Spermatogenesis Flashcards
What is gametogenesis?
Formation & development of gametes
- formed through process of meiosis in gonads
What is spermatogenesis?
Process which transform spermatogonia (diploid germ cells) into mature Spermatozoa (sperms)
Where does spermatogenesis occur?
It occurs in the seminiferous tubules of the testes (male sex organs)
When does spermatogenesis occur?
Begins at puberty with proliferation of stem & progenitor cells called spermatogonia
What are spermatogonia?
- small round stem cells located at outermost in direct contact with epithelial basal lamina
- closely associated with Sertoli cells
Spermatogenesis has 3 major stages?
- Mitotic proliferation
- Meiosis
- Spermiogenesis (packaging)
What is mitotic proliferation?
Spermatogonia – Primary Spermatocyte via mitosis
What are the 3 types of Human Spermatogonia seen in histological sections?
- Type A dark (Ad) Spermatogonia
- Type A pale (Ap) Spermatogonia
- Type B
Describe type A dark (Ad) spermatogonia?
- Ovoid nucleic, dark-staining stem cell
- are stem cells that divide at irregular intervals to give rise to either Type Ad spermatogonia that remain as stem cells or Type Ap spermatogonia
Describe Type A pale (Ap) Spermatogonia?
- Ovoid nuclei, lightly/pale staining
- Committed/progenitor cell
- is committed to the differentiation process that produces the sperm
- They undergo several successive mitotic divisions, increasing their number
Describe Type B spermatogonia?
- pushed adluminal - committed for meiosis
- Undergo final mitotic division & produce 2 Primary Spermatocyte (spherical & euchromatic, pale-stained)
- Primary Spermatocyte replicate DNA & enter Meiosis
Describe the clonal nature of spermatogenesis?
- Mitosis in spermatogonia A occurs with incomplete cytokinesis, leaving the cytoplasm of most or all of these cells connected by cytoplasmic bridges.
- Type A Spermatogonia divide mitotically two or three more times, then differentiate as type B spermatogonia that undergo a final round of mitosis to form the cells that then enter meiosis and become primary spermatocytes
- They are still interconnected by intercellular/cytoplasmic bridges.
Function of intercellular bridges in spermatogenesis?
- Intercellular bridges allow free cytoplasmic communication among the cells, essential for synchronous development.
Describe the duration of the intercellular bridges?
- persist up to first & second meiotic divisions
- they are lost as the haploid spermatids differentiate into sperm.
What is the stage of meiosis?
Spermatocytes to Spermatids
Describe the stage of meisosis?
- Primary spermatocyte, soon after their formation, enter meiotic prophase I
- Homologous chromosomes separate in the first division : produces smaller cells called secondary spermatocytes with only 23 chromosomes
- 22 + X or 22 + Y
- Each still has 2 chromatids - Division of each secondary spermatocyte separates the chromatids of each chromosome and produces 2 haploid cells called spermatids
- Spermatids later differentiate into sperms
Describe the locations of germ cells in various stages of spermatogenesis?
- Spermatogonia - reside in basal compartment,
2. primary + secondary spermatocytes & spermatids - reside in the adluminal compartment
How do newly formed spermatocytes travel to the adluminal compartment from the basal compartment?
Newly formed spermatocytes temporarily disassemble the local tight junctions between Sertoli cells that act as the “blood-testis barrier” in order to move from the basal compartment to the adluminal compartment of the tubule
All stages of spermatogenesis and spermiogenesis occur where?
with cells intimately associated with the surfaces of adjacent Sertoli cells (SC)
What are the functions of the Sertoli cells?
- form tight junctions which function as Blood-testis- barrier
- they provide support, protection & nutrition to developing spermatogenic cells
- Since developing spermatocytes, spermatids & sperm are isolated from blood by the BTB
Function of the blood-testis barrier?
- isolate germ cells residing in adluminal compartment from circulatory & lymphatic systems providing immunoprivileged microenvironment for completion of meiosis
- so the bodies immune system does not attack the germ cells of spermatogenesis
- these cells are recognized by the body as foreign as they develop after the immune system has been developed
What is the stage of spermiogenesis of packaging?
Spermatids – Sperms
Describe the stage of spermiogenesi?
- Process by which spermatids differentiate into spermatozoa, which are highly specialized to deliver male DNA to the ovum
- A spermatid sheds its superfluous cytoplasmic baggage with help of Sertoli cells
Describe the structure of sperm?
- head – with nucleus, and acrosome (has hydrolytic enzymes)
- Mid Piece – with mitochondria (for energy production)
- Tail – flagellum for locomotion
