MCAT Biology Review - Chapter 2: The Cell Cycle and Mitosis Flashcards
1
Q
When autosomal cells are said to be diploid (2n), what does this mean?
A
They contain two copies of each chromosome.
2
Q
What cells are considered haploid (n), where they only contain one copy of each chromosome?
A
Reproductive cells in the human body AKA Germ cells (i.e., sperm cell in males and egg cells in women)
3
Q
Are many chromosomes do haploid (n) and diploid (2n) cells have?
A
23 and 46, respectively.
23 chromosomes are inherited each parent.
4
Q
What is a specific series of phases during which a eukaryotic cell grows, synthesizes DNA, and divides?
A
The cell cycle
Derangements of the cell cycle can lead to unchecked cell division and may be responsible for the formation of cancer.
5
Q
What stages exist within the cell cycle for actively dividing cells?
A
G1, S, G2, and M.
5
Q
What are the three stages collectively known as interphase?
A
The first three, G1, S, G2.
Interphase is the longest part of the cell cycle even actively dividing cells spend about 90 percent of their time in interphase.
6
Q
Where do cells that DO NOT divide spend all of their time within the cell cycle?
A
An offshoot of G1 called G0.
The cell is simply living and carrying out its functions, without any preparation for division.
7
Q
During interphase, why are individual chromosomes not visible with light microscopy and why?
A
They are in a less condensed form known as chromatin in order for the DNA to be available to RNA polymerase so that genes can be transcribed.
8
Q
When is it preferable to condense the DNA into tightly coiled chromosomes to avoid losing any genetic material during cell division?
A
During mitosis
9
Q
What are cells doing during the G1 (Presynthetic) stage of the cell cycle?
A
Cells create organelles for energy and protein productions (mitochondria, ribosomes, and endoplasmic reticulum), while also increasing their size.
10
Q
How is passage in the cell cycle to the S stage governed by?
A
A restriction point.
Certain criteria, such as containing the proper complement of DNA, must be met for the cell to pass the restriction point and enter the S (synthesis) stage.
11
Q
What stage within the cell cycle involves the cell replicating its genetic material so that each daughter cell will have identical copies?
A
The S (synthesis) stage
12
Q
After DNA is replicated within the cell cycle during the S stage, what do the chromosomes consist of?
A
Two identical chromatids that are bound together at a specialized region known as the centromere.
Cells entering G2 phase from the S phase have twice as much DNA as cells in G1.
13
Q
Which stage within the cell cycle is another quality control checkpoint where the DNA has already duplicated and the cell checks to ensure that there are enough organelles and cytoplasm for two daughter cells; and, also checks to make sure that DNA replication proceeded correctly to avoid passing on an error to daughter cells that may further pass on the error to their progeny?
A
The G2 Stage: Postsynthetic Gap
14
Q
What does the M stage within the cell cycle consist of?
A
Mitosis itself along with cytokinesis
15
Q
What are the 4 stages that mitosis is divided into?
A
Prophase, Metaphase Anaphase, and Telophase.
16
Q
What is cytokinesis within the M stage; the last stage within the cell cycle?
A
Cytokinesis is the splitting of the cytoplasm and organelles between the two daughter cells
17
Q
T/F Autosomal and germ cells when undergoing division produce identical daughter cells.
A
False. Only when autosomal cells divide are their daughter cells identical. With germ cells, the daughter cells are NOT identical.
18
Q
Where are the two notable checkpoints within the cell cycle located?
A
Between G1 and S phase and between G2 and M phase.
19
Q
The first control checkpoint, G1/S or restriction point, checks to see if there has been damage to DNA, otherwise the cell goes into arrest until the DNA has been repaired. What protein is in control of this process?
A
p53
P53 also plays a role in the G2/M checkpoint where the cell is mainly concerned with ensuring that it has achieved adequate size and the organelles have been properly replicated to support two daughter cells.
20
Q
What molecules are responsible for the cell cycle?
