REB 15. Gametogenesis, Implantation, Foetal Membranes Flashcards
What are gametes? Give examples.
Gametes are the specialized reproductive cells.
Females = Ovum Males = Sperm
What is gametogenesis? What process does it go through? What cells are involved?
Gametogenesis: the creation of gametes
- e.g spermatozoa and ova
Gametes are formed from Germ Cells
- Germ Cells are DIPLOID
- Germ Cells undergo MEIOSIS
- Germ Cells become HAPLOID (Gametes)
How many pairs of chromosomes are the same in males and females?
22 pairs
- 1 unique pair (sex chromosomes)
What is sexual reproduction?
It is where 2 distinct types of specialized reproductive cells (gametes) fuse together
What are primordial germ cells (PGCs)? Where are they created and where do they end up?
PGC’s are created in the YOLK SAC
PGC’s migrate to the gonadal ridge (the gonadal ridge becomes the male + female gonads - ovaries/testes)
What is a teratoma? What is a possible cause?
- teratoma contains a variety of tissue (bone, hair, muscle, gut epithelia and others…)
- thought to contain pluripotent stem cells that can differentiate into any of the 3 germ layers or their derivatives
possible cause: PGCs that have strayed from their migratory path
What happens in each stage of Meiosis I?
PROPHASE I:
- 46 homologous pairs (92 chromosomes - duplicated themselves in interphase)
- crossing over (exchange of genetic material) between homologous pairs
METAPHASE I:
- the chromosomes align along the equatorial plane and the spindle fibres
ANAPHASE I:
- homologous chromosomes pulled to opposite poles of cell
TELOPHASE I:
- the cell pinches off to create 2 new cells
At what stage of meiosis does crossing over take place?
Prophase I
What is non-disjunction? What is an example?
When there normal separation of chromosomes in meiosis does not occur
- trisomy (3 chromosomes)
What happens when there is not the normal separation of chromosomes in meiosis?
Non-Disjunction
- can lead to miscarriage or illnesses
What is Trisomy 21?
down syndrome
What is Prader-Wili syndrome?
it occurs when there is a microdeletion on the paternal chromosome 15
What is Turner Syndrome?
it is when the child (female) is born with only 1 X chromosome
What is oogenesis? Explain the process.*
Oogenesis: the production or development of an ovum
[1] PGCs differentiate (undergo mitosis) to create oogonia
[2] oogonia give rise to primary oocytes
[3] oocytes start meiosis before birth, but are stopped in meiosis I (prophase I)
[4] meiotic arrest
[5] at puberty, meiosis continues and produces 1 ovum each month
What is meiotic arrest in oogenesis?
oocytes begin meiosis before birth, but are stopped in meiosis I (prophase I) until puberty
What are the 2 main processes involved in the creation of viable sperm?
[1] Spermatogenesis - formation of spematids
[2] Spermiogenesis - maturation of spermatids into spematazoa
Explain the steps involved in spermatogenesis.
- germ cells (PGCs) differentiate into spermatagonia through mitosis
- spematogonis give rise to primary spermatocytes through mitosis
- primary spermatocytes give rise to secondary spermatocytes through meiosis
- secondary spermatocytes give rise to spermatides
Where does spermatogenesis occur?
the haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis
What is involved in spermiogenesis?
- spermatids are turned into spermatozoa
- some changes are:
- — formation of acrosome
- — condensation of nucleus
- — formation of neck, middle piece + tail
- — shedding of most of cytoplasm
What is Mittelscherz?
the pain a woman may feel on one side, once a month, while she’s ovulating (midway through the cycle - day 14)
What is Menarche age?
it is the first occurrence of menstruation (age 8 to 14)
What is menopause?
stopping of period
- occurs around age 45 to 55
What are the 3 distinct phases of the menstrual cycle? Explain the phases.
[1] Menstrual Phase
- Day 1 is the first day of menstrual bleed
- period
[2] Proliferative Phase
- the endometrium thickens, blood vessels + glands develop
[3] Secretory Phase
- the corpus luteum secretes estrogen + progesterone
- progesterone stimulates glands to secrete substances that maintain the endometrium
What happens during/after the secretory phase if pregnancy does not occur?
then menstrual bleeding takes place and endometrium sheds
What happens during/after the secretory phase if pregnancy occurs?
