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Body Logistics > Embryology > Flashcards

Embryology Flashcards

1
Q

What is a zygote?

A

A fertilised ovum - single cell

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2
Q

What is meant by the term cleavage?

A

A period after fertilisation where the zygote undergoes several mitotic divisions to become multicellular. The resulting cells are called blastomeres, no cell growth, just division

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3
Q

What is the zona pellucida and what is its function?

A

A glycoprotein shell that surrounds the zygote. It provides protection e.g. stops other sperm cells from trying to fertilise the already fertilised egg

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4
Q

What is the morula?

A

Formed once several mitotic divisions have occurred and the zygote consists of 8-16 blastomeres

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5
Q

What is an ovary?

A

A small gland located on either side of the uterus that produces and stores eggs. One ovary releases an egg each month in ovulation.

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6
Q

What are the fallopian tubes?

A

Hollow ducts between your ovary and uterus. Fertilisation of oocyte occurs in ampulla of fallopian tube (commonly) and the fertilised ovum travels along in first week for implantation in uterus

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7
Q

What is the blastocyst?

A

Categorised by presence of blastocyst cavity. First differentiation of cells has occurred. Consists of outer cell mass (trophoblast) and inner cell mass (embryoblast). Cells have released fluid and formed blastocyst cavity.

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8
Q

What is the trophoblast?

A

A layer of tissue (outer cell mass) that surrounds the inner cell mass. These cells later go on to form the placenta. Pluripotent.

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9
Q

What is the inner cell mass?

A

Also known as the embryoblast and is a collection of cells located within the trophoblast that will later go on to form the fetus.

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10
Q

What is implantation?

A

The process by which the blastocyst becomes embedded in the uterine lining

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11
Q

What is the cytotrophoblast?

A

Inner layer of the outer cell mass formed through first differentiation of trophoblast. It supports the syncytiotrophoblast - cells in cytotrophoblast divide and migrate to form part of snycytiotrophoblast

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12
Q

What is the syncytiotrophoblast?

A

The outer layer of the outer cell mass formed in first differentiation of trophoblast. It is a multinucleated sheet of tissue that invades the maternal sinusoids in implantation to begin uteroplacental circulation

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13
Q

What is the bilaminar disc?

A

First differentiation of inner cell mass forms two layers of cells - epiblast and hypoblast. Amniotic cavity forms within epiblast tissue

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14
Q

What is the primitive yolk sac?

A

Cavity formed by hypoblast lining the blastocyst cavity. Later pushed away from cytotrophoblast layer

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15
Q

What is the secondary yolk sac?

A

Also known as definitive yolk sac. Pinches off from primitive yolk sac

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16
Q

What is morphogenesis?

A

The development of form and structure in the conceptus

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17
Q

What is meant by the term germ layers?

A

Formed when epiblast differentiates to create the trilaminar disc and describes the 3 layers that make up the disc. Dorsal ectoderm and ventral endoderm with mesoderm in middle

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18
Q

What is ectoderm?

A

-Dorsal layer of trilaminar disc
-Ecto = outside
-Leads to formation of organs and tissues that maintain contact with the outside world
-E.g. CNS and epidermis

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19
Q

What is mesoderm?

A

-Middle layer of trilaminar disc
-Meso - middle
-Supporting tissue
-E.g. muscle, cartilage, bone, vascular system - heart and blood vessles

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20
Q

What is endoderm?

A

-Ventral layer of trilaminar disc
-Endo - inside
-Internal structures
-E.g. Epithelium lining of GI and respiratory tract, functional tissue of glands

21
Q

What is the primitive streak?

A

-It is a midline structure that forms in the caudal region of the embryo at the beginning of week 3
-It appears on the dorsal side where epiblast is located

22
Q

What happens during gastrulation?

A

-gastrulation occurs in the 3rd week and marks the start of the embryonic period
-primitive streak forms and causes the epiblast to migrate and invaginate
-this leads to differentiation of the epiblast into 3 germ layers
-hypoblast displaced
-trilaminar disc replaces bilaminar disc

23
Q

What is the trilaminar disc?

A

-formed during gastrulation at start of embryonic period
-2 layer bilaminar disc made up of epiblast and hypoblast is replaced as epiblast differentiates and hypoblast displaced
-3 layer trilaminar disc - ectoderm, mesoderm, endoderm

24
Q

When is the pre-embryonic period?

A

First 2 weeks of development

25
Q

When is the embryonic period?

A

Weeks 3-8 of development - formation of organs

26
Q

When is the fetal stage of development?

A

Weeks 8-40 (+/- 2 weeks) - growth

27
Q

What is the ideal site for implantation?

