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Year 1 - Semester 1 > Week 2 - Embryology > Flashcards

Week 2 - Embryology Flashcards

1
Q

Definition of sex

A

Blending the genetic characteristics of two individuals in generation to create the (n+1)th generation

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2
Q

Pros and cons of sex

A

Pros:
New individual has new mix of genes that can give it immunity to pathogens (red Queen hypothesis)

New genes determine its environmental interactions

Cons:
You need to find a partner
If you have ‘perfect’ genes, the next generation will be diluted

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3
Q

Describe females

A

Produce relatively few, large gametes

Tends to provide nurture (if only a yolk)

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4
Q

Describe males

A

Produce many small gametes

Provides no nurture other than behavioural

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5
Q

What is the germ line

A

Cells put aside early in development to become nothing but gametes

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6
Q

What is the typical sperm count per ml and what is classed as subfertility?

A

Typical 10^8/ml

Subfertility - <2x10^7/ml

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7
Q

What is the function of myoid cells?

A

Muscle like cells - movement of sperm

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8
Q

What is the function of leydig cells?

A

Make androgen hormones (testosterone)

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9
Q

What is the function of Sertoli cells?

A

Nurse developing sperm (think s for support)

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10
Q

Define spermatogenesis

A

Proliferation of germ line cells by mitosis (on basal side - far from lumen)

Reduction to haploid by meiosis

Differentiation

myoid -> spermatogonia -> primary -> secondary -> spermatids -> maturing

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11
Q

What happens to sperm after they are released into the lumen?

A

Flow into epididymis which activates the sperm with fructose and glycoproteins etc

seminiferous tubules -> rete testes -> vas efferentia -> epididymis -> vas deferens -> prostate -> urethra

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12
Q

What is the role of the seminal vesicle?

A

Secretes seminal fluid into the vas deferens as it passes into the prostate

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13
Q

Where is follicle stimulating hormone produced and what does it do?

A

In the pituitary at puberty

Causes an egg to mature and stimulates the ovaries to release oestrogen

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14
Q

Describe the steps in response to FSH

A

Follicles resume development (around 50 per month)

Oocyte grows and synthesises RNA (85 days)

Then synthesises a glycoprotein zona pellucida and granulosa cells multiply (10 days)

Granulosa cells secrete follicular fluid that form the antrum

Needs Luteinising hormone from pituitary to become Graafian follicle or dies

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15
Q

What happens after fertilisation?

A

Meiosis II only occurs after fertilisation

Remains of ruptured follicle become corpus luteum which produces progesterone and oestrogen - readies womb lining

If no pregnancy, CL dies

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16
Q

What happens in response to exogenous FSH or drugs that block oestrogen?

A

Can stimulate oogenesis

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17
Q

What is capacitation?

A

The removal of glycoprotein coat (acquired by the sperm in the epididymis) by uterine and cervical fluids

This causes the membrane to be more permeable to calcium ions which allows strong tail lashing and the acrosome reaction

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18
Q

What is the acrosome?

A

Organelle derived from the Golgi apparatus that develops over the anterior half of the head of the sperm

Fuses with the ZP and acrosomal contents spill out and digest the ZP. This causes a wave of calcium entry which release cortical granules (make the ZP impenetrable to more sperm) and cause meiosis to resume

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19
Q

What is cleavage?

A

Mitosis with no growth

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20
Q

What are some reasons assisted contraception may be used?

A

Blocked/absent oviducts
Blocked vas deferens
Impotence
Low male advanced female age

21
Q

Describe the steps of assisted fertilisation

A 
Superovulation (through hormones)
Oocyte harvesting
Sperm harvesting
Artificial capacitation
Mixing of gametes
Observation of early development
Embryo transfer
22
Q

Which part of the blastocyst becomes what?

A

Cells on inside become inner cell mass (becomes body)

Cells on outside become trophoblast (develops into placenta) - Trophoblast invades the uterine epithelium

23
Q

What does the layer of inner cell mass that faces the fluid become?

A

Hypoblast - move down to create a layer under trophectoderm to form lining of yolk sac

24
Q

What happens to cells directly contacting the hypoblast?

A

Become epiblast - these let go of cells above to form amniotic cavity

25
Q

How can monozygotic twins form?

A

Either at 2 cell stage which forms 2 inner cell masses and 2 trophectoderms

Only 2 inner cell masses form - 2 embryos in the same trophectoderm - share placenta and chorionic cavity

Very rare - 2 distinct sites of Hex-expressing cells can lead to twins which share an amniotic cavity and chorionic cavity - no membrane - can lead to conjoined twins

26
Q

Describe how the primitive streak is formed.

