Spermatogenesis Flashcards
(29 cards)
Spermatogenesis
Production of spermatozoa by the testis
-spermatogonia – spermatocyte – spermatid – spermatozoa
What all is included in spermatogenesis?
Consists of all cell divisions and morphological changes of developing germ cells occurring in epithelium of seminiferous tubules
What are the 3 phases of growth?
Proliferation, meiosis and differentiation occur in tubular compartment of seminiferous tubules
What is the proliferation stage?
Mitotic divisions of spermatogonia (A to B) and stem cell renewal (infinite supply of spermatogonia)
-occurs in basal compartment of seminiferous tubules, between basal lamina and sertoli junctions
What is the meiotic stage?
B-spermatogonia differentiate into 1 degree spermatocyte and undergo meiosis
-meiosis 1: DNA replication and crossing over
- meiosis 2: 2 degree spermatocyte divides into haploid spermatids
-meiotic stage occurs in adluminal compartment, closer to compartment than lumen
What is differentiation?
No cell divisions, spherical spermatid differentiates into a specialized spermatogonia
-occurs in adluminal compartment, close to lumen
Differentiation of Sperm
First set of steps in conferring sperms ability to swim, deliver genetic material, and activate the oocyte for zygote development
Spherical Spermatids
Undergo a series of modifications: becoming motile, condensing their nuclei (for protection), and forming acrosomes for fertilization
Golgi Phase
Small vesicles of golgi fuse, form proacrosomic granules on one side of nucleus
Cap Phase
Acrosomic vesicle forms a cap over one side of nucleus (anterior position) while golgi and other cytoplasmic organelles migrate towards distal portion
Acrosomal Phase
Nucleus begins to elongate and microtubules organize and form manchette
Maturation Phase
Manchette forms post-nuclear cap and mitochondria migrate to posterior side of nucleus to form a spiral assembly (defining feature)
Main Components of Sperm Head
Nucleus, acrosome and post nuclear cap
Nucleus in head of Sperm
Oval, flattened, with condensed DNA (di-sulfide cross-linking)
-degree of cross-linking determines level of maturation of sperm
-DNA remains inert until fertilization
Acrosome in Head of Sperm
Membrane vesicle with hydrolytic enzymes covering anterior 2/3 of nucleus
-acrosome resides within apical ridge of head
Postnuclear Cap of Sperm Head
Membrane component posterior to acrosome
Components of Sperm Tail
Capitulum, Middle piece, principal piece, and terminal piece
Capitulum of sperm tail
Neck of sperm, attaches flagellum to head
Middle piece of sperm tail
Mitochondrial sheath, provides swimming power to spermatozoon
-mitochondria arranged in helical structure around middle flagellum
Principal piece of sperm tail
Main part of flagellum, necessary for movement
Terminal piece of sperm tail
End of microtubule
Spermiation
Release of fully differentiated spermatozoa into lumen of seminiferous tubules
How does spermatozoa formation occur?
In spermatogenic cycles/waves whose length is species dependent
Is a segment of seminiferous tubules always undergoing spermiation?
Yes, it is a continuous and uniform process under constant/uniform endocrine control
