Reproductive System Flashcards
(21 cards)
What is the role of the SRY gene in sexual differentiation? How does the absence of this gene influence embryonic development?
Determines male or female embryo development. Presence of SRY gene = male, absence = female.
Describe the three layers of the uterus and briefly explain the primary function of each layer.
- Endometrium: Inner lining that thickens and is shed during the menstrual cycle to support a potential embryo.
- Myometrium: Thick muscular layer responsible for uterine contractions during childbirth.
- Perimetrium: Outer protective layer).
Outline the key differences between oogenesis and spermatogenesis in terms of timing and the number of viable gametes produced.
Oogenesis: Begins before birth, pauses during childhood, and resumes at puberty, releasing one viable ovum per cycle. Spermatogenesis: Begins at puberty and continuously produces millions of viable sperm.
Briefly explain the two-cell hypothesis of steroidogenesis in the ovary, highlighting the roles of the theca and granulosa cells.
- Theca cells are stimulated by LH to produce androgens from cholesterol.
- These androgens are then transported to granulosa cells, which, under FSH stimulation, convert them into oestradiol.
What are the key events that occur during the follicular phase of the ovarian cycle, and which hormones primarily regulate this phase?
- The follicular phase involves the growth and maturation of ovarian follicles.
- FSH primarily stimulates follicular development and oestrogen production by the developing follicles.
- Rising oestrogen levels exert negative feedback initially, followed by positive feedback leading to the LH surge.
Describe the hormonal cascade leading to ovulation, specifically mentioning the roles of GnRH, LH, and oestrogen.
- Hypothalamus releases GnRH with increasing frequency.
- This stimulates anterior pituitary to release FSH and LH.
- FSH promotes follicular growth, leading to increased oestrogen production.
- High oestrogen levels exert positive feedback on the hypothalamus and pituitary, causing a surge in LH, which triggers ovulation.
What changes occur in the ovary following ovulation, leading to the formation and function of the corpus luteum?
- Ruptured follicle collapses, and blood vessels invade.
- Granulosa and theca cells luteinise under the influence of LH, forming the corpus luteum, which becomes a temporary endocrine gland.
Explain the role of progesterone secreted by the corpus luteum on the uterus and the hypothalamic-pituitary axis.
- Prepares the endometrium of the uterus for embryo implantation by promoting glandular growth and vascularisation.
- Exerts negative feedback on the hypothalamus, reducing GnRH pulse frequency and inhibiting the release of FSH and LH.
Describe the process of luteolysis and the hormonal changes that accompany the degeneration of the corpus luteum.
Luteolysis is the degeneration of the corpus luteum in the absence of pregnancy. It is triggered by PGF2α released from the uterine endometrium, leading to a decrease in progesterone and oestrogen levels, and the formation of the corpus albicans (scar tissue).
Briefly outline two contrasting effects of oestrogen and progesterone on the tissues of the female reproductive system.
Oestrogen generally increases secretions, cilia activity, and muscle activity in the oviduct, while progesterone reduces these activities. In the uterus, oestrogen stimulates the growth of the endometrium, whereas progesterone promotes further glandular development and secretion of nutrient-rich fluids.
What are the two primary functions of the ovaries?
Gametogenesis (production of eggs/ova)
Endocrine function (production of sex hormones like oestrogen and progesterone).
Briefly describe the key differences between the oestrous and menstrual cycles.
The oestrous cycle in mammals often involves overt behavioural changes associated with sexual receptivity (heat) occurring just before ovulation, whereas the human menstrual cycle is characterised by monthly shedding of the uterine lining without such pronounced behavioural changes.
At what stage of meiosis are primary oocytes arrested before puberty?
Prophase I of meiosis.
Outline the two main phases of follicular development and what primarily regulates each phase.
Pre-Antral Phase: Largely hormone-independent and involves the development from primordial to secondary follicles.
Antral Phase: Hormone-dependent (primarily on FSH and LH from the pituitary) and involves the formation of the large antrum in the tertiary/Graafian follicle.
Explain the role of GnRH in the hormonal control of the ovarian cycle.
GnRH (Gonadotropin-Releasing Hormone) from the hypothalamus controls the release of LH (Luteinizing Hormone) and FSH (Follicle-Stimulating Hormone) from the anterior pituitary, which in turn regulate ovarian follicle development, ovulation, and steroid hormone production throughout the ovarian cycle. The frequency of GnRH pulses changes during the cycle, influencing LH and FSH secretion patterns.
Describe the positive feedback mechanism of oestrogen during the follicular phase.
As follicles mature during the follicular phase, they produce increasing levels of oestrogen. When oestrogen reaches a high enough threshold, it exerts positive feedback on the hypothalamus, leading to an increase in GnRH frequency and a surge in LH release from the anterior pituitary. This LH surge is essential for triggering ovulation.
According to the two-cell hypothesis, which ovarian cell type produces androgens, and which converts them to oestradiol?
Theca cells produce androgens (like testosterone) in response to LH stimulation. Granulosa cells, under the influence of FSH and having received androgens from the theca cells, possess the enzymes necessary to convert these androgens into oestradiol.
What are two major effects of progesterone on the uterus?
Two major effects of progesterone on the uterus are: promoting further glandular growth and increased secretion of thick, glycoprotein-rich fluid to create a suitable environment for potential embryo implantation, and reducing myometrium contractility to prevent expulsion of a fertilised egg. It also supports the development of spiral arteries in the endometrium.
What hormonal event directly triggers ovulation?
The LH surge, a rapid and significant increase in luteinizing hormone secreted by the anterior pituitary, directly triggers ovulation, the release of the mature oocyte from the dominant follicle.
What is the primary hormone produced by the corpus luteum, and what is its main function?
The primary hormone produced by the corpus luteum is progesterone. Its main function is to prepare and maintain the uterine lining (endometrium) for the implantation of a fertilised egg and to support early pregnancy by suppressing uterine contractions and inhibiting the development of new follicles.
Why do developing sperm cells need to be protected by the blood-testis barrier, and how is this protection achieved?
After meiosis, spermatogonia become haploid and are recognised as “foreign” by the body.
Tight junctions between Sertoli cells, which form the blood-testis barrier. Spermatogonia develop outside this barrier in the basal compartment; once they become spermatocytes, they move into the adluminal compartment inside the barrier.
