Chapter 28 Human Development 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 from 12 to 24 hours (one day)
- sperm is viable 24-48 hours after ejaculation (two days)
- for fertilization to occur, coitus must occur no more than two days before ovulation OR 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 movement of their flagella
- forceful uterine contractions which disperse them throughout uterine cavity
- ejaculation 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 thousands) reach the uterine tubes
- total trip=5 inches
accomplishing fertilization
- sperm need to pass 2 layers (corona radiata and zone pellucida) to reach oocyte
- sperm must be capacitated before they can penetrate the oocyte
- secretion of the female tract weaken acrosome membrane
- capacitation- sperm membranes become fragile so hydrolytic enzymes can be released and break through the first layer of the oocyte
acrosomal reaction
- sperm binds to zona pellucida, releases enzymes that digest holes in this layer
- Ca+ levels within the sperm rise to trigger the reaction
sperm penetration
- an acrosomal process forms and binds to receptors on oocytes plasma membrane
- sperm and oocyte membranes fuse
- nucleus is pulled into oocyte cytoplasm
- only one sperm is allowed to penetrate the oocyte (monospermy)
once sperm enters oocyte…
- waves of Ca+ are released into oocytes cytoplasm this activates:
- oocyte to prepare for 2nd meiotic division
- cortical reaction- zonal inhibiting proteins (ZIPS) are released, this blocks other sperm from entering
sperm inside the oocyte
- after the sperm penetrate the secondary oocyte it completes meiosis 2 forming the ovum and second polar body
- sperm and ovum nuclei swell, forming pronuclei
- pronuclei approach each other and mitotic spindle forms between
- chromosomes of the pronuclei intermix
- fertilization is complete
cleavage
- rapid mitotic division of zygote without increase in size
- this increases surface area, increases # of cells
- easier for uptake in nutrients, O2, and removal of wastes
evolution of the zygote
- zygote
- blastomeres (36 hours) - 2-8 cells
- morula (72 hours)- 16 or more cells
- blastocyst (4-5 days)- fluid filled hollow sphere -> this reaches the uterus to implant
identical twins
-one egg and one sperm
fraternal twins
-two eggs and two sperms
cojoined twins
split occurs late
-two identical twins are not fully separated
blastocyst- two types
- trophoblast cells- single layer of flat cells that are immunosuppressive and participate in placenta formation
- inner cell mass- becomes the embryonic disc
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
- if implantation fails the blastocyst is aborted
- a minimum of 2/3 of zygotes fail to implant
which of the following stages is the true moment of fertilization
- when the sperm penetrates the oocyte membrane
- once the male pronucleus is present inside the oocyte
- once the chromosomes of the male and female pronuclei are united*
- when the zygote implants in the wall of the uterus
what happens if 2 sperm penetrate the egg
- the zygote would be non functional**
- you would have twins
capacitation refers to changes occurring in _____
- sperm before fertilization*
- sperm during fertilization
- oocytes before fertilization
- oocytes after fertilization
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
- placenta:
- embryonic tissues- the chorion (develop from the inner cell mass) (baby)
- maternal tissue -> decidua basalis (comes from mom)
- mother and baby’s blood supply lie close but do NOT intermix
chorionic villi
-grow into blood-filled lacunae (maternal)
placenta
-nutritive, respiratory, excretory, and endocrine organ for the fetus
after successful implantation has occurred, the corpus luteum is maintained by the hormone ____ secreted by the trophoblast cells
- FSH (follicle stimulating hormone)
- hCG (human chorionic gonadotropin)**
- decidua basalis
- relaxin
which of the following develops into the embryo
- placenta
- macula densa
- inner cell mass*
- zona pellucida
- trophoblast
embryonic development: 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- form amnionic sac
- yolk sac- forms part of digestive tube
- allantois- umbilical cord
- chorion- helps form the placenta
- all formed within first 2-3 weeks of development
gastrulation
-embryonic disc (2 layer) becomes a 3 layered embryo (endoderm, mesoderm, and ectoderm)
-appearance of primitive streak (dorsal groove)
-notochord: mesodermal cells and form axial support
-
ectoderm
- nervous system and skin, hair, nails epidermis
- endoderm and ectoderm are considered epithelia
endoderm
- epithelial linings of the digestive, respiratory, and urogenital systems
- endoderm and ectoderm are considered epithelia
mesoderm
- forms all other tissues
- ie: muscles
