SUGER: Reproduction Flashcards
Human eggs (ova) are small, develop slowly, and the female reproductive system is adapted to provide an environment for fertilisation and prolonged gestation, followed by parturition (birthing of live young).
What term describes this reproductive system?
Viviparous
What do primordial germ cells develop from?
Pluripotent cells (stem cells)
What are primordial germ cells?
Early precursors of gametes (spermatozoa/ova).
Epigenetics describes heritable changes in gene expression (gene turned on/off) that occur without alterations to the DNA sequence itself, influenced by factors like environment and lifestyle.
Give an example of an epigenetics mechanism of gene expression.
DNA methylation: methyl groups are added to DNA, blocking transcription from occuring.
Pluripotent (stem) cells have a distinct epigenetic pattern compared with non-pluripotent (differentiated) cells.
When does the change between pluripotent epigenetic pattern and the gametes epigenetic pattern occur?
During gametogenesis.
Parental imprinting occurs during gametogenesis, where epigenetic modifications (usually methyl groups) are placed in a sex-specific manner.
How does parental imprinting ensure monoallelic expression?
Parental imprinting means only one allele will be expressed in the child (monoallelic expression) because certain genes are always silenced in the egg, and others in the sperm. These are then again reset in gametogenesis in the offspring, depending on the sex of the offspring.
Briefly describe the HPG (hypothalamic-pituitary-gonadal) axis.
HYPOTHALAMUS releases gonadotropin-releasing hormone (GnRH).
GnRH stimulates the PITUITARY gland to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
LH and FSH act on the GONADS.
FSH is released from the pituitary gland in response to GnRH (gonadotropin-releasing hormone).
What effect does FSH have in males and females?
Stimulates sperm production in males (acts on sertoli cells) and follicle development in females.
LH is released from the pituitary gland in response to GnRH (gonadotropin-releasing hormone).
What effect does LH have in males and females?
Stimulates testosterone production (acts on Leydig cells) in males and ovulation in females.
What are the two key functions of the gonads?
Produce gametes and synthesise sex steroid hormones.
How do cells synthesise oestrogens (as a category of steroid hormone)?
Enzymes convert androgens (e.g. testosterone) into oestrogens.
How do cells synthesise androgens such as testosterone?
Through enzymatic reactions, usually from progestagens such as progesterone, which are originally synthesised from cholesterol.
Mesonephric (wolffian) ducts are the embryonic precursors to what structures?
Vas deferens, epididymis and seminal vesicle
In the ovary, when do the first follicles start growing?
During foetal development
Which hormone acts on Sertoli cells of the seminferous tubules to enhance spermatogenesis?
FSH
What provides the main source of oestrogens throughout pregnancy?
Placenta
During pregnancy, heart rate and stroke volume increase, causing cardiac output to increase by what %?
30-50%
When do primordial germ cells stop proliferating and enter meiosis, then becoming oocytes individually encapsulated by somatic cells (the primordial follicle)?
During foetal development.
When does a female have the most number of oocytes?
During foetal development (at 20 weeks post-conception)
How does the oocyte obtain nutrients within the zona pellucida in preantral follicles (primary/secondary)?
Through gap junctions at the end of transzonal processes (cytoplasmic projections that cross the zona pellucida) from granulosa cells.
What cells in the antral follicle have LH receptors, and are stimulated by LH to produce androgens?
Theca interna cells
What cells in the antral follicle have FSH receptors and are stimulated by FSH to convert androgens into oestrogens?
Mural granulosa cells (the granulosa cells towards the periphery of the follicle).
What effect do androgens from the theca interna cells in the antral follicle have on mural granulosa cells?
Along with FSH, they stimulate proliferation of mural granulosa cells (and also provide substrate for oestrogen production).
Explain the positive feedback mechanism involved in oestrogen production from mural granulosa cells in the developing antral follicle.
Oestrogens from mural granulosa cells stimulates mural granulosa cell proliferation (which is already stimulated by FSH and androgens from theca interna cells).
More mural granulosa cells = more cells which can produce oestrogen = major increase in oestrogen output as follicle develops.