MCAT Biology Review - Chapter 2: The Cell Cycle and Mitosis

Question 1

When autosomal cells are said to be diploid (2n), what does this mean?

Answer 1

They contain two copies of each chromosome.

Question 2

What cells are considered haploid (n), where they only contain one copy of each chromosome?

Answer 2

Reproductive cells in the human body AKA Germ cells (i.e., sperm cell in males and egg cells in women)

Question 3

Are many chromosomes do haploid (n) and diploid (2n) cells have?

Answer 3

23 and 46, respectively.

23 chromosomes are inherited each parent.

Question 4

What is a specific series of phases during which a eukaryotic cell grows, synthesizes DNA, and divides?

Answer 4

The cell cycle

Derangements of the cell cycle can lead to unchecked cell division and may be responsible for the formation of cancer.

Question 5

What stages exist within the cell cycle for actively dividing cells?

Answer 5

G1, S, G2, and M.

Question 5

What are the three stages collectively known as interphase?

Answer 5

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.

Question 6

Where do cells that DO NOT divide spend all of their time within the cell cycle?

Answer 6

An offshoot of G1 called G0.

The cell is simply living and carrying out its functions, without any preparation for division.

Question 7

During interphase, why are individual chromosomes not visible with light microscopy and why?

Answer 7

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.

Question 8

When is it preferable to condense the DNA into tightly coiled chromosomes to avoid losing any genetic material during cell division?

Answer 8

During mitosis

Question 9

What are cells doing during the G1 (Presynthetic) stage of the cell cycle?

Answer 9

Cells create organelles for energy and protein productions (mitochondria, ribosomes, and endoplasmic reticulum), while also increasing their size.

Question 10

How is passage in the cell cycle to the S stage governed by?

Answer 10

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.

Question 11

What stage within the cell cycle involves the cell replicating its genetic material so that each daughter cell will have identical copies?

Answer 11

The S (synthesis) stage

Question 12

After DNA is replicated within the cell cycle during the S stage, what do the chromosomes consist of?

Answer 12

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.

Question 13

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?

Answer 13

The G2 Stage: Postsynthetic Gap

Question 14

What does the M stage within the cell cycle consist of?

Answer 14

Mitosis itself along with cytokinesis

Question 15

What are the 4 stages that mitosis is divided into?

Answer 15

Prophase, Metaphase Anaphase, and Telophase.

Question 16

What is cytokinesis within the M stage; the last stage within the cell cycle?

Answer 16

Cytokinesis is the splitting of the cytoplasm and organelles between the two daughter cells

Question 17

T/F Autosomal and germ cells when undergoing division produce identical daughter cells.

Answer 17

False. Only when autosomal cells divide are their daughter cells identical. With germ cells, the daughter cells are NOT identical.

Question 18

Where are the two notable checkpoints within the cell cycle located?

Answer 18

Between G1 and S phase and between G2 and M phase.

Question 19

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?

Answer 19

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.

Question 20

What molecules are responsible for the cell cycle?

Answer 20

Cyclins and cyclin-dependent kinases (CDKs)

In order to be activated, CDKs require the presence of the right cyclins.

Question 21

Explain how CDKs and cyclins influence the cell cycle throughout its stages.

Answer 21

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.

Question 22

After CDKs and cyclins form the CDK-cyclin complex, what is the job of the complex?

Answer 22

The complex can be then phosphorylate transcription factors which promote transcription of genes required for the next stage of the cell cycle.

Question 23

Why is the cell cycle SO essential?

Answer 23

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.

Question 24

What is the most common mutation found in cancer?

Answer 24

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.

Question 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?

Answer 25

Metastasis

Question 26

What are cancer-causing genes classified as?

Answer 26

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.

Question 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?

Answer 27

Mitosis.

Question 28

What is the first phase of mitosis called where the first step within this phase involves condensation of the chromatin into chromosomes?

Answer 28

Prophase

The centriole pair separate and move toward opposite poles of the cell as well during this step of this phase.

Question 29

Where are the paired cylindrical organelles, known as the centrioles, located and what are they responsible for?

Answer 29

They are located in the centrisome and are responsible for the correct division of DNA.

Question 30

At what point, during the prophase, do the centrioles start to form spindle fibers, which are made of microtubules?

Answer 30

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.

Question 31

As the fibers radiate outwards from the centrioles of the cell to the center, what do some of the microtubles form?

Answer 31

Asters

These asters anchor the centrioles to the cell membrane.

Question 32

What dissolves during prophase, which allows the spindle fibers to contact the chromosomes?

Answer 32

The nuclear membrane

The nucleoli become less distinct and may disappear completely.

Question 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)?

Answer 33

Kinetochores

Question 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?

Answer 34

Metaphase

Question 35

During which phase do the centromeres split so that each chromatid has its own distinct centromere, thus allowing the sister chromatids to separate?

