11.4 sexual reproduction Flashcards
what is gametogenesis? (short defin.)
the process whereby gametes are produced
internal fertilisation requires ________________ and ____________
behavioural interactions and compatible sexual organs
external fertilisation is possible in water environments as… (2, short)
- gametes will not get dehydrated
- gametes can travel in the water
the process of releasing gametes into the water is called…
spawning
why is internal fertilisation preferred for some animals?
- prevent physical injury
- prevent desiccation of gametes
gametogenesis for males is called…
spermatogenesis
when does sperm production start
at puberty
where does sperm production take place (specific)
the seminiferous tubules of the testes
what cells does gametogenesis begin with?
germ cells
are gametes haploid or diploid?
haploid
undifferentiated germ cells are…
spermatogonia
why do germ cells undergo asymmetrical cell division? (short)
- one spermatogonia is dedicated to become sperm
- the other maintains a constant pool of undifferentiated spermatogonia for continual spermatogenesis
before a cell undergoes cell division, it undergoes a period of ________ to incr in _____
growth, size
what is the result of mitosis of spermatogonia?
primary spermatocytes
how many sets of chromosomes do the primary spermatocytes have? (n/2n?)
2n
how are secondary spermatocytes formed?
from the 1st meiotic division of primary spermatocytes
secondary spermatocytes are [haploid/diploid]
haploid
how many times does the spermatogonia undergo meiosis in spermatogenesis?
2
what cell does the 2nd meiotic division involve?
secondary spermatocyte
what does the 2nd meiotic division of the secondary spermatocyte produce?
2 spermatids
what are the changes from germ cell to sperm cell? (germ cell -> X -> Y…-> sperm)
spermatogonia -> primary spermatocyte -> secondary spermatocyte -> spermatids -> sperms
what’s another name for spermatogonia?
germ cells
what are the cells that nourish the development of germ cells?
sertoli cells
how many spermatids are produced from one spermatogonia?
4
spermatids have ___ set(s) of chromosomes
1
what is the function of sertoli cells? (2, short)
- nourish the development of germ cells
- assist spermatid differentiation into spermatozoa
how do spermatids become spermatozoa?
by differentiation into spermatozoa
what are the changes to the spermatids when it becomes spermatozoa? (3)
- development of tails
- loss of cytoplasm
- flattened acrosome
newly formed spermatozoa are _______ and _______ unlike mature sperms
immotile, infertile
where do the spermatozoa develop into mature sperms?
at the epididymis
how are the sperms carried out of the testes to the epididymis?
via fluid at the center of the seminiferous tubules
what happens in spermatogenesis? (6)
- undifferentiated spermatogonia undergo mitosis in the form of asymmetrical cell division
- one spermatogonia is dedicated to become a sperm
- the other stays undifferentiated for continual spermatogenesis
- the undifferentiated spermatogonia undergo mitosis + grow larger
- to give 2 primary diploid spermatocytes
- primary spermatocyte will undergo 1st meiotic division
- to produce 2 haploid secondary spermatocyte
- secondary spermatocyte undergoes 2nd meiotic division
- to produce 2 spermatids
- sertoli cells assist the differentiation of spermatids into spermatozoa
- this is with the development of tails, loss of cytoplasm and flattening of acrosome
- newly formed spermatozoa detach from Sertoli cells
- carried out of the testes via the fluid at the center of seminiferous tubules to epididymis
- there, they develop into mature motile sperms and stored
- during intercourse they are ejaculated via sperm duct
what is the role of testosterone? (3)
- stimulates prenatal development of male genitalia in fetus
- development of secondary sexual characteristics e.g. spermatogenesis
- maintenance of sex drive and continual sperm production
what are the cells that secrete testosterone?
