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Human Architecture > Early Embryo > Flashcards

Early Embryo Flashcards

1
Q

endocrine

A

diffusible molecules that act globally

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2
Q

paracrine

A

diffusible molecules that act over short distances

  • action is often determined by diffusion gradient
  • target cells may be under the influence of multiple inducers
  • ex: hormones, neurotransmitters, chemokine, cytokines
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3
Q

Juxtacrine

A

non-diffusible molecules

  • direct interaction of cell surface proteins or extracellular matrix components with receptors
  • gap junctions- direct connection between the cytoplasm of adjacent cells
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4
Q

autocrine

A

cells act on themselves. This is a type of paracrine signal

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5
Q

gametogenesis

A

production of sperm and ova

diploid 2 N stem cells -> (meiosis) -> Haploid 1 N cells -> (maturation) -> viable gametes

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6
Q

Primordial germ cells (PGCs)

A
  • reside in the wall of the yolk sac
  • form the gametes
  • migrate around the developing GI tract and onto the posterior body wall to the genital ridge (form gonads)
  • migration is guided by chemokine released by the genital ridge
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7
Q

Spermatogenesis

A
  • Primordial germ cells (PGCs) lie dormant in the seminiferous tubules of the testis until puberty
  • elevated testosterone levels have an effect on Sertoli cells that influence them to become spermatogonia, the stem cell population for sperm
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8
Q

Spermatogenic sequence

A

Primordial germ cells (PGCs) -> spermatogonia (mitotic; diploid 2N) -> primary spermatocytes (diploid 4N; crossover time) -> meiosis 1 -> secondary spermatocytes (haploid 2N) -> Meiosis II -> spermatids (haploid 1N = 22 + X or Y)

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9
Q

Relation of Sertoli cells to developing sperm

A
  • creates isolated microenvironment formed by tight and gap junctions (blood-testis barrier)
  • produce growth factors and other control substances
  • absorb excess cytoplasm
  • released sperm are still immotile and unable to fertilize an ovum
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10
Q

sperm cell

A

Head: contains nucleus; capped by the acrosome (hydrolytic enzymes: across, hyaluronidase)

mid piece: mitochondria; anchors tail

tail: big flagellum

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11
Q

Spermiogenesis

A

refers to sperm maturation

  • sperm is stored in the epididymis
  • sperm moves through the vas deferens to the urethra where seminal secretions are added- produced by the seminal vesicles, prostate, and bulbourethral glands
  • sperm must undergo capacitation in the female tract before it is able to fertilize the ovum.
  • capacitation: changes in the acrosome that prime it for release of its enzymes
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12
Q

Oogenesis

A
  • Begins in the 5th month of gestation
  • Oogonia remain arrested at prophase in primordial/primary follicle until the menstrual cycle starts
  • dependent on menstrual cycle so the process stops at menopause
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13
Q

Oogenic sequence

A

Primordial germ cells (PGCs) -> mitosis -> oogonia (diploid 2N) -> initiation of meiosis -> primary oocyte (diploid 4N) -> progression of meiosis 1 -> secondary oocyte (haploid 2N) -> Meiosis II -> definitive oocyte (haploid 1N = 22 + X)

process produces 1 definitive oocyte and 3 polar bodies

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14
Q

folliculogenesis

A
  • Puberty increases FSH
  • primordial follicle -> primary follicle (cuboidal and surrounded by zone pellucida, a glycoprotein coat that acts as a sperm barrier
  • follicle becomes multi-layered then forms a cavity (astral follicle) -> mature follicle surrounded by thecae cells (steroidogenic)
  • primary oocyte -> secondary oocyte and first polar body
  • second meiotic arrest occurs before ovulation (metaphase II)
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15
Q

ovulation

A

involves the proteolytic breakdown of the follicular wall and thecae smooth muscle contraction

-meiosis II does not start until ovum is fertilized

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16
Q

Pituitary hormones

A

FSH: peaks at ovulation and promotes follicle and oocyte maturation; steroids produced by the follicle control the Fallopian tube and uterus to produce an hospitable environment

LH: stimulates ovulation and converts follicle into corpus luteum (CL) which produces progesterone for a short period

17
Q

ovarian hormones

A

Estrogen peaks before ovulation and increases again during the corpus luteum phase

Progesterone peaks at the corpus luteum

both estrogen and progesterone tapers off if fertilization does not occur

18
Q

coverings of the ovum

A
  • Cumulus remains in contact with the oocyte via processes and it regulated meiosis. There is also a hyaluronic acid-rich ECM associated with it that is a barrier to sperm
  • Zona Pellucida is a more significant barrier to the sperm; may facilitate transportation of the embryo down the Fallopian tube
19
Q

post-ovulatory events

A

oocyte is picked up by the Fallopian tube; transported to the ampulla where it meets capacitated sperm. sperm are attracted to the ampulla through chemotropic factors
- follicle is converted to a corpus luteum- source of progesterone needed to maintain pregnancy

