Embryology 1 & 2

Question 1

What are the phases of development of the human?

before birth

Answer 1

Pre-embryonic (0-3 weeks)

Embryonic (4-8 weeks)

Foetal (9-40 weeks)

Question 2

Spermatogenesis is the process of sperm formation

From what cells do sperm form from?

Answer 2

Spermatogonium

Question 3

What is the process of egg formation?

Answer 3

Oogenesis

Question 4

Describe the process of egg formation

Answer 4

Oogonium cell in ovaries

Undergoes meiosis

Forms 1 ovum and 3 polar bodies

Question 5

What is the collective term for the sites of gamete formation?

(testes and ovaries)

Answer 5

Gonads

Question 6

Describe the process of fertilisation

Answer 6

Several sperms surround ovum in uterine/fallopian tube, only 1 penetrates

Pronucleus of sperm fuses with pronucleus of ovum

This produces diploid cell - zygote

Question 7

From a zygote, what is the next stage of development?

Answer 7

Morula

Zygote divides by mitosis several times to form a solid ball of cells, a morula

Question 8

“The morula will develop into a ______”

Answer 8

Blastocyst

Question 9

Describe the structure of a Blastocyst

Answer 9

Trophoblast - outer lining of cells

Inner cell mass - accumulation of cells at one side

Blastocyst cavity - hollows it out

Question 10

Why is it necessary for the morula to develop into a blastocyst?

Answer 10

As the morula becomes larger, it becomes difficult to get nutrients to cells in the middle

Forming the cavity and inner cell mass allows nutrients to reach these cells - allowing further growth

Question 11

Once a zygote is formed, it begins to divide (morula, blastocysts etc)

What else happens?

Answer 11

It moves from the uterine tube to the uterine cavity

Question 12

What facilitates movement through the uterine tubes?

Answer 12

Cilia

Question 13

How long does it take for a zygote to first divide?

Answer 13

36 hours

Question 14

After the first division of a zygote, how does the time taken for successive divisions change?

Answer 14

Successive divisions are faster

1: 36 hours
2: 24 hours
3: 12 hours

Question 15

What happens in the 2nd week of the pre-embryonic phase?

3

Answer 15

Implantation of blastocyst into endometrium

Formation of bilaminar disc

Sacs, membranes and cord used for nourishment, form

Question 16

“In order for implantation to take place, the _______ must develop into _______”

Answer 16

Trophoblast

(must develop into)]

Chorion

Question 17

How does chorion form, and what does it do?

Answer 17

Trophoblast divides to form 2 layers

Ultimately develops into chorion

Chorionic villi form - these are finger like processes that implant and eventually form part of the placenta

It also releases HCG

Question 18

What is HCG?

Answer 18

Human chorionic gonadotropin

It is secreted to maintain the endometrium, which is normally shed

Question 19

What is the muscle that surrounds the uterine cavity?

Answer 19

Myometrium

Question 20

After implantation, what name is given to the endometrium?

Answer 20

Decidua

Question 21

What is the decidua basalis?

Answer 21

Part of the endometrium (decidua) that is ‘deep’ to the implanted conceptus

This is where the interface between maternal blood vessels and the placenta will be

Question 22

After implantation, what happens to the inner cell mass of the blastocyst?

Answer 22

They form a 2-layered flat disc called the bilaminar disc:

• Epiblast (faces the endometrium)
• Hypoblast (faces away)

This splits the blastocyst cavity:

• Amniotic sac (epiblast)
• Yolk sac (hypoblast)

Question 23

Once implanted, what are the sources of nutrition for the embryo?

Answer 23

Yolk sac

Maternal nutrition via placenta

Question 24

“Waste products from embryonic development are secreted into the _______”

Answer 24

Allantoic sac

Question 25

What sac is the embryo contained in?

Answer 25

Amniotic cavity

Question 26

What cavity encases the amniotic cavity, the yolk sac, the allantoic sac and the umbilical cord?

Answer 26

Chorionic cavity

Question 27

The placenta has 2 faces What is the structure of the foetal face?

Answer 27

Smooth Contains foetal blood vessels Start of the umbilical cord

Question 28

How is the maternal face of the placenta different from the foetal face?

Answer 28

Maternal face is rough, and contains maternal blood vessels instead of foetal blood vessels

Question 29

What causes the development of fraternal/dizygotic twins?

