chapter 29: development & inheritance Flashcards
sperm penetrates the corona radiata using what enzyme?
whereas acrosin is important to penetrating the zona pellucida.
hyaluronidase
upon sperm binding, calcium inside the oocyte triggers the cortical reaction, an
increase in the metabolic rate & the completion of what?
completion of meiosis II
what is amphimixis?
when chromosomes from ovum, mix with chromosomes of sperm
what is the initial cell created from fertilization that contains 46 chromosomes?
zygote
when the pre-embryo consists of a solid ball of identical blastomeres that have
not begun differentiation what’s it called?
morula
the outer layer of cells called the what will be important to first, digest the zona pellucida & then both thicken and trench into the endometrium to create lacunae that allow the blastocyst to diffuse nutrients from
the material blood?
trophoblast
as embryonic membranes begin forming, what extension of the yolk sac will serve as the structural basis for the umbilical cord by creating the body stalk where the fetal blood vessels will attach & contributes to formation of the urinary bladder?
allantois
the placenta is a disc-shaped highly vascularized organ that is composed of
chorionic villi & syncytial trophoblast from the embryonic tissues and what from the mother’s tissue?
decidua basalis
the placenta produces 8 hormones. Name the one that is important for maintaining the uterine lining.
progesterone
of the three primary germ layers, from which do the muscle & connective tissue develop?
mesoderm
why does the glomerular filtration rate increase during pregnancy?
to remove excess wastes from fetus
why does the vital capacity of respiration decrease during pregnancy?
abdominal organs push diaphragm into thoracic cavity, less space to fill lungs with air
in the final weeks during pregnancy estrogen levels increase which triggers oxytocin receptors to be expressed on the myometrium. Where does this estrogen come from?
the placenta
what are the chemicals or infectious agents that can cause congenital abnormalities?
teratogens
what twins are a result of two ovum
having been fertilized by two sperm and the children are only as genetically similar as any other siblings would be?
dizygotic (fraternal twins)
what initial secretion produced by the mammary glands is
rich in protein & IgA antibodies?
colostrum
what’s the hormone from the anterior pituitary that is
necessary to stimulate activity of the mammary glands?
prolactin
what’s the human growth/development stage that spans from
puberty to maturity and is largely driven by sex hormones?
adolescence
what is a functional unit of DNA, the instructions to create a necessary product?
gene
humans have 23 pairs of chromosomes: 1 pair is the sex chromosomes, the
other 22 pairs are what chromosomes?
autosomal
when both of the alleles for a single gene trait are homozygous the genotype & phenotype will be what?
match/ be the same
when there is incomplete dominance of alleles for a single gene trait, the phenotype of a heterozygote will be what?
intermediate, a blending
if one partner has cystic fibrosis, a recessive disorder, & the other partner is heterozygous for cystic fibrosis, what are the chances that the child they produce will have cystic fibrosis?
50%
what blood types are possible in the children for a couple where one is homozygous Type A and the other is heterozygous type B?
50% chance AB, 50% chance A
what is percent chance of hemophilia for the boy children produced by a couple
where the mother has hemophilia & the father does not?
100%
why can each person have the potential to make ~8.5 million different versions
of their gametes?
random cross over during synapsis in meiosis I provides the variability
when cross-over occurs between non-homologous chromosomes, what kind of defect has occurred?
