Embryology 1 & 2

Question 1

What is the name of the cell in males that divides to form sperm?

Answer 1

Spermatogonium

Question 2

What type of cell is spermatogonium, diploid or haploid?

Answer 2

Diploid

Question 3

What happens to the spermatogonium?

Answer 3

It undergoes meiosis (two phases), to produce 4x sperm cells.

Question 4

What type of cell is sperm?

Answer 4

Haploid

Question 5

What is the name of the cell in females that divides to form an ovum?

Answer 5

Oogonium

Question 6

What type of cell is an oogonium, and how many chromosomes does it have?

Answer 6

Diploid, 46 chromosomes.

Question 7

What happens to the oogonium?

Answer 7

It undergoes meiosis in two phases, the first in utero but the second does not take place until roughly teenage age, whereby an ovum and three polar bodies are produced.

Question 8

What type of cell is an ovum, and how many chromosomes does it possess?

Answer 8

Haploid, 23 chromosomes.

Question 9

What is the name given to sperm and ovum cells?

Answer 9

Gametes

Question 10

What name is given to the production of sperm?

Answer 10

Spermatogenesis

Question 11

What name is given to the production of an ovum?

Answer 11

Oogenesis

Question 12

What are the three prenatal periods of embryology?

Answer 12

1. Pre-embryonic phase (week 1-3)
2. Embryonic phase (week 4-8)
3. Foetal phase (week 9-40)

Embryogenesis
Fetogenesis

Question 13

What happens during fertilisation?

What new cell is formed?

Answer 13

The pro-nucleus of a sperm enters penetrates the ovum and fuses with the pro-nucleus of the ovum to form a zygote.

Question 14

Why do males with low sperm count struggle to fertilise a female egg?

Answer 14

In order for fertilisation to take place, there must be lots of sperm surrounding the egg, even though only one penetrates (normally).

Question 15

What is a zygote?

Where about is it formed, and in which week of pregnancy?

Answer 15

The first cell formed after fertilisation.

It is formed from the sperm and ovum fusing together, it is a diploid cell with 46 chromosomes.

It is formed in the uterine tube, in week one.

Question 16

Why is the zygote genetically unique?

Answer 16

It contains genetic information from both mum and dads chromosomes. Also, each sperm and ovum is genetically unique thus the reason siblings have different physical and personal traits.

Question 17

What is the morula?

Answer 17

After fertilisation, the zygote begins to undergo a process of division (mitosis), it divides into 2, then 4, then 8 and so on.

This produces a solid ball of cells called the morula, which can then go on to form the blastocyst.

Question 18

Why is the fact that only the nucleus of the father fuses with the ovum clinically important?

Answer 18

It means that all organelles are inherited from the mother so in genetic abnormalities carried in the mitochondrial DNA will only be passed on by the mother.

Question 19

Why does the morula form a blastocyst?

Answer 19

As the morula grows in size, the cells become compressed and struggle to receive nutrition.

To get around this, a blastocystic cavity is formed where nutrients can reach the growing mass of cells.

Question 20

Describe the structure of a blastocyst.

Answer 20

There is an inner blastocystic cavity, an inner mass of cells which accumulates at one end and an outer layer called the trophoblast.

Question 21

What does the trophoblast differentiate to form?

Answer 21

The placenta and the membranes around sacs around the foetus (amniotic sac), and also the umbilical cord.

Question 22

Describe the movement of the zygote from the ovaries to the uterus and the changes that it undergoes?

How long does this process take?

Answer 22

The ovum is usually fertilised by sperm to form the zygote shortly after release from the ovary at the distal end of the uterine tube.

The zygote begins to undergo mitosis as it travels along the uterine tube toward the uterus, it becomes the morula in the process. The morula is aided by the ciliated squamous cells which surface the fallopian tubes.

By the time the cell reaches the uterus, it is a blastocyst. This process takes about one week.

Question 23

What issues in the uterine tube can lead to serious complications?

Answer 23

Uterine tubes can become seriously affected by infection (e.g. chlamydia), pelvic inflammatory disease, fibrous/scar tissue etc.

