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Embryology & Gametogenesis Flashcards

1
Q

Cleavage

A

Initial cell division and blastomeres
Unicellular zygote divides by mitosis to become multicellular Embryo
Each daughter cell is called a blastomere
No increase in size so termed as cleavage

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2
Q

The morula

A

Blastomeres continue to divide into a compact ball of 16-31 cells within the zone pellucid
Looks like a mulberry

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3
Q

The blastocyst

A

As the morula grows a cavity (blastocoele) forms within it

Inner cell mass (embryo blast) surrounded by outer cells (trophoblast)

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4
Q

Blastocyst: inner cells

A

Embryoblast forms entire embryo
Forms bilaminar disc of Epiblast (dorsal) and Hypoblast (ventral)
Establishes dorsoventral axis

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5
Q

Blastocyst: Outer cells

A

Trophoblast will expand to form the extra embryonic membranes (placentation)

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6
Q

Stem cells

A

Specialized cells capable of self renewal; they may be-

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7
Q

Totipotent

A

From zygote- can form every cell in embryo and trophoblastic placenta

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8
Q

Pluripotent

A

from inner cell mass- can form all embryonic cells (not trophoblastic placenta)

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9
Q

Multipotent

A

Can form a limited number of subtypes within a broader category (epithelial cells, WBCs etc)

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10
Q

Unipotential

A

can form a specific cell type

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11
Q

Migration, differentiation

A

a complex interaction controlled by gene interactions and cell signaling

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12
Q

The zygote contains

A

1 cell

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13
Q

Gastrulation

A

Inner cell mass –> Bilaminar disc –> trilaminar disc

Cells from epiblast migrate leaving a primitive streak (craniocaudal axis)

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14
Q

Trilamminar disk

A

Renamed as 3 germ layers:
Ectoderm
Mesoderm
Endoderm

These layers are formed by migration of epiblast cells

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15
Q

Ectoderm derivatives

A

Epidermal structures (skin), lining of oral, nasal cavity and anus. Nervous system (neuroectoderm - specialized ectoderm)

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16
Q

Mesoderm derivatives

A

Connective tissues, muscle tissue, mesothelium, cardiovascular system, urogenital tract

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17
Q

Endoderm derivatives

A

Epithelial lining and glands of digestive and respiratory system

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18
Q

Neural tube

A

Mesoderm forms notochord under primitive streak
Notochord induces ectoderm to form neural tissue (neuroectoderm)
Neural tube and neural cost cells formed; early somites formed
Cranial part of the neural tube–> brain
Caudal part of neural tube –> spinal cord

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19
Q

Embryonic folding

A

Cranial-caudal and lateral body folds create the head, tail, primitive anus and mouth

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20
Q

The yolk sac is lined by

A

endoderm

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21
Q

Mesoderm differentiates further

A

Axial: notochord
Paraxial: somites
Intermediate: urogenital system
Lateral plate: somatic and splanchnic mesoderm

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22
Q

Somites

A

Dermatome –> dermis
Myotome –> muscles
Sclerotome –> vertebrae and ribs

Somatic and splanchnic mesoderm separate with formation of coelom (peritoneum) in between
Limb buds- all other cartilage and bones of the body and limbs are formed from lateral plate mesoderm
Skull is formed of a combination of lateral plate mesoderm, paraxial (somite) mesoderm and neural crest cells