translocation
fertilization
-23 chromosome haploid sperm + 23 chromosome haploid ovum = 46 chromosome diploid zygote
-sperm viable for 24-72 hours post ejaculation
-oocyte viable for 12-24 hours post ovulation
sperm transport & capacitation (fertilization step 1)
-millions of sperm released into vagina
-1% cross cervix (others killed by acid pH or trapped in cervical mucus)
-thousands more destroyed in uterus by phagocytes
-survivors propelled by flagella (5 inch/hr) & uterine contractions into uterine tubes, undergo capacitation while in transit
capacitation (sperm transport & capacitation -> fertilization)
removal of proteins and cholesterol from membrane over acrosomal cap to weaken it for release of enzymes at oocyte: process takes 6-8 hrs and requires uterine secretions
acrosomal reaction & sperm penetration (fertilization step 2)
-sperm meet oocyte in ampulla of uterine tube
a. sperm penetrate corona radiata around secondary oocyte with hyaluronidase (digests intercellular connections)
b. sperm bind to zona pellucida and undergo acrosomal reaction releasing acrosin & other proteases to digest thick glycoprotein of zona pellucida
c. one sperm will bind a sperm receptor on the secondary oocyte membrane, the sperm & oocyte membranes fuse, sperm nucleus enters the oocyte cytoplasm triggering oocyte activation
oocyte activation (fertilization step 3)
fusion of membranes triggers Na+ channels on oocyte open causing depolarization which triggers Ca++ release from the smooth endoplasmic reticulum
calcium causes (oocyte activation -> fertilization):
a. cortical reaction: oocyte releases enzymes to inactivate sperm receptors & cause hardening of zona pellucida to prevent polyspermy
b. completion of meiosis II: a second polar body is formed & the ovum now has 23 single chromosomes
c. increased metabolic rate: mRNA is activated & protein synthesis accelerates
nuclear fusion (fertilization step 4)
-sperm nucleus separates from tail and midpiece & migrates toward center of ovum
-ovum & sperm nuclei swell, becoming pronuclei
-pronuclei membranes rupture & chromosomes mix in a process called amphimixis creating the zygote with 46
chromosomes
-DNA replication & mitosis begin
cleavage & blastocyst formation (pre-embryonic development-> fertilization to implantation)
~day 1-6
-@36hr post-fertilization, first division is complete: zygote → pre-embryo
-pre-embryo consists of 2 identical blastomeres
-blastomeres continue division to create a cell cluster called a morula
-trophoblast cells digest zona pellucida & blastocyst receives nourishment from uterine secretions
from endometrial glands
cleavage (cleavage & blastocyst formation -> pre-embryonic development-> fertilization to implantation)
rapid mitotic divisions of zygote with little growth
@ day 4 morula differentiates into a blastocyst of 100+ cells (cleavage & blastocyst formation -> pre-embryonic development-> fertilization to implantation)
-outer layer of cells called the trophoblast (will become part of placenta)
-inner cluster of cells called the inner cell mass (will become the embryonic disc)
-central cavity called the blastocoele which is filled with fluid
implantation pt.1 (pre-embryonic development-> fertilization to implantation)
~day 6-14
-blastocyst contacts uterine lining on inner cell mass side
-trophoblast cells secrete digestive enzymes & growth factors triggering thickening of endometrial lining at point of contact
-blastocyst erodes a path into endometrium
trophoblast proliferates & forms two layers (implantation ->pre-embryonic development-> fertilization to implantation)
- inner cellular trophoblast: remains as wall of blastocyst
- outer syncytial trophoblast: multinuclear cytoplasmic mass in contact with endometrium
implantation pt.2 (pre-embryonic development-> fertilization to implantation)
-syncytial trophoblast digests endometrial cells & blood vessels creating channels called lacunae that fill with maternal blood bringing nutrients to blastocyst
-trophoblast cells produce hCG/ human chorionic gonadotropin to maintain the corpus luteum, progesterone from the corpus luteum prevents mensus
gastrulation (embryonic development)
-week 2-3
-inner cell mass divides into epiblast (superficial) & hypoblast (deep), forming a two-layer
embryonic disc
-three-layer embryonic disc further differentiates to form the embryo
-primitive streak formed
primitive streak
embryo is centered on a raised groove & the streak appears on dorsal surface of embryonic disc (“backbone”)
amnion (embryonic membrane -> gastrulation -> embryonic development)
-develops superior to epiblast
-forms a transparent membrane sac that fills with amniotic fluid to support & protect
fetus during development
yolk sac (embryonic membrane -> gastrulation -> embryonic development)
-develops inferior to hypoblast
-serves as site of early blood cell production
-later forms part of the gut
