Transcript Ch 29 Student_ Severely shortened Development lecture Fall 16

Chapter 29
Development and Inheritance
3/21/2017
29-1
Pregnancy and Development
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Fertilization - also called conception
Implantation – attachment of embryo to the wall of the uterus
Gestation - fertilization  birth; 38 weeks of pregnancy
Differentiation Creation of different types of cells
Development – changes in anatomical / physiological characteristics
• Prenatal Development - time before birth.
– Embryological Development first two months after fertilization
– Fetal Development Begins at start of ninth week till birth
• Postnatal Development- Commences at birth
• Inheritance- Transfer of genetic material from generation to generation
Neonatal period – first 42 days after birth
Labor - events that lead to birthing
Parturition - birthing process
Ectopic pregnancy - development of an embryo or fetus outside the
uterine cavity--- Occurs in 1 out of 300 pregnancies
Obstetrics: medicine that deals with pregnancy, labor and delivery
Alternative: Midwife/doula
Certified Professional Midwife (CPM),
Certified Midwife (CM)
Sperm Capacitation
• Fertilization cannot occur without capacitation.
• Capacitation involves destabilization of the sperm acrosomal
membrane allowing greater binding between sperm and oocyte.
1. As capacitation begins, the sperm acrosome membrane becomes
more permeability to Ca2+.
• Ca2+ stimulates flagellum to initiate deeper bends,
propelling the sperm more forcefully (harder and faster)
through the viscous environment.
• Sperm hyperactivity is necessary to penetrate ovum corona
radiata layer and zona pellucida; head and midpiece enter egg; egg
destroys the sperm mitochondria
2. The acrosomal membrane is toughened by cholesterolprevents premature release of acrosomal enzymes while sperm
still in male body which could damage sperm ducts.
• Female secretions in the vagina and uterus LEACH the
cholesterol and break down the membrane causing the releases
of enzymes to enable the sperm to fuse with oocyte.
Sperm Capacitation Actions
1st stage: penetration of
corona radiata by sperm;
releases enzyme
hyaluronidase from the
acrosome.
hyaluronidase breaks down
bonds between granulosa
cells surrounding the oocyte;
allows spermatozoon to reach
oocyte.
2nd Acrosomal reaction:
sperm initiates acrosome
reaction as they approach zona
pellucida;
acrosome membrane fuses
with the plasma membrane of
the oocyte.
The acrosome enzymes and
surface antigens enable sperm
to penetrate the egg's tough
coating and produce fertilization
The fusing is SPECIESSPECIFIC and prevents the
sperm and egg of different
species from binding together.
Egg
Sperm
Corona radiata
Sperm Migration
Spermatozoa reach uterine tube as little as 30 minutes up to several
hours after ejaculation, but cannot fertilize the egg for up to 10
hours until the sperm has undergone full capacitation.
– Sperm can remain viable for up to 6 days after ejaculation!!
• Chemicals substances (chemotaxis) released by egg attract
sperm from a short distance
• Of 200- 300 million ejaculated, 10,000 enter uterine tube ; fewer
than 100 reach the isthmus- the vicinity of the egg
• The vast majority of sperm NEVER arrive at the egg
1.destroyed by vaginal acid or drain out of vagina
2.fail to penetrate the mucus of the cervical canal
3.destroyed by leukocytes (ex: NK cells) in the uterus
4.get trapped in uterine/fallopian tube cilia
5.go up wrong uterine tube
• Dozens of sperm are needed - 1 sperm does not have sufficient
enzymes to penetration the oocyte layers
Prevention of Polyspermy
• Polyspermy – fertilization by two or more sperm
• OOCYTE has two mechanisms for prevention of polyspermy
1. FAST BLOCK – binding of the sperm to the egg opens Na+
channels in oocyte membrane
• Depolarizes OOCYTE membrane and inhibits the attachment
of any more sperm; sperm cannot fuse to a membrane that is
not -70mV. Positive charged molecules in sperm
membranes are REPELLED by the depolarized positive
charged state of the oocyte membrane preventing
additional binding by other sperm.
