Reproductive System - MCAT Biological and Biochemical Foundations of Living Systems

The scrotum is a bag of skin containing the testes. The importance of the scrotum is to regulate temperature because sperm synthesis in the testes must occur at a few degrees below body temperature. The testes are the location of sperm synthesis, androgen synthesis occurs in the interstitial cells, nourishment of the sperm takes place in the seminal vesicles, and lubrication occurs in the bulbourethral glands.

Sperm cells in the male reproductive tract are first created in the seminiferous tubules of the testes. From there they travel through the epididymis, vas deferens, ejaculatory duct, urethra, and penis.

Follicles are stimulated to grow when FSH level rises. The follicles produce estrogen that exerts a positive feedback on LH, whose levele begin to rise. When LH levels peak on the 14th day of the cycle, the follicle ruptures, releasing the egg from the ovary and leaving the corpus luteum behind in the ovary. After ovulation, the corpus luteum secretes both estrogen and progesterone to inhibit GnRH. When GnRH is inhibited, FSH and LH will also be inhibited.

The most likely localization of the toxin would be to the ovaries, since this is where gamete production begins for females. For males, gametes are produced in the testes. The incorrect answers are all parts of the female reproductive system. The oviduct is where fertilization takes place. The endometrium (the lining of the uterus) is where the embryo will eventually implant.

Follicle-stimulating hormone stimulates the growth of granulosa cells surrounding the primary oocyte within the ovary, which further promotes maturity of the immature follicle. Prolactin is the hormone that promotes milk production from mammary glands during pregnancy. In females, luteinizing hormone (LH) supports theca cells in the ovaries, which subsequently give rise to precursors to estrogen production. Thyroid hormones regulate metabolism by increasing basal metabolic rate.

The corpus luteum is the remnant structure of the secondary follicle after the egg is released during ovulation. It secretes progesterone following this process. The other structures do not release appreciable amounts of progesterone; the primary follicle differentiates into the secondary follicle, which in turn releases the ovum, or the egg. The spermatozoon is involved with the fertilization of the egg, and does not release any progesterone.

Human chorionic gonadotropin (hCG) is a hormone produced by a fertilized egg and can be detected about six days after conception; it is only found in pregnant women, and can be used to help detect pregnancy.

The other answers are hormones that are present in both pregnant and nonpregnant women, so they cannot be used to determine pregnancy.

At puberty, the oocytes arrested at birth in meiosis I resume growth. This most often happens once a month, if fertilization has not occurred, and continues from puberty until menopause. The oocytes arrested at birth complete meiosis I, and are then arrested in meiosis II until fertilization occurs. During ovulation, the follicle ruptures and develops into the corpus luteum. Without fertilization, the endometrium is shed and the cycle continues. Once menopause is reached, this cycle ceases and most often women are no longer fertile.

The most likely site of egg (also know as ovum) storage in Lorempis marengis females is the ovaries. This is the correct answer because we are told to assume that Lorempis marengis female reproductive anatomy is identical to that of humans, and in human females, the site of egg storage is the ovaries.

Females are born with all of the eggs that they will have throughout their lifespan, and they are stored in the ovaries. When females begin menarche, ovulation begins, in which a single egg is released from one of the ovaries every 28-35 days (until menopause) in preparation for fertilization by sperm. The egg is released from the ovary into the fallopian tube, also known as the oviduct, at which time it may be fertilized by sperm. If fertilization successfully occurs, then the fertilized egg, also known as the zygote, travels down the fallopian tube to the uterus, where it may implant and continue to develop, eventually into a fetus. Thus, each of the above answer choices, other than ovaries, is incorrect, as they represent structures within the female reproductive tract that do not store eggs, but rather are sites than an egg may pass through after it is stored and released from the ovary.

Bartholin's Glands is an incorrect choice, as they are not sites of egg storage, but rather they serve to secrete lubricating mucus to the vagina.