Answer 35

Anaphase

The sister chromatids are pulled toward the opposite poles of the cell by the shortening of the kinetochore fibers.

Question 36

Explain Telophase, the fourth and final phase within mitosis.

Answer 36

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

Question 37

What do the two nuclei during telophase currently have when it comes to genomic material?

Answer 37

They recieved a complete copy of the genome identical to the original genome and to each other.

Question 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?

Answer 38

Cytokinesis.

Question 39

T/F Each cell undergoes a finite number of divisions before programmed for death.

Answer 39

True. For human somatic cells, this is usually 20 to 50. After that, a cell can no longer divide continously.

Question 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)?

Answer 40

Meiosis

Question 41

What are the similarities that meiosis shares with mitosis? (3)

Answer 41

• Genetic material is duplicated in both processes
• Chromatin is condensed to form chromosomes
• Microtubules emanating from centrioles are involved in dividing genetic material

Question 42

In contrast to mitosis, which consists of one round of replication and division, how many rounds of replication and division exist in meiosis?

Answer 42

One round of replication followed by two rounds of division

Question 43

What results from reductional division in Meiosis I?

Answer 43

Homologous chromosomes are separated, generating two haploid (n) daughter cells

Question 44

What results from equational division in Meiosis II?

Answer 44

It is similiar to mitosis, in that it results in the separation of sister chromatids without a change in ploidy.

Question 45

What is the human genome comprised of?

Answer 45

23 Homologous pairs of chromosomes (homologues)

Each of which contains one chromosome inherited from each parent.

Question 46

What is the differenence between homologous pairs and sister chromatids?

Answer 46

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.

Question 47

During Meiosis l, in which phase does the chromatin condense into chromosomes, the spindle apparatus forms, and the nucleoli and nuclear membrane disappear?

Answer 47

Prophase I

Question 48

What is the first major difference between meiosis and mitosis in prophase?

Answer 48

Homologous chromosomes come together and intertwine in a process called synapsis

Question 49

After synapsis and when the homologous chromosomes become a synaptic pair containing four chromatids, what is this referred as?

Answer 49

A tetrad

Question 50

What are the homologous chromosomes held together by a group of proteins called?

Answer 50

Synaptonemal complex

Question 51

Where might chromatids of homologous chromosomes break at the point of contact called?

This process allows them to exchange equivalent pieces of DNA

Answer 51

The chiasma (plural chiasmata)

Question 52

When the chromatids of homologous chromosomes break off at the chiasma, this process is called?

Answer 52

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.

Question 53

What does crossing over lead eventually lead to?

Answer 53

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.

Question 54

What does genetic linkage refer to?

Answer 54

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.

Question 55

What type of advantage does sexual reproduction provide over asexual reproduction?

Answer 55

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.

Question 56

Which Mendel’s law does crossing over explain?

Answer 56

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.

Question 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?

Answer 57

Metaphase l

Question 58

What is the difference between Metaphase for Mitosis and the Metaphase for Meiosis?

Answer 58

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.

Question 59

What happens during Anaphase l for Meiosis where the homologous pairs separate and are pulled to opposite poles of cell?

Answer 59

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.

Question 60

In Anaphase l, what do you call the separation of the two homologous chromosomes?

Answer 60

Segregation

Question 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.

Answer 61

Telophase I

The cells are now becoming haploid; once homologous chromosomes separate, only n chromosomes are found in each daughter cell (23 in humans).

Question 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?

Answer 62

Cytokinesis; Interkinesis

Question 63

T/F Meiosis ll is very different to mitosis.

Answer 63

False. It is very similar to mitosis in that sister chromatids–rather than homologues–are separated from each other.

Question 64

Briefly explain what happens in Prophase II.

Answer 64

The nuclear envelope and nucleoli disappear

The centrioles migrate to opposite poles, and the spindle apparatus begins to form

Question 65

Briefly explain what happens in Metaphase II.

Answer 65

The chromosomes line up on the metaphase plate.

Question 66

Briefly explain what happens in Anaphase II.

Answer 66

The centromeres divide, separating the chromosomes into sister chromatids.

These chromatids are pulled to opposite poles by spindle fibers.

Question 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?

Answer 67

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).

Question 68

Explain briefly what happens in Telophase ll.

Answer 68

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)

Question 69

What are the 4 main differences between Mitosis and Meiosis?

Answer 69

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

Question 70

How is biological sex determined?

Answer 70

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.

Question 71

Which sex chromosome carries a significant amount of genetic information; and mutations in these genes can cause sex-linked disorders?

Answer 71

The X chromosome

Sex-linked disorders AKA X-linked disorders.

Question 72

What are males termed with respect to many of the genes on the X chromosome because they only have one copy?

Answer 72

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.

Question 73

T/F Most X-linked disorders are recessively inherited; therefore, females express these disorders far more frequently than males.

