embryo implantment and foetal development

Question 1

how does the hypothalamus stimulate ovaries to release oestrogen/progesterone

Answer 1

hypothalamus releases GnRH
- hits receptors in anterior pituitary gland

APG releases LH/FSH
- stimulating ovaries to release oestrogen and progesterone

(positive feedback)

Question 2

explain the negative feedback in the ovaries

Answer 2

with increased progesterone release from ovaries, it will inhibit APG from releasing LH/FSH (thus stop ovaries from releasing oestrogen/progesterone)

Question 3

only follicle with most receptors chosen to fertilise

Question 4

summarise the ovarian cycle, what hormones are released at what stage, what happens as a result, what gets inhibited or what gorws

Answer 4

1. follicular phase/pre-ovulation
   - day 1-14
   - GnRH–>LH/FSH
   - FSH stimulates ovary folicles to grow
   - follicles release oesgtrogen as they grow
   - initially, increase oestrogen inhibits FSH (negative feedback)
   - but eventually HIGH level oestrogen simulates release of LH (positive feedback)
2. ovulation
   - day 12-14
   - LH surge = dominant follicle to rupture releasing oocyte/ovum
   - oocyte travel down Fallopian tube
   (burst of follicle = decrease in oestrogen but the ovum itself will secrete oestrogen)
3. luteal phase
   - day 15-28
   - ruptured follicle forms corpus luteum, this secretes progesterone (thickening the endometrial lining) - and oestrogen
   - progesterone and oestrogen exhibits negative feedback, inhibiting GnRH, FSH and LH
   - if no fertilisation, corpus leuteum degenerates areoung day 24 (decreasing progesterone and oestergen levels), removing the negative feedback thus cycle starts again

Question 5

why is there need for progesterone to thicken the endometrial lining

Answer 5

to prep for implantation of fertilised egg

Question 6

summarise 3 phases of endometrial cycle and what hormonal release causes what

Answer 6

1. proliferative phase
   - ovarian follicles growing releasing oestrogen
   - growth of endometrium and myometrium. secretion of mucus alongside vagina and uterus
   - day 6-14
2. secretory phase
   - progesterone softens connective tissue in prep for implantation and promotes secretion of nutrients (endometrium becomes even thicken and more vascularised)
   -oestrogen for growth of endometrium
3. menstrual phase (if no fertilisation)
   - day 1-5
   - corpus luteum degenerates
   - progesterone/oestrogen support lost
   - uterine prostaglandins –> vasoconstriction –> tissue death
   - blood and endometrial debris lost thru vagina

Question 7

whats the role of FSH and LH

Answer 7

FSH= recruits follicle

LH= causes ovulation

Question 8

why is it important for the release of progesterone and oestrogen from the corpus collosum (ruptured follicle)

Answer 8

to inhibit APG from releasing FSH/LH so another follicle doesnt get recruited

Question 9

note: fertilisation occurs in Fallopian tube. the corpus luteum is simply a structure in the ovary that forms after ovulation

Question 10

explain how fertilisation causes a missed period and or morning sickness

Answer 10

• blastocysts (early stage of embryo) releases hCG (Human chorionic gonadotropin)
• hCG is a relaxant + relaxes gut muscles causing morning sickness

-hCG also supports the corpus luteum (which releases progesterone)

• progesterone (also a relaxant) which maintains the womb (prevents degeneration of lining so missed period occurs)

Question 11

explain how sperm gets into the egg and fertilises

Answer 11

• sperm penetrates corona radiata
• binds to ZP3 receptors
• this triggers release of enzyme from acrosome (in head of sperm) that digests zone pellucid
• sperm head has DNA, penetrating ovum triggering cortical reaction

Question 12

what is corona radiata

Answer 12

outer layer of follicular (granulosa) cells that form around a developing oocyte in the ovary and remain with it upon ovulation

Question 13

know: healthy egg membrane prevents additional sperm fertilising egg

• certain receptors on cell membrane allows ONLY 1 sperm to enter

Question 14

how long after triggering embryonic develpment does the fusion of nuclei from egg and sperm happen

Answer 14

1hr

Question 15

how long can sperm last in females repro tract

Answer 15

5 days (but only viable for 48hrs)

Question 16

after 4 days of fertilisation, the blastocysts develops what feature for better implantation on membrane

Answer 16

sticky

• implantations better on side of uterus not bottom otherwise causing pain and bleeding

Question 17

explain process of implantation/embedding of embryo into endometrium

Answer 17

• sticky blastocysts sticks to endometrium
• membrane of trophoblast cells disintegrate
• endometrium makes prostaglandins increase vascularity locally, increasing nutrients in that specific area
• embryo gets embedded into endometrium (it divides INTO membrane

Question 18

what are trophoblasts

Answer 18

surface layer of cells of clastocytes

Question 19

endometrium makes prostaglandins increase vascularity locally, increasing nutrients in that specific area, what do you call this modified endometrium

Answer 19

decidua

Question 20

how long after implantation does the placenta fully develop, what does this mean

Answer 20

5 weeks

• here embryonic heart starts pumping blood into placental villi (heart beating)

Question 21

what is the placenta responsible for

Answer 21

delivering oxygen, nutrients and removal of waste, c02 from foetus

Question 22

fetal part of placenta secretes hCG and progesterone

• placenta is endocrine organ producing many hormones

Question 23

the placenta is high permeable to alcohol (and drugs, disease e.g hiv), and can result to foetal alcohol syndrome

Question 24

what is molar / hydatidiform mole pregnancy

Answer 24

when the fertilisation of the egg by the sperm goes wrong. This leads to the growth of abnormal cells or clusters of water filled sacs inside the womb.