This question requires knowledge of the different cell types in the human male’s reproductive anatomy. The cells of Leydig (also known as the interstitial cells) secrete testosterone and other androgens (male sex hormones), while the Sertoli cells are responsible for nourishing developing sperm. Spermatogonia are sperm cell precursors, and the zona pellucida refers to one of the layers surrounding an ovum.

This question requires knowledge of the ejaculatory path in human males. The quick mnemonic for memorizing the pathway is SEVEn UP (Seminiferous tubule, Epididymus, Vas deferens, Ejaculatory duct, nothing, Urethra, Penis). Additionally, this alerts us to an important characteristic of the MCAT. Oftentimes, answer choices for pathway questions will neither start at the beginning of the pathway nor end at the absolute end of the pathway. Because of this, be sure to know all steps of a pathway, not just the beginning or end.

During spermatogenesis, one spermatogonia will become 4 separate functioning spermatozoa. In oogenesis, a primary oocyte will become 1 functioning ovum (or egg) while 3 polar bodies are also produced, which are nonfunctioning and never become eggs.

When a female ovulates, the oocyte is in metaphase II, until it becomes fertilized by a sperm. It then completes the second phase of meiosis to make a mature ovum. Remember that, unlike spermatogenesis, oogenesis begins during development. All oocytes undergo meiosis I during fetal development, and are kept suspended in prophase II until ovulation, when they shift to metaphase II. Meiosis only continues beyond metapahse II if fertilization occurs.

Spermatogenesis takes approximately 64 days in adult humans. Males begin producing sperm at puberty, and continue until death.

Oogenisis halts in the female embryo while the oocytes are trapped in meiosis II. At the beginning of the menstrual cycle a number of oocytes in primordial follicles are stimulated by pituitary gonadotropins to continue maturation.

Parthenogenesis is the activation and development of an egg without sperm. Parthenogensis, therefore, is not sexual reproduction, but can still result in a fully developed offspring.

Isogamy is a condition of indistinguishable male and female gametes, but they retain the ability to join in sexual reproduction. Hermaphroditism and pseudohermaphroditism are rare conditions in which a single organism produces both sperm and eggs and is able to self-fertilize in sexual reproduction.

Hormone balance is extremely important in both developing the male and female fetus. Hormone levels can regulate and determine the relative level of sex characteristics that we see in individuals. Both sexes produces testosterone and estrogen, but utilize the hormones in different ways. Testosterone is produced at higher levels in males and is used to develop male secondary sex characteristics. Estrogen is produced at higher levels in females and is used to develop female secondary sex characteristics.

Progesterone is a secondary sex hormone that is also produced in both sexes. Females use progesterone to regulate the menstrual cycle, and levels of the hormone vary in women.

The menstrual cycle has four phases:

1. Menstrual phase (days 1-5): the uterus sheds its lining, which exits the body through the vagina in the form of menstrual fluid.

2. Follicular phase (days 1-13): the pituitary gland releases a hormone that stimulates the egg cells to grow. One egg cell matures in a sac-like follicle for 13 days; while it is maturing, the follicle releases a hormone that causes the uterus to develop its lining.

3. Ovulatory phase (day 14): the events listed in the question occur.

4. Luteal phase (days 15-28): the egg released during ovulation stays in the fallopian tube for 24 hours, disintegrating if not fertilized during that time. During this phase, the hormone that causes the uterus to retain its lining is used up, causing another menstrual phase to begin.

The scrotum is a bag of skin containing the testes. The importance of the scrotum is to regulate temperature because sperm synthesis in the testes must occur at a few degrees below body temperature. The testes are the location of sperm synthesis, androgen synthesis occurs in the interstitial cells, nourishment of the sperm takes place in the seminal vesicles, and lubrication occurs in the bulbourethral glands.

Sperm cells in the male reproductive tract are first created in the seminiferous tubules of the testes. From there they travel through the epididymis, vas deferens, ejaculatory duct, urethra, and penis.