Pregnancy and human development Flashcards
Define embryo vs fetus
Embryo: fertilization –> week 8
Fetus: week 9 –> birth
Define parturition, gravidity and parity
Parturition: events involved in giving birth
Gravidity: number of times a woman is pregnant (does not need to be a viable pregnancy, twins = 1)
Parity: number of pregnancies exceeding 20w
When sex for fertilization to occur?
2 days before ovulation,
24 hours after ovulation
** but lots of exceptions
How do secretions of the female tract help accomplish fertilization?
Destabilize acrosome covering
Increase sperm motility
** sperm need to be treated with secretions in order to penetrate the egg!
What are the 5 events involved in the sperm penetrating the egg?
1) bad bois weave their way past the granulosa cells of the corona radiata
2) Spermies bind to ZP3 receptors, increasing calcium levels, triggering an acrosome reaction. Enzymes from many sperm digest holed through the ZP
3) Sperm membrane binds to sperm binding receptors
4) Sperm and oocyte membranes fuse and sperm contents enter oocyte
5) Increased calcium levels lead to a cortical reaction, hardening the ZP and clipping off sperm binding receptors
What are the 4 events of fertilization?
1) Once spermy penetrates, oocyte completes meiosis II, forming ovum and second polar body
2) Sperm and ovum nuclei swell, each forming pronuclei
3) Pronuclei approach each other and mitotic spindle forms between them
4) Chromosomes of pronuclei intermix and fertilization is accomplished.
What is an embryo with 2, 16 and 100+ cells called?
2: blastomere
16: morula
100+: blastocyst
What happens 2,3,4,7 days post fertilization?
2: formation of blastomere, still floating in fallopian tube
3: formation of morula, still in fallopian tube
4: formation of early blastocyst, hatches for the ZP and no longer has the ZP protecting it
7: Implanting blastocyst
What do trophoblast cells and the inner cell mass do?
Trophoblast cells: immunosuppressive (otherwise ma will destroy embryo), and participates in placenta formation
Inner cell mass: becomes embryonic disc
What is required for a trophoblast to adhere to the uterus? What happens once it’s attached?
Requires proper receptors and chemical signals, otherwise it’ll detach and travel towards the cervix and try again
Inflammatory-like response happens as the conceptus eats it way into the uterus and inflammatory cells invade the area
During implantation, what does the trophoblast turn into?
Trophoblast proliferates and forms 2 layers:
Syncytiotrophopblast: outer layer, invade and digest endometrium
Cytotrophoblast: inner layer of trophoblast cells
By what day is implantation complete?
Day 12
How do levels of human chorionic gonadotropin change during pregancy?
Secreted by trophoblast cells, later by chorion. Promotes corpus luteum to continue secretion of progesterone and estrogen, keeping it alive
Levels spike around month 2/3
What is gastrulation?
Occurs during week 3, going from 2 layers to 3 layers
Inner cell mass develops into embryonic disc
Embryonic disc turns into epiblast and hypoblast, which become the 3 primary germ layers and extraembryonic membranes
What are the 3 layers of the embryo during gastrulation?
Ectoderm
Mesoderm
Endoderm
What is the primitive streak
Appears during gastrulation, determines superior and inferior body axis
Describe how the 3 layers of the embryo form during gastrulation
First cells that migrate through the primitive streak form the endoderm
Cells that follow push laterally, forming the mesoderm
cells that remain on the embryo’s dorsal surface form the ectoderm
Go from epiblast and hypoblast to ectoderm, mesoderm and endoderm. All the layers come from epiblast cells
What does the ectoderm form?
Epidermis, hair, nails and glands of skin
Brain and spinal cord
Neural crest and derivatives
What does the endoderm form?
Epithelial lining and glands of digestive and respiratory tracts
What does the mesoderm form?
Everything that isn’t from endoderm and ectoderm
What are the 4 extraembryonic membranes?
- Amnion
- Yolk sac
- Allantois
- Chorion
What is the amnion? What are its 3 functions?
Epiblast cells form a transparent sac filled with amniotic fluid
Provides buoyant environment that protects embryo
Maintains a constant temperature
Allows freedom of movement and prevents parts from fusing
What is the yolk sac?
Source of earliest blood cells and blood vessels
Forms from hypoblast, disappears ~week 14
What is the allantois?
Structural base for umbilical cord
Helps with waste removal and becomes part of urinary bladder
What is the chorion?
Helps form placenta
Surrounds everything
Combination of mesoderm and trophoblast
What are the steps of placentation?
