Chapter 28: Pregnancy Flashcards
Pregnancy
events that occur from fertilization until the infant is born
Conceptus
the developing offspring
Gestation period
time from the last menstrual period until birth (about 280 days)
embryo
conceptus from fertilization through week 8
fetus
conceptus from week 9 through birth
From egg to zygote
- > The oocyte is viable for 12 to 24 hours
- > sperm is viable 24 to 48 hours after ejaculation
- > for fertilization to occur, coitus must occur no more than
- 2 days before ovulation
- 24 hours after ovulation
fertilization
when the sperms chromosomes combine with those of a secondary oocyte (immature egg) to form a fertilized egg (zygote)
sperm transport
- > propelled by whiplike tail movements of their flagella
- > Forceful uterine contractions which disperse them throughout uterine cavity
- > Ejaculated sperm (40- 500 million):
- Leak out of the vagina immediately after deposition
- Are destroyed by the acidic vaginal environment
- Fail to make it through the cervical mucus
- Are dispersed in the uterine cavity or destroyed by phagocytes
- Few (100 to a few thousand) reach the uterine tubes
accomplishing fertilization
-> sperm need to pass 2 layers (corona radiata and zona pellucida) to reach oocyte
- > sperm must be capacitated before they can penetrate the oocyte
- secretions of the female tract weaken acrosome membrane
*capacitation: sperm membranes become fragile so hydrolytic enzymes can be released
acrosomal reaction
sperm binds to zona pellucida, releases enzymes that digest holes in this layer
sperm penetration
- > an acrosomal process forms and binds to receptors on oocyte’s plasma membrane
- > sperm and oocyte membranes fuse
- > nucleus is pulled into oocyte cytoplasm
- > only 1 sperm is allowed to penetrate the oocyte (monospermy)
Once sperm enter oocyte
- > waves of Ca+ are released into oocyte’s cytoplasm this activates:
1. oocyte to prepare for 2nd meiotic division
2. cortical reaction- Zonal inhibiting proteins (ZIPS) are released, this blocks other sperm from entering
embryonic development
Cleavage:
- rapid mitotic divisions of zygote without increase in size (dosen’t get bigger bc still in fallopian tube so it still needs to be able to travel)
- this increases surface area, increases # of cells
- easier for uptake in nutrients, O2, and removal of wastes
cleavage
zygote -> blastomeres (36 hours) 2 to 8 cells -> morula (72 hours) 16 or more cells -> blastocyste (4-5 days) fluid filled hollow sphere, this reaches the uterus
Twins
- Identical: one egg/ one sperm
- fraternal: 2 eggs/ 2 sperm
- conjoined: split occurs late
blastocyst
- Trophoblast cells- single layer of flat cells
- immunosuppressive
- participate in placenta formation
- Inner cell mass
- becomes the embryonic disc
ectopic pregnancy
fertilized egg implants itself in fallopian tubes. usually winds up being miscarriage
implantation
- blastocyst floats for 2-3 days
- nourished by uterine secretions
- implantation begins 6-7 days after ovulation
- trophoblast adheres to the endometrium
- secrete enzymes which irritate the endometrium
Which of the following stages is the true moment of fertilization?
Once the chromosomes of the male and female pronuclei are united
What happens if 2 sperm penetrate the egg?
The zygote would be non functional
Capacitation refers to changes occurring in ______.
sperm before fertilization
Hormonal changes during pregnancy
Human chorionic gonadotropin (hCG):
-secreted by trophoblast cells, later the chorion
- prompts corpus luteum to continue secretion of progesterone and estrogen
- hCG levels rise until the end of the second month, then decline as the placenta begins to secrete progesterone and estrogen
- hCG levels are used in pregnancy tests
placentation
Formation of the placenta from embryonic and maternal tissues
1. embryonic tissues: the chorion (develop from the inner cell mass)… comes from baby
- Maternal tissue: decidua basalis… comes from mother
**mother and baby’s blood supply do not mix
After successful implantation has occurred, the corpus luteum is maintained by the hormone ______ secreted by the trophoblast cells.
hCG (human chorionic gonadotropin)
Which of the following develops into the embryo?
Inner cell mass
Gastrula to fetus
gastrulation:
-during implantation, the blastocyst starts to convert to a gastrula
- inner cell mass develops into the embryonic disc (subdivides into epiblast and hypoblast)
- the 3 primary germ layers and the extraembryonic membranes develop (week 3)
extraembryonic membranes
- Amnion- forms amnionic sac
- yolk sac- forms part of digestive tube
- Allantois-unbilical cord
- chorion- helps form the placenta
- all formed within the first 2-3 weeks of development
gastrulation
embryonic disic (2 layer) becomes a 3-layered embryo (endoderm, mesoderm and ectoderm)
-appearance of primitive streak (dorsal groove)
- Notochord:
- mesoderm cells
- form axial support
ectoderm
nervous system and skin epidermis
endoderm
epithelial linings of the digestive, respiratory, and urogenital
mesoderm
forms all other tissues i.e: muscles
endoderm and ectoderm are considered epithelia
true
organogenesis
-formation of body organs and systems
- at 8th week
- all organ systems are recognizable
- end of the embryonic period
ectoderm
Neurulation:
-first major event of organogenesis
- gives rise to brain and spinal cord
- neural plate folds inward as a neural groove and fuse into neural tube
- neural crest cells-> cranial, spinal, and sympathetic ganglia, and adrenal medulla
Neural tube defects
Tx: folic acid
spina bifida
Which of the following structures form the placenta?