Answer 73

False. Females express these disorders far LESS frequently than males since they have two X sex chromosomes.

Question 74

What do you call females carrying a diseased allele on an X-chromosome but not exhibiting the disease?

Answer 74

A carrier.

Question 75

T/F The Y chromosome contains very little genetic information.

Answer 75

True.

Question 76

What is the notable gene on the Y chromosome?

Answer 76

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.

Question 77

In males, what do their primitive gonads develop into and what are their two functional components?

Answer 77

The testes

The two functional components are the seminiferous tubules and the interstitial cells of Leydig

Question 78

Where are the sperm produced? What are sperm nourished by?

Answer 78

In the highly coiled seminiferous tubules.

They are nourished by Sertoli cells.

Question 79

What does the cells of Lydig accomplish?

Answer 79

They secrete testosterone and other male sex hormones (androgens).

Question 80

Where are the testes located?

Answer 80

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.

Question 81

What does the body do in order for the testes to maintain the proper temperature for sperm development?

Answer 81

The layer of muscle around the vas deferens (dutus deferens) that can raise and lower the testis from the body to maintain proper temperature.

Question 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?

Answer 82

The epididymis

Question 83

Where do the sperm travel during ejaculation?

Answer 83

They travel through the vas deferens and enter the ejaculatory duct at the posterior edge of the prostate gland.

Question 84

What forms the urethra, which carries sperm through the penis as they exit the body?

Answer 84

The fusion of both ejaculatory ducts.

Question 85

T/F The reproductive and urinary systems in both men and women share a common pathway.

Answer 85

False. Men do, however, females do not.

Question 86

What are sperm mixed with as they pass through the reproductive tract?

Answer 86

Seminal fluid

Question 87

What are the three components of the male reproductive system that, through combined effort, produce seminal fluid?

Answer 87

Seminal vesicles, prostate gland, and bulbourethral gland.

Question 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?

Answer 88

Seminal vesicles

Question 89

What produces a clear visvous fluid that cleans out any remnants of urine and lubricates the urethra during sexual arousal?

Answer 89

Bulbourethral (Cowper’s) glands

Question 90

What is the name for combination of sperm and seminal fluid?

Answer 90

Semen

Question 91

Quick Review of the Pathway for Sperm through the male reproductive system:

SEVE(N) UP

Answer 91

Seminiferous tubules
Epididymis
Vas deferens (also called the ductus deferens)
Ejaculatory duct
(N)othing
Urethra
Penis

Question 92

What happens to the prostate in men when they age?

Answer 92

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.

Question 93

What do you call the formation of haploid sperm through meiosis, that occurs in the seminiferous tubules?

Answer 93

Spermatogensis

Question 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?

Answer 94

Spermatogonia.

Primary Spermatocytes

Secondary Spermatocytes; Spermatids

Spermatozoa

Four functional sperm for each spermatogonium

Question 95

What are the three parts that mature sperm consist of and what do they accomplish? Vague answer OK

Answer 95

The head (containing genetic material), a midpiece (which generates ATP from fructose), and a flagellum (for motility)

Question 96

Why does the midpiece of the sperm that is filled with mitochondria need to generate energy?

Answer 96

It needs the energy to swim through the female reproductive tract to reach the ovum in the fallopian tubes.

Question 97

Why does each sperm head covered by a cap known as an acrosome and where is it derived from?

Answer 97

The acrosome is necessary to penetrate the ovum and it is derived from the Golgi apparatus.

Question 98

Bonus Question

Once reaching sexual maturity, how much sperm does a male produce per day for the rest of his life?

Answer 98

3 million sperm!

Question 99

What are the gonads called within the female reproductive system?

Answer 99

Ovaries which produce estrogen and progesterone.

Question 100

What do the ovaeries, located within the pelvic cavity, consist of?

Answer 100

Consists of thousands of follicles, which are multilayered sacs that contain, nourish, and protect immature ova (eggs).

Question 101

Between puberty and menopause, how many eggs per month are ovulated into the peritoneal sac, which lines the abdominal cavity?

Answer 101

One egg

Question 102

Where does the ovulated egg go once leaving the ovary?

Answer 102

It is drawn into the fallopian tube or oviduct, which is lined with cilia to propel the egg forward.

Question 103

What is the site of fetal development within the female reproductive system and how is it connected?

Answer 103

The muscular uterus and it is connected by the fallopian tubes for ovulated eggs.

Question 104

What is the lower end of the uterus called and what does it connect to which is where sperm are depositied during intercourse?

Answer 104

The cervix and it is connected to the vaginal canal.

The vagina is also the passageway through which childbirth occurs.

Question 105

What do you call the external female anatomy collectively?

Answer 105

The vulva

Remember: Females have separate excretory and reproductive tracts

Question 106

What is the production of female gametes called?