- implantation of the blastocyst
- HCG (human chorionic gonadotropic hormone) maintains the corpus luteum in the ovary
- the corpus luteum stimulates estrogen + progesterone
- an increase in progesterone leads to endometrium thickening
Where does fertilization occur?
ampulla of the fallopian tube
What is the blastocyst? What are some defining characteristics?
Blastocyst: a hollow ball of cells
Characteristics:
- outer trophoblast
- inner cell mass
- fluid filled cavity (blastocoel)
- — this happens when fluid penetrates through zona pellucida of morula
- NO zona pellucida
What is the function of the trophoblast?
- forms the outer layer of a blastocyst
- it penetrates the endometrum of the uterus wall
What are the 2 parts that the trophoblast differentiates into?
[1] Syncythiotrophoblastic Cells
[2] Cytotrophoblast Cells
What does the trophoblast secrete?
it secretes Human Chorionic Gonadotropin hormone (HCG)
- when HCG is detectable in the urine/blood, this is a positive pregnancy test
What do stromal cells of the uterine wall become?
decidual cells (the decidua)
What is the decidua?
a thick layer of modified mucous membrane that lines the uterus during pregnancy
- remains through the first trimester
- after that, it becomes the placenta
What is the chorion?
- the outermost foetal membrane
- comes from trophoblast layer
What is the amnion?
- chorion + amnion make up and contain the amniotic sac
- they fuse and burst just before labour (breaking of the waters)
What is the yolk sac?
- the allantois and yolk sac make up the umbilical cord
What are the functions of foetal membranes?
- contain and protects the embryo/foetus
- function in nutrition and collection of waste from the foetus
- help develop the blood + oxygen supple of the foetus
- involved in signalling between maternal decidua and foetus
What is an important function that the outer syncythiotrophoblast layer does? Explain the steps involved.
- involved in blood exchange between foetus and mother
[1] develops projections into the endometrium
[2] small spaces within the layer form = lacunae
[3] the syncythiotrophoblast invades endometrial blood vessels + glands
[4] lacunae become filled with blood + secretions
[5] lacunae coalesce to produce primitive maternofoetal circulation
— maternal + fetal blood do not mix
— all exchanges occur between the 2 bloodstreams take place across an extremely thin barrier
What is an important function that the inner cytotrophoblast layer does? Explain the steps involved.
- it is important for gas exchange
[1] cytotrophoblasts project into the syncythiotrophoblasts - primary villi develop
[2] secondary villi develop
[3] tertiary villi develop
Where is the umbilical cord located? What does it contain?
- goes between the placenta and fetus
- formed by 5th week of development
contains:
- 2 arteries (carrying deoxygenated blood)
- 1 vein (carrying oxygenated blood)
- in loose connective tissue (Wharton’s Jelly)
What is Wharton’s Jelly?
a gelatinous substance that provides insulation and protection within the umbilical cord
What are the functions of the placenta?
- nutrient uptake
- gas exchange via the mother’s blood supply
- secretes progesterone and estrogen
- thermo-regulation
- waste elimination
- protects the fetus against internal infection
- it metabolizes a number of substances
List the clinical problems that can arise from the placenta
- Placenta Praevia
- Placenta Abruptia
- Placental Degradation
- Placenta Accretia
- Hydatidyform Mole
- — the placenta forms a mass with little/no fetal tissue
- — secretes high levels of human chorionic gonadotrophin (HCG)
- — may become carcinogenic (2%)
- — paternal genes only
What is In-Vitro Fertilization (IVF)? Explain the process.
IVF = a type of assisted reproduction
- ovaries hyperstimulated and ova collected under general anaesthetic
- sperm is collected from the male
- a sperm + ovum put together in a lab dish to produced fertilized ovum which becomes a blastocyst
- good quality blastocyst(s) collected and transferred into the uterus
- – OR they are frozen for later on
