Gametogenesis and Fertilization Flashcards
1
Q
What are the two basic characteristics of asexual reproduction?
A
- Offspring are clones.
- There is no fusion of gametes.
2
Q
What are the four basic characteristics of sexual reproduction?
A
- Non-motile egg fuses with motile sperm.
- Offspring are usually genetically distinct.
- Fertilization can be either internal or external.
- Sexual replication facilitates genetic variation, at a reproductive cost.
3
Q
How does a population grow through asexual reproduction?
A
The population grows quickly through log growth as clones undergo binary fission.
4
Q
Define spermatogenesis.
A
Spermatogenesis is the formation and development of sperm.
5
Q
Where does spermatogenesis occur?
A
It occurs in the seminiferous tubules contained within the testes.
6
Q
How many sperm are produced each day, and how long do they take to develop?
A
Millions are produced each day, and each takes about 7 weeks to develop.
7
Q
Where is the genetic material of a sperm cell located?
A
The genetic material is located in an acrosome inside the nucleus, which is inside the head of the sperm.
8
Q
Where are the mitochondria of a sperm cell located?
A
The mitochondria are located within the midpiece.
9
Q
List the stages of spermatogenesis in the order in which they occur. Also state whether they are haploid or diploid.
A
- Primordial germ cells (haploid)
- Spermatogonial stem cell (diploid)
- Spermatogonium (diploid)
- Spermatocytes (diploid)
- Spermatid (haploid)
- Sperm (haploid)
10
Q
Where are male primordial germ cells located?
A
In the embryonic testes.
11
Q
Where are spermatogonial stem cells located?
A
In the seminiferous tubules of an adult.
12
Q
What are the two possible outcomes for the offspring of a spermatogonial stem cell?
A
It can produce a copy of itself (another stem cell) or give rise to a spermatogonium, which is then committed to becoming a sperm cell.
13
Q
In the sperm life cycle, when does meiosis occur?
A
Meiosis begins with the primary spermatocyte. The result of meiosis I is two secondary spermatocytes, which conclude meiosis by creating four early spermatids (haploid).
14
Q
When do sperm cells move from the testes to the epididymis?
A
After the spermatids differentiate, the mature sperm cells move from the testes to the epididymis.
15
Q
List the steps of the journey of the sperm.
A
- Testes produce sperm in highly coiled seminiferous tubules.
- Sperm traverse epididymis and complete maturation.
- During ejaculation, sperm are propelled via a muscular vas deferens.
- Vas deferens joins duct from the seminal vesicle–becomes ejaculatory duct.
- Ejaculatory duct joins the urinary tract–becomes the urethra.
16
Q
What is the role of the seminal vesicles (2)?
A
The seminal vesicles produce 60% of the semen: yellowish mucus, protein, and fructose. This dense fluid allows the male to deposit it deeper into the female.
17
Q
What is the role of the prostate?
A
The prostate gland produces a thin, milky fluid: anticoagulant enzymes and citrate (nutrient). This part of the semen thins out the part from the seminal vesicles so that the sperm are able to swim.
18
Q
What is the role of the bulbourethral glands (2)?
A
These glands’ secretions neutralize the acidity in the urethra to protect the sperm as they exit.
19
Q
What is the role of the urethra?
A
The urethra is a conduit for semen and urine.
20
Q
Define oogenesis.
A
Oogenesis is the formation and development of oocytes that occurs in the ovaries.
21
Q
Describe the life cycle of oocytes.
A
- Immature oocytes form in the embryo and undergo developmental arrest for years or a decade.
- At birth, the ovaries have 1-2 million primary oocytes, and about 500 mature between puberty and menopause.
- The production of mature oocytes stops at around the age of 50: menopause.
22
Q
What happens to the female primordial germ cell while it is in the embryo?
A
The germ cells undergoes mitotic division to form an oogenium, which then divides to form the primary oocyte.
23
Q
Describe the transition from primary oocyte to secondary oocyte.
A
During puberty, the primary oocyte from the embryonic stage (arrested in prophase I) completes meiosis I and begins meiosis II, leading to the first polar body and the secondary oocyte.
24
Q
When does developmental arrest first occur in oogenesis?
