Embryogenesis and Development Flashcards
ampulla
widest part of the fallopian tube where fertilization usually occurs
acrosomal apparatus
once first sperm comes into direct contact with the secondary oocyte’s cell membrane it forms this tubelike structure which extends to and penetrates the cell membrane
cortical reaction
after penetration of the sperm through the cell membrane, a release of calcium ions occurs
these ions depolarize the membrane of the ovum
- prevents fertilization of the ovum by multiple sperm cells
increased Ca+ concentration increases the metabolic rate of the newly formed diploid zygote
fertilization membrane
depolarized and impenetrable membrane of the diploid zygote
dizygotic
fraternal twins
form from fertilization of two different eggs released during one ovulatory cycle by two different sperm
each will implant in uterine wall and each develops its own placenta, chorion, and amnion
placentas may fuse if zygotes implant close together
monozygotic
identical twins
form when a single zygote splits into two
because genetic material is identical, so too will be the genomes of the offspring
type of twinning occurs as a result of when separation occurred
conjoined twins
incomplete division of monozygotic twins, results in two offspring which are physically attached at some point
cleavage
process in which zygote undergoes rapid mitotic cell divisions in moving to uterus for implantation
first one officially creates embryo, nullifies one of zygote’s defining characteristics: unicellularity
several rounds of mitosis occur, but total size of embryo remains unchanged during first few divisions
divides into progressively smaller cells, increasing nuclear-to-cytoplasmic (N:C) ratio and surface area-to-volume ratio
cells achieve increased area for gas and nutrient exchange relative to overall volume
two types: indeterminate and determinate
indeterminate cleavage
results in cells that can still develop into complete organisms
i.e. why monozygotic twins have identical genomes
determinate cleavage
results in cells with fates that are already determine
cells are committed to differentiating into a certain type of cell
morula
solid ball of cells that results from the early stages of cleavage in an embryo
undergoes blastulation
blastula
hollow ball of cells with fluid-filled inner cavity
in mammals, consists of two cell groups: trophoblast and inner cell mass
moves through the fallopian tube to the uterus, where it burrows into the endometrium
blastocoel
fluid-filled inner cavity of blastula
blastulation
formation of the blastula from the morula
blastocyst
mammalian blastula
consists of two cell groups: trophoblast and inner cell mass
trophoblast cells
surround the blastocoel and give rise to the chorion and later the placenta
specialized to create an interface between the maternal blood supply and the developing embryo
form chorionic villi
inner cell mass
protrudes into the blastocoel and gives rise to the organism itself
chorion
formed from trophoblasts
extraembryonic membrane that develops into the placenta
also forms an outer membrane around amnion, adding an additional level of protection
chorionic villi
formed from trophoblasts
microscopic fingerlike projections that penetrate the endometrium
develop into the placenta, support maternal-fetal bas exchange
umbilical cord
connects embryo and placenta
consists of two arteries and one vein encased in a gelatinous substance
vein carries freshly oxygenated blood rich with nutrients from placenta to embryo
arteries carried deoxygenated blood and waste to placenta for exchange
yolk sac
supports embryo until placenta is functional
site of early blood cell development
allantois
extraembryonic membrane
involved in early fluid exchange between the embryo and yolk sac
umbilical cord formed from remnants of this and yolk sac
amnion
extraembryonic membrane
surrounds allantois
thin, tough membrane filled with amniotic fluid, which serves as shock absorber during pregnancy, lessening impact of maternal motion on developing embryo
gastrulation
generation of three distinct cell layers
gastrula
small invagination in the blastula
cells continue moving toward the invagination, resulting in elimination of the blastocoel
membranes merge, resulting in a tube through the middle
archenteron
membrane invagination of the blastocoel
later develops into the gut
blastopore
opening of the archenteron in deuterostomes (i.e. humans), develops into the anus in protostomes, develops into the mouth
primary germ layers
some cells migrate into what remains of blastocoel
ectoderm, mesoderm, endoderm
ectoderm
outermost primary germ layer
gives rise to integument, including epidermis, hair, nails, and epithelia of nose, mouth, and lower anal canal
lens of eye, nervous system (including adrenal medulla), and inner eye also derived from this
mesoderm
middle primary germ layer
develops into several different systems including the musculoskeletal, circulatory, and most of the excretory systems
also gives rise to the gonads, as well as the muscular and connective tissue layers of the digestive and respiratory systems and the adrenal cortex
endoderm
innermost primary germ layer
forms epithelial linings of the digestive and respiratory tracts, including the lungs
pancreas, thyroid, bladder, and distal urinary tracts, as well as parts of the liver, derived from this
selective transcription
how cells with the same genes are able to develop into such distinctly different cell types with highly specialized functions
only the genes needed for a particular cell are transcribed
related to induction
induction
related to selective transcription
ability of one group of cells to influence the fate of other nearby cells
mediated by chemical substances (inducers)
ensures proximity of different cell types that work together within an organ
inducers
mediate induction
diffuse from the organizing cells to the responsive cells
