Embryology 1

Question 1

What is an oocyte?

Answer 1

An egg before maturation

Question 2

What is a zygote?

Answer 2

A diploid cell made from the fusion of two haploid gametes (the maternal ovum and the paternal spermatazoa)

Question 3

What is an embryo?

Answer 3

Everything from 2 cells to eight weeks of age, including a morula and a blastula

Question 4

What makes up the fundamentals of the development process?

Answer 4

Cell division - mitosis
Patterning - how the cell knowns what it is meant to becomes, e.g upper limb rather than a lower limb
Cell specilisation or differentiation - regulation of gene expression to become a specifically adapted cell for its function
Morphogenesis - the movement of cells/tissue to create anatomy.

Question 5

Describe the process of fertilisation

Answer 5

Occuts in the ampulla of the uterine tube, ovum is transported here by the fimbria
Sperm head penetrates the corona radiata, zona pellucida and plasma membrane of the egg.
Cell membrane of the sperm head fuses with that of the oocyte, releasing genetic material into the cytoplasm
The zona pellucida reforms
This is a zygote

Question 6

What three layers surround the ovum?

Answer 6

The plasma cell membrane
The zona pelluicida - dense glycoproteins
The coronoa radiata - loose circle of follicle cells

Question 7

How does the sperm cell break throught the zona pellucida?

Answer 7

Receptors on the sperm head bind to receptors on the zona perlucida.
Initiates the acrosome reaction, where vesciles containing proteases are released from the acrosome of the sperm, hydrolyses proteins in the zona pellucida.

Question 8

What are the initial cell types that develop from a zygote?

Answer 8

Morula
Blastocyte

Question 9

Describe how a morula is formed?

Answer 9

The zygote divides rapidly by mitosis within the zona pellucida.
Division is so fast that is does not grow in size only in cell number.
Once there are 16 cells this is a morula

Question 10

Describe how a blastocyst is formed.

Answer 10

Formed from a morula
Undergoes morphogenetic reorganisation.
Outer cells or the morua becomes tighlt adhesvie and transport fluid into the embryonic mass, forming a cavity called the blastocyst cavity.
This forms a blastocysts, containing an inner cell mass and a layer of trophoblasts (trophectoderm)

Question 11

What is meant by the blastocyte hatchin?

Answer 11

By day 5/6 the blastocyte secretes protein to digest the zona pellucida and burst out, forming a hatched blastocysts.
During this process the blastocyst has migrated from the fallopina tubes to the uterus

Question 12

Describe the process of implanation.

Answer 12

The trophocyte cells surrounding the inner cell mass aid implantation.
L-selectin receptors bind to aligosaccharides on the uterine wall, this provides apposition (loose connection)
This connection is reinforces by intergrin cell adhesion molecules,
Matrix Mellatopproteinases aids the invasion of the endometrium by degrading the ECM.

Question 13

What morphogenetic process occurs during implantation?

Answer 13

The inner cell mass develops into and epiblast and a hypoblast layer, This is known as the bilaminar disk, and is where gastrulation occurs.

Question 14

What is the clinical importance of spontaneous abortions?

Answer 14

50% of fertilised eggs are lost as spontaneous abortions, mainly within the first few weeks.
These are often unrecognised events as a later or heavy period.
This is caused by chromosomal abnormalities or faults during replaciation, due to the speed at which the process happens
This is why many couples struggle to get pregnant when they first start trying.

Question 15

What is the deal with ectopic pregnancies?

Answer 15

When implanation of the zygote occurs in the incorrect antomical position (not inside the uterus).
This occurs in 1/90 pregnancies.
This can cause lower abdominal pain, vaginal bleeding, abdominal discharge, referrend shoulder pain.
can be a surgical emergency if their is fainting, dizziness, sudden sharp pain, pallor.
Pregnancy must be terminated, often occurs spontaneously.

Question 16

What is the process of gastrulation?

Answer 16

When the bilateral disk, develops into the germ layers as a multidimensional structre called the gastrula.
Body axis starts to develop

Question 17

What are the two different sacs in an embryo?