A
The primary oocyte in the embryo undergoes developmental arrest during prophase of meiosis I.
25
When does the second developmental arrest occur in oogenesis?
The secondary oocyte undergoes developmental arrest during metaphase II.
26
When does ovulation occur?
Ovulation occurs during the second developmental arrest that occurs during metaphase II in the secondary oocyte.
27
What is ovulation?
Ovulation is the discharge of the secondary oocyte into the oviduct.
28
What causes the secondary oocyte to complete meiosis II?
Fertilization by a sperm.
29
What is the outcome of oogenesis in a female?
One oocyte and three polar bodies.
30
What is the follicle?
The place where the developing oocyte develops.
31
What happens to the follicle after ovulation?
After ovulation, the leftover cells of the ruptured follicle develop into the corpus luteum.
32
What does the corpus luteum do if fertilization occurs?
It secretes estradiol and progesterone, maintaining the uterine lining during pregnancy. It sends signals to the uterus and brain instructing proper hormone secretion.
33
What does the corpus luteum do if fertilization does not occur?
It degenerates, and a new follicle matures during the next cycle.
34
Describe the journey of the oocyte.
1. Ovaries are filled with follicles consisting of an oocyte and support cells.
2. At ovulation, one oocyte is released into the body cavity.
3. Cilia on the oviduct collect the oocyte and move it toward the uterus.
4. Sperm meets the oocyte in the oviduct. Fusion results in fertilization.
5. Fertilized egg enters the uterus and implants in the endometrium (lining).
35
Where is the location of fertilization?
The oviduct.
36
What is the cervix?
The cervix is the opening into the vagina from the uterus.
37
What is the vagina?
The vagina is a muscular but elastic chamber where the male penis is inserted and sperm is deposited.
38
Describe the female reproductive structure beyond the uterus.
The vagina opens to the outside of the vulva. The labia major encloses the vulva. Within, the labia minora and the clitoris, together with the vagina, engorge with blood during sexual arousal.
39
What is the difference in cytokinesis between spermatogenesis and oogenesis?
In spermatogenesis, all four products of meiosis develop into mature gametes (1 cell -> 4 sperm). In oogenesis, cytokinesis during meiosis I and II is unequal, with almost all the cytoplasm segregated to a single daughter cell; therefore, meiosis results in only one gamete (1 cell -> 1 oocyte -> 3 polar bodies).
40
What is the difference in the timeline between spermatogenesis and oogenesis?
Spermatogenesis occurs throughout adolescence and adulthood. In oogenesis, mitotic divisions are completed before birth, and the production of mature gametes ceases at around 50 years of age (menopause).
41
What is the difference in developmental sequence between spermatogenesis and oogenesis?
In spermatogenesis, gametes are produced from precursor cells in a continuous sequence. In oogenesis, developmental arrest leads to long interruptions in gamete production.
42
Which structures coordinate mammalian tropic and sex hormones?
The hypothalamus, anterior pituitary, and the gonads.
43
What part of the sex hormone signaling pathway occurs in both males and females?
By releasing GnRH, the hypothalamus tells the anterior pituitary to release two hormones: FSH and LH. These hormones signal to the gonads to do something depending on the sex of the organism.
44
What does the release of FSH stimulate in males?
FSH causes Sertoli cells in the seminiferous tubules of the testes to nourish the developing sperm.
45
What does the release of LH stimulate in males?
LH causes Leydig cells in the connective tissue between the tubules to produce testosterone, which promotes spermatogenesis.
46
What happens after a sufficient number of sperm have been made?
The Sertoli cells produce a hormone called inhibin, which gives negative feedback to the anterior pituitary to inhibit the release of FSH and LH.
47
How is testosterone used in a negative feedback loop?
It feeds back to both the anterior pituitary and the hypothalamus when enough spermatogenesis has occurred, which slows down the production of GnRH, FSH, and LH.
48
What is the ovarian cycle?
The cycle recurrence of the follicular phase, ovulation, and the luteal phase.
49
What is the uterine cycle?
Cyclic changes in the endometrium that occur in the absence of pregnancy, including menstruation.
50
What links the ovarian and uterine cycles?
Hormonal activity.
51
What happens on day 0 of the ovarian cycle?
