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Rob's RDA > Embryology parts 1-4 > Flashcards

Embryology parts 1-4 Flashcards

1
Q

When is conceptus referred to as foetus

A

8 weeks

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2
Q

For how long does development within fallopian tube usually occur

A

Preimplantation development normally occurs within the Fallopian tube (oviduct) over a period of ~6 day

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3
Q

What development happens in fallopian tube

Define morula

A

Series of cleavage divisions, which sequentially double the number of cells in the conceptus (2, 4, 8, 16 cells) to produce a ball of undifferentiated cells (the Morula)

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4
Q

What does the morula differentiate into

A

First level of differentiation, into

BLASTOCYST

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5
Q

What is blastocyst

A

From morula.

Still has zona pellucida

Outer layer of cells=trophoblast

Inner cell mass

Fluid-filled cavity

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6
Q

T/f the zona pellucia implants into the lining of the uterus

A

F:

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7
Q

What happens to blastocyst

A

The Blastocyst then hatches from the Zona Pellucida (within which it has developed up to this time, about day 6 after fertilisation), and begins to implant in the uterine lining

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8
Q

By what day is the blastocyst implanted

A

complete about 10 days post-fertilisation

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9
Q

What is the structure of the blastocyst after it has implanted into uterus

A

he inner cell mass, which was a group of undifferentiated cells has become a bilayer disk, composed of hypoblast and epiblast cells

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10
Q

What is the importance of the bilayer in the blastocyst

A

his bilayer disk gives rise to all the tissues of the human fetus, through a complex series of changes.

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11
Q

What is the first change that occurs to the blastocyst

A

Gastrulation. Day 14-18 PA

Converts bilayer–> trilaminar embryo with 3 layers of germ cells:

  1. Ectoderm
  2. Mesoderm
  3. Endoderm
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12
Q

How are each of the 3 layers formed in gastrulation

A

The ectoderm originates from the epiblast cells.

Epiblasts also differentiate into mesoderm cells.

These mesoderms cells move into the space between epiblast and hypoblasts.

The mesoderm cells form mesoderm layer, but also differentiate into endoderm cells.

Hypoblast layer lost by apoptosis

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13
Q

What does ectoderm give rise to

A

skin and the central nervous system

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14
Q

What does mesoderm give rise to

A

muscles, blood, skeleton, heart and kidney

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15
Q

What does the endoderm give rise to

A

gut, lungs and liver

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16
Q

T/F tissues usually originate from a single germ layer type

A

F…. Muscular and vascular tissue are generally of mesodermal origin, so tissues are normally a mixture of germ layer types (e.g. muscle in the skin and gut).

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17
Q

What stage is next from gastrulation

A

Neurulation. Occurs before gastrulation is complete.

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18
Q

What is neurulation. What controls it

A

ifferentiation of the Ectoderm (Epiblast) to generate the central nervous system (Brain and Spinal cord), under the control of the notocord in the mesoderm of the developing embryo.

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19
Q

Outline the formation of the neural tube

A

development of the neural plate on the ectoderm; this develops two folds, which increase in size until the meet over the neural groove and fuse to form the neural tube

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20
Q

When does fusion of the neural plate occur

A

during week 4 of development.

Now the neural tube is formed

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21
Q

What cell groups are outside the embryo proper

A

primordial germ cells (PGC) –> in yolk sac endoderm at caudal end

cardiac and vascular progenitors–> in primary heart field at cranial end

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22
Q

Where do each of the cell types that were outside the embryo proper move to

A

PGCs to hindgut

Heart progenitors under head of embryo

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23
Q

Which folding occurs in the third week of development

A

LATERALLY –> the sides curve round to fuse at the front (ventral midline)

ANTEROPOSTERIOR –> folds the PGCs into the hind gut, and the developing heart progenitors under the head of the embryo

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24
Q

What sacs are there, dorsal and ventral to embryo

A

Dorsal is the amnionic cavity

Ventral is the yolk sac

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25
Q

What happens in the transverse plane in day 19-28

A

Fig 5.2.8

You can see the ecto, endo and meso derm

The ectoderm is undergoing formation of neural tube

The amniotic cavity is just an extension of ectoderm

The yolk sac is continuous with the endoderm

There is a visceral part of mesoderm which is in contact with the endoderm/yolk (i,,e the pink layer around the yellow from the first image)

Then there is a somatic or parietal layer of mesoderm which comes to surround the endoderm and the visceral layer

Look back to year 1 abdo anatomy

Note that in the foregut and the hindgut, it will look like E and the gut tube closes

