Developmental biology Flashcards
over the course of 9 months, a human zygote undergoes ___, ____ and _____ in preparation for life outside the uterus
cell division, cellular differentiation and morphogenesis
2 early developmental stages
fertilization and cleavage
when does fertilization occur in mammals?
12-24 hours after ovulation
where does fertilization occur?
in the lateral, widest portion of the oviduct where sperm travelling from the vagina encounter an egg
what may result from the fertilization of more than one egg?
fraternal (dizygotic) twins may be conceived
What occurs when one zygote divides into two separate embryos?
identical (monozygotic) twins
early embryonic development is characterized by a series of rapid mitotic divisions known as ____
cleavage
during cleavage, what happens to the total volume of the cytoplasm?
it remains constant
cleavage results in progressively smaller cells with an increasing ratio of ___ to ___
nuclei to cytoplasm
When do the first, second, and third complete cleavage of zygote occur?
1st: approx 32 hours after fertilization
2nd: approx 60 hours “”
3rd: approx 72 hours “”
how many cells are present following 3 complete cleavages of the zygote?
8
define morula
once embryo reaches the uterus, cell division continues and forms a SOLID BALL OF EMBRYONIC CELLS known as morula
What is blastulation?
process by which a morula develops a fluid-filled cavity called the BLASTOCOEL, which by the fourth day becomes a hollow sphere of cells called the BLASTULA
What is the name of the stage of the embryo which implants in the uterus?
blastula
What occurs in an ectopic pregnancy?
embryo implants outside the uterus (e.g., in the Fallopian tube)
Describe gastrulation
After week 2, the embryo is fully implanted in the uterus and cell migrations transform the single cell layer of the blastula into a THREE-LAYERED STRUCTURE called a GASTRULA
3 primary germ layers:
- ectoderm
- endoderm
- mesoderm
what structures does each primary germ layer give rise to?
- ectoderm: INTEGUMENTARY SYSTEM (including the EPIDERMIS, hair, nails, and epithelium of the nose, mouth, and anal canal), the LENS OF THE EYE, the RETINA, and the NERVOUS SYSTEM.
- endoderm: EPITHELIAL LININGS OF THE DIGESTIVE AND RESPIRATORY TRACTS (including the lungs) and parts of the LIVER, PANCREAS, THYROID, and BLADDER LINING
- mesoderm: MUSCULOSKELETAL SYSTEM, CIRCULATORY SYSTEM, EXCRETORY SYSTEM, GONADS, CONNECTIVE TISSUE THROUGHOUT THE BODY, and portions of the DIGESTIVE and RESPIRATORY ORGANS.
define neurulation
neurulation occurs after gastrulation and is the process by which regions of the germ layers begin to DEVELOP INTO A RUDIMENTARY NERVOUS SYSTEM
When does neurulation occur?
before week 3
The rod of ______ cells is called the notochord
mesodermal
what kind of effect does the notochord have on the overlying ectoderm? What occurs?
the notochord has an INDUCTIVE EFFECT on the overlying ectoderm, causing it to BEND INWARD and form a GROOVE along the dorsal surface of the embryo.
The dorsal ectoderm FOLDS on either side of the tube, forming the NEURAL TUBE
the neural tube gives rise to:
the brain and spinal cord (CNS)
the cells at the tip of each neural fold are called the ___ ___ ___
neural crest cells
neural crest cells give rise to:
many components of the PNS, including the sensory ganglia autonomic ganglia, adrenal medulla, and Shwann cells
what causes spina bifida?
When the neural tube does not close properly during its development
3 components of development (following neurulation)
- organogenesis
- growth
- gametogenesis
What occurs in organogenesis?
the body organs begin to form.
Cells interact, differentiate, change physical shape, proliferate, and migrate.
What happens during the developmental process of growth?
organs increase in size.
Continual process from infancy through childhood to adulthood.
What happens in gametogenesis?
eggs develop in women and sperm develop in men, which allows for reproduction.
Two components of specialized circulatory system which supplies fetus with oxygen
placenta and umbilical cord
4 extra-embryonic membranes formed during development:
- amnion
- chorion
- allantois
- yolk sac
define amnion
the amnion is a thin, tough membrane containing a watery fluid called amnionic fluid.
role of amniotic fluid
SHOCK ABSORBER of external pressure during gestation and localized pressure from uterine contractions during labour.
Placenta formation begins with the ____, a membrane that completely surrounds the amnion.
chorion
role of chorion
assists with the transfer of nutrients from the mother to the fetus
what does the allantois become?
The allantois develops as an outpocketing of the gut.
The blood vessels of the allantoic wall enlarge and become the UMBILICAL VESSELS, which will connect the fetus to the developing placenta.
the yolk sac is the site of early development of ___ ____ and becomes associated with the umbilical ___
the yolk sac is the site of early development of BLOOD VESSELS and becomes associated with the umbilical VESSELS
3 stages of labor
- First: cervix thins and dilates, amnionic sac ruptures, mild contractions.
- Second: rapid contractions, birth of baby.
- Third: uterus contracts, expelling the placenta and the umbilical cord.
chemicals and biological agents that cause congenital disorders are called ____
teratogens
define “vertical transmission”
when a mother passes on an infection directly to her developing offspring.
Can occur either during development or during birth.
Plant embryo consists of 5 parts:
- epicotyl
- cotyledons
- hypocotyl
- endosperm
- seed coat
epicotyl is precursor of…
epicotyl is precursor of the UPPER STEM AND LEAVES
cotyledons
SEED LEAVES
dicots have __ seed leaves, while monocots have ___
dicots have TWO seed leaves, while monocots have ONE
hypocotyl
the lower stem and root
endosperm
feeds the embryo
what happens to endosperm in dicots?
cotyledon absorbs the endosperm
seed coat
develops from the outer covering of the ovule.
The embryo and its seed coat together comprise the seed.
embryonic cells in higher plants are called ____ ____
meristem cells
where is apical meristem found?
in the tips of the roots and stems
growth in length of plants occurs only at:
tips of roots and stems
location of lateral meristem
lateral meristem (or cambium) is located between the xylem and phloem.
What tissue in plants allows for growth in diameter and can differentiate into new xylem and phloem cells?
lateral meristem (cambium)
Membrane which stores and transports wastes from the fetus to the placenta in mammals?
allantois
The _____ ____functions to provide nutrients to a developing placental fetus, only until the placenta is ready to take over that role
The YOLK SAC functions to provide nutrients to a developing placental fetus, only until the placenta is ready to take over that role
