Flashcards in Unit 7 - Male Reproductive System Deck (64)
where are the testes located? when do they descend?
within scrotum, suspended by spermatic cords
-scrotum maintains testes at temperature 2 degrees below abdominal temp (for sperm production)
-testes descend from abdomen into scrotum via inguinal canal at 26 weeks gestation
serous sac of simple squamous epithelium consisting of outer parietal and inner visceral layers
-visceral layer adheres to tunica albuginea on anterolateral surface of each testes
-extension of abdominal peritoneum that was carried along during descent
where do testes receive blood? get blood taken away?
testicular artery - highly convoluted near testis
pampiniform venous plexus - surrounds testicular artery and carries blood away from each testis
thick capsule of dense irregular connective tissue covering each testis
what are the 2 genital ducts?
intratesticular ducts and excretory ducts
thickening of tunica albuginea on posterior surface
-vessels and ducts pass thru it as they enter/leave testes (no tunica vaginalis)
-projects inward giving rise to incomplete septa that divide each testis into 250 lobules
~250 per testis with 2 major components
-1-4 seminiferous tubules per lobule
-loose connective tissue stroma (interstitial tissue) with blood vessels, lymphatics, nerves, and Leydig cells
where spermatozoa are produced via spermatogenesis and aided by Leydig cells
-lined with stratified germinal epithelium
-each forms a convoluted U-shaped loop beginning and ending near mediastinum
-surrounded by tunica propria with myoid cells and fibroblasts
straight tubules; short tubules within mediastinum that connect seminiferous tubules with rete testis
-lined with epithelium consisting of only Sertoli or simple cuboidal cells
-supported by a dense CT sheath (no spermatogenic cells present)
anastomotic network of channels in mediastinum that connect tubuli recti to ductuli efferentes
-lined with simple epithelium that varies from squamous to low columnar
-produces testicular fluid for sperm transport (also made by Sertoli)
efferent ductules; 10-20 ducts that connect rete testis to epididymis
-lined with simple epithelium that appears scalloped due to alternating groups of cells:
--non-ciliated cuboidal (low columnar) cells with microvilli on apical surface
---absorb most of the testicular fluid made in seminiferous tubules
--ciliated tall columnar cells
---contain the only true cilia in male reproductive system
---cilia beat in direction of epididymis sweeping spermatozoa along in that direction
what are myoid cells?
cells in tunica propria of seminiferous tubules that have contractile properties that help move spermatozoa and testicular fluid through seminiferous tubules
fibrous peritubular tissue that surrounds seminiferous tubules
-has layers of fibroblasts and myoid cells
what are the steps of spermatogenesis?
formation of haploid spermatozoa (spermatozoids or sperm) from undifferentiated diploid germ cell (spermatogonium)
-occurs in inward direction from basal lamina towards lumen
-takes 64 days
-needs testosterone from Leydig cells in interstitial tissue (normal adult makes >100 million sperm/day)
what are spermatogonia? difference between type A and B?
diploid (2N DNA) and begin dividing by mitosis at puberty
-A: continue dividing as stem cells
-B: progenitor cells that differentiate into primary spermatocytes
--increase number through mitosis
--daughter cells remain attached to each other by cytoplasmic bridges; allow coordination of spermatogenesis events between cells b/c of communication via bridges
what do spermatogonia look like histologically?
round cells sitting on basal lamina
-heterochromatic (dark) nuclei
what are primary spermatocytes?
diploid (4N DNA)
-made by mitotic division of spermatogonia B followed by DNA replication
-enter prophase I after formation (takes 22 days)
-genetic material is exchanged between paired homologous Xm (recombination) to generate genetic diversity (reduction division)
-each creates 4 haploid gametes
what do primary spermatocytes look like histologically?
largest germ cells
-large nuclei containing thick strands of condensed chromatin
what are secondary spermatocytes
haploid (2N) made by meiosis (reduction division)
-short lived so hard to find in sections
-immediately enter prophase without making new DNA (NO S PHASE)
-undergo meiosis II to create 2 spermatids
what are spermatids?
haploid (1N DNA)
-differentiate into spermatozoa via spermiogenesis
what do spermatids look like histologically?
small cells that are numerous near lumen of seminiferous tubule
-early spermatids have small condensed nuclei
-late spermatids have tiny, highly condensed nuclei
what is spermiogenesis?
the final step of spermatogenesis converting spermatids into spermatozoa
-involves no cell division
-occurs while spermatids are bound to Sertoli cell membrane
what are 5 changes that happen during spermiogenesis?
1. acrosome formation
2. flagellum formation
3. nuclear changes
4. change in orientation
5. later changes (spermiation)
what happens in acrosome formation?
granules accumulate in Golgi and coalesce into a large acrosomal vesicle adjacent to nuclear envelope
-vesicle spreads over anterior half of condensing nucleus forming acrosomal cap (acrosome) which has hydrolytic enzymes that dissociate cells of corona radiata and digest zona pellucida of oocyte
what happens in flagellum formation?
centrioles migrate from next to nucleus to a position near cell surface opposite the forming acrosome
-one centriole initiates assembly of microtubues, forming flagellum
-mitochondria aggregate around proximal part of flagellum forming middle piece where swimming movement is generated
what are nuclear changes that occur in spermiogenesis?
nucleus condenses, elongates, and moves anteriorly, displacing cytoplasm posteriorly
how is the orientation changes in spermiogenesis?
halfway through, the spermatid reorients itself so the head points toward the basal lamina, and developing flagellum extends into lumen
what is spermiation?
excess cytoplasm (residual body) is released and phagocytosed by Sertoli cells
-spermatids are released from Sertoli cells and from each other into lumen as spermatozoa
what is the structure of the spermatozoa?
head - flattened and pointed; consists of highly condensed nucleus with anterior 2/3 covered by acrosomal cap containing enzymes required for penetration of ZP of oocyte
midpiece - contains mitochondria wrapped around flagellar axoneme
tail - has fibrous sheath wrapped around flagellar axoneme