responsible for processes such as the guidance of neuronal axons
neurulation
development of the nervous system
begins once the three germ layers are formed
notochord
rod of mesodermal cells
forms along the long axis of the organism like a primitive spine
induces a group of overlying ectodermal cells to slide inward to form neural folds, which surround a neural groove
neural folds
grow toward one another until they fuse into a neural tube
neural tube
forms from fusion of neural folds
gives rise to the central nervous system
neural crest cells
at the tip of each neural fold
migrate outward to form the peripheral nervous system (including the sensory ganglia, autonomic ganglia, adrenal medulla, and Schwann cells), as well as specific cell types in other tissues (such as calcitonin-producing cells of the thyroid, melanocytes in the skin, and others)
teratogens
substances that interfere with development, causing defects or even death of the developing embryo
each does not have the same effect on every embryo or fetus
genetics, route of exposure to, length of exposure to, rate of placental transmission of, and exact identity of all affect outcome
i.e. alcohol, prescription drugs, viruses, bacteria, and environmental chemicals (polycyclic aromatic hydrocarbons)
determination
commitment of a cell to having a particular function in the future
prior to this, the cell can become any cell type
after this, the cell is committed to a specific lineage
multiple pathways:
- asymmetric splitting of cell–presence of specific mRNA and protein molecules may result in this
- may occur due to secretion of specific molecules from nearby cells (morphogens)
morphogens
may cause nearby cells to follow a particular developmental pathway
differentiation
changes in structure, function, and biochemistry of the cell to match the cell type once determined
stem cells
cells that have not yet differentiated, or which give rise to other cells that will differentiate
exist in embryonic tissues as well as in adult tissues
potency
determines the tissues a particular stem cell can differentiate into
spectrum, not a series of strict definitions
totipotent
cells with the greatest potency, include embryonic stem cells
can ultimately differentiate into any cell type, either in the fetus or in the placental structures
pluripotent
can differentiate into any cell type except for those found in the placental structures
multipotent
can differentiate into multiple types of cells within a particular group
responder
cell that is induced
to be induced, must be competent, or able to respond to the inducing signal
autocrine signals
act on the same cell that secreted the signal in the first place
paracrine signals
act on cells in the local area
juxtacrine signals
do not usually involve diffusion, but rather feature a cell directly stimulating receptors of the adjacent cell
endocrine signals
involve secreted hormones that travel through the bloodstream to a distant target tissue
growth factors
peptides that promote differentiation and mitosis in certain tissues (inducers)
only function on specific cell types or in certain areas, as determined by the competence of these cells
reciprocal development
induction not always a one-way pathway
apoptotic blebs
self-contained pieces of a cell that are formed when cell undergoes apoptosis
can be digested by other cells, which allows for recycling of materials
contained by a membrane, which prevents the release of potentially harmful substances into extracellular environment
necrosis
process of cell death in which a cell dies as a result of injury
internal substances can be leaked, causing irritation of nearby tissues, or even an immune response
regenerative capacity
ability of an organism to regrow certain parts of the body
varies from species to species
complete regeneration
lost or damaged tissues are replaced with identical tissues
i.e. salamanders, newts
incomplete regeneration
implies that the newly formed tissue is not identical in structure or function to the tissue that has been injured or lost
(i.e. humans)
senescence
biological aging
occurs as changes in both molecular and cellular structure accumulate and can occur at the cellular or organismal level
telomeres
ends of chromosomes
when shortened, may lead to aging of cells
prevent loss of genetic info and help prevent DNA from unraveling
difficult to replicate
fetal hemoglobin (HbF)
exhibits a greater affinity for oxygen than does maternal (adult) hemoglobin (primarily HbA)
assists with the transfer (and retention) of oxygen into the fetal circulatory system
umbilical arteries
carry blood away from the fetus toward the placenta
carry deoxygenated blood
umbilical vein
carries blood toward the fetus from the placenta
carries oxygenated blood
shunts
developing child’s body constructs three of these to actively direct blood away from lungs (foramen oval, ductus arteriosus) and liver (ductus venosus) because underdeveloped and sensitive to high blood pressures
foramen ovale
one-way valve that connects right atrium to left atrium
allows blood entering right atrium from inferior vena cava to flowing left atrium instead of right ventricle, and thereby be pumped through the aorta into systemic circulation directly
ductus arteriosus
shunts leftover blood from pulmonary artery to the aorta
blood pushed into systemic circulation
ductus venosus
used to bypass liver
shunts blood returning from placenta via umbilical vein directly to inferior vena cava
fetus
by end of eight weeks
most of organs have formed, brain is fairly developed
contractions
coordinated by prostaglandins and peptide hormone oxytocin
afterbirth
placenta and umbilical cord expelled
3 phases of childbirth
- cervix thins out and amniotic sac ruptures (water breaking)
- strong uterine contractions result in birth of fetus
- placenta and umbilical cord expelled (afterbirth)
