Development and Inheritance

1
Development and Inheritance

• From fertilization to birth
• fertilization
• implantation
• placental development
• fetal development
• gestation
• labor
• parturition (birth)

2
Terminology of Development

• Gestation period
• time span from fertilization to birth (38 weeks)
• Prenatal period (before birth)
• embryological development
• developing human for first 2 months after
  fertilization is known as an embryo
• all principal adult organs are present
• fetal development
• from 9 weeks until birth is known as a fetus
• by end of 3rd month, placenta is functioning
• Neonatal period is first 42 days after birth
• obstetrics is branch of medicine that deals with
  the neonatal period, pregnancy and labor

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From Fertilization to Implantation
4
Events Before Fertilization

• Haploid sperm nucleus haploid secondary oocyte
  nucleus merge to form a single diploid nucleus
• Occurs in uterine tube within 24 hours after
  ovulation (oocyte dies in 24 hours)
• Events occurring before fertilization
• peristalsis of uterine tube movement of cilia
  transport the oocyte towards the uterus
• oocyte releases chemical attractants
• sperm swim towards oocyte by means of flagella
• prostaglandins within the semen stimulate uterine
  contractions that help move sperm towards the
  oocyte
• capacitation or final maturation of the sperm
  occurs within female
• acrosomal membrane becomes fragile

5
Sperm Contact during Fertilization

• Sperm penetrates the granulosa cellsaround the
  oocyte (corona radiata)
• Sperm digests its way throughthe zona pellucida
• when ZP3 glycoprotein binds to spermhead, it
  triggers the acrosomal reaction(enzyme release)
• First sperm to fuse with oocyte membrane triggers
  the slow the fast block to polyspermy
• 1-3 seconds after contact, oocyte membrane
  depolarizes other cells can not fuse with it
  fast block to polyspermy
• depolarization triggers the intracellular release
  of Ca2 causing the exocytosis of molecules
  hardening the entire zona pellucida slow block
  to polyspermy

6
Events Within the Egg

• Sperm entry, triggers oocyte to complete meiosis
  II and dump second polar body
• Once inside the oocyte, the sperm loses its tail
  becomes a male pronucleus
• Fusion of male female haploid pronuclei is the
  true moment of fertilization
• Fertilized ovum (2n) is called a zygote
• zona pellucida still surrounds it

7
Nature of Twins

• Fraternal twins (dizygotic)
• independent release of 2 oocytes fertilized by 2
  separate sperm
• as different as any 2 siblings
• Identical twins (monozygotic)
• 2 individuals that develop from a single
  fertilized ovum
• genetically identical always the same sex
• if ovum does not completely separate, conjoined
  twins (share some body structures)

8
Formation of the Morula

• Rapid mitotic cell division of embryo is called
  cleavage
• 1st cleavage in 30 hours produces 2 blastomeres
• 2nd cleavage on 2nd day
• By 3rd day has 16 cells
• By day 4 has formed a solidball of cells called
  a morula

9
Development of the Blastocyst

• A blastocyst is a hollow ball of cells that
  enters the uterine cavity by day 5
• outer covering of cellscalled the trophoblast
• inner cell mass
• fluid-filled cavity calledthe blastocele
• Trophoblast part of innercell mass will
  develop into fetal portion of placenta
• Most of inner cell mass will become embryo

10
Implantation

• Attachment of blastocyst to endometrium
• occurs 6 days after fertilization
• implants with inner cell mass in contact with the
  endometrium
• Trophoblast develops 2 distinct layers
• syncytiotrophoblast secretes enzymes that digest
  the endometrial cells
• cytotrophoblast is distinct layer of cells that
  defines the original shape of the embryo
• Trophoblast secretes human chorionic gonadotropin
  (hCG) that helps the corpus luteum maintain the
  uterine lining

11
Implantation Notice distinct syncytiotrophoblast
and cytotrophoblast layers.
12
Ectopic Pregnancy

• Development of an embryo outside the uterus
• Most often in uterine tube
• common causes are blockages of uterine tube such
  as tumors or scars from pelvic inflammatory
  disease
• symptoms are missed menstrual cycles, bleeding
  acute pain
• Twice as common in smokers because nicotine
  paralyzes the cilia

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Beginnings of Organ Systems(Gastrulation)

• Day 8
• cytotrophoblast forms amnion amnionic cavity
• cells of inner cell mass on amnionic cavity form
  ectoderm
• cells bordering on blastocele form endoderm
• ectoderm endoderm together form embryonic disk
• Day 12
• endodermal cells divideto form a hollow
  sphere(yolk sac)
• cytotrophoblast cellsdivide to fill the
  spacessurrounding the yolk sac with
  extraembryonic mesoderm
• spaces develop in that layer to form future
  ventral body cavity

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Primary Germ Layers

• Day 14 --cells of embryonic disc produce 3
  distinct layers
• endoderm forms epithelial lining of GI
  respiratory
• mesoderm forms muscle, bone other connective
  tissues
• ectoderm develops into epidermis of skin
  nervous system

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Formation of Embryonic Membranes