The hypothalamus produces GnRH, which tells the anterior pituitary to produce FSH and LH. FSH and LH travel through the blood to reach the ovaries.
52
Describe hormonal levels through the first ~14 days of the ovarian cycle.
GnRH, FSH, LH, progesterone, and estradiol levels are all low.
53
What stimulates the development of a follicle?
Low hormonal levels.
54
What happens as a follicle grows?
It makes estradiol.
55
What is the relationship between estradiol levels and FSH and LH levels?
When estradiol levels are low, that keeps FSH and LH levels low.
56
What happens when estradiol is high?
High estradiol levels send a positive feedback loop to the hypothalamus to stimulate an increase in GnRH, leading to an increase in FSH and LH as well. This is called the LH/FSH surge.
57
What triggers ovulation?
On day 14 of the ovarian cycle, the LH/FSH surge triggers ovulation.
58
What happens to estradiol levels after ovulation?
Estradiol levels decrease.
59
What happens as the corpus luteum develops?
It produces high levels of progesterone and increases the levels of estradiol. Where before the oocyte produced these hormones, now the corpus luteum is.
60
What two effects do the increased levels of progesterone and estradiol from the corpus luteum have?
1. It signals to the endometrium to thicken.
2. It tells the hypothalamus to stop producing GnRH, FSH, and LH.
61
How is a second fertilization event prevented?
The corpus luteum's increased levels of progesterone and estradiol signal to the hypothalamus to stop producing GnRH, FSH, and LH, ensuring another fertilization event does not occur.
62
How does the corpus luteum respond to fertilization?
It continues producing estradiol and progesterone, inhibiting hormones from the hypothalamus, and thickening the endometrium.
63
What does the corpus luteum do if fertilization does not occur?
It degrades, causing estradiol and progesterone to decrease. This induces menstruation and stops the negative feedback to the hypothalamus, causing it to start producing GnRH, FSH, and LH again.
64
What are days 0-14 of the ovarian cycle called?
The follicular phase.
65
What are days 15-28 of the ovarian cycle called?
The luteal phase.
66
What are the phases of the uterine cycle?
Days 1-5: menstrual flow phase
Days 6-14: proliferative phase
Days 15-28: secretory phase
67
What happens in the menstrual flow phase?
Ovarian hormone levels drop, which induces the shedding of the endometrial lining.
68
What happens in the proliferative phase?
Estradiol secreted by the growing follicles signal the endometrium to thicken.
69
What happens in the secretory phase?
After ovulation, the estradiol and progesterone secreted by the corpus luteum maintain and continue to develop the endometrium.
70
How long does it take the egg to travel from the ovary to the uterus?
3-4 days.
71
How long do the unfertilized egg and sperm survive?
2-3 days.
72
What is an ectopic pregnancy?
The implantation of the embryo into the oviduct: very dangerous.
73
What happens if more than one sperm enters an egg?
Fertilization will not occur and the oocyte will not undergo division to create a zygote.
74
What process leads to the yield of a zygote?
A sperm unites with an egg, and the egg completes meiosis II. Then the nuclei from the sperm and the egg fuse into one diploid cell: that is the zygote.
75
When the zygote divides, what is it called?
A blastocyst.
76
What happens after the blastocyst implants in the endometrium?
Estradiol and progesterone from the corpus luteum signal to the endometrium to nourish the embryo.
77
What do the estradiol and progesterone released from the corpus luteum signal to?
It signals to the hypothalamus and anterior pituitary a stop signal for GnRH, FSH, and LH. This stops the ovarian cycle.
78
In the first trimester, what maintains the pregnancy and stops another ovarian cycle from beginning?
The embryo implanted in the endometrium secretes its own hormone called hCG (human chorionic gonadotropin) to maintain the corpus luteum, which continues to secrete estradiol and progesterone.
79
What maintains the pregnancy and stops another ovarian cycle from beginning in the second trimester?
The corpus luteum disintegrates and the placenta maintains pregnancy.
80
How do pregnancy tests work?
They detect the hCG secreted by the blastocyst.
81
List the general steps of fertilization.
