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Microanatomy > Gametogenesis, Fertilization, Cleavage and Gastrulation (Germ layers) > Flashcards

Gametogenesis, Fertilization, Cleavage and Gastrulation (Germ layers) Flashcards

1
Q

Spermatogenesis (metamorphosis)

A

Spermatogonium (2N), 1
——– S phase (mitosis/ differentiation) ——-
Primary spermatocyte (2N, # of chromos decrease, diploid, 16), 1
——-Meiosis 1———
Secondary spermatocytes (1N, haploid, no DNA duplication, 32), 2
——- Meiosis 2———–
Spermatids (1N, haploid, don’t divide, 64), 4
———- Metamophosis ———
Spermatozoa (1N, flagellum), 4

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2
Q

When is mitosis completed for females?

A

In fetal state, before birth
At birth all eggs are primary oocytes

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3
Q

Oogenesis

A

Oogonium
——– S phase (mitosis/ differentiation) ——-
Primary Oocyte (diplotene, 2N)
——-Meiosis 1———
Secondary Oocyte and First polar body (1N)
——- Meiosis 2———–
Ootid and second polar bodies (1N)
———- differentiation ———
Ovum

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4
Q

What will the primary oocytes undergo?

A

Atresia
360 will ovulate out of the 100,000 after puberty

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5
Q

When is meiosis 1 arrested in females?

A

During primary oocyte at diplotene stage

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6
Q

When is meiosis 1 completed in females?

A

Just before ovulation (all mammals) or after ovulation in the ampulla without sperm (mare and dogs)

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7
Q

When is Meiosis II completed?

A

After sperm penetration at secondary oocyte and polar body

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8
Q

What are the ovulated eggs?

A

Female dogs and mares: primary oocyte
All other species: secondary oocyte

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9
Q

Steps prior to fertilization in females

A
  1. Capacitation of sperm
  2. Binding of sperm with zona pellucida
  3. Acrosome reaction
  4. Penetration of zona pellucida
  5. Sperm-egg cell membrane fusion
  6. Cortical reaction
  7. Completion of Meiosis II (2nd polar body forms)
  8. Pronuclei formation
  9. Union of male and female pronuclei
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10
Q

Capacitation

A

Removal of certain sperm membrane proteins

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11
Q

Acrosome reaction

A

Rupture of outer acrosomal membrane
Hydrolytic enzymes released
Motility increases resulting in zona penetration

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12
Q

Cortical reaction

A

Release of glycoprotein granules from cytoplasm of egg
Hardens the zona pellucida and alters oocyte membrane to prevent polyspermy

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13
Q

Pronuclei formation

A

Sperm nucleus is heterochromatic (must condense)
Ovum chromos must coil

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14
Q

Union of pronuclei

A

Fertilization
Results in restoration of 2N chromo number
Forms zygote

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15
Q

What are the results of fertilization?

A

Completion of Meiosis II
Restoration of diploid chromo number
Determination of genetic sex
Initiation of cleavage

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16
Q

Cleavage

A

Division of zygote into many cells without an increase in mass cytoplasm

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17
Q

Blastomeres

A

Cells that lie within the confines of zona pellucida

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18
Q

Morula

A

A clumped group of 8-16 cells formed by cleavage
Latin name for “small mulberry”

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19
Q

Most embryos reach the ______ at the _________ stage.

A
  1. Uterus
  2. Morula
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20
Q

When is morula stage (uterus) reached for most species?

A

4-5 days

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21
Q

What happens to blastomeres after stage 8?

A

They lose their universal potential
Each blastomere can no longer become an embryo

22
Q

What is the second stage of the blastomere?

A

Blastula

23
Q

Blastocoel

A

Cavity formed when fluid-filled spaces coalesce among blastomeres

24
Q

Trophoblast

A

Formed when blastomeres surround the blastocoel
Future amnion and chorion

25
Q

Inner cell mass (embyro proper)

A

When some blastomeres form a mass at one end of the blastcoel

26
Q

How long does the blastula stage last?

A

5-9 days after ovulation

27
Q

What are the stages of the blastomere?

A
  1. Blastomere
  2. Morula
  3. Blastula
  4. Hatching (degeneration of zona pellucida)
  5. Gastrulation (germ layers developed)
28
Q

Hatching

A

Degeneration of the zona pellucida
Degenerates one day after completion of blastula

29
Q

Which species are exceptions to hatching?

A

Horses
Pigs and ruminants

30
Q

What happens to the zona pelucida in horses?

A

It’s replaced by glycoprotein capsule (neo-zona)
Remains until 21 days of gestation

31
Q

What happens after hatching in pigs and ruminants?

A

Trophoblast undergoes a rapid elongation
Up to 1 meter long in pigs and 35 cm in ruminant

32
Q

For pigs, when is elongation completed?

A

9-16 days of gestation

33
Q

For ruminants, when is elongation completed?

A

12-14 days of gestation

34
Q

Formation of Primitive Streak (P.S.)

A

Thickening of caudal end of epiblast cells due to proliferation
Formation of 2 ridges and a central groove along the diameter of a streak

35
Q

What is the significance of PS?

A

First step in the formation of mesoderm
Establishes cranial and caudal ends of the embryo

36
Q

Primitive node (Hensen’s node)

A

Formed by the cranial most end of the primitive streak

37
Q

What is the notochord remnant in adults?

A

Nucleus pulposus

38
Q

How is the mesoderm split?

A

Paraxial (closer to notochord)
Intermediate
Lateral (develops coelom and divided into somatic and splanchnic)

39
Q

Differentiation of somite

A

Paraxial/ mesoderm differentiates on each side of notochord into somite
Somite formation begins cranially and extends caudally

40
Q

What is each vertebral somite represented by?

A

One pair of somite, each pair constant for each species
Number of pairs can be related to age of embryo

41
Q

What are the parts of a somite?

A
  1. Sclerotome: vetebrae (axial skeleton)
  2. Myotome: skeletal musculature of body except head region
  3. Dermatome: dermis underlying CT of skin
42
Q

What does ectoderm form?

A

Epidermis of the skin
Epithelium of the oral and nasal cavities
Nervous system and sense organs

43
Q

What does mesoderm form?

A

Muscle and CT
Including bone, components of circulatory, urinary and genital systems

44
Q

What does endoderm form?

A

Mucosal epithelium and glands of respiratory and digestive systems

45
Q

Aplasia/ hyplasia

A

Dwarfism

46
Q

Cranio-facial defects

A

Abnormal neural crest migration

47
Q

Amelia

A

Absense of extremities

48
Q

Meromelia

A

Partial absence of extremity

49
Q

Micromelia

A

Short extremity

50
Q

Polydactyly

A

Extra digits

51
Q

Syndactyly

A

Fused digits

Microanatomy (18 decks)

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