Leydig cells
what is the female version of spermatogenesis?
oogenesis
when does oogenesis begin?
during fetal development
the primordial cells in oogenesis differentiate into…
oogonia
the _________ ____________ undergoes mitosis to produce oogonia
germinal epithelium
what does oogonia undergo to become primary oocytes?
cell growth
oogonia ________ as they undergo cell growth
enlarge
what phase of the 1st meiotic division are primary ooctyes arrested in?
prophase 1
when do primordial follicles develop?
during the prenatal development of the fetus
how do primordial follicles develop from primary oocytes?
granulosa cells surround primary oocytes to form follicles
when do primary follicles begin to develop?
during puberty
what stimulates the development of primary follicles?
FSH
what is a primordial follicle?
it consists of a primary oocyte surrounded by one layer of granulosa cells
what stimulates the primary oocyte to resume meiosis?
surge in LH
FSH stimulates the development of primary _____________ and LH stimulates the primary ______________ to resume meiosis
follicles, oocyte
does the first meiotic division in oogenesis form haploid or diploid cells?
haploid
the 2 haploid cells from the 1st meiotic division in oogenesis are have ________________ of cytoplasm
unequal distribution of cytoplasm
the [bigger/smaller] haploid cell is the first polar body
smaller
after the 1st meiotic division of oogenesis, what is the the cell that retains the entirety of the cytoplasm?
secondary oocyte
why are polar bodies formed?
polar bodies discard genetic material
what is the fate of polar bodies?
it remains trapped within the follicle until it eventually degenerates
what phase in meiosis is the secondary oocyte arrested at?
metaphase II
the ____ meiotic division stops at prophase I while the ______ meiotic division stops at metaphase II
first, second
during ovulation where is the secondary oocyte released from?
Graafian follicle
recap: what causes ovulation?
surge in LH
when is the second meiosis completed?
during fertilisation
what happens to the granulosa cells surrounding the oocyte during ovulation?
they form a corona radiata
what is the function of the corona radiata?
it nourishes the secondary oocyte
what triggers the completion of meiosis II? (short)
- fertilisation by sperm
- chemical changes trigger completion of meiosis II
meiosis II forms another ___________
polar body
why might 2 polar bodies be formed from the first polar body?
it may undergo 2nd meiotic division (along w the secondary oocyte)
how many polar bodies are formed in oogenesis?
2-3
what is the difference between a oocyte and an ovum?
- ovum is mature
- it has completed meiosis II
what happens in oogenesis? (8)
- process begins during foetal development
- a large no. of oogonia are formed by mitosis
- oogonia undergoes cell growth until they are large enough to undergo meiosis
- they form primary oocytes
- primary ooctyes begin 1st meiotic division
- arrested at prophase I
- from puberty, a few primary follicles will develop each month in response to incr FSH at the start of each menstrual cycle
- primary ooctyes are induced to complete the first meiotic division to form two haploid cells of different sizes
- there is unequal distribution of cytoplasm
- smaller haploid cell is the first polar body
- larger haploid cell is the secondary oocyte
- secondary oocyte proceeds to second meiotic division but is arrested at metaphase II
- during ovulation under surge in LH, the secondary ooctye is released from the Graafian follicle
- it enters the oviduct
- meiosis is only completed if the secondary oocyte is fertilised by a sperm
- this results in the formation of an ovum and second polar body
- all 3 polar bodies degenerate
annotate a diagram of the seminiferous tubule
-
annotate a diagram of the ovary
-
what part of the sperm contains enzymes that digest the zona pellucida of the egg?
the acrosome
why do sperms have a high density of mitochondria?
to produce ATP for flagellum to execute its corkscrew movements and propel the sperm to swim up the female reproductive tract
sperms have [haploid/diploid] nucleus
haploid
what is the function of the flagellum?
its corkscrew movement propels the sperm forward in fluid
centrioles are present in a sperm to… (2 short)
- for cell division as the egg has no centrioles
- organises microtubules in tail resulting in sperm motility
annotate a diagram of a mature sperm
-
which part of the secondary oocyte releases chemicals to prevent polyspermy?
