Embryogenesis Flashcards

1
Q

What is the ovarian cycle?

A

The physiological changes that occur in the ovaries that are essential for the preparation and release of an oocyte.

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2
Q

What is the menstrual cycle?

A

The physiological changes in the endometrial layer of the uterus which are essential to receive a fertilised oocyte.

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3
Q

Describe the menstrual PHASE

A

Day 1-5
First day of menstruation, uterus sheds its endometrium down to the basal layer due to reduced level of oestrogen and progesterone which causes the endometrium to spasm and withdraw its blood supply.
50-150ml blood loss, enzyme plasmin inhibits clotting.

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4
Q

What is eumenorrhoea?

A

Normal regular menstruation

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5
Q

Describe the follicular phase

A

Day 1-13 runs alongside mestural phase but carries on longer.
Low levels of oestrogen and progesterone stumlaute the hypothalamus to produce gonadotrophin releasing hormone (GnRH).
GnRH causes production of FSH and LH by the anterior pituitary gland.
A series of endocrine functions take place to mature an oocyte within s Graafian follicle.
Maturation takes approx 7 days

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6
Q

Describe the ovulation phase

A

Days 14
High oestrogen levels cause an increase in LH around days 12-13 which lasts 48 hours. This matures the oocyte and weakens the follicle wall.
Ovulation occurs on day 14
Fimbrae guide the oocyte into the uterine tube to await fertilisation.
Meiotic cell division resumes and the diploid oocytes become haploid.
Mucus in the cervix awaits spermicide from intercourse. Following ovulation the oocyte travels to the uterus.

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7
Q

Describe the luteal phase?

A

Day 15-28
Cells from ruptured follicle produce corpus luteum.
Corpus luteum produced oestrogen, relaxin, inhibin and progesterone for 2 weeks
Relaxin creates uterine quiescence-ideal environment for fertilised oocyte to implant
Corpus luteum continues its role until the placenta is formed and mature
If oocyte is unfertilised the corpus luteum degenerates leading to low levels of oestrogen and progesterone which causes a high level of GnRH causing the release of FSH which ultimately restarts the cycle.

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8
Q

What forms a zygote?

A

The fusion of genetic material from the haploid sperm cell and the secondary oocyte

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9
Q

How long is the fertilisation process?

A

12-24 hours

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10
Q

How many sperm reach the oocyte?

A

200 out of 300 million (avg)

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11
Q

What is capacitation?

A

The removal of the glycoprotein coat and increased flagellation of the sperm

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12
Q

What is the zona pellucida?

A

The extra cellular matrix surrounding the oocyte.

Creates chemicals to attract capacitated sperm

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13
Q

What is an acrosome reaction?

A

The acrosomal layer of the sperm releases hyaluronidase to allow access to the zona pellucida. Many sperm are involved in this. The first sperm to reach the zona pellucida penetrates it

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14
Q

What happens to the oocyte upon penetration?

A

It undergoes a cortisol reaction making it impermeable to other sperm. The nuclei of the oocyte and the sperm fuse to form a zygote with a full set of 46 chromosomes

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15
Q

What is the blastocyst called once it has embedded into the decidua?

A

The embryo

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16
Q

When does an embryo become a foetus?

A

At 8 weeks gestation

17
Q

Where does the embryo develop from?

A

The embryonic disc

18
Q

What are the 3 layers of cell development?

A

Ectoderm - closest to the amniotic sac. Forms the skin and most of the CNS
Mesoderm - forms the bones, muscles, heart and blood vessels. Also kidneys and reproductive organs
Endoderm - forms digestive and respiratory organs

19
Q

Outline what happens at day 13 of embryonic development

A

Chorionic villi secrete hCG which stimulates the corpus luteum to continue producing hormones to continue the pregnancy

20
Q

Outline day 15 of embryonic development

A

Primitive streak appears in midline of dorsal surface. Blood vessels form

21
Q

Outline day 18 of embryonic development

A

Primitive nervous system folds into position. Heart begins to twitch. Eyes and ear develop.

22
Q

Weeks 3-4 of embryonic development

A

Heart pumps blood, brain divides into fire mid and hind

Lungs firm, gastrointestinal system identifiable

23
Q

Outline week 5 of embryonic development

A

Rapid brain growth. Limb buds appear. Umbilical cord formed

24
Q

Outline week 6 of embryonic development

A

Liver behind to function. Rudimentary kidneys and genitalia form. Cartilage forms skeleton

25
Q

Outline week 7 of embryonic development

A

Eyelids, gall bladder, palate and tongue form. Diaphragm develops. Arms and legs begin movement.

26
Q

Outline weeks 8 of embryonic development

A

Hands and feet are well formed, heart has 4 chambers and major blood circulation begins. 40-60 bpm. By the end of the 8th week all major body systems are formed and the embryo becomes a foetus

27
Q

Outline weeks 8-12 of fetal development?

A

Head constitutes 1/2 of fetal length. Intestines established. Amniotic fluid swallowed and foetus uriniates

28
Q

Outline weeks 13-16 of fetal development?

A

Doubles in length. Facial features migrate to correct position. Meconium develops in the gut

29
Q

Outline weeks Weeks 17-24 of fetal development?

A

Fetal heart heard by stethoscope, movements felt. Vernix formed, hair on head

30
Q

Outline weeks 25-28 of fetal development

A

Subcutaneous fat laid down, eyes open, lung physiology sufficient to allow gaseous exchange

31
Q

Outline week 29 of fetal development

A

Foetus is fully formed and rig and can work to an extent. For the remainder of the pregnancy organ physiology matures