week one + two - general embryology - prenatal development Flashcards
define :
gamete
haploid
diploid
oocyte
stem cell
gamete = mature female/male germ cells [ovum//sperm]
haploid = SINGLE chromosome set carried by sperm + egg cells –> recombined after fertilisation = diploid chromosome set
diploid = cell w TWO chromosome sets [eg somatic cell]
oocyte = mature female germ cell; egg
stem cell = undifferentiated cell - precursor to specialised cell types
describe the human developement stages [3]
germinal period [0-14 days]
- rapid cell division
- implantation + formation of embryonic discs
embryonic perion [3rd-8th wk]
- visible advances in differentiation
- devel of CNS, heart, eye, arms, legs, teeth, palate
fetal period [9th-40th wk]
- differentiation + growth + organisation of tissues occur and rate of body growth increases
- devel of palate, ear, external genitalia, brain
briefly describe fertilisation
- fusion of haploid gametes
- forms diploid zygote
- nuclear membrane breaks down, DNA replication commences [mitosis]
- fertilisation occurs at distal ends of fallopian tubes [oviducts]
- newly formed zygote then travels –> uterus by contractions and cilia
describe the breakdown of germinal period
day 1 = fertilisation
- zygote fused from haploid gametes
**day 0-3 = cleavage **
- rapid mitotic div w/o cell growth –> total cytoplasm = remains constant
- cell size = rapidly decreases as # of cells ^
**day 4 = morula **
- ball of 32 cells flattened against zona pellucida [protective membrane + limits cell growth]
- morula loc. at proximal end of oviduct
**day 5 = blastocyst **
- cavity forms in morula –> now termed blastocyst
- outer shell layer = trophoblast
- inner layer = inner cell mass [pushed off to one side - some become embryoblast
- rest of fluid filled cavity = blastocoel
- zona pellucida disappears = allows blastocyst to grow + change shape
**day 7 = implantation **
- motility slows
- adhesion –> uterine epi. as bloastocyst cells digest uterine periotoneum = deeper penetration/attachment
**day 8-9 = epiblast // hypoblast **
- epiblast = future germ cell layers [away from blastocoel
- hypoblast = does NOT contribute to embryo –> gives rise to some umbilical tx [faces blastocoel
describe the formation of the bilaminar embryo [4]
- FOUR embryonic membranes devel
1. amniotic sac // amnion [on epiblast side]
2. yolk sac for nourishment of disc [on amniotic cavity side
3. chorion –> becomes chorionic sac + uterine wall = placenta
4. allantois [connecting stalk] –> becomes umbilical cord - contributes blood ves. from embryo –> placenta
define the bilaminar disc
where epiblast + hypoblast cells meet
- disc splits sphere –> makes two cavities either lined by epiblasts or hypoblasts
define gastrulation
**2-3wks **
emergence of primitive streak [caudal] + node formation
- induction + migration of cells –> THREE layers = **trilaminar embryonic disc **
1. ectoderm
2. mesoderm
3. endoderm
list what structures the layers of the trilaminar disc give rise to
ectoderm
- CNS, PNS
- parts of sensory sys
- epi of skin, oral mucosa, nasal + sinus cavities
- teeth enamel
mesoderm
- blood, bone muscles, some organs
- remainder of teeth structures
endoderm
- epi lining of pharynx, intestines, lungs, bladders, organis of urogenital tract
explain embryonic folding
after trilaminar disc established at 2-3wk –> embryonic folding cont. –> 4th wk = establish body axis
- allows formation of body cavities as series of tubes + organogensis
- cranial end of developing embryo advances before caudal end
- begx of facial devel –> formation of mouth
describe the formation of the mouth [4 aspects]
1. stomatodeum
- primitive mouth
- formed by invagination of ectoderm tx [noticeable by EO3rdwk]
2. frontal process
- above stomatodeum –> large bulge of ectoderm + mesoderm
- becomes upper part of face, nasal septum and ant. palate
3. rathke’s process
- roof of stomatodeum –> invagination of stomodeal ectoderm
- moved –> base of brain = becomes ant pit gland
**4. oropharyngeal membrane **
- separates stomatodeum from foregut
- combo of ectoderm + endoderm
- membrane dissolves in 4th wk
briefly describe the formation of the pharyngeal arches
- pouches of endoderm extend into surface ectoderm –> divs mesoderm into arches + clefts
- creates FIVE pharyngeal arches [involved in devel of orofacial structures]
- each arch contains arterym cartilage, cranial nerve, mesodermal tx
describe the events of early facial development
1. maxillary process
- buds of pharyngeal arch 1 extend up and medially = forms upper cheeks, sides of lips, maxilla and most of palate
**2. mandibular process **
- forms lower cheeks, lower jaw and part of tongue
**3. frontal process **
- AFTER max process formed –> pair of olfactory pits [depressions] appear on lower border of frontal process
- divs lower frontal process –> THREE sections
- TWO lateral nasal process [makes sides of nose]
- ONE median nasal process [centre of nose]
- tip of nose, primary palate and nasal septum
**4. median nasal process **
- at lower border –> process grows in length –> produces pair of bulges [globular process]
- grows downwards below olfactory pits = forms centre of lip and ant. palate
- median nasal processes shrink due to differential growth of structures around it
describe the primitive eyes + ears development
primitive eyes [optic placodes] first appear on side of head –> eventually relocate to front of head
primitive ear first appear at neck region –> eventually relocate to side of head
list and describe the THREE fusion processes
**1. upper lip **
- fusion of maxillary and globular processes at 8wks
2. angle of mouth
- fusion of max + mand processes
**3. mandibular arch **
- fusion of both mandibular processes
- site of fusion = mental symphysis
describe tongue development
- first indications of tongue devel = near end of 4th wk —> median triangular elevations [lingual swellings] appear rostral to foramen cecum
