Male Reproductive System II Flashcards
(33 cards)
1
Q
What is the typical sequence of spermatogenesis?
A
- Starting at the basement mb and moving towards the lumen, basally, Spermatogonia (A”1”) -> 2 Spermatogonia (A”2”) -> 4 Spermatogonia (A”3) & so on during PROLIFERATION (# of divisions depends on sp)
Spermatogonia (A”3”) -> Spermatogonia (A”4”) -> Spermatogonia (I) -> Spermatogonia (B) -> then adluminally -> primary spermatocytes -> meiosis I -> secondary spermatocytes -> meiosis II -> Spermatids -> undergo DIFFERENTIATION
2
Q
What is another name for proliferation?
A
spermatocytogenesis
3
Q
what is another name for differentiation?
A
spermiogenesis
4
Q
What do male germline stem cells do?
A
- thread 1 generation to the next
- include PGCs, gonocytes, SPERMATOGONIAL STEM CELLS (SSCs)
5
Q
What are spermatogonial stem cells?
A
- can self-renew & produce differentiated germ cells
- are the only adult stem cells that can pass on genes to the next generation
6
Q
What are the two proposed models for the formation of spermatogonial stem cells (SSCs)?
A
- all gonocytes are the same but some (randomly) transition to SSCs, which can renew & give rise to progenitors, while others directly give rise to differentiating spermatogonia
- PGC -> gonocyte -> (SSC -> progenitor -> A”1” -> sperm) OR (A”1” -> sperm) - different types of gonocytes are responsible for forming the SSC pool, initial progenitor population, & initial differentiating spermatogonial population
- PGC -> Gonocyte -> (SSC -> progenitor -> A”1” -> sperm) OR (progenitor -> A”1” -> sperm) OR (A”1” -> sperm)
7
Q
What are the possible outcomes of SSC division?
A
- self-renewal capability is important in ensuring SSC pool maintenance
- self-renewal & maintenance must be kept in balance, or it may lead to either germ cell tumour or depletion of SSCs
- DURING NEONATAL DEVELOPMENT & FOR REGENERATION of spermatogenesis after cytotoxic insult, SYMMETRICAL SELF RENEWAL may predominate
Symmetrical self renewal:
SSC -> SSC & SSC - DURING STEADY-STATE SPERMATOGENESIS, BALANCE OF SYMMETRICAL SELF-RENEWAL & SYMMETRICAL DIFFERENTIATION may occur @ defined frequencies
Symmetrical differentiation:
SSC -> committed progenitor spermatogonia - RECENT EVIDENCE SUPPORTS ASYMMETRIC DIVISION of an SSC to produce 1 new SSC & 1 transient amplifying progenitor
Asymmetric division:
SSC -> (SSC) OR (transient amplifying progenitor spermatogonia -> committed progenitor spermatogonia) OR (transient amplifying progenitor spermatogonia -> transient amplifying progenitor spermatogonia -> committed progenitor spermatogonia)
8
Q
Process of A”1” to spermiation?
A
Spermatogenic stem cell (pool of undifferentiated spermatogonia -> transit amplifying progenitor cells ) -> differentiating spermatogonia (8.6 days) -> preleptotene -> meiosis -> spermiogenesis -> spermiation
(approximately 35 days from A”1” to spermiation)
9
Q
What happens at the undifferentiated spermatogonia stage?
A
- spermatogonia classified into undifferentiated & differentiating
- in rodents & most domestic spp, spermatogenesis starts w/ division of SPERMATOGONIA TYPE A”single” (A”s”)
- divide to form 2 new A”s” for self-renewal or a connected pair called A”pair” (A”pr”) for differentiation
- in rodents, further divisions lead to formation of type A”aligned” (A”al”) which remain as chains of 4, 8, or 16 cells
- UNDIFFERENTIATED SPERMATOGONIA (TYPES A”s”, A”pr”, & A”al”) HAVE SIMILAR CELLULAR MORPHOLOGY
- A”s” are rare & relatively quiescent & represent ‘TRUE SSC’
- A”pr” & A”al” cells may have some SSC potential but are on way toward differentiation & called ‘TRANSIT AMPLIFYING PROGENITOR CELLS’
10
Q
What are differentiating spermatogonia?
A
- Retinoic acid causes A”al” to transition (w/o cell division) to A”1” to start differentiation
- involves major changes in morphology & mitotic behaviour
- then 5 synchronized cell divisions to form A”2”, A”3”, A”4” intermediate (In), & B-spermatogonia
- DIFFERENTIATING SPERMATOGONIA include A”1-4”, I, & B-spermatogonia
- B-spermatogonia must physically pass through the blood-testis barrier before further germ cell differentiation
11
Q
What are primary & secondary spermatocytes?
A
- once in adluminal compartment, B- spermatogonia divide again to produce 2 PRIMARY SPERMATOCYTES that immediately enter the 1st phase of meiosis
- during the long prophase of 1st meiosis, DNA undergoes complete replication to form tetrads, followed by crossing over of homologous chromosomes to ensure genetic heterogeneity of gametes
- primary spermatocytes go through 5 stages, PRELEPTOTENE, LEPTOTENE, ZYGOTENE, PACHYTENE, & DIPLOTENE
- @ end of 1st meiosis, each primary spermatocyte has produced 2 SECONDARY SPERMATOCYTES (haploid, N), which are relatively short-lived & immediately undergoes the second meiotic division
12
Q
How are round & elongating/elongated spermatids formed?
A
- @ end of Meiosis II, each secondary spermatocyte has produced 2 haploid ROUND (spherical) SPERMATIDS
- no further cell division will occur
- testosterone drives round spermatids to undergo extensive morphological differentiation known as SPERMIOGENESIS
- which leads to formation of ELONGATING/ELONGATED SPERMATIDS
- retinoic acid causes spermatozoa to be released into lumen of the seminiferous tubule during SPERMIATION process
13
Q
What is differentiation or spermiogenesis?
