Sexual reproduction Flashcards
Describe the follicular phase of ovulation
(what days does this occur on?)
FOLLICULAR PHASE (Days 1-14)
1) Gonadotropin releasing hormone released from the hypothalamus stimulates the anterior pituitary to secrete FSH and LH
2) At puberty, FSH triggers the proliferation and enlargement of the primordial follicle to form a primary follicle (oogonium becomes primordial follicle pre puberty)
A primary follicle
- A primary oocyte halted in prophase 1 with a single layer of cuboidal/columnar epithelium around it.
- A zona pellucida forms around it.
- 2 discrete layers are formed, the theca interna and theca externa. Theca interna secretes estrogen.
3) Continued action of FSH causes proliferation of granulosa cells and a secondary follicle is formed.
A secondary follicle
- Spaces with follicular fluid form between granulosa cells
4) Continued action of FSH causes proliferation of granulosa cells and a graafian follicle is formed
A graafian follicle
- Spaces of follicular fluid come together to form the follicular antrum
Primordial follicle (primary oocyte, halted in prophase 1)
Primary follicle (primary oocyte, halted in prophase 1)
Secondary follicle (primary oocyte, halted in prophase 1)
Graafian follicle (Secondary oocyte, halted in metaphase 2) –> Corona radiata surrounds the zona pellucida of the secondary oocyte
Granulosa cells undergo mitosis, oogonia undergoes meiosis
How does estrogen levels affect FSH and LH (what days)
When estrogen levels are middle, they inhibit the hypothalamus from releasing GnRH and inhibit anterior pituitary from releasing FSH and LH - middle of follicular phase
When they are much higher towards the end of the follicular phase, it stimulates the production of LH and FSH (but the graafian follicle produces inhibin which inhibits FSH so only LH is produced)
Describe the ovulatory phase (what days)
Day 14-15
1) Towards the end of the follicular phase, high levels of estrogen stimulate the production of LH and FSH (but the graafian follicle produces inhibin which inhibits the release of FSH) —-> LH SURGE
2) The LH surge increases collagenase activity which disrupts collagen, weakening the follicular wall. This combined with muscular contractions of the ovarian wall will result in the graafian follicle rupturing through the germinal epithelium onto the surface of the ovary where it is taken into the fallopian tube by the fimbriae. –> it is held in the ampulla where most fertilisation happens (OVULATION)
Describe the luteal phase (what days?)
Day 15-28
1) The corpus luteum is the tissue in the ovary that forms at the site of a ruptured follicle (residual follicular cells via LH)- comprised mainly of granulosa cells and theca interna
2) The corpus luteum produces oestrogen, progesterone and inhibin to maintain conditions for fertilisation and implantation.
Describe the menstruation phase of the menstrual cycle
How much blood is lost
What days is this happening on?
Days 1-5
Marks the beginning of a new menstrual cycle.
In the absence of fertilisation → implantation does not occur → Human chorionic gonadotropin is not produced (usually synctitio trophoblastic cells of the placenta produce it upon implantation) → without HcG, corpus luteum is not stimulated to produce progesterone and it regresses into a corpus albicans → blood vessels (like spiral and coiled arteries) are no longer able to be maintained without progesterone from the corpus luteum → the blood vessels that rupture and slough off the endometrium and the blood that is lost exits via the vagina (menstruation - 10-80ml of blood is lost)
Describe the proliferative phase of the menstrual cycle
Proliferative phase (Days 6-14)
- Happens alongside the follicular phase
1) Regeneration of stratum functionalis (endometrium) - and thickening
2) Oestrogen initiates fallopian tube formation, thickening of the endometrium, increased growth and motility of the myometrium and production of a thin alkaline cervical mucus to facilitate sperm transport (and help with capcitation.
Describe the secretory phase of the menstrual cycle
Secretory phase (Days 15-28)
- (happens alongside the luteal phase)
1) Progesterone stimulates further thickening of the endometrium
2) Production of thick acidic cervical mucus (to prevent polyspermy- can result in embryonic death), stimulates the uterine glands to secrete glycogen, lipids and proteins
3)It also inhibits FSH and LH production by the anterior pituitary
Describe spermatogenesis
Spermatogenesis starts at puberty
1) Spermatogonia divide by mitosis to give 2 identical cells.
Type A cells- used to replenish the pool of spermatogonia (can form type A and B cells)
Type B cells- differentiate to become primary spermatocytes
2) The primary spermatocytes undergo meiosis. Meiosis 1 produces 2 haploid secondary spermatocytes. Meiosis 2 produces 4 haploid spermatids.
Describe the maturation of sperm as they are released into the seminiferous tubules
1) As the spermatids travel through the seminiferous tubule, straight tubules and rete testes (possibly efferent ductules as well), they undergo spermiogenesis.
2) Spermiogenesis - The transformation of spermatids into streamlined, more motile spermatozoa
- They sprout a flagellum and discard cytoplasm to become lighter.
- (mitochondria is concentrated into the flagellum and nucleus becomes more compact)
3) They are then stored in the epididymis.
How much sperm is produced per gram of testis per second?
About 300-600 sperm made per gram of testis per second
Usually testes are about 50g each
How many days does it take to complete spermatogenesis (spermatogonia to spermatozoa)?
64 days
(new group of spermatogonia arise every 16 days)
What is the final maturation stage of the spermatozoa?
In the uterus, sperm undergo capacitation which is the removal of cholesterol and glycoproteins from the head of the sperm cell, allowing it to bind to the zona pellucida of the egg
Motility of sperm is hyperactivated
What are the 3 regions of the flagellum?
The principal piece - axoneme surrounded by fibres
Midpiece- containing mitochondria around axoneme of the flagellum
Endpiece- axoneme only, near tip of flagellum
What are the accessory glands that produce seminal plasma?
Seminal vesicles, prostate gland and bulbourethral glands
Explain the acrosomal reaction and the characteristics of the zona pellucida
Zona pellucida is composed of 3 glycoproteins: ZP1, ZP2, and ZP3.
1) ZP3 proteins bind to receptors on the plasma membrane of the capacitated human sperm.
2) The sperm releases hydrolytic and proteolytic enzymes which digest the zona pellucida, enabling the sperm to reach the cell membrane.