In the midgut, there is still connection to the yolk sac, which can be seen in D

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26
Q

What happens in longitudinal plane

A

Image 5.2.9

Left is cranial

Right is caudal

The top of the image is dorsal and the bottom is ventral

You can see how the heart progenitors have moved from the angiogenic cell cluster (outside of embryo proper) into the embryo by AP folding

You can also see how there is movement of the PGCs from outside to behind the foregut

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27
Q

When is all the lateral and transverse foling occurring

A

Week 3-4

28
Q

By what time have the precursors of all internal tissues have been laid down

A

End of week 4

29
Q

Development of what happens in month 2 of development

A

Urogenital, cardiac, facial and lung and limb

30
Q

Where do the limbs grow out from

A

lateral plate mesoderm rapidly under control of special signalling regions

31
Q

When does limb formation begin and end

A

Forelimb bud appears at d27/8

Hindlimb bud at d29

both fully formed d56

32
Q

What was thalidomide and what did it effect

A

Morning sickness drug

Affected upper limb most

33
Q

Mechanism of thalidomide action

A

it damages developing blood vessels, thus depriving the adjacent cells of nutrients and preventing their proper growth and development

34
Q

Why did thalidomide affect upper limb

A

In humans, it seems that the timing of thalidomide administration (8 weeks of pregnancy onwards, as this is the starting point for severe cases of morning sickness), matches with upper limb development (Figure 5.3.1), 6 weeks post-fertilisation.

upper limb blood vessels seem to be particularly sensitive to thalidomide,

35
Q

What could thalidomide be used for now

A

thalidomide has been found to be a useful and effective treatment in some cancers, and also for some complications of leprosy

36
Q

Where do digits arise from

A

Digital rays on the flat hand plate

These grow out in response to sonic hedhog protein

If the sonig hedghodg protein is replicted, you could get mirror image of a hand

37
Q

Stages of kidney development

A

Pronephros is the most immature form of kidney

Mesonephros, an intermediate phase

Metanephros is most developed and persists as the definitive adult kidney.

38
Q

What do gonads arise from

A

intermediate mesoderm within the urogenital ridges of the embryo

39
Q

What do genital ducts arise from

A

paired mesonephric and paramesonephric ducts

40
Q

T/F embryonic gonads begin differentiating immediately after fertilisation

A

F … Gonads show no differentiation in development until about Week 7 post fertilisation

41
Q

What is development of male reproductive system dependent on

A

he activity of sex-determining region Y (SRY) protein, coded for by the SRY gene on the Y chromosome.

42
Q

Which ducts give rise to female and male genital ducts

A

The mesonephric ducts give rise to MALE genital ducts

The paramesonephric ducts give rise to FEMALE genital ducts

43
Q

Primative forms of kidney do not contribute to final kidney that develops from metanephros T/F?

A

During human development, primitive forms of kidney develop (pronephros and metanephros), which do not contribute to the final kidney that develops from the metaneophros

44
Q

Where do the kidneys move from and do during development and when

When are the gonads developing

A

Weeks 6-9

You have the mesonephros (which DOES NOT become the kidney, it is just a primative form) attached ti the bladder via mesonephric duct (from which male gonads develop)

Then the kidneys (arise from metanephros) are connected to the bladder by ureters. They are receiving blood from bifurcation of aorta

The kidneys then ascend up along the mesonephros and form a new arterial supply at a higher up level. The blood supply comes from furhter and furhter up the aorta as the kidneys move up (i.e. former renal arteries degraded).

They end up immediately under the suprarenal glands

As kidney is moving up, the mesonephros is shrinking, and then gonads developed from the mesopnephric duct which the mesonephros was attached to

45
Q

Differentiate the kidney and the ureter during development

A

he ureters, which connect the kidneys to the bladder, extent in length during this process, retaining the kidney-bladder connections

in contrast the kidneys form new connections with the developing arterial system as they move, so that renal arteries break down and re-form during this process.

46
Q

Outline renal abnormalities in development

A

One kidney may be retained in the pelvis

Retention of an extra artery (or another problem) may obstruct (partly or fully) the ureter, and cause enlargement of the renal pelvis

kidneys form separately, but may fuse to form a horseshoe kidney (Figure 5.4.3B); the extra tissue makes it impossible for it to move, so it will remain

47
Q

T/f one functional kidney always sufficies both in development and adulthood

A

F:

All these abnormalities may compromise kidney function. In an adult, one functional kidney may suffice, but this may not always apply during development.