Answer 106

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….

Question 107

What happens once a woman reaches menarche (first menstrual cycle)?

Answer 107

One primary oocyte per month will complete meiosis l, producing secondary oocyte and a polar body.

Question 108

Why does meiosis l in oogenesis produce one secondary oocyte and one polar body?

Answer 108

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.

Question 109

What happens after the primary oocyte is divided into a secondary oocyte and one polar body?

Answer 109

The seconday oocyte remains arrected in metaphase ll and does not complete the remainder of meiosis ll unless fertilization occurs.

Question 110

What are the two layers that the oocytes are surrounded by?

What are their roles?

Answer 110

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.

Question 111

When is Meiosis ll triggered in oogensis and what is produced?

Answer 111

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.

Question 112

What are some basic facts about the mature ovum?

Answer 112

• 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

Question 113

What does the haploid pronuclei of the sperm and the ovum create once joining? Include ploidy!

Answer 113

They create a diploid zygote

Question 114

What is the ability to reproduce under control of?

Answer 114

HORMONES!

Question 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?

Answer 115

HORMONES!

The hypothalamus restricts production of the gonadotropin-releasing hormone (GnRH)

Question 116

Once puberty starts and the hypothalamus releases pulses of gonadotropin-releasing hormone (GnRH), what is triiggered and what is released?

Answer 116

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.

Question 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?

Answer 117

Nine weeks after fertilization until birth.

Question 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?

Answer 118

Low

Testosterone

Question 119

In order for testosterone production to increase dramtically during puberty, what needs to happen in respect to other hormones?

Answer 119

FSH stimulated the Sertoli cells and triggers sperm maturation

LH stimulates interstitial cells to produce testosterone.

Question 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.

Answer 120

Testosterone; while also maintaining the male reproductive system

However, production of this hormone does remain high but then decreases as men age.

Question 121

How does testosterone affect and influence the hypothalamus and anterior pituitary gland so that production is kept within the appropriate range?

Answer 121

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.)

Question 122

T/F The ovaries are also under the control FSH and LH secreted by the anterior pituitary.

Answer 122

True.

Remember: The ovaries produce estrogens and progesterone.

Question 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)?

Answer 123

Estrogens

Question 124

What do estrogens do in the embryo? What do estrogens do in adults?

Answer 124

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.

Question 125

Real World

If the receptors for testosterone are absent or defective, what happens?

Answer 125

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)

Question 126

What is progesterone secreted by? When does this particular situation end?

Answer 126

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.

Question 127

What is interesting about how progesterone influences the body?

Answer 127

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.

Question 128

What are the reproductive years of a woman?

Answer 128

From menarch to menopause.

Question 129

What are the two general variables of a woman’s menstrual cycle?

Answer 129

• 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!

Question 130

What are the four events within the menstrual cycle?

Answer 130

• The follicular phase
• Ovulation
• The luteal phase
• Menstruation

Question 131

When does the follicular phase begin?

Answer 131

It begins when the menstrual flow, which sheds the uterine lining of the previous cycle, begins.

Question 132

What does GnRH secretion from the hypothalamus increase in response to?

And what do higher concentrations of GnRH cause?

Answer 132

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.

Question 133

Once GnRH has increased in concentration, and more FSH and LH are being secreted, what do these two hormones accomplish?

Answer 133

These hormones work in concert to develop several ovarian follicles.

Question 134

While the follicular phase has begun and the ovarian follicles have developed, what do the follicles accomplish?

Answer 134

The follicles begin to produce estrogen, which has negative feedback effects and causes the GnRH, LH, and FSH concentration to level off.

Question 135

In the follicular phase, the estrogen has caused hormone levels to level off, but what as the produced estrogen from the follicles stimulate?

Answer 135

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.

Question 136

What stages of the menstrual cycle belong within the follicular phase?

Answer 136

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).

Question 137

Getting close to ovulation, how does estrogen secreted from the follicles act as both a negative and positive feedback?

Answer 137

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.

Question 138

Why is the surge in LH (much higher than FSH, estrogen, and progesterone) so important during the menstrual cycle?

Answer 138

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.

Question 139

During the Luteal phase, after ovulation, what causes the ruptured follicle to form the corpus luteum, which secretes what?

Answer 139

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.

Question 140

How does the body, during the luteal phase, prevent the body from ovulating multiple eggs?

Answer 140

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.

Question 141

Knowing what you know about the mentrual cycle now, how do oral contraceptives (OCPs) work on the female body?

Answer 141

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.

Question 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?

Answer 142

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.

Question 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?

Answer 143

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.

Question 144

In the second trimester of pregnancy, what begins to happen to the hCG levels?

Answer 144

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.

Question 145

What happens to a woman’s ovaries as she ages?

Answer 145

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.

Question 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.

Answer 146

(No Answer)