Reproduction Flashcards
What do the terms biological sex, sexual intercourse and sexual reproduction describe?
Biological sex is the category of an organism based off their chromosomes, morphological characteristics and the gamete they produce.
Sexual reproduction produces offspring that differ
genetically from both parents.
Sexual intercourse is required for sexual reproduction, but also provides sexual pleasure and human bonding.
What biological systems are involved in sexual motivation?
Strong associations between systems involved in parenting, fertility, reward, and pleasure, which in turn link human bonding with reproduction and parenting.
Much of sexual motivation and behaviour modulated by testosterone and oestrogen.
What nervous stimuli can cause erection of the penis? Via what pathway?
Tactile stimulation on penis can cause erection via pudendal nerve without cortical input.
Non-physical stimulation (psychological) also cause erection via the cortex and spinal cord
What changes occur to the penis in erection?
Initiated by increased parasympathetic activity to smooth muscle of pudendal artery
Increases Nitric Oxide Synthase (NOS) activity, more NO
NO increases production of cyclic GMP which induces dilatation of arterial smooth muscle, counters symp maintained myogenic tone
Increases blood flow in corpus cavernosum, which compresses the dorsal vein, restricting the outflow of blood
The urethra is protected from increased pressure by surrounding corpus spongiosum (less turgid)
How does viagra work?
Cyclic GMP is normally de-activated by a phosphodiesterase enzyme, and this will reverse the changes leading to penile erection. Viagra inhibits the phosphodiesterase, thus potentiating the effects of cyclic GMP.
Describe the structure of the male reproductive system
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What cells in the male reproductive system respond to LH and FSH? What do they do?
FSH - Acts on sertoli cells (Also requires testosterone stimulation via androgen binding protein) to support spermatogenesis and also produce inhibin
LH - Acts on leydig cells to produce testosterone
What are the stages of sperm development? Which involve meiosis?
Cycle of spermatogenesis takes around 70 days. Occurs from puberty for remainder of adult life - (Quality and quantity of sperm thought to decrease with age)
Primordial germ cell Spermatogonium Primary spermatocyte MEIOSIS I DIVISION into Secondary Spermatocyte MEIOSIS II DIVISION into spermatid Mature sperm
What erectile tissue exists within the female reproductive system?
The female equivalent of the penis is the clitoris
The clitoris, like the penis, increases in size as a result of an increased blood flow into the tissue
The mechanism is the same (i.e. release of NO)
What cells in the female reproductive system respond to LH and FSH? What do they do?
LH and FSH act on follicular cells in the ovaries, LH to produce progesterone and FSH to allow follicular development and production of Oestradiol and inhibin B.
What are the changes in hormone level through the stages of the menstrual cycle?
Follicular phase - 14 days
LH and FSH cause growth of ovarian follicles and stimulate 17beta-oestradiol production. Oestrogen -VE feedback on FSH and LH – many follicles undergo atresia but one follicle becomes LH independent ‘Graafian Follicle’. In high levels of oestrogen for 36 hours and absence of progesterone, oestrogen switches to +VE feedback of FSH and LH. LH surge occur that triggers ovulation.
Ovulation – mid-cycle event
Luteal phase – 14 days
Corpus luteum develops and produces high progesterone and oestrogen, oestrogen returns to -VE feedback due to progesterone. Fertilisation must occur within 24 hours of ovulation or corpus luteum will degrade.
What are the key stages of the endometrial cycle and how do these connect with the menstrual cycle?
Menstrual stage - 5 days Endometrium is shed in absence of high hormones (corpus luteum has degraded) (2-4mm)
Proliferative stage - 9 days Oestrogen from follicles causes proliferation
Secretory Stage - 13 Days Oestrogen and progesterone from corpus luteum cause further proliferation and secretory changes (7-16mm)
Ischaemic Stage - 1 day Constriction of the spiral arteries of the endometrium that results from decreasing secretion of estrogen and progesterone
There are changes in follicular structure as they develop and increase in size
Follicles may not develop all the way to ovulation - atresia is common
The thecal cells of the developing follicles are responsible for the production of oestrogens
The granulosa-luteal cells produce oestrogens/ progesterone during the second half of the ovarian cycle
How does fertilisation occur?
Deposition of sperm in female system following intercourse. (deposited near cervix)
Cervical mucus is normally hostile to sperm, forming physical barrier but Cervical mucus changes mid-cycle permitting sperm to enter uterus. Sperm passes into Fallopian tube, swim to ampulla of tube (~30 µm/sec average speed) Survival of the fittest (a few days)
Capacitation – takes time within uterus (Essential preparation before sperm meets oocyte) Egg and sperm meet followed by fusion (within 24 hours post ovulation)
Acrosome reaction: penetration of Zona Pellucida (& Coronal cells) Calcium flux.
Resumption of meiosis, release of 2nd polar body. Alignment of maternal and paternal chromosomes to generate zygote. ZP3 broken down to prevent additional sperm fusing with zygote. Initiation of mitotic (cleavage) divisions in embryo.
How does fusion of egg and sperm occur?
Fusion of the sperm with the egg complex, requires interaction with ZP (digested during sperm capacitation).
The earliest changes in the oocyte following fertilisation is where cortical reaction is initiated, leads to hardening of the ZP (exclusion of other sperm). Other sperm and the cumulus cells will still be present at next stage although they play no further role.
Meiosis II in maternal chromosomes is completed, leads formation of polar body II, and female pronucleus. Sperm head undergoes decondensation, tightly packed paternal chromosomes form looser structure. Both pronuclei are haploid at this stage.
Next DNA in both pronuclei is duplicated, making 2n chromosomes of maternal and of paternal origin. Followed by mitotic division, giving 2 daughter cells, which must have the same chromosomal complement. Maternal and paternal chromosomes mix for the first time, as the metaphase plate of the first cleavage division is formed.