http://biology.kenyon.edu/courses/biol114/Chap13/fastblock.gif
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Fertilization
2. SLOW BLOCK –CORTICAL REACTION involves secretory
cortical granules, just below the membrane
• Sperm penetration releases an inflow of Ca2+ by oocyte
• Ca2+ stimulates cortical reaction where the cortical granules
release their secretion BENEATH the zona pellucida
• The secretions swell
with water, pushes
away remaining sperm
and creates an
impenetrable
(hardened) fertilization
membrane between the
egg and zona pellucida
Excellent Summary Animation
(5.42 mins)
http://www.youtube.com/watch?
v=_5OvgQW6FG4
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Cortical Reaction
“Slow Block”
Fertilization
Animation Ovulation
http://www.youtube.com/watch?v=wcVC3TFI7fQ
Secondary oocyte:
• Haploid cell (22X) that is released after meiosis II (ovulation) with zona
pellucida and corona radiata
• Moves into uterine tube using peristalsis and ciliated epithelial cells
• Remains active for a 12-24 hour windown after ovulation.
Fertilization must occur within this time to insure survival of ovum
• Takes approximately 72 hours for the egg to reach the UTERUS
Sperm:
• One sperm fuses with secondary
oocyte (syngamy) in oviduct,
• Syngamy triggers secondary
oocyte to complete meiosis II
• Male pronucleus (nuclear
material) and female pronucleus
FUSE (fertilization) producing
 Diploid zygote (44XX or 44XY)
• Need 100s of sperm to clear path for
the one that will penetrate the egg.
Biological Stages of Development
• Pre-embryonic
and Embryonic
stage
• first 16 days
development
culminating in
the existence
of an embryo
• cleavage
• implantation
• embryogenesis
• placentation
• Fetal stage
1
2
morula
“Hatching”
Pre-embryonic CLEAVAGE Divisions
1) Zygote divides by mitosis in the fallopian tube 30 hours after
fertilization = 2 identical BLASTOMERES are formed; then 4, etc.
2) Blastomeres form a pre-embryo = MORULA 72 hours (3 days)
arrives AT the uterus; lies free for 4-5 days- continues dividing
• Morula not much larger than zygote but very compact
3) Continued division produces BLASTOCYST. First sign of cell
differentiation
 Blastocyst reaches the uterus by day 5 or 6.
 Inner layer contains Inner cell mass or EMBRYOBLAST that
forms the embryo.
 Outer layer of cells collectively called the TROPHOBLASTS
 Surrounds the inner cell mass and a fluid-filled cavity known as the
blastocoel.
 The trophoblast provides nutrients and will form the future embyronic
membranes and gives rise to the placenta
© 2012 Pearson Education, Inc.
Blastocyst must rid
itself of the zona
pellucida before
implanting in uterus.
• The trophoblast
releases
hormones that
erodes the zona
pellucida
(hatching).
© 2012 Pearson Education, Inc.
IMPLANTATION–Embryo Attachment to Uterus
Implantation occurs approximately seven (7) days after fertilization
• Blastocyst adheres to uterine lining
• Trophoblast cells divide rapidly, creating multiple layers
• Cellular trophoblast – inner cells closest to interior of blastocyst
• Syncytial trophoblast outer layer erodes a path through uterine
epithelium secrete hyaluronidase - digest endometrial cells
which react by growing over the blastocyst embedding it in
endometrial tissue; covers the entire surface of the placenta.
• Invasion into the uterine wall, ruptures maternal capillaries
establishing an interface between maternal blood and
embryonic extracellular fluid, facilitating passive exchange of
material between the mother and the embryo.
• Secretes human chorionic gonadotropin (hCG)
• hCG maintains the uterine lining
• stimulates corpus luteum to release estrogen and
progesterone
• progesterone suppresses menstruation
• Reaches peak after 32 weeks
1. Development Animation:
http://www.youtube.com/watch?v=ARERGD0neMI (1.56 mins)
2. http://www.youtube.com/watch?v=J_knnENhzwg (3.02 mins)
Embryogenesis
Animation:
http://www.hhmi.org/biointeractive/
human-embryonic-development
• Formation of viable embryo
• Establishes foundations for all
major organ systems
• Arrangement of blastomeres
into 3 primary germ layers.
