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Human Structure & Function II > Embryology > Flashcards

Embryology Flashcards

1
Q

What are the three prenatal development stages?

A
  • Pre-embryonic period (0 to 2 weeks)
  • Embryonic period (3 to 8 weeks)
  • Fetal period (9 weeks to birth)
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2
Q

Which is the most sensitive and critical prenatal development stage?

A

Embryonic period: all major organs are formed, higher chance of miscarriage

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3
Q

What is gametogenesis ?

A

The formations of gametes (sperms and ova)
Two haploid cells form a diploid one containing both maternal and paternal genetic material.

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4
Q

What happens during gametogenesis?

A

Replication of DNA in chromosomes (mitosis)
The duplicated chromosomes are called sister chromatids, they are connected at the centromere.
Crossing over can occur to exchange genetic material causing variation.
Then two different divisions of meiosis occur in order to produce the haploid cells.

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5
Q

What is spermatogenesis?

A

The formation of sperm cells

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6
Q

What happens during spermatogenesis?

A

There is a primary spermatocyte that comes from the spermatogonia in the seminal vesicles. This undergoes the first meiotic division to form secondary spermatocytes (23X and 23Y ). These then undergo the second meiotic division forming spermatids. Spermatids are immature sperm cells so they have to undergo spermiogenesis to develop into normal sperms.

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7
Q

How many sperm cells are produced at the end of spermatogenesis?

A

4 sperms

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8
Q

Where does spermiogenesis take place?

A

In the seminal vesicles

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9
Q

How many spermatozoa are released and how many actually reach the uterus?

A

About 300 million spermatozoa are released but only 3 million reach the uterus.

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10
Q

How many spermatozoa actually reach the uterine tube?

A

Only 1.4 million reach the uterine tube, which is where fertilization takes place

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11
Q

How long do spermatozoa survive?

A

Most survive 24-48 hours, however, some can last up to 4 days.

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12
Q

What is capacitation?

A

The removal of glycoprotein and seminal proteins from the surface of the acrosome.

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13
Q

What is the function of capacitation?

A

To increase mobility and metabolism

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14
Q

Where does capacitation occur?

A

Female reproductive tract

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15
Q

What are the stages of development of follicles?

A

Primordial follicle: 2 million at birth, about 400 thousand are left by puberty.

Primary follicle: 15 to 20 primordial follicles develop into primary follicles monthly.

Secondary follicle: primary follicles develop into secondary.

Graafian follicle: one secondary follicle develops into a Graafian follicle.

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16
Q

What is oogenesis?

A

The formation of egg cells

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17
Q

What happens during oogenesis?

A

Primary oocyte: 46 XX in growing follicle (surrounded by follicular cells)

Primary oocyte: 46 XX in larger follicle (surrounded by zone pellucida and follicular cells)

After the first meiotic division: a secondary oocyte is formed: 23 X in mature follicle (first polar body is visible and antrum)

Second meiotic division occurs if fertilisation occurs: Second polar body is visible, fertilised oocyte and corona radiata

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18
Q

What is ovulation?

A

The release of the ovum from the Graafian follicle, for it to enter the fallopian tube

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19
Q

When does the Graafian follicle rupture?

A

When the follicle is the same size as the ovary

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20
Q

What is the corona radiata?

A

Radially arranged follicular cells around the zone pellucida

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21
Q

Where does fertilization happen?

A

In the ampulla of the uterine tube

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22
Q

What are the three phases of fertilization?

A
  • Penetration of corona radiata: about 1.4 million sperms reach the ampulla of the uterine tube, only capacitated sperms pass through the corona radiata freely, and only one sperm fertilizes the oocyte
  • Penetration of the zone pellucida
  • Fusion of the oocyte and sperm cell membranes to form zygote
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23
Q

What is the acrosomal reaction and why does it happen?

A
  • Membrane of acrosome breaks.
  • Release of enzymes within the acrosome facilitate penetration of zona pellucida.
  • Establishment of a pathway for sperm through zona pellucida
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24
Q

What are the enzymes released from the acrosome during acrosomal reaction?

A

Across, hyaluronidase, esterase

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25
Q

What is the cortical reaction and why does it happen?

A

A change in properties of the oocyte membrane and zona pellucida the make it impermeable to other sperms.
- Release of lysosomal enzymes from cortical granules.

It is necessary to prevent polyspermy

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26
Q

What happens to the zygote in the case of polyspermy?

A

The zygote will not survive

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27
Q

What is the process of formation of a zygote?

A
  • The pronuclei approach each other, and the membranes break.
  • The pairing of tech paternally and maternally derived chromosomes restore the diploid number of 46.
  • The zygote us unique as it contains a new combination of chromosomes
  • The zygote starts dividing by mitosis.
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28
Q

What is cleavage?

A

The mitotic divisions of the zygote, which result in a rapid increase in the number of cells.

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29
Q

What are the embryonic cells known as after the cleavage?

