embryology terms and early development

Question 1

why is embryology important?

Answer 1

• Understanding pregnancy and infertility
• Understanding congenital abnomralities
• Understanding gross anatomy

Question 2

define pre-embryo

Answer 2

pre-implantation (cell division period)

• weeks 1-2

Question 3

define embryo

Answer 3

embryonic period

• organogenesis - development of more complex organs
• weeks 3-8

Question 4

define foetus

Answer 4

growth phase

Question 5

define caudal

Answer 5

tail of embryo (analogus to inferior in adults)

Question 6

define cranial/rostral

Answer 6

head of embryo (analogous to superior in adults)

Question 7

define dorsal

Answer 7

front

Question 8

define ventral

Answer 8

back

Question 9

list the key processes of early embryonic development in chronological order (up to day 28)

Answer 9

1. Fertilisation
2. Cleavage (cell division), blastocyst and bilaminar disc formation
3. Implantation of blastocyst into the uterine wall and beginning of placental villus formation
4. Primitive streak formation, gastrulation and trilaminar disc (germ layer) formation
5. Neurulation
6. Completion of placental villus formation, Embryonic folding.

Question 10

label this diagram of fertilisation

Answer 10

A: spermatozoon

B: acrosome

C: corona radiata

D: acrosome reaction

E: zona pellucida

F: plasma membrane of ovum

Question 11

describe the process of fertilisation

Answer 11

1. Penetration of corona radiata
2. Attachment to zona pellucida - shell of oocyte
3. Acrosome reaction – hat of sperm
4. Penetration of zona pellucida
5. Binding to plasma membrane and sperm entry

Question 12

describe the stages of pre-implantation development (days 0 to 5)

Answer 12

zygote divides during cleavage process

1. Zygote (one cell) 0-1 days post-fertilisation
2. Four-cell pre-embryo (four blastomeres) 1-2 days post-fertilisation.
3. Morula stage pre-embryo (16 blastomeres) 3 days post-fertilisation.
4. Blastocyst stage pre-embryo (approx 128 blastomeres) 4-5 days post-fertilisation. Cell differentiation begins (represented by red and blue cells). Blastocyst has characteristic cavity (blastocoel).

Question 13

label this image of the process of implantation

Answer 13

A: Uterine epithelium (External lining of uterine endometrium).

B: Blastocyst (pre-embryo becoming embryo during implantation)

C: Syncytiotrophoblast cells of the blastocyst (will form the placenta)

D: Inner cell mass cells of the blastocyst (will form the foetus)

E: Maternal blood vessel (will provide maternal blood supply to the foetus via the placenta)

Question 14

The nervous system is derived from a sub-population of which embryonic germ layer?

Answer 14

neuroectoderm in the ectoderm gives rise to the nervous system

Question 15

Which embryonic structure is responsible for inducing this sub-population of cells to become the nervous system and how does it do so?

Answer 15

notochord

• releases molecular signals that induces part of the ectoderm (called the neural plate) to become neuroectoderm.
• this process is known as neural inductio

Question 16

Describe how embryonic folding alters the form of the trilaminar embryo

Answer 16

produces a 3D embryo

Question 17

identify the body cavities formed during folding that will surround the heart, lungs and gut in the adult

Answer 17

• pericardium (heart)
• pleura (lungs)
• peritoneum (gut)

all develop from a cavity in the mesoderm (intraembryonic coelom)

Question 18

what happens day -5 to 0 of development?

Answer 18

ovarian follicle ruptures and release oocyte into uterine tubes, which cannow be fertilised

Question 19

what happens days 5 - 11?

Answer 19

implantation

• 5 - 6: formation of blastocyst and attaches to uterine wall
• 9 - 10: blastocyst almost completely embedded. uterine lining reforms to enclose blastocysts. trophoblasts form placenta

Question 20

what happens days 13-18?

Answer 20

gastrulation

Question 21

what is gastrulation?

Answer 21

development of 3 germ layers: ectoderm, mesoderm, endoderm, which form different tissues of the body

Question 22

describe the process of gastrulation

Answer 22

• blastocyst is a two layered embryo (hypoblast and epiblast) known as a bilaminar disc
• the primitive streak on the epiblast allows cells to move through into the primitive groove, where they are told to become either mesoderm or endoderm
• cells which don’t move in become ectoderm

Question 23

describe features of embryonic ectoderm

Answer 23

• neural ectoderm = induced to form neural plate by notochord. forms nervous system and sensory organs
• surface ectoderm = epidermis
• nerual crest = clinically important cell population (cranial NC and cardiac NC) - can cause craniofacial and cardiac defects if not formed properly

Question 24

describe features of embryonic mesoderm

Answer 24

• notochord
• forms many adult tissues = endothelium, blood, cartilage, skeletal and smooth muscle, blood, lymph, heart, kidneys, spleen, reproductive system, limbs

Question 25

which adult features that come from the embryonic endoderm?

Answer 25

• Gut tube
• Abdominal organs: liver and pancreas
• Trachea and lungs
• Auditory system
• Urinary system

Question 26

what happens days 16 - 17?

Answer 26

neural indication

• signals from the notochord induce neural ectoderm to form neural plate

Question 27

what happens days 20 - 21

Answer 27

neurulation and mesoderm induction

Question 28

describe the process of neurulation

Answer 28

• neural plate sinks below surface ectoderm into embryo and rolls up to form a tube
• neural tube will later differentiate to form the spinal cord and brain (CNS)
• neural crest cells arise from neural tube and will differentiate to form the peripheral nervous system
• mesoderm told to differentiate into somites (precursors of the axial skeleton and skeletal muscle)
• intraembryonic coelom formed around 20th day in the mesoderm ( eventual body cavity)

Question 29

what happens day 22-28?

Answer 29

embryonic folding