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embryology > 1. spermatognesis > Flashcards

1. spermatognesis Flashcards

1
Q

what are spermatogonia

A
  • stem cells
  • PGCs differentiate into as they enter meiosis in foetal gonad
  • escape from this fate by diffusible male meiosis inhibitor produced by Sertoli cells in male gonad
  • do not proceed until testosterone in puberty
  • spermatogenesis proceeds throughout adult life
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2
Q

semen/seminal fluid

A
  • contains the spermatozoa + liquid component derived from the glands
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3
Q

male gonads

A
  • genital excurrent ducts
  • accessory sex glands
  • external genitalia
    gonads are endocrine glands: hormones produced by Leydig cells in interstitial (stromal) tissue
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4
Q

semiferous tubules

A
  • parenchyma of testis
  • surrounded by myoid cells: tubule wall
    -wall: germinal epithelium: seminiferous epithelium: sertoli cells (somatic) and spermatogenic cells (germ line)
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5
Q

leydig cells

A
  • well developed lipid metabolism
  • abundant SER, many LD, glycogen, golgi, lysosomes, occasional RER
  • secrete testosterone initiating spermatogenesis
  • stimulated accessory sex gland secretion, secondary sec characters, metabolism
  • in embryo (2-5mo) testo required for normal gonad development: insulin-like 3 stimulates testis descent
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6
Q

sperm cells

A
  • adapted for delivering haploid DNA to an egg
  • highly specialised cells by differentiation
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7
Q

where does spermatogenesis occur?

A

in the seminiferous tubules

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8
Q

sertoli cells strcucture

A
  • post-mitotic after puberty
  • extend through full thickness of seminiferous epithelium with extensive processes
  • surround and envelope spermatogenic cells
  • form tight junctions in epithelium: determine basal and luminal compartment
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8
Q

spermatogenic cells

A
  • undergo mitosis/meiosis,
  • organised in poorly defined layers from the wall (spermatogonia) to the lumen (spermatids) of semini tubule
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9
Q

sertoli cells function

A
  • support gametogensis
  • create a niche for germ cells
  • account for the testicular immune privilge
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10
Q

three phases of spermatogenesis

A
  • spermatogonial phases (mitotic amplification): spermatogonia
  • spermatocyte phase (meiosis): primary, secondary spermatocytes, spermatids
  • spermatid phase (spermiogenesis, differentiation): golgi, cap, acrosome, maturation phase
  • spermatozoon formed
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11
Q

spermatogonial phases (mitotic amplification)

A
  • type A dark are spermatogonial stem cells: dormant and increase in number at puberty
  • type A pale are renewing stem cells
  • cytoplasmic division complete only in type A dark, all other remain connected by intercellular bridges
  • type B are committed to give rise to spermatocytes: not stem cells any longer
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12
Q

spermatocyte phase (meiosis)

A
  • spermatocytes undergo meiosis generating four spermatids
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13
Q

spermatid phase (spermiogenesis)

A
  • spermatids are transformed into mature sperm (differentiation
  • seperate into individual spermatozoa as they are released from seminiferous epithelium
  • residual bodies remain connected: phagocytosed by sertoli cells
    1. acrosome formation
    2. modifications of nucleus (chromatin compaction) and cell shape (cytoplasm reduction)
    3. tail formation
    4. release into the lumen
  • golgi,cap,acrosome,maturation phase
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14
Q

the acrosome

A
  • organelle for massive exocytosis
  • cap-like saccular organelle in head
  • wraps 2/3 of nucleus
  • contains hyaluronidase, neuroaminidase, acid phosphatase, acrosin (trypsin-like protease)
  • from golgi
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14
Q

nuclear condensation

A
  • protomines replace histones in the chromatin allowing for denser packaging
15
Q

cytology of spermatozoon

A
  • neck contains centrioles
  • mitochondria occupy middle piece
  • principal piece contains fibrous sheath, outer dense fibers, axonemal complex (9+2 microtubule array
16
Q

mechanisms of cell movement

A

flagellum:
- basal body, passive part in motion, propeller like motion
cilia
- basal body, back and forth beating motion

17
Q

microtubule organization in in flagella

A
  • 9+2, radial spoked keep axonema in place
  • axonemal dyneins are responsible of sliding of one couple of tubules against the adjacent
18
Q

timeline for spermatogenesis

A
  1. 24 days
  2. meiosis
  3. 26 days
    - 74 days
18
Q

clonal growth and differentiation of germ cells make cell associations recognisable

A
  • six cyclic, distinct cell stages are noticeable in human seminiferous epithelium
  • stages are artificially designed
19
Q

involved hormones

A
  • regulated by GnRH, FSH, LH, DHT cascade

embryology (9 decks)

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