4.1 sexual reproduction in humans Flashcards
what does the male reproductive system include?
- seminal vesicle
- prostate gland
- epididymis
- vas deferens
- testis
- urethra
- seminiferous tubules
what does the seminal vesicle do in the male reproductive system?
produces secretion, to aid sperm mobility
what does the prostate glad do in the male reproductive system?
produces alkaline secretion to neutralise acidity of urine
what does the seminiferous tubules do in the male reproductive system?
produces spermatozoa
each testi contains around one thousand _______ _____ where spermatozoa are formed
seminiferous tubules
spermatozoa collect in the _____ where their mobility improves
epididymis
- seminal vesicles secrete mucus and prostate fluid mixes with spermatozoa during ejaculation
- these fluids maintain:
- sperm mobility
- provide nutrients e.g fructose
- and are alkaline which neutralises acidity found in urine and the vagina
- (the resultant fluid containing sperm is called semen, and leaves by the urethra)
it’s prostate gland NOT prostrate
what does the female reproductive system include?
- ureter
- uterus
- oviduct/fallopian tube
- ovary
- cervix
- bladder
- urethra
- vagina
- vulva
how many ovaries are there in the female reproductive system?
2
where do oocytes mature from germinal epithelial cells in the female reproductive system?
in the ovaries
each month, one secondary oocyte is released during _____ from the surface of one of the ovaries
ovulation
- cillia lining the _____ ____ waft the secondary oocyte along
- fallopian tube (oviduct)
what does the uterus consist of?
- a thin outer layer called the perimetrium
- inside this is the muscle layer or myometrium
- the endometrium is the innermost layer consisting of a mucous membrane which is well supplied with blood (this layer is shed each month during the menstrual cycle if an embryo fails to implant)
what is gametogenesis?
the production of gametes through a series of mitotic and meiotic divisions in the testis and ovaries
sperm is produced by _____
spermatogenesis
eggs are produces by ______
oogenesis
as you move from the outside towards the centre of the seminiferous tubule, the cells become (more/less) mature?
more
germinal epithelium cell —>
spermatogonium —>
primary spermatocyte —>
secondary spermatocytes —>
spermatids —>
spermatozoa
diploid germinal epithelial cells divide by means of (mitosis/meiosis) to produce diploid ____
- mitosis
- spermatogonia
primary spermatocytes (2n) divide by means of (meiosis I/ meiosis II /mitosis) to produce _____
- meiosis I
- secondary spermatocytes (n)
secondary spermatocytes (n) undergo (mitosis / meiosis I / meiosis II) to make ____
- meiosis II
- spermatids (n)
spermatids (n) differentiate and mature into _____
spermatozoa (n)
what cells provide spermatozoa with nutrients and protect them from the male’s immune system?
sertoli cells
what cells secrete testosterone?
interstitial cells
diploid = 2n
haploid = n
(where n is number of chromosomes)
ovulation is the release of a secondary oocyte NOT an ovum
what does an ovary contain?
- primary follicle
- developing secondary follicle
- stroma
- Graafian follicle
- secondary oocyte released at ovulation
- corpus luteum
- degenerating corpus luteum
before birth, germinal epithelial cells divide by means of mitosis to produce _____ and then _____
- oogonia (2n)
- primary oocytes (2n)
primary oocytes are surrounded by germinal epithelial cells which form the _______
primary follicle
primary oocytes begin (mitosis/meiosis) but stop at what stage?
- meiosis I
but stop at prophase I
(division resumes from puberty)
each month, a primary oocyte continues meiosis I to produce :
- a secondary oocyte
- and a polar body
(both of which are haploid)
the primary follicle also develops into a secondary follicle, which matures into a ______?
Graafian follicle
what does the Graafian follicle do?
