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Describe the structure of the testis.
- Dense irregular CT capsule and septae-
- - capsule is thick/white/collagenous = 'tunica albuginea'
- - septae devide testicular tissue into lobules
- Lobules consist of:
- - loose connective tissue containing clusters of Leydig cells which secrete testosterone
- - seminiferous tubules which are lined by a simple columnar epithelium of supportive 'sertoli cells'
- -Developing 'Germ cells' are embedded in the epithelium
Describe the structure of Leydig cells.
Leydig cells are endocrine glands. They exist as Leydig cells Islands which are clusters of steroidogenic cells embedded in highly vascular CT
What do Leydig cells secrete, and how is this accomplished?
- Produce Testosterone
- Cell surfaces contain Leutenizing Hormone cell receptors. When LH binds to them, it triggers a G-coupled signalling pathway involving cAMP. cAMP activates protein kinases which activate cholesterol esterases which cleave free cholesterol. Free cholesterol is passed between mitochondria and SER (via LTPs) because cholesterol is not stably freely existing in cytoplasm. Instead, it's generally found as esterified cholesterol in lipid droplets.
- Testosterone is secreted into loose CT and picked up by fenestrated capillaries and nearby Sertoli cells
What are myoid cells?
Slightly contractile fibroblasts which are found in the lobules of the seminiferous tubules
What are the four types of germ cells during development?
- 1) Spermatogonia: testosterone-dependent, basal 'stem'-like cells (diploid)
- 2) Spermatocytes: haploid cells which migrate across/through tight junctions of seminiferous epl to the adluminal compartment (immunoprotected)
- 3) Spermatids: luminal haploid cells which undergo morphological changes aka spermiogenesis
- 4) Spermatozoa: haploid cells released in to seminiferous tubule lumen which is filled with nutritive Sertoli cell secretions/fluid; not yet motile
How long does a wave of germ cell development typically take?
Describe the structure of spermatazoa.
- Head: contains nucleus with condensed chromatin and the acrosome with modified/fused lysosomes (to get through the egg's zona pellucida)
- Neck: Centrioles (root of the axoneme)
- Midpiece: Mitochondria rich area for ATP production
- Annulus: -9 outer pairs and 2 central microtubules (axoneme) which drives flaggellar motility
- Tail: flaggellar for motility- axoneme and intermediate filaments
Describe the structure of the Rete Testis.
- Intratesticular duct
- Net-like network of tubes that collect spermatozoa and move them through the Tunica Albuginea
- Lined by simple cuboidal epithelium
What is the functional role of the Rete Testis?
Passice transport of non-motile spematozoa by bulk flow due to Sertoli cell secretions and myoid cell contractions
Describe the structure of the Ductuli Efferentes.
- Intratesticular duct, continuous with the Rete Testis
- Simple 'scalloped' epithelium - cuboidal cells are resorptive (initiate a flow out of Rete Testis) and columnar cells are ciliated (beat to further facilitate flow out of Rete Testis)
- Thin layer of smooth muscle in wall (peristaltic)
What is the functional role of the Ductuli Efferentes?
Weak active transport of non-motile spermatozoa.
Describe the epithelium in the epididymis.
- Pseudostratifed epithelium
- basal stem cells
- principal cells which resorb excess seminal fluid and phagocytose excess spermatozoan cytoplasm (they then become slightly motile)
- Principal cells have stereocilia= long non-motile microvilli to increase surface area (no microtubule core)
How is the muscle arranged in the epididymis?
One prominent layer, circularly arranged- initiates active ejaculatory transport of spermatozoa towards the vas deferens
What is the major site of storage of spermatozoa?
What is the first extratesticular duct?