Week 9 - Embryology

Question 1

What is a primordial germ cell?

Answer 1

Earliest recognised germ cell originates in epiblast close to the yolk sac - week 3 after conception
They migrate through the hind gut to the genital ridge day 24 post conception -m move along mesentery top genital ridge

Question 2

Describe the male primordial germ cells in relation to sex chords

Answer 2

Association of somatic cells in gonadal region, male germ cells associated with chords and end up inside seminiferous tubules.
They enter presumptive seminiferous tubules with pro-sertoli cells, primordial germ cells settle on tubule wall first

Question 3

Describe Sertoli cells maturation (males)

Answer 3

Form tight junctions and form the blood testes barrier, earliest germ cell outside this barrier

Question 4

Describe male primordial germ cells

Answer 4

Proliferate via mitosis and develop gonocytes as testes are developing - pro-spermatogonia into spermatogonia by the end of the foetal stage

Question 5

Describe the pre-pubertal phase in males

Answer 5

Some spermatogonia become stem cells and acquire self renewal - stem cell pool

• Perinatal spermatogonia produces spermatocytes
• All post stem cell donation is as synctiia until just before sperm cell release
• Spermatocytes arrest at prophase pf 1st mitotic division

Question 6

Give the 4 spermatocytes and there role

Answer 6

1. Preleptotene - s’ phase
2. Leptotenes - chromatin remodelling
3. Zygotene - chromatin remodelling
4. Packytene -transcription / translation
   Diplotene - enter mitosis
   1st mitotic division
   Secondary spermatocytes Second mitotic division
   SPERM

Question 7

Describe spermatids

Answer 7

Development = spermigenesis

3 types - round, elongation, maturation

Question 8

describe the second mitotic division and spermatids

Answer 8

Round spermatids, nucleus capable of division, nuclear histones replaced by transcription proteins

Question 9

Describe elongation spermatids

Answer 9

• Transcriptionally inactive
• Transcription proteins replaced by protamines
• Higher packing order and reduction of nuclear size
• Cytoplasm shrinks to form droplet

Question 10

Describe maturation of spermatids

Answer 10

• Sheding? lumen of tubule age spermatination

- Cytoplasmic droplet phagocytksed by Sertoli cells

Question 11

Describe oogenesis

Answer 11

Primordial germ cells - primary oocyte in prophase of meiosis 1

Question 12

Describe diplotene

Answer 12

4th stage of meiosis where paired chromosomes separate into chromatids

Question 13

Describe gametogenesis

Answer 13

Primordial cells give rise to oogonium therefore differentiate into 1st oocyte, surrounded bey granulose cells and germinal vesicle

Question 14

Describe the 2nd follicle - antral follicle

Answer 14

• Granulose cells proliferate and increase in follicle size
• Secretion of follicular fluids- multi polysaccharides and serum = antrum fluid
• Oocyte connected by stalk to thick granulose cell layer: cumulus oophorus
• Gonadotrophin dependent synthesis of steroid
• Thecal cell layer around glomerulosa cells

Question 15

Describe the 3rd follicle - graafion follicle

Answer 15

• Transient peak of LH stimulates ovulation
• Breakdown of nuclear membrane, separation of chromosomes
• Unequal division of cytoplasm, extrusion of 1st polar body
• Separation of chromatids - metaphase plate - 2nd mitotic division

Question 16

Describe ovulation

Answer 16

• Disappearance of cytoplasmic processes
• Synthesis of cortisol granules and new protein
• Follicle 25mm from more fluid
• Loosening’s of outer granulosa cell layers and increase in follicle blood supply
• Steroid synthesis - progesterone, bulge in ovary wall shining of stigma
• Rupture cilia on fimbriae sweep oocyte and cumulus cells - oviduct

Question 17

Describe thecal cells

Answer 17

Smaller lutein cells - synthesise androgens, progesterone and inhibit

Question 18

Describe lukeolysis

Answer 18

Regression of corpus luteum - depends whether fertilisation has occurred

Question 19

Describe pulsatile secretion in males

Answer 19

• GnRH diffuses to pituitary and causes release of gonadotropins - LH and FSH
• GnRH reserves are replenished between pulsations
• Overstimulation can cause depletion and deficiency as all GnRH is used up
• Under stimulation = not stimulated enough to release
• FSH acts on Sertoli cells, production of androgen binding protein for transport of testosterone around the bloodied direct germ cells via Sertoli cells producing inhibin - acting on leydig cells which produce testosterone

Question 20

Describe testosterone

Answer 20

Stimulates germ cells, bone, skin and hair
Testosterone to dihydrotestosterone effects on prostate and oestradiol - important in epiphysal closure and reproductive system

Question 21

Describe FSH Regulation

Answer 21

Negatively regulated by inhibin produced by Sertoli cells acts at pituitary to inhibit FSH
Positively regulated by actin and follistatin

Question 22

Describe LH regulation

Answer 22

Regulated by testosterone both at level of pituitary and hypothalamus

Question 23

Describe oestrogen effects in females during the menstrual cycle

Answer 23

• Maintains bone mass
• Effects CNS
• Effects lipid metabolism
• Effects on fat distribution
• Promotes oestrogen secretion
• Effects on blood clotting

Question 24

Describe effects of progesterone males during the menstrual cycle

Answer 24

• Increase in body temperature
• Changes to cervix lining - thickens + cervical mucous secreted
• Exerts negative feedback control on the hypothalamus and pituitary

Question 25

Describe embryonic development

Answer 25

``` Fertilisation Zygote Cleavage Morula Blastocyte Gastrulation - ectoderm, mesoderm and endoderm Orangogenesis Foetal development ```

Question 26

Describe the implantation after fertilisation

Answer 26

- Fertilised at ampulla region - Zona pellucida at first cleavage division - Blastocoel forms as fluid builds, hatching and naked blastocyst implants

Question 27

Describe zygote formation

Answer 27

- Some unequal distribution of cellular products - Cleavage results in blastomeres - two cells - Rotational cleavage - 8 cell - Compaction flattening of blastomeres maximising cell - cell contacts tight junctions form - 16 cell Each cleavage occurs in an different plane / axis to ensure cells are in a spherical shape and compact

Question 28

Describe the zygote entering the uterine cavity - day 6

Answer 28

- External polarised trophectoderm - Inner non polarised cells - inner cell mass - Trophectoderm to synctiotrophoblast - spreads around blastocyst - ICM to epiblast and hypoblast Epiblast - Embryonic embryo aminocytes, secrete fluid, embryo itself, bilaminer disc Hypoblast - Lines blastocoel and forms yolk sac - Trophectoderm forming around blastocoel/trophoblast, forms synctitium and invade uterine wall forming amniotic cavity

Question 29

Describe the synctiotrophoblast

Answer 29

``` Day 9 3 germ layers - trilaminer disc Ectoderm Mesoderm Endoderm Pattern formation - spacial and temporal pattern of cell activities is organised within the embryo ```

Question 30

Describe induction

Answer 30

- Cell types under influence of different cell types | - Production of signals that bring about response in target cells

Question 31

Describe macrophogenesis

Answer 31

The achievement of developmental diversity by formation off different structures from the same initial structure e.g gastrulation, neurulation and limb formation - Juxtacrine and paracrine signals lead to yes/no responses however can add variable result of modulation by interplay with other signals

Question 32

What is morphogen?

Answer 32

A signalling molecule that forms on the extra cellular concentration gradient

Question 33

Describe gastrulation

Answer 33

3 germ layers are formed, once committed to germ layer lineage cells don't change path - Blastocyst around implantation, ICM differentiates into two layers forming bilaminer disc with amniotic cavity above and the blastocoel below - Reorganises the epiblast into a trilaminer disc - Initiated by organiser which is in the future dorsal posterior region - Formation if primitive streak and node in epiblast - Posterior extension streak, migration of epiblast cells through node - endoderm anterior notochord and precordial mesoderm - Migration of epiblast cells through streak - ventral and lateral mesoderm - Regression of streak and replacement of notochord

Question 34

Describe neurulation

Answer 34

Formation of neural tube - to spinal cord and brain - neural plate - Embryo is a trilaminer disc between amniotic cavity and yolk sac - Heart in position after cranio-caudal folding - Lateral plate mesoderm is splitting into the somatic and splanchic layers with intra embryonic coelom between

Question 35

Describe the organisers in mesodermal tissue during neurulation

Answer 35

- Formation of neural plate and ectodermal layer - Changes in cell shape and surface properties - Folding of neural plate hinge regions, edge folds fuse - Failure to complete fusion = spinabifida - posterior or anencephaly - anterior - Tube separates sinks away from ectoderm Formation of neural tube and non neural ectoderm's is covering - Neural crest cells migrate around spinal cord

Question 36

What can excessive egg overstimulation cause during assisted reproduction ?

Answer 36

Oedema in abdomen and increase thrombosis risk

Question 37

Describe implantation of fertilised egg into the uterus

Answer 37

Cleavage stage - most common don't want to get growth arrest in culture - 3 days after fertilisation blastocyst stage - allow selection of best quality embryo for success

Question 38

Describe grade A for day 3 blastomere implantation

Answer 38

Even blastomeres with no fragmentation

Question 39

Describe the expansion grade for blastocoel implantation

Answer 39

1. Cavity of blastocoel less than 1/2 vol of embryo 2. Blastocoel cavity more than 1/2 embryo vol 3. Full blastocyst cavity larger than the embryo 4. Expanded blastocyste cavity larger than the embryo with thinning of the shell 5. hatching out of the shell 6. Hatched out of cell

Question 40

Describe the ICM grade and trophectoderm grade of blastocoel implantation

Answer 40

ICM A many tightly packed cells B several loosely grouped cells Trophectoderm A Many cells form cohesive layer B Few cells from cohesive layer C Very few large cells