- migrates to the surface (of the ovary?) and bursts releasing the secondary oocyte (ovulation)
the secondary oocyte undergoes (mitosis / meiosis I / meiosis II), stopping at what stage?
meiosis II
- stopping at metaphase II
if a sperm meets the secondary oocyte and enters, meiosis II is completed resulting in the production of:
- the ovum (n)
- and second polar body (n)
the sperm pronucleus can now fuse with the ovum pronucleus to produce a diploid ____
zygote
following fertilisation, the Graafian follicle becomes the ______ ____ and produces progesterone
corpus luteum
(if no fertilisation occurs it regresses)
germinal epithelium (2n) —mitosis-> spermatogonium (2n) —mitosis-> primary spermatocyte (2n) —meiosis I-> secondary spermatocytes (n) —meiosis II-> spermatids (n) —maturation-> spermatozoa (n)
germinal epithelium (2n) —mitosis-> oogonium (2n) —mitosis-> primary oocyte (2n) —meiosis I-> (first polar body) + secondary oocyte (n) —meiosis II-> (secondary polar body) + ovum (n)
what does a spermatozoon (single spermatozoa) include?
- acrosome
- nucleus
- mid piece (with mitochondria)
- tail
each sperm head is approximately 5 µm long with a 50 µm tail
within the head is a haploid nucleus and the acrosome
what does the acrosome contain/do?
- contains proteases to digest the cells of the corona radiata and zona pellucida (on female secondary oocyte)
why does the mid piece of a spermatozoon contain many mitochondria?
as they provide ATP for movement
how does the tail of a spermatozoon move?
- in a circular wave motion to propel itself forwards
what does a secondary oocyte include?
- cytoplasm
- pronucleus
- zona pellucida
- corona radiata
a typical ovum measures 120 µm in diameter, and is one of the largest cells in the human body
what is the function of the fats and albumins contained within the cytoplasm of a secondary oocyte?
- provide nutrition for the developing embryo until it implants in the wall of the uterus and the placenta can provide nutrients
what prevents polyspermy (entry of additional sperm)?
changes to the zona pellucida following entry of a single spermatozoon
what is the process of the human menstrual cycle controlled by?
- gonadotrophic hormones
- from the anterior pituitary
- and hormones from the ovary itself
what does FSH stand for?
follicle-stimulating hormone
where is FSH released from?
the anterior pituitary
what does the release of FSH promote?
- maturation of the Graafian follicle
- stimulating the production of the hormone oestrogen by the ovary
what is the hormone oestrogen produced by?
the ovaries
what effect does oestrogen have?
- increasing the thickness and vascularity of the uterus lining, the endometrium, in preparation for the implantation of a fertilised ovum
- from about day 5 of the cycle, FSH is released, which then stimulates oestrogen to be produced
what happens once oestrogen levels are high enough?
- it inhibits further production of FSH by negative feedback
- and stimulate the release of LH
what does LH stand for?
luteinising hormone
what does the sudden release of LH lead to?
- it induces ovulation
- and also promotes the formation of a corpus luteum
- and stimulates the release from it of the hormone progesterone
by about day 14, oestrogen levels are high enough to inhibit further production of FSH and stimulate the release of LH
the high levels of progesterone that builds up from about the 14 day of the cycle to the 24th day, leads to what?
- it inhibits both FSH and LH
what happens once the oestrogen and progesterone levels drop?