Answer 29

2 ovum are released, and fuse with 2 sperm Thus 2 zygotes are formed 2 placentas

Question 30

What causes identical/monozygotic twins to develop?

Answer 30

1 ovum and 1 sperm fuse Zygote splits to form 2 embryos Shared placenta and may share same amniotic and chorionic sac

Question 31

Summarise what happens in the 3rd week of gestation

Answer 31

Gastrulation (formation of germ layers) Neuralation (formation of neural tube) Development of somites Early development of cardiovascular system

Question 32

What happens to the bilaminar disc before gastrulation can happen?

Answer 32

Epiblast and hypoblast must separate Primitive streak must form This forms in the midline of the epiblast through the dipping of the cells

Question 33

What information does the direction of the primitive streak tell us?

Answer 33

Axis of the embryo

Question 34

Describe the process of gastrulation

Answer 34

Epiblast cells migrate into the space between epiblast and hypoblast layers These cells then displace the hypoblast Trilaminar disc is then formed and cells have become specialised

Question 35

What are the layers that make up the trilaminar disc?

Answer 35

Ectoderm Mesoderm Endoderm

Question 36

From which layer of cells does the notochord form? Which part of this layer does it form from?

Answer 36

Ectoderm Forms from the primitive streak

Question 37

What is the notochord?

Answer 37

Solid tube of cells

Question 38

What is the function of the notochord?

Answer 38

It induces the ectodermal cells in the primitive streak to form the neural plate, which then separates and sinks down to form the neural tube

Question 39

Describe what happens after the neural tube is formed?

Answer 39

NT induces the mesoderm to thicken and separate into 3 parts: Paraxial Intermediate plate Lateral plate

Question 40

"The lateral plate mesoderm splits to form a ________ and a ________"

Answer 40

Somatic mesoderm and a splanchnic mesoderm

Question 41

What is the name given to the space between the somatic mesoderm and the splanchnic mesoderm?

Answer 41

Intraembryonic coelom

Question 42

What do the somites form from?

Answer 42

Paraxial mesoderm

Question 43

What forms from the intermediate plate mesoderm?

Answer 43

Urogenital system (kidneys and repro)

Question 44

What forms from the lateral plate mesoderm?

Answer 44

Body cavity and coverings

Question 45

What is the appearance of the somites compared to the paraxial mesoderm?

Answer 45

The PM segments to form the somites They look like a row of teeth

Question 46

When is the organogenetic period?

Answer 46

4th - 8th week

Question 47

How many somites are formed from the paraxial mesoderm?

Answer 47

43 pairs These differentiate further

Question 48

What happens in the organogenetic period?

Answer 48

Lateral folding completes Forebrain, midbrain, hindbrain and spinal cord develop Heart starts to beat on day 24 Gut formation from endoderm Urogenital system forms Body cavities form Somites form and differentiate Limb buds form Neck develops - pharyngeal arches

Question 49

What do the somites develop into?

Answer 49

Dermatome Myotome Sclerotome

Question 50

What do dermatomes form?

Answer 50

Dermis of skin

Question 51

What do myotomes form?

Answer 51

Muscles

Question 52

What do sclerotomes form?

Answer 52

Bones (inc. vertebrae)

Question 53

What is a teratogen?

Answer 53

Environmental factor that causes abnormal development

Question 54

German measles is an example of a teratogen What is it's effect?

Answer 54

It can cause congenital rubella

Question 55

Give a famous teratogen and it's effect

Answer 55

Thalidomide Causes malformation of limbs

Question 56

What environmental agents can harm a baby's development?

Answer 56

Alcohol Tobacco Other drugs Radiation Infectious agents

Question 57

What are the ToRCH agents and why are they significant?

Answer 57

Toxoplasma, Rubella, Cytomegalovirus, Herpes These can be transferred through the placenta and affect the baby's development

Question 58

Give examples of genetic factors that could affect the development of a baby

Answer 58

Too many/few chromosomes Structural changes/mutations of chromosomes

Question 59

When is the risk of teratogenesis greatest?

Answer 59

weeks 3 - 8

Question 60

When is the risk of death highest?

Answer 60

Weeks 1 - 2 Low teratogen risk though

Question 61

What are the methods of diagnosing malformations prenatally?

Answer 61

Blood - AFP Ultrasound scan Invasive tests such as chorionic villus sampling and amniocentesis

Question 62

What are the methods of diagnosing malformations post-natally?

Answer 62

Hip stability Testes (descent) Fingers and toes Hearing