cortical granules
what is the function of the corona radiata?
it supplies proteins needed for growth of the egg
what is the function of the cortical granules? (some detail)
release chemicals that cause the zona pellucida to harden when a sperm penetrates it, preventing polyspermy
the zona pellucida _______ the secondary ooctye and _______ the entry of sperm
protects, impedes
which part of the secondary oocyte impedes the entry of sperm?
zona pellucida
the cytoplasm contains drops of _______ and ________ needed for early development of the embryo
fats, nutrients
annotate a diagram of a mature egg
-
what is another name for copulation?
sexual intercourse
how is polyspermy prevented? (2)
- presence of zona pellucida surrounding ovum -> sperm cannot directly enter and fuse
- hardening of the zona pellucida by chemicals produced by cortical granules
how do sperms know where the egg is?
they are attracted by chemical signals released by follicular cells
what occurs during capacitation? (2)
- destabilisation of acrosomal cap through:
- removal of proteins thus exposing receptors on membrane surface -> enhance binding btw sperm and oocyte
- incr membrane permeability to Ca2+ -> incr motility
how is the acrosomal reaction triggered?
when a sperm binds to a receptor on the zona pellucida
the acrosome releases _________ (type) enzymes
hydrolytic
how does the sperm reach the zona pellucida?
it pushes through the corona radiata
what happens during the acrosome reaction? (5)
- when the sperm approaches the egg in the oviduct, it breaks through the corona radiata to reach the zona pellucida
- sperm then binds to receptor on the zona pellucida
- this triggers acrosomal reaction
- acrosome vesicle fuses with the zona pellucida -> releases hydrolytic enzymes that digest the zona pellucida
- as it burrows into the zona pellucida, it reaches the egg’s plasma membrane
- binds to docking proteins on the membrane
- causes sperm and egg plasma membrane to fuse
- sperm nucleus enters egg
what triggers the cortical reaction?
the entry of sperm nuclei into egg
the entry of sperm nuclei into the egg causes stored _____ to be released from ____
Ca2+, ER
what does the release of Ca2+ in the egg cause?
- causes incr in intracellular Ca2+
- stimulates depolarisation of egg plasma membrane
- sets off signal cascade
- results in cortical reaction
- cortical granules fuse with the plasma membrane and release their enzymes by exocytosis
what do the enzymes from the cortical granules do? (2)
- cause cross-linking of glycoproteins in the zona pellucida -> hard -> cannot be penetrated by sperm
- digests receptors for sperm on zona pellucida -> prevent sperm from binding
what sets off the cortical reaction?
- cortical reaction is set off by the entry of sperm nuclei
- stored Ca2+ released from ER
- results in incr in intracellular Ca2+ -> causes depolarisation
- sets off signal cascade
what occurs in the cortical reaction? (5, short)
- cortical granules fuse with the plasma membrane
- enzymes are released by exocytosis
- enzymes cause cross-linking of glycoproteins in zona pellucida
- thus it becomes hard and impenetrable by sperm
- digests receptors for sperm on zona pellucida
- prevents sperm binding
- thus the cortical reaction prevents polyspermy
what prompts the secondary oocyte to complete meiosis II? (specific)
the influx of Ca2+
a fertilised cell with diploid nuclei is called a…
zygote
the zygote undergoes mitosis to become a _________ which then divides and differentiates to form a __________
morula, blastocyst
what are the sections of the blastocyst? (3)
- inner cell mass
- trophoblast
- blastocoele
what produces hCG?
placenta
what is the role of hCG in early pregnancy? (short)
- hCG prevents degeneration of corpus luteum in early pregnancy for continued production of predominantly progesterone and estrogen
- this prevents menstruation
what is the role of progesterone in early pregnancy? (3)
- keeps endometrium intact for fetal development
- prevents further ovulation
- due to (-)ve feedback which prevents anterior pituitary fr releasing FSH and LH
- inhibits muscle contraction of uterus
how does the blastocyst attach to the endometrium?
