Embryology

Question 1

Where does fertilisation normally occur?

Answer 1

Ampullary region of the fallopian tube

Question 2

What surrounds the ovum?

Answer 2

A layer of cells called the corona radiata

Question 3

What is the zone pellucida?

Answer 3

the thick transparent membrane surrounding a mammalian ovum before implantation

Question 4

What lies between the corona radiata and the ovum?

Answer 4

The zone pellucida

Question 5

What are the male and female nuclei called called just before they fuse within the ovum?

Answer 5

Pronuclei

Question 6

What is embryonic age?

Answer 6

The time since fertilisation

Question 7

What is gestational age?

Answer 7

The time since the last menstruation

So embryonic age plus 2 weeks

Question 8

What is the Germinal stage of a pregnancy called?

Answer 8

The time from fertilisation to the end of the second week

Question 9

What is the embryonic period of pregnancy?

Answer 9

The time from the the third to the end of the 8th week

Question 10

What is the foetal period of pregnancy?

Answer 10

The time from the beginning of the ninth week to to birth at 38 weeks (38-embryonic age/40-gestational age)

Question 11

What happens at the point of fertilisation and what type of zygote is formed as a result?

Answer 11

Immediate mitosis produces a 2 cell zygote

Question 12

When does implantation of the blastocysts occur?

Answer 12

Day 6

Question 13

After fertilisation the zygote begins to divide, what restricts the size of the ball of cells?

Answer 13

The zone pellucida

Question 14

What is a morula?

Answer 14

a solid ball of cells resulting from division of a fertilized ovum

Question 15

Within the zona pellucida the morula develops into two cell masses, what are these called?

Answer 15

Inner and outer cell mass

Question 16

What does the outer cell mass become?

Answer 16

The trophoblast

Question 17

What does the trophoblast become during the later stages of pregnancy?

Answer 17

The placenta and yolk sac

Question 18

Where does normal implantation occur?

Answer 18

Superior posterior wall of uterus

Question 19

What happens if the zygote implants in an abnormal site within the woman’s reproductive organ?

Answer 19

An ectopic pregnancy

Question 20

During which period of pregnancy is there the most change?

Answer 20

The embryonic period (weeks 3-8)

Question 21

What stgage of pregnancy is at the greatest risk o major congenital malformation and why?

Answer 21

The embryonic period because it is very sensitive to teratogenic agents and it is the stage where all major structures and systems are formed

Question 22

What are the 4 main events/processes occurring in early development of a foetus following fertilisation and implantation?

Answer 22

Gastrulation
Neurulation
Segmentation
Folding

Question 23

What appears on the epiblast in the third week of development and where exactly is this?

Answer 23

The primitive streak, pit and node appear on the dorsal surface of the epiblast

Question 24

What forms the bilaminar disk in gastrulation?

Answer 24

Epiblast and hypoblast

Question 25

How does the the bilaminar disc become the trilaminar disc?

Answer 25

The cells in the epiblast migrate and invaginate to form a mesoderm

Question 26

What are the layers of the trilaminar disc in gastrulation?

Answer 26

Ectoderm, mesoderm, endoderm

Question 27

Why are there two points at which there is no mesoderm?

Answer 27

So the endoderm and ectoderm are touching, | These points will become the future mouth and future anus

Question 28

List some structures that will arise form the ectoderm (2)

Answer 28

Organs and structures that maintain contact with outside world: Nervous system Epidermis

Question 29

List some structures that will arise from the mesoderm (4)

