embryogenesis and development flashcards

Fertilization

occurs in the fallopian tube: ampulla

• sperm comes in contact with the acrosomal apparatus

  • release of calcium ions (cortical reaction): depolarizes the membrane of the ovum

    • prevents fertilization by multiple sperm

    • and increases metabolic rate of zygote

Twins

1. dizygotic (fraternal)

   1. two eggs are released and fertilized by two sperm

2. monozygotic (identical)

   1. a single zygote splits in two

After fertilization

• zygote must travel to the uterus

  • undergoes rapid cleavage

  • an embryo is created; surface area to volume ratio is increased to ensure gas exchange and nutrient exchange

• determinism: indeterminate and determinate cleavage

Blastulation

morula: big mass of cells is formed

• blastula is surrounded by trophoblast cells

  • chorion —> placenta

• inner cell mass = organism

implantation

blastula goes to the uterus, where it burrows into the endometrium

• trophoblastic cells create chorion —> placenta

• trophoblastic cells create chorionic villi —> penetrate endometrium (support mother-child gas exchange)

• supported by the yolk sac: site of early blood development

The embryo is connected to the placenta by the

umbilical cord; two arteries and one vein

• arteries carry deoxygenated blood and waste to the placenta for exchange

allantois

involved in early fluid exchange between embryo and yolk sac

• with the yolk sac and allantois forms the umbilical cord

amnion

a thin, tough membrane filled with amniotic fluid

• shock absorber to protect the embryo

• chorion forms outer layer around amnion

Gastrulation

the generation of three distinct layers

• blastula —> gastrula

archenteron

develops into the gut

blastopore

opening of the Archenteron

• protosomes: blastopore develops into the mouth

• deuterostomes (humans): blastopore develops into the anus

Primary germ layers

some cells will eventually migrate into what is left of the blastocoel

• ectoderm “attracto”derm: epidermis, hair, nails, etc, nervouse system

  • adrenal medulla

• mesoderm “means of”: musculoskeletal, circulatory, excretory

  • gonads, musclar/connective tissue

  • adrenal cortex

• endoderm linings of “endernal” organs: epithelial linings of many organs

neurulation

development of the nervous system; ectoderm cells go inside the body

• notochord (mesodermal cells) forms

• slides inwards to form neural folds, which fuse into a neural tube —> central nervous system

  • at the tip of each fold = neural crest cells —> form the periphery nervous system

• then, the ectodermal cells will migrate over to the tube and cover it

teratogens

substances that interfere with development

Mechanisms of development: cell specialization

three stages: specification, determination, differentiation

Specification/Determination

specification: reversibly designated

determination: commitment, irreversible

• presence of specific mRNA and protein molecules from cleavage

• secretion of molecules from nearby cells (morphogens)

Differentiation

• changes the structure, function, and biochemistry of cell

stem cells (totipotent) —> pluripotent (anything but placental structures) —> multipotent (multiple types of cells within a certain group)

• embryonic cells art pluripotent

cell-cell communication

competent (able to respond) or responder

paracrine vs juxtacrine vs endocrine

paracrine: local

juxtacrine: directly simulating receptors of an adjacent cell

endocrine: bloodstream

Inducers are…

growth factors

• can cause reciprocal development

Fetal circulation is controlled by

diffusion; a pressure gradient

• partial pressure of oxygen higher in maternal than fetal

  • fetal cells contain: fetal hemoglobin, which has greater affinity for oxygen than maternal

umbilical arteries…

carry blood away from the fetus towards the placenta (deoxygenated)

umbilical veins…

carry oxygenated blood from the placenta to the fetus

The three shunts

• fetus lungs and liver are sensitive to the high blood pressure they will receive in post natal life —> shunts direct blood away from organs as they develop

Away from lungs:

1. foramen ovale: right atrium to left atrium

   1. entering blood through the inferior vena cava —> right —> left —> aorta —> directly through circulation

2. ductus arteriosus

   1. left over blood from the pulmonary artery to the aorta

Away from liver

1. ductus venosus

   1. blood returning from the placenta directly into the inferior vena cava

First trimester

major organs begin to develop

• brain is fairly developed, embryo becomes a fetus

  • 9 cm

second trimester

begins to move, 30 - 36 cm

third trimester

antibodies are transported (highest )

• growth rate slows

birth

parturition

• rhythmic contractions of uterine smooth muscle

• coordinated by prostaglandins and oxytocin