Gametogenesis, implantation, Flashcards
what is gametogenesis?
•The process of meiosis and cytodifferentiation converting germ cells to mature male and female gametes or sex cells
where do the germ cells originally differenciate?
the wall of the yolk sac (endoderm in origin- that grows outside of the developing embryo)- then they migrate back into the developing embryo and end up on the psoterior wall
what is the term for gametogenesis in men and women?
Males = spermatogensis
Female = oogenesis
when do the oogonia begin meiosis?
they begin meiosis by the 5th month
Under what condition does meiosis complete in the ova?
meiosis does not complete unless fertilization occurs
what is the result of oogenesis?
•Results in one mature oocyte (viable) and three polar bodies
what is the result of spermatogenesis in men?
Spermatogenesis
•Primordial cells differentiate into spermatagonia
Produce in 4 spermatids
describe the order of spermatogenesis in men?
first spermatogenesis
then spermiogenesis (
- Spermatids undergo dramatic changes to convert them to mature sperm
- Formation of acrosome
- Condensation of nucleus
- Formation of neck, middle piece and tail
- 64 days spermatagonia sprematids spermatazoa)
how long is the process of spermatogenesis?
64 days
Describe the 3 main phases from fertilization til birth
–The first 3 weeks = pre-embryonic period
–Weeks 4 to 8 = embryonic period
–Week 9 until birth = fetal period
where does fertilization occur in the fillopian tube?
normally in the ampulla (widest part) - however it can occur anywhere in the tube
Describe the stages of the ova after it is fertilized
Describe the blastocyst stage of development
At what point doe the blastocyst emerge from the zona pellucida and begin to adhere to the uterine wall
Day 6
the first differentiation of the inner cell mass is into what types of cells?
ectoderm and endoderm (aka the epiblast and hypoblast)
What is the purpose of syncytiotrophoblast?
They are Highly invasive - they eat into the uterine wall
What type of cells form the yolk sac?
endoderm
What layers form the placenta?
the trophoblast and extraembryonic mesoderm (from mother) along with the inner layer of the endometrium will develop into the placenta
What are the stages of endometrial change during menstrual cycle
- Proliferative
- Ovulation
- Then secretory
What occurs to the endometrium when no implantation?
- After ovulation
- Endometrium - maximum thickness
- Glands - corkscrew shape & producing glycogen.
- No implantation spasmodic constriction of spiral arterioles & degeneration and loss of functional layer = menses
invasion of the corionic villi cause what?
it causes breakdown of the spiral arteries - allowing for pools of maternal blood (lacunae) that are closely associated with the chorionic villi - therefore nutrients can pass from the mother to the developing baby
are cytotrophoblasts or syncytiotrophoblasts closer to the baby?
Cytotrophoblast
What are the functions of the placenta
- Exchange of gasses
- Exchange of nutrients & electrolytes
- Maternal IgG
Endocrine functions – amongst others
•Secretes hCG – NB to maintain progesterone output
»And for pregnancy test
•Secretes oestrogens & progesterone
as the pregnancy continues, what layer becomes predominant?
the syncytiotrophoblast
Know the various structures in this picture
do the fetal and maternal blood circulations mix?
no - there is an endothelial barrier -
however, if there is rupture of the villi - then you have Rhesus incompatibility
as the pregnancy progresses, what layer begins very thin?
the trophoblastic layer
Where is there intricate development of the chorionic villi?
at the chorion frondosum
which cavity decreases in size as the baby gets larger?
the chorionic cavity
as the embryo grows , what happens tothe decidual capsularis?
the decidua capsilaris attaches to the opposite side of the uterus - eliminating the uterine cavity - so now you have the amnion and chorion fused - these two membranes rupture during labor
what is the umbilical cord composed of?
3 blood vessels - 2 arteries and 1 vein - embedded in loose connective tissue = Wharton’s Jelly
What is a Hydatidifom mole?
implantation occurs - but the problem is that two spermatazoa pass through and they fuse together- this forms a diploid paternal cell which undergoes mitosis and develops - only develops the trophoblastic layer - which is highly invasive and can become cancerous -
where can abnormal implantation occur?
normally occurs on the anterior/posterior wall of uteris but it can implant all the way down at the internal os - which is a challenge b/c during labor the blood supply to the baby is cut off and then the baby is in distress