A
Cyclins and cyclin-dependent kinases (CDKs)
In order to be activated, CDKs require the presence of the right cyclins.
21
Q
Explain how CDKs and cyclins influence the cell cycle throughout its stages.
A
The right cyclins must be present to activate a variety of CDKs.
During the cell cycle, concentrations of the various cyclins increase and decrease during specific stages.
These cyclins bind to CDKs, creating an activated CDK-cyclin complex.
22
Q
After CDKs and cyclins form the CDK-cyclin complex, what is the job of the complex?
A
The complex can be then phosphorylate transcription factors which promote transcription of genes required for the next stage of the cell cycle.
23
Q
Why is the cell cycle SO essential?
A
It ensures that cells that are damaged or inadequately sized do not divide.
When the cell cycle control becomes deranged, and damaged cells are allowed to undergo mitosis, cancer may result.
24
What is the most common mutation found in cancer?
The mutation of the gene that produces p53, called TP53 which plays a role withint he checkpoints of the cell cycle.
The cell cycle never stops when a damaged cell is produces and replicates which allows mutations to accumlate, eventually resulting in a cancerous cell that divides continously and without regard to the quality or quantity of the new cells produced.
Often, cancer cells undergo rapid cell division, creating tumors.
25
What word describes when eventually, a damaged cell begins to produce the right factors (such as proteases that can digest basement membranes or factors that encourage blood vessel formation), and the cells are able to reach other tissues, either localized or distant, via the bloodstream or lymphatic systems?
Metastasis
26
What are cancer-causing genes classified as?
Oncogenes (genes that, when mutated, actively promote cell division)
Tumor suppressing genes (genes that, wehn mutated, lose their ability to regulate or arrest the cell cycle)
Different cancer types are often associated with one or the other or both of these cancer-causing genes.
27
What is the process by which two identical daughter cells are created from a single cell, has four distinct phases (prophase, metaphase, anaphase, and telophase), and occurs in somatic cells, or cells that are not involved in sexual reproduction?
Mitosis.
28
What is the first phase of mitosis called where the first step within this phase involves condensation of the chromatin into chromosomes?
Prophase
The centriole pair separate and move toward opposite poles of the cell as well during this step of this phase.
29
Where are the paired cylindrical organelles, known as the centrioles, located and what are they responsible for?
They are located in the centrisome and are responsible for the correct division of DNA.
30
At what point, during the prophase, do the centrioles start to form spindle fibers, which are made of microtubules?
The centrioles begin spindling fibers once they migrate to opposite poles of the cell.
This establishes the centrosome as one of the two microtubule organizing centers of the cell--the other being the basal body of a flagellum or cilium.
31
As the fibers radiate outwards from the centrioles of the cell to the center, what do some of the microtubles form?
Asters
These asters anchor the centrioles to the cell membrane.
32
What dissolves during prophase, which allows the spindle fibers to contact the chromosomes?
The nuclear membrane
The nucleoli become less distinct and may disappear completely.
33
What are the protein structures that appear and are located on the centromeres that serve as attachment points for specific fibers of the spinde apparatus (appropriately called kinetochore fibers)?
Kinetochores
34
What phase involves the kinetochore fibers interacting with fibers of the spingle apparatus to align the chromosomes at the metaphase plate (equatorial plate), which is equidistant from the two poles of the cell?
Metaphase
35
During which phase do the centromeres split so that each chromatid has its own distinct centromere, thus allowing the sister chromatids to separate?
Anaphase
The sister chromatids are pulled toward the opposite poles of the cell by the shortening of the kinetochore fibers.
36
Explain Telophase, the fourth and final phase within mitosis.
Telophase is essentially the reverse of prophase.
- Spindle apparatus dissapears
- Nuclear membrane reforms around each set of chromosomes; nucleoli reappears.
- Chromosomes uncoil, resuming their interphase (the resting phase between succesive mitotic divisions) form
37
What do the two nuclei during telophase currently have when it comes to genomic material?
