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Developmental Physiology > First Week of Human Development > Flashcards

First Week of Human Development Flashcards

1
Q

What is a zygote?

A

When a sperm fuses with an oocyte and contains maternal and paternal genes and chromosomes.

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2
Q

What is gametogenesis?

A

Gamete formation. Formation and development of specialized generative cells (gametes)

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3
Q

What is a special type of cell division that only occurs during gametogenesis?

A

meiosis

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4
Q

What occurs during Meisois 1 of spermatogensis?

A

Primary spermatagoenia become secondary spermatocytes or sister chromatids.

Primary spermatocyte (46 xy) split to become secondary spermatocytes: (23x) and (23y)

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5
Q

What happens during Meiosis II of Spermatogenesis?

A

Secondary Spermatocytes (23x) and (23y) divide and become 4 spermatids.

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6
Q

Once the four spermatids are developed how do they transform into mature sperm?

A

Gradually the 4 spermatids transform into mature sperm thru process of spermiogenesis.

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7
Q

What is spermiogenesis and how long does it take?

A
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8
Q

Where is the nucleus contained in a sperm?

A

The head of the sperm.

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9
Q

What is the acrosome?

A

The anterior 2/3rds of the sperm head that contains the enzyme that allows for penetration of the egg.

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10
Q

What happens to the Corona Radiata when the sperm releases enzymes?

A

The enzymes facilitate dispersion of the follicular cells allowing sperm penetration of zona pellucida.

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11
Q

What is the middle piece of the sperm do?

A

Contains mitochondria that fuels energy needed for motility.

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12
Q

What is oogenesis?

A

Oogonia are transorfed into mature oocytes.

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13
Q

What are the steps of Oogenesis?

A
  1. Primary Oocyte (46xx) forms
  2. Follicular cells develop around it
  3. Primary oocyte begin first meiotic division before birth
  4. First Meiotic phase produces a secondary oocyte and a first polar body during puberty.
  5. At ovulation the secondary ooctye begins the second meiotic division but only progresses if fertilized.
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14
Q

Where does fertilization of the egg occur?

A

Fallopian tubes

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15
Q

Walls of the ovarian follicle become what?

A

The corpus luteum.

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16
Q

What does the corpus luteum do?

A

Secretes estrogen and progesterone.

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17
Q

What does progesterone secreted from the corpus luteum do?

A

Prepares the endometrium for implantation of the ovum (blastocyte).

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18
Q

What prevents the degeneration of the corpus lutuem during pregnancy?

A

HCG

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19
Q

What hormone influences the development of the corpus luteum?

A

LH

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20
Q

What secretes HCG?

A

The Synctiotrophoblast of the blastocyte

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21
Q

How long does the corpus luteum remain functionally active after fertilization?

A

Throughout the first 20 weeks until the placenta assumes production of estrogen and progesterone to maintain the pregnancy.

22
Q

What happens to the corpus lutuem if the oocyte is not fertilized?

A

The corpus luteum involutes and degenerates 10-12 days after ovulation.

23
Q

What marks the beginning of fertilization?

A

Contact between a sperm and an oocyte.

Sperm penetrates the corona radiata

Then enters the zona pellucida.

24
Q

What is Acrosin?

A

A digestive enzyme in the head of the sperm (acrosome) that helps penetrate the egg.

25
Q

Once the sperm penetrates what occurs?

A

The zonal reaction occurs making the zona pellucida impermeable to other sperm.

26
Q

What happens after the sperm penetrates the oocyte and becomes impermeable to other sperm?

A

Fusion of the cell membranes of the oocyte and the sperm occurs. The head and tail enter the cytoplasm of the oocyte.

Completes the second meiotic division.

Forms a mature oocyte and second polar body. Forms the female pronucleus.

27
Q

After the female pronucleus develops what happens next?

A

Sperm enlarge to form male pronucleus & tail degenerates

Membranes of pronucleus break down & 23 chromosomes from each combine

Makes a Zygote with 46 chromosomes

28
Q

What are the results of fertilization?

A
  1. Stimulates secondary oocyte to complete 2nd meiotic division
  2. Restores diploid (46) number of chromosomes in Zygote
  3. Mingling of maternal & paternal chromosomes
  4. Determines sex of embryo
  5. Causes metabolic activation of oocyte & initiates cellular division in Zygote
29
Q

What is EPF?

A

Immunosuppressant protein (EPF)

  1. secreted by trophoblast cells which give rise to the placenta later.
  2. in maternal serum 24-48 hrs after fertilization
  3. Not typically used for detecting pregnancy typically use hCG test urine or blood
30
Q

What happens to the zygote after fertilization?

A
  1. Repeated mitotic division of the zygote occurs - rapid􏰀in # of cells - blastomeres (replicated cells)
  2. Divides into 2 blastomeres, 4, 8, etc.
  3. Occurs as zygote moves along the uterine tube to the uterus
  4. Process begins about 30 hrs after fertilization

Once 12-32 blastomeres develop the zygote becomes a morula.

31
Q

What is a morula?

A

A cluster of 12-32 blastomeres that is the name of a developing human.

32
Q

When does the morula form after fertilization?

A

About 3 days after fertilization as it enters the uterus.

33
Q

Where does blastocyst formation occur?

A

In the uterus.

34
Q

When does the developing embyro enlarge in size?

A

Does not occur until the zona pellucida degenerates.

35
Q

What is the sequence of blastomere growth?

A

By 30 hours- 4 blastomeres

By three days there are 6-12 blastomeres

By day four there are 16-32 blastomeres.

36
Q

What is nondisjunction?

A

Chromosomes can be added or lost containing 2 or more cell lines of different chromsome complements. Occurs during early cleavage of the embryo.

37
Q

When does the morula form and when does it enter the uterus?

A

Forms on day 3 and enters uterus on day 4.

38
Q

How does a blastocyst form?

A

Inside the morula a fluid filled cavity is formed.

Called the Blastocyst cavity.

39
Q

What is the purpose of the blastocyst cavity?

A

The cavity expands and the cells seperate into 2 parts:

  1. Trophoblast layer
  2. Embryoblast layer
40
Q

What is the purpose of the trophoblast layer?

A

Gives rise to the placenta

41
Q

What is the purpose of the embryoblast?

A

Gives rise to the embryo.

42
Q

Where does the fluid inside the morula come from?

A

The Uterus

43
Q

What is blastogenesis?

A

When the embryo and its membranes form the blastocyst.

44
Q

What does the blastocyst look like at this stage?

A

The blastocyst cavity is surrounded by a wall of trophoblast cells (will later become the placenta).

The zona pellucida surrounds the trophoblast cells.

45
Q

After the blastocyst has floated in uterine secretions for about 2 days what happens?

A

THe zona pellucida gradually degenerates and disappears.

46
Q

What does shedding of the zona pellucida allow?

A

Rapid growth of the blastocyst.

47
Q

What happens at about 6 days after fertilization?

A

The blastocyst attaches to the endometrial epithelium.

48
Q

What happens as soon as the blastocyst attaches to the endometrium?

A

The trophoblast layer seperates into two layers.

  1. Cytotrophoblast
  2. Sycncytiotrophoblast-

allows for deep burrowing of the blastocyst into the endometrium.

49
Q

What are syncytiotrophoblasts and what do they do?

A

Finger like processes that extend through the endometrial epithelium and invade the connective tissue. Allow for deep burrowing and implantation.

50
Q

When does implantation occur?

A

1) 4-5 Days - morula reaches uterus
2) Day 6 - begins implantation

51
Q
A

Developmental Physiology (4 decks)

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