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human development > spermatogenesis and fertilisation > Flashcards

spermatogenesis and fertilisation Flashcards

1
Q

where does stage 4 of gametogenesis take place in boys?

A

seminiferous tubules of testes after puberty

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2
Q

what are Type A spermatagonia?

A

mitotically active throughout reproductive life

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3
Q

what are Type B spermatagonia made from?

A

Type A spermatagonia

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4
Q

where are spermatagonia found?

A

the base of seminiferous epithelium by interlocking Sertoli cells connected by intercellular cytoplasmic bridges

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5
Q

how is the blood testes barrier formed?

A

by sertoli processes forming an immunological barrier

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6
Q

what happens if the blood testes barrier is broken?

A

autoimmune infertility can occur

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7
Q

what is spermatogenesis?

A

the production or development of mature spermatozoa

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8
Q

explain the process of spermatogenesis

A

type a spermatognia –> type b spermatagonia –> primary spermatocyte –> secondary spermatocyte –> spermatids –> mature sperm

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9
Q

where does spermatogenesis occur?

A

from periphery of seminiferous tubule to the lumen

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10
Q

what are primary spermatocytes?

A

Type B spermatogonia when they enter meiosis

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11
Q

how are primary spermatocytes made?

A

o During early meiosis I, become immunologically distinct from other cells
o Move through barrier to interior of seminiferous tubule

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12
Q

what phase of cell division converts primary spermatocytes to secondary spermatocytes?

A

meiosis I

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13
Q

what phase of cell division converts secondary spermatocytes to spermatids?

A

meiosis II

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14
Q

what do primary spermatocytes do during meiosis I?

A

o During this time they make mRNA for later protein production
o mRNA is stored until its required later

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15
Q

what can early translation into protein cause?

A

sterility

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16
Q

when do secondary spermatocytes enter meiosis II?

A

immediately after meiosis I is completed

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17
Q

what is spermiogenesis?

A

Spermatids undergo spermiogenesis to become spermatozoa

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18
Q

what occurs during spermiogenesis?

A
  • Reduction in nuclear size
  • Golgi apparatus condenses to form acrosome
  • Flagellum grows out of centriole
  • Cytoplasm streams away from nucleus
  • Mitochondria in spiral arrangement around flagellum
  • Head partitioned into domains
  • Cytoplasm moves to residual body which is phagocytosed by Sertoli cells
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19
Q

what is the final step of sperm maturation?

A

capacitation

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20
Q

where does capacitation take place?

A

in the female genital tract

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21
Q

why does capacitation occur in the female genital tract?

A

requires contact with the secretions of the oviduct

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22
Q

why is capacitation needed?

A

Only capacitated sperm are capable of the acrosome reaction + fusion with oocyte

23
Q

what does GnRH stand for?

A

Gonadotrophin releasing hormone

24
Q

where is GnRH produced?

A

hypothalamus

25
Q

what does GnRH stimulate?

A

FSH and LH release from the anterior pituitary

26
Q

what does LH stimulate?

A

testosterone production by Leydig cells (which surround the seminiferous tubules)

27
Q

where are FSH and LH released from?

A

anterior pituitary

28
Q

what is the main target of testosterone and FSH?

A

sertoli cells

29
Q

what do sertoli cells secrete when stimulated by testosterone and FSH?

A

androgen binding protein (ABP)

Tubular fluid

30
Q

how is spermatogenesis stimulated?

A

ABP binds to testosterone & carries it to area of seminiferous tubule where it stimulates spermatogenesis

31
Q

what are the essential “ingredients” for fertilisation?

A

o Functioning hypothalamic-pituitary-gonadal axis
o Normal oogenesis & spermatogenesis
o Normal structure and function of reproductive tract
o Trouble free transport of gametes
o Gamete fusion
o Trouble free transport of embryo

32
Q

where is sperm deposited?

A

cervical OS

33
Q

what helps sperm towards the cervical canal?

A

ciliated surface of the cervical os

34
Q

what helps transport of sperm into the uterus and oviducts?

A

o Sperm’s own propulsion

o Fluid currents caused by uterine cilia

35
Q

how long does it take sperm to travel 13-15cm?

A

2-7 hours

36
Q

what happens to sperm during the journey into the uterus and oviduct?

A

sperm undergo capacitation

37
Q

what is capacitation

A

removal of the glycoprotein coat so sperm become hyperactive and sensitive to surrounding signals

38
Q

at the time of ovulation, what happens to the properties of the cervix mucus?

A

changes from a sperm-hostile to sperm-friendly environment

39
Q

how is an egg fertilised?

A
  1. Sperm finds egg
  2. Sperm recognises egg.
  3. Sperm has acrosome reaction to penetrate extracellular layer
  4. Sperm cell membrane fuses with egg cell membrane and triggers Ca2+ wave in egg.
  5. Polyspermy is blocked.
  6. Fertilisation cone forms around sperm head.
  7. Movement and fusion of pronuclei
40
Q

describe what happens in the acrosome reaction

A
  • acrosome membrane fuses with the overlying plasma membrane
  • enzymes released
  • sperm finishes journey between zona pellucida and oocyte membrane
  • sperm becomes enveloped and fusion occurs
  • large increase in intracellular Ca2+ which forms a wave across the egg
41
Q

what is the oolemma?

A

the oocyte membrane

42
Q

what enzymes are released during the acrosome reaction and what do they do?

A

hyaluronidase – dissolves the intercellular matrix between the cumulus cells

Other enzymes dissolve the zona pellucida

43
Q

describe how egg/sperm fusion occurs

A
  • sperm undergoes acrosome reaction and binds with egg receptor
  • Cortical vesicles fuse w plasma membrane –> exocytosis -> release contents into peri-vitelline space
    • Modified fertilisation membrane detaches + rises
    • Sperm is pulled into egg w help from fertilisation cone
    • Microtubules radiating from centrosome associated w male pronucleus helps guide nucleus to centre of egg where it fuses w female pro-nucleus
44
Q

how do the sperm and egg find each other?

A

• They need to recognise each other from a distance;
o Sperm attracted to egg via chemotaxis
o Only found in mature eggs and sperm
o Mechanisms vary depending on species

45
Q

how do the cells fuse with each other in a species-specific way?

A
  • in mammals there’s a glycoprotein called ZP3 in the zona pellucida
  • Binds to β1, 4 galactosyl transferase receptor on the sperm plasma membrane
  • Capacitated sperm are species-specific in their binding to ZP3
  • Binding triggers changes in Ca2+ and pH in sperm and acrosome reaction
46
Q

how is the number of cells fusing restricted?

A

• Production of second messengers on sperm/egg binding triggers polyspermy blocking.
• Slow block:
o release of calcium in a wave
o calcium triggers cortical granule
o release and activation of cell division

47
Q

what happens to the fertilised ovum as it travels down the oviduct?

A
  • As it travels down the Fallopian tube (oviduct) the fertilised oocyte or zygote will begin to divide.
  • It undergoes cleavage to form 2 cells
48
Q

what happens at the 16-32 cell stage of a fertilised ovum?

A

polarisation of 2 cell populations to form a morula;
o The outer cells form one population and are trophoblast precursors.
o The inner cells are the pluriblast cells

49
Q

when does the 32-64 cell stage occur?

A

4 to 5 days after ovulation

50
Q

what occurs at the 32-64 cell stage?

A

the cells which have been polarised start to differentiate into different cell types - known as a blastocyst

51
Q

when does hatching occur?

A

around day 5

52
Q

how does hatching occur?

A

o Around day 5 the blastocyst frees itself from the zona pellucida.
o It does this through a series of expansion-contraction cycles and with the help of enzymes that dissolve the zona pellucida

53
Q

when does the blastocyst attach itself to the uterine wall?

A

7-9 days post ovulation

human development (20 decks)

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