Answer 17

The amniotic sac -space above the epiblast layer
the yolk sac - space below the hypoblast layer

Question 18

Explain what happens during gastrulation.

Answer 18

The epithelial cells undergo a mesenchymal transition (EMT) meaning they become mobile.
Cells of the apiblast rush inwards and down at the midline forming a primitive node and streak.
The cells replace the hypoblast layer to become the endoderm and form a middle layer called the mesoderm. The remaining epiblast becomes the ectoderm.
Other morphological changes occur in the ectoderm to create the head plate.

Question 19

Why is the EMT transition in embryonic development important to oncologists?

Answer 19

The epithelial mesenchymal transition occurs in cancer cells, understanding what causes and how to stop this change may help stop cancer metastasis.

Question 20

How do the embryonic axis develop?

Answer 20

The primitive streak and node are the main references for the body axis
The cranial end is by the node and the caudal end at the bottom of the streak.
The anterior axis is the mouth, and posterior the bum
The ventral surface is the face and dorsal the back
(CHECK WITH OLIVIA)

Question 21

What do the three different germ layers become?

Answer 21

The ectoderm becomes the nervous system, the integumentary system and the pituitary gland
The mesoderm - becomes the muscular skeleton, cardiovascular system, reproductive system and connective tissue
THe endoderm becomes the epithelial layers of organs, the GI tract, the bladder and the thyroid.

Question 22

What is the significant of the blastopore?

Answer 22

Invagination in the embryonic disk, becomes the anus. Human equivalent is the primitive streak.

Question 23

Describe the process of neuralation?

Answer 23

The dorsal ectoderm undergoes neuraltion forming the central canal and neural tube
Parts of the ectoderm thicken forming the neural plate
The edges of the plate fold upwards known as the neural folds.
They get to a point where they are almost connected known as the neural crest.
The two folds connect forming the neural tube
Some neural crest cells are released these are known as migratory neural crest cells.

Question 24

What are some of the functions of the neural crest cells?

Answer 24

Migrate away from the neural tube, often down a concentration gradient.
Contribute to meninges, thyroid, cartilage and bones in the face, neurons and glia
Heart development (septa, pericytes, smooth muscle)
Enteric nervous system, mesencyhme
Dorsal root ganglia
Sympathetic ganglia
Neurons}Adrenal medulla
Schwann cells
Melanocytes

Question 25

What is Hirchsprung disease?

Answer 25

Failure in the development of the vagal neural crest.
Does not innervate all of the descending colon so no peristalsis as no muscle tone
Section of bowel needs removing.

Question 26

What is segmentation of the embryo?

Answer 26

During development the embryo is split into may sections
THe main division is from the mesoderm which gives rise to somites hence the vertebral column, giving transverse sections
We are also segmented in the medulla (ectoderm) and the pharangeal arches (ecto, endo and mesoderm)

Question 27

What is somitogenesis?

Answer 27

Somites form the paraaxial mesoderm
First the mesoderm is segmented, new segments are added in a cranial caudal reaction.
The clock and wavefront model, describes this process.
The caudal end extends due to high conc of FGF and Wnt.
Regularly times waves of notch activity pass through the presomite mesoderm, causes the area to sequentially develop into somites by a mesenchynal to epithelial transition.

Question 28

What is meant by a homoeotic phenotype?

Answer 28

Based on the hox genes, the development of features in the correct anatomical position

Question 29

What are Hox genes?

Answer 29

Have a major role in the positional development of structures, if malfunction functionaly structures will develope in the wrong place.
They control the development of major body segments and seperate different anatmoical regions.
Act as transcription factors
Specify cell identity and positioning.

Question 30

How are hox genes arranged in the genome?

Answer 30

Arranged in four different clusters on different chromsomes.
Arranged in a collinearty pattern meaning they are expressed in the body in the order they are found on the chromosome
Each cluster A,B C and D contains multiple hox genes (total of 39 hox genes)
The different proportions of hox genes relates to different anatomical regions.