric arteries
• L and R grastro-epiploic arteries
• Short gastric artery from spleen (branches off splenic artery)

Question 31

Describe the pathway of the hepatic portal vein?

Answer 31

caudal vein: branch runs ventrally, forms a loop around the anus then continues as subintestinal vein
subintestinal vein drains GIT and anastomoses with the vitelline veins in the lvier

connection with caudal vein lost
thus becomes hepatic portal vein since it now drains the GIT into the hepatic sinusoids

Question 32

What are hepatic sinusoids?

Answer 32

• Veins in the liver with incomplete vessel walls
• Allow good contact between hepatocytes and the blood

Question 33

Describe the development of gastrointestinal tract from primitive gut to adult

Answer 33

Primitive Gut Development:
The gastrointestinal (GI) tract originates from the primitive gut tube formed during embryogenesis. This tube is divided into the foregut, midgut, and hindgut.
- Foregut Development:
The foregut gives rise to structures such as the esophagus, stomach, and the beginning of the duodenum. It also forms the liver, pancreas, and parts of the biliary apparatus.
- Midgut Development:
The midgut forms the remainder of the duodenum, jejunum, ileum, cecum, appendix, ascending colon, and the proximal part of the transverse colon.
- Hindgut Development:
The hindgut develops into the distal part of the transverse colon, descending colon, sigmoid colon, rectum, and upper part of the anal canal.

Question 34

Describe the development and rotation of the stomach in monogastric animals:

Answer 34

• In monogastric animals (e.g., horses, pigs), the stomach undergoes a 90-degree clockwise rotation around the longitudinal axis. This rotation positions the greater curvature to the left and the lesser curvature to the right.
• Further development involves differential growth of the stomach walls, leading to the characteristic J-shape.

Question 35

Describe the rotation of the gut loop tube and the formation of the caecum, ascending and descending colon, and rectum in order to appreciate the form and position of these structures in the adult horse, ruminant, and carnivore:

Answer 35

Gut Loop Rotation:
The midgut loop undergoes a 270-degree counterclockwise rotation around the axis of the superior mesenteric artery.
Formation of Structures:
Horse:
The cecum is large and sacculated, the ascending colon forms a double horseshoe shape with right and left ventral and dorsal colons, and the descending colon is relatively short.
Ruminant:
The cecum is relatively smaller compared to monogastric herbivores. The ascending colon forms a complex spiral loop.
Carnivore:
The cecum is small, the ascending colon is relatively short and straight, and the descending colon is proportionally longer.

Question 36

list/Describe common developmental defects of the gastrointestinal tract:

Answer 36

• umbilical hernia = faulty closure of abdominal wall leaves larger opening for abdominal contents to escape from abdominal cavity
• abnormal organogenesis (too small, too big, grow in wrong place etc)