Reproduction Flashcards
Spermatogenesis: Where and what?
Occurs in the seminiferous tubules in the testes.
Mitosis: Spermatogonium produces 2 daughter cells. One remains in contact with B membrane and the other becomes the primary spermatocyte that moves towards lumen. (aprx 16 days)
Meiosis I:
Primary spermatocyte divides again producing 2 more daughter cells, secondary spermatocytes, each possessing 23 chromosomes. (Aprx 24 days)
Meiosis II: Secondary spermatocytes yield 4 haploid spermatids each containing 23 chromosomes. (aprx a few hours)
Spermiogenesis:
The physical maturation of spermatids into sperm. (Aprx 24 days)
Hormonal control of spermatogenesis (5)
GnRH:
- Hypothalamus
- Stimulates Gonadotropins (FSH & LH)
FSH:
- Anterior Pituitary (in response to GnRH)
- Stimulates spermatogenesis in sustentacular cells
LH:
- Anterior pituitary (in response to GnRH)
- Stimulates secretion of androgens in interstitial cells
Inhibin:
- Sustentacular cells
- Inhibits secretion of gonadotropins from Anterior Pituitary
Testosterone:
- Interstitial cells of testes
- Many different functions and targets:
Male sex characteristics, stimulates erythropoiesis + spermatogenesis, libido, bone density and muscle mass.
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Oogenesis: what and where?
Occurs in the ovaries
Mitosis:
Oogonia (female reproductive stem cells) complete their mitotic divisions before birth.
Meiosis I:
The primary oocytes start meiosis I but only get as far as prophase. Process halts and is suspended until puberty when rising levels of FSH trigger the start of the ovarian cycle. Once a month from then on, some of the oocytes are stimulated to complete Meiosis I, yielding a polar body and secondary oocyte.
Meiosis II:
Once a month, one secondary oocyte leaves the ovary and is suspended in metaphase of meiosis II. A second polar body is formed when fertilization occurs, changing the secondary oocyte to a mature ovum, thus completing meiosis II.
Hormonal control of oogenesis
GnRH:
- Hypothalamus
- Stimulates Gonadotropins (FSH + LH)
FSH:
- Anterior Pituitary (in response to GnRH)
- Stimulates follicular phase of Ovarian cycle
LH:
- Anterior Pituitary (in response to GnRH)
- When oocyte finished meiosis I it causes rupture of follicular wall, ovulation, development and maintenance of corpus luteum
Estrogens:
- Ovary
- Promotes development of follicle, GnRH release and growth of endometrium
Progesterone:
- Corpus Luteum
- Inhibits GnRH (& FSH/LH) so no new follicles develop
Events of the Ovarian cycle
Follicular Phase:
Primordial follicle -> primary follicle -> secondary -> tertiary (mature) follicle
- Oocyte is surrounded by follicular cells that grow
- Forms large chamber: Antrum
Ovulation:
Tertiary follicle ruptures, releases secondary oocyte (and support cells; the corona radiata)
Luteal Phase:
- Corpus Luteum is formed from empty tertiary follicle which begins secreting progesterone
- Eventually breaks down to form corpus albicans
Events of the Uterine cycle
Menstrual Phase:
Degeneration of the the functional layer of endometrium - “soughed off” and are expelled
Proliferative Phase:
Functional layer is rebuilt by cells in basal layer
Secretory Phase:
Functional layer is functional again, with enlarged and actively secreting glands.
Conception: Why is the depolarization of the oocyte significant during fertilization?
When fertilization occurs, the membrane of the oocyte depolarizes. This is important because:
- It increases metabolic rate
- It signals the completion of meiosis II
- Most importantly: it causes a cortical reaction in the oocyte that releases enzymes that harden the zona pellucida, (closing sperm receptors) preventing polyspermy
Why is hCG significant in pregnancy?
Human chorionic gonadotropin
- Unique to pregnancy
- Released soon after implantation
- Initially produced by cells of embryo
- Maintains corpus luteum
If no hCG were present, the corpus luteum would degenerate, causing a progesterone decrease and menstruation would continue as normal (no pregnancy)
Methods of contraception (3)
Barrier methods:
- Abstinence
- Condoms
- Rhythm
- Spermicide
Hormonal treatment:
- Birth control pills
Implantation prevention:
- IUD
- Morning after pill
Changes to A&P during pregnancy (7)
- Increased uterus size
- Increased mammary glands
- Increased Respiratory rate (& TV)
- Increased blood volume/ CO but decreased blood pressure
- Increased GFR
- Increased BMR
- Increased need for nutrients/vitamins
Why is oxytocin critical for labour and lactation?
Oxytocin causes a positive feedback loop of contractions in order to cause parturition and does not stop until the child is expelled.
During lactation, oxytocin causes the milk in the mammary tissue to flow easier by contracting the muscles inside the breasts for current feeding, known as the “let-down” reflex.
What is the purpose of Prolactin?
Prolactin is an enzyme that stimulates milk production by causing the mammary glands to grown during pregnancy; priming them for feeding post child birth.