They recieved a complete copy of the genome identical to the original genome and to each other.
38
What occurs at the end of the telophase within mitosis, and is the separation of the cytoplasm and organelles, giving each daughter cell enough material to survive on its own?
Cytokinesis.
39
T/F Each cell undergoes a finite number of divisions before programmed for death.
True. For human somatic cells, this is usually 20 to 50. After that, a cell can no longer divide continously.
40
Since mitosis occurs in somatic tissue and results in two identical daughter cells, what process occurs in gametocytes (germ cells) and results in up to four nonidentical sex cells (gametes)?
Meiosis
41
What are the similarities that meiosis shares with mitosis? (3)
- Genetic material is duplicated in both processes
- Chromatin is condensed to form chromosomes
- Microtubules emanating from centrioles are involved in dividing genetic material
42
In contrast to mitosis, which consists of one round of replication and division, how many rounds of replication and division exist in meiosis?
One round of replication followed by two rounds of division
43
What results from reductional division in Meiosis I?
Homologous chromosomes are separated, generating two haploid (n) daughter cells
44
What results from equational division in Meiosis II?
It is similiar to mitosis, in that it results in the separation of sister chromatids without a change in ploidy.
45
What is the human genome comprised of?
23 Homologous pairs of chromosomes (homologues)
Each of which contains one chromosome inherited from each parent.
46
What is the differenence between homologous pairs and sister chromatids?
Homologous pairs are considered separate chromosomes (such as maternal chromosome 15 and paternal chromosome 15)
Sister chromatids, however, are identical strands of DNA connected at the centromere.
Thus, after the S phase, there are 92 chromatids organized into 46 chromosomes, which are organized into 23 homologous pairs.
47
During Meiosis l, in which phase does the chromatin condense into chromosomes, the spindle apparatus forms, and the nucleoli and nuclear membrane disappear?
Prophase I
48
What is the first major difference between meiosis and mitosis in prophase?
Homologous chromosomes come together and intertwine in a process called synapsis
49
After synapsis and when the homologous chromosomes become a synaptic pair containing four chromatids, what is this referred as?
A tetrad
50
What are the homologous chromosomes held together by a group of proteins called?
Synaptonemal complex
51
Where might chromatids of homologous chromosomes break at the point of contact called?
This process allows them to exchange equivalent pieces of DNA
The chiasma (plural chiasmata)
52
When the chromatids of homologous chromosomes break off at the chiasma, this process is called?
Crossing over
It can be characterized by the number of crossover events that occur in one strand of DNA, including single crossovers and double crossovers.
Note: Crossing over occurs between homologous chromosomes and not between sis chromatids of the same chromosome--the latter are identical, so crossing over would not produce any change.
Those chromatids involved are left with an altered but structurally complete set of genes.
53
What does crossing over lead eventually lead to?
Genetic recombination and the resultant recombiant chromosomes.
This can unlink linked genes, thereby increasing a variety of genetic combinations that can be produced via gametogenesis.
54
What does genetic linkage refer to?
It referes to the tendency of genes to be inhereted together; genes that are located farther from each other physically are less likely to be inherited together, and more likely to undergo crossing over relative to each other.
55
What type of advantage does sexual reproduction provide over asexual reproduction?
As opposed to asexual reproduction, which produces identical offspring, sexual reproduction provides the advantage of great genetic diversity, which is believed to increase the ability of a species to evolve and adapt to a changing environment.
56
Which Mendel's law does crossing over explain?
Mendel's second law of independent assortment, which states that the inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes.
57
During Meiosis I, which phase has the homolgous pairs (tetrads) align at the metaphase plate, and each pair attaches to a separate spindle fiber by its kinetochore?
Metaphase l
58
What is the difference between Metaphase for Mitosis and the Metaphase for Meiosis?
In mitosis, each chromosome is lined up on the metaphase plate by two spindle fibers (one from each pole); in meiosis, homologous chromosomes are lined up across from each other at the metaphase plate and are held by one spindle fiber.
