embryology

Question 1

what are the 4 cellular processes that are involved in embryological development

Answer 1

-Proliferation
-differentiation
-reorganisation
-apoptosis
The combinations of these processes give rise to all the events of embryology.

Question 2

what does the Ectoderm give rise to

Answer 2

Ectoderm gives rise to skin and the central nervous system

Question 3

what does the Mesoderm give rise to

Answer 3

mesoderm to muscles, blood, skeleton, heart and kidney

Question 4

what does the Endoderm give rise to

Answer 4

endoderm to gut, lungs and liver

Question 5

describe 1st step post implantation aka gastrulation (convertion of the bilayer of hypoblast and epiblast cells into a trilaminar embryo)

Answer 5

epiblast cells PROLIFERATE and DIFFERENTIATE into mesoderm and then MOVE into the space between the epiblast cells and the hypoblast cells. these mesoderm cells then DIFFERENTIATE further to form the endoderm cells which replace the hypoblast cells which are lost by APOPTOSIS

Question 6

describe neurilation

Answer 6

Neurulation is the differentiation of the Ectoderm (Epiblast) to generate the central nervous system– as seen in neuro– neural plate folds and meets to form neural tube (under the control of the notocord in the mesoderm of the developing embryo)This fusion process continues during week 4 of development

Question 7

what happens at the same time as neurilation

Answer 7

precursors of other tissues are developing within the embryo, and it is being converted from a flattened structure into a 3-dimensional embryo (during 3rd week)

Question 8

what happens to the yolk sac after day 21?

Answer 8

After day 21, the body cavity then closes by day 28 and pinches off the yolk sac
into the umbilical cord (allantois)

Question 9

when do the digits develop

Answer 9

fingers and toes are distinctly separated by day 56

Question 10

what was the most common maldevelopment seen with thalidomide babies

Answer 10

maldevelopment of the upper limbs was one of the most common outcomes

Question 11

how does thalidomide cause maldevelopment

Answer 11

it seems that it damages developing blood vessels, thus depriving the adjacent cells of nutrients and preventing their proper growth and development. the upper limb is particularly sensitive to it, and also the timing at which morning sickness occurs co-incides with development of upper limbs

Question 12

what are the 3 forms of kidney during development

Answer 12

• Pronephros is the most immature form of kidney
• Mesonephros, an intermediate phase
• Metanephros is most developed and persists as the definitive adult kidney.

Question 13

describe the formation of the kidneys

Answer 13

during development, the pronephros (till week 4) and mesonephros (till week 8 ish) function as kidneys until the metanephros has fully developed. kidneys arise from ureteric bud (forms collecting duct) and metanephrogenic blastema (forms nephron). initial blood supply comes from common iliac arteries but kidneys migrate upward to their normal position where they meet the adrenals and then receive blood supply from aorta via renal arteries (they can retain their old arteries as polar arteries)

Question 14

what is the problem with retention of the polar renal artery

Answer 14

it can cause obstruction of the ureter which then enlarges

Question 15

describe another kidney maldevelopment

Answer 15

The kidneys form separately, but may fuse to form a horseshoe kidney, the extra tissue makes it impossible to move so the joint kidney often remains in the pelvis. this may compromise kidney function.

Question 16

what gives rise to the male genital ducts

Answer 16

mesonephric ducts

Question 17

what gives rise tot he female genital ducts

Answer 17

paramesonephric ducts

Question 18

what three sources are the gonads derived from

Answer 18

mesothelium

from mesonephros

Question 19

what determines the development pathway the gonads take

Answer 19

SRY+ = male
SRY- = female

Question 20

describe the movement of primordial germ cells into the gonads

Answer 20

PGC migrate through the hind-gut and dorsal mesentery to the mesonephros and thence to the developing gonads

Question 21

what do primordial germ cells differentiate into

Answer 21

gametes in the gonads

Question 22

whats another key regulator in male gonadal development, where is it produced and whats it stimulated by

Answer 22

testosterone produced in testis Leydig cells and stimulated by maternal hGC

note: Testis Sertoli cells produce anti-Mullerian hormone (AMH), which causes the regression of the Mullerian (paramesonephric) ducts

Question 23

describe the differences in development of the external genitalia

Answer 23

-same for both genders until about week 7
MALES:
-genital swellings move downwards (towards anus) to form the scrotum
-urogenital sinus closes
-phallus becomes glans penis

FEMALES:

• genital swellings move upwardswards and encase the phallus
• urogenital sinus remains open to form vaginal orifice andurethral orifice
• phallus becomes clitoris and genital fold becomes labia minora

