11.4 Sexual reproduction Flashcards
What is gametogenesis?
The formation of gametes (sex cells) by meiosis from a diploid germ cell
What is oogenesis?
The production of egg cells in the ovaries
Where does oogenesis start?
In the ovaries of a female fetus
What are germ cells?
A reproductive cell of the body
What are germ cells?
A reproductive cell of the body
How do germ cells divide and where do they go?
They divide by mitosis and the cells formed move to distrubute themselves through the cortex of the ovary
What happen to germ cells when the fetus is about 4-5 months old?
These cells grow and start to divide by meiosis
By the 7th month of the fetus, what stage of meiosis are the germ cells at and what is formed?
- still in first dividion of meiosis
- single layer of cells, called follicle cells has formed around them
What is a follicle cell?
A single layer of cell that forms around the germ cells undergoing first stage meiosis in the 7th month of the fetus
What happens to the germ cells undergoing the first division of meiosis before puberty?
Nothing
No further development takes place until after puberty
What happens to the germ cells undergoing the first division of meiosis before puberty?
Nothing
No further development takes place until after puberty
What is a primary follicle?
The cell that has started to divide by meiosis, together with the surrounding follicle cels
How many primary follicles are there in the ovaries at birth?
around 400,000
Are there any production of primary follicles after birth?
No. No more primary follicles are produced
What happens to the primary follicles at the start of each mentrual cycle?
A small batch are stimulated to develop by FSH
Usually only one goes on to become a mature follicle, containing a secondary oocyte
What stimulates the development of a primary follicle?
FSH
What is the difference between a mature ovarian follicle compared to a primary follicle?
Many more follicle cells, outer and inner follicle cells and cavities
What is the difference between a mature ovarian follicle compared to a primary follicle?
Many more follicle cells, outer and inner follicle cells and cavities
What is spermatogenesis?
the production of sperm
Where does spermatogenesis occur?
in testes
What are testes composed of?
compoased of a mass of narrow tubes, called seminiferous tubutles, with small groups of cells filling the gaps between the tubules, called interstices, so the cells in them are interstitial cells
What are sometimes also called Leydig cells?
Interstitial cells
What is the seminiferous tubules also made of?
Cells
What is the outer layer of cells of the seminiferous tubules called
Germinal epithelium
Also where the process of sperm production begins
Where does the process of sperm production begin?
In the outer layer of cells of the seminiferous tubules called the germinal epithelium
What can be found inside the germinal epithelium?
Cells in various stages of sperm production
Where can you find the cells with the most mature stages of sperm production in the germinal epithelium?
Closest to the fluid-filled centre of the seminiferous tubule
What are cells that have developed tails called?
Spermatozoa (abbv. sperm)
What are sertoli cells and where can they be found?
They are large nurse cells foundin the wall of the seminiferous tubule
What are the stages of spermatogenesis?
What are the stages of oogenesis
Annotate the egg
Annotate the sperm
Annotate the sperm
What does each mature sperm consist of?
- a haploid nucleus
- a system for movement
- a system of enzymes and other proteins that enable the sperm to enter the egg
What does each mature sperm consist of?
- a haploid nucleus
- a system for movement
- a system of enzymes and other proteins that enable the sperm to enter the egg
What does each complete meiotic division of sperm result in?
4 spermatids
What happens when sperm differentiate?
They elimiate most of their cytoplasm
What happens when sperm differentiate?
They elimiate most of their cytoplasm
How is the cytoplasm different in eggs and sperms?
Sperm eliminate most cytoplasm during differentiation, but eggs must increase its cytoplasm
How is the cytoplasm different in eggs and sperms?
Sperm eliminate most cytoplasm during differentiation, but eggs must increase its cytoplasm
All requirement for what must be present in the egg?
All of the requirements for beginning the growth and development of the early embryo must be present in the egg
In females, what does the first division of meiosis produce?
One large cell and one very small cell (first polar body)
What happens to the first polar body?
it eventually degenerates
What happens to the large cell that is produced in the first division of meiosis?
It undergoes the second division of meiosis, completeing it after fertilisation
What happens to the large cell that is produced in the first division of meiosis?
It undergoes the second division of meiosis, completeing it after fertilisation
What is produced after the second division of meiosis?
Again, one large cell and one very small cell (second polar body and it also degenerates and dies)
What is produced after the second division of meiosis?
Again, one large cell and one very small cell (second polar body and it also degenerates and dies)
What is the only product of meosis that survives in females?
Only the large cell, which is the female gamete, survives
What is the result of only the large cell of the secon division of meiosis surviving?
