DEVELOPMENT Flashcards
CHECK ON LEARNING
what day?
Nucleus from mother and nucleus from father fuse in the ovum creating a zygote
Occurs in the fallopian tube (ampulla)
Day 1: Pronuclei Fusion
week 1
what day?
Blastocyte formation Only 2 cells
Day 2: first cleavage
week 1
what day?
4-cell stage, surrounded in zona
pellucida
Day 3
week 1
what day?
8 cell stage, surrounded in zona
pellucida
Day 4
week 1
what day?
Morula developed from 64 blastomeres (6th cleavage) Compaction-smaller cells and differentiation
Still inside the fallopian tubes about to enter the uterus
Day 5: Morula
**3 days after fertilization
week 1
what day?
Cells form inner cell mass, blastocyst cavity, trophoblast, and zona pellucida, entering into the uterus, does not need nutrients from mother
because 1-layer cell thick
Day 6: Early Blastocyst
week 1
what day?
Zona Hatching, the
blastocyst hatches out of the zona pellucida to carry out implantation to posterior
endometriumuterine wall
*Days of 6-7 vary in time frame
Day 7: Late blastocyst
week 1
(within implantation
window)
what week is known as superficial implantation?
week I
what day?
Blastocyst attaches superficially to the endometrium of the uterine wall.
Trophoblastic layer will attach to the pinopodes on the uterine wall that stimulate change in the uterus as well as the trophoblast to be synotrophoblasts cells that will eat away at the uterine wall to receive blood supply.
Inner cell mass show polarity and face towards the wall in implantation.
Human choronic gonadotrophin is released and maintains corpus luteum.
Embryonic disc formation: hypoblast and epiblast (first sign of differentiation), amniotic cavity forms, amnion forms, primitive yolk sac.
Cell continually eats its way into the wall
Day 8 and Day 9: Early Implantation (time can vary)
week 2
what is significant about week 2?
completion of implantation
what day?
Closure has a closing plug (epithelia cells have fibrin clot) over site of entry into decidua
Embryonic disc developed
Blood supply of blastocyst is “bathed in maternal blood”
Day 10: Completion of implantation
development of embryonic disc
establishment of
nutrient support
week 2
what day?
Primitive yolk sac forms stalk to attach embryo to wall of developing system by migrating to the bottom of the cell wall, acting as a anchor.
Closing off to start formation of
secondary yolk sac
Day 13: Completion of embryonic Disc
week 2
what day?
Secondary yolk sac formed, Completed embryo and completely implanted
Extraembryonic coelom expands to form the chorion cavity
Extraembryonic coelom: splits into two layers splanchnic and somatic cells that push together/pinching off.
And form the secondary yolk sac.
*primary villus developing!
Trophoblast + chorion =placenta Chorion= cytotrophoblast + mesoderm
Primary chorion villi emerge from the chorion and invade endometrium and allow transfer of nutrients from maternal to embryo blood— connecting stalk
Day 14: Completion of embryonic Disc
week 2
what are the six critical events to week 3 development?
Development of trilaminar embryonic disc (gastrulation) with the formation of the primitive
streak
Development of the Notochordal Process and Notochord and development of Neural tube:
Neurulation
Development of primitive cardiovascular system
chronic villi to transfer nutrients from maternal
blood to remove and anchor embryo
beginning of segmented somite formation
what is significant about week 4-8?
embryogenesis
what week is this?
Neural tube closes
1.Embryo elongates and Curvature of embryo
- Somite formation
- Formation of brachial arches
- Head and tail folds
- Appearance of limb buds
- Lens placode and otic pit
- Closure of neurpores
- Internal organs
- Midgut is open to yolk sac
Week 4: Days 22-
28
what week is this?
- Growth of head
- Lens pit and vesicle (thickening/cascade of induction events sealed up by overlying ectoderm)
- Nasal pits
- Hand plate also in lower limbs (paddle shaped)
- Heart prominence-heart folding into 4 chamber vessels
- Tail
- Somites prominent
- *beginning of facial structure (arch 1—maxillary prominence and mandibular prominence)
Week 5: Days 29-
36
what week is this?