A

Cells in the centre of the hypoblast express Hex and cling to each other while moving out to the rim. Then secrete proteins which inhibit progress in the epiblast layer above. Cells which are far enough away from these proteins begin making the tail end of the primitive streak. This then extends towards the middle and become the future trunk. The other end forms the head

27
Q

Describe gastrulation

A

Epiblast cells converge on the primitive streak and dive through it. These drop down into the hypoblast layer and push it aside to form the endoderm which forms the gut, lungs, liver and pancreas. The next cells to fall through form a loose layer between the endoderm and epiblast called the mesoderm which forms connective tissues, bones and skeletal muscle. The cells which do not fall through become the ectoderm which forms CNS and adrenal gland.
Some cells from the endoderm form the notochord.

28
Q

Describe neurulation

A

Ectoderm folds inwards, driven by local cell shape changes, to form the neural tube which becomes the CNS

29
Q

What can be caused by improper neurulation?

A

Spina bifida and anencephaly (where the brain is open to the back of the head) can be caused when the sealing up and separation of the ectoderm fails

Very rarely, another foetus may become trapped leading to foetus in fetu

30
Q

What are somites?

A

Segments on either side of the neural tube which are precursors to vertebrae and skeletal muscle.
They form from the head end downwards

31
Q

Describe SHH signalling

A

Produced by the notochord

SHH spreads to neighbouring tissues and different tissues form depending on what concentration of SHH they receive

32
Q

What does the neural crest become?

A

The neural crest is the the dorsal surface of the neural tube.

It becomes much if the nervous system and face along with some other tissues

33
Q

How does a cleft palate form?

A

When the secondary palate fails to fuse

34
Q

What can happen when the ventral body wall fails to seal?

A

Anatomical umbilical hernia

Foetus in fetu can also occur if another feotus is trapped when the ventral wall seals

35
Q

Where is growth hormone produced?

A

Pituitary

36
Q

Describe Laron syndrome

A

Where the body has no receptors for growth hormone so body is smaller but with vitruvian proportions

37
Q

How does gigantism happen

A

Excess production of growth hormone, usually due to a pituitary tumour

38
Q

Describe how bones grow

A

Long bones have a growth plate which has a zone of proliferation containing stem cells which divide to replace themselves and make daughter cells which enlarge and differentiate, then replaced by mineral rich bone and finally die to leave holes which are invaded by bone cells.

39
Q

Describe how limbs grow to a normal size if one lags behind (such as the rabbit experiment)

A

Differentiating cells send signal to bone sheath and the sheath send a signal back to the zone of proliferation. When the bone is small, the distance between sheath and back is short, but when it’s large the distance is greater and so the signal weakens, so the cells proliferate less

40
Q

Describe the action of thalidomide

A

Limb growth occurs very rapidly and has high oxygen demands and therefore needs the vascular system to grow very quickly into elongating limbs. Thalidomide reduced blood vessel growth and causes phocomelia, or ‘seal limbs’ in babies

41
Q

Describe achondroplasia

A

Aka short-limbed dwarfism. Mutation in a receptor causes cartilage proliferation to stop early. Trunk and head normal size but limbs short

42
Q

Explain why skin only grows to cover the limb

A

Skin grows in relation to tension and not genetics, so is always in proportion to body

43
Q

Describe mechanically independent organs

A

Organs such as the spleen will grow to the correct total volume of tissue. If you add multiple feotal spleens into mice, their total mass will grow until it reaches the mass of one normal spleen.

This does not happen with all organs e.g. the thymus would each grow to the size of a normal

44
Q

Describe testosterone

A

A weak androgen

Converted to 5a -dihydrotestosterone (which is much stronger) by 5a reductase

45
Q

Describe the two types of cell which make up the gonads

A

Gametes which develop from the primordial germ cell which come from epiblast cells which were removed to the yolk sac around the time of gastrulation

Somatic cells which develop from the mesoderm and support the gametes

46
Q

Describe how germ cells reach the gonads

A

They become a migratory population and use the gut to to travel to the mesentery, where they enter the gonadal ridge and invade the gonads

47
Q

How is sex determined?

A

The SRY genes on the Y chromosome determines gender. Embryos are female by default and only become male if somatic cells of the gonad express SRY - become testes and produce androgenic hormones.

These hormones are the ONLY WAY in which somatic cells become male. Other somatic cells do not express SRY so only change in response to androgenic hormones from the gonads

48
Q

Describe androgen insensitivity syndrome

A

Mutation in androgen receptor means they embryo will have male gonads but female features as the body cannot detect the hormones

49
Q

Describe what happens what a embryo has deficient 5a-reductase enzyme

A

Will have female features with undescended testes before puberty, at which point the high level of testosterone will stimulate androgen receptors even without the enzyme, changing their features to male. Known as guevedoces - meaning eggs at twelve

Year 1 - Semester 1 (9 decks)

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