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MCAT Biology > Reproductive System and Development > Flashcards

Reproductive System and Development Flashcards

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1
Q

Where are sperm produced?

A

Seminiferous tubules

They mature in the epididymis

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2
Q

What is the biggest consequence from the first division of meiosis?

A

It is the reduction division, where chromosomes go from being 2N to N (haploid, 23 for humans)

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3
Q

Give the steps for meiosis

A

Prophase I: Chromosomes condense and spindle fibres appear. Homologous chromosomes pair and exchange genetic material by chiasmata formation

Metaphase I: chromosomes line up at equatorial plate (4 chromatids, 2 chromosomes, each attached to a spindle fiber)

Anaphase I: Homologous chromosomes migrate to opposite poles of the spindle (centromeres do not divide)

Telophase I: The parent cell divides into two daughter cells (cytokinesis)

Short interphase before second meiotic division (which proceeds same as above)

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4
Q

List the steps for spermatogenesis

A

After sexual maturation, spermatogonia (primordial germ cells) prolifically multiply throughout a male’s life.

  • Spermatogonia (2N) differentiate by mitosis in the seminiferous tubules, to become primary spermatocytes (2N)
  • Primary spermatocytes undergo meiotic division to produce secondary spermatocytes (N), followed by spermatids.
  • Each primary spermatocyte produces four spermatids, which are transformed into four motile sperm by spermiogenesis
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5
Q

What is the head of sperm?

A

Contains genetic material and is surrounded by the acrosome, which contains the enzyme hyaluronidase

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6
Q

What are sertoli cells?

A

Found in the seminiferous tubule. support and nourish developing sperm

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7
Q

What are leydig cells?

A

Produce and secrete testosterone in the testes

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8
Q

What stimulates testosterone secretion?

A

Luteinizing hormone stimulates testosterone secretion from leydig cells

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9
Q

What hormone stimulates primary spermatocytes to undergo meiosis?

A

Follicle stimulating hormone

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10
Q

Describe the steps of oogenesis

A
  • Ovarian follicles develop from the germinal epithelium in fetuses
  • Oogonia (2N) produce primary oocytes (2N), which are surrounded by epithelia (follicular cells)
  • Oocytes come out of prophase I in ovulation to become Graafian follicles and produce a secondary oocyte (1N) by a reductive division
  • The secondary oocyte is surrounded by zona pellucida (thick membrane), follicular cells and estrogen secreting thecal cells
  • All maturing follicles (about 20 in one cycle) will degenerate (atresia), except one which is expelled from ovary during ovulation
  • The ovum migrate through fallopian tubes, if fertilization occurs, second meiotic division happens. If not, ovum degenerates)
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11
Q

How many games are produced from primary germ cells in females and males?

A

Males: four

Females: one, because up to 3 polar bodies (degenerated nuclear material) are formed from the division of primary oocyte

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12
Q

List (but don’t describe) the stages of the menstrual cycle

A
  • Menses
  • Follicular phase
  • Ovulation
  • Luteal phase
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13
Q

Describe the menses stage of menstruation

A

First five days of the cycle. Menstrual blood flow as a result of estrogen and progesterone withdrawal occurs. Estrogen and progesterone withdrawal causes vasoconstriction in the uterus, causing the uterine lining (endometrium) to disintegrate and slough away

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14
Q

Describe the follicular stage of menstruation

A

FSH promotes the maturation of the follicle, which in turn produces and secretes estrogen. Estrogen causes the uterine lining to thicken.

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15
Q

Describe ovulation and the luteal (secretory phase) of menstruation

A

A high concentration of estrogen is followed by an LH surge at day 14 (midcycle), which stimulates ovulation

The follicular cells degenerate into corpus luteum, which secretes estrogen and progesterone. Progesterone is responsible for a transient body temperature rise immediately after ovulation. It stimulates the uterine lining to become more vascular and glandular. Estrogen continutes to stimulate uterine wall development and, along with progesterone, inhibits the secretion of LH and FSH (negative feedback)

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16
Q

What happens when an ovum is fertilized? What happens if it is not fertilized?

A

The implanted embryo would produce human chorionic gonadotropin (hCG), which would stimulate the corpus luteum to continue the secretion of estrogen and progesterone (hCG is the basis for most pregnancy tests)

If not fertilized, the corpus luteum is degenerated, causing a withdrawal of estrogen and progesterone, and thus continuing the menstrual cycle.