The layers are determined by
their physical position.
Day 14:
Cells of embryonic disc produce
3 distinct layers
• Endoderm  thyroid,
pancreas, liver, mucus
epithelium, bladder
• Mesoderm  muscle, bone,
connective tissues, dermis,
hypodermis, adrenals, kidneys,
lymph, cardiac. gonads
• Ectoderm  epidermis, ossicle
bones, entire nervous system,
mucus epitheilum, pituitary
Placenta, Embryonic Membranes Fetal Circulation
• Accessory organs that develop alongside embryo. Support
embryological and fetal development
• Embryonic membranes form around the embryo: Formed
from trophoblasts.
► amnion
► chorion
► allantios
► yolk sac
• Placenta
• Umbilical cord
• Fetal Circulation
http://www.mhhe.com/biosci/genbio/enger/student/olc/art_q
uizzes/genbiomedia/0565.jpg
Embryonic Membranes
AMNION - transparent sac filled with amniotic fluid that completely
enclose the embryo and is penetrated only by the umbilical cord
1. protects embryo from trauma, infections
2. allows freedom of movement
3. develop symmetrically- prevents body parts from adhering to
each other
3. stimulates lung development as the fetus ‘breathes’ fluid
4. fetus urinates into the amniotic cavity
ALLANTOIS forms the foundation for the UMBILICAL CORD and
becomes part of the urinary BLADDER
YOLK SAC first element seen in the gestational sac during pregnancy,
usually at 3 days gestation. Acts as developmental circulatory
system before fetal circulatory system is formed; important site of
blood cell formation
CHORION - outermost membrane - First step in creation of
functional placenta
• Blood source - Chorionic villi sprout from the chorion to give
maximum area of contact with the maternal blood.
PLACENTA
• Formed by chorion and portion of mother’s uteral endometrium
during 3rd month. The syncytiotrophoblast covers the surface of the
placenta.
• Maternal & fetal blood vessels do not join  blood does not mix
• Allows diffusion of O2, nutrients, wastes; BLOCKS most microbes
• IS NOT A BARRIER TO DRUGS, ALCOHOL, TOXINS IN
CIGARETTES
Animation:
https://www.youtu
• Secretes several hormones to support pregnancy
be.com/watch?v=
• Detaches from the uterus at birth time (afterbirth)
bped-RVWsLk
• Acts as respiratory and urinary system for fetus
http://www.ridgenet.net/~do_while/sage/images/v4i12g9.jpg
Umbilical cord
• Composed of
Wharton's jelly, a
gelatinous substance
• 2 ARTERIES that carry
deoxygenated blood
Vein
TO the placenta
AWAY from fetus
Arteries
• 1 UMBILICAL VEIN that
carries oxygenated
blood TO the fetus
• Not directly connected to the mother's circulatory system, but
joins the placenta, transfers materials to and from the mother's
blood without allowing direct mixing.
• Cut at the time of delivery
• Stub drops off in 2 weeks  leaving a scar (umbilicus)
Twins
Fraternal twins (dizygotic – from two zygotes)
• 2 oocytes fertilized by 2 sperms; form two zygotes two embryos
• genetically as different as any 2 siblings
• Each fetus lies within it's own two membranes (chorion and amnion)
and they do not share blood vessels Dichorionic/Diamniotic
Identical twins (monozygotic – from one zygote)
• 1 oocyte fertilized by 1 sperm; form one zygote  zygote divides into
2 blastomeres that separate to independently into 2 embryos
• genetically identical & always the same sex
• Monochorionic/Diamniotic: twins share placenta and chorionic sac but
have their own amniotic sac- Split between 3-8 days after fertilization
• Dichorionic/Diamniotic: each twin has his/her own placenta, chorion
and amniotic sac -Split Before 3-4 days after Fertilization
• Monoamniotic/Monochorionic: twins share placenta, chorionic and
amniotic sacs; separate umbilical cords. -Split between 8-13 days after
fertilization
• can cause complications in pregnancy. For example. the umbilical
cords of monoamniotic twins can become entangled.
