Physiology of embryo, fetus and neonate

Question 1

what are the steps of fertilisation

Answer 1

1. capacitation
2. acrosome reaction
3. fusion of plasma membranes. Sperm nucleus enters the egg cytoplasm
4. block to polyspermy
5. prezygote

Question 2

explain what the capacitation stage of fertilisation is

Answer 2

spermatozoa penetrate the corona radiata

Question 3

how is polyspermy prevented

Answer 3

• the oocyte cell membrane depolarises preventing membrane fusion with additional spermatozoa
• cortical reaction - cortical granules fuse with the membrane and release their contents into the zona pellucida, which hardens the zone

Question 4

what is the morula

Answer 4

12-16 cell stage

Question 5

what does the blastocyst differentiate into

Answer 5

inner cell mass
trophoblast
blastocoele

Question 6

explain the further differentiation of the trophoblast and inner cell mass

Answer 6

trophoblast

• syncytiotrophoblast
• cytotrophblast

inner cell mass
- bilaminar disk (epiblast and hypoblast)

Question 7

what is gastrulation and what is it controlled by

Answer 7

• process of cellular rearrangement (migration, invagination and differentiation of the epiblast)
• controlled by the primitive streak

Question 8

3 layers of the epiblast

Answer 8

endoderm
mesoderm
ectoderm

Question 9

what structures derive from the ectoderm

Answer 9

epidermis of skin
cornea and lens of eye
nervous system

Question 10

what structures derive from the mesoderm

Answer 10

notochord
MSK
muscular layer of stomach, intestine etc
circulatory system

Question 11

what structures derive from the endoderm

Answer 11

• epithelial lining of digestive and respiratory tracts
• lining of urethra, bladder and reproductive system
• liver and pancreas

Question 12

what are the 6 regions of the primitive heart tube

Answer 12

aortic roots
truncus arteriosus
bulbus cordis
ventricle
atrium
sinus venosum

Question 13

what are the 3 fetal circulatory shunts

Answer 13

• foramen ovale (shunts majority of blood from R to L side of the heart through atria)
• ductus arteriosis (shunts the small amount of blood that managed to enter the pulmonary trunk back to the distal arch of the aorta)
• ductus venosus (shunts 30% of umbilical blood directly into the IVC bypassing the liver)

Question 14

how does the foramen ovale close

Answer 14

first breath –> pulmonary resistance falls –> higher pressure in LA –> pressure in LA>RA = blood unable to shunt across FO

Question 15

how does the ductus arteriosus close

Answer 15

muscular wall encouraged to close by bradykinin after birth

Question 16

describe the initial formation of the respiratory system

Answer 16

out-pocketing of the foregut = respiratory diverticulum

Question 17

how does the gut and respiratory system become separated

Answer 17

by the formation of the tracheoesophageal septum

Question 18

describe the 3 stages of the respiratory system embryological development

Answer 18

pseudoglandular stage
canalicular stage
terminal sac stage

Question 19

what are the 2 primitive embryological urinary systems called

Answer 19

pronephros

mesonephros

Question 20

how is fetal urine production regulated

Answer 20

by renal blood flow - controlled by renin-angiotensin system, the SNS, prostaglandins, and ANP

Question 21

which embryological layer is the CNS formed from

Answer 21

ectoderm

Question 22

what week of development does the neural tube close

Answer 22

4th week of development (4th week from conception, 6th week from LNMP)

Question 23

3 main types of spina bifida

Answer 23

spina bifida occulta
meningocele
myelomeningocele

Question 24

at what week of gestation does differentiation of the reproductive system start to occur

Answer 24

week 7 and finish week 9

Question 25

how are the fallopian tubes, uterus, and vagina formed

Answer 25

- fallopian tubes = fusion of the paramesonephric ducts cranially - uterus, broad ligament, and upper vagina = fusion of the paramesonephric ducts caudally - lower vagina = formed from the urogenital folds

Question 26

the female reproductive organs develop in the absence of which 3 things

Answer 26

- SRY gene on y chromosome - testosterone --> persistence of mesonephric duct - AMH - regression of paranephric duct

Question 27

what mechanisms help the newborn to initiate its first breath

Answer 27

- tactile stimulation - oxygen deprivation and carbon dioxide accumulation trigger chemoreceptors - thoracic compression (vaginal birth)

Question 28

what are the major changes in the cardiovascular system that occur at birth

Answer 28

- large reduction in pulmonary pressure (due to first breath) - removal of the placental circulation This leads to a reduction in R to L shunting --> closure of the foramen ovale, and closure of the ductus arteriosus

Question 29

how is nonshivering thermogenesis achieved in newborns

Answer 29

thermal receptors transmit impulse to hypothalamus --> stimulate SNS --> noradrenaline release in brown fat --> activates lipase --> lipolysis and fatty acid oxidation

Question 30

describe what thyroid hormones/thyroid medications cross the placenta

Answer 30

- TSH does NOT cross - small amounts of T3 and T4 cross - TRH, iodine, TSH Immunoglobulin do cross - Propylthiouracil does cross

Question 31

fetal hyperthyroidism is usually caused by

Answer 31

maternal Graves disease - transplacental passage of thyroid stimulating immunoglobulins - usually in women who have been treated for Graves with ablation or resection (continue to produce IgG to TSH)

Question 32

treatment of fetal hyperthyroidism

Answer 32

maternal anti-thyroid treatment with propylthiouracil

Question 33

treatment of fetal hypothyroidism

Answer 33

- discontinuation of maternal antithyroid medication | - intraamniotic levothyroxine treatment