Pregnancy and human development

Question 1

Define embryo vs fetus

Answer 1

Embryo: fertilization –> week 8
Fetus: week 9 –> birth

Question 2

Define parturition, gravidity and parity

Answer 2

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

Question 3

When sex for fertilization to occur?

Answer 3

2 days before ovulation,
24 hours after ovulation
** but lots of exceptions

Question 4

How do secretions of the female tract help accomplish fertilization?

Answer 4

Destabilize acrosome covering
Increase sperm motility
** sperm need to be treated with secretions in order to penetrate the egg!

Question 5

What are the 5 events involved in the sperm penetrating the egg?

Answer 5

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

Question 6

What are the 4 events of fertilization?

Answer 6

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.

Question 7

What is an embryo with 2, 16 and 100+ cells called?

Answer 7

2: blastomere
16: morula
100+: blastocyst

Question 8

What happens 2,3,4,7 days post fertilization?

Answer 8

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

Question 9

What do trophoblast cells and the inner cell mass do?

Answer 9

Trophoblast cells: immunosuppressive (otherwise ma will destroy embryo), and participates in placenta formation
Inner cell mass: becomes embryonic disc

Question 10

What is required for a trophoblast to adhere to the uterus? What happens once it’s attached?

Answer 10

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

Question 11

During implantation, what does the trophoblast turn into?

Answer 11

Trophoblast proliferates and forms 2 layers:
Syncytiotrophopblast: outer layer, invade and digest endometrium
Cytotrophoblast: inner layer of trophoblast cells

Question 12

By what day is implantation complete?

Answer 12

Day 12

Question 13

How do levels of human chorionic gonadotropin change during pregancy?

Answer 13

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

Question 14

What is gastrulation?

Answer 14

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

Question 15

What are the 3 layers of the embryo during gastrulation?

Answer 15

Ectoderm
Mesoderm
Endoderm

Question 16

What is the primitive streak

Answer 16

Appears during gastrulation, determines superior and inferior body axis

Question 17

Describe how the 3 layers of the embryo form during gastrulation

Answer 17

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

Question 18

What does the ectoderm form?

Answer 18

Epidermis, hair, nails and glands of skin
Brain and spinal cord
Neural crest and derivatives

Question 19

What does the endoderm form?

Answer 19

Epithelial lining and glands of digestive and respiratory tracts

Question 20

What does the mesoderm form?

Answer 20

Everything that isn’t from endoderm and ectoderm

Question 21

What are the 4 extraembryonic membranes?

Answer 21

1. Amnion
2. Yolk sac
3. Allantois
4. Chorion

Question 22

What is the amnion? What are its 3 functions?

Answer 22

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

Question 23

What is the yolk sac?

Answer 23

Source of earliest blood cells and blood vessels

Forms from hypoblast, disappears ~week 14

Question 24

What is the allantois?

Answer 24

Structural base for umbilical cord

Helps with waste removal and becomes part of urinary bladder

Question 25

What is the chorion?

Answer 25

Helps form placenta Surrounds everything Combination of mesoderm and trophoblast

Question 26

What are the steps of placentation?

Answer 26

1. Embryonic tissues from mesoderm cells line the trophoblast forming the chorion and chorionic villi 2. Maternal tissues develop blood-filled lacunae in decidua basalis 3. Chorionic villi grow into the lacunae and pick up O2 from maternal blood 4. 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

Question 27

What does the placenta secrete?

Answer 27

1. human placental lactogen (breast maturation, fetal growth promotion, maternal glucose sparing) 2. Human chorionic thyrotropin (increases maternal metabolsim) 3. Relaxin (relaxes pelvic ligaments and pubic symphysis)

Question 28

Why is gastrulation important?

Answer 28

Sets the stage for organogenesis (formation of body organs and systems)

Question 29

What developments have happened by the end of 8 weeks?

Answer 29

First brain waves Cardiovascular system is fully functional Ossification has begun

Question 30

What developments have happened to fetus by 9-12 weeks?

Answer 30

Lungs begin to develop, fetus inhales and exhales amniotic fluid

Question 31

What developments have happened to fetus by 17-20 weeks? What are we looking for at the 18-22 week anatomical scan?

Answer 31

``` Vernix caseosa covers the body (helps with thermoregulation) Fetal movements (quickening) 18-20 week scan: looking for any major deformations in systems ```

Question 32

What is the critical period?

Answer 32

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

Question 33

Why do progesterone levels increase throughout pregnancy?

Answer 33

It's a smooth muscle relaxant

Question 34

Why are parathyroid hormone and vitamin D levels high throughout pregnancy?

Answer 34

Control calcium-- they grow the skeletal system

Question 35

What is Chadwick's sign?

Answer 35

vagina and menses develop a purplish hue during pregnancy

Question 36

What is melasma

Answer 36

Pigmentation of facial skin that can happen during pregnancy

Question 37

What nervous system changes can happen during pregnancy?

Answer 37

Carpal tunnel syndrome Eye dryness and vision changes Sciatica

Question 38

What changes in the GI tract happen during pregnancy?

Answer 38

Bleeding gums | Morning sickness due to increased hcg levels, estrogen and progesterone

Question 39

What is the rate of weight gain during the first and second trimesters?

Answer 39

First: 2-4lbs gained | Second trimester onwards: 1lb/week

Question 40

What does the fetus secrete in order to initiate labour?

Answer 40

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

Question 41

What does the hypothalamus release during initiation of labour?

Answer 41

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

Question 42

What happens during dilation (labour)?

Answer 42

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

Question 43

What happens during expulsion (labour)?

Answer 43

``` Contractions q2-3mins Urge to push increases Crowning: largest dimension of head distends the vulva Delivery of infant Umbilical cord is clamped and cut ```

Question 44

What happens during the placental stage of labour?

Answer 44

Delivery of afterbirth (placenta and membranes) occurs 5-30 minutes after birth All placenta fragments must be removed to prevent postpartum bleeding

Question 45

What is the average weight, length and head circumference of a newborn?

Answer 45

Average newborn is 7.5lbs, 50cm long, and has a head circumference of 35cm

Question 46

What is the neonatal period?

Answer 46

4-0week period immediately after birth

Question 47

What is APGAR and what is a healthy score?

Answer 47

Activity, Pulse, Grimace, Appearance, Respiration Assess at 1 and 5 minutes after birth Score of 8-10 is healthy

Question 48

How is a baby's first breath stimulated?

Answer 48

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

Question 49

How is lactation stimulated towards the end of pregnancy?

Answer 49

Plactental estrogens, progesterone, and human placenta lactogen stimulate the hypothalamus to release prolactin-releasing factors

Question 50

What is colostrum

Answer 50

Released in first 2-3 days, rich in vitamin A, protein, minerals and IgA antibodies

Question 51

What is the let-down reflex?

Answer 51

Ejects milk form both breasts

Question 52

What are advantages of breastmilk? (6)

Answer 52

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

Question 53

What are maternal advantages of breastmilk? (5)

Answer 53

``` Reduced postpartum blood loss delay in resumption of ovulation reduced cancer risk reduced type II diabetes risk Cost savings ```