allantois (embryonic membrane -> gastrulation -> embryonic development)
-forms as out-pocketing at caudal end of yolk sac
-serves as structural basis for umbilical cord
-later develops into part of urinary bladder
chorion (embryonic membrane -> gastrulation -> embryonic development)
-forms from cellular trophoblast
-develops chorionic villi that are later vascularized to become fetal half of the placenta
two-layer embryonic disc differentiates into three primary germ layers (embryonic membrane -> gastrulation):
- ectoderm - faces the amnion (skin, nervous system)
- endoderm - faces the yolk sac (mouth to anus lining)
- mesoderm - layer of cells that migrates between endoderm & ectoderm (muscle, CT)
placentation (embryonic period) pt.1
-week 2-12
-chorionic villi enlarge & become vascularized
-arteries & veins connect to developing embryo at body stalk which forms from allantois
-as embryo enlarges, it bulges out of endometrium in amniotic sac
placentation (embryonic period) pt.2
-chorion surrounding bulge thins & covered by decidua capsularis (endometrium)
-chorion facing uterine wall retains large vascularized chorionic villi that extend into blood-filled lacunae in thickened endometrium (fetal half of placenta)
-blood filled endometrium called decidua basalis forms maternal half of placenta
placenta
disc-shaped tissue consisting of chorionic villi + syncytical trophoblast + decidua basalis, functions to connect fetal blood supply to large surface area for nutrient, gas, & waste exchange with maternal blood supply (complete at 12 weeks)
organogenesis (embryonic period) (week 3-8)
-notochord develops in mesoderm under primitive streak of embryonic disc & defines long axis on body
-as three germ layers differentiate, they fold
around toward yolk sac, creating a cylindrical shape with ectoderm on the outside & endoderm on the inside
-fetal vessels & yolk sac protrude through cylinder -> will form the umbilical cord
neutralization (embryonic period -> specialization of ectoderm -> organogenesis)
-ectoderm overlying notochord differentiates & folds inward forming neural tube
-neural tube pinches off into mesoderm: anterior end will form brain, remainder will form spinal cord
epidermis (embryonic period -> specialization of ectoderm -> organogenesis)
most ectoderm differentiate into epidermis & epidermal structures (hair, nails, skin glands, lining of mouth & anus, special sense organs)
specialization of endoderm (embryonic period-> organogenesis)
-differentiates to form epithelial linings of digestive & respiratory tracts
-forms all associated glandular tissues (thyroid, parathyroid, thymus, liver, pancreas)
-forms urethra & most of urinary bladder (some from allantois)
specialization of mesoderm (embryonic period -> organogenesis)
differentiates to form all tissues & structures between epidermis and mucosal linings: muscle, bone & bone marrow, blood, blood & lymphatic vessels, all connective tissue, serosa, reproductive organs, kidneys
what happens at the end of the embryonic period?
all body systems are present, ossification has begun &
cardiovascular system is fully functional *embryo (week 0-8) now called a fetus (week 8-birth).
fetal development
-week 9-38
-body structures & organ systems continue development to form all specific cell types & tissues of
human body
gestational trophoblastic neoplasia
trophoblast cells grow as a tumor, normal placenta & embryo do not form
placenta as an endocrine organ:
fetal tissue secretes hormones
-hCG, hPL, placental prolactin, relaxin, progesterone & estrogen
human chorionic gonadotropin (hCG) (placenta as an endocrine organ)
maintains corpus luteum ->
progesterone -> maintain uterine lining
human placental lactogen (hPL) (placenta as an endocrine organ)
placental prolactin: both prepare mammary glands for milk production
relaxin (placenta as an endocrine organ)
-↑ flexibility of pubic symphysis
-dilates cervix
-suppresses release of oxytocin to delay labor
progesterone (placenta as an endocrine organ)
prevents mensus
estrogen (placenta as an endocrine organ)
levels increase 3rd trimester, stimulates labor & delivery
first trimester (month 0-3) (summary of gestation)
-zygote formation -> embryogenesis
-rudiments of all organ systems & structures are formed
second trimester (month 4-6) (summary of gestation)
-rapid growth & development
-most organ systems complete development
amniochorionic membrane (second trimester -> summary of gestation)
amnion & chorion fuse (“amniotic sac”)
third trimester (month 7-9) (summary of gestation)
-period of weight gain
-adipose tissue forms
-organ systems become fully functional
physical changes (pregnancy & maternal systems)
-reproductive organs more vascularized
-uterus expands
-abdominal organs push diaphragm into
thoracic cavity
-shift in center of gravity -> lordosis
-mammary glands increase, produce milk