(trophoblast tissue overgrows and shows as cysts)

Question 25

how long does it take the placenta to take over from the corpus luteum

Answer 25

10-12 weeks

Question 26

what 4 things are secreted by placenta

Answer 26

oestrogen progesterone hCG Human placental lactogen

Question 27

function of human placental lactose from placental

Answer 27

responsible for movement of glucose into embryo for growth

Question 28

how long is average full term for growth of baby

Answer 28

37/38 weeks

Question 29

3 most common congenital anomalies are: heart, neurotube defects down syndrom

Question 30

what is a teratogen

Answer 30

agent or factor causing malformation of embryo

Question 31

give some examples of a teratogen

Answer 31

thalidomide (causes loss of limbs) (from drugs treating skin cancer) infections (rubella, heart defect causing) alcohol drugs

Question 32

what genetic factor affect kids

Answer 32

maternal age chromosomal abnormalities mutant genes

Question 33

Down syndrome risk increases with maternal age

Question 34

what is gastroschisis/exompholos (type of defect visible at birth)

Answer 34

abdominal wall doesnt close (intestines spill out)

Question 35

what is achondroplasia

Answer 35

dominant inherited abnormality to convert cartilage to bone

Question 36

what is the most critical period of development

Answer 36

week 3-8 (during embryo development) - very susceptible to pathogens etc - major congenital anomalies

Question 37

define the terms ectoderm, mesoderm, endoderm (3 germ layers)

Answer 37

ectoderm = structure maintain contact with outside e.g nose, eyes,CNS mesoderm = peritoneal, pleural, etc endoderm = GI tract, respiratory tract, epithelial lining etc

Question 38

neural tube defects sensitive across what period of development

Answer 38

3-16 weeks

Question 39

what is neurulation

Answer 39

formations of neural tube - starts thickening at neural plat at cranial end of embryo

Question 40

ectoderm folds and joins to form neural tube, what sends signals to control this

Answer 40

notochord - an embryonic midline structure common to all members of the phylum Chordata, providing both mechanical and signaling cues to the developing embryo

Question 41

what 3 things may cause neural tube defects

Answer 41

- anti epileptic meds - maternal diabetes - hyperthermia e.g sauna

Question 42

what medication/supplement is take to prevent neural defect

Answer 42

folic acid

Question 43

what is spina bifida and its different variations

Answer 43

neural tube fails to close at its length - spin bifida aperta (spinal cord and nerves open to outside) - spina bifida occulta (covered with skin - spina bifida cystica / meningocele/ mylomeninocele (covered with just surrounding membrane)

Question 44

spina bifida occulta, meningocele, myelomeningocele are the same issue increasing in severity, describe the difference

Answer 44

occulta = no closing of neural tube but no sac/bulge meningocele = no closing of neural tube and bulging myelomeningocele = no closing of neural tube and bulging with spinal cord and nerves in the bluge

Question 45

what is Arnold chiari malformation

Answer 45

lower part of brain pushes down into spinal canal (cerebellum and brain stem pushing into foramen magnum)

Question 46

what is hydrocephalus

Answer 46

accumulation fo cerebrospinal fluid in brain

Question 47

how do you detect and diagnose nerutal tube defects - how long does it take fo ultrasound to pick it up on screen

Answer 47

antenatal screening - positive if elevated alpha fetoprotein levels - 12 - 20 weeks

Question 48

what signals for segregation of brain into fore, mid,hind brain and facial development

Answer 48

homeobox genes / hox gene

Question 49

what are the names for the fore, mid, hind Brian in development

Answer 49

fore = prosencephalon mid = mesencephalon hind = rhombencephalon

Question 50

whats anencephaly

Answer 50

no closure of neural tube at top end 100% fatality

Question 51

failure of fusion b/w maxillary prominence and inter maxillary segments during the 7th week results in what disorder

Answer 51

cleft lip

Question 52

what week does the intermaxillary process form the philtrum of the upper lip

Answer 52

14th

Question 53

whats frontonasal dysplasia

Answer 53

is a congenital malformation of the midface.

Question 54

why are there minor anomalies occurring during metal development week 9-36?

Answer 54

hox gene mainly only in action during embryo development which controls many things such as facial development and Brian development/segmentation

Question 55

what day of development does heart begin beating and blood flow

Answer 55

day 22-24 heart beating blood flow starts week 4

Question 56

whats the issue with heart defects such as septal defect

Answer 56

mixed oxygenated and deoxygenated blood

Question 57

what is persistent trunks arteriosus and hypopplastic left heart

Answer 57

- PTA congenital defect where pulmonary trunk and aorta fails to divide properly - Hypoplastic left heart syndrome is a rare congenital heart defect in which the left side of the heart is severely underdeveloped and incapable of supporting the systemic circulation

Question 58

failure of what process during development causes syndactyly (webbed tigers)

Answer 58

apoptosis (programmed cell death)

Question 59

what cells form skeletal and muscular parts of the limbs

Answer 59

lateral plate cells = skeletal formation myotome = muscular components

Question 60

formation of limb buds = proliferation of somatic lateral plate mesoderm and myotome cells (stops muscle and skeletal formation)

Question 61

formation of limbs buds secrete FGF 7/10, this stimulates what

Answer 61

Apical ectodermal ridge (AER) - determines pattern of limb - formation of early skeleton - muscles tendons vasculature

Question 62

what are the following limb develpment anomalies: meromelia Amelia polydactyly triphalageal dysplasias

Answer 62

mero = reduction of limb Amelia = missing limb poly = extra digits tri = 3 phalangeal bones (not 2) (so as long as normal finger) dysplasia = fusion of limb/disproportional growth