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17
Q

Simply list the eight steps of embryogenesis, morphogenesis and parturition (in order)

A
  • Fertilization
  • Cleavage
  • Blastulation
  • Gastrulation
  • Neurulation
  • Determination and induction (cell differentiation)
  • Morphogenesis to fetus
  • Parturition (fetus to birth)
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18
Q

Describe the fertilization step of embryogenesis

A
  • Sperm penetrates corona radiata and zona pellucidum due to release of lytic enzymes
  • Plasma membranes of sperm and egg fuse, forming mature ovum
  • Nuclei of ovum and sperm now called pronuclei, which fuse to become zygote (2N)
  • Fertilization completed within 24 hours
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19
Q

Describe the cleavage step of embryogenesis

A
  • Rapid, repeated mitotic divisions beginning with the zygote. Because the resultant daughter cells or blastomeres are still contained within the zona pellucidum, the cytoplasmic mass remains constant
  • The increasing number of cells requires that each daughter cell be smaller than its parents cell
  • A morula is a solid ball of about 16 blastomeres, which enters the uterus
20
Q

Describe the blastulation stage of embryogenesis

A
  • The morula develops a fluid filled cavity (blastocoel), thus converting it to a blastocyst (blastula)
  • Blastula implants into uterine lining (endometrium)
  • Inner cell mass develops into embryo
21
Q

Describe the gastrulation step of embryogenesis

A
  • The blastula invaginates and the inner cell mass is converted into a three layered disk (trilaminar), which includes the three primary germ layers
  • Embryo called gastrula
22
Q

What are the three primary germ layers of the trilaminar disk (and what do they give rise to)?

A
  • Outer ectoderm (epidermis + nervous system)
  • Middle mesoderm (muscle, connective tissue and circulatory, reproductive and excretory organs)
  • Inner endoderm (epithelial lining of respiratory and digestive tracts, and accessory organ glands - eg. pancreas)
23
Q

Describe the neurulation step of embryogenesis

A
  • The neural plate and neural folds form and close to produce the neural tube
  • Neural plate is formed by thickening of ectoderm, which is induced by developing notochord (defines axis of embryo and provides rigidity)
  • Neural plate invaginates along central axis, producing central neural groove, which neural folds on each side.
  • The neural folds come together and fuse, thus converting the neural plate into a neural tube, which separates from surface ectoderm.
  • Neural crest cells migrate to either side of the developing neural tube to neural crest
  • Left with surface ectoderm (becomes epidermis), neural tube (CNS) and neural crest (becomes cranial and spinal ganglia and nerves, also medulla of the adrenal gland)
  • Embryo called neurula
24
Q

What does the ectoderm develop into (3 things) during neurulation?

A
  • Surface ectoderm (becomes epidermis)
  • Neural tube (becomes CNS)
  • Neural crest (becomes cranial and spinal ganglia and nerves, also medulla of the adrenal gland)
25
Q

What is determination of embryogenesis?

A

The stage where cells are becoming more committed to a certain fate (eg. neural tube cells becoming CNS cells)

26
Q

What is the placenta?

A

A complex vascular structure formed by part of the maternal endometrium (the decidua basalis) and cells of embryonic origin (the chorion).

27
Q

When does the placenta begin to form?

A

When the blastocyst implants in the endometrium.

28
Q

How does the placenta form?

A

A cell layer from the embryo invades the endometrium with fingerlike bumps (chorionic villi), which project into intervillous spaces, which contain maternal blood.

Maternal spiral arteries enter the intervillous spaces, allowing blood to circulate

29
Q

What are the four main functions of the placenta?

A
  • Transfer of substances necessary for development of embryo or fetus from the mother
  • Transfer of wastes from embryo/fetus to mother
  • Synthesis of substances (eg. glycogen and fatty acids) to sue as energy source for itself and fetus/embryo
  • Producing and secreting hormones (including hCG, estrogen and progesterone)
30
Q

How is oxygenated blood directed to the fetus? How does the blood then circulate in the heart?

A

Directed to the inferior vena cava through the ductus venosus

This blood then divers from pulmonary circulation to the left atrium via a hole in the atrial septum (foramen ovale).

31
Q

How does deoxygenated blood flow in fetuses?

A

Collapsed lungs increase pulmonary artery pressure so much, that most blood is diverted via the ductus arteriosus to the aorta. Blood from the aorta now enters systemic circulation. Umbilical arteries divert some aortal blood to the placenta for oxygenation.

