EMBRYOLOGY

Pregnancy 280d 40w

full term w37-42

pre-term b4 w37

post term after w42

first trimester w1-13

second w14-27

third w38-42

parturition: process of giving birth

cell division

purpose of meiosis:

crossover 

provides each germ cell with n DNA 

spermatogenesis 64-75d

sperm=acrosome, head DNA, middle piece mitochondria, tail microtubule, condensation of nucleus, shed cytoplasm

sertoli cells secrete seminal fluid 

Leydig cells btwn seminiferous tubules secrete testosterone

gametogenesis

oogenesis 

ovulation

Graafian follicle size+ by FSH LH

oocyte + cumulus oophorus 

rearrange around zona pellucida

corona radiata

granulosa cells, theca interna vascularized 

luteal cell by LH

corpus luteum

progesterone + estrogen

secretory stage 

oocyte transport 

fimbriae 

if no fertilization, corpus luteum degenerate 

corpus albicans (fibrotic scar tissue)

if fertilization, hCG prevent corpus luteum degenerate 

corpus luteum produce progesterone 

placenta produce progesterone 

fertilization -ampullary region of uterine tube

sperm=capacitation, acrosome reaction

penetration of corona radiata - only one capacitated sperm penetrate

penetration of zona pellucida - acrosomal enzymes, zona reaction 

fusion of oocyte & sperm cell membranes - sperm head tail enter oocyte cytoplasm 

oocyte response - zona reaction, resumption of meiosis 2, metabolic activation of egg 

results:

restore 2n chromosomes

determine sex

initiation of cleavage = mitosis of fertilized ovum

2 cell 30h, 4 cell 40h, 8 cell, morula 16 cell d4, blastocyst d4-21 (trophoblast, embryoblast, blastocyst cavity), organogenesis/embryonic period w3-8

zygote=blastomere 

No fertilization oocyte arrested at M2

implantation 6d after fertilize

trophoblast (cyto & syncytio) penetrate uterine mucosa (secretory phase)

occurs in superior portion of body of uterus, towards posterior wall

bilaminar germ disc d8

embryoblast: 

epiblast 

hypoblast

trilaminar germ disc

gastrulation: establish 3 germ layers

ectoderm

mesoderm

endoderm

primitive streak: groove, node, pit

notochord

midline axis, support embryo

future site of vertebral bodies

induce overlying ectoderm to form neural plate (CNS)

growth of germ disc 

initial flat and round 

gradually elongates 

broad cephalic end

round caudal end 

invagination of surface cells in primitive streak til end of W4

regress and diminish in size 

allantois 

D16

early blood formation W3-5

blood vessels of allantois become umbilical arteries and veins 

clinical correlates 

holoprosencephaly - single lobe brain, severe skull, facial defects 

caudal dygenesis - sirenomelia, insufficient mesoderm

sacrococcygeal teratoma - remnants of primitive streak 

folding of embryo

lateral folding

cephalocaudal folding

Flat to cylindrical 

Median horizontal plane 

embryonic period w3-8

germ layer give rise to number of specific tissue organ

main organ system established 

recognizable external body 

ectoderm: 

neural tube (CNS)

skin

hair

nails

glands 

neural crest cells: 

melanocytes 

Schwann cell 

ganglia 

leptomeninges 

facial dermis

cranio facial bone 

odontoblast 

adrenal medulla 

septum heart

paraxial mesoderm: somitomere (neuromere & somite)

neuromere - head region

somitomere 1235 - extrinsic muscles of eye

somitomere 46 - striated muscles of face and jaw

somitomere 7 - stylopharyngeus muscle 

42-44 pairs somites: occipital, cervical, thoracic, lumbar, sacral, coccyx 

first and last 5-8 form axial skeleton 

sclerotome - vertebrae column

dermomyotome: myotome, dermatome 

intermediate mesoderm: urogenital 

kidney 

gonads 

lateral plate mesoderm: 

parietal - lateral and ventral body wall

visceral - wall of gut

blood, lymphatic cells, heart and vessels

skeletal muscle

cortex of adrenal gland

spleen 

serosa

endoderm: epithelial lining 

GIT and RT

bladder, urethra 

tympanic cavity, antrum, auditory tube

parenchyma of tonsils, thyroid, parathyroid, thymus, liver, pancreas 

fetal membranes

protection 

provide nutrition, respiration, excretion

yolk sac:

transfer nutrient

blood development in w3

hematopoietic activity in liver in w6

amnion: 1L

protective water cushion absorb shocks

permits symmetrical external growth

barrier to infection

equalize pressure

prevent adherence of amniotic membrane

control embryo's temp

allow change in position of fetus - free movement 

water wedge dilate cervix b4 delivery 

400 mL = oligohydramnios

>1.5-2L = polyhydramnios 

chorion:

extra embryonic coelom

amniotic sac (bag of water): inner amnion, outer chorion 

allantois:

blood formation in w3-5

form umbilical vessels 

fluid from amniotic cavity diffuses into umbilical vein and enters fetus circulation

umbilical cord:

1-2 cm diameter

30-90 cm length 

average 55 cm

center of fetal surface 

primitive umbilical ring pass connecting stalk, umbilical vessels, yolk sac stalk, cannal 

chorion frondosum

placenta

full term is discoid

15-20 cm diameter

2-3 cm thickness

500-600 gms weight 

fetal surface = smooth surface cover by amnion, umbilical attachment

maternal = rough surface, lobulated due to 15-20 cotyledons, peripheral continuous with fetal membrane 

anterior/posterior wall of endometrium near fundus 

fetal portion = chorion frondosum

maternal portion = decidua basilis 

fx: 

exchange gas by simple diffusion

transfer nutrients electrolytes from mom

eliminate waste

endocrine HCG, progesterone

transmit maternal Ab passive immunity 

anchor fetus by umbilical cord

maternal heat transfer 

anomalies:

according to attachment of umbilical cord

according to site of implantation: placenta previa - in lower uterine 

accessory placenta - placenta succenturiata

according to degree of adhesion

according to shape of placenta 

twin:

monozygotic/identical 

-split zygote at 2 cell/early blastocyst stage/bilaminar

2/3 dizygotic/fraternal

-2 oocyte + 2 sperm, differ gene, implant individually, own placenta amnion chorion, chorionic sacs may come into apposition & fuse 

cojoined 

thoracopagus

pygopagus

craniopagus 

teratology = cause of structural, fx, behavioral, metabolic ds at birth

size, arrangement, composition of any organ

principles:

- depends on genotype of fetus & mom

- development stage w3-8 of gestation = most sensitive period 

failure of development: agenesis, scrotum agenesis 

incomplete development: gigantism, dwarfism, multiple breast 

embryonic persistence: Meckel's diverticulum, cervical cyst, thyroglossal cyst

misplacement: ectopic organ

- hereditary

genes

chromosomes - non disjunction

- environment 

physical

irradiation

chemical 

hormones

heavy metals

growth inhibitors

vitamin deficiency 

infection

antigens 

smoking