• Yolk sac
• site of early blood formation
• gives rise to gonadal stem cells (spermatogonia
  oogonia)
• Amnion
• surrounds embryo with fluid shock absorber,
  regulates body temperature prevents adhesions
• fluid is filtrate of mothers blood fetal urine
• examine a sample of it for embryonic cells
  (amniocentesis)
• Chorion
• becomes the embryonic contribution to the
  placenta
• derived from trophoblast mesoderm lining it
• gives rise to human chorionic gonadotropin (hCG)
• Allantois
• outpocketing off yolk sac that becomes umbilical
  cord

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Amnion, Yolk sac, Chorion, allantois
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Placenta Umbilical Cord

• Placenta forms during 3rd month
• chorion of embryo stratum functionalis layer of
  uterus
• Chorionic villi extend into maternal blood filled
  intervillous spaces --- maternal fetal blood
  vessels do not join blood does not mix
• diffusion of O2, nutrients, wastes
• stores nutrients produces hormones
• barrier to microorganisms, except some viruses
• AIDS, measles, chickenpox, poliomyelitis,
  encephalitis
• not a barrier to drugs such as alcohol
• Placenta detaches from the uterus (afterbirth)

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Parts of Endometrial Lining

• Decidua all of endometrium lost as placenta
• equals all of the endometrium, except stratum
  basalis
• Decidua basalis---portion ofendometrium deep to
  chorion
• Decidua capsularis---part ofendometrial wall
  that coversimplanted embryo
• Decidua parietalis---part ofendometrial wall not
  modifiedby embryo until embryo bumps into it as
  it enlarges
• Decidua capsularis fuses with decidua parietalis

20
Umbilical Cord

• Contents
• 2 arteries that carry blood to the placenta
• 1 umbilical vein that carries oxygenated blood to
  the fetus
• primitive connective tissue
• Stub drops off in 2 weeks leaving a scar called
  the umbilicus

21
Placenta Previa

• Placenta is implanted near or covering os of
  cervix
• occurs in 1 to 250 live births
• May lead to spontaneous abortion, premature birth
  or increased maternal mortality
• Major symptom is sudden, painless bright red
  vaginal bleeding in the 3rd trimester
• Cesarean section is preferred delivery method

22
Fetal Ultrasonography

• Transducer emits high-frequency sound waves
• reflected sound waves converted to on-screen
  image called sonogram
• patient needs full bladder
• Used to determine fetal age, viability, growth,
  position, twins and maternal abnormalities

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Amniocentesis

• Fetal cells from 10 ml sample of amniotic fluid
  examined for genetic defects
• Test at 14-16 weeks
• Results back in one month
• Needle through abdominal wall uterus
• Chance of spontaneous abortion is 0.5

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Chorionic Villi Sampling

• As early as 8 weeks
• Results in few days
• Chance of spontaneous abortion 1-2
• 30 mg of placenta removed by suctionthrough
  cervix or with needle through abdomen
• Chromosomal analysis reveals same results as
  amniocentesis

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Hormones of Pregnancy

• Chorion
• from day 8 until 4 months secretes hCG which
  keeps corpus luteum active
• corpus luteum produces progesterone estrogen to
  maintain lining of uterus
• Placenta
• by 4th month produces enough progesterone
  estrogen that corpus luteum is no longer
  important
• relaxin which relaxes CT of pelvis and cervix
• human chorionic somatomammotropoin (hCS) or human
  placental lactogen (hPL)
• maximum amount by 32 weeks
• helps prepare mammary glands for lactation
• corticotropin-releasing hormone (CRH) increases
  secretion of fetal cortisol (lung maturation)
  acts to establish timing of birth

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Hormone Blood Levels

• Human chorionic gonadotropin (hCG) produced by
  the chorion is less important after 4 months,
  because the placenta takes over the hormonal
  secretion of the corpus luteum.

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Hormonal Secretion by the Placenta
28
Early Pregnancy Tests

• Detect human chorionic gonadotropin (hCG) in the
  urine as soon as 8 days after fertilization
• color change hen reaction between urine
  antibodies in kit
• False-negatives false-positives do occur
• excess protein or blood in urine
• rare type of uterine cancer
• steroid, diuretics, hormones and thyroid drugs
  alter test results

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Developmental Changes

• Read Table 29.2 to get a full description of the
  timing of fetal events during development

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Maternal Changes During Pregnancy

• Uterus nearly fills the abdominal cavity
• GI tract compressed causing heartburn
  constipation
• Pressure on bladder causing changes in frequency
  urgency
• Compression of vena cava causing varicose veins
  edema in the legs
• Compression of renal vessels causing renal
  hypertension

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Changes During Pregnancy

• Cardiovascular changes to meet needs of fetus
• rise in cardiac output of 20-30 due to placenta
• increase in heart rate 15 increase in blood
  volume 30-50
• Respiratory changes
• increase in tidal volume 30
• decrease in expiratory reserve volume airway
  resistance
• minute respiratory volume increases as O2 needs
  increase
• Reproductive system changes
• uterus increases in size from 80 g to 1200g
• hyperplasia and hypertrophy
• Urinary system changes
• increase in glomerular filtration rate of 40

