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ESA 1 Steven > Embryology > Flashcards

Embryology Flashcards

0
Q

Define the germ layer

A

A layer from which other developed tissues come from.

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1
Q

Define bilaminar disk

A

The epiblast and hypoblast. Derived from the embryoblast. Will later become the trilaminar disk with the formation of the primitive streak

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2
Q

What is the ectoderm and what can it give rise to?

A

The outer most layer of cells. Gives rise to nervous tissues and the epidermis

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3
Q

What is the mesoderm and what can it give rise to?

A

The middle layer of cells. Can give rise to the supporting tissues such as bone, cartilage and muscle

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4
Q

What is the endoderm and what can it give rise to?

A

The inner most layer of cells. Can give rise to the epithelial lining of the GI tract, respiratory tract and parenchyma of glands

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5
Q

What is the dorsal surface and what is the ventral surface?

A

Dorsal=outermost
Ventral=innermost
Surface during early development

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6
Q

What is the primitive streak, what does it consist of and why is it important?

A

A narrow groove on the dorsal surface of the epiblast. The primitive node is at the cranial end and the primitive pit is in the centre of the node. Important for deciding the orientation of the embryo

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7
Q

Describe gastrulation and outline the basic steps

A

The reorganisation of germ layers into the trilaminar disk (ectoderm, mesoderm and endoderm) hence establishing the origin of all tissues. Sets the axes.
Primitive streak forms. Cellular rearrangement occurs - migration and invagination

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8
Q

What is the trilaminar disk made up off?

A

Ectoderm, mesoderm and endoderm

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9
Q

Why is week 3 of embryonic development known as the “week of 3’s”?

A

Three cavities are formed (amniotic sac, yolk sac and chorionic sac) and three germ layers are formed

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10
Q

What is the notochord and what does it do?

A

It’s the basis for the axial skeleton. Defines the midpoint. Gives rise to the nervous system. Then regresses

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11
Q

What is situs invertus and how does it normally occur?

A

A complete mirror image of the body usually occurring due to the ciliates cells which send messenger signals on the left hand side being immobile. No associated morbidity unless mix of regular and reverse

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12
Q

At what stages can a monozygotic twin be created?

A

After the first cleavage, when the inner cell mass duplicates, when the primitive streak duplicates or not at all (conjoined)

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13
Q

What is teratogenic and name some common agents

A

The process through which normal embryo development is disrupted. Thalidomide, rubella and alcohol

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14
Q

What 3 things must occur to turn one cell into a multicellular body?

A

Growth, morphogenesis and differentiation

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15
Q

What is the development of a baby during the first 2 weeks after conception called?

A

Pre-embryonic

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16
Q

Which weeks does the embryonic stage occur during?

A

3 to 8 weeks

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17
Q

Briefly outline the process of fertilisation

A

Oocyte released from ovary and travels along the Fallopian tube where it is fertilised by the sperm in the ampulla

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18
Q

What is cleavage and when does it occur?

A

First mitotic division resulting in 2 blastomeres and the formation of the zona pellucida. Occurs 30 hours after fertilisation.

19
Q

What is the morula?

A

A ball of approximately 8 totipotent cells

20
Q

Briefly outline IVF

A

Oocyte is fertilised in vitro and allowed to divide to the 4-8 cell stage before being transferred into the uterus

21
Q

Briefly explain what PGD is

A

Pre-implantation genetic diagnosis - removal of a cell from the morula and testing it for a serious inheritable defect

22
Q

What is formed during compaction?

A

The embryoblast, trophoblast and blastocystic cavity. Zona pellucida is still there

23
Q

What does “hatching” refer to?

A

The blastocyst breaks out from the zona pellucida and is now free to enlarge and to implant in the uterus

24
Q

How many cells does the conceptus have before implantation?

A

107 - 99 make fetal membranes and 8 make embryo

25
Q

Sum up what happens in order in the first week of pre-embryonic development

A

Fertilisation, cleavage, compaction, hatching and the beginnings of implantation

26
Q

Why is week 2 referred to as the week of twos?

A

2 distinct cellular layers emerge from: outer cell mass (syncytiotrophoblast and cytotrophoblast) and inner cell mass (epiblast and hypoblast)

27
Q

What will have occurred by the end of week 2?

A

The conceptus has implanted and the embryo and its two cavities (amniotic cavity and yolk sac) will be suspended by a connecting stalk within a supporting sac called the chorionic cavity

28
Q

How does implantation occur?

A

The uterine epithelium is breached and the conceptus implants in the uterine stroma. Maternal sinusoids are invaded by the syncytiotrophoblast and uteroplacental circulation begins.

29
Q

What is the ideal site for implantation and what are some problems caused by implantation defects?

A

Posterior uterine wall. Ectopic pregnancy - implanted somewhere other than uterus (usually Fallopian tube) can be life threatening as it leads to haemorrhaging. Placenta praevia - implanted lower down the uterus and placenta may block exit so a C-section is required

30
Q

How are the amniotic sac, primitive yolk sac, secondary yolk sac and chorionic cavity formed?

A

Amniotic sac - formed from spaces within epiblast
Primitive yolk sac - formed from hypoblast lining lining blastocoele
Secondary yolk sac - formed from within PYS
Chorionic cavity - formed from spaces within extra embryonic reticulum and mesoderm

31
Q

What is neurulation?

A

The notochord driven induction of ectoderm to form nervous tissue

32
Q

What are the steps in neurulation?

A

Signals from the notochord drive the overlying ectoderm to thicken. The outer edges elevate up and curl towards each other to form the neural tube

33
Q

What are the 4 parts of the mesoderm?

A

Paraxial mesoderm, intermediate mesoderm, somatic mesoderm and splanchnic mesoderm

34
Q

What are somites?

A

Somites are regular blocks of paraxial mesoderm tissue arranged around a cavity.

35
Q

When do somites form and how many are there?

A

1st pair form on day 20. 3 appear a day until 42/44 are present by the end of week 5. Some then disappear leaving 31.

36
Q

What happens to somites after all 31 have formed?

A

They undergo organised degeneration. The ventral wall breaks down giving sclerotome and the dorsal section degenerates to give dermomyotome.

37
Q

What does dermotome, myotome and sclerotome form?

A

Dermo - skin
Myo - muscle
Sclero - bones

38
Q

What is the significance of somite formation?

A

Gives rise to repeating structure like vertebrae, intercostal muscles, ribs and spinal cord segments. Helps to guide innervation

39
Q

What are the derivatives of the paradaxial mesoderm?

A

Axial skeleton (vertebral column & ribs)
Dermis
Muscles of the axial body wall
Some limb muscles

40
Q

What are the derivatives of the intermediate mesoderm?

A

Urogenital system e.g. kidneys, Ureters, gonads

41
Q

What are the derivatives of the somatic mesoderm?

A

Connective Tissue of limbs

Contributes to the axial body wall

42
Q

What are the derivatives of the splanchnic mesoderm?

A

Smooth musculature

Connective tissue and vasculature of gut

43
Q

What does embryonic folding achieve?

A

Creates a ventral body wall, suspends embryo in amniotic sac, pulls connecting stalk centrally, puts heart and diaphragm in the correct place, creates the primordial of the gut from the yolk sac and creates a new cavity in the embryo

44
Q

Summarise what has happened by in week 4

A

Nervous system starts to form, sections start becoming specialised and the embryo has folded, putting things in the right place

ESA 1 Steven (4 decks)

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