Reproductive physiology Flashcards
What is the anatomy of the male reproductive tract?
Look at photo.
What is the ductus deferens?
AKA the vas deferens: Small muscular tube in the male reproductive system that carries sperm from the epididymis (emerging tube of the testicle) to the ejaculatory duct (created when the seminal vesicle’s duct merges with the ductus deferens).
What are seminal vesicles?
AKA vesicular glands: a pair of simple tubular glands posteroinferior to the urinary bladder that secrete fluid that partly composes the semen.
What are bulbourethral glands?
Located beneath the prostate that add fluids to semen during ejaculation.
What is the cellular makeup of the testis? (x2)
Contains seminiferous tubules (which produce sperm – made of Sertoli cells) and Leydig (interstitial) cells which produce testosterone (and some other androgens). Testosterone is released into the circulation, from where it can affect the whole body.
What is the structure and function of the hypothalamus-pituitary-testicular axis?
□ Gonadotrophin releasing hormone (GnRH) is released from the hypothalamus in a pulsatile manner and stimulates the anterior pituitary to produce LH and FSH. □ LH acts on Leydig cells in the testis which are stimulated to produce testosterone. This testosterone passes into the seminiferous tubules of the testis to help with production of sperm. □ FSH acts on Sertoli cells on seminiferous tubules which produce androgen binding protein (ABP) which binds testosterone, regulates the function of Sertoli cells, and promotes the production of sperm. □ Testosterone feedbacks onto the hypothalamus and pituitary gland. Inhibin is produced by Sertoli cells which feedback on the pituitary also.
What is the function of Sertoli cells?
Nutritional and hormonal support for spermatogenesis.
What happens in the process of spermatogenesis?
□ Germ cell differentiates into spermatogonia in very early life. This germ cell is diploid (SO WILL DEVELOP INTO 4 sperm).
□ Spermatogenesis doesn’t actually start UNTIL PUBERTY. Spermatogenesis– process occurs in conjunction with the immature germ cell dissociating from the basal lamina of the tubule.
□ In puberty, release of hormones including testosterone means spermatogonia mitotically divide – half are kept as spermatogonia, the other half become primary spermatocytes.
□ Primary spermatocytes undergo their first meiotic division to secondary spermatocytes which are HAPLOID.
□ These undergo their second and final meiotic division to give spermatids which are haploid and contain 23 chromosomes in each.
□ The spermatid undergoes further maturation to form Spermatozoa. The process is called spermiogenesis and when the spermatid develops a tail, acrosome, and mitochondria neck region.
Passage of sperm from testis and through penis?
Spermatids collect into the lumen of the seminiferous tubules and drained by the vasa efferentia into the epididymis. Sperm are released from the testis and stored here prior to ejaculation. At ejaculation sperm pass through the two Vas Deferens (which are contractile) and are mixed with fluid from the seminal vesicles. The fluid then leaves the ejaculatory duct and passes into the urethra where it mixes with secretions from the prostate gland.
How much sperm is produced each day?
200 million per day.
What is the structure and function of the hypothalamus-pituitary-ovarian axis?
□ Also called the OVARIAN CYCLE. □ Gonadotrophin releasing hormone (GnRH) is released from the hypothalamus in a pulsatile manner and stimulates the anterior pituitary to produce LH and FSH. □ FSH stimulates some development of ovarian follicles and 17B-estradiol synthesis. □ LH acts on the ovaries which stimulate progesterone production. □ The steroids progesterone and 17B-estradiol regulate uterine development. □ Oestrogen and progesterone negatively feedback onto the hypothalamus and pituitary.
What two cycles are involved in the menstrual cycle? And their locations.
Ovarian cycle (occurs in the ovaries); Endometrial cycle (occurs in the uterus).
What occurs in the ovarian cycle? (x3 phases) When do each occur?
FOLLICULAR PHASE (follicles in the ovary mature. This occurs when LH levels fall and FSH is high.) – from Day 1; OVULATION – Day 14; LUTEAL PHASE (oestrogen and progesterone increase and prepare the endometrium to accept an embryo) - until Day 1 OR, as soon as menstruation begins.
What happens in the endometrial cycle? (x2)
PROLIFERATIVE PHASE – endometrium builds up and thickens; SECRETORY PHASE – (after ovulation) – corpus luteum secretes progesterone which stimulates development of glands and arteries in the endometrium, causing it to become thick and spongy.
How does the ovarian cycle influence the endometrial cycle? (x2)
□ In follicular phase of the ovarian cycle, oestrogen rises (17B-oestradiol), which has a proliferative effect on the endometrium. It does this by causing implantation of more oestrogen and progesterone receptors into the endometrium (progesterone receptors are for later in the menstrual cycle).
□ In the luteal phase, 17B-oestradiol and progesterone levels increase (again). Progesterone removes oestrogen receptors from the endometrium and create a more ideal environment for egg implantation.
How do the feedback loops change during ovarian cycle in the hypothalamus-pituitary-ovarian axis?
- In the follicular phase, estradiol negatively feedbacks onto the hypothalamus and anterior pituitary which reduce the production of GnRH and FSH/LH.