Conjoined twins - Split occurs 13-15 days after fertilization
• If the blastomeres do not completely separate  newborns remain
attached to different extents  share some body structures
Monochorionic/Diamniotic
Monoamniotic/Monochorionic
Stages of
Prenatal
Development
Pregnancy is
divided into
3- month intervals
= trimesters
• first trimester – from fertilization through 12 weeks
• Most dangerous period in pre-natal life - vulnerable to stress,
drugs, nutritional deficiencies
• Only 40% of conceptions produce embryos that survive past first
trimester
• second trimester – weeks 13 through 24
• organs complete most of their development
• chance of survival if born near end of this trimester
• third trimester – week 25 to birth
• fetus grows rapidly and organs achieve enough cellular
differentiation to support life outside of the womb
• at 35 weeks and 5.5 lb fetus is 29-25
considered mature
Hormones of Pregnancy
• Estrogen- increases to 30x normal;
– enlarges uterus and external genitalia
– mammary ducts grow, breasts increase 2x normal size; inhibits
lactation and milk production
– relaxes pubic symphysis and widens pelvis
• Progesterone
– suppresses FSH and LH prevents follicular development during
pregnancy
– suppresses uterine contractions
– prevents menstruation, thickens endometrium
– stimulates growth of mammary alveoli and lobes; inhibits prolactin
• Human chorionic gonadotropin (hGC)
– detectable in urine 8 to 9 days after conception
– stimulates growth of corpus luteum; w/o hCG CL would atrophy
• CL secretes increasing amounts of progesterone and estrogen
• ALL primarily secreted by the placenta
– corpus luteum is important source for the first several weeks
– if corpus luteum removed before 7 weeks results in abortion
– from week 7 to 17, the corpus luteum degenerates and placenta
takes over its endocrine function
Adjustments to Pregnancy
• Morning sickness –hormonal changes- nausea forces mother to
avoid foods that are potentially toxic to fetal development
• Constipation and heartburn - intestinal motility
• Basal metabolic rate (BMR) increases 15% –stimulates
appetite-weight gain (average 20-25 lbs)
• Nutrition- increase in iron, protein, calcium, folic acid
• Urinary system –Increase retention of Na+ and water; GFR
increases 50% to remove fetal and mother’s waste
• Integumentary system
– fat deposition
– skin grows to accommodate expansion; stretching can tear
connective tissue and cause “stretch marks”
• Increases in respiratory rate and blood volume
• Increases in the size of uterus and mammary glands
Adjustments to Pregnancy
Preparation for Delivery
• Hormones (estrogen) SOFTEN LIGAMENTS between the bones in your
PELVIS, widening pelvic girdle allowing more room for birth.
• Relaxin contributes to CERVIX SOFTEN; stimulated by the corpus luteum
towards end of pregnancy and increased contractions due to higher
production of cortisol by the fetus. “Much of the work of labor is in
opening the cervix to the passage of the baby.” Some women may have
closed cervixes until labor starts. Others have pre-labor contractions that
dilate their cervix to 3 or 4 centimeters (or even more) before labor begins.
• Baby moving lower in the pelvis - called engagement. Causes increased
pressure in low abdomen; appears the "baby has dropped."
• "MUCOUS PLUG" is disintegrating inside the cervix; the cervix begins to
soften and open, the “plug” loosens and passes through the vagina. Some
women may experience release of mucus plug a few days (or weeks)
before labor begins, others may not notice it at all.
• The breaking of the AMNION (ruptured membranes) can also occur before
labor begins. For most women, contractions will follow within a day.
