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Weeks 4: Male Endicrinology & Spermatogenesis & Folliculogenesis

Terms in this set (98)

Leydig cells
Luteinizing hormone acts on these cells within the testes. They are named after German Franz von Leydog and are analogous to the cells of the thecca interna of antral follicles in the ovary.
Lh hormone receptors. When LH binds to these receptors, Leydig cells synthesize progesterone, most of which is then converted to testosterone.
Leydig cells have receptors for what hormone? When these receptors are bound what hormone is produced and then converted into testosterone and long after receptor binding does this occur?
refractory (unresponsive or not yielding to treatment). This is caused by reduction in the number of LH receptors in the cells, and as a result, rediced secretion of testerone by the cells follows.
LH pulses are important because sustained levels of LH could result in the Leydig cells becoming ____________. How does this occur?
1. adequate secretion of GnRH from the hypothalamus
2. FSH (follicle stimulating hormone) and LH (luteinizing hormone) secretion from the anterior love of the pituitary
3. secretion of gonadal steroids (testosterone and estradiol)
What are the endocrine requirements for spermatozoa can be produced?
discharge of GnRH occurs in frequent, intermittent episodes that occur day and night. these short-lived bursts of GnRH last only few minutes and cause the discharge of LH that follow almost immediately. LH episodes last 10-20 minutes and occur 4-8 times/day every 24 hours.
How long are the pulses that discharge GnRH? How long are the pulses for LH?
FSH concentrations are lower, but the pulses are longer duration than LH b/c of the relatively constant secretion of inhibin by the adult testis Sertoli cells and longer half-life of FSH.
What are pulses for FSH like?
1. high concentrations of testosterone in the seminiferous tubules
2. low concentrations of testosterone in a systemic blood
3.pulsatile GnRH secretion every 3-6 hours
4.adequate LH receptors in Leydig cells
What five requirements are needed for successful testis function?
This is important b/c it keeps system concentrations well below that which would cause down-regulation of the GnRH/LH feed-back system.
Why is it important that testosterone levels are heavily diluted before entering the systemic blood?
Sertoli cells
These cells convert testosterone to estradiol utilizing a mechanism identical to the granulosal cells of the antral follicle in the female. They also secrete inhibin that in females suppresses FSH secretion from the anterior love of the pituitary. This cell's function is FSH dependent.
follicle theca interna cells, follicular granulosal cells
Leydig cells are equivalent to the ____________________ in females, while Sertoli cells are the equivalent to the ______________________ in females.
Estradiol is a hormone that has a negative feedback role on the hypothalamus, hence a (-) feedback on GnRH, and in turn LH and FSH.
What is a possible reason for Sertoli cells converting testosterone to estradiol?
seminiferous tubules
Spermatogenesis occurs solely in the _______________.
1. provide a continual supply of male gametes(up to decades) through stem cell renewal
2. provide genetic diversity
3. provide billions of sperm each day to maximize reproduction by both natural service and artificial insemination
4. provide an immunologically priviledged site where developing germ cells are not destroyed by the male's immune system
What are the goals of spermatogenesis?
1.proliferation phase
2.meiotic phase
3.differentiation phase
What are the three phases of spermatogenesis?
In meiosis I, genetic diversity is guaranteed by DNA replication and crossing over during the production of secondary spermatocytes. so genetically no two sperm are the same.
How are no two sperm genetically identical?
proliferation phase
first phase of spermatogenesis in which all mitotic divisions of spermatogonia occur. A-spermatogonia udnergo divisions to generate a lto of B-spermatogonia. this phase includes stem cell renewal
stem cell renewal meiotic phase
this process is a part of the proliferation phase. loss of intercellular bridges allows some spermatogonia to revert to stem cells providing continual renewal of these stem cells from which new spermatogonia can develop
meiosis / meiotic phase
second phase in spermatogenesis that begins w/ primary spermatocytes. In meiosis I, genetic diversity is guaranteed by DNA replication and crossing over during the production of secondary spermatocytes. Conclusion of meiosis II produces haploid (1N) spermatids
spermatids
one of the haploid cells that are formed by the second division in meiosis of a spermatocyte and that differentiate into spermatozoa
differentiation phase
third & final phase of spermatogenesis, no further cell divisions occur. This phase is also referred to as "spermiogenesis" in which a spherical undifferentiated spermatid undergoes a remarkable transformation that results in the production of a fully differentiated, specialized spermatozoon
spermatogonia
immature germ cells that are specialized diploid (2n) are also called
intercellular bridges
tissue that connects developing germ cells, made up of the cytoplasm of the entire group of cells that are the same type. these structures provide communication b/w cells that contributes to synchronized developement of the group
head (nuclear material), a flagellum including a mid-piece (w/ a mitochondrial helix), and a principal piece
What are the three pieces of a sperm?
basal compartment
place within the seminiferous epithelium where primitive spermatogonia are found
cohort (groups of cell of the same type)
Various phases of sperm are connected by intercellular bridges which means their __________ is interconnected.