Chorion and decidua basalis
Embryonic ectoderm gives rise to the ________ in the adult organism.
skin and nervous tissue
Which of the following is the first major event in organogenesis?
Neurulation
what tissue does the heart come from
mesoderm
development of fetal circulation
- first blood cells arise in the yolk sac
- by the end of the third week
- embryo has a system of paired vessels
- can hear baby’s heart beat
- unique vascular modifications
- ** umbilical arteries (deoxygenated blood)
- **umbilical vein (oxygenated blood)
Relaxin (placenta)
- causes pelvic ligaments and the pubic symphysis to relax to ease birth passage
- increase in lordosis
- reproductive organs become engorged with blood
- pigmentation may increase
physiological changes: GI TRACT
Morning sickness due to elevated levels of estrogen and progesterone
physiological changes: URINARY SYSTEM
increased in Urine production due to increased metabolism and fetal wastes, Stress incontinence
physiological changes: RESPIRATORY SYSTEM
Tidal volume increases; Dyspnea (difficult breathing) may occur later in pregnancy.
physiological changes: CARDIOVASCULAR SYSTEM
Blood volume increases 25–40%; Blood pressure and pulse rise; Venous return from lower limbs may be impaired
Teratogens
- Harmful substances that can cross placental barriers and enter the fetal blood which may cause congenital abnormalities or even death:
- Alc- mental retardation
- nicotine- hinders O2 delivery
- medications-sedatives, antihypert
- thalidomide: sedative of 1960s to prevent morning sickness
parturition
- Parturition giving birth to the baby
- Labor events that expel the infant from the uterus
- Stages of labor:
1. dilation
2. expulsion
3. placental
Initiation of labor
During the last few weeks of pregnancy:
- Fetal secretion of cortisol stimulates the placenta to secrete more estrogen
- causes production of oxytocin receptors
- antagonizes calming effects of progesterone, leading to Braxton Hicks contractions (weak irregular contractions) in uterus- false labor
Initiation of labor
Surfactant protein A:
-from fetal lungs causes softening of the cervix
Fetal oxytocin:
-causes the placenta to produce prostaglandins
- > maternal emotional and physical stress
- activates the hypothalamus, causing oxytocin release, causing powerful uterine contractions
- positive feedback mechanism occurs
Stages of labor
- Dilation
- longest stage can last 6-12 hours or more - expulsion
- lasts about 30 min - Placental-afterbirth. occurs about 30 min later
stages of labor: dilation stage
- Initial weak contractions:
- 15-30 min apart, 10-30 seconds long
- become more vigorous and rapid
- cervix dilates fully to 10 cm
- amnion ruptures, releasing amniotic fluid- “water breaking”
- engagement occurs: head enters the true pelvis
Stages of labor: expulsion stage
- strong contractions every 2-3 min, about 1 min long
- urge to push increases (in absence of local anesthesia)
- crowning occurs when the largest dimension of the head distends vulva
- lasts about 30-50 min
- delivery of infant
stages of labor: placental stage
- strong contractions continue, causing detachment of the placenta
- delivery of the afterbirth (placenta and membranes) occurs about 30 min after birth
- all placenta fragments must be removed to prevent postpartum bleeding
placenta previa
- placenta formation adjacent to uterus
- presents a problem when uterus and cervix stretch may cause separation of placenta
Neonatal period
4-week period immediately after birth
-physical status is assessed 1-5 minutes after birth
- apgar score: 0-2 points each for
- heart rate
- respiration
- color
- muscle tone
- reflexes
First breath
increase in CO2-> central acidosis -> stimulates respiratory control centers to trigger the first inspiration
*Surfactant in alveolar fluid helps reduce surface tension
Respiratory rate: ~45 per minute for first two weeks, then declines
*Premies usually put on respirators, lungs still immature
Lactation
- production of milk by the mammary glands
- anterior pituitary releases prolactin
-oxytocin causes the letdown reflex-actual ejection of milk from mammary glands
- colostrum:
- yellowish secretion rich vitamin A, protein, minerals, and IgA antibodies
- released the first 2-3 days
what is the definition of cleavage
A period of fairly rapid mitotic divisions of the zygote without intervening growth
Which does not occur during gastrulation?
Zygote formation