Answer 29

``` Supporting tissues: Muscle Bone Cartilage Vascular system (including heart and vessels) ```

Question 30

List some structures that will arise from the endoderm (3)

Answer 30

Internal structures: Epithelial lining of GI tract Respiratory tract Parenchyma of glands

Question 31

What is situs inversus?

Answer 31

When someone has complete mirror image viscera

Question 32

What can situs inversus commonly result from?

Answer 32

Immotile cilia

Question 33

When might situs inversus be an issue?

Answer 33

If there is a mixture of both normal and mirror image dispositions

Question 34

Prior to gastrulation what state is the embryonic disk in?

Answer 34

Bilaterally symmetrical

Question 35

What type of cells can you find at the node on the trilaminar disk?

Answer 35

Ciliated cells

Question 36

What do the ciliates cells present on the node of the trilaminar disk cause?

Answer 36

Leftward movement of signalling molecules which causes a sight specific signalling cascade

Question 37

How would cells migrate toward the left and right side of the trilaminar disk through the action of the ciliated cells on the node?

Answer 37

Move to left=The cilia would be leftward | Move to right= absence of any cilia movement, meaning signalling molecules aren't moved

Question 38

Gastrulation marks the start of which period of pregnancy?

Answer 38

Embryonic period (3-8 weeks)

Question 39

Name a key structure that appears as a result of gastrulation

Answer 39

The notochord (runs straight down the mid line of the embryonic disk)

Question 40

What is neurolation?

Answer 40

The process by which we begin the develop the nervous system

Question 41

What is the notochord? (In terms of structure?)

Answer 41

A solid chord of cells that lies in the mesoderm

Question 42

What do the cells in the notochord do?

Answer 42

Release signalling molecules which directs conversion of overlying ectoderm to neurectoderm

Question 43

How does ectoderm become neurectoderm? (3)

Answer 43

Ectoderm thickens Slipper shaped neural plate is formed Edges of the plate elevate up and curl towards each other creating the neural tube

Question 44

During neurolation in pregnancy, what 4 types does the mesoderm differentiate into and where are the types found?

Answer 44

Paraxial mesoderm - next to the neural tube (next to the axial) Intermediate mesoderm- lateral to the paraxial mesoderm Somatic mesoderm- a fork of mesoderm just below the ectoderm (lateral to the intermediate mesoderm) Splanchnic mesoderm- a fork of mesoderm just above the endoderm (lateral to the intermediate mesoderm)

Question 45

What is the space created between the somatic and splanchnic mesoderm called?

Answer 45

Intraembryonic coelom

Question 46

What does the paraxial mesoderm become?

Answer 46

Somites- body segments

Question 47

Where do the 1st somites appear?

Answer 47

1st pair appear at day 20 in the occipital region

Question 48

By the end of week 5 how many somites are there?

Answer 48

42-44 pairs | Which will eventually become 31 pairs

Question 49

What doe somites give us?

Answer 49

The building blocks of the musculoskeletal system

Question 50

How do somites initially appear? Structure.

Answer 50

As regular blocks of mesoderm cells arranged around a small cavity

Question 51

What do the cells in somites undergo in order to become precursor cells?

Answer 51

'Organised degeneration'

Question 52

What the mesoderm undergoes 'organised degeneration' what are the two categories of cells formed?

Answer 52

Dermomyotome and sclerotome

Question 53

What is sclerotome?

Answer 53

Precursor of bone

Question 54

The dermomyotome (mesoderm cells in the somites of a developing embryo) separate into two groups. Name the groups and what they are precursors of

Answer 54

Dermatome- precursor for dermis | Myotome- precursor of skeletal muscle

Question 55

What are two reasons for segmentation of the body during development?

Answer 55

Guides innervation | Gives rise to repeating structures (ie ribs/vertebrae)

Question 56

What is the area of the mesoderm in the trilaminar disc that gives rise to the future heart and where would you find it?

Answer 56

Cardiogenic area- found right at the cranial end of the embryonic disc (even above the mouth!)

Question 57

During development the embryonic disc needs to be folded in order to put structures in their correct place (the heart for example). In simple terms how is this achieved?

Answer 57

The formation of the neural tube causes folding at the head and tail end of the embryonic disc And the formation of somites caused folding of the lateral edges

Question 58

What is the head and tail folding of the embryonic disc called and why does it occur?

Answer 58

Cephalocaudal folding | Caused by the formation of the neural tube

Question 59

What is the folding of the lateral edges of the embryonic disc called?

Answer 59

Lateral folding

Question 60

What does folding of the embryonic disc achieve? (3)

Answer 60

Creates a ventral body wall Pulls amniotic sac around embryo Ensures structures are in the correct place

Question 61

What is the lining of the uterus called?

Answer 61

Endometrium

Question 62

What layer of the embryonic disc gives rise to the cardiac tissue?

Answer 62

Splanchnic mesoderm