1. preleptotene
2. leptotene
3. zygotene
4. pachytene
5. diplotene
What are the five stages of the meiotic prophase?
It refers to segments of one chromosome crossing-over to a homologous chromosome when the chromatids separate, which results in a random assortment of different segments of each chromosome. This means that prophase of the first meiotic division insures genetic heterogeneity so each secondary spermatocyte and every spermatid will be genetically unique
What does the term "crossing-over" refer to and why is it important?
A-spermatogonia
spermatogonia that undergo several mitotic divisions in which they progress from A1-A4. stem cells also divide mitotically to give a continuous source of these types of spermatogonia
I-spermatogonia
...
B-spermatogonia
spermatogonia that undergo mitotic division to form primary spermatocytes that then enter the first meiotic prophase. they must go through all phases before meiotic divisions occurs.
crossing-over
this process occurs within the preleptotene phase, DNA replication forms tetrads without separation. these tetrads then fuse at random points called chiasmata.
purpose is to deliver the male's genetic material to an oocyte during fertilization
what is the purpose of a spermatozoon?
flagellum
a slender threadlike structure, especially a microscopic whiplike appendage that enables spermatozoa to swim.
1. golgi phase
2. cap phase
3. acrosomal phase
4. maturation phase
Name and describe the four phases that take place during differentiation
...
During what phase does the nucleus begin to elongate?
mitochondrial helix
metabolic "powerplant" needed for spermatids to swim
golgi phase
phase one of differentiation characterized by the first steps in the development of the acrosome/acrosomic vesicle. Spermatid has a golgi apparatus that is the intra cellular "packaging" system in secretory cells.
1. proacrosomic vesicles are formed and fused to create a large acrosomic vesicle one one side of the nucleus. this vesicle contains dense acrosomic granule.
2. centrioles migrate from cytoplasm to base of the nucleus and proximal centriole will give rise to an implantation apparatus that allows flagellum to be anchored to the nucleus. distal centriole creates axoneme.
acrosomic vesicle
vesicle created by proacrosomic vesicles that form and fuse from the golgi.
acrosomic granule
dense material found within acrosomic vesicles
cap phase
second phase of differentiation for spermatids where acrosomic vesicle spreading over the nucleus occurs, forming a distinct cap over the anterior portion of the nucleus.
1. golgi moves away from the nucleus towards the caudal end of the spermatid and eventually disappears.
2. primitive flagellum (tail) begins to project from the spermatid toward the lumen of the seminiferous tubule
acrosomeal phase
third phase of spermatid differentiation during which nuclear and cytoplasmic elongation occurs.
1. acrosome continues to spread until it covers about 2/3 of the anterior nucleus
2. nucleus begins to elongate
3. microtubules system (manchette) develops near the area of the posterior nucleus
4. portions of the manchette attach to the region of the nucleus just posterior to the acrosome
spermatids become deeply embedded in Sertoli cells w/their tails protruding toward the lumen of the seminiferous tubule
manchette
unique system of microtubules that develops during the acrosomal phase
ponstnuclear cap
structure formed by some of the microtubules of the manchette
maturation phase
final phase of spermatid differentiation in which microtubules of manchette direct formation of the postnuclear cap
1. mitochondria migrate toward and cluster around the flagellum in the region posterior to the nuclear
2. mitochondria quickly assemble around the flagellum in a spiral fashion from the base of the nuclear to the anterior 1/3 of the tail and form the middle piece in fully differentiated spermatozoa
3.dense out fibers of the flagellum and fibrous sheath are made and final assembly is complete
entire spermatozoon is covered with a plasma membrane, which is necessary for survival and function of spermatozoa
spermiation
the final release of spermatozoa from the Sertoli cells into the lumen of the seminiferous tubules after the maturation step.
keratinized
the chromatin in the nuclear membrane is compacted and almost intern because it is ______________. Keratinoid proteins (hair, claws, hoofs and feathers) have a high degree of disulfide cross-linking and are quite insoluble.
protamines
small, arginine-rich nuclear proteins thought to be essential for DNA condensation. these proteins replace nuclear histones of the haploid sperm nucleus during spermiogenesis . the sufihydral groups of these proteins form disulfide bonds, which are the basis for nuclear condensation that results in a highly compact stable nucleus that forms the sperm head.
