Development Flashcards
What’s the difference between pluripotent, totipotent, and multipotent? How can you relate a spermatogonium, a primary spermatocyte, and a spermatid? Use these cards to see how all of these topics connect, and you can master reproduction and development as tested on the MCAT.
What is the function of the reproductive system?
It generates new offspring from parent organisms, facilitating the survival of the species.
Some reproductive methods also increase genetic variation. This allows a species to adapt to changes in its environment.
What is the difference between sexual and asexual reproduction?
- Sexual reproduction involves two organisms and results in offspring that genetically differs from both of them.
- Asexual reproduction is carried out by a single organism and produces genetically identical offspring.
All prokaryotes use asexual reproduction, though they have alternative methods of gene transfer. Eukaryotic species can reproduce sexually, asexually, or through both mechanisms.
Define:
gamete
A haploid cell that combines with another gamete during sexual reproduction. Together, the fused cells form a zygote that develops into a new organism.
In humans, the male gamete is the sperm while the female gamete is the egg or ovum.
Label the parts of the sperm cell below.
What is spermatogenesis, and when and where does it begin?
It is the production of the male gametes, sperm, in the seminiferous tubules of the testes.
Spermatogenesis begins at puberty.
Order the following terms from least to most mature: spermatid, spermatogonium, spermatozoon, secondary spermatocyte, primary spermatocyte.
- Spermatogonium
- Primary spermatocyte
- Secondary spermatocyte
- Spermatid
- Spermatozoon
Both meiosis and mitosis are involved in this differentiation process.
During which step of spermatogenesis do cells become haploid?
Meiosis I - the division from primary to secondary spermatocyte.
After this transition, the gamete will be haploid but with replicated chromosomes.
Meiosis II, on the other hand, refers to the division from secondary spermatocyte to spermatid. After this step, the gamete will be haploid with only one copy of each chromosome, as in its final state.
Around what age in men does sperm production cease?
Spermatogenesis never ceases; it continues throughout a man’s adult life.
In contrast, oogenesis does not occur as a steady process. Virtually all of a woman’s eggs are partially differentiated by birth, and all differentiation ceases completely at menopause.
What is oogenesis, and where and when does it begin?
It is the production of the female gametes, ova, in the ovaries.
Oogenesis begins before birth. Specifically, all of a female’s oocytes are produced and arrested at prophase I by the time she is born.
Order the following terms from least to most mature: primary oocyte, ovum, oogonium, secondary oocyte.
- Oogonium
- Primary oocyte
- Secondary oocyte
- Ovum
Both meiosis and mitosis are involved in this differentiation process.
Define:
polar body
A haploid cell produced by meiosis I or meiosis II of oogenesis.
Though they possess normal amounts of genetic material, polar bodies contain little cytosol and few organelles.
Oogenesis is thus characterized by uneven division of cytoplasm. Most of the cytoplasm is allocated to the functioning oocyte, while little is given to the polar body.
How many cells are produced in the differentiation of one primary oocyte into one mature ovum?
Oogenesis produces three cells per primary oocyte:
- one ovum
- two polar bodies
In meiosis I, the primary oocyte divides into one secondary oocyte and one polar body. This first polar body generally does not divide further. If fertilized, the secondary oocyte undergoes meiosis II, where it divides into one ovum and a second polar body.
From birth until puberty, all of a female’s oocytes are arrested at which stage of oogenesis?
All of a female’s oocytes are primary and are arrested in prophase I of meiosis.
Meiosis I corresponds to which step of oogenesis?
Meiosis I involves the division of a primary into a secondary oocyte.
Meiosis II, which is only completed if the egg is fertilized, involves the division of this secondary oocyte into a mature ovum.
Name two differences between spermatogenesis and oogenesis.
- Spermatogenesis produces four equally functional gametes; it takes place continuously from puberty to death.
- Oogenesis produces one mature ovum and two nonfunctional polar bodies; it begins before birth and ends at menopause.
Which gamete contributes mitochondria to the developing zygote?
ovum
While sperm contain mitochondria, they are destroyed by the ovum shortly after fertilization. As a result, mitochondrial diseases are inherited maternally.