59
What happens during Anaphase l for Meiosis where the homologous pairs separate and are pulled to opposite poles of cell?
Process called disjunction, and it accounts for Mendel's first law of segregation.
During disjunction, each chromosome of paternal origin separates (or disjoins) from its homologue of maternal origin, and either chromosome can end up in either daughter cell. Thus, the distribution of homologous chromosomes to the two intermediate daughter cells is random with respect to parental origin.
60
In Anaphase l, what do you call the separation of the two homologous chromosomes?
Segregation
61
During Meiosis I, during what phase does a nuclear membrane form around each new nucleus? And at this point, each chromosome still consists of two sister chromatids joined at the centromere.
Telophase I
The cells are now becoming haploid; once homologous chromosomes separate, only n chromosomes are found in each daughter cell (23 in humans).
62
During Telophase l in Meiosis I, how does the cell divide into two daughter cells? And what is the short rest period during which the chromosomes partially uncoil?
Cytokinesis; Interkinesis
63
T/F Meiosis ll is very different to mitosis.
False. It is very similar to mitosis in that sister chromatids--rather than homologues--are separated from each other.
64
Briefly explain what happens in Prophase II.
The nuclear envelope and nucleoli disappear
The centrioles migrate to opposite poles, and the spindle apparatus begins to form
65
Briefly explain what happens in Metaphase II.
The chromosomes line up on the metaphase plate.
66
Briefly explain what happens in Anaphase II.
The centromeres divide, separating the chromosomes into sister chromatids.
These chromatids are pulled to opposite poles by spindle fibers.
67
Real World
What happens if, during anaphase l or ll of meiosis, homologous chromosomes (anaphase l) or sister chromatids (anaphase ll) fail to separate?
So subsequently, during fertilization, the resulting zygote may have too many or too few copies of that chromosome which results in what?
One of the resulting gametes will have two copies of a particular chromosomes and the other gamete will have none.
Nondisjunction can affect both autosomal chromosomes (such as trisomy 21, resulting in Down syndrome) and the sex chromosomes (such as klinefelter and Turner syndromes).
68
Explain briefly what happens in Telophase ll.
A nuclear membrane forms around each nucleus. Cytokinesis follows and two daughter cels are formed. Thus, by completion of Meiosis, up to four haploid daughter cells are produced per gametocyte.
We use the phrase up to because oogenesis may result in fewer than four cells if an eff remains unfertilized after ovulation. (only 1 of 4 sex cells becomes an egg cell that can be fertilized)
69
What are the 4 main differences between Mitosis and Meiosis?
Mitosis is 2n -> 2n, which Meiosis is 2n -> n
Mitosis occurs in all dividing cells while meiosis occurs in sex cells only
In mitosis, the homologous chromosomes do not pair, which the ones in meiosis do pair and align on opposite sides of the metaphase plate
No crossing over occurs in Mitosis while it can occur in Meiosis
70
How is biological sex determined?
The 23rd chromosome
XX being female, while XY being male.
Ova can only carry the X chromosome, while the sperm can carry X or Y chromosome.
71
Which sex chromosome carries a significant amount of genetic information; and mutations in these genes can cause sex-linked disorders?
The X chromosome
Sex-linked disorders AKA X-linked disorders.
72
What are males termed with respect to many of the genes on the X chromosome because they only have one copy?
Hemizygous
Therefore, a male with a disease-causing allele on the unpaired part of X chromosome will necessarily express that allele.
Females, on the other hand, may be homozygous or heterozygous with respect to genes on the X chromosome.
73
T/F Most X-linked disorders are recessively inherited; therefore, females express these disorders far more frequently than males.
False. Females express these disorders far LESS frequently than males since they have two X sex chromosomes.
74
What do you call females carrying a diseased allele on an X-chromosome but not exhibiting the disease?
A carrier.
75
T/F The Y chromosome contains very little genetic information.
True.
76
What is the notable gene on the Y chromosome?
