29 Flashcards
(21 cards)
embryology definition
study of developmental events during the prenatal period
prenatal period (span and phases)
- spans from conception to delivery
- is divided into three periods:
- pre-embryonic development
- embryonic development
- fetal development
pre-embryonic development (overview)
- consits of fertilization, cleavage, implantation (weeks 1 & 2)
- conceptus is called the pre-embryo
embryonic development (overview)
- week 3-8 after fertilization
- organogenesis
- conceptus is called an embryo
fetal development (overview)
- week 9 - delivery
- maturation of the organ systems
- cenceptus is called a fetus
fertlilization
sperm fuses w an egg:
- capacitation happens - modification of acrosome - can take 24 hours
- sperm penetrates the egg
- formation of male and female pronuclei inside cell then
- formation of the zygote (fertilized egg - final product of fusion)
cleavage
period of cell division of the zygote:
- blastomere cells produced - dividing into more and more cells
- then morula made (72 hours)
- then blastocyst formed (5 days)
- blastocyst contains: the blastoceole (fluid filled cavity), inner mass cells (future baby) and the trophoblast cells (future placenta) whole thing = blastula`
implantation
- begins 6 days after fertilization
- trophoblast adheres and embeds into endometrium
- froms the cellular trophoblast (portion of cells connected) and the syncytial trophoblast (portion of endometrium connected)
- day 8: embryoblast (inner mass of cells) divides into a 2 layer bilaminar disk: hypoblast (outer) and epiblast (inner)
- day 9: amniotic cavity begins to form
- implantations complete at 14 days
identical twins can split at?
- 2 cell stage
- early balstocyst stage
- bilaminar disc stage
fromation of the trilaminar disc
- happens in embryonic development stage by gastrulation
- trilaminar disc is the initial development of the embryo into three germinal layers: ectoderm, mesoderm and endoderm
primitive streak
- narrow midline groove on surface of epiblast
- cells of epiblast invaginate the streak and get beneath the epiblast
- this movement of cells creates the three layers
germ layers
- inner layer becomes endoderm
- outer layer (epiblast) becomes the ectoderm
- new middle layer becomes the mesoderm
notochord
-axis around which the vertebral column forms
3-8 weeks
- main organ systems begin their development from the three germ layers
- major malformations can occur if the mebryo is exposed to teratogens
derivatives of the ectodermal layer
forms structures that maintain contact with the external environment:
- nervous system, epithelium of ear, nose and eye
- epidermis of skin and epidermal derivatives (hair, nails, sweat glands, mamary glands)
- enamel of teeth
- pituitary gland
- lens of eye
- adrenal medulla
derivatives of mesodermal germ layer
forms supporting tissues:
- ct including bone and cartillage
- muscle (sm and striated)
- subcutanious tissue of skin
- blood and blood vessels
- kidneys and ureters
- gonads and their ducts
- spleen
- adrenal cortex
- heart
- *medial mesoderm segments into somites which give rise to parts of the skull, vertebral column, skeletal muscles and dermis of skin**
derivatives of the endodermal germ layer
- forms all epithelial lining of GI tract, repiratory tract, urinary bladder and middle ear
- forms functional tissue of liver, pancreas, thyroid, parathyroid, thymus and tonsils
organogenesis
- occurs in emryonic development
- process by which the germ layers develop into organs
fetal developmental stage
- development and maturation of the organs and organ systems
- cell differentiation
- rapid cell growth
- growth of uterus
- crown to butt length = 30mm - 360 mm (2.7-4.1 kg)
total length at birth
-550 mm
teratogens
- alcohol
- nicotine
- drugs
- maternal infections