acrosome
membrane-bound lysosome covering 2/f of the nucleus that contains hydrolytic enzymes acrosin, hyaluronidase, zona lysin, esterases, acid hydrolases. these enzymes are necessary for penetration of the cellular investments and the zona pellucida of the ovulated oocyte
acrosome reaction
an ordered, highly specialized exocytosis during fertilization that allows the release of the enzymes that are packaged in it to digest or penetrate the zona pellucida
nucleus, acrosome
middle piece, principal piece
The spermatozoa is comprised of a head and tail. The head contains ________, __________ and a post-nuclear cap while the tail contains ____________, ________________ and a terminal piece
ovulation, except that spermiation occurs continuously throughout the testis
Spermiation is analogous to ___________ in the female
disulfide bonds
What type of bonds are essential for nuclear condensation that results in a highly compact and stable nucleus that form the sperm head?
the inert nature of DNA is thought to be a mechanism to prevent damage to the DNA b/w spermiation and fertilization. At fertilization the process of reversed b/c disulfide cross-links within the sperm nucleus are reduced by the glutathione in the cytoplasm of the oocyte. similar to ovulation in the female
What is the reason behind the inert nature of DNA within the sperm head before fertilization? What is this similar to in the female?
glutathione
____________ in the oocyte cytoplasm is able to reduce the disculfide cross-links within the sperm nucleus, resulting in decondensation of the nucleus and formation of the male pronucleus
capitulum
part of sperm tail that fits into the implantation socket, a depression in the posterior nucleus.
middle piece
part of the sperm tail that consists of laminated columns that give the neck region flexibility so the tail can move side-to-side, a mitochondrial helix, and coarse outer fibers
principal piece
part of the sperm tail that consists of majority of the tail and continues to almost the end of the flagellum. It includes the fibrous helix, axoneme, coarse outer fibers, and longitudinal elements. The annulus demarcates the juncture between the middle and principal piece.
terminal piece
end of the sperm tail made up of microtubules
female's famete supply is produced entirely before birth. Maturation, meiosis and release of female gametes is pulsatile. In contrast, the male produces gametes continually and informally throughout his reproductive lifespan.
What are some differences between male and female gametogenesis?
seasonal
Male gametes are continually produced except for in _____________ breeders
2-4 week delay before the effects of deleterious events can be observed. 6-12 weeks is required before restoration of normal spermatogenesis can be accomplished after these events.
How long would it take to see a deleterious effect in sperm due to negative outside factors? (i.e. heat stress, exposure to toxins?
generations are a cohort of cells that develops as a synchronous group
When viewing a cross-section of a seminiferous tubules, one can see 4/5 "generations" of sperm. Explain what these generations are.
specific zones( cross-sections) where spermatozoa are released. the cells in other zones have not reached the appropriate stage of maturity for spermiation to occur, so that explain the specificity of cross-sections
At any given time, are spermatozoa ready to be released in any part of the seminiferous tubules or only specific zones? Explain
8, 13.5
There are _______ stages in the cycle of the seminiferous epithelium (according to your book) and requires _________ days to complete.
cycle of the seminiferous epithelium
progression through a complete series of cellular associations (stages) at one location along a seminiferous tubule.
stages of the cycle of the seminiferous epithelium
I, II, III, IV, V, VI, VII, VIII (see page 214/215). arbitrarily defined cellular associations that transition one to the next at predictable intervals.
4.5
In the bull, the complete process of spermatogenesis takes 61 days and ________ cycles of the seminiferous epithelium
every year a new class of fresh (committed A-spermatogonia) enters the university in the fall (enters the spermatogenic pathway). Freshmen (A-spermatogonia) undergo changes during the first year, and then are sophomores (primary spermatocytes). They then undergo maturational changes and become juniors (secondary spermatocytes, though short-lived). Finally they are seniors (spermatids) and graduate after four years.
The "school year" for the cycle is only 13.5 days (in the bull). Every 13.5 days a new generation enters and a generation of seniors graduates. Graduation=spermiation. It takes 4 years to graduate, and 4.5 cycles for A-spermatogonium to become differentiated spermatozoon. major difference is that germinal elements have different lifespans, so primary has 21 days but secondary only exists for 1.7 days. at university, all classes have similar lifespans. another major difference is that primary secondary spermatocytes and spermatogonia (freshmen) divide and generate many spermatids. but at university, freshmen will have some drops outs, so there are always more freshmen than seniors. while in the differentiation cycle, there are more sperm as differentiation occurs.
Also there is death of primary spermatocytes, in contrast from a university where each student can choose their pace, the pace through spermatogenesis is identical and not affected by environment.