The egg is much larger than the sperm cell
How often does the process of egg formation happen?
Once per menstrual cycle in humans and usually only one egg per cycle is produced
From puberty to menopause, how likely are female gametes produced?
Only a few hundred female gametes are likely to be produced
From puberty onwards, how likely are male gametes produced?
From puberty onwards, the testes produce sperm continuously. At any time, there are millions of sperm at all stages of development
What is fertilization?
The union of a sperm and an egg to form a zygote
What is fertilization?
The union of a sperm and an egg to form a zygote
What is a zygote?
a diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum.
What is a zygote?
a diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum.
What allows directional swimming of the sperm to the egg?
The membrane of sperm have rceptors that can detect chemicals released by the egg
What allows directional swimming of the sperm to the egg?
The membrane of sperm have rceptors that can detect chemicals released by the egg
What is polyspermy?
When multiple sperm enters a single egg
What are the events that allows the union of a sperm and an egg?
- The acrosome reaction
- Penetration of he egg membrane
- The cortical reaction
What happens in the acrosome reaction?
The sperm binds to the zona pellucida and the contents of the acrosome are released. The enzymes from it digest the zona pellucida
What happens in the acrosome reaction?
The sperm binds to the zona pellucida and the contents of the acrosome are released. The enzymes from it digest the zona pellucida
What happens in the acrosome reaction?
The sperm binds to the zona pellucida and the contents of the acrosome are released. The enzymes from it digest the zona pellucida
What is the zona pellucida?
A coat of glycoproteins that surrounds the egg
What is the acrosome?
Large membrane-bound sac of enzymes in the head of the sperm
What is the acrosome?
Large membrane-bound sac of enzymes in the head of the sperm
What happens in the penetration of the egg membrane?
- The acrosome reaction exposes an area of the membrane on the tip of the sperm that has proteins that can bind to the egg membrane
- The first sperm gets through the zona pellucida and binds
- the membranes of sperm and egg fuse together
- sperm nucleus enters the egg cell
- this is the moment of fertilization
What are cortical granules?
Vesicles located near the egg membrane
* there are thousands of these vesicles
* the enzymes in them result in the digestion of binding proteins
What happens in the cortical reaction?
- Activation of the egg by the sperm penetrating the egg
- cortical granules release their contents from the egg by exocytosis
- the cortical vesicles enzymes result in the digestion of binding proteins so that no furhter sperm can bind
- The enzymes also result in the general hardening of the zona pellucida
What is the difference between aquatic and terrestrial animals fertilization, what is the exception?
Aquatic: release their gametes directly into the water in a process that will lead to external fertilization
Terrestrial: Dependent on internal fertilization
What is the difference between aquatic and terrestrial animals fertilization, what is the exception?
Aquatic: release their gametes directly into the water in a process that will lead to external fertilization
Terrestrial: Dependent on internal fertilization
Marine mammals which have reinvaded aquatic habitats still use internal fertilization
How do aquatic animals bring eggs into proximity with sperm?
Such animals often have certain behaviours
How do aquatic animals bring eggs into proximity with sperm?
Such animals often have certain behaviours
What are some risks of external fertilization?
- predation
- susceptibility to environmntal variation such as temperature and pH fluctuation
- pollution
Why are terrestrial animals dependent on internal fertilisation?
Risk of drying out
What does internal fertilisation ensure?
The sperm and ova are placed in prolonged close proximity to each other
the developing embryo can be protected inside the female
What does internal fertilisation ensure?
The sperm and ova are placed in prolonged close proximity to each other
the developing embryo can be protected inside the female
What happens after fertilization?
- the fertilized ovum divides by motosis to form two diploid muclei and the cytoplasm of the fertilized egg cell divides equally to form a two cell embryo, then mitosis again, then a 4 cell embryo
- The cells replicate their DNA
- Further mitosis occurs but some divisions are unequal
- Migration of cells give the embryo a hollow ball shape -> blatocyst
What is a blastocyst?
The embryo in the shape of a hollow ball due to the migration of cells and unqual divisions of the original fertilized ovum
What happens to a 7 year old blastocyst?
- consists of 125 cells
- reached the uterus, having been moved down the oviduct by the cilia of cells i the oviduct wall
What happens to a 7 year old blastocyst?
- consists of 125 cells
- reached the uterus, having been moved down the oviduct by the cilia of cells in the oviduct wall
How does the blastocyst move down the oviduct?
By the cilia of cells in the oviduct
How does the blastocyst move down the oviduct?
