15 - Spermatogenesis Flashcards
Goals of spermatogenesis (4)
- provide a male with continual supply of gametes
- provide billions of sperm each day to maximize reproductive efficiency
- provide genetic diversity (each sperm has unique DNA)
- provide an immunologically privileged site where spermatogenic cells will not be destroyed by males immune system
Where does spermatogenesis occur? What happens after
Occurs in the seminiferous tubules in the parenchyma
Sperm then drains into the mediastinum then the epididymis head, then body then is stored in the tail until ejaculation
Three phases of spermatogenesis
- proliferation
- meiosis
- differentiation
What is the proliferation stage of spermatogenesis
Mitotic division of spermatogonia to form primary spermatocytes
Constant replacement of spermatogonia
What is the meiosis phase of spermatogenesis? How is genetic diversity guaranteed?
Diploid (2N) primary spermatocytes go through meiotic division to produce haploid (1N) spermatids
Genetic diversity is guaranteed by processes such as homologous recombination and DNA methylation
What is differentiation phase of spermatogenesis
Spermogenesis
Spermatids develop into fully formed spermatozoa
Slide 8**
phases of spermatogenesis
Slide 9
Important diagram: been in like every slideset
What is the blood-testis barrier
Cellular barrier that prevents immune system from affecting developing sperm (sperm can be recognized as foreign cells and be attacked by immune response)
Blood-testis barrier has two cellular layers:
- peritubular cells: surrounding the seminiferous tubules
- junctional complexes: tight connections between the sertoli cells within the seminiferous tubules
Junction complexes divide the seminiferous lumen into 2 distinct compartments
- Basal compartment
- Adluminal compartment
Slides 11, 12
Blood testis barrer*
Duration of spermatogenesis in the bull, stallion
Bull
- spermatogonia to spermatid = 13.5 days
- spermatid to spermatozoa = 61 days
Stallion
- spermatogonia to spermatid = 12.2 days
- spermatid to spermatozoa = 55 days
Slide 13***
Spermatozoa consist of … (6)
- nucleus + genetic material
- little cytoplasm
- no endoplasmic reticulum
- numerous mitochondria
- a tail
- plasma membrane + acrosome
Why do sperm have numerous mitochondria
Provides energy for motility to reach fertilization site and to penetrate
Four phases of change spermatids go through during differentiation
- Golgi phase = acrosomic vesicle formation and centriole migration
- cap phase = acrosomic vesicle spreads over nucleus & initiation of axoneme (tail) formation
- acrosomal phase = nuclear + cytoplasmic elongation & neck + annulus formation
- maturation phase = final assembly of sperm
Slide 15-25
Differentiation phases (so much info)
In differentiation, the golgi becomes what? The centrioles become… The mitochondria? The cytoplasm? Manchette?
Golgi -> acrosome
Centrioles
- proximal -> sperm neck
- distal -> tail
Mitochondria -> mitochondrial sheath
Cytoplasm -> lost as cytoplasmic droplet
Manchette -> postnulear cap
How is testicular weight related to sperm production?
Association with testicular growth weight and sperm produced
More weight in testes = more sperm per gram of testicular parenchyma = more daily sperm production
What animal has high testes weight and daily sperm production
Boar
750 gram testes
Slide 26
Three functions of the epididymus
- sperm concentration: fluids that suspended the sperm in sem tub absorbed by epididymal head and uppder body
- sperm maturation: as they move through epid body into upper tail they mature, become motile and gain potential to fertilize
- storage: sperm stored in distal tail of the epidid until time of ejaculation (or reabsorbed into body)
Slides 28, 29, 30, 31
Sperm stages
Epididymal transit time
What animal has the longest epididymal transit time?
Bull = 14 days (10 days in tail)
Boar = 9-14 days
Describe the golgi phase
- small vesicles of the golgi fuse and start to produce proacrosomic granules
- centrioles (proximal and distal) migrate around nucleus opposite of golgi
- fusion of golgi vesicles continues, producing large acrosomic vesicle containing dense acrosomic granule
- proximal centrioles position to become point of attachment btw sperm head and tail. Distal centrioles positioned to become axoneme (tail)
Describe the cap phase
- remainder of golgi migrates around nucleus towards centrioles
- distal centriole starts forming the axoneme (tail)
- acrosomal vesicle flattens and begins to form outer acrosomal membrane, inner acrosomal membrane and acrosomal contents
Describe the acrosomal phase
- nucleus elongates & acrosome stretches to cover most of developing sperm head
- manchette microtubules and stretch plasma membrane down to give mitochondria access to developing tail
- Sperm neck and annulus form
Describe the maturation phase
- mitochondria form spiral assembly around the tail to create well defined middle piece
- manchette tubules regress and form the postnuclear cap
- cytoplasm sloughs off and forms cytopalsmic droplet
- annulus forms a defined junction between the middle and principle pieces