- Foot plate
- Pigmented eye (neural crest drive)
- Finger rays
- External ear (auricular hillox)
- Mandible pretty much formed
- Lung-no alveoli
- Kidney development
Week 6: days 37-
42
what week is this?
- Toe rays
- Elbow
- Disappearing somites—to form muscle and bone
- Disappearing tail
- Limbs length
- Starting to look like a real human
- Eyes are laterally moving medially
- Lungs, kidneys, nasal and facial structures forming
- Primary ossification begins
Week 7: days 43-
49
what week is this?
- Lengthening of limbs
- Fingers and toes separate
- Midgut in umbilicus— lengthens rapidly, will retract at 9 weeks
- Scalp vascular plexus— generate in head
- External ears prominent- identifiable
- Nail pads
- Eyelids form—seal off eye until roughly 20-28 weeks
- Head rounding and straightening
- Tail disappears
- **looks human
- Primary ossification begins
Week 8: days 50-
56
End of embryogenesis
what weeks describe the following?
characterized by growth, completion, and refinement of the organ systems laid down during embryonic period
week 9-38
fetal development
what are the major critical events that happen in weeks 9-38?
maturation of the lungs to the point that alveolar cells are producing surfactant to allow the lungs to remain patent for respiratory function.
At week 22 termed transition to viable fetus (minimal age fetus can survive outside of the uterus)
what weeks are this? significance
- Head growth slows
- Primary ossification centers expand (begins in 7-8th weeks)—clavicle forms first
- Eyelids grow eye and seal them (developing)
- Intestines retract from umbilicus into abdominal cavity
- External genitalia become distinguishable (can physically determine sex of baby)
6.Un-Concentrated (very dilute) Urine formed and excreted into amniotic fluid and is
absorbed and swallowed
Weeks 9-12
Pre-viable fetus Will not survive out of uterus
what weeks are this? significance
- Rapid growth in weight by 4x and length by 2x
- Bone ossification extensive
- External ear auricles well- developed and move to side of head
- Eyes are more anterior (remained shut)
- Finger and toes long and nail beds
- Skin thin with blood vessels
- Fine hair on scalp, eyebrows, and eyelids
8.There is movement of the fetus (thumb-sucking) BUT it
is not perceptible
Weeks 13-16
Pre-viable fetus
what weeks are this? significance
- Growth slows
- Sebaceous glands become active and vernix caseosa covers body (white waxy material)
- Body hair (lanugo)— temporarily hair
- Eyelids, eyebrows, fingernails well-developed
- Brown fat formed at base of neck, behind sternum, in perirenal area, and on posterior abdominal wall
- Fetal movement is detectable!!!
- F: uterus formed
- M: tests have begun descent to scrotum
- Child is in position in the uterus (head towards uterine opening)
Week 17-20
Pre-viable fetus
what weeks are this? significance
- Muscle growth
- Skin wrinkled and red-pinkish coloring
- Head hair, eyebrows, eyelashes clearly visiable
- Alveolar cells of lungs produce surfactant to provide lung patency
- Skin thickens (keratinized layers become apparent)
Weeks 21-25
Transition to viable fetus
what weeks are this? significance
- Growth slows (metabolically or physically)—fills amniotic space ad uterus
- Nervous system matured to support rhythmic breathing—gulping and swallowing of amniotic fluid
- eyes reopen
- bone marrow takes over erythropoiesis from spleen
5.subcutaneous fat beginning to
be formed
Week 26-29
RBCs made in yolk sacliverspleenmarrow
what weeks are this? significance
- body is plumber, skin light because of subcutaneous fat
- pupils of eyes respond to light
- usually assumes head-down position in uterus
- lanugo disappearing (body hair that was covering)
- fingernails and toenails long
- cranial nerve development is more functional
Week 30-34
Amnion membrane will bind to walls of placenta
what weeks are this? significance
- grasp reflex present
- lanugo hairs almost absent but vernix caseous present
- tests descend into scrotum (potentially not until after birth)
- period of significant fat deposition
5.chest and abdomen well
developed
Weeks 35-38
Pregnancy typically 40 weeks The unborn baby spends around 38 weeks in the uterus, but the average length of pregnancy, or gestation, is counted at 40 weeks. Pregnancy is counted from the first day of the woman’s last period, not the date of conception which generally occurs two weeks later.