Define:
gonads
These are endocrine organs that produce gametes.
The female gonads are the ovaries while the male gonads are the testes.
What is an androgen?
It is a general term for a hormone that influences male development.
The most important androgen to know is testosterone, a steroid hormone.
Name the major male and female sex hormones.
- testosterone in males
- estrogen and progesterone in females.
While these hormones are steroids, their production is closely related to that of the peptides FSH and LH.
Give two structural differences between the male and female reproductive systems.
Male:
- reproductive organs are mainly found outside of the body
- the urethra serves both reproductive and urinary purposes
Female:
- reproductive organs are located internally
- the urethra solely involved in urination
Define:
puberty
The period of the human lifespan during which the reproductive system becomes mature.
In females, this process is marked by menarche, or the first menstrual period. In males, spermatogenesis begins at puberty.
In females, which process involves a decrease in sex hormones and the halting of ovulation?
menopause
Specifically, menopause is the period when menstrual cycles stop occurring and a female can no longer become pregnant.
On the diagram below, label the ovaries, Fallopian tubes, uterus, and vagina.
What is another term used for the Fallopian tubes?
oviducts
Each Fallopian tube connects a single ovary to the uterus.
What are follicles, and in which female reproductive structure are they located?
These are multicellular structures located within the ovaries. Each follicle surrounds and nourishes a single oocyte.
During ovulation, the follicle bursts and develops into the corpus luteum.
Once every 28 days, one follicle ruptures inside the ovary, releasing an oocyte into the Fallopian tube. What term is used to refer to this process?
ovulation
In which structure of the female reproductive system does the fertilized zygote implant?
The endometrium (lining) of the uterus.
Immediately after ovulation, this lining begins to thicken to provide a favorable environment for the potential zygote.
What is the length of an average menstrual cycle?
28 days
How do the phases of the uterine cycle match up with the ovarian cycle?
The follicular phase encompasses both menstruation and the proliferative phase, while the luteal phase aligns perfectly with the secretory phase.
Define:
placenta
The organ through which a fetus obtains nutrients and performs gas exchange.
The placenta also performs endocrine functions, secreting estrogen, progesterone, and hCG.
On the diagram below, label the testes, epididymis, vas deferens, prostate gland, and urethra.
What process occurs in the epididymis?
The sperm become fully mature and motile. This structure also stores sperm after they are made.
Name two male reproductive glands and describe their functions.
- Prostate gland secretes a basic solution that protects the sperm from acidic conditions.
- Bulbourethral or Cowper’s glands produce a lubricating fluid prior to ejaculation.
Trace the path of a zygote from the point of fertilization to the point of implantation. What structures does it encounter?
Fertilization occurs in the Fallopian tubes. From there, the zygote travels directly to the uterus and implants in the endometrium, or uterine lining.
Define:
morula
The name given to the embryo after multiple cleavage divisions. This structure is extremely dense.
The morula later develops into the blastula.
What is a blastocyst, and from what other structure does it arise?
A hollow cell arrangement that develops from the morula. A blastocyst contains a central blastocoel, a dense inner cell mass, and a surrounding trophoblast.
What is gastrulation, and which germ cell layers does it produce?
It is the differentiation of the blastula into three distinct layers: the ectoderm, the mesoderm, and the endoderm.
Define:
ectoderm
It is the outermost germ layer formed during development.
Structures arising from the ectoderm include the eyes, skin, hair, nails, and nervous system.
Define:
mesoderm
It is the middle germ layer formed during development.
Structures arising from the mesoderm include blood vessels, gonads, and the muscular and skeletal systems. Note that the kidneys also derive from mesoderm, not endoderm.
Define:
endoderm
It is the innermost germ layer formed during development.
Structures arising from the endoderm include internal organs such as the pancreas and urinary bladder. The endoderm also gives rise to the linings of the digestive tract and lungs.
What process involves the differentiation of ectodermal tissue into the structures that will become the nervous system?
neurulation
The final product of neurulation is the neural tube, which develops into the central nervous system. Peripheral nervous structures arise from cells of the neural crest.