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23
Q

The smooth muscle of the GIT arise from

A

Splanchnic mesoderm

24
Q

Pluripotent stem cells arise from the

A

inner cell mass

25
Summary of embryology
Sperm +ovum =pronucleum --> zygote --> morula --> blastocyst ---> trophoblast and inner cell mass Trophoblast --> placenta Inner cell mass --> epiblast --> ectoderm, mesoder, endoderm --> foetus or talk sac Hypoblast --> yolk sac
26
Teratogens
Any age or factor that can cause congenital (present at birth) anomalies in an embryo or fetus Genetic factors Radiation Chemical agents (nicotine, drugs, alcohol) Infectious agents (bovine viral diarrhea virus) Hormones (anti-paramesonephric duct hormone in freemartins)
27
Teratogenic influences on development
At predifferentiation stageL embryo dies During organogenesis stage: structural defects (major morphologic defects) During fetal growth stage: affects functional maturation (and minor structural defects)
28
At which of the following stages does action by a teratogen result in the most severe consequences
Predifferentiation
29
Which are part of the brain
Cerebrum Cerebellum Brainstem Pineal gland
30
Gametogenesis
Production of haploid (1N) germ cells at the right place at the right times Gametes have 1/2 the chromosome number Spermatozoa or ova
31
Fertilization
Fusion of 2 haploid gametes creates a diploid (2N) zygote with full complement of chromosomes
32
Embryological origins of germ cells
Primordial germ cells from yolk sac and allantois migrate to genital ridge via dorsal mesentery --> become biopotential gonad
33
Male XY
Seminiferous cords (no lumen) -spermatogonia -supporting sertoli cells Interstitial cells of leydig
34
Female XX
Primordial germ cells (oogonia) form peripherally arranged primordial follicles in a stroma Primordial follicles all formed in the developing embryo before birth
35
Formation of duct systems
Male: mesonephric duct -forms epididymis, ductus deferens Female: paramesonephric duct -formed uterine tubes, uterus, cervix Anti-mullerian hormone produced by sertoli cells directs male development
36
The gonads arise from
intermediate mesoderm
37
The cell cycle
G1 phase S phase G2 phase M phase
38
Mitosis
DNA duplicates in S phase of interphase Each chromosome has 2 sister chromatids Final products are 2 2n Clones of the original cell
39
Meiosis in males
2 cells ends in 4 haploid cells at end of meiosis 2
40
Spermatogenesis
1. Spermatocytogenesis: Spermatogonia divide by mitosis several times and produce primary spermatocytes 2. Meiosis: primary spermatocytes divide by meiosis into secondary spermatocytes and spermatides 3. Spermiogenesis: transformation (metamorphosis) of spermatids into spermatozoa
41
Meiosis in females
Stops in prophase 1 until puberty- primary oocyte puberty meiosis continues Stops on metaphase 2 in oviduct until sperm contact then it will complete meiosis 2
42
Oogenesis
Production of an ovum 1. oogonia- prenatal mitosis produces primary oocytes 2. Primary oocytes (diploid) arrested in meiosis I until puberty 3. After puberty- orderly maturation of the oocyte and supporting cells within a protective ovarian follicle under hormonal influence 4. Ovarian follicle- meiosis I is completed just before ovulation to produce secondary oocyte and 1st polar body except for dogs and mares (these ovulate primary oocytes) 5. Meiosis II starts immediately but arrests until 6. In oviduct, secondary oocyte (haploid) awaits fertilization 7. Meiosis II completed on sperm contact (2nd polar body is produced) 8. Result is ovum (haploid) and 2nd polar body (haploid) Polar bodies are remnant of cytoplasm and nucleus formed during meiosis
43
Mitosis vs meiosis
Mitosis results in formation of 2 diploid daughter cells Meiosis results in formation of 4 haploid cells and exchange of genetic material Gametes are haploid and of different genetic constitution
44
Common features of male and female gametogenesis
Occur in specialized sexually dimorphic organs (testis/organs) Multiplication of spermatogonia and oogonia by mitosis Formation of gametes by meiosis- importance of crossing over and independent assortment for variability= extensive morphological variation (evolution) Incapacity of surviving for very long if fertilization does not occur
45
Differences of male and female gametogenesis
Sperm: supply continuously renewed - one primary spermatocyte produces 4 sperm - Gametogenesis results in small cells - Motile cells - X or Y sex chromosome Oocyte: all present at birth - one primary oocyte produces 1 ovum - Gametogenesis results in a large cell - immotile cell - x chromosomes only
46
Chromosome number halved during
meiosis 1
47
Ovulation
Oocyte departs the ovary leaving behind a structure known as the corpus hemorrhagicum- a (transient structure) that becomes the corpus luteum of luteal cells
48
Spermatozoa
``` Haploid cell (nucleus) for fertilization Motility to deliver the nucleus to the ovum Energy Mechanism of entry into ovum ```
49
Maturation of sperm
acrosome covered by extension of pm
50
Spermatogenesis: Histology
Peripheral on basement membrane (basolateral): spermatogonia -divid and produce more spermatogonia and primary spermatocyte -sertoli cells- support ``` Towards Lumen (apical): primary spermatocytes (secondary spermatocytes are short lived) -round and elongated spermatides ``` Lumen: sperm
51
Spermatogenesis: metamorphosis
Transformation of the round spermatid to a spermatozoon - formation of the acrosome from golgi vesicles (contains enzymes) - condensation of the nuclear chromatin - outgrowth of a motile tail (flagellum-from centrioles) surrounded by mitochondria - loss of excess spermatid material (cytoplasm, water, organelles)
52
Spermatozoon morphology
Head: nucleus, plasma membrane, acrosome (enzymes) Mid piece: spirally arranged mitochondria. Intense energy production Tail: Motility. classified's flagellum/cilia structure. Axoneme- outer ring of 9 doublet microtubules
53
Fertilization: capacitation
Occurs in uterine environment Biochemical change in response to uterine secretions Hyperactivity of the spermatozoon tail Allows acrosomal reaction to occur
54
Fertilization: Acrosome reaction
enzymes released ti digest zone pellucida
55
Fertilization: cortical reaction
Sperm contact with oocyte plasma membrane Release of proteases from cortical granules in oocyte Zona pellucida is then a barrier to other seem penetration
56
Fertilization
Nuclear material of spermatozoon and ovum are called pronuclei Syngamy
57
Syngamy
Union of male and female haploid pronuclei. They merge restoring diploid set of chromosomes and enter the first mitotic division= zygote

Microanatomy (21 decks)

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