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MD3002 WEEK 10 - A > 2. Coitus, Fertilisation and Preimplantation > Flashcards

2. Coitus, Fertilisation and Preimplantation Flashcards

1
Q

Describe the human sexual response? and justify

A

• Human ovula/on however is ‘hidden’.
• Human females are recep/ve to males throughout their
menstrual cycle.
• It has been suggested that human sexual behaviour has developed as a way of strengthening pair bonding to support the long development of human children.

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2
Q

What are the 4 phases of the human sexual response?

A

EPOR: Excitement, Plateau. Organism, Resolution

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3
Q

What is the excitement phase of the human sexual response?

A

Sexual arousal – psychological and physical stimula/on of erogenous zones.
Tumesence and erec/on of penis and clitoris, engorgement of female tract
• Parasympathetic - erection
• Sympathetic - ejaculation

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4
Q

What is the plateau phase of the human sexual response?

A

Intensification of arousal

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5
Q

What is the orgasm phase of the human sexual response?

A

Series of involuntary muscular contractions in both sexes with intense pleasurable sensations

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6
Q

What is the resolution phase of the human sexual response?

A

Detumescence and time during which re-arousal is impossible (may not be true in women)

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7
Q

Variation of ovarian cycle?

A

Luteal fixed at 14 days

Follicular and menstrual vary

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8
Q

How long are sperm and oocytes viable for?

A

Sperm: 24-72 hours
Oocytes: 12-24 hours

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9
Q

For fertilisation to occur, coitus must occur….

A

Between:

  • 3 days before ovulation
  • 1 day after ovulation
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10
Q

For pregnancy to occur…

A

Sperm introduction should be between 5 days before and one day after ovulation

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11
Q

After fertilisation will switch from maternal to …

A

foetal

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12
Q

What are the time spans of the different trimesters of pregnancy?

A

First trimester weeks 1-12 (most miscarriages occur)
Second trimester weeks 13-28 (At 24 weeks 50% survival rate for early prematurity)
Third trimester weeks 29-40

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13
Q

What does parturition mean?

A

Birth

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14
Q

How likely are women to conceive?

A

50% pregnant after 2 cycles
85% pregnant after 6 months
Leaves 5% subfertile
10–15% of all pregnancy miscarry

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15
Q

Abnormal development?

A

Only 20% of unprotected intercourse results in development to blastocyst stage
Sponanteous abortion (pre- and post-implanation failure) occurs frequently
8-20% of blastocysts fail to implant
Clinically detected pregnancies 15-20% will fail in the first 12 weeks
Possible that 15-20% of human conceptions survive to successful birth

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16
Q

Why do sperm show high rate of mutation?

A

Lack DNA repair system

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17
Q

What are the two periods of foetal development?

A

Embryonic period 0-8 weeks

  • Preimplantation embryo
  • Implantation
  • Differentiation and development of the organ system

Foetal period 8-40 weeks

  • Differentiation continues
  • Growth
18
Q

How is the egg/oocyte transported at ovulation?

A
  1. Egg extruded onto surface of ovary
  2. Smooth muscle of fimbriae cause them to pass over ovary while cilia beat in waves toward interior duct
  3. Cumulus cells from the surface of the ovary aid transport. They cling to the ciliated surHface of the fimbriae.
  4. Transport by a ciliary current (+ peristalsis) to the ampulla.
19
Q

How is sperm transported to the egg from ejaculate?

A
  1. Ejaculation deposits semen into vagina then movement into cervix
  2. Passage into cervical mucus is dependent on oestrogen-induced changes in mucus consistency
  3. Sperm can reach uterus minutes/hours after ejaculation. Can survive 1-2 days within cervical mucus before release to enter uterus
  4. Movement through uterus and fallopian tubes is via sperm’s own propulsions and uterine contractions
  5. Sperm mortality from vagina to fallopian tubes is large.
20
Q

Sperms movement through uterus and fallopian tubes is via….

A

Sperm’s own propulsions and uterine contractions

21
Q

Why is Sperm mortality from vagina to fallopian tubes large?

A
  1. Vaginal environment is acidic

2. Length and energy requirements of trip

22
Q

What is capacitation?

A

Capacitation is a functional maturation of the spermatozoon. The changes take place via the sperm cell membrane in which it may be that receptors are made available through the removal of a glycoprotein layer. The area of the acrosomal cap is also so altered thereby that the acrosome reaction becomes possible.
Due to female tract secretions

23
Q

What is the result of capacitation?

A
  1. Change from wavelike beats of sperm tail to whip-like action to propel sperm forward
  2. Sperm’s plasma membrane is altered so it is capable of fusing with surface membrane of egg (acrosome reaction)
    - Destabilises surface membrane to enhance fusion capability
24
Q

What are the 4 changes in the sperm membrane during capacitation that enhance its fusion abilities with oocytes?

A
  1. Increase in Ca2+ permeability = Rise in intracellular Ca2+
  2. Removal of membrane proteins (glycoprotein)
  3. Change in surface charge
  4. Depletion of cholesterol
25
Q

Where is the normal site of fertilisation occurring?