By the cilia of cells in the oviduct
When does implantation occur?
when the blastocyst is 7 days old
What also happens to the blastocyst at 7 years old that its undergoes a process called implantation?
- the zona pellucida which surrounded and protected the embryo breaks down
- the blastocyst has used up the reserves of the egg cell and needs an external supply of food
- obtains this by sinking into the endometrium or uterus lining in a process called implantation
What is the process of implantation?
- the zona pellucida which surrounded and protected the embryo breaks down
- the blastocyst has used up the reserves of the egg cell and needs an external supply of food
- obtains this by sinking into the endometrium or uterus lining
How does the blastocyst penetrate the uterus lining during implantation?
The outer layer of the blastocyst develops finger-like projections allowing the blastocyst to penetrate the uterus lining
How does the blastocyst penetrate the uterus lining during implantation?
The outer layer of the blastocyst develops finger-like projections allowing the blastocyst to penetrate the uterus lining
What does the finger-like projections of the blastocyst allow for?
- penetration of the uterus lining
- exchange materials with the mother’s blood, including absorbing foods and oxygen
What does the finger-like projections of the blastocyst allow for?
- penetration of the uterus lining
- exchange materials with the mother’s blood, including absorbing foods and oxygen
What happens to the embryo by 8 weeks after implantation?
- the embryo grows and develops rapidly and by eight weeks has started to form bone tissue
- considered to be a fetus rather than an embryo
- is recognizably human and soon visibly either male or female
What does pregnancy depend on?
The maintenance of the endometrium
How is the endometrium maintained?
Depends on the continued production of progesterone and estrogen
* these hormones prevent the degeneration of the uterus lining which is required to support the developing fetus
What is HCG? What does it stimulate?
Human chorionic gonadotropin
* stimulates the corpus luteum in the ovary to continue to secrete progesterone and estrogen
* Stimulate the continued development of the uterus wall, which supplies the embry with everything that it needs
What is HCG? What does it stimulate?
Human chorionic gonadotropin
* stimulates the corpus luteum in the ovary to continue to secrete progesterone and estrogen
* Stimulate the continued development of the uterus wall, which supplies the embry with everything that it needs
Why is the continued development of the uterus wall important?
It supplies the embryo with everything that it needs
Why is the continued development of the uterus wall important?
It supplies the embryo with everything that it needs
What are the 3 groups of mammals?
- placental mammals (humans)
- monotremes (lay eggs)
- Marsupials (give brith to relarively undeveloped offspring that develop inside a pounch
By the time a marsupial is born, what stage would a human fetus be at?
A human fetus has developed a relatively complex placenta and so can remain in the uterus for months longer
By the time a marsupial is born, what stage would a human fetus be at?
A human fetus has developed a relatively complex placenta and so can remain in the uterus for months longer
Why is a placenta needed?
Because the body surface area to volume ration becomes smaller as the fetus grows larger
What is the placenta made of?
- fetal tissues
- in intimate contact with maternal tissues in the uterus wall
- the fetus also develops membranes that form the amniotic sac
What is contained in the amniotic sac?
amniotic fluid, which supports and protects the developing fetus
What is the basic functional unit of the placenta?
A finger-like piece of fetal tissue called a placental villus
Why does the placental villus increase in number during pregnancy?
to cope with the increasing demands of the fetus for the exchange of materials with the mother
Why does the placental villus increase in number during pregnancy?
to cope with the increasing demands of the fetus for the exchange of materials with the mother
Where does the maternal blood flow in the placental villus?
They flow in the inter-villous spaces around the villi
Why is the type of circulation in the placental villus unusual?
Blood is almost always confined in blood vessels but fetal blood circulates in blood capillaries, close to the surface of each villus
Why is important that the mother’s and fetus’ blood do not mix in the placenta?
Different blood type -> coagulation
Different pressure -> mother’s is too high for the fetus capilarries
What is the structure of the placenta?
Why is the distance between fetal and maternal blood very small?
Fetal blood circulates in blood capillaires, close to the surface of each villus
What is the placental barrier?
The cells that separate maternal and fetal blood form the placental barrier
* selectively permeable allowing some subtances to pass, but not others
What are exchanged between the fetal and maternal blood through the placental barrier?
Fetal to maternal
* Carbon dioxide (diffusion)
* Urea
* water
Maternal to fetal
* Oxygen (diffusion)
* glucose (facilitated diffusion)
* antibodies (endocytosis)
By the ninth week of pregnancy, what secretes estrogen and progesterone?