A

Posterior uterine wall

28
Q

Explain the features and viability of an ectopic pregnancy

A

-Implantation of the conceptus in any area other than uterine body
-Most common area is fallopian tubes - zygote doesn’t travel towards uterus as it would in normal pregnancy
-Can be peritoneal or ovarian
-Uterus adapted to support development of embryo, other areas not
-Can quickly become life threatening situation
-Not viable pregnancy as conceptus has no space to grow

29
Q

Explain what placenta praevia is

A

-Implantation in lower uterine segment
-Can cause haemorrhage in pregnancy as placenta is close to cervix
-Requires a c-section delivery as the placenta blocks the exit

30
Q

Where does fertilisation normally occur?

A

In ampulla of fallopian tube

31
Q

What has occurred by the end of the pre-embryonic period (end of 2nd week)?

A

-Conceptus has been fully implanted in uterine stroma
-Embryo and its 2 cavities (amniotic cavity and yolk sac) will be suspended by a connecting stalk within a supporting sac known as the chorionic cavity

32
Q

How is the neural tube formed and what is its later fate?

A

-Appearance of notochord in midline of mesoderm marks the beginning of neuralation
-Notochord signals the overlying ectoderm to differentiate into neuroectoderm and thickens - forms neural plate
-Edges extend out of plane of disc and curl inwards to form the neural tube
-Later forms the CNS

33
Q

How does the mesoderm differentiate?

A

Mesoderm differentiates into paraxial mesoderm, intermediate mesoderm, and lateral plate

34
Q

What are the derivatives of paraxial mesoderm?

A

Forms somites that result in formation of skin, muscle, and bony tissue

35
Q

What are the derivatives of intermediate mesoderm?

A

Forms adrenal tissue and kidneys

36
Q

What are the derivatives of lateral plate mesoderm?

A

Forms serous membranes, heart, circulatory system

37
Q

How are somites formed?

A

Paraxial mesoderm organises itself into segments (somites) in craniocaudal sequence. By end of fifth week there are 42-44 pairs of somites, some disappear to end up with 31 pairs (important as 31 sets of spinal nerves)

38
Q

How do somites differentiate into sclerotome, dermatome, and myotome?

A

Somites appear as an organised block of mesoderm tissue arranged around a small cavity. They then undergo organised degradation which leads to further differentiation into sclerotome. Dorsal sclerotome undergoes further organisation into combined dermamyotome. Myotome proliferates and dermatome disperses

39
Q

What are the derivatives of sclerotome?

A

Hard tissue section - bones

40
Q

What are the derivatives of myotome?

A

Muscle section - muscles

41
Q

What are the derivatives of dermatome?

A

Skin section - dermis

42
Q

How is the intra-embryonic coelom formed?

A

When mesoderm differentiates it forms the lateral plate. The somatic mesoderm is dorsal and interacts with the ecotderm, ventral splanchnic mesoderm interacts with the endoderm. The space in the middle is known as the intra-embryonic coelom and gives rise to the space in the embryo later formed

43
Q

How are the terms dermatome and myotome used clinically to describe skin and muscle in adults?

A

Used to define an area of skin or muscle supplied by a single spinal nerve root (spinal cord thought of having segments where each segment gives rise to a nerve root)

44
Q

Briefly describe innervation of dermatome and myotome

A

Spinal nerve roots growing out of neural tube enter and innervate dermatome and myotome. Sclerotome rearranged to lie between nerve roots and become vertebrae

45
Q

When does embryonic folding begin and what drives the folding at the cranial end?

A

Starts in the fourth week and is partly driven by the continued growth of the neural tube

46
Q

What is the result/importance of embryonic folding in fourth week?

A

-Ectoderm is folded over endoderm so endoderm tucked away
-Amniotic cavity now surrounds embryo and embryo becomes suspended in protective amniotic sac
-Create primordium of gut, puts heart in the right place, creates new cavity in embryo
-Yolk sac now separate to embryo

47
Q

How is sidedness achieved?

A

-before gastrulation, embryonic disc is bilaterally symmetrical but asymmetry is needed as left and right sides of body have different features
-primitive node has ciliated cells that cause a left-ward flow of sidedness molecules which leads to a cascade of side-specific singalling

48
Q

What is situs inversus?

A

-mirror-image of organs often caused by a defect in cilia
-can be situs inversus totalis where everything inverted or can be partial
-e.g. only heart is on the wrong side
- if totalis then normally doesn’t cause problems and only picked up when in hospital for something else
-dextrocardia (heart on wrong side) can cause severe heart defects as other organs related to the heart are still where they’re supposed to be

49
Q

What is Kartagener Syndrome?

A

-an genetic condition caused by an autosomal recessive gene that causes a defect in cilia
-leads to situs inversus, infertility, chronic sinustis, and bronchiectasis

Body Logistics (2 decks)

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