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FHMP > FHMP 023 + 024 intro to developmental biology and fertilisation and cleavage divisions > Flashcards

FHMP 023 + 024 intro to developmental biology and fertilisation and cleavage divisions Flashcards

1
Q

what are the stages of human embryonic development?

A
  • fertilisation
  • cleavage (days 1-5)
  • implantation (days 6-9)
  • gastrulation and neurulation (weeks 3-4)
  • body plan (week 4)
  • organogenesis (weeks 4-8)
  • foetal development (weeks 8-40)
  • birth
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2
Q

how common are congenital defects?

A
  • in 20% of pregancies

- 2% of live births in england

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3
Q

Name some common congenital defects

A
  • anencephaly
  • spina bifida
  • club foot
  • polydactyly
  • phocomelia ( reduced or missing long bones/limbs - thalidomide survivors)
  • cleft lip
  • treacher collins syndrome (affects development of the head)
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4
Q

describe the development process of egg cells (oogenesis)

A
  • in foetus the oogonium undergoes meiosis but stops at prophase 1
  • then once puberty has occurred it can continue meiosis until metaphase 2
  • then it splits into a polar body and the ooctye which then stays at this point of development until ovulation and fertilisation
  • after fertilisation the egg undergoes more meiosis to form a second polar body and a fertilised egg cell (which forms the embryo)
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5
Q

describe the developmental processes of spermatogenesis

A
  • after puberty spermatogonium undergoes mitosis into a spermatocyte which undergoes meiosis 1
  • then the 2 spermatocytes undergo meiosis 2 to form 4 spermatids
  • the spermatids undergo spermiogenesis (differentiation) into spermatozoa ( sperm cells)
  • (no polar body produced)
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6
Q

describe the structure of human eggs

A
  • 100 micrometers in diameter
  • surrounded by zona pellucida and cortical granules which help with fertilisation/implantation
  • plasma membrane underneath surrounding cytoplasm and haploid nucleus
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7
Q

describe the structure of spermatozoa

A
  • 50 micrometers long
  • head contains the haploid nucleus, the centriole (produce microtubules) and the acrosome ( contains enzymes that digest egg outer coating)
  • midpiece contains mitochondria and microtubules to help tail move
  • then the rest is the flagellum (tail)
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8
Q

what happens in the first week of embryonic development?

A
  • a matured oocyte is released from the ovaries during ovulation
  • the fimbriae of the fallopian tubes pick of the released egg
  • spermatozoa will fertilise the egg in the ampulla of the oviduct
  • once fertilised the egg will begin to divide and form an embryo, moving down the oviduct into the uterus
  • in the uterus, it hatches from the zona pellucida and implants into the uterine wall
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9
Q

what is an ectopic pregnancy?

A
  • when the embryo implants outside of the uterus

- 98% in the fallopian tubes but can also be in the cervix, ovary or abdomen

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10
Q

what happens during ferilisation?

A
  • the egg signals its position by secreting progesterone once a sperm has reached the egg
  • this progesterone activates a calcium channel which is only present in the sperm’s tail
  • the calcium influx into the sperm’s tail helps it move faster and initiate capacitation
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11
Q

what happens during ferilisation?

A
  • the egg signals its position by secreting progesterone once a sperm has reached the egg
  • this progesterone activates a calcium channel which is only present in the sperm’s tail
  • the calcium influx into the sperm’s tail helps it move faster and initiate capacitation
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11
Q

what happens during ferilisation?

A
  • the egg signals its position by secreting progesterone once a sperm has reached the egg
  • this progesterone activates a calcium channel which is only present in the sperm’s tail
  • the calcium influx into the sperm’s tail helps it move faster and initiate capacitation
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12
Q

what happens during fertilisation?

A
  • the egg signals its position by secreting progesterone once a sperm has reached the egg
  • this progesterone activates a calcium channel which is only present in the sperm’s tail
  • the calcium influx into the sperm’s tail helps it move faster and initiate capacitation
  • the sperm cannot fertilise the egg without capacitation
  • capacitation causes de-stability of the plasma membrane around the acrosome
  • the acrosome now fuses with the plasma membrane of the ovum and secretes hydrolytic enzymes (acrosomal reaction) which allow the sperm to penetrate the zona pellucida
  • the calcium increase stimulates meiosis of the egg to mature to the final stage
  • cortical granules fuse with the plasma membrane (cortical reaction) releasing contents into extracellular space
  • enzymes then modify the zona pellucida so no more sperm can bind to the egg
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13
Q

what is capacitation?

A
  • causes de-stability of the acrosome vesicle

- promotes acrosome reaction

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14
Q

what is the acrosome reaction?

A
  • when the acrosome vesicle of the sperm fuses with the plasma membrane of the egg
  • secretes hydrolytic enzymes to penetrate zona pellucida
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15
Q

what is the cortical reaction?

A
  • calcium increase in the egg causes cortical granules to fuse with the plasma membrane and releasing contents into extracellular space
  • enzymes then modify the zona pellucida so no more sperm can penetrate the egg
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16
Q

what is parthenogenesis?

A
  • where the egg develops without fertilisation

- seen in plants and invertebrates

17
Q

what are andromorphs and gynomorphs?

A
  • andromorph = embryo with only male chromosomes

- gynomorph = embryo with only female chromosomes

18
Q

what are cleavage divisions?

A
  • mitotic divisions without cell growth

- the cells/blastomeres get smaller

19
Q

whats the morula?