1. The sperm penetrates any protective layer surrounding the egg and reaches the plasma membrane.
2. Molecules on the sperm surface bind to receptors on the egg surface--ensures species compatibility.
3. Sperm enters the egg.
4. The surface of the egg is changed to prevent polyspermy.
82
How is species compatibility ensured in fertilization?
There are specific receptors on the surface of the egg that bind to ligands on the acrosome of the sperm.
83
Define polyspermy.
A situation in which multiple sperm enter the same egg.
84
What is the purpose of the jelly coat on the eggs of sea urchins?
Protection of the egg in sea water.
85
What happens after the head of the sperm comes in contact with the jelly coat?
The head releases enzymes onto the jelly coat in order to digest it. This paves the way for the sperm to enter the plasma membrane.
86
What happens after the acrosomal reaction to prevent polyspermy?
In the sea urchin, sodium ion channels open, allowing sodium to flow into the cell and change the voltage of the membrane.
87
What happens when the voltage of the membrane is changed due to the influx of sodium ions?
The ligands found on the acrosomes of sperm can no longer bind to the receptors on the egg. They will repel each other because of charge. This is called a fast block of polyspermy.
88
How long does the fast block of polyspermy last?
About one minute, though it takes about 2-3 seconds to initiate.
89
What does the binding of sperm and egg trigger?
It triggers a signal transduction pathway and the release of calcium into the cytosol from the ER (additional ions to the sodium ions).
90
What effect does the release of calcium have in the egg?
The calcium tells cortical granules near the plasma membrane to release their contents.
91
What two effects does the release of the contents of the cortical granules near the plasma membrane have?
1. It will cleave the receptors on the egg's surface.
2. It will sever the plasma membrane from the exterior membrane and create the space known as the fertilization envelope.
92
What is the slow block to polyspermy?
The cleavage of the receptors that worked in the ligand-receptor signaling system between egg and sperm.
93
How long does it take the slow block to polyspermy to develop, and how long does it last afterwards?
30 seconds to a minute, but after that it is permanent.
94
How do humans block polyspermy?
While sea urchins first use the fast block and then the slow block, humans only use the slow block.
95
Why do sea urchins use the fast block and humans don't?
In sea urchins, the competition for fertilization is fierce and the likelihood for polyspermy is very high because there are so many gametes in one location. In humans, the sperm must travel a farther distance to reach the egg, and the likelihood of two reaching the egg at the same time is small.
96
What is the cortical reaction?
The cortical reaction is a process initiated during fertilization that prevents polyspermy, the fusion of multiple sperm with one egg.
97
What drives the slow block to polyspermy?
The influx of calcium ions into the cytoplasm.
98
Besides blocking polyspermy, what other role does calcium have?
As a second messenger, calcium can activate the egg.
99
What does cleavage mean?
Cleavage refers to the first few division events of the fertilized egg and is characterized by rapid cell division but little growth in size.
100
How does cleavage change the structure of the developing embryo?
Cleavage results in blastomeres that form a blastula that surrounds a blastocoel.
101
Do humans mediate the blockage of polyspermy through calcium or sodium ions?
Calcium-mediated slow block only.
102
The sea urchin has a jelly coat surrounding its oocyte. What do humans have instead?
The zona pellucida.
103
Why is menopause an unusual phenomenon?
In most animals (including mammals), adults can reproduce throughout their lifetime. During menopause ovaries lose responsiveness to LH and FSH, thus reducing estradiol production.
104
About how many ovulation cycles do human females experience?
500 ovulation cycles.
105
Only humans and some primates undergo menstruation. What is the alternative for other animals?
Other animals have estrous cycles, where the uterus reabsorbs the endometrium.
106
What causes endometriosis?
Uterine cells migrate to an ectopic location and respond to hormones, causing pain and discomfort.
107
What is "the pill"?
The pill is synthetic estrogens and progestins that prevent pregnancy by inhibiting the production of GnRH, LH, and FSH. It shuts down the ovarian cycle.
108
What is "the morning after pill"?
Levonorgestrel or Plan B. It is a type of progestin that prevents ovulation (it is unclear how it works).
109
How does Mifepristone or RU-486 work?
The abortion pill prevents the activation of progesterone receptors in endometrial cells, thereby inducing menstruation. Mifepristone is followed a couple of days later by Misoprostol to control bleeding.