SRY (sex-determining region Y), which codes for a transcription factor that initiates testis differentition and, thus, the formation of male gonads.
Therefore, in the absence of the Y chromosome, all zygotes will be female. In the presence of the Y chromosome a zygote will be male.
There are actually a handful of Y-linked diseases, most of which result in reduced fertility, most of which result in reduced fertility. A father will pass a Y-linked disease to all of his sons, assuming fertility has not been lost. These diseases are extremely rare.
77
In males, what do their primitive gonads develop into and what are their two functional components?
The testes
The two functional components are the seminiferous tubules and the interstitial cells of Leydig
78
Where are the sperm produced? What are sperm nourished by?
In the highly coiled seminiferous tubules.
They are nourished by Sertoli cells.
79
What does the cells of Lydig accomplish?
They secrete testosterone and other male sex hormones (androgens).
80
Where are the testes located?
In the scrotum, an external pouch that hangs below the penis, a position that allows it to maintain a temperature 2 degrees Celsius to 4 degrees Celsius lower than the body.
81
What does the body do in order for the testes to maintain the proper temperature for sperm development?
The layer of muscle around the vas deferens (dutus deferens) that can raise and lower the testis from the body to maintain proper temperature.
82
Once the sperm are developed in the seminiferous tubules, where are they passed to where the flagella gain motility, and are stored until ejaculation?
The epididymis
83
Where do the sperm travel during ejaculation?
They travel through the vas deferens and enter the ejaculatory duct at the posterior edge of the prostate gland.
84
What forms the urethra, which carries sperm through the penis as they exit the body?
The fusion of both ejaculatory ducts.
85
T/F The reproductive and urinary systems in both men and women share a common pathway.
False. Men do, however, females do not.
86
What are sperm mixed with as they pass through the reproductive tract?
Seminal fluid
87
What are the three components of the male reproductive system that, through combined effort, produce seminal fluid?
Seminal vesicles, prostate gland, and bulbourethral gland.
88
Within the male reproductive system, what contributes fructose to nourish sperm, and helps (prostate glands help, too!) give seminal fluid its mild alkaline properties so the sperm can survive in the relative acidity of the female reproductive tract?
Seminal vesicles
89
What produces a clear visvous fluid that cleans out any remnants of urine and lubricates the urethra during sexual arousal?
Bulbourethral (Cowper's) glands
90
What is the name for combination of sperm and seminal fluid?
Semen
91
Quick Review of the Pathway for Sperm through the male reproductive system:
SEVE(N) UP
Seminiferous tubules
Epididymis
Vas deferens (also called the ductus deferens)
Ejaculatory duct
(N)othing
Urethra
Penis
92
What happens to the prostate in men when they age?
It enlarges frequently causing problems, including benign prostatic hyperplasia.
Because the prostate surrounds the urethra, classic symptoms of this condition include urinary frequency, urgency, and nighttime awakenings to use the bathroom.
93
What do you call the formation of haploid sperm through meiosis, that occurs in the seminiferous tubules?
Spermatogensis
94
In males, what is the name of DIPLOID stem cells?
What are they called after replicating their genetic material (S stage)?
What are they then called AFTER the first meiotic division? Second meiotic division?
Lastly, when the sperm mature, what are they called?
Ok... Through this whole process of division to maturation, what does spermatogenesis result in?
Spermatogonia.
Primary Spermatocytes
Secondary Spermatocytes; Spermatids
Spermatozoa
Four functional sperm for each spermatogonium
95
What are the three parts that mature sperm consist of and what do they accomplish? Vague answer OK
The head (containing genetic material), a midpiece (which generates ATP from fructose), and a flagellum (for motility)
96
Why does the midpiece of the sperm that is filled with mitochondria need to generate energy?
It needs the energy to swim through the female reproductive tract to reach the ovum in the fallopian tubes.
97
Why does each sperm head covered by a cap known as an acrosome and where is it derived from?
