Embryology part 2

Question 1

What are the three germ layers?

Answer 1

They are the primary layers from which all tissues and organs of the body develop.

They are made up of the Ectoderm, Mesoderm, and Endoderm.

Question 2

Describe the Ectoderm

Answer 2

The outermost layer, which gives rise to structures such as the skin, hair, nails, and the nervous system (including the brain and spinal cord), as well as parts of the eyes and ears.

Question 3

Describe the Mesoderm

Answer 3

The middle layer, which forms muscles, bones, the cardiovascular system (heart and blood vessels), kidneys, reproductive organs, and connective tissues like cartilage and blood.

Question 4

Describe the Endoderm

Answer 4

The innermost layer, which develops into the lining of the digestive tract, respiratory system, liver, pancreas, and other internal organs.

Question 5

What is neurulation?

Answer 5

The stage of development where the neural plate forms the neural tube. It marks the beginning of the formation of the central nervous system.

Question 6

Summarise the process of neurulation:

Answer 6

1. Formation of thickened area of cells (neural plate).
2. Neural induction.
3. The neural plate forms at the cranial end of the embryo and grows in a caudal direction.
4. The lateral edges of the neural plate become elevated, and fold to form the neural fold.
5. The folding of the neural plate creates the neural groove.
6. The 2 neural folds approach each other, beginning around the level of the fourth somite.
7. The folds fuze together, and the neural plate becomes the neural tube
8. Fusion of the neural tube
9. Neural tube closes, with cells on the lateral side of the neural plate detaching and creating the neural crest.
10. Neural crest cells migrate and displace the cells of the ectoderm to enter the mesoderm.
11. Once the neural tube has completley fused, the process of neurulation is complete.

Question 7

What is neural induction and when does it happen?

Answer 7

The notochord induces the ectodermal cells lying just cranial to the primitive node to differentiate into columnar neuroepithelial cells, approximately 19 days after fertilisation.

Question 8

What does the cranial end of the neural plate represent?

Answer 8

The region of the eventual brain

Question 9

What does the narrower caudal end of the neural plate represent?

Answer 9

The eventual region of the spinal cord.

Question 10

When does the neural plate elevate and form the neural fold?

Answer 10

By the end of the third week of development

Question 11

How long after fertilisation do the folds fuse together and transform the neural plate into the neural tube?

Answer 11

Approximately 25 days after fertilisation

Question 12

What is the neural tube the precursor to?

Answer 12

The central nervous system

Question 13

Where does the fusion of the neural tube usually begin?

Answer 13

In the cervical region, extending in both the cranial and caudal directions.

Question 14

What are the openings that are formed at the cranial and caudal ends of the embryo called?

Answer 14

Cranial and caudal neuropores

Question 15

What do the neural crest cells contribute to the formation of?

Answer 15

The peripheral nervous system, including the formation of neurons and glial cells of the sympathetic, parasympathetic and sensory nervous systems.

Question 16

What is organogenesis?

Answer 16

Organogenesis is the process during embryonic development in which the three germ layers (ectoderm, mesoderm, and endoderm) differentiate into specific organs and tissues. It begins after gastrulation, typically during the third to eighth week of development.

Question 17

Summarise the development of the muscular system

Answer 17

• Begins with the formation of muscle cells called myoblasts.
• Myoblasts originate from the mesoderm and fuse together to form long and multinucleated muscle fibres.
• Muscle fibres are attached by collagenous connective tissues, and the entire muscle is enclosed in a fibrous capsule.
• All skeletal and cardiac muscles and most smooth muscles arise from mesoderm cells, except pupillary muscles and the sweat and mammary glands, which arise from ectoderm.

Question 18

When does the development of the muscular system begin

Answer 18

Week D

Question 19

Which muscles does the mesoderm create?

Answer 19

The vast majority of muscles

Question 20

Which muscles does the Paraxial mesoderm create?

Answer 20

Becomes skeletal muscle

Question 21

Which muscles does the Visceral/splanchnic mesoderm create?

Answer 21

becomes cardiac muscle, some smooth muscle

Question 22

Which muscles does the Ectoderm create?

Answer 22

becomes remaining smooth muscle, pupillary muscles, sweat and mammary glands

Question 23

Summarise the development of the circulatory system

Answer 23

• Heart starts with a horseshoe-shaped structure (the primary heart field), which has a pair of tubes that fold so that the heart structures will be in the proper position.
• Next, septa appear, which help to partition the heart into two atria and two ventricles.
• The electrical conduction system of the primitive heart initially lies in the sinus venosus.
• As the sinus venous becomes absorbed by the right atria, the pacemaker cells appear in the sinoatrial node in the right atrium wall.
• The development of blood vessels involves the endothelium, which undergoes angiogenesis.
• This process is driven by growth factors such as VEGF (vascular endothelial growth factor).

Question 24

At which week does the cardiovascular system develop

Answer 24

Beginning of week 3 in gestation

Question 25

Summarise the development of the respiratory system

Answer 25

It begins with a primitive gut tube, which later becomes the gastrointestinal system.

At around week 4, the respiratory diverticulum detaches as an outpocketing on the proximal part of the primitive gut tube.

A longitudinal ridge called the tracheoesophageal septum forms between the gut tube and the respiratory diverticulum, becoming two separate structures.

The respiratory diverticulum later gives lung buds, where the lungs and trachea develop.

The larynx arises from the fourth and sixth pharyngeal arches around week 12.

Question 26

At which week does the respiratory system begin to develop

Answer 26

Week 4

Question 27

Summarise the development of the digestive system

Answer 27

The primitive gut starts to form when the yolk sac becomes incorporated into the embryo. It then forms a blind-ended tube, which becomes the foregut on the cephalic end, and the hindgut on the caudal end. The middle part of the midgut also forms but remains temporarily attached to the yolk sac via the vitelline duct (yolk stalk). The accessory organs of the digestive system form as outpouchings alongside the primitive gut tube.

Question 28

Which germ layers does the digestive system develop from?

Answer 28

All three germ layers (ectoderm, mesoderm, and endoderm).

The ectoderm gives rise to the enteric nervous system

Mesoderm gives rise to the connective tissue, including the wall of the gut tube and the smooth muscle

The endoderm gives rise to the epithelial lining of the digestive tract, as well as to all of the associated glands and organs such as the liver, gallbladder, and the pancreas.

Question 29

At which week does the GI system start to develop

Answer 29

Week 3

Question 30

Summarise the development of the urinary system