20
Q

fertilization (time zero)

A

capacitated sperm must penetrate the cumulus oophorus and bind to receptors on the zone pellucida (ZP3 protein), thereby releasing acrosomal enzymes

  • cortical reaction: release of cortical granules into the perivotelline space; enzymes make the ZP3 protein non receptive to other sperm
  • completion of meiosis in the ovum -> female pronucleus (1N haploid genome)
21
Q

pronuclei

A
  • the sperm nucleus enters the ovum, forming the male pronucleus
  • male and female pronuclei fuse to form a diploid 2N nucleus = zygote
22
Q

preimplantation development

A

zygote -> morula -> blastocyst

embryo is still encased in ZP until implantation

23
Q

initial differentiation of the embryo

A
  • blastomeres are identical and totipotent up until the 8 cell stage blastomeres
  • compaction occurs at 8-cell stage -> gap junctions dorm between cells and the blastomeres become polarized so that they have an outer surface and a n inner surface

outer cells -> trophoblast -> placenta

inner cells -> inner cell mass (ICM) -> embryo

24
Q

formation of the blastocyst

A

blastocyst cavity forms from the result of tight junctions forming between outer cells

fluid (H2O) and ion (Na+) transport leads to cavity formation

25
Q

implantation

A

hatching: combination of embryonic and uterine protease activity breaks down the ZP
attachment: occurs at the ICM end of the blastocyst
invasion: occurs by proteolytic breakdown of the endometrium

26
Q

in vitro fertilization (IVF)

A

Indications: Fallopian tube blockage; some male factor infertility

ova and sperm collected then combined in vitro where fertilization takes place

embryo grown in vitro to 4-16 cell stage, then transferred to uterus

27
Q

Zygote intrafallopian transfer (ZIFT)

A

similar to IVF except time of transfer is just after fertilization and transfer is to the ampulla of the Fallopian tube

28
Q

Gamete intrafallopian transfer (GIFT)

A

indications: low sperm count or poor sperm quality; unexplained female infertility

sperm and eggs mixed and placed in ampulla

29
Q

sperm collection

A

if the vas deferent is obstructed or absent sperm can be obtained from the testis or epididymis

  • microepididymal sperm extraction (MESA): microsurgical procedure performed under general anesthesia; results in enough sperm for IVF
  • Percutaneous epididymal sperm aspiration (PESA): a needle is guided into the epididymis to collect just a few sperm. few and relatively immature sperm are obtained
  • Testicular sperm extraction (TESE): immobile sperm are obtained; they are not as viable as epididymal sperm
  • intracytoplasmic sperm injection (ICSI): when PESA or TESE are used to collect few immature sperm, IVF will not work. Sperm must be directly inserted into the ovum. A single sperm is injected directly into the egg cytoplasm. ICSI results in higher a incidence of chromosomal anomalies than natural fertilization
30
Q

sex selection

A
  • based on X sperm having more DNA than Y sperm
  • stain DNA and sort by flow cytometry- individual sperm are directed to a collection container based on the amount of DNA detected
31
Q

Analysis during IVF

A
  • remove one or more cells from an 8-cell embryo
  • chromosomal analysis: looking for abnormal numbers of chromosomes or gross abnormalities
  • polymerase chain reaction: amplification of small amounts of DNA for specific gene analysis
32
Q

Bilaminar disc

A

ICM becomes two layers:
epiblast + hypoblast = bilaminar disc

basement membrane develops between these two layers

33
Q

development of the trophoblast

A

Original trophoblast has two pathways:

1) cytotrophoblast: dividing stem cell population
2) syncytiotrophoblast: many nuclei in an undivided cytoplasm; formed by the fusion of cytotrophoblast cells. it can not undergo further mitosis; very invasive tissue going into endometrium; source of hCG

34
Q

Invasion of the conceptus -Day 8

A

trophoblast: syncytium grows into the endometrium and cytotrophoblast continues to divide

ICM: formation of the amnion and amniotic cavity begins within the epiblast. this cavity will eventually become a fluid-filled space surrounding the embryo

35
Q

first step in formation of the yolk sac (day 9)

A

hypoblast: migrates out into former blastocoel as the exocoelomic membrane

36
Q

epiblast (day 9)

A

expansion of the amnionic cavity; the roof of this cavity is called the amnion and is composed of amnioblasts

Human Architecture (17 decks)

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