48
Q

What is the wolffian system

A

The mesonephric ducts give rise to MALE genital ducts (Wolffian system)

49
Q

What is the mullerian system

A

The paramesonephric ducts give rise to FEMALE genital ducts (Mullerian system)

50
Q

T/f the gonads and reproductive tracts are different from the start of development

A

F:
The gonads and reproductive tracts are indifferent up until 7 weeks of development; differentiation is influenced largely by the presence or absence or SRY (on the Y chromosome)

51
Q

What happens if SRY +, what if -

A

If SRY+, then development proceeds along the male path

If SRY-, then development proceeds along the female path

52
Q

Where do the ducts involved in genital tract development come from.

Where do the gonad precursors develop

What are gonad precursors surrounded by

A

So the mesonephric and paramesonepric will become genital tracts, and then there are precutrsors which bvecome the gonads too!

Within the mesonephros, the mesonephric and paramesonephric ducts develop, and are readily identifiable by week 5 post fertilisation

At the same time, the gonad precursor is developing from the mesonephric mesoderm, and is covered by coelomic epithelial cells.

in 5.4.4 diagram just look at where the mesonephric and paramesonephric ducts are

The paramesonephric duct is medial to the mesoneprhic duct

53
Q

t/f the gametes which will end up in the gonad, develop in the mesonephric mesoderm, along with the gonads themselves.

A

f In parallel with the developing reproductive tissues, the primordial germ cells (PGC) are following a separate developmental pathway.

54
Q

Which layer do the gametes develop from

A

They develop different from the gonads

In parallel with the developing reproductive tissues, the primordial germ cells (PGC) are following a separate developmental pathway.

PGC will give rise to the gametes within the gonads

They originate in the epiblast

55
Q

Where do PGCs migrate after developing in the epiblast

A

migrate to the caudal part of the yolk sac

Once the main caudal structures of the embryo proper have developed

the PGC migrate through the hind-gut and dorsal mesentery to the mesonephros and thence to the developing gonads (a result of antero-posterior folding, remember!)

56
Q

What does the indifferent gonadal system look like and when is it formed by

A

By week 7

Coming off of the urogenital sinus (basically the cloaca, separates into urogenital sinus and the anus just before this. UG sinus gives rise to bladder and then urethra and other stuff in women), so the mesonephric duct comes from the UG sinus and into the mesonephric mesoderm (Wollfian)

The paramesonephric duct comes off the UG sinus (or bladder shown in other images) next to the mesonephric mesoderm (mullerian)

57
Q

In the presence of SRY, when will male gonadal development start and why

A

Weeks 7-8 (weeks 9-10 gestational age)

Because hCG levels peak at this time, and they stimulate the testosterone needed for male development

58
Q

What are the key regulators of male gonadal devlopment

A
  1. Testosterone from Leydig cells (under stimulation from hCG from maternal circulation). Support development of wollfian ducts, which give rise to male reproductive tract
  2. AMH (anti-Mullerian hormone) produced from sertoli cells, to regress mullerian ducts
59
Q

What causes regression of mullerian ducts in males

A

estis Sertoli cells produce anti-Mullerian hormone (AMH), which causes the regression of the Mullerian (paramesonephric) ducts.

60
Q

When does the female gonadal development begin in the absence of SRY

A

8-9 post fertilisation (later than men, which is 7-8 weeks)

61
Q

What is an important factor in the development of the early indifferent genitalia

A

The key regulator seems to be dihydrotestosterone (DHT), a potent androgen that is produced from testosterone originating in the Leydig cells of the testis.

62
Q

Most common maldevelopments in males

A

(a) the inability to produce the appropriate hormones (testosterone and anti-Mullerian hormone (AMH)

or

(b) the inability of target tissues to respond to these hormones (cognate receptors)

63
Q

What causes an inability for male embryo to respond to AMH or testosterone

A

defects in the cognate receptors.

64
Q

What is androgen insensitivity syndrome

A
  1. No virilisation of external genitalia (they look like female); lacking mesonephric (woolfian) ducts; testis structure variable; do not descend

DUE TO mutant androgen receptor

  1. AMH from sertoli cells normal, so mullerian (paramesonephric) ducts regress. No female structures such as uterus of oviducts are present.
65
Q

What is congenital adrenal hyperplasia

A

IN ENDO!!!

Mutation in cytp450 21 hydroxylase.

Means limited cortisol production from adrenal fetus.

Lack of cortisol leads to ACTH output from piutuitry, and overstimulation of foetal adrenals, which make eak androgens (e.g. androstenedione)

Cause partial virilisation of genitalia

66
Q

Why is only genitalia and not internal systems affected in congenital adrenal hyperplasia

A

The internal systems are female, as there is no SRY (no testicular development), no male ducts (no testosterone) and female ducts develop (no AMH, as no Sertoli cells).

Rob's RDA (10 decks)

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