REB 15. Gametogenesis, Implantation, Foetal Membranes Flashcards by Jennita Ariaratnam

What are gametes? Give examples.

Gametes are the specialized reproductive cells.

Females = Ovum 
Males = Sperm

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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)

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How many pairs of chromosomes are the same in males and females?

22 pairs

- 1 unique pair (sex chromosomes)

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What is sexual reproduction?

It is where 2 distinct types of specialized reproductive cells (gametes) fuse together

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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)

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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

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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

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At what stage of meiosis does crossing over take place?

Prophase I

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What is non-disjunction? What is an example?

When there normal separation of chromosomes in meiosis does not occur

trisomy (3 chromosomes)

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What happens when there is not the normal separation of chromosomes in meiosis?

Non-Disjunction

- can lead to miscarriage or illnesses

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What is Trisomy 21?

down syndrome

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What is Prader-Wili syndrome?

it occurs when there is a microdeletion on the paternal chromosome 15

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What is Turner Syndrome?

it is when the child (female) is born with only 1 X chromosome

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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

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What is meiotic arrest in oogenesis?

oocytes begin meiosis before birth, but are stopped in meiosis I (prophase I) until puberty

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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

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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

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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