- (and the endometrial lining breaks down)
- resulting in menstruation
if fertilisation had occurred, progesterone levels will remain (low/high) and this will inhibit the release of FSH and LH by the pituitary
high
capacitation definition
changes in the sperm membranes that increase its fluidity and allow the acrosome reaction to occur
acrosome reaction definition
acrosome enzymes digest the zona pellucida allowing the sperm and oocyte cell membranes to fuse
cortical reaction definition
- occurs when the cortical granule membranes fuse with the oocyte cell membrane
- the zona pellucida is converted into fertilisation membrane
sperm responds to chemicals produced by the oocyte and begin to swim through the uterus and into the _____
oviduct
- once in the oviduct, sperm can remain viable for a few days, but are most fertile in the 12-24 hours following intercourse
- the oocyte remains viable for only ____ hours following ovulation
24
- so needs to be fertilised relatively quickly after ovulation
what are the events that lead to fertilisation? summary
- capacitation
- acrosome reaction
- cortical reaction
- second meiotic division completes + ovum is formed
what are the events that lead to fertilisation? detailed
- cholesterol and glycoproteins are removed from the cell membrane covering the sperm’a acrosome making the membrane more fluid. this is called capacitation and occur several hours after sperm are deposited
- the acrosome releases protease enzymes which digest cells forming the corona radiate surrounding the oocyte allowing the sperm head to contact the zona pellucida. now acrosin (another protease) hydrolyses the zona pellucida, allowing the head to enter the oocyte. this is called the acrosome reaction
- the cell membranes of the sperm and oocyte fuse, the male nucleus can begin to enter the oocyte cytoplasm. this triggers the cortical reaction, where cortical granule membranes fuse with the oocyte cell membrane causing it to expand and harden forming the fertilisation membrane which prevents polyspermy - the further entry of sperm
- meanwhile, the second meiotic division completes, and the ovum is formed containing the female nucleus and a second polar body
- fertilisation is the sequence of events from the point where the sperm and oocyte make contact until the male and female chromosomes join on the mitotic equator. the first mitotic division produces two cells, and the resulting cell is referred to as an embryo
the embryo continues to divide by mitosis as it passes down the oviduct, forming a ball of cells (by day 3 it’s) called a _____
morula
- by a process called cleavage
by day 7, what does a morula become?
- a hollow ball of cells called a blastocyst forms
a blastocyst has an outer layer of cells referred to as a _____
trophoblast
what does the trophoblast do?
develops protrusion called the trophoblastic villi
the endometrium thickens allowing ____ of the blastocyst to occur by day 8-10
implantation
trophoblast definition
cells forming the outer layer of blastocyte
implantation definition
the sinking of the blastocyst into the endometrium
what develops from the trophoblast?
- chorion
- forming the larger chorionic villi which acquire capillaries and embed into the endometrium
- they are supplied by the developing umbilical artery and vein, and form the placenta
as the embryo develops into a foetus, the placenta takes on a number of roles. these include:
- allows exchange of oxygen, co2, nutrients and waste between mother’s and foetus’s blood. the blood is never in direct contact, but is separated by just a few mm, and a counter current blood flow ensures that concentration gradients are maintained across the entire length of the placenta
- it produces hormones to support pregnancy
- acts as a physical barrier between the two circulations. this is important as maternal blood pressure is much higher and would ruptured delicate capillaries in the foetus, and it separates the maternal immune system from the foetus preventing an immune response
- antibodies can cross the placenta giving the foetus some passive immunity to diseases however, some microorganisms can cross the placenta e.g Rubella virus and many drugs e.g nicotine and heroin
what does the umbilical artery do?
carrying blood containing waste including carbon dioxide from the foetus to the placenta
what does the umbilical vein do?
carries blood rich in nutrients e.g glucose and amino acids, towards the foetus
how many weeks does pregnancy last for?
around 39 weeks
- pregnancy is divided into three trimesters
- and runs from the first day of the last period until birth
as the foetus develops, it is enclosed by a membrane called the ____
amnion
what does the membrane surrounding the foetus called the amnion do?
produces amniotic fluid
(by the fifth week)
what are some importance functions that amniotic fluid has?
- acts as a shock absorber protecting the developing foetus
- helps to maintain the foetus’ body temperature
- provides lubricant
- allows movement
what does hCG stand for?
human chorionic gonadotrophin
where is the hormone hCG secreted by?
- the blastocyst
- and later the chorion
what is the hormone hCG responsible for?
- maintaining the corpus luteum which secretes progesterone (maintains endometrium) up to about 16 weeks when progesterone is produced directly by the placenta
during pregnancy, what happens to the secretion of oxytocin?
progesterone inhibits oxytocin preventing contraction of the myometrium
(and oestrogen stimulates the growth of the uterus and mammary glands)
to initiate birth, what happens to the production of oxytocin?
- oxytocin is secreted by the posterior pituitary gland resulting in contractions of the myometrium
- the contractions in turn cause an increased secretion of oxytocin and so on (positive feedback) causing more frequent and stronger contractions
what is prolactin secreted by?
the posterior pituitary gland
what does the production of prolactin lead to?
- causing milk to be produced
- (and is expelled from the nipples by contraction of muscles around milk ducts brought about by oxytocin)