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IMMS session 4: introduction to the cardiorespiratory system > embryo > Flashcards

embryo Flashcards

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1
Q

what enzyme activates the oocyte and what changes does this bring about within the oocyte?

A

sperm releases phospholipase c zeta (PLCz) which activates the egg to release calcium from internal stores to facilitate fertilisation

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2
Q

what is the male and female pro-nucleus and when does it form?

A

the two sets of haploid chromosomes form the female and male pro-nucleus (23 chromosomes each), this occurs 4-7 hours after fertilisation. the pro-nuclei are equal in size

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3
Q

what is the process of syngamy?

A

the male and female pro-nucleus migrates to the centre, and the haploid chromosomes pair up and replicate DNA for the first mitotic division the pro-nuclear membranes also break down and spindle fibres form

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4
Q

what is cleavage and when does it start?

A

several mitotic cell divisions, that start on day 2. the ooplasm divides in half. during cleavage, the cell mass does not change but the number of nuclei increases

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5
Q

whose genetics control the initial cell divisions and what controls it after?

A

the maternal stores of RNA lay down developmental control prior to the 4-8 cell stage. afterwards, the embryonic genome becomes activated and embryonic transcription can occur

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6
Q

what is significant about day 3 of development?

A

8 cells have formed, which is the number that is required to form an entire foetus. these cells are totipotent

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7
Q

what is the compaction stage of embryological development and what occurs during it?

A

day 4: the cells flatten, tight junctions occur, the outer cells become polarised and roughly 16 cells are present

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8
Q

what is the presence of 16 cells in embryology called?

A

a morula

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9
Q

what happens on day 5 of embryological development, and roughly how many cells are there?

A

tight junctions form between the outer cells which forms the trophectoderm. sodium is pumped in, which leads to water following by osmosis leading to a fluid cavity. there are now greater than 80 cells. the cells are now pluripotent. this cavity will continue to expand

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10
Q

what happens on day 6 of embryological development?

A

due to the expansion (and enzymatic factors), the blastocyst hatches from the zona pellucida

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11
Q

what is the main energy substrate in the preimplantation stages of the embryo and the blastocyst stage?

A

preimplantation stage: pyruvate
blastocyst stage: glucose

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12
Q

compare the genetic control in the early cleavage with the blastocyst?

A

cleavage: maternal
blastocyst: embryonic

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13
Q

compare the metabolic activity in the early cleavage with the blastocyst?

A

cleavage: low
blastocyst: high

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14
Q

compare the biosynthetic activity in the early cleavage with the blastocyst?

A

cleavage: low
blastocyst: high

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15
Q

compare the nutrient requirements in the early cleavage with the blastocyst?

A

cleavage: simple (low glucose, non essential amino acids and pyruvate)
blastocyst: complex (high glucose, essential and non-essential amino acids as well as vitamins)

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16
Q

what nutrients does the developing embryo receive and where does it receive these from?

A
  1. cumulus cells (a group of closely associated granulosa cells that surround the oocyte)
  2. fallopian tube (calcium, sodium, glucose, chloride and proteins)
  3. uterine secretion (iron, fat soluble vitamins and glucose)
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17
Q

what growth factors and cytokines are important in embryonic growth and differentiation?

A
  1. insulin-like growth factor - IGF–I and IGF–II increase cell numbers in blastocyst
  2. leukaemia inhibitory factor (LIF) enhances embryo-endo interaction
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18
Q

what happens when the embryo has implanted on day 10?

A

gastrulation, where three germ layers form ectoderm, mesoderm and endoderm

19
Q

how does the uterus adapt for implantation?

A

the endometrial cells change to help with the absorption of uterine fluid, which allows the blastocyst to come nearer to the endometrium to become immobilised. blood supply also improves and the maternal uterine tissue (decidua) also improves

20
Q

how long is the implantation window?

A

4 days (6-10 days post ovulation)

21
Q

how is the implantation process regulated?