A
  • 16 cell stage of the embryo
20
Q

what is compaction

A
  • by the 32-cell stage, they undergo sudden compaction where the blastomeres become more adhesive to each other, forming water-tight junctions
  • differentiation occurs - a fluid-filled cavity (blastocoel) forms within the embryo which is now called the blastocyst which has outer (trophoblast) and inner (inner cell mass) cell populations
21
Q

what is a blastocyst?

A
  • an embryo after 32 days and after compaction
  • contains the: z
    - zona pellucida
    - trophoblast (outer layer)
    - inner cell mass (inner layer)
    - blastocoel (fluid-filled cavity)
22
Q

what is blastulation?

A
  • occurs after cleavage divisions
  • hatches from the zona pellucida
  • inner cell mass now develops another cavity (amniotic cavity)
  • inner cell mass aka embryoblast
  • ICM/embryoblast also differentiates into hypoblast and epiblast
  • these 2 layers form the bilaminar disk
23
Q

what is the bilaminar disc?

A
  • when the ICM/embryoblast differentiates into 2 layers:
    - epiblast (touching outer trophoblast)
    - hypoblast (inner side)
24
Q

what are the 2 ways of dividing the embryo to form monozygotic (identical) twins?

A
  • 70% from splitting the ICM

- 30% from splitting during cleavage stages

25
Q

what is tetragametic chimera?

A
  • when 2 fertilised eggs fuse to form a single chimeric embryo
  • the baby will show to have 2 genetically distinct cell types
26
Q

what is the pathway/divisions from egg through embryo to fetus?

A

egg –> 16-cell morula –> blastocyst containing ICM, trophoblast and blastocoel

trophoblast –> chorion (contributes to placenta)

ICM —> hypoblast and epiblast (bilaminar disc)

hypoblast —> extraembryonic endoderm (heuser’s membrane)

epiblast —> extraembryonic mesoderm (vasculature of cord and plasenta), extraembryonic ectoderm (amniotic membrane) and the fetus ( ectoderm, mesoderm and endoderm)

27
Q

how can you do genetic testing on an embryo?

A
  • only requires a single cell from a pre-implanted embryo
  • the rest of cells go on to form the blastocyst
  • genetically test the single cell and if no genetic diseases are detected, the blastocyst is implanted into mother
28
Q

what are the functions of the trophoblast?

A
  • implantation into the uterus
  • differentiates into the chorion which contributes to the placenta
  • immunosuppression - as embryo expresses paternal antigens, so it protects it from being attached by mothers body
  • endocrine gland - produced HCG which maintains the corpus luteum in the ovary which produces progesterone to maintain uterine lining
29
Q

give an example of a trophoblast disease

A
  • hydatidiform moles
  • affect 1 in 500 pregnancies
  • happens when trophoblast grows out of control
  • most are miscarried but some will form a tumour
30
Q

when does implantation occur?

A
  • 6-7 days after fertilisation
31
Q

what is the process of implantation?

A
  • the blastocyst attaches to the uterine wall, ICM side first ( called apposition/adplantation)
  • the trophoblast proliferates to form syncytiotrophoblast and cytotrophoblast (remains)
  • the syncytiotrophoblast secretes enzymes to break down the uterine wall and vessels so the embryo can invade and penetrate the wall
  • lacunae form within the syncytiotrophoblast and fill will maternal blood
  • the stromal cells in the uterine wall undergoes a reaction and become filled with glycogen to supply the embryo until the placenta is vascularised
32
Q

what is the cytotrophoblast?

A
  • after trophoblast has proliferated

- inner layer of cells around the outside on opposite side of implantation, undergoing rapid mitotic activity

33
Q

what is the syncytiotrophoblast?

A
  • after trophoblast has proliferated
  • multinucleated with no cell boundaries as cells have fused together
  • it secretes enzymes that break down and digest the uterine wall and capillaries for the blastocyst/embryo to implant
34
Q

what are lacunae?

A
  • small areas within the syncytiotrophoblast that fill with the mothers blood after implantation to provide blood supply (before placenta)
35
Q

what is the structure of the embryo after implantation has occured?

A
  • underneath top layer of uterine wall now
  • surrounded by syncytiotrophoblast and lacunae
  • the hypoblast layer of the bilaminar disk has now formed Heuser’s membrane which surrounds the yolk sac (empty cavity atm)
  • the Heuser’s membrane also produces extracellular reticulum above it which will soon form chorionic cavity
  • the epiblast layer has formed the amniotic sac (below yolk sac (deeper in uterine wall)
36
Q

what is the yolk sac for?

A
  • forms part of the gut, produces the earliest red blood cells and vessels and is a source of germ cells for the gonads
  • lined by Heuser’s membrane (extraembryonic endoderm)
37
Q

what is the amniotic sac for?

A
  • where the fetus will develop inside
  • will become fluid filled
  • protects fetus from trauma and maintain constant temp
38
Q

what is the development by day 14?

A
  • the embryo ( is now suspended in the chorionic cavity (where the extracellular reticulum was) by a connecting stalk coming from the mesoderm
  • the cytotrophoblast and mesoderm extend into the syncytiotrophoblast between the lacunae, forming the stem villi
  • the mesoderm forms the vasculature of the placenta
  • the connecting stalk forms the umbilical cord
39
Q

what is the stem villi?

A
  • formed from cytotrophoblast and mesoderm extending up away from the embryo into the syncytiotrophoblast
  • kinda holding it in place deeper in the uterine wall
40
Q

what does the connecting stalk form?

A
  • umbilical cord
41
Q

what does the extra-embryonic mesoderm form?

A
  • vasculature of the placenta

FHMP (18 decks)

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