How is the cycle of seminiferous epithelium analogous to the university system and how is it different?
constant
The physiologic importance of the spermatogenic wave is to provide a ______________ supply of spermatozoa to the epididymis.
spermatogenic wave
the differences at any given instant in time along the length of the seminiferous tubules. the sequential ordering of stages along the length of the seminiferous tubule.
daily sperm production
the total number of spermatozoa produced per day by both testicles of the male.
efficiency of sperm production
the number of spermatozoa produced per day per gram of testicular parenchyma
measuring total number of spermatozoa ejaculated into an artificial vagina with daily ejaculations for 2-3 weeks gibes a good estimate of DSP
What is one non-invasion way to measure daily sperm production?
tom cat: produces the most daily spermatozoa
man: produces the least daily spermatozoa
rooster: produces the most sperm per gram of testicular parenchyma
man: produces the least sperm per gram of testicular parenchyma
What species in table 10-2 produces the most daily spermatozoa? What species produces the least? What species produces the most sperm per gram of testicular parenchyma? The least?
Sertoli
The higher number of ________ cells, the higher the spermatozoal production rates.
testicular
Theoretically, the greater the ___________ circumference, the greater the sperm producing capability.
scrotal width or length is used as the measurement in boar and stallion
How is the scrotum measured in species with non-pendular scrotums?
Hormonally induced ovulation is generally coupled with induced estrus and requires premature luteolysis. Superovulation is due to an abnormally high # of follicles that are selected followed by ovulation. It requires the administration of exogenous gonadotropins that cause abnormally high numbers of follicles to be selected. Superovullated female ovulate abnormally high numbers of ova.
What is the difference between hormonally induced ovulation and superovulation?
prostaglandin F2a
Premature luteolysis can be accomplished by administering exogenous _______________.
endogenous GnRH, which stimulates the release of FSH and LH from the anterior lobe of the pituitary
The decline in progesterone in response to luteolysis allows________________ to be released. This hormone stimulates further of what two hormones and from where?
methods of superovulation include injections of equine chorionic gonadotropin (eCG) or FSH followed by LH, GnRH, or human chorionic gonadotropin (hCG) several days later to induce ovulation. they must be given a higher than normal FSH level so more follicles are recruited and selected.
What hormones are involved in superovulation and why are they used?
Maturation begins during embryonic development of the female and continues throughout her reproductive lifetime.
1. Mitotic division of primordial germ cells (prenatal)
2. nuclear arrest (dictyotene)
3. cytoplasmic growth
4. resumption of meiosis
What are the four phases of oocyte maturation?
prenatally to ensure the female is born w/ a complete supply of germ cells that will provide a future follicular reserve. last mitotic division from oogonia to the primary oocyte is important b/c the primary oocyte enters the first meiotic prophase.
When does mitotic division of primordial germ cells occur in the female?
nuclear arrest. the purpose is to inactivate the DNA in the female gamete so that it may not be vulnerable to possible insult during the lifetime of the female. Insults (damage) to DNA could compromise reproduction b/c embryo death would likely occur after fertilization.
What phase does the oocyte remain in until puberty? What is the purpose of this arrest?
It is the cytoplasm formed by primary oocytes during cytoplasmic growth phase , and this is formed during the secondary follicle stage
What is the zona pellucida and when is it formed?
junctions at which cells contact for communication between the oocyte and the adjacent granulosal cels. permits ionic and electronic coupling between different cell types. their presence is important after the formation of the zona pellucida b/c it would serve as a barrier limiting diffusion of materials needed for growth of the oocyte. junction complexes help overcome this transport problem.
What are junctional complexes/gap junctions?
granulosal
_____________ cells mediate oocyte maturation.
oocyte
The ______________ is responsible for synthesis of the zona pellucida
mucopolysaccharide
_____________________ is the precursor to the zona pellucida
oocyte, LH surge
When the oocyte reaches its maximum size, ___________ resumes when the ovulatory ___ ________ occurs
Cyclic AMP (cAMP) Preovulatory discharge of gonadotropins is needed to release the oocyte from granulosal cells. When granulosal projections dissociate from the cytoplasm of the oocyte, cAMP is not longer available to inhibit the oocyte.
___________ produced by granulosa cells is the primary inhibitor of meiotic resumption. How does the oocyte become free of this inhibition?
a substance thought to assist in controlling the resumption of meiosis, though its exact role remains uncertain.
What is oocyte meiotic inhibitor?
dog and the fox
In what species does ovulation occur before meiosis is resumed?
this constitutes an early morphologic sign of the initiation of final oocyte maturation. this takes place after the preovulatory surge of LH in rodents and carnivores
What is peripheral migration of the nucleus a sign of and when does it occur?
the first polar body is formed via the first meiotic division that occurs before ovulation. the second polar body is produced after fertilization and after the second meiotic division.
What are the first and second polar bodies and when do they occur?
Gonadotrophin releasing hormone : hypothalamus
Testosterone: testes
Lutienizing hormone: Pituitary
Follicle Stimulating Hormone: Pituitary
There are three levels of hormone regulation required for sperm production. Match the hormone to the organ that produces it.
Primary spermatocyte
The meiotic phase of spermatogenesis begins with which cell type
VIII
When a spermatid nears spermiation it has entered what stage?
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