GI system (functional changes -> pregnancy & maternal systems)
-nausea
-heartburn
-constipation
urinary system (functional changes -> pregnancy & maternal systems)
-↑ GFR (by 50%)
- incontinence
respiratory system (functional changes -> pregnancy & maternal systems)
-↑ respiratory rate & tidal volume
-↓ residual volume
cardiovascular system (functional changes -> pregnancy & maternal systems)
-↑blood volume (25-40%)
-↑BP
-↑CO (20-40%)
metabolism (functional changes -> pregnancy & maternal systems)
-nutrient requirements increase 10-30%
-hunger
parturition
-280 days from last menstruation
-through pregnancy progesterone inhibits
smooth muscle
-weak, irregular contractions occur
(Braxton-Hicks contractions / false labor)
last few weeks, estrogen ↑, causing (parturition):
- oxytocin receptors in myometrium
- antagonistic effect on progesterone
near birth, fetal pituitary releases oxytocin (parturition) ->
triggers prostaglandin release by placenta, both cause powerful uterine contractions
contractions trigger maternal release of
oxytocin (positive feedback loop)(parturition) ->
labor
dilation stage (labor onset to cervix dilated) (stage 1 of labor)
-uterine contractions 10-30min intervals, last
10-30sec, force fetus toward vagina
-cervix softens, thins, dilates (10cm =full) -amniochorionic membrane ruptures
-contractions increase
expulsion stage (full dilation to delivery) (stage 2 of labor)
-contractions 1-3 min intervals, last up to 1min
-continues until fetus is delivered (20-50min)
placental stage (stage 3 of labor)
-30min post birth: contractions + compression
of uterine blood vessels causes placenta to detach from endometrium
-afterbirth (placenta + fetal membranes) exits
teratogens (complications to fetus)
cause congenital abnormalities
-most damaging first 8 weeks
spontaneous abortion (complications to fetus)
termination of pregnancy due to chromosomal defects
or inadequate hormone levels
premature labor (complications to fetus)
labor & delivery before
fetus fully developed
complications to fetus
-before week 28: survival poor, respiratory, cardiovascular & urinary systems not
complete
-survival rates increase
with birth weight
face up (difficult delivery)
slow, requires
assistance (vacuum, forceps)
dystocia (difficult delivery)
small pelvis, slows /stops birth, can cause brain damage: CP or epilepsy may require Cesarean section
breech (difficult delivery)
buttocks first, head trapped in cervix (same problems as above)
multiple births (natural)
-twins 1:89
-triplets 1:8000
-quadruplets 1:705,000
-most due to multiple oocytes ovulated
dizygotic twins (fraternal)
-72% of all twins
-two fertilized ovum: children as different as
any siblings
monozygotic twins (identical)
-division of single zygote
-8% divide immediately post-fertilization:
each has own chorion & amnion
-65-75% divide 4-8 days post fertilization:
share chorion but have own amnion, may or not share placenta
-1% divide after day 8: share amnion, chorion
& single placenta (risk one fetus dominates nutrients)
-after day 12 = conjoined twins
3rd trimester (lactation)
↑ estrogen + lactogen -> ↑ PRH -> ↑ prolactin = secretion by mammary glands
initial lactation -> colostrum
high protein, low fat,
IgA rich
1 week post delivery -> milk (lactation)
lipids, sugars, ions, vitamins, complement, lysozyme: 750C/L (infant consumes ~850ml/day,
640C)
after delivery prolactin ↓, milk production depends on mechanical stimulation (lactation):
suckling ->↑ PRH-> ↑ prolactin -> ↑ milk production for next feeding
suckling also triggers milk letdown reflex (lactation):
-> ↑ oxytocin -> contraction of
myoepithelial cells for milk ejection
neonatal period (first 4 weeks) (post-natal development)
- lungs take over gas exchange, high respiratory rate (45 breaths/min)
-ductus arteriosus & foramen ovale close,
high heart rate (120 beats/min)
-digestive system begins function, meconium cleared
-kidneys begin to filter waste & dilute urine:
inability to concentrate
-body temp fluctuates: hypothalamus learns thermoregulation
-metabolic rate 2X adult (per weight)
infancy (1 month - 2 years) (post-natal development)
-rapid growth & change in body proportions
-organs & features become more adult-like
childhood (2 years - adolescence) (post-natal development)
growth continues, driven by GH & thyroid hormones
adolescence (puberty - maturity) (post-natal development)
period of sexual & physical maturation
driven by sex hormones
senescence (maturity -death) (post-natal development)
aging: changes reduce functional abilities of
cells & systems ultimately affecting
homeostasis
gene (human genetics)
functional unit of DNA: encodes product (protein)
genotype (human genetics)
all genes in a cell or person
phenotype (human genetics)
anatomical or physiological
characteristics due to the genotype
human genetics
-all somatic cells contain same 46
chromosomes as original zygote
-differentiated cells only express certain genes & turn off others