A

The ampulla of the uterine tube

26
Q

Stages of fertilisation:

From fusion of sperm to egg –> Contents of sperm-cell entering oocyte

A
  1. Fusion of sperm to egg
  2. The sperm cell weaves past follicular cells and binds to the zona pellucida
  3. A rise in [Ca2+]i inside the cell triggers the exocytosis of the acrosome (acrosome reaction) which contains hydrolytic enzymes
  4. Hydrolytic enzymes contained in the acrosomal cap are released. These enzymes locally dissolve the ZP. The whip-like action of the tail pushes the sperm head towards the oocyte membrane
  5. With the head of the sperm now lying sideways, microvilli on the oocyte surround the sperm head. The two membranes fuse. The contents of the sperm-cell enter the oocyte, the sperm-cell membrane remains behind.
27
Q

What is the acrosome reaction?

A

Induced by the sperm head contacting the zona pellucida and binding to glycoproteins ZP2 and ZP3

  1. Fusion of acrosome plasma membranes
  2. Releases contents of the acrosome
  3. Causes entry of more Ca++
  4. Sperm then digests a path through the ZP via proteolytic enzymes

i.e. exocytosis of acrosomes hydrolytic enzymes to dissolve ZP

28
Q

What are the stages of fertilsation:

From the contents of sperm-cell entering oocyte –> male and female pronuclei fusion

A
  1. A rise in [Ca2+]i inside the oocyte triggers the cortical reactions. The enzymes released result in ZP protein changes, causing the ZP to harden which prevented other sperm entry.
  2. The rise in [Ca2+]i inside the oocyte induces the completion of the oocytes 2nd meiotic division + formation of 2nd polar body
  3. The sperm head enlarges to become the male pronucleus
  4. The male and female pronuclei fuse.
29
Q

What is the cortical reaction?

A

Exocytosis of granules that previously lay immediately beneath the plasma membrane.

30
Q

What is the male and sperm contribution during pronuclei fusion in fertilisation?

A

Sperm: Nuclear material and centrioles
Oocyte cytoplasm: All other organelles
Mitochondrial DNA inherited exclusively via maternal route

31
Q

2 results of rise of [Ca2+]i in oocyte

A
  1. ZP hardening via cortical reaction

2. Completion on 2nd meiotic division of oocyte + formation of 2nd polar body

32
Q

For the following stages of ovulation-fertilisation-implanation, what is the day after LH peak and location:

  1. Ovulation
  2. Fertilisation
  3. Cell division to 32 cells
  4. Blastocyst enters uterine cavity
  5. Implantation
  6. Human chorionic gonadotropin (hCG) from implanted blastocyst (trophoblast cells) rescues CL
A
  1. Ovulation
    - 1 day after LH peak
    - In ovary
  2. Fertilisation
    - 2 days after LH peak
    - In Fallopian tube, ampulla
  3. Cell division to 32 cells
    - 2-4 days after LH peak
    - In fallopian tube
  4. Blastocyst enters uterine cavity
    - 5 days after LH peak
    - In uterus
  5. Implantation
    - 6-7 days after LH peak
    - Uterus
  6. Human chorionic gonadotropin (hCG) from implanted blastocyst (trophoblast cells) rescues CL
    - 9-10 days after LH peak
    - In Trophoblast then maternal ovary
33
Q

What is conceptus?

A

The embryo in the uterus

34
Q

Features of conceptus? Why in fallopian tube, formation of new structures, cell type?

A

Cenceptus is held in the fallopian tube as oestrogen maintains contraction of smooth muscle near where the fallopian tube enters wall of uterus

Conceptus undergoes mitotic cell divisions i.e. cleavage and morula is formed

Cells are totipotent

35
Q

Why is the conceptus the same size as the fertilized egg?

A

As no cell growth has occurred before each division

36
Q

What are totipotent cells?

A

Totipotent cells can form all the cell types in a body (plus the extraembryonic or placental cells)
Embryonic cells within the first couple of cell divisions after fertilization are the only cells that are totipotent.

37
Q

What are pluripotent cells?

A

Pluripotent cells can give rise to all of the cell types that make up the body.
E.g. Embryonic stem cells are considered pluripotent.

38
Q

What is multipotent cells?

A

Multipotent cells can develop into more than one cell type, but are more limited than pluripotent cells
E.g. Adult stem cells and cord blood stem cells are considered mul/potent.

39
Q

Why can blastocyst cells be removed whilst damage to embryo?

A

As the cells are pluripotent

40
Q

What are the events that occur when the conceptus/blastocyst enters uterine cavity?

A
  1. Plasma progesterone levels rise 3-4 days after fertilisation, smooth muscle relaxes and conceptus passes into uterus
  2. Approx 4-5 days after fertilisation, cavities develop between the cells
  3. For approx 3 days, conceptus/blastocyst lies free in the uterine cavity supported by uterine secretions, received nutrients from it.
  4. Day 6 the blastocyst attaches to the endometrium adjacent to the inner cell mass (embryonic pole)
  5. Trophoblast differentiates into: Inner cytotrophoblast and outer syncytiotrophoblast
    - Fingers of syncytiotrophoblast invade the endometrium
41
Q

What is the structure of the blastocyst

A

Inner cell mass: Forms entire body
Fluid filled cavity i.e. blastocoele
Trophoblast: Outer layer of blastocyst, gives rise to placenta
Zona pellucida= Egg shell

MD3002 WEEK 10 - A (10 decks)

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