The acrosome is necessary to penetrate the ovum and it is derived from the Golgi apparatus.
98
Bonus Question
Once reaching sexual maturity, how much sperm does a male produce per day for the rest of his life?
3 million sperm!
99
What are the gonads called within the female reproductive system?
Ovaries which produce estrogen and progesterone.
100
What do the ovaeries, located within the pelvic cavity, consist of?
Consists of thousands of follicles, which are multilayered sacs that contain, nourish, and protect immature ova (eggs).
101
Between puberty and menopause, how many eggs per month are ovulated into the peritoneal sac, which lines the abdominal cavity?
One egg
102
Where does the ovulated egg go once leaving the ovary?
It is drawn into the fallopian tube or oviduct, which is lined with cilia to propel the egg forward.
103
What is the site of fetal development within the female reproductive system and how is it connected?
The muscular uterus and it is connected by the fallopian tubes for ovulated eggs.
104
What is the lower end of the uterus called and what does it connect to which is where sperm are depositied during intercourse?
The cervix and it is connected to the vaginal canal.
The vagina is also the passageway through which childbirth occurs.
105
What do you call the external female anatomy collectively?
The vulva
Remember: Females have separate excretory and reproductive tracts
106
What is the production of female gametes called?
Oogenesis
Although gametocytes undergo the same meiotic process in both females and males, there are some significant differences between the two sexes.
First, there is no unending supply of stem cells analogous to spermatogonia in females; all of the oogonia a woman will ever have formed during fetal development. By birth, all of the oogonia have already undergone DNA replication and are considered primary oocytes (2n).
These cells are then arrested in prophase l until menarch.
Wow....
107
What happens once a woman reaches menarche (first menstrual cycle)?
One primary oocyte per month will complete meiosis l, producing secondary oocyte and a polar body.
108
Why does meiosis l in oogenesis produce one secondary oocyte and one polar body?
The division is characterized by unequal cytokinesis, which distributes ample cytoplasm to one daughter cell (the secondary oocyte) and nearly none to the other (the polar body).
The polar body generally does not divide any further and will never produce functional gametes.
109
What happens after the primary oocyte is divided into a secondary oocyte and one polar body?
The seconday oocyte remains arrected in metaphase ll and does not complete the remainder of meiosis ll unless fertilization occurs.
110
What are the two layers that the oocytes are surrounded by?
What are their roles?
The zona pellucida and the corona radiata.
The zona pellucida surrounds the oocyte itself and is an acellular mixture of glycoproteins that protect the oocyte and contain compounds necessary for sperm cell binding
The corona radiata lies outside the zona pellucida and is a layer of cells that adhered to the oocyte during ovulation.
111
When is Meiosis ll triggered in oogensis and what is produced?
Meiosis ll is triggered once the sperm cell penetrates the zona pellucida and the corona radiata.
The secondary oocyte undergoes the second meiotic division to split into a mature ovum and another polar body, which will eventually be broken down.
112
What are some basic facts about the mature ovum?
- It is a very large cell consisting of large quantities of cytoplasm and organelles
- The ovum contributes nearly everything to the zygote (half the DNA and all of the cytoplasm, organelles [including mitochondria], and RNA for early cellular processes
- Sperm only contribute to half of the DNA
113
What does the haploid pronuclei of the sperm and the ovum create once joining? Include ploidy!
They create a diploid zygote
114
What is the ability to reproduce under control of?
HORMONES!
115
What is the ability to reproduce under control of?
Prior to puberty, WHAT restricts production of WHAT and the restriction is lifted at the start of puberty?
HORMONES!
The hypothalamus restricts production of the gonadotropin-releasing hormone (GnRH)
116
Once puberty starts and the hypothalamus releases pulses of gonadotropin-releasing hormone (GnRH), what is triiggered and what is released?
The anterior pituitary gland is triggered to synthesize and release follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
These hormones trigger the production of other sex hormones that develop and maintain the reproductive system.