In normal infants, the foramen ovale and the ductus arteriosus both fuse shut.

32
Q

What happens to Müllerian ducts when the genotype is

XX
XY

A

XX: Maturation into uterus, fallopian tubes and part of vagina

XY: Involution of Müllerian ducts and maturation of Wolffian ducts into the vas deferens, seminiferous tubules and prostate

33
Q

After an egg reaches the fallopian tube, what must happens to it if it is to become fertilized?

How is this different with ectopic pregnancies?

A

It is normally fertilized and then transported to the uterus.

In ectopic pregnancies, the zygote implants in the fallopian tubes.

34
Q

Delayed ovulation, as a cause of tubal (ectopic) pregnancy, would most likely be associated with delayed secretion of which hormone? Why?

A

Luteinizing hormone.

Luteinizing hormone is responsible for triggering ovulation.

A surge of LH is triggered by estrogen, but estrogen does not start ovulation. LH causes a surge in progesterone.

35
Q

What is the pregnancy hormone?

A

hCG (human chorionic gonadotropin)

hCG is a hormone produced by the syncytiotrophoblast, a component of the fertilized egg, after conception. Following implantation, the syncytiotrophoblast gives rise to the placenta

36
Q

Which type of animals should have the strongest (densest) bones? Least dense?

A

Land animals should have the strongest bones, as they must withstand load bearing from gravity.

Amphibians would have second strongest bones, as they must spend some time in water.

Water animals would have even less dense bones, as effects of gravity are reduced.

Flying animals would have the least dense bones, necessary for flight.

37
Q

Which of the following can initiate a second meiotic division?

A. FSH
B. LH
C. Estrogen and progesterone
D. Fertilization

A

D. Fertilization

38
Q

Why is the fetus better able to compete for Oxygen at the placenta?

A

Compared to maternal Hb, fetal Hb has an increased ability to bind O2 at lower O2 concentrations.

39
Q

High P50 (Oxygen gas pressure at which Hb binds to 50% of amount of oxygen gas at buffered standard conditions) is adaptive for cats, mice and deer because they enable these animals to ___?

A

Be very active.

High P50 values indicate that Hb molecules have low affinities for O2 and will readily offload O2 to tissues. Having a higher P50 is beneficial to an active organism because the Hb will more easily offload O2 to tissues to support the oxygen demand associated with the high rates of aerobic respiration in active tissues.

40
Q

The cell type in the male reproductive system that is most analogous to the female ovum is the: ?

A

Spermatozoon

The mature ovum is the female gamete that has completed meiosis and contains the haploid number of maternally derived chromosomes. This makes it most analogous to spermatozoa, the mature male gametes that contain the haploid number of paternally derived chromosomes.

41
Q

What is parthenogenesis?

A

An alternative to sexual reproduction, which requires only one individual.

42
Q

What is isogamy?

A

A term for sexual mating strategy in which both gametes are identical in form, rather than, for instance, being distinguishable as egg and sperm.

43
Q

Which of the following structures is derived from the same germ cell layer as the heart?

A. Eye
B. Bone
C. Spinal Cord
D. Liver

A

B. Bone

In gastrulation, the three cell regions, or germ layers are formed in the embro. From the outer layer (ectoderm) come cells of the nervous system and epidermis, from the inner layer (endoderm) come cells of the lining of the digestive tube and associated organs, and from the middle layer (mesoderm) come the blood cells, connective tissues and several organs (kidney, heart and gonads). Thus, the eye and spinal cord are formed from ectoderm, the liver is formed from endoderm and the heart and bones are formed from mesoderm.

44
Q

Describe cell division (cytokinesis) in vertebrate oocytes in meiosis.

A

The cytoplasm is distributed to the two daughter cells. Most of it goes to the daughter cell destined to be the ovum. The other daughter cells, the polar bodies, are cast off with little cytoplasm. The amount of nuclear material in each, however, is the same. The distribution of cytoplasm is uneven.

45
Q

In human females, mitotic divisions of oogonia that lead to formation of presumptive egg cells (primary oocytes) occur between what stages of life?

A

Between fertilization and birth.

That is, all mitotic divisions that form primary oocytes (eggs), occur prior to birth.

46
Q

How are bacteria and eukaryotes similar in ATP production?

A

They both utilize ATP synthase to produce ATP.

Bacteria: plasma membrane

Eukaryote: inner mitochindrial membrane

MCAT Biology (29 decks)

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