S9-10) Embryology Flashcards

1
Q

What is embryology?

A

Embryology is the study of the molecular, cellular and structural factors involved in the progression from a single cell to a baby in 9 months

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2
Q

Describe the process of oogenesis

A
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3
Q

Where does fertilisation normally occur?

A

The ampullary region of the fallopian tube

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4
Q

Sperm must be introduced into the female reproductive tract within 5 days before ovulation.

How long are the sperm and secondary oocyte viable?

A
  • Sperm are viable for 5 days
  • Secondary oocyte is viable for 12-24 hours
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5
Q

Why is there a need for capacitation?

A
  • Sperm are initially incapable of fertilisation
  • Capacitation allows the tail of the sperm to move faster, causing the oocytes plasma membrane to alter
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6
Q

Describe the process of fertilisation

A
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7
Q

Define the following terms:

  • Embryonic age
  • Gestational age
A

- Embryonic age: time since fertilisation

- Gestational age: time since last menstruation (embryonic age minus 2 weeks)

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8
Q

Define the following terms:

  • Germinal stage
  • Embryonic period
  • Foetal period
A
  • Germinal stage: time from fertilisation to the end of the 2nd week

- Embryonic period: time from the 3rd to end of the 8th week

- Foetal period: time from the beginning of the 9th week to birth at 38 weeks

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9
Q

Before the blastocyst can implant it has to lose the zona pellucida.

What is this process called and why does it happen?

A

Hatching is the process in which the blastocyst emerges from its zona pellucida as the zona pellucida prevents the morula/blastocyst adhering to the oviduct and enlarging

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10
Q

Distinguish between histiotrophic nutrition and haemotrophic nutrition

A
  • Histiotrophic nutrition is the nutrition provided to the embryo which is not from the maternal blood and is important in humans up to the 12th week

- Haemotrophic nutrition is the nutrition provided by the mother’s blood and is important in humans from 12th week on

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11
Q

Where and when does the blastocyst implant?

Why is this important?

A
  • Normal implantation of the blastocyst occurs in the posterosuperior wall of the uterine cavity on the 6th day
  • The implantation site determines the site of formation of the placenta
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12
Q

Identify 7 abnormal implantation sites

A
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13
Q

Differentiate between the following terms:

  • Trophoblast
  • Synctiotrophoblast
  • Cytotrophoblast
A
  • Trophoblast is a layer of tissue on the outside of a mammalian blastula, supplying the embryo with nourishment

- Syncytiotrophoblast are cells that merge together in the trophoblast

- Cytotrophoblast are cells in the trophoblast

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14
Q

What is the bilaminar disc?

A
  • The bilaminar embryonic disc refers to the epiblast and the hypoblast, evolved from the embryoblast
  • These two layers are sandwiched between the primitive yolk sac and the amniotic cavity
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15
Q

Differentiate between the following terms:

  • Hypoblast
  • Epiblast
A
  • Hypoblast is a tissue type, lying beneath the epiblast, that forms from the inner cell mass and consists of small cuboidal cells

- Epiblast is the outermost layer of an embryo before it differentiates into ectoderm and mesoderm

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16
Q

Differentiate between the follow structures:

  • Amniotic cavity
  • Yolk sac
  • Chorionic cavity
A
  • Amniotic cavity is the closed sac between the embryo and the amnion, containing the amniotic fluid

- Yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast adjacent to the embryonic disk

- Chorionic cavity is the space surrounding the primary yolk sac and amniotic sac (not around connecting stalk)

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17
Q

Why is the second week of development called the week of 2’s?

A
  • The trophoblast differentiates into 2 layers (cytotrophoblast & syncytiotrophoblast)
  • The embryoblast forms 2 layers (epiblast & hypoblast)
  • The hypoblast contributes to the formation of two cavities (yolk sac & chorionic cavity)
18
Q

Identify the 6 key events/processes in early development

A
  • Fertilisation
  • Implantation
  • Gastrulation
  • Neurulation
  • Segmentation
  • Folding
19
Q

Gastrulation happens in the 3rd week.

What occurs during gastrulation?

A

During gastrulation, the bilaminar disk is converted to a trilaminar disk consisting of three germ layers: ecotoderm, mesoderm and endoderm and the primitive streak forms in the caudal epiblast

20
Q

What is the importance of the primitive streak?

A
  • The primitive streak forms in the caudal epiblast, leading to migration and invagination of epiblast cells
  • This process ensures the correct placement of precursor tissues to allow sub sequent morphogenesis to occur
21
Q

What is the germ layer derivative of the ectoderm?