117
At what point during the gestation period does the presence of the Y chromosome lead to production of androgens, resulting in male sexual differentiation?
Nine weeks after fertilization until birth.
118
For the duration of infancy and childhood, is androgen production low or high?
And what, produced by the testes, increases dramatically during puberty, and sperm production begins?
Low
Testosterone
119
In order for testosterone production to increase dramtically during puberty, what needs to happen in respect to other hormones?
FSH stimulated the Sertoli cells and triggers sperm maturation
LH stimulates interstitial cells to produce testosterone.
120
What results in the development of secondary sexual characteristics such as facial and axillary hair, deepening of the voice, and increased muscle and bone mass.
Testosterone; while also maintaining the male reproductive system
However, production of this hormone does remain high but then decreases as men age.
121
How does testosterone affect and influence the hypothalamus and anterior pituitary gland so that production is kept within the appropriate range?
Through negative control
(Negative feedback occurs when a system's output acts to reduce or dampen the processes that lead to the output of that system, resulting in less output. In general, negative feedback loops allow systems to self-stabilize. Negative feedback is a vital control mechanism for the body's homeostasis.)
122
T/F The ovaries are also under the control FSH and LH secreted by the anterior pituitary.
True.
Remember: The ovaries produce estrogens and progesterone.
123
What hormone is secreted in response to FSH in female sexual development and results in the development and maintenance of the female reproductive system and female secondary sexual characteristics (breast growth, widening of the hips, changes in fat distribution)?
Estrogens
124
What do estrogens do in the embryo? What do estrogens do in adults?
In the embryo, estrogens stimulate the development of the reproductive tract.
In adults, estrogens lead to the thickening of the lining of the uterus (endometrium) each month in preparation for the implantation of a zygote.
125
Real World
If the receptors for testosterone are absent or defective, what happens?
It cannot exert its effects.
The result is a condition called androgen insensitivity syndrome (AIS), in which a genetic male (XY) has female secondary characteristics.
In complete AI, a genetic male will appear female at birth. Oftentimes these individuals are not discovered until puberty, when they are examined for amenorrhea (failure to menstruate)
126
What is progesterone secreted by? When does this particular situation end?
Corpus Luteum -- the remains of the ovarian follicle following ovulation--in response to LH.
By the end of the first trimester of a pregnancy, progesterone is supplied by the placenta, while the corpus luteum atrophies and ceases to function.
127
What is interesting about how progesterone influences the body?
It is involved with development and maintenance of the endometrium, but not in the initial thickening of the endometrium (this is actually the role of estrogen)
Both are needed for the development of the endometrium to make it capable of supporting a zygote.
Mnemonic - ESTrogen ESTablishes and PROgesterone PROtects the endometrium.
128
What are the reproductive years of a woman?
From menarch to menopause.
129
What are the two general variables of a woman's menstrual cycle?
- Estrogen and progesterone levels rise and fall in a cyclic pattern
- In response, the endometrial lining will grow and shed
This is know as the menstrual cycle!
130
What are the four events within the menstrual cycle?
- The follicular phase
- Ovulation
- The luteal phase
- Menstruation
131
When does the follicular phase begin?
It begins when the menstrual flow, which sheds the uterine lining of the previous cycle, begins.
132
What does GnRH secretion from the hypothalamus increase in response to?
And what do higher concentrations of GnRH cause?
The decreased concentrations of estrogen and progesterone, which fall off toward the end of each cycle.
Higher concentrations of GnRH cause increased secretions of both FSH and LH.
133
Once GnRH has increased in concentration, and more FSH and LH are being secreted, what do these two hormones accomplish?
These hormones work in concert to develop several ovarian follicles.
134
While the follicular phase has begun and the ovarian follicles have developed, what do the follicles accomplish?
The follicles begin to produce estrogen, which has negative feedback effects and causes the GnRH, LH, and FSH concentration to level off.
135
In the follicular phase, the estrogen has caused hormone levels to level off, but what as the produced estrogen from the follicles stimulate?
