Early Stages

Question 0

What is a morula?

Answer 0

It the hollow ball of cells formed after the fertilised ovum has undergone a series of mitotic divisions

Question 1

At what gestational age does the morula form a blastocyst?

Answer 1

Day 4

Question 2

The blastocyst consists of an inner cell mass and outer cell mass (the trophoblast). What does each cell mass go on to form?

Answer 2

• Inner cell mass forms the embryo

- the extra-embryonic membranes

Question 3

Up to the blastocyst stage the developing embryo is surrounded by a capsule of extra cellular matrix. What is this capsule called?

Answer 3

Zona Pellucida

Question 4

By what gestational age does the Zona Pellucida dissolve?

Answer 4

Day 7

Question 5

What function do enzymes secreted by the trophoblast have in implantation?

Answer 5

The enzymes erode the wall of the uterus allowing implantation

Question 6

As implantation proceeds the trophoblast divides to form a multinucleate tissue which makes intimate contact with the endometrium and forms part of the placenta.
What is this tissue called?

Answer 6

Synctiotrophoblast

Question 7

Following implantation the cells of the Inner cell mass change and form two cavities, what are these and what do they do?

Answer 7

• Amniotic cavity - surrounds embryo in protective fluid

* Primary yolk sac - contributes blood vessels from embryo to placenta

Question 8

The cells between the amniotic cavity and the primary yolk sac become organised into which two layers?

Answer 8

• Endoderm

- Ectoderm

Question 9

What connects the embryo to the trophoblast?

Answer 9

The body stalk

Question 10

Where is the body stalk derived from?

Answer 10

The trophoblast

Question 11

At what gestational age is the embryo connected to the trophoblast by the body stalk completed by?

Answer 11

13 days

Question 12

What stage follows implantation in embryonic development?

Answer 12

Formation of the germ layers

Question 13

What tissues are derived from the ectoderm?

Answer 13

• epidermis, skin glands, mammary glands, tooth enamel.
• neural tube, CNS, Retina
• neural crest, sensory nerves, sympathetic NS, pigment cells

Question 14

What tissues are derived from the Mesoderm?

Answer 14

• bone
• muscle
• connective tissues
• blood
• dermis

Question 15

What tissues are derived from the endoderm?

Answer 15

• linings of the gut
• liver via bile duct
• bladder
• lungs
• trachea

Question 16

What is gastrulation?

Answer 16

It is the process whereby the 3 primary germ layers are formed.

Question 17

What does the ectoderm divide to form?

Answer 17

The primitive streak

Question 18

How is the mesoderm formed?

Answer 18

• Starting at the cranial end and proceeding down the length of the primitive streak cells migrate through a hole in the ectoderm and crawl between the ectoderm and endoderm forming the mesoderm.

Question 19

When does neurulation occur?

Answer 19

After gastrulation

Question 20

What layer differentiates to form the neural tube?

Answer 20

The ectoderm

Question 21

What happens during neurulation?

Answer 21

•Cells of the ectoderm start roll up forming a long tube with a bubble at the end.

• tube becomes spinal cord
• bubble becomes brain

• cells that separate migrate away to become the neural crest

Question 22

What tissue do somites differentiate from ?

Answer 22

Mesenchyme

Question 23

What do somites form?

Answer 23

• Vertebrae
• Ribs
• Muscles

Question 24

What does the notocord form?

Answer 24

The centrum of the vertebrae

Question 25

How are the embryonic head and tail folds formed?

Answer 25

• process like pulling on drawstrings of purse
• edges of disk end up at belly button
• amnion expands obliterating extra-embryonic coleom. Yolk sac pushed against body stalk.
• blood vessels contribute to umbilicus & placenta
• allantois (outpushing of hindgut) adds blood vessels to placenta.