Spermatogenesis Flashcards
(57 cards)
3 Phases of Spermatogenesis
Proliferation: Mitotic divisions of spermatagonia
Meiosis: Meiotic Divisions resulting in haploid spermatids
Differentiation: Morphological transformation of spermatids into spermatozoa
Endocrine Regulation of Testis Requirements
Pulsatile LH and FSH
Pulsatile GnRH
High [ ] of test. in seminif tubules
adequate number of LH receptors in Leydig Cells
Pulsatile GnRH
every 3-6 hours
frequent, intermittent episodes lasts for only a few minutes at a time
causes LH and FSH discharge
LH and FSH discharge from GnRH
LH: 10-20 minutes and 4-8 times a day
FSH: lower [ ] than LH but longer duration. Is inhibited by inhibin from adult testis (sertoli cells)
lasts 100 minutes?
Sustained Testosterone Secretion in Men
Lack of Surge Center
-LH remains consistent
-Episodic pattern
-Steady Pulses of GnRH and LH= steady release of testosterone
High Testosterone in Seminiferous tubules
Leydig Cells
- Blood LH elevates about 30-75 minutes
-synthesize and secrete test
-convert P4 to Test
Low Testosterone in Systemic Blood
High Testosterone is neccesarry for spermatogenesis
intratesticular testosterone [ ] is 100-500 x greater than systemic
Low test. in systemic prevents down regulation of of GnRH and LH (test has - feedback on GnRH and LH)
LH receptors in Leydig Cells
Importance for testicular function
Prevents sustained LH
Sustained LH would decrease LH receptors in Leydig Cells
Leydig Cells
Below Basement membrane
LH stimulates P4 production, most of which is converted into testosterone
-pulsatile LH thus important
-testosterone in testis 100-500x greater
Sertoli Cells
-Converts Testosterone to Estradiol and a-DHT (- hypothal feedback)
-Androgen Binding Protein
(increases test [ ] in seminif)
Produces inhibin –> FSH suppression
-FSH stims tight junction formation btwn Sertoli cells (FSH dependent)
Goals of Spermatogenesis
-Male supplied with continual gametes through stem cell renewal
- Genetic Diversity
-Billions of sperm to maximize repro opportunity
-immuno privileged sites where germ cells not destroyed while developing
Participating Cell Types in Spermatogenesis
Spermatagonia (stem cells)
-goes from 2n to 1n and then change shape to become spermatazoa
Sertoli Cells
-support for germ cells
-env’t for maturation
-substances for meiosis
-hormonal signals to control spermatogenesis
-Primary spermatocyte
-Secondary Spermatocyte (spermatid)
Proliferation
Stem Cell Renewal (2n)
A, I, and B spermatagonia
Mitotic Division (lots of B)
Intercellular Bridges lost to allow spermatagonia to go back to stem cells
-Basal Compartment
-Maintenance of Stem Cells, keeps spermatogenesis going indefinitely
replenishes stem cells in case of trauma/ high heat
Meiotic Phase
Haploid Spermatids (n)
Crossing Over = diversity
each spermatid unique (heterogeneity)
Differentiation Phase
Spermatazoan (n)
-Head and Flagellum (middle and principle piece)
- NO further cell division
Where does spermatogenesis take place?
Entirely in Seminiferous Tubules
Intercellular Bridges
Communication for synchronizing development
spermatagonia, spermatid, and spermatocytes all connected by these bridges
Differentiation (spermiogenesis) phases
Golgi Phase
Cap Phase
Acrosomal Phase
Maturation Phase
Golgi Phase
Acrosomic Vesicle Formation
centrioles –> axoneme
???
Cap like structure contains enzymes– also central portion of flagellum
Cap Phase
Acrosomic Vesicle Spreading over the nucleus
1) acrosomic vesicle spreading over nucleus
2) prim flagellum: DC goes towards seminiferous tubule lumen
Acrosomal Phase
nuclear and cytoplasmic elongation
1) acrosome covers 2/3 of nucleus
2) nucleus elongates
3) manchette forms
Maturation
Final Assembly that form spermatazoan
-postnuclear cap forms
-formation of middle piece
principle piece forms
-plasma membrane integrity important for survival of sperm
released into lumen
Sperm Head Parts (main)
Nucleus, Acrosome, post-nuclear- cap
nucleus
nuclear condensation
chromatin keratinized
histone replaced by protamines