A
- extensive morphological changes occur to turn a round spermatid into a sperm
- these changes include: formation of acrosome, condensation of nuclear material, outgrowth of a motile tail, & loss of excess cytoplasm, organelles, water (volume in later maturation phase is 20-30 % of a cap phase spermatid)
- can be divided into 4 phases (golgi phase -> cap phase -> acrosomal phase -> maturation phase)
14
Q
What is the golgi phase?
A
- newly formed spermatid is spherical & has a well-developed Golgi apparatus
- small golgi vesicles fuse to form “PROACROSOMIC” secretory granules & centrioles start migrating to opposite side
- ACROSOMAL VESICLE (granule is formed), PROXIMAL CENTRIOLE (PC; will give rise to attachment point of tail), DISTAL CENTRIOLE (DC; will give rise to axoneme)
15
Q
What is the cap phase?
A
- golgi migrates to caudal pole & distal centriole (DC) forms AXONEME (AX) or flagellum
- acrosomic vesicle flattens & begins to form a cap & CAP has an outer acrosomal membrane (OAM) & an inner acrosomal membrane (IAM) & enzymes
16
Q
What is the acrosomal phase?
A
- nucleus begins to elongate & acrosome covers most of its anterior & MANCHETTE forms from caudal half & extends down
- neck & annulus are formed, all components still w/in cytoplasm
17
Q
What is the maturation stage?
A
- mito form a spiral assembly around the flagellum that defines the middle piece
- POSTNUCLEAR CAP is formed from manchette microtubules
- ANNULUS forms the junction btwn the middle piece & the principal piece
18
Q
How do sperm vary in length btwn spp?
A
- 50 microm in humans
- 60 in boar & stallion
- 75 in Ru
- 150-250 rodents
19
Q
What 2 parts do the sperm seem to only consist of under a light microscope?
A
head & tail
20
Q
What does the post-nuclear cap consist of & what does it help evaluate?
A
fibrous sulfur-rich proteins (stain intense w/ eosin-bromophenol blue in dead sperms, helps in evaluating the quality of the ejaculate)
21
Q
What is the structure of the sperm head?
A
- head differs in different spp (generally spatula shaped in most but in rodents is sickle shaped)
- nucleus is oval, flat, & covered by a nuclear membrane
- chromatin is compacted & inactive due to high keratinoid proteins
- anterior 2/3rds of nucleus is covered by acrosome
22
Q
what is an acrosome?
A
membrane covered lysosome containing hydrolytic enzymes (ex: acrosin, hyaluronidase, zona lysin, esterases, acid hydrolase)
23
Q
what is an acrosome reaction?
A
during fertilization acrosome undergoes a specialized exocytosis
24
Q
What is the post-acrosomal sheath?
A
region contains receptors for recognition of homologous oocyte
25
What is the structure of the sperm tail?
- tail is composed of capitulum, middle piece, principal piece, & terminal piece
26
What is the capitulum of the sperm tail?
fits into the implantation socket of the head
27
What is the middle piece of the sperm tail?
- has laminated columns, gives side-to-side flexibility to neck
- 9 course outer fibers
- axoneme composed of 9 pairs of microtubules (DOUBLETS) around 2 central filaments
- all covered by a helical mitochondrial sheath
28
What is the principal piece of the sperm tail?
forms majority of tail & continues to almost the end of the flagellum
29
What is the terminal piece of the sperm tail?
is where only microtubules remain
30
When do the stages of spermatogenesis take place?
- sperm production takes time & in non-seasonal males should be continuous
- before 1 spermatogenic series is completed, generally 4 or more new series are initiated
- all descendants of B-spermatogonia develop synchronously
- successive generations follow each other
- so spermatogenic cycle is divided into stages or cellular associations
- these are arbitrarily defined associations that transition 1 to the next at predictable intervals
- identical associations are found in cross sections
- ex: in bulls, rams, & sw there are 8 stages
31
What are the stages along a seminiferous tubule?
- @ any given cross section along a seminiferous tubule a different stage of cycle can be seen
- each stage follows or precedes adjacent stages
- complete sequence of stages (I through VIII) along a length of tubule is called a spermatogenic wave
- spermatogenic wave in bulls is ~10 mm long
32
How are LH & testosterone linked?
- each LH pulse drives a pulse of testosterone release by Leydig cells
- each remains high in serum for ~0.5-1 hr
33
How is spermatogenesis regulated by hormones?
- involves interplay btwn endocrine & paracrine/autocrine systems
- FSH acts on Sertoli cells to promote their function & facilitate spermatogenesis
- LH acts on Leydig cells to stimulate production of testosterone
- testosterone & inhibin act through a negative feedback mechanism to temporarily inhibit further release of GnRH, FSH, & LH
- FSH increases proliferation of spermatogonia
- w/in tubules, FSH receptors are only found on Sertoli cells, suggesting indirect FSH effects on germ cells
- FSH has little or no direct effect on completion of meiosis & spermatogenesis
- testosterone is crucial for transition of spermatocytes to spermatids
- owing to countercurrent system of pampiniform plexus, testosterone in testis is 100-500x higher than in circulation
- both testosterone withdrawal & lack of androgen receptors can result in lack of post-meiotic germ cells
- similar to FSH, any effect of testosterone on germ cells is indirect & mediated through somatic cells
- androgen receptors are absent in germ cells but abundant in Sertoli, peritubular myoid, & Leydig cells
- E"2" is converted from testosterone by aromatase in Sertoli cells
- lack of ERalpha or aromatase leads to spermatogenesis impairment in mice