- In the midcycle (up to and during ovulation) of menstrual cycle, the sensitivity of the hypothalamus and anterior pituitary changes, and estradiol has a positive feedback effect on the axis. FSH and LH production is consequently upregulated.
- In the luteal phase of the menstrual cycle – after ovulation, progesterone becomes the main steroid hormone produced, which negatively feedbacks on the hypothalamus and anterior pituitary.
What happens in oogenesis in the ovary? !!!
- Germ cell differentiates into oogonia during embryonic development. Oogonia are diploid.
- Mitosis of oogonia produces some oogonia which undergo atresia, while others form primary oocytes – also diploid. Primary oocyte is an immature ovum that undergoes growth and some maturation (some follicle cells grow around the oocyte to form a primary follicle). During embryogenesis, primary oocyte also begins meiosis I, but stopped during prophase I.
- Ovaries become inactive.
- During puberty, the primary oocytes continue their meiotic division again and the follicle continues to grow as a result of hormonal changes. The first meiotic division occurs asymmetrically – this still produces two cells with the same number of chromosomes in each, it’s just the actual cell that is split differently so one is bigger than the other.
- This produces a ‘first polar body’ (which immediately degrades), and a secondary oocyte.
- The secondary (haploid) oocyte is the precursor of an egg. Secondary oocytes still have 46 chromosomes and released into the Fallopian tubes in meiotic arrest (held in metaphase II).
- If fertilised, the secondary oocyte completes its development, producing a haploid ovum and second polar body. The ovum has a large cytoplasm because of the asymmetrical process.
- The rest of the oocytes remain dormant, and supplies remain until they run out and menopause happens.
What is the process of follicle maturation?
- Follicles selected spontaneously for further development right through life (including embryogenesis). They are selected independent of gonadotrophin and form pre-antral (or primordial) follicles – they start with just a single layer of granulosa cell. NOTE that the time taken for a primordial follicle to develop into a secondary (mature) oocyte is more than one month.
- If they form pre-antral follicles when FSH levels are not raised, they undergo atresia. If they form pre-antral follicles when FSH levels are raised, they go on to develop further and are the dominant follicles.
- The follicle gets larger and there is now an antrum – fluid-filled space. Called the EARLY ANTRAL FOLLICLE.
- The thecal and granulosa-luteal cells grow, and more oestrogen is therefore secreted. Called the LATE ANTRAL FOLLICLE. At this point, if there are still multiple follicles, the dominant one will be selected, and others will enter atresia.
- Then you have the GRAFFIAN FOLLICLE, which has a large fluid-filled space, and the ovum is embedded in the walls of the follicle.
- Ovulation – usually at 14 days!
How do levels of LH, FSH, 17B-oestradiol and progesterone change throughout the menstrual cycle? What happens in each phase? (x5 phases) !!!
- EARY FOLLICULAR PHASE: FSH levels are raised. Follicles start to mature and grow. They compete to become the dominant follicle.
- EARLY-MID FOLLICULAR PHASE: FSH and LH levels do not change; oestradiol levels begin to rise as one follicle becomes bigger than the rest (the dominant follicle). These increased levels have a positive feedback effect on the granulosa cells around it. Oestradiol results in increased growth of the granulosa cells, so more oestrogen can be synthesised.
- MID-FOLLICULAR PHASE: Graafian follicle has developed which produces very high levels of oestradiol. This has a negative feedback effect on the pituitary and hypothalamus which results in reduced levels of gonadotrophins (FSH and LH). Graafian follicle no longer relies on the FSH and LH, so remaining follicles undergo atresia.
- LATE-FOLLICUALR PHASE: high oestradiol results in positive feedback, leading to surge in LH and small surge in FSH –> ovulation. There is a small increase in the progesterone 17OH-progesterone, which enhances the positive feedback effect that results in the surge of gonadotrophins.
- LUTEAL PHASE: follicle that remains transforms to corpus luteum which continues to produce oestrogen and lots of progesterone. These both negatively feedback on the gonadotrophins to keep those levels low. The progesterone prepares the endometrium for implantation by a fertilised egg.
What happens in fertilisation? !!!
- Sperm arrive at egg and release their package of digestive enzymes (called the acrosome). This helps sperm travel through and digest the zona pellucida and coronal cells of the egg.
- When the sperm reached the cell membrane of the egg, it is taken up by the secondary oocyte, and the chromosomes packed into the sperm head decondense into male pronucleus.
- Fertilisation takes the secondary oocyte out of meiotic arrest, and the female diploid nucleus of secondary oocyte splits – this produces the mature ovum (with a HAPLOID PRONUCLEUS) and a second polar body which migrates to the side of the ovum. NB: that each pronuclei contain 23 CHROMATIDS.
- The zona pellucida change to prevent further fusion of sperm.
- The sperm and ovum pronuclei immediately duplicate, so the egg contains producing 92 chromatids in total.
- MITOSIS BEGING: These arrange into a mitotic spindle, and chromosomes are separated. This division produces two identical cells –> called FIRST CLEAVAGE DIVISION OF THE EMBRYO.
What is the anatomy of the female reproductive system?
Look at photo.