Uterine Contractions
• Contractions occur throughout menstrual cycle affecting only the subendometrial layer of the myometrium. Higher level of contractions
involved in labor/delivery
• Contractions initiated by a DECREASE in progesterone levels
(progesterone inhibits contractions); commence approx. 30 minutes
apart down to 1 to 3 minutes apart
• 1st stage of labor baby moves towards birth canal forcing fetal head
into cervix causes cervix to thin and stretch (efface); head
pushing against pressure receptors in the cervix causing them to
stretch.
• The receptors stimulate release of OT which heightens muscular
tension increasing stimuli to the pressure receptors and stimulating
contractions; OT also causes fetal membranes to release
prostaglandins that stimulates smooth muscle; this increases action
of oxytocin
• Each contraction causes the uterine muscles to slightly shorten
pulling the cervix up into the lower segment of the uterus. The
shortening of uterine muscles decreases the size of the uterine
space, which pushes the baby down and out the birth canal.
• Cervical stretching induces a woman’s need to “bear down”
Stages of Labor
1. Dilation – longest 8-24 hours requires regular uterine contractions
– True labor: regular intervals contractions induces dilation of
cervix
– False labor: contractions at irregular intervals no dilation
• Braxton Hicks contractions – relatively weak contractions of
the uterus over the course of gestation usually 2nd or 3rd
trimester
– during dilation of amniotic sac rupture - amniotic fluid discharged
(water breaking);
– Cervix dilates to 10 cm by Effacement: thinning of the cervix
2. Expulsion - 10 minutes to several hours
- baby moves through birth canal
- episiotomy; mucus suction; cord cut
3. Placental - 30 minutes
– placenta (afterbirth) expelled by uterine contractions
– constriction of blood vessels that were torn during placenta
detachment reduce the possibility of hemorrhage
Cesarean section (C-section): incision through lower abdominal wall and
uterus to remove baby
http://www.ahutton.com/cgw/images/A2892-r10-18x24-sq-cut--embossed-alum--01.png
Lactation
1) During pregnancy anterior pituitary increases PROLACTIN but
high levels of progesterone inhibits the effect of prolactin
• Prolactin can contribute to INSULIN RESISTANCE
• Gestational diabetes development
2) At delivery prolactin levels have dropped to non-pregnancy levels
• Infant sucking stimulates prolactin secretions 10-20x
stimulating MILK PRODUCTION
• sucking action increases the release of oxytocin facilitating
MILK EJECTION. If sucking action stops, milk secretion stops
• colostrum released 1 to 3 days after birth
– thin watery consistency, similar to breast milk
– contains IgA to protection the baby from gastroenteritis
– colonizes intestine with beneficial bacteria
– Has a laxative effect that clears intestine
– cow’s milk not a good substitute - 3x as much protein
• harder to digest
• more nitrogenous waste (diaper rash)
3) Breast feeding reduces GnRH decreasing secretions of FSH and
LH limiting ovarian cycling - “ovulation”. Only 5-10% of women
become pregnant while nursing.
Inheritance and Genetic Disorders
• Inheritance: passing of traits from one generation to another.
• Genetics: branch of biology that deals with inheritance.
• Sex linked conditions generally occur with X chromosomemore common among males
• colorblindness, hemophilia, baldness, muscular dystrophy
Nondisjunction of autosomes the failure of
autosomal chromosome pairs to separate properly)
• Only three autosomal trisomies (3 copies of the
same chromosome) are survivable: 13, 18, 21
 Chromosome 13 & 18 survival rate is one year
or less.
 Down syndrome: male or female has 3 copies
of chromosome 21
Testing for Genetic Disorders
Ultrasound: Transducer emits high-frequency sound waves
 reflected sound waves are converted to on-screen image
called sonogram
Amniocentesis: done at 14-16 weeks gestation amniotic fluid around fetus is
extracted  fetal cells are examined for genetic defects
“Lifespan”
Make the most of yours!
Extraordinary Animation from TED!
http://www.youtube.com/watch_popup?v=fKyljukBE70
Alexander Tsiaras: Conception to birth -- visualized
http://www.youtube.com/watch?v=fKyljukBE70&feature=player_embedded