11.4 Sexual Reproduction Flashcards
Spermatogenesis
- begins at puberty when the germline epithelium of the seminiferous tubules divides by mitosis forming more spermatogonia
- spermatogonia then undergo a period of cell growth, becoming primary spermatocytes
- The primary spermatocyte then undergo meiosis 1 forming two secondary spermatocytes
- The two secondary then undergo meiosis 2 forming 4 haploid spermatids.
- spermatids then undertake a process of differentiation in order to become functional sperm cells (spermatozoa)
- developing spermatozoa are aided by Sertoli cells
Oogenesis
- begins during foetal development
- oogonia undergo mitosis to form many oogonia, then undergo a period cell growth and become primary oocytes
- primary oocytes begin meiosis but stop in prophase I when granulosa cells surround them to form follicles
- primary oocytes remain stopped in prophase I until puberty (menstrual cycle)
- Each month, FSH will triggers the primary oocytes to undergo the first meiotic division
- A secondary oocyte and a polar body is formed
- Polar body is discarded
- Secondary oocyte begins the second meiotic division but is stopped in metaphase II
- Secondary oocyte is released into the fallopian tube during ovulation.
- The follicular cells surrounding the oocyte form a corona radiata and function to nourish the secondary oocyte
- If fertilised by a sperm, meiosis II occurs and the formation of a second polar body
- 2nd polar body is discarded.
Spermatozoa label
Follicle maturity in Ovarian cycle
- Primordial follicle
- Primary Follicle
- Primary Oocyte
- Mature (Graafian) Follicle
- First Polar body and Secondary Oocyte
- Ovulation
- Corpus Luteum
- Corpus Albicans
Blastocyst implantation the on endometrium lining
- zygote formed
- zygote will undergo several mitotic divisions to form a solid ball of cells called a morula
- As the morula continues to divide, it undergoes differentiation to form a blastocyst
- The blastocyst breaches the jelly coat that was surrounding it and preventing its attachment to the endometrium
- Digestive enzymes are released which degrade the endometrial lining
- autocrine hormones released from the blastocyst trigger its implantation into the uterine wall
Human Choroinic Gonadotropin (HCG)
- Produced by the blastocyst into mothers blood, then filtered out by urination
- hCG promotes the maintenance of the corpus luteum within the ovary and prevents its degeneration
As a consequence of this it continues to produce both oestrogen and progesterone: - Oestrogen inhibits FSH and LH production by the pituitary gland, preventing the release of more eggs from the ovaries
- Progesterone functions to maintain the endometrium and thicken cervix
Placenta structure and functions
The placenta functions as the life support system for the foetus by:
- facilitating the exchange of materials between the mother and fetus
- Estrogen and progesterone are secreted by the placenta, preventing endometrium lining shedding.
- High levels of progesterone prevent further ovulation, taking over the corpus luteum role
Similarities between Spermatogenesis and oogenesis
Similarities:
- Both start w/ proliferation of cells by mitosis
- Both involve cell growth before meiosis
- Both involve 2 divisions of meiosis
- Both have helper cells
Differences between Spermatogenesis and oogenesis
Spermatogenesis:
- millions produced daily
- Released during ejaculation
- Sperm formation starts during puberty
- 4 sperm are produced per meiosis
- Testes
Oogenesis:
- 1 produced every 28 days
- Released on about day 14 of menstrual cycle
- Early stages happen during fetal development
- Only 1 egg produced per meiosis
- Ovaries
Fertilization
can be internal or external
- external usuallu = aquatic
- Many sperm and egg produced bc of risk
internal fertilization process
follicle = corona radiata + Zona pellucida + oocyte
1. Capacitation occurs after ejaculation
2. Chemicals released by uterus dissolve the sperm’s cholesterol coat improving sperm mobility and destabilising the acrosome cap
3. The sperm reaches an egg causing the Acrosome Reaction, allowing the sperm to break through the surrounding jelly coat of the egg.
4. The sperm pushes through the follicular cells of the corona radiata and binds to the zona pellucida
5. acrosome vesicle fuses with the zona pellucida
6. sperm then pushes its way through the softened jelly coat and binds to exposed docking proteins on the egg membrane
7. membrane of the egg and sperm then fuse and sperm nucleous entres the egg.
8. cortical reaction then occurs once a sperm has successfully penetrated
9. Cortical granules within the egg’s cytoplasm release enzymes
10. Enzymes destroy sperm binding sites and also the jelly coat
11. Preventing more sperm from penetrating the egg.
12. Egg then finished oogenesis undergoing meiosis 2, becoming a zygote
What is transfered from Mother to fetus through placenta
Oxygen
Nutrients
Hormones
Vitamins & minerals
Alcohol, drugs
Some viruses (HIV)
What is transfered from Fetus to Mother through placenta
Carbon dioxide
Urea
Water
Hormones (HCG)
Birth process
- Birth is mediated by positive feedback involving estrogen and oxytocin
1. fetal growth eventually causes stretching of the uterine walls, which is detected by stretch receptors
2. This triggers the release of oxitocin
3. inducing uterine muscles to contract, causing less space in womb
4. This causes more stretching and hence more contraction until the baby is born
Hormonal Regulation of the Birth Process
- When baby is fully grown and stretches the walls of the uterus, places a strain on both mother and infant
- This stress triggers a rise in the levels of estrogen
- estrogen prepares the uterus for hormonal stimulation by increasing its sensitivity to oxytocin, also inhibiting progesterone allowing uterine contractions
- the brain then triggers the release of oxytocin from the posterior pituitary gland
- Oxytocin stimulates the uterine muscles to contract, initiating the birthing process
- As the uterine contractions trigger, the foetus responds by releasing prostaglandins, causing more contractions
- Therefore a positive feedback loop ensues
- Contractions will stop when labour is complete and the baby is birthed, due to no more stretching of the uterine wall.
Estriol = a type of Estrogen