A

Blastomeres

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30
Q

What happens to the size of the cells as their number increases (zygote)?

A

They become smaller in size

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31
Q

What is a morula?

A

The spherical cluster of blastomeres

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32
Q

What is compaction?

A

It begins at the 8-cell stage (3 mitotic divisions later)
Blastomeres form a tightly packed ball of cells
Outer cells maximize their contact with each other and seal the interior of the mould

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33
Q

What cells are formed after compaction?

A

Trophoblasts and embryoblasts

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34
Q

What are trophoblasts?

A

They are the cells responsible for implantation and placental formation

They make no contribution to the embryo

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35
Q

What are embryoblasts?

A

Will form the embryo, amniotic membrane, and the lining of the primitive yolk sac.

36
Q

What is the formation of the blastocyst?

A

4 days after fertilization: the morula enters the uterus,
A fluid-filled cavity (blastocyst cavity) appears within the morula,
The fluid passes into the morula through the zona pellucida from the uterine cavity,
The conceptus at this stage (blastocyst) is surrounded by the trophoblasts
The blastocyst cavity displaces inner cell mass to the embryonic pole
It is still contained within zona pellucida

37
Q

What is the hatching of the blastocyst?

A

Day 6 after fertilization: trophoblast produces enzymes that disrupt the zone pellucida

The zona pellucida degenerates and disappears

This leads to the hatching of the blastocyst

38
Q

How does the formation of syncytiotrophoblasts and cytotrophoblasts occur?

A
  • Trophoblasts proliferate and the daughter cells fuse together with the uterine wall to form a multinucleated mass of cytoplasm known as syncytiotrophoblasts
  • The rest of the trophoblast is now known as cytotrophoblast (they are separate cells)
39
Q

Formation of the bilaminar embryonic disc:

A
  • Inner cell mass is converted into a two-layered structure: hypoblasts and epiblasts
  • Cavity appears in the epiblasts, the amniotic cavity
  • Blastocyst cavity (from hypoblasts) becomes primitive yolk sac, lined by primitive yolk sac membrane
40
Q

What are hypoblasts and epiblasts?

A

Hypoblasts: cuboidal cells adjacent to the blastocyst cavity
Epiblasts: columnar cells temporarily in contact with trophoblasts

41
Q

What is an ectopic pregnancy?

A

When the embryo is implanted in a place outside of the uterus.

The uterine tube will rupture as a result of its inability to sufficiently enlarge to accommodate embryo which will lead in a miscarriage.

42
Q

What is the incidence of an ectopic pregnancy ?

A

1 in 100

43
Q

What is the embryonic period?

A

3 to 8 weeks of pregnancy

3rd week: the appearance of the third tissue layer converts the bilaminar embryo to trilaminar one

3rd and 4th weeks: flat 2D embryonic disc becomes a complex 3D form

Organogenesis begins with the development of neural tube and primitive gut tube

8th week: most structures are formed

44
Q

What is gastrulation?

A

Transformation of a bilaminar disc into a trilaminar disc

It begins with the formation of primitive streak

Epiblast cells in the region of the primitive streak detach and migrate

45
Q

How does the formation of the trilaminar disc occur?

A
  • Some epiblast cells migrate to the region of hypoblast cells and form a single layer of cells, endoderm.
  • The migrating epiblast cells between the endoderm end epiblast from the mesoderm.
  • The non-migrating epiblast tissue that remains on the surface is now called ectoderm.
46
Q

What is the folding of the embryo?

A

It occurs in the 4th week
It is important in the conversion of flat embryonic disc into a cylindrical embryo
It is due to the growth of the embryo and it occurs in two planes:
- Median plane: cephalocaudal folding
- Horizontal plane: lateral folding

47
Q

What is the cephalocaudal folding of the embryo?

A

It occurs mainly due to the growth of the brain and spinal cord
- The cranial part of the endoderm is folded upon itself and forms the primitive foregut
- The caudal part of the endoderm us folded upon itself and forms the primitive hindgut.

48
Q

What is the traverse folding of the embryo?

A

It takes place at the same time as the longitudinal folding
The endoderm in the middle of the embryo is rolled into primitive midgut

49
Q

What is the fate of the endoderm?

A

It forms:
- The lining of the GIT and respiratory system
- Secretory cells of the liver, gall bladder and pancreas,
- Lining of the ducts of these organs

50
Q

What is the fate of the mesoderm?

A
  • Forms most muscles and connective tissues
51
Q

What is the mesoderm divided into?

A

Paraxial,
Intermediate,
Lateral

52
Q

What does the paraxial mesoderm form?

A

The vertebrae and intervertebral discs
Ribs
Skeletal muscles of body walls and limbs
Connective tissue of body wall

53
Q

What does the intermediate mesoderm form?

A

The urinary and reproductive systems

54
Q

What does the lateral plate mesoderm form?

A

The connective tissue, blood vessels, and smooth muscle of the body wall and limbs
Smooth muscles, blood vessels and connective tissue of GIT and associated organs.