The placenta
By the ninth week of pregnancy, what secretes estrogen and progesterone?
The placenta
What causes miscarriage after 9 weeks?
If the switchover of the corpus luteum secreting estrogen and progesterone to the placenta fails
What causes miscarriage after 9 weeks?
If the switchover of the corpus luteum secreting estrogen and progesterone to the placenta fails
Once the placenta secretes the hormones estrogen and progesterone, what is not needed?
The corpus luteum is no longer needed for this role
What is the role of estrogen and progesterone secreted by the placenta?
Estrogen
* stimulate the growth of uterine muscles (myometrium)
* development of the mammary glands
Progesterone
* Maintains. theendometrium
* reduce uterine contractions and potential maternal immune responses
What happens to levels of estrogen and progesterone near the time of birth?
Levels drop
What does high levels of estrogen do in women?
They inhibit FSH release
High levels of estrogen mimic preganancy
How do contraceptive pills work?
They contain estrogen, which would mimic preganancy and inhibit the development of mature follicles thus preventing preganancy
How do contraceptive pills work?
They contain estrogen, which would mimic preganancy and inhibit the development of mature follicles thus preventing preganancy
What is the problem of using too much contraceptive pill?
The hormones can be found in water and in sewages
What are some problems regarding fish linked to estrogen pollution?
86% of male fish were intersex and that male fish showed signs of feminization
reduce male fertility
What are some problems regarding fish linked to estrogen pollution?
86% of male fish were intersex and that male fish showed signs of feminization
reduce male fertility
What can be done to treat estrogen pollution?
- upgrading technology for wastewater treatment could eliminate most of the pollution
- Preventing animals from urinating close to rivers as they the drugs are also widely used in livestock
During pregnancy, what does progesterone do?
They inhibit secretion of oxytocin by the pituitary gland and also inhibits contractions of the muscular outer wall of the uterus - the myometrium
At the end of pregnancy, what signals the placenta to stop secreting progesterone?
The hormones produced by the fetus signals to the placenta and oxytocin is therefore secreted
Where is oxytocin secreted?
The pituitary gland
What does oxytocin stimulate?
contractions of the muscle fibres in the myometrium
What are the contractions in the myometrium due to oxytocin detected by?
Detected by stretch receptors
How is oxytocin in pregnancy an example of a positive feedback system
- oxytocin stimulates contractions of the muscle fibres in the myometrium
- contractions are detected by stretch receptors
- signas the pituitary gland to increase oxytocin secretion
- increased oxytocin makes the contraction more frequent and more vigorous, causing mroe oxytocin secretion
What is the advantage of causing a gradual increase in the myometrium contractions?
Allows the baby to be born with the minimum intensity of contractions
What causes the cervix to dilate?
Relaxation of the muscle fibres in the cervix
What do uterine contractions do?
Bursts the amniotic sac and the amniotic fluid passes out
* there are further uterine contractions and finally push the baby out through the cervix and vagina
What do uterine contractions do?
Bursts the amniotic sac and the amniotic fluid passes out
* there are further uterine contractions and finally push the baby out through the cervix and vagina
What is parturition?
Birth
Once the baby is pushed out, what happens to the umbilical cord?
The umbilical cord is broken and expelled out the body along with the placenta
What are the stages of childbirth?
- Baby positions itself before birth so that its head rests close to the cervix
- Baby passes into vagina and amniotic fluid is released
- Baby is pushed out of mother’s body
- Placenta and umbilical cord are expelled from body
What is gestation period?
Fetal development period from the time of conception until birth
What do altricial species give birth to?
- relatively helpless
- incompletly developed offsprings
- relatively immobile
- lack hair
- unable to obtain food on thir own
What are precocial mammals?
- open eyes
- hair
- immediately mobile
- somewhat able to defend themselves against predators
What are mammals with a large body size most likely to be? Altricial or precocial?
Precocial
this is correlated with a long gestation period
Explain the graph
Estrogen and Progesterone
* once placenta is deveoped, it starts to secrete both estrogen and progesterone at higher conc.
* oestrogen to build up the endometrium
* progesterone to maintain the endometrium throughout the preganancy -> for rich blood supply (O2 + glucose)
HCG
* In the first 8-10 weeks, HCG is required to stimulate the corpus luteum to produce estrogen and progesteron
* By week 8, the placenta is fully developed and no need for HCG anymore so conc. decrease
Why does HCG stimulate the corpus luteum. inthe ovary to continue to secrete progesterone and oestrogen?
to inhibit FSH and LH to prevent further eggs developing or ovulation occuring