patterns of inheritance
-somatic cells -> 23 pairs homologous
chromosomes (egg + sperm): 1 pair = sex chromosomes
-alleles & autosomal
XX & XY
female & male
autosomal
-22 pairs, somatic characters
alleles
genes on same locus (place) of homologous
chromosomes (version of the gene)
-alleles can code for the same or alternate
versions of same gene
homozygous (autosomal chromosome alleles)
same allele on both
chromosomes: genotype & phenotype
match
heterozygous (autosomal chromosome alleles)
two different alleles of the gene: phenotype depends on the
relationship between alleles: dominant, recessive, incomplete dominance & codominance
dominant (relationship between alleles)
one allele determines
phenotype regardless of other
-capital letter in Punnet squares
recessive (relationship between alleles)
requires homozygous
alleles to cause phenotype
-lowercase letter in Punnet squares
incomplete dominance (relationship between alleles)
intermediate phenotype
codominance (relationship between alleles)
expression of two or
more alleles over another
simple inheritance
-phenotype determined by interaction between
single set of alleles
-use Punnett square to calculate probability of
offspring (graph for mixing alleles)
cystic fibrosis (simple inheritance)
-recessive disorder
-mom = sick -> homozygous recessive (ff)
dad = appears normal (FF or Ff)
-If Dad homozygous
dominant, 0% chance sick kids, 100% are carriers
-If Dad heterozygote, 50% chance of sick kids, 50%carriers
blood types (simple inheritance)
-Mom = heterozygous type A (IAi)
-Dad = heterozygous type B (IBi)
-25% chance type AB (IAIB)
-25% chance type A (IAi)
-25% chance type B (IBi)
-25% chance type O (ii)
sex-linked inheritance
-phenotype determined by somatic genes located on sex chromosome: X-linked
-X-linked disorders more common in males since they have only one X
-female requires two copies of recessive gene to have disorder
color blindness (sex-linked inheritance)
-Mom = carrier of color blindness (XXc)
-Dad = normal (XY)
-50% chance of color
blind sons, all daughters normal
vision but 50% are carriers
polygenic inheritance
phenotype determined by interaction of several genes, hard to predict
suppression (polygenic inheritance)
one gene suppresses another so it doesn’t contribute to phenotype
complementary gene action (polygenic inheritance)
two dominant alleles from different genes interact to produce different phenotypes than either alone
genotype ≠ phenotype (nature vs nurture)
other genes &
environment alter outcome
penetrance (nature vs nurture)
% individuals in population with genotypes that show phenotype
expressivity (nature vs nurture)
extent of expression of any allele (often only one allele is expressed
or one is expressed more than the other)
genomic imprinting (nature vs nurture)
different phenotype
effects depending on if egg or sperm allele is expressed
meiosis (genetic recombination -> individual variation)
synapsis + cross-over swap genes on homologous chromosomes (random)
-each person can make ~8.5 million different
gametes
translocation defect (genetic recombination-> defects in gamete formation -> individual variation)
cross over between
different chromosomes, genes are lost
extra/missing chromosomes (genetic recombination-> defects in gamete formation -> individual variation)
unequal separation during meiosis1
trisomy (genetic recombinaton-> extra/missing chromosome -> defects in gamete formation -> individual variation)
one gamete has two copies of a chromosome, so zygote ends up with three
monosomy (genetic recombinaton-> extra/missing chromosome -> defects in gamete formation -> individual variation)
one gamete missing a
chromosome so zygote has only one copy
is it true that most chromosomal abnormalities are fatal?
yes
spontaneous mutation (mutation -> individual variation)
error rate of DNA
replication (1:109 bases)
nonfatal mutations create variability (mutation -> individual variation)
different alleles
dominant bad mutations (mutation -> individual variation)
50% of zygotes fail at
cleavage, 10% don’t reach month 5
recessive bad mutations (mutation -> individual variation)
silent until combined with another recessive
counseling (genetic screening & counseling)
risk analysis for parents who know genetic disorder is in their family: tests determine parent genotypes to predict offspring
amniocentesis (fetal testing -> genetic screening & counseling)
cells collected from
amniotic fluid, analyzed for genetic
disorders, only after week 14
chorionic villi sampling (fetal testing -> genetic screening & counseling)
cells collected
from chorion, as early as week 8
in vitro fertilization (fetal testing -> genetic screening & counseling)
-one cell extracted at the eight-cell stage
morula for genetic screening
-healthy seven-cell embryos can be chosen based on genetic profile and implanted, will develop normally
