Testes and Spermatogenesis Flashcards
main testis function (general)
sperm and androgen production
- nearly all testosterone is made by them (Leydig cells
5% is made in zona reticularis of adrenal gland)
dense irregular CT surrounding the testes
tunica albuginea
mediastinum testis
inward projection of the tunica albuginea on the posterior surface of the testis
holds the rete testis
septa in testis
CT going from the capsule inward
splits the testis into 250 lobules
Cells that are not inside the convulted tubule in testis
fibroblasts = cells with a thin nucleus outside of the tubule
Leydig cells = bigger cells with bigger nucleus outside of the tubule
Leydig cells
make and secrete testosterone
variable in size but round usually
cytoplasm = acidophilic
a lot of large smooth ER and filled with lipid droplets to create steroids
inside the convoluted seminiferous tubule
consists of lamina propria with myoid cells and collagen fibrils
basement membrane
seminiferous epithelium = complex stratified
- has sertoli cells and spermatogenic cells on top of one another
myoid cells in convoluted seminiferous tubule
flat elongated SmM like cells that contract to move sperm and fluid in the duct system
where a more immature spermatogenic cells located?
rest on basal lamina = ‘spermatogonia’
spermatids
most mature spermatogenic cells
located at the apical portion of sertoli cells (bordering the lumen)
progression of spermatogenesis (general)
1 spermatogonum –>
1 primary spermatocyte –> 1st round of meiosis
2 secondary spermatocyte –> 2nd round of meiosis
4 total spermatids –> maturation (spermiogenesis)
4 spermatozoa (mature sperm cells)
the secondary spermatocyte cells to the late spermatids are connected via….
cytoplasmic bridge
essential for synchrous development
allow free communication between cells
***allow haploid cells to be supplied with proteins and RNAs encoded by complete diploid genome
how does the cytoplasmic bridge go away
sertoli cells phagocytose the unneeded cytoplasm while making mature…
spermatozoa
what spermatocyte are really hard to find histologically
secondary
spermatogonia
most immature and relatively large
rounded nucleus with chromatin
always in contact with basal lamina, so very easy to spot
divide and differentiate into primary spermatocytes
3 types:
- type A dark
- type A pale
- type B
do not need to be able to tell the difference
primary spermatocyte
largest germ cell present and cells that are spherical or ovoid
large round nucleus with heterochromatin***
undergo first meiosis to produce 2 secondaries
when does genetic variation via crossover and random inclusion of either paternal chromosome occur?
1st meiosis
primary –> secondary spermatocyte
secondary spermatocyte
half the size as primary
differentiates into 2 spermatids
spermatids
will undergo no further division…instead undergo spermiogenesis and differentiate into spermatozoa
early spermatids =
- small size, with round nuclei and condensed chromatin
late
- elongated, condensed nucleus
- has a tail and is attached to apical portion of sertoli bordering the lumen
- looks like sperm but the cytoplasmic cross bridge still present
4 processes of spermiogenesis
- nuclear condensation and elongation
- acrosome formation to break down zona pellucida of ovum and allow for fertilzation to occur
- flagellum formation
- cytoplasm reduction
rate of spermiation determines what
of sperm in semen
spermatozoon
free in lumen
much of cytoplasm has been phagocytosed by sertoli cells
released as non-motile, gain motility in epididymis, wehre they are stored before ejaculation
sertoli cells GENERAL function
- structural organization to the tubules
- support and nurse maturing sperm cell by exchanging substrates and wastes…also phagocytosed unneeded cytoplasm
- unable to differentiate
- extend from basement membrane to lumen surface of epithelium
structure of sertoli cells
tall and columnar
nucleus is ovoid, triangular, and large and lightly staining
nucleolus is large and prominent (like eye of owl)
cell borders are not visible
well developed RER, SER, lipid droplets, and lots of mitochondria
endocrine functions of sertoli cells
estradiol = aromatase converts testosterone –> estradiol in neonatal and prepubertal mammals to inhibit testosterone production by leydig cells and regulate spermatogenesis
inhibin B = (-) feedback on FSH
mullerian-inhibiting factor (MIH) = cause regression of mullerian ducts
growth factors (GDNF and stem cell factor) = maintain the number of spermatogonia
exocrine sertoli cell
fluid = helps move sperm along seminiferous tubules to intra-testicular ducts
androgen binding protein (ABF) - promoted by FSH
- binds testosterone to make it lipophilic and keep it in the lumen of the tubules
- more testosterone in lumen is best for sperm production
tight junction between sertoli cells
divide epithelium into basal and adluminal compartments
basal = spermatogonia and early spermatocytes
adluminal = rest of the cells
early spermatocytes move to adluminal compartment by sertoli cells making a new tight junction under the cell that is moving compartments…the tight junction above the cell degrades
forms the basis for blood-testis barrier
- allow ionic, amino acid, carb, and protein composition to be different from that of blood plasma
where does meiosis and spermiogenesis occur
adluminal compartment
what is very sensitive to elevated temperature
seminiferous epithelium (not spermatogonia)
why testis dangle outside body
Cryptorchidism
undescended testis - causes degeneration of spermatogenic cells, besides spermatogonia, leaving only intersitial structures like fibroblasts and leydig cells
how is temperature in testis regulated
through the pampiniform plexus
has a countercurrent heat exchange between the plexus and the testicular artery to cool off the arterial blood
also uses cremaster muscle and dartos muscle
pampiniform veins
have uncharacteristically thick SmM, which allows for propulsion of blood against gravity into abdominal veins
Cremaster reflex
works by contraction and relaxation of the cremaster (skeletal) allowing scrotum to move toward or away from the body to regulate temperature
cold temperature also causes dartos (SmM) muscle of the scrotum to contract
–> scrotum wrinkles which helps regulate heat loss