A

Ectoderm – organs and structures that maintain contact with the outside world e.g. nervous system, epidermis

22
Q

What is the germ layer derivative of the mesoderm?

A

Mesoderm – supporting tissues e.g. muscle, cartilage, bone, vascular system

23
Q

What is the germ layer derivative of the endoderm?

A

Endoderm – internal structures e.g. epithelium of GI tract, respiratory tract and parenchyma of glands

24
Q

Discuss the left-right asymmetry that arises from gastrulation

A
  • Prior to gastrulation the embryonic disk is bilaterally symmetrical
  • However, in the body there are clear left vs right differences:

I. Thoracic viscera – left lung has 2 lobes while the right has 3

II. Abdominal viscera – liver on right, stomach and spleen on the left

25
Q

What is neurulation?

A

Neurulation refers to the folding process in vertebrate embryos, which includes the thickening of the ectoderm to form the neural plate and its transformation into the neural tube (neurectoderm)

26
Q

What is the role of the notochord?

A
  • The notochord is formed during gastrulation and drives neurulation
  • It has no function in adult life and forms the nucleus pulposus of the intervertebral disc
27
Q

Somites appear as regular block of mesoderm cells arranged around a small cavity.

Explain the degeneration of somites into the myotome and dermatome

A
  • The ventral wall of the somites break down and the sclerotome forms
  • Further organisation of the dorsal portion forms the dermomyotome
  • Myotome proliferates and migrates & dermatome disperses
28
Q

Differentiate between the dermatome, myotome and sclerotome

A
  • Dermatome – skin section i.e. dermis
  • Myotome – muscle section i.e. muscles
  • Sclerotome – hard tissue section i.e. bones
29
Q

What are the implications of segmentation?

A
  • Organisation of mesoderm into somites gives rise to repeating structures e.g. vertebrae, ribs, spinal cord segments
  • Guides innervation
30
Q

What does embryonic folding do?

A
  • Folding draws together the margins of the disk
  • It creates a ventral body wall
  • It pulls the amniotic membrane around the disk
  • It pulls the connecting stalk ventrally
31
Q

Briefly described how the intraembryonic coelem is formed

A
  • The intraembryonic coelom is the cavity between the somatopleure (dorsal) and the splanchnopleure (ventral) which forms during the 3rd week of development from the splitting of the lateral mesoderm
  • This space will give rise to the thoracic and abdominal cavities
32
Q

Why do the buccopharyngeal membrane and the cloacal membrane have no mesoderm?

A
  • The buccopharyngeal and cloacal membrane have no mesoderm as these membranes form the upper and lower parts of the GI tract
  • The mesoderm derives into muscle, cartilage and bone; which are not part of the GI tract, hence not necessary
33
Q

Saccrococcgeal teratomas are common in newborns. The developmental basis for these tumours is the excessive persistence of the primitive streak.

Why are these tumours composed of many tissue types?

A
  • The primitive streak gives rise to the mesoderm which is a derivative of supporting tissues (muscle, cartilage & bone)
  • Hence, saccrococcgeal tumours would consist of precursor cells of the mesoderm
34
Q

What are embryonic stem cells?

A

Embryonic stem cells are pluripotent stem cells derived from the inner cell mass of a blastocyst

35
Q

What can umbilical cord stem cells be used for?

A

Umbilical cord blood collected at birth is a rich source of stem cells that can be used in research and in the clinic to treat diseases of the blood and immune system

36
Q

Where can adult stem cells be found?

A

Adult stem cells have been identified in many organs and tissues, including brain, bone marrow, blood, liver, gut, heart, skin and teeth

37
Q

What is placenta praevia?

A

Placenta previa is a condition wherein the placenta covers all or part of the cervix during the last months of pregnancy and can cause severe bleeding before/during labour (emergency C-section may be necessary)

38
Q

Why is it that ectopic pregnancy can quickly become a life-threatening emergency?

A
  • The narrow fallopian tube cannot distended largely and with the progression of pregnancy, the fallopian tube ruptures
  • This can cause heavy internal bleeding and abdominal pain
39
Q

Identify 5 of commonest causes for maternal mortality globally

A
  • Post-partum bleeding
  • Complications from unsafe abortion
  • Hypertensive disorders of pregnancy
  • Postpartum infection
  • Obstructed labour
40
Q

Identify 5 of the commonest causes for maternal mortality in the UK

A
  • Thrombosis and thromboembolism
  • Antepartum and postpartum haemorrhage
  • Amniotic fluid embolism
  • Genital tract sepsis
  • Ectopic pregnancy