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Pregnancy-Induced Hypertension

• Elevated blood pressure
• Major cause is preeclampsia
• sudden hypertension
• large amounts of protein in the urine
• generalized edema, blurred vision headaches
• Autoimmune or allergic reaction to presence of
  fetus
• Eclampsia convulsions coma in mother

33
Exercise and Pregnancy

• In early pregnancy
• avoid excessive exercise heat buildup
• linked to neural tube defects
• Moderate exercise has beneficial effects
• no evidence of inadequate blood flow to the
  placenta

34
Labor and Parturition

• Parturition means giving birth labor is the
  process of expelling the fetus
• Labor begins when progesterones inhibition is
  overcome by an increase in the levels of estrogen
• progesterone inhibits uterine contraction
• placenta stimulates fetal anterior pituitary
  which causes fetal adrenal gland to secrete DHEA
• placenta converts DHEA to estrogen
• estrogen overcomes progesterone and labor begins

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Positive Feedback during Labor

• Uterine contraction forces fetal head into cervix
  (stretch)
• Nerve impulses reach hypothalamus causing release
  of oxytocin
• Oxytocin causes more contractions producing more
  stretch of cervix more nerve impulses

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True Versus False Labor

• True labor begins when contractions occur at
  regular intervals
• produces pain
• back pain increases with walking
• dilation of cervix with a discharge of
  blood-containing mucus in the cervical canal
• False labor produces pain at irregular intervals
  but there is no cervical dilation

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Stages of Labor

• Dilation
• 6 to 12 hours
• rupture of amniotic sac dilation of cervix
• Expulsion
• 10 minutes to several hours
• baby moves through birth canal
• Placental
• 30 minutes
• afterbirth is expelled by muscular contractions

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Dystocia Cesarean Section

• Dystocia difficult labor
• due to fetal position or size
• breech presentation is butt or feet first in
  birth canal
• Cesarean section (C-section)
• horizontal incision through lower abdominal wall
  and uterus
• a history of multiple cesarean sections does not
  preclude a vaginal birth

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Adjustments of the Infant at Birth

• Respiratory System
• after cord is cut, increased CO2 levels in blood
  cause muscular contractions and first breath
• breathing rate begins at 45/minute for the first
  2 weeks declines to reach normal rate
• Cardiovascular System
• foramen ovale closes at moment of birth
• ductus arteriosus umbilical vein close down by
  muscle contractions become ligaments
• pulse rate slows down (120 to 160 at birth)
• increase in rate of RBC hemoglobin formation

40
Premature Infants

• Preemie is any baby weighs less than 5lb. 8oz at
  birth
• Causes
• poor prenatal care
• drug abuse
• young or old mother (below 16 or above 35)
• Below 36 weeks
• respiratory distress syndrome due to insufficient
  surfactant is major problem

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Physiology of Lactation

• Lactation production release of milk
• Prolactin from anterior pituitary increases
  during pregnancy, but progesterone inhibits
  effects of prolactin until after delivery
• After delivery, progesterone levels drop
  suckling increases the release of prolactin
  oxytocin (milk ejection reflex)
• Colostrum cloudy fluid released for few days
• True milk produced by 4th day
• If suckling stops, milk secretion stops

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Milk Ejection Reflex

• Oxytocin cause release of milk into mammary ducts
• Stimulation of touching nipple causes
  hypothalamus to release oxytocin
• Oxytocin causes contraction of myoepithelial
  cells
• Milk moved from alveoli into mammary ducts
• Oxytocin release by other stimuli
• hearing a babys cry or touching the genitals

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Benefits of Breast-feeding

• Faster better absorption of the right
  nutrients
• Beneficial cells
• functional white blood cells
• neutrophils help ingest bacteria in babys gut
• macrophages produce lysozymes
• plasma cells provides antibodies prevent
  gastroenteritis
• Decreased incidence of diseases later in life
• reduction in allergies, respiratory GI
  infections, ear infections diarrhea
• Parent-child bonding
• Infant in control of intake

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Nursing and Childbirth

• Nursing of first-born twin speeds birth of second
  child
• stimulates release of oxytocin
• Nursing of only child
• promotes expulsion of the placenta
• helps control hemorrhage after birth
• helps uterus return to normal size

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Inheritance

• Passing of hereditary traits from one generation
  to the next
• Genotype
• all human cells contain 23 pairs of chromosomes
• one chromosome in each pair came from the mother
  and the other came from the father
• similar locations on each pair of chromosomes
  code for the same trait (alleles)
• if one allele controls the express of a trait, it
  is the dominant allele
• if the other allele is completely masked it is
  the recessive allele
• a person with the same alleles on both
  chromosomes is said to be homozygous for the
  trait----heterozygous for the trait is having
  different alleles on homologous chromosomes
• heterozygous individuals are carriers of a
  recessive gene

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Genotype Phenotype

• Genotype your genetic makeup
• Phenotype what you look like (outward
  expression of your genes)
• Punnett square
• method of showing 4 possible genetic combinations
  in offspringof 2 individuals

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Genetic Problