The Reproductive System

Now we're up to the reproductive system! This is a system that I know a bit more about, since we did a fair bit on it last semester. As usual, though, if you see something wrong, please point it out to me :)

1. Why do the testes need to be outside the body cavity in the scrotum? What structure(s) regulate or affect the distance from the body?

The testes need to be outside the body cavity because the optimal temperature for sperm production is slightly below body temperature. There are several muscles that regulate the distance of the testes from the body. The cremaster muscle can contract to pull the testes up, while the dartos muscle can contract to pull the scrotum against the body and make it wrinkled (possibly to conserve heat?).

2. Describe the pathway taken by sperm from the testes to the urethra.

Sperm production takes place in the seminiferous tubules located within the testes. After sperm are produced, they travel through several ducts. The first one is called the rete testis, which branches into a series of 12 (if I remember correctly) efferent ductules, which combine into the epididymis, a long, coiling duct in which further sperm production takes place. They then move into the vas deferens, a long, muscular tube which runs to the prostate. From there it goes through an ejaculatory duct through to the urethra.

3. What occurs during the preovulatory phase of the menstrual cycle? What is considered day 1?

Day 1 of the menstrual cycle is the first day of bleeding, as that is the easiest to determine. During the preovulatory phase, FSH (follicle-stimulating hormone) stimulates the follicles to grow. Under the influence of LH (luteinising hormone), theca cells on the outside of the follicles increase their number of cholesterol receptors, allowing them to receive more cholesterol which can be converted into androgen (I think that's how it works anyway- can't remember where I read this). Granulosa cells, which are the second layer of the follicle, contain the enzyme aromatase which converts androgens into oestrogens. These oestrogens help to begin rebuilding (proliferating) the functional layer of the endometrium of the uterus after its shedding off during menstruation. Hence the preovulatory phase is also called the proliferative phase.

4. At what stage is there rupture of the corpus luteum? What occurs at this time?

Rupture of the corpus luteum occurs during the end of the menstrual cycle, towards the end of the secretory phase. Since the corpus luteum secretes oestrogen and progesterone which maintains the lining of the uterus, its rupture means that the lining is no longer able to be maintained. The functional layer of the endometrium is then shed during menstruation.

5. What is the purpose of X chromosome inactivation? In which sex does it occur?

X chromosome inactivation, which occurs in females, alleviates the issue of females having "too much genetic information" from two X-chromosomes. If I remember correctly, this phenomena is also known as "dosage compensation." Due to X-chromosome inactivation, only one X-chromosome is active.

6. A father has PKU and the mother does not. Together, they have a child who also has PKU. What is the father's genotype?

PKU (phenylketonuria) is an autosomal recessive disease. To have PKU, therefore, a person must have two recessive alleles for the disease. Hence, the father has two recessive alleles for PKU.