Reproductive system Flashcards
How are gametes produced?
Via the process of meiosis
List some of the advantages of sexual reproduction compared to asexual reproduction
Creates variations among individuals, thus increasing the chance of survival, which leads to species preservation
Unfavourable genes will be eventually removed
Disadvantages of sexual reproduction compared to asexual reproduction
Need male and female
Need effort to choose mates
May prevent favourable genes from being passed on to offspring
Produces fewer offspring than asexual reproduction
Define the term ‘gonad’
The organ where gametes are produced. They also produce hormones that control secondary sexual characteristics
Name the gonad in males
Testis
Name the gonad in females
Ovary
Define the term ‘germ cells’
Any cell in the series of the germ line that eventually become gametes
Often indicate the cells before meiosis during spermatogenesis and oogenesis
What are the germ cells in females?
Oogonia
What are the germ cells in males?
Spermatogonia
What are primordial germ cells?
The origin of germ cells
Arises and stay in the posterior yolk sac
At 4-6 weeks in human, migrate into the gonad and then reside as germ cells
When do the semibiferous tubules mature?
They mature at puberty because of testosterone
What type of cell is the resident stem cell population of the seminiferous tubule of the testis?
Spermatogonium
What are testes made of?
Seminiferous tubules, which is where meiosis occurs in males
Define the term ‘spermiogenesis’
The differentiation step of spermatids to become a highly specialised spermatozoa
Give the main stages of spermiogenesis (5)
- Nucleus condense
- Formation of the acrosome
- Formation of the flagellum
- Mitochondria gathered at the midpiece
- Removal of excess cytoplasm
What is the acrosome?
A secretory vesicle containing enzymes required for penetrating the oocyte
What is the flagellum?
a tail-like structure homologous to cilia
Why do sperm need a lot of mitochondria?
For the moving flagellum
When does spermiogenesis take place?
Spermiogenesis takes place when spermatids are still surrounded by Sertoli cells.
Describe sertoli cells
Span from the basement membrane to the lumen, thus surrounding differentiating spermatogonia
Produce enzymes and growth factors required for spermatogenesis
Also function as a phagocyte to clean-up residual cytoplasm of sperm
What are Leydig cells?
Leydig cells are interstitial cells that reside outside of seminiferous tubules. They secrete testosterone in response to LH
What is spermiation?
The process of sperm being released in to the lumen from the sertoli cells
What’s the epididymis?
A highly convoluted duct behind the testis, along which sperm passes to the vas deferens.
Define the term ‘infertility’
An inability to conceive within 12 months
List the causes of male infertility
- Primary hypogonadism (Kleinfelter, cryptorchidism (absence of testes), chemotherapy, radiation, torsion etc) (30-40%)
- Secondary hypogonadism (hypothalamic-pituitary disease) (2%)
- Disordered sperm transport (10-20%)
- Unknown (40-50%)
Define ‘oogenesis’
The production or development of an ovum.
What are the germ cells in females called when they enter the first phase of meiosis?
Primary oocytes
One follicle=
One oocyte + surrounding follicular cells
Why are polar bodies formed in female meiosis?
In the meiotic cell division, most of the cytoplasm is taken by one, so as not to waste cytoplasm
What is the germ cell called when ovulation takes place?
A secondary oocyte
Define the term ‘primordial follicle’
A primary oocyte with an enlarged cytoplasm, with a flat one-cell layer of follicular (granulosa) cells. The dormant status
What are primary follicles?
Follicles chosen to re-commence growth. Follicular cells become cuboid and proliferate into multiple layers
Define the term ‘zona pellucida’
A layer of glycoprotein, translucent.
What are secondary follicles?
A follicle with antrum (a cavity) with fluid from granulosa cells
What are preovulatory follicles?
Among several secondary follicles, one is chosen to mature for ovulation
When is the first day of the menstrual cycle?
The first day of menstruation.
What causes the endometrial lining to thicken?
After day 5, the follicle and thecal cells proliferate and secrete oestrogens. Oestrogens in turn cause the endometrial lining of the uterus to proliferate.
What induces ovulation?
On about day 13 or 14, levels of FSH and LH suddenly rise very sharply, which induces ovulation and progresses meiosis
What is ovulation?
The expulsion of the secondary oocyte from the follicle. It takes place about 38 hours after the LH surge
What happens after ovulation?
After ovulation, the remaining follicle becomes a corpus luteum and secretes oestrogen and progesterone. This leads to the endometrium secretory phase, preparing for implantation
What happens if implantation of a fertilised egg doesn’t take place?
If implantation doesn’t occurs, the corpus luteum degenerates after 14 days and becomes a scar-like structure called corpus albicans)
When sperm reach the oocyte, what do they have to do in order to fertilise it?
When they encounter the oocyte, the sperm has to;
a) migrate through the layer of follicular cells (corona radiata)
b) penetrate the zona pellucia using enzyme in acrosome
c) fuse the plasma membrane to that of oocyte
When does the second meiotic division of oocytes happen?
The second division of meiosis of oocyte completes when the sperm enters
Describe implantation of the fertilised eg
- Blastocyst attaches to the endometrium at the embryonic pole
- Some trophoblast cells invade the endometrium, beginning to form a part of the placenta
- The inner cell mass becomes a flat sheet consisting of epiblasts and hypoblasts
- The amniotic cavity appears on the epiblast side
- human chorionic gonadotrophin (hCG), produced by the syncytiotrophoblast, enter the maternal blood
What does human chorionic gonadotrophin do?
hCG maintains the hormonal activity of the corpus luteum in the ovary. The corpus luteum secretes estrogen and progesterone to maintain pregnancy.