55
Q

What is neurulation?

A

The process by which the neural tube is formed and forms the brain and spinal cord

56
Q

What is the process of neurulation?

A
  1. Introduction of neural plate: part of the ectoderm to differentiate into a neural plate
  2. Formation of neural folds: elevation of edges of neural plate –> neural folds
57
Q

What is the space between the neural folds called?

A

The neural groove

58
Q

What is the fusion of neural folds?

A

In day 21: the neural folds approach each other and fuse to form the neural tube

59
Q

Where does the fusion of the neural folds begin?

A

In the cervical region (5th somite) and proceeds cranially and caudally

60
Q

What do the cranial and caudal parts of the neural tube form?

A

The brain and spinal cord, respectively.
The space in the tube will develop into the ventricular system

61
Q

What are the neural crest cells?

A

Special cells that lie at the apices of the neural fold,
As neurulation takes place, neural crest cells migrate out of the neural fold into the body

62
Q

What structures/ cells are produced fro the neural crest cells?

A

Autonomic ganglia
Adrenal medulla
Melanocytes
Schwann and glial cells of peripheral nerves

63
Q

What are some examples of neural tube defects?

A

Anencephaly: partial absence of the brain due to failure of neural folds to fuse in the brain region
Spina bifida: protrusion of neural tissue through a defect in vertebral arches and skin

64
Q

What happens during the 2nd month of pregnancy?

A

Recognizable limbs
Head enlarges and eyes, ears, and nose appear and migrate to adult positions
Tail disappears, face is more human-like
Ossification begins
Kidneys begin to produce urine
All major organs are in place

65
Q

What is the placenta?

A

An organ that facilitates the physiological exchange of substances between the mother and the fetus.

66
Q

What does each section of the placenta consist of?

A

The maternal portion is subdivided into several lobes known as cotyledons

The fetal portion contains:
- two umbilical arteries which carry deoxygenated blood and waste products away from the fetus to the mother
-umbilical vein which carries oxygenated blood and nutrients from the mother to the fetus.

67
Q

What is the placenta made out of?

A

The chorion frondosum and the decidua basalis

68
Q

What is the chorion frondosum?

A

Cytotrophoblasts, syncytiotrophoblasts and extraembryonic mesoderm, contains villi and it forms the fetal part.

69
Q

What is the decidua basalis?

A

The endometrium of the mother and forms the maternal part of the placenta

70
Q

How do the chorionic villi develop?

A

Primary villi: column of cells formed by the proliferation of cytotrophoblasts.

Secondary villi: formed from the invasion of the core of the primary villi by extraembryonic mesoderm

Tertiary villi: blood cells and vessels develop from the mesoderm in the core of the secondary villi transforming them into tertiary

71
Q

Formation of placenta:

A

Bushy chorion (chorion frondosum): further branching and growth in the region of the decidua basalis

Smooth chorion (chorion lave): area of recession of villi

Decidua basalis: part of the decidua basalis over the chorion frondosum. Cytotrophoblastic shell joins the chorion frondosum with decidua basalis

72
Q

What are the two different kinds of twins?

A

Dizygotic: ovulation and subsequent fertilization of two oocytes

Monozygotic: splitting of the zygote or splitting of the inner cell mass of the blastocyst

73
Q

What are conjoined twins?

A

Monozygotic twins who have an incomplete splitting of the inner cell mass

74
Q

What happens during the fetal period (weeks 9 to 12)?

A
  • Sex is distinguishable externally,
  • Urine is excreted into the amniotic fluid
  • Erythropoiesis starts in the liver and later in the spleen.
  • Head is half of fetal length
75
Q

What happens during the fetal period (weeks 13 to 16)?

A
  • Growth continues, and no new structures are formed
  • Heart beat can be detected
  • Circulation is completely functional
76
Q

What happens during the fetal period, after week 16?

A

Continued growth and acquiring human morphology and function.
No new structures are formed

77
Q

What causes birth defects?

A

Teratogens

78
Q

What is the use of ultrasonography?

A

To determine fetal age and growth
To determine size and position
To determine any congenital malformations

79
Q

What congenital malformations can ultrasonography detect?

A
  • Neural tube defects
  • Cardiac and facial defects
  • Abdominal wall defects
80
Q

What is amniocentesis used for?

A

Genetic testing and karyotyping and α - fetoprotein

81
Q

What is chronic villous sampling used for?

A

Genetic analysis and karyotyping
Paternity testing

82
Q

What is cordocentesis?

A

A procedure that involves the insertion of a needle into the umbilical cord to withdraw blood

83
Q

When is cordocentesis done?

A

Usually after 18 weeks

84
Q

What is the purpose of cordocentesis?

A

To detect certain genetic disorders, blood conditions, and infections,
Used to deliver blood transfusions or medication to fetus

85
Q

Which hormone controls the development of follicles?

A

Luteinising Hormone (LH)

Human Structure & Function II (9 decks)

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