- Embryonic tissues from mesoderm cells line the trophoblast forming the chorion and chorionic villi
- Maternal tissues develop blood-filled lacunae in decidua basalis
- Chorionic villi grow into the lacunae and pick up O2 from maternal blood
- Placental barriers (membranes of chorionic villi + endothelium of embryonic capillaries) on the fetal side ensure maternal and fetal blood supplies don’t mix
Placenta=chorionic villi+decidua basalis
What does the placenta secrete?
- human placental lactogen (breast maturation, fetal growth promotion, maternal glucose sparing)
- Human chorionic thyrotropin (increases maternal metabolsim)
- Relaxin (relaxes pelvic ligaments and pubic symphysis)
Why is gastrulation important?
Sets the stage for organogenesis (formation of body organs and systems)
What developments have happened by the end of 8 weeks?
First brain waves
Cardiovascular system is fully functional
Ossification has begun
What developments have happened to fetus by 9-12 weeks?
Lungs begin to develop, fetus inhales and exhales amniotic fluid
What developments have happened to fetus by 17-20 weeks? What are we looking for at the 18-22 week anatomical scan?
Vernix caseosa covers the body (helps with thermoregulation) Fetal movements (quickening) 18-20 week scan: looking for any major deformations in systems
What is the critical period?
If a system is affected during this period, it will result in incompatibility with life or major deformations
CNS is susceptible throughout the entire pregnancy
Why do progesterone levels increase throughout pregnancy?
It’s a smooth muscle relaxant
Why are parathyroid hormone and vitamin D levels high throughout pregnancy?
Control calcium– they grow the skeletal system
What is Chadwick’s sign?
vagina and menses develop a purplish hue during pregnancy
What is melasma
Pigmentation of facial skin that can happen during pregnancy
What nervous system changes can happen during pregnancy?
Carpal tunnel syndrome
Eye dryness and vision changes
Sciatica
What changes in the GI tract happen during pregnancy?
Bleeding gums
Morning sickness due to increased hcg levels, estrogen and progesterone
What is the rate of weight gain during the first and second trimesters?
First: 2-4lbs gained
Second trimester onwards: 1lb/week
What does the fetus secrete in order to initiate labour?
Adrenocortical hormones (especially cortisol) secreted to stimulate the placenta to secrete more estrogen.
Estrogen causes:
1. production of more oxytocin receptors
2. promotes gap junction formation between uterine smooth muscle cells
3. antagonizes calming effects of progesterone, leading to contractions in the uterus
- also releases surfactant protein-A to cause softening of cervix
What does the hypothalamus release during initiation of labour?
Oxytocin released in response to emotional and physical stress
Causes placental to release prostaglandins, which synthesize more gap junctions in uterine smooth muscle
Oxytocin and prostaglandins are powerful uterine muscle stimulants
What happens during dilation (labour)?
Initial weak contractions, 15-30 minutes apart and 10-30 seconds long
At first, only the superior uterine muscle is active, but more of the uterus becomes involved as labour progresses
Cervix dilates to 10cm
Amnion ruptures, releasing amniotic fluid
Engagement occurs: head enters true pelvis
What happens during expulsion (labour)?
Contractions q2-3mins Urge to push increases Crowning: largest dimension of head distends the vulva Delivery of infant Umbilical cord is clamped and cut
What happens during the placental stage of labour?
Delivery of afterbirth (placenta and membranes) occurs 5-30 minutes after birth
All placenta fragments must be removed to prevent postpartum bleeding
What is the average weight, length and head circumference of a newborn?
Average newborn is 7.5lbs, 50cm long, and has a head circumference of 35cm
What is the neonatal period?
4-0week period immediately after birth
What is APGAR and what is a healthy score?
Activity, Pulse, Grimace, Appearance, Respiration
Assess at 1 and 5 minutes after birth
Score of 8-10 is healthy
How is a baby’s first breath stimulated?
Increased CO2 leads to central acidosis, which stimulates respiratory control centres to trigger first inspiration
Bebe has a high respiration rate in the first 2 weeks of life
How is lactation stimulated towards the end of pregnancy?
Plactental estrogens, progesterone, and human placenta lactogen stimulate the hypothalamus to release prolactin-releasing factors
What is colostrum
Released in first 2-3 days, rich in vitamin A, protein, minerals and IgA antibodies
What is the let-down reflex?
Ejects milk form both breasts
What are advantages of breastmilk? (6)
Nutrients are easily absorbed
Beneficial chemicals that protect from infections
Glycoproteins prevent H pylori from attaching to stomach mucosa and causing ulcers
Natural laxative, helps eliminate meconium, preventing jaundice
Encourages bacterial colonization of large intestine
Promotes skin to skin contact
What are maternal advantages of breastmilk? (5)
Reduced postpartum blood loss delay in resumption of ovulation reduced cancer risk reduced type II diabetes risk Cost savings