This can affect the cilia, and the transport of the zygote to the uterus. If the zygote/blastocyst becomes lodged in the uterine tube, it can lead to an ectopic pregnancy which could rupture and cause serious complications.

Question 24

What is the next stage that happens, once the blastocyst has reached the uterus?

Roughly, when does this happen?

Answer 24

Implantation

At the end of week one (day 6)

Question 25

Where does the blastocyst implant in the uterus?

Answer 25

Uterine endometrial layer (endometrium)

Question 26

What happens to the trophoblast during implantation?

Answer 26

It divides to form two layers. It ultimately forms the chorion.

Question 27

What three main things does the chorion do?

Answer 27

1. Facilitates implantation into the endometrium (chorionic villi). 2. Goes on to form the placenta. 3. Releases hormone HCG (Human Chorionic Gonadotropin).

Question 28

What does the hormone HCG do?

Answer 28

The chorion secretes HCG into the bloodstream, this hormone sends a messenger to the ovaries to continue secreting oestrogen which maintains the endometrium with implanted blastocyst. It is also what is used to detect pregnancy in urine.

Question 29

What is the decidua basalis?

Answer 29

``` Decidua = endometrium Basalis = basal layer ``` It is part of the endometrium deep to the implanted conceptus, it becomes the mothers side of the placenta.

Question 30

What does the inner mass of the blastocyst form on implantation?

Answer 30

The cells of the inner cell mass form a 2–layered flat disc called the bilaminar disc.

Question 31

What are the two layers of the bilaminar disc?

Answer 31

Epiblast | Hypoblast

Question 32

What is the cavity above and below the bilaminar disc known as?

Answer 32

Above - amniotic cavity Below - yolk sac

Question 33

What is the cavity called into which metabolic waste products of the feotus drain into? What does this cavity go on to form in the embryo?

Answer 33

Allantoic cavity Bladder etc.

Question 34

Why is it possible for mother and baby to have different blood groups?

Answer 34

Mother blood vessels and foetal vessels in the placenta do not touch one another due to the chorionic villi.

Question 35

What are the three main functions of the placenta?

Answer 35

1. Foetal nutrition 2. Transport of waste and gas 3. Immune protection

Question 36

Describe the foetal end of the placenta?

Answer 36

Smooth with foetal blood vessels and end of umbilical cord.

Question 37

Describe the maternal end of the placenta?

Answer 37

Decidua basalis of endometrium. Rough and has maternal blood vessels.

Question 38

What separates the placenta between mother and foetus?

Answer 38

Chorionic villi

Question 39

What are the two different types of twins?

Answer 39

Dizygotic (non-identical) | Monozygotic (identical)

Question 40

Explain how dizygotic twins form.

Answer 40

- 2 ovum - 2 sperm - 2 zygotes (genetically unique) - 2 placenta

Question 41

Explain how monozygotic twins form.

Answer 41

- 1 ovum - 1 sperm - 1 zygote (initially - Zygote splits and goes on to form two embryos (identical) - 1 placenta - May or may not share amniotic and chorionic sacs.

Question 42

When can a monozygotic pregnancy be problematic?

Answer 42

If the division of the zygote happens late on in pregnancy (e.g. conjoined twins)

Question 43

Summarise what happens in first two weeks in terms of conceptus.

Answer 43

Fertilisation - zygote - morula - blastocyst - inner cell mass - bilaminar disc - epiblast and hypo blast - amniotic cavity and yolk sac

Question 44

Summarise what happens in first two weeks in terms of location.

Answer 44

Morula in uterine tube - cilia - blastocyst reaches uterus - implantation in endometrium - outer cell mass (trophoblast) - chorionic villi faciltates - deciduas basalis formed - placental formation begins

Question 45

What is the primitive streak? What does it form in terms of the embryo?

Answer 45

It is the midline of the epiblast, viewed from above. It is formed by the dipping of cells through invagination. It forms the axis for the embryo.

Question 46

What is the formation of germ layers in week 3 called?

Answer 46

Gastrulation

Question 47

What happens during gastrulation?