A

coordination and communication between the endometrium and the developing embryo, regulated by hormones, cytokines and growth factors, proteases, genetics and cell adhesion molecules

22
Q

what are the three phases of embryo implantation?

A
  1. apposition
  2. attachment
  3. invasion
23
Q

what is the apposition stage of embryo implantation?

A

the blastocyst adheres to the uterine lining at the area above the ICM

24
Q

what is the attachment stage of embryo implantation?

A

the adhesion to the endometrium becomes stronger, and the endometrium gets penetrated by the microvilli that protrudes from the trophoblast. the blastocyst and endometrium communicate via receptor-ligand interactions. the adhesion always occurs below the inner cell mass

25
Q

what is the invasion stage of embryo implantation?

A

the trophoblastic protrusions continue to invade the endometrium, and differentiate to form the syncytiotrophoblast

26
Q

what does the syncytiotrophoblast do?

A

erodes endometrial blood vessels till it comes into contact with maternal blood to form the chorionic villi. this is the initiation of the formation of the placenta

27
Q

what is the lacunae and its significance?

A

formed by the syncytiotrophoblast; maternal blood filled spaces where nutrients are exchanged and waste products are removed

28
Q

what is the decidual reaction stage of embryological development?

A

stromal cells adjacent to the blastocyst differentiate into metabolically active, secretory cells or Decidual Cells (under influence of progesterone)

29
Q

what do the secretions of decidual cells do?

A

contain growth factors/proteins to support growth of implanting blastocyst in the initial stages before the placenta is fully developed, which improves the vascularisation of the uterine wall

30
Q

is the decidual reaction required for implantation?

A

no, ectopic implantation can occur anywhere in the abdominal cavity

31
Q

how is the foetus protected from the mothers immune system?

A

at the same time as the decidual reaction, leukocytes in the endometrial stroma secrete interleukin-2 which prevents maternal recognition of the embryo as a foreign body during the early stages of implantation

32
Q

what is are the two roles of human chorionic gonadotropin?

A
  1. ensures the corpus luteum continues to produce progesterone throughout the first trimester of pregnancy (prevents menstruation and maintains the endometrium lining).
  2. immunosuppressive – has highly negative charge, may repel the immune cells of the mother & protect the foetus
33
Q

what happens to hCG levels during pregnancy?

A

levels double every 1-3 days for the first 10-12 days. a short doubling time signifies a healthy pregnancy

34
Q

what does a slow rate of hCG increase indicate?

A

early abortion, ectopic pregnancy, delayed implantation

35
Q

what are the components of in vitro culture during days 1-3?

A

water, salts, ions, lactate, proteins, no/low glucose, non essential amino acids

36
Q

what are the components of in vitro culture during days 3+?

A

water, salts, ions, pyruvate, lactate, proteins glucose, essential and non-essential amino acids, vitamins

37
Q

what are some maternal factors that influence embryo growth in vitro?

A

follicle environment

38
Q

what are some embryonic factors that influence embryo growth in vitro?

A

cleavage rate, size of blastomeres, variation in embryo metabolism

39
Q

what factors affect embryo growth in vitro?

A

exposure to light, oxygen, pH, osmolarity and culture medium

40
Q

on what day is the embryo transferred to the mother and what happens to the remaining embryos?

A

day 5. the rest are preserved by being frozen if they are of good quality and at the correct stage of development

41
Q

what is the embryo transferred to the mother with?

A

with embryo glue which increases cell-cell adhesions increasing the likelihood that the embryo undergoes apposition and attachment

42
Q

why may IVF implantation fail?

A

insufficient trophoblast invasion of maternal blood vessels, an issue with the sperm, issues with the embryo (40% IVF fertilised eggs are abnormal)

43
Q

what is recurrent implantation failure classed as?

A

failure to achieve a clinical pregnancy after transfer of at least 4 good quality embryos in at least 3 cycles, with the female being under the age of 40

44
Q
A

IMMS session 4: introduction to the cardiorespiratory system (11 decks)

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