The regrowth of the endometrial lining, stimulating vascularization and glandularization of the decidua (It is formed during the secretory phase of the menstrual cycle as a result of elevated ovarian hormones such as estrogen and progesterone)
So towards the end of this phase in the menstrual cycle is preparing the basal membrane to begin supporting the functional layer of the endometrium.
136
What stages of the menstrual cycle belong within the follicular phase?
The menses stage (when menstruation begins and endometrium is shed) and the proliferative stage (when the endometrium begins to grow; at the end of this stage, ovulation (day 14) begins).
137
Getting close to ovulation, how does estrogen secreted from the follicles act as both a negative and positive feedback?
As higher and higher concentrations of estrogen are secreted from ovarian follicles, they eventually reach a threshold which results in a positive feedback and GnRH, LH, and LSH spike; whereas estrogen is reduced right before the spike of the hormones.
138
Why is the surge in LH (much higher than FSH, estrogen, and progesterone) so important during the menstrual cycle?
It induces ovulation, the release of the ovum from the ovary into the abdominal (peritoneal) cavity.
Ovulation is the process in which a mature egg is released from the ovary.
139
During the Luteal phase, after ovulation, what causes the ruptured follicle to form the corpus luteum, which secretes what?
LH causes the ruptured follicle to form the corpus luteum, which then secretes progesterone.
Remember: Estrogen helps regenerate the uterine lining, but progesterone maintains it for implantation.
140
How does the body, during the luteal phase, prevent the body from ovulating multiple eggs?
Progesterone levels continue to rise higher as estrogen remains high, and these high levels of progesterone cause a negative feedback loop on GnRH, FSH, and LH, which prevents multiple eggs ovulating.
141
Knowing what you know about the mentrual cycle now, how do oral contraceptives (OCPs) work on the female body?
These OCPs are simply estrogen/progesterone (or progesterone-only) preparations. These block conception by inhibiting LH and FSH release through negative feedback, thereby inhibiting ovulation. When a woman takes the placebo pills at the end of the month, withdrawal menstruation still occurs because estrogen and progesterone levels drop, but no egg passes with the menstrual flow.
142
Assuming that implantation (egg is attached to the uterine lining) does not occur, what happens next?
What happens when the body loses its high levels of estrogen and progesterone?
The corpus luteum loses its stimulation from LH, progesterone levels decline, and the uterine lining is sloughed off.
It removes the block on GnRH so that the next cycle may begin.
143
In the case that fertilization has occured and the zygote develops into a blastocyst that will implant on the uterine lining, what will it begin to secrete?
What is the role of this hormone?
Human chorionic gonadotropin (hCG), an analog of LH -- it looks very similar chemically and can stimulate LH receptors.
hCG maintains the corpus luteum, and is CRITICAL in the first trimester development because the estrogen and progesterone secreted by the corpus luteum keep the uterine lining in place.
144
In the second trimester of pregnancy, what begins to happen to the hCG levels?
They decline because the placenta has grown to sufficient size to secrete enough progesterone and estrogen by itself. The high levels of estrogen and progesterone continue to serve as negative feedback on GnRH secretion.
145
What happens to a woman's ovaries as she ages?
Her ovaries become less sensitive to FSH and LH, resulting in ovarian atrophy.
As estrogen and progesterone levels drop, the endometrium also atrophies, and menstruation stops. Also, because the negative feedback on FSH and LH is removed, the blood levels of these two hormones rise. This is called menopause.
146
Menstrual Cycle Review (No Answer)
- Follicles mature during the follicular phase (FSH, FH)
- LH surge at midcycle triggers ovulation
- Ruptured follicle becomes corpus luteum, which secretes estrogen and progesterone to build up uterine lining in preparation for implantation; LH and FSH are inhibited.
- If fertilization does not occur, corpus luteum atrophies, progesterone and estrogen levels decrease, menses occurs, and LH and FSH levels begin to rise again.
(No Answer)