Answer 47

Epiblast cells migrate into space between epiblast and hypoblast layers. They then form three layers (trilaminar disc).

Question 48

What are the three layers formed in the trilaminar disc, from top to bottom?

Answer 48

Ectoderm Mesoderm Endoderm

Question 49

Summarise the process of blastocyst to specialisation.

Answer 49

Blastocyst - inner cell mass - bilaminar disc - epiblast and hypo blast - primitive streak invagination - ectoderm, mesoderm and endoderm - cells become specialised.

Question 50

Cells from the ectoderm sink down into the trilaminar disc to form what?

Answer 50

Notochord - a solid tube

Question 51

Explain the process of neurulation.

Answer 51

The notochord induces the ectodermal cells in the primitive streak to thicken and form a neural plate. This then sinks down to form the neural tube.

Question 52

What week does gastrulation and neurulation take place in?

Answer 52

Week 3

Question 53

Explain how the neural tube interacts with the mesoderm, and what is produced from this.

Answer 53

Neural tube induces mesoderm to thicken. Mesoderm splits into three: Paraxial mesoderm Intermediate plate mesoderm Lateral plate mesoderm Lateral plate mesoderm splits into somatic and splanchnic mesoderm.

Question 54

What is the space generated in the lateral plate mesoderm called?

Answer 54

Intraembryonic coelom

Question 55

Where do somites originate?

Answer 55

From segmentation of paraxial mesoderm.

Question 56

What does the intermediate plate mesoderm go on to form?

Answer 56

Urogenital system (kidneys and reproductive organs)

Question 57

What does the lateral plate mesoderm go on to form?

Answer 57

pleura, peritoneum and body cavities.

Question 58

What does the neural tube develop into?

Answer 58

The brain and spinal cord

Question 59

Where does gut formation develop from?

Answer 59

Endoderm

Question 60

Where does uritogenital system develop from?

Answer 60

Intermediate plate mesoderm

Question 61

Where do body cavities develop from?

Answer 61

Lateral plate mesoderm (i.e. the somatic and splanchnic mesoderm)

Question 62

How many pairs of somites from in the paraxial mesoderm?

Answer 62

43

Question 63

How does each somite further differentiate?

Answer 63

It divides into three: Dermatome (dermis) Myotome (muscle) Sclerotome (bone)

Question 64

Where does respiratory system develop from?

Answer 64

Endoderm

Question 65

What occurs in the embryonic period, in terms of developing of the neck?

Answer 65

Pharyngeal arches form

Question 66

What is teratology?

Answer 66

Study of when things go wrong during development.

Question 67

What are teratogens?

Answer 67

Environmental factors that cause abnormal development.

Question 68

Give example of some teratogens?

Answer 68

Drugs - thalidomide Infection - measles Radiation Alcohol/tobacco

Question 69

Give example of some genetic factors that lead to abnormality?

Answer 69

Chromosomal number (too many, or too few) Structural changes in chromosomes

Question 70

What does ToRCH stand for (for infectious teratogens)?

Answer 70

toxoplasma rubella CMV herpes

Question 71

In what stage of pregnancy is the foetus most sensitive to teratogens?

Answer 71

Weeks 3-8 (embryonic phase)

Question 72

What are the three factors that constitute to the risk of teratogenesis?

Answer 72

1. Time of exposure 2. Dosage of teratogen/exposure length 3. Genetic constitution of embryo ie some more susceptible than others at equivalent doses etc.

Question 73

How are malformations identified and diagnosed in prenatal phase?

Answer 73

Blood - AFP Ultrasound scan – 12 week anomaly scan Invasive tests: chorionic villus sampling and amniocentesis

Question 74

How are malformations identified and diagnosed in postnatal phase?

Answer 74

Hip stability Testes (descent) Fingers and toes Hearing

Question 75

Summarise the first four weeks of embryonic development.

Answer 75

Week 1 - fertilisation, zygote formation, uterine tube to uterus, blastocyst Week 2 - implantation, bilaminar disc, chorionic villi, placenta formation Week 3 - primitive streak invagination, gastrulation, neurulation, somite formation Week 4 - organogenesis, lateral folding