organogenesis
- formation of body organs and systems
- at 8th week:
- all organ systems are recognizable
- end of the embryonic period
specialization of ectoderm: neurulation
- 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
- Treatment- folic acid
- spina bifida
Which of the following structures form the placenta
- chorionic villi and lacunae
- decidua capsularis and decidua basalis
- trophoblast and decidua capsularis
- chorion and decidua basalis*- chorion (fetus), decidua basalis (mom)
embryonic ectoderm gives rise to the ______ in the adult organism
- skin
- nervous tissue
- epithelial lining of the gut
- both a and b*
- all of the above
which of the following is the first major event in organogenesis
- neurulation*
- cardiovascular formation
- urinary system development
development of fetal circulation
- first blood cells arise in the yolk sac
- by the end of the 3rd week embryo has a system of paired vessels and can hear babys heart beat
- unique vascular modifications
- **umbilical arteries (deoxygenated blood) and umbilical vein (oxygenated blood)
week 9 fetus
-time of rapid growth of body structures established in the embryo
effects of pregnancy: anatomical changes
- 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
expansion of uterus
- occupies most of the abdominal cavity
- before conception- size of fist and resides in pelvis
- 4 months- fundus is halfway between pubic symphysis and umbilicus
- 7 months- fundus is well above the umbilicus
- 9 months- fundus reaches the xiphoid process
physiological changes in pregnancy: GI tract
-morning sickness due to elevated levels of estrogen and progesterone
physiological changes in pregnancy: urinary system
- increased urine production due to increased metabolism and fetal wastes
- stress incontinence
physiological changes in pregnancy: respiratory system
- tidal volume increases
- dyspnea
- may occur later in pregnancy
physiological changes in pregnancy: CV 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
- alcohol- 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:
- dilation-
- expulsion
- 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
initiation of labor: fetal oxytocin
-causes the placenta to produce prostaglandins
initiation of labor: maternal emotional and physical stress
- activates the hypothalamus, causing oxytocin release, causing powerful uterine contractions
- positive feedback mechanism occurs
- oxytocin stimulates placenta to make prostaglandins which stimulates more vigorous contractions of uterus
stages of labor
- dilation- longest stage can last 6-12 hours or more
- expulsion- lasts about 30 mins
- placental- afterbirth- occurs about 30 mins later
stages of labor
- dilation- longest stage can last 6-12 hours or more
- expulsion- lasts about 30 mins
- placental- afterbirth- occurs about 30 mins later
stages of labor
- dilation- longest stage can last 6-12 hours or more
- expulsion- lasts about 30 mins
- placental- afterbirth- occurs about 30 mins later
dilation stage
- initial weak contractions
- 15-30 minutes apart
- 10-30 seconds long
- becomes more vigorous and rapid
- cervix dilates fully to 10 cm
- amnion ruptures, releasing amniotic fluid - water breaking
- engagement occurs- head enters the true pelvic
- babys head is sideways to pass through true pelvis
- in late dilation babys head rotates posteriorly once past the true pelvis
expulsion stage
- strong contractions every 2-3 minutes about 1 minute 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
placental stage
- strong contractions continue, causing detachment of the placenta
- delivery of the afterbirth (placenta and membranes) occurs about 30 mins 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
- four weeks period immediately after birth
- physical status is assessed 1-5 minutes after birth -> apgar score
apgar score
- heart rate
- respiration
- color
- muscle tone
- reflexes
- 0-2 points each
- 8-10 score is healthy
first breath
- increase CO2 -> central acidosis -> stimulates respiratory control centers to trigger the first inspiration
- surfactant in alveolar fluid helps reduce surface tension
- respiratory rate- about 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 in vitamin A, protein, minerals, and IgA antibodies -> released in the first 2-3 days
what is the definition of cleavage
- a period of fairly rapid mitotic divisions of the zygote without intervening growth*
- the attachment and burrowing of the blastocyst into the uterus
- formation of the placenta
- the transformation of the two-layered embryonic disc into a three layered embryo
which does not occur during gastrulation
- formation of the 3 germ layers
- appearance of the primitive streak
- the blastocyst converts to a gastrula
- zygote formation*
- all of the above