- it breaches the zona pellucida surrounding it
- digestive enzymes degrade endometrial lining
- autocrine hormones are released fr blastocyst -> triggers implantation into uterine wall
what happens in the implantation? (5)
- on day 7~, the blastocyst implants itself into the endometrium
- endometrium is maintained by progesterone by corpus luteum
- blastocyst breaches zona pellucida surrounding it, allowing it to attach to endometrium
- digestive enzymes degrade the endometrial lining
- autocrine hormones released from blastocyst trigger its implanation into the uterine wall
- during implantation, the endometrium grows over the blastocyst and a placenta is formed
- placenta releases hCG to prevent menstruation
the _______ takes over the role of the corpus lutem
placenta
the _______ develops to become the placenta while the _______ develops to become the feuts
trophoblast, inner cell mass
what is the function of the placenta? (short)
facilitate the exchange of materials btw the mother and the fetus
what adaptation of the placenta facilitates the exchange of materials?
chorionic villi
how does the chorionic villi facilitate the exchange of materials btw mother + fetus?
- secrete digetive enzymes to break down the walls of maternal blood vessels
- thus they are bathed in maternal blood -> exchange of materials btw maternal + fetal blood
what is are the structural adaptations of the placenta? (5, short)
- chorionic villi + microvilli
- incr SA:VR
- fetal capillaries have single celled walls
- ensure fast diffusion of materials
- abundant mitochondria
- generate ATP for AT
- maternal blood flows into lacunae
- to surround the chorionic villi of fetus
- chorionic membrane
- prevents mixing of incompatible maternal and fetal blood types
who’s tissues is the placenta made out from?
the mother and the child’s tissues
the embryo becomes a fetus when…
it starts to develop bone tissue
what is the role of estrogen and progesterone at 12 weeks of pregnancy? (2,2)
progesterone:
1. maintains endometrium
2. reduces uterine contractions
estrogen:
1. stimulates growth of myometrium
2. promotes growth of mammary glands
what are the hormones involved in birth?
estrogen, oxytoxin, relaxin
what is the release of oxytocin triggered by during the process of childbirth?
stretching of the walls of the uterus by fully grown fetus
what detects stretching?
stretch receptors
during the process of childbirth, ______ incr the no. of __________ receptors in the uterus
estriol, oxytocin
what are the effects of estriol? (2)
- increases the no. of oxytocin receptors on the smooth muscle of uterus
- inhibits release of progesterone, which prevents contractions
when do progesterone levels decline in pregnancy?
38-40 week
oxytocin is produced by the…
posterior pituitary
what are the effects of relaxin? (2)
- softens the cervix
- relaxes ligaments in the pelvin region
- aids the birthing process
what is relaxin secreted by?
ovaries and placenta
uterine contractions by oxytocin cause _____________ to be produced by uterine walls
prostaglandins
what happens during the process of birth? (8)
- throughout pregnancy, progesterone maintains the endometrium + prevents uterine contractions. as pregnancy nears 38-40 weeks, progesterone levels decline
- drop in progesterone removes its inhibition on the secretion of oxytocin
- estrogen levels rise -> incr the no. of oxytocin receptors in e uterus
- this also activates prostaglandin synthesis
- as baby grows -> stretching of the uterus stimulates oxytocin to be released from the posterior pituitary
- oxytocin stimulates uterine contractions -> uterine contractions push the fetus onto the cervix
- when the cervix is stretched, nerve signals are sent to the posterior pituitary for the secretion of more oxytocin -> to induce faster + stronger uterine contractions
- (+)ve feedback
- oxytocin stimulates the release of prostaglandins from uterine walls -> which reinforce the contraction
- relaxin is secreted by the ovaries and placenta
- help soften the cervix and loosen the ligaments that hold the pelvic bones together
- as contractions of labour intensify -> fetus and placenta is pushed through cervix and vagina