Question 24

what are the abnormalities in male and female reproductive systems development

Answer 24

MALES: (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, normally the result of defects in the cognate receptors. eg Androgen Insensitivity Syndrome : There is no or limited virilisation of external genitalia (which show relatively normal female structures but no uterus/oviducts)

FEMALES: Congential Adrenal Hyperplasia (CAH), ie no negative feedback on pituitary ACTH output, leading to high ACTH due to lack of cortisol, therefore overproduction of androgens from fatal adrenals, partial virilisation (The internal systems are female, as there is no SRY )

Question 25

what is the process leading to spina bifida

Answer 25

Formation of the neural tube, the precursor of the central nervous system occurs early in pregnancy, about 3 weeks after fertilisation . Fusion should occur through the neural tube, but in spina bifida this process is not completed.
-Anencephaly – compromised development of the head and skull is a rarer complication- the result of a lack of closure of the anterior neuropore

The most effective treatment is folic acid; if the maternal diet is low in folate, then the risks of spina bifida increase

Question 26

what is the process leading to congenital cardiac abnormalities

Answer 26

Abnormalities in cardiac development occur in 0.8-1% of pregnancies

teratology of fallot has 4 defects:

1. Pulmonary stenosis
2. thickened right ventricle wall
3. ventricular septal defects
4. aorta overrides septal defects

treatment= maintain patent ductus arteriosus and foramen ovale via prostaglandins and transpose major arteries (switching of the two arteries,)

Question 27

what is the process leading to cleft palate

Answer 27

as described in facial development, for the structures to move and come together, repeated formation of clefts in the face, and then filling in of the clefts is required, but in cleft lip/pallate this doesn’t happen properly so the groove isn’t filled in and as a result there is a separation (cleft)

Note that cleft lip is often asymmetric
cleft palate is usually symmetric as the halves of the palate do not meet and fuse correctly

Question 28

summarise Septation

Answer 28

formation of interventricular septum and formation of septum primum and secundum (leaving the foramen ovale between the atria until the 2 atrial septum’s fuse after birth

Question 29

summarise Septation

Answer 29

formation of interventricular septum and formation of septum primum and secundum (leaving the foramen ovale between the atria until the 2 atrial septum’s fuse after birth

Question 30

difference between foetal and child heart

Answer 30

foramen ovale: shunt between left and right atria (blood bypasses the lungs)- becomes oval fossa

Ductus arteriosus: connection between pulmonary artery and aorta, again bypassing the lungs (as they are not really used in foetus)- becomes legamentum arteriosum

Question 31

describe development of face

Answer 31

eyes, nose, cheeks, lips, develop on each lateral side of the face, and then move medially to fuse in the middle (except eyes)
mouth and chin are already in the middle, and just move downwards into place as nosed cheeks come together
how this happens seems to be that repeated formation of clefts in the face, and then filling in of the clefts, leads to sequential loss of tissue from the centre of the face, and the movement of tissues to the correct places.

Question 32

describe development of face

Answer 32

eyes, nose, cheeks, lips, develop on each lateral side of the face, and then move medially to fuse in the middle (except eyes)
mouth and chin are already in the middle, and just move downwards into place as nosed cheeks come together
how this happens seems to be that repeated formation of clefts in the face, and then filling in of the clefts, leads to sequential loss of tissue from the centre of the face, and the movement of tissues to the correct places.

Question 33

time frame of lung development:

Answer 33

begins during the first trimester, but is not completed until after delivery.

Question 34

why is it sometimes useful to delay pre term birth

Answer 34

Preterm infants often suffer from lung complications due to low levels of surfactant (Respiratory Distress Syndrome, RDS).

The production of surfactant begins early in the third trimester of pregnancy and gradually increases. Adequate production of surfactant is necessary for normal lung function at birth.

delaying birth can allow for more surfactant production, and this can be accelerated by an injection of glucocorticoid to the mother, which also increases surfactant production in the infant’s lungs

Question 35

describe the 4 stages of lung development

Answer 35

4 histologic stages:
-pseudoglandular stage (5-17 weeks) -bronchi, bronchioles and terminal bronchioles develop

• canalicular stage (16-25 weeks)- respiratory bronchioles develop
• terminal saccular stage (24 weeks to late foetal period) - alveolar ducts develop/ surfactant produced
• Alveolar stage (32 (pre birth)-8 years post delivery)- alveolar sacs develop/ surfactant produced

surfactant is produced from beginning of saccular stage ie from week 20-22 ish

Question 36

from what week is breathing possible if foetus is delivered

Answer 36

end of canalicular stage (26 weeks) as some of the terminal sacs (alveolar sacs) have developed and lung tissue is well vascularised however they do not have surfactant so will suffer from respiratory distress