Reproduction and Embryology Flashcards
Dissadvantages to Sex
- Need to find partner
- Dillution of good genes
Advantages to Sex
- Each individual has a new mix of genes giving immunity to pathogens
- Each individual has a new mix of genes that determine it’s environmental interactions (evolution)
Gamete
Reproductive cells of an animal or plant
Germ line
The germ line is set aside from the rest of the bodies cells early in embryonic developments to for the gametes
Prefix “Orch”
Comes from Orchid and refers to anything to do with testicles
What is the Seminiferous Tubule?
It is a coiled tube of the testies, the walls of which make sperm
What is this taken froma cross section of the testes?
Seminiferous Tubule
Can you identify what is going on in each of these areas of a seminiferous tubule?
What are the 3 stages of spermatogenesis?
Describe the whole process of stem cells to sperm?
What is hidden here?
What is hidden here?
What is hidden here?
What is hidden here?
What is hidden here?
What is hidden here?
Once sperm are made how do they mature?
Sperm are shed from the seminiferous tubules to the epididymis
The epididymis alter the seminal fluid
Epididymal secretions activate sperm and make them capable of swimming
Why can’t women makes more oocytes?
Adult women have no germ line stem cells
Describe the life cycle of an oocyte?
Hormonal inputs involved in making sperm
Don’t necessarily need to memorise this flashcard but use it as reference to study it and understand it
Describe the development of a sperm
Again not sure we need to know this, just here in case
Why can’t women make more oocytes?
Adult women have no functional germ-line stem cells
What is a primordial follicle?
Primordial follicles are the starting point of follicular development and the basic functional unit of female reproduction. Primordial follicles are formed around birth
What is a granulosa cell?
Granulosa cells are a type of cell in your ovaries that produce hormones including estrogen and progesterone
What is a primary follicle?
This is the next stage of follicle development after primordial follicle. It involves the rRNA and mRNA and is defined by the granulosa cells forming a single layered ring around the follicle.
They then don’t progess any further unless they are going to mature fully.
What is a ripening follicle?
This is the next stage of development after a primary follicle and is where the granulosa cells multiply and a zona pellucida forms.
Next granulosa cells secrete follicular fluid and creates the fluid filled Antrum
At this stage (formation of the antrum) the Theca gain LH receptors and the granulosa cells gain FSH receptors.
What happens next depends on stimulation by FSH
What is LH and FSH?
Luteinizing Hormone and Follicle Stimulating Hormone. They are released by the pituitary gland and stimulate hormone production in the follicle
LHS peaks for serveral days duirng the menses and trigger matruation of a ripened follicle. However several follicles ripen every day. How does only follicle mature at a time?
In the brief period during mentruation FSH is high enough to go over the threshold to induce maturation of a ripened follicle. However a follicle also needs to be exposed for a certain ammount of time.
When one has been exposed for long enough it becomes a Graafan follicle on the surface of the ovary. Now it becomes more sensitive to FSH thus realeasing more oestrogen. This increase in oestrogen then tells the pituitry to stop releasing high levels of FSH. This then stunts the other maturing follicles however the primary one can still develop as it has become hyper sensitive to FSH.
What happens to ripened follicles that don’t get the FSH surge when they need it?
They die (atresia)
How to fertility drugs work?
They block oestrogen receptors in the pituitry therefore increaseing the length of time FSH is released therefore encouraging more follicles to fully mature
What is the late antral stage of follicle maturation?
This is where a follicle is fully matured by FSH but before ovulation
It is characterised by a huge antrum
What promotes ovulation?
A surge in LH
For reference here is a mentrual cycle diagram with the stages of follicle development and corpus luteum alongside hormone levels.
Estradiol is the main type of oestrogen
What is the acrosome and what is the acrosome reaction?
It is the little pocket at the head on the sperm.
The acrosome reaction occurs when the sperm reaches the zona pellucida of the oocyte.
Acrosome membrane and plasma membrane fuse releasing acrosomal contents digesting the zona pellucida
What happens when a sperm fuses with the oocyte membrane?
After fusion waves of calcium entry occur
This waves promote the release of cortical granules which blocks the zona pellucida making it inpenetrable to further sprerm and also prevents further fusion.
It also resumes meiosis II
What are the the pronuclei?
These occur after the sperm has fused with the membrane. The chromosomes of the haploid nuclei condense and the oocyte nucleus becomes the female pronucleus whilest the sperm nucleus becomes the male pronucleus
What ICSI stand for?
Intra-Cytoplasmic Sperm Injection
What is the first stage of embryonic development?
Cleavage, this is where the embryo undergoes mitosis (copying of nucleus) but with no growth.
Imagine a tomato becoming salsa - splits up but overall volume doesn’t change.
The second stage is the formation of the blastocyst. This is the first first where an embryo forms two different types of cells. How does it do it?
What happens to the blastocyst after it forms?
It hatches from the zona pellucida and lives unattached as it travels down the fallopian tube
What happens to the blastocyst on attachment to the uterus?
The trophoblast invades the epithelium of the uterus forming the placenta.
The pluriblast (ball of cells in the middle) becomes the body.
Now that we have a blastocyst and the inner cell mass (puriblast) is going to becoe the body. However inner cell mass is all one type of cell? How does it begin to differentiate?
The ones facing the fluid become the hypoblast (hypo - underneath)
Now we have a hypoblast how is the epiblast formed?
Describe the two ways monozygotic twinning occurs?
Which one is accosiated with foetal transfusion syndrome?
One occurs where the cells separate within the zona pellucida forming two blastocysts.
The other is where two inner cell masses form within the same blastocyst resulting in a shared placenta
The one with the shared placenta is accosiated with foetal transfusion syndrome
The next mathematical problem of the embryo is that it only has two axis, a vertical and a radial (jellyfish). How does it create an east and a west from the radial?
Cells within the center of the hypoblast form a hex and migrate to the edge.
These then excrete proteins that inhibit progression in the epiblast.
The epiblast then forms a primitive streak on the opposite side which becomes a node.
This node is the future trunk while the side the hex was on becomes the head
What happens if the hex expressing cells form two sites?
You get the third very rare form of monozygotic twinning.
Two heads/ foetuses can form however they will have a shared amniotic cavity therefore nothing separates them and this can result in conjoined twins
Copare the three types of identicle twinning and at which stage each occurs?
Alternate form of conjoined identicle twinning?
This is where two head sites agree on the same tail resulting in two heads sharing a body
Gastulation (formation of the gut) first stage. How does the embryo form an ectoderm, mesoderm and endoderm?
Gastulation (formation of the gut) second stage. How does the endoderm from a tube?
What part forms the neural tube?
The ectoderm.
It seals off like an oxbow lake
What is this called and what has happened?
Spina Bifida
It is where the early neural tube doesn’t close
How is mamalian body size regulated?
The pituitary gland releases growth hormone which in turn stimulates other body tissues to produce IGF1 and IGH2 which actually act on the body and stimulate growth.
Side note: growth hormone does affect post-natal muscle growth directly but nothing else.
What things can affect growth?
Too much or too little GH
Missing IGF
The rabbit experiment: If growth of one limb in inhibited for a time then the inhibition is stopped then the inhibited catches up with the other bone.
The bone regulates it’s size therefore the bone’s response to growth factors must decrease with size.
How does this work?
As well as growth factor there is a second signal that originates in the growth plate, is recieved by the sheith then a new growth promoting signal is relayed back.
Therefor the signal gets smaller the larger the obne
What happens if vascular growth is inhibited during limb growth?
Limb growth happens rapidly and is very oxygen intensive therfor it also requires simulaneous fast vascular growth.
Thalidomide inhibits new vascular growth hence the limbs
What causes achondroplasia?
Activating mutations in FGFR3 causes growth plates full of chondrocytes and premature closure of growth plates
Germ line - where do they develop and how do they get into the gonads?
They are derived form epiblast cells and end up in the yolk sac which is outside the developing body.
The yolk sac however has a connection to the gut. The move through this, upwards through the gut then cross the mesentrry (connectin between gut and rest of body) and invade the developing gonads.
Key points:
- In yolk sac
- Into gut
- Upwards through gut
- Across mesentery
How does SRY act?
