Reproductive System and Development - MCAT Biological and Biochemical Foundations of Living Systems

The failure of the lens to form in the absence of the optic cup indicates that the optic cup is necessary for lens development, and may in fact induce it.

This fact says nothing in regards to the timing of neurulation, nor the timing of eye development. Finally, cell differentiation is a gradual process, not all-or-nothing, and the statement is irrelevant to the development of the optic cup and lens.

Anti-Mullerian hormone is present only in male fetuses. It is responsible for the degeneration of the Mullerian ducts, which form the oviducts, uterus, and upper vagina in females.

Osteoporosis is a disease that causes a decrease in bone mass and density and can be induced by malnutrition or calcium deficiency. Even if the disease appears unfamiliar, the prefix "osteo-" indicates a relationship to bone, which is closely linked to calcium levels int he body.

Calcium is also an important ion involved in neural action potentials; it is responsible for triggering the release of neurotransmitters into the synaptic cleft. A calcium deficiency may cause improper action potentials that result in spasms.

Oxygen diffuses from maternal blood to fetal blood through the placenta. Within the womb, the lungs are not able to work properly and so blood is rerouted through the foramen ovale and the ductus arteriosus. The liver is also underdeveloped, and not ready to perform the functions it will do in adulthood. The placenta takes over for the liver during gestation, and so blood is shunted away from the liver by the ductus venosus. This prevents oxygen that could be useful in other places from being wasted in the liver.

The ductus arteriosus shunts blood from the pulmonary artery to the aorta in order to bypass the lungs, since the fetal lungs are not active.

The foramen ovale shunts blood from the right atrium to the left atrium, serving as another method to bypass the lungs. The ductus venosus shunts blood away from the fetal liver. There is no shunt from the aorta to the pulmonary artery, and there is no shunt from the left atrium to the right atrium.

A pregnancy consists of three trimesters, each of which is approximately 12 weeks. The fetus's heart, brain, spinal cord, and other organs begin to form in approximately the fifth week of pregnancy—in the first trimester.

Erythroblastosis fetalis is a rare conditon in which the mother's anti-Rh antibodies enter the fetal bloodstream and attach to fetal erythrocytes. If not caught, it can result in "blue-baby syndrome." Erythroblastosis is only present in patients negative for the Rh factor, and carrying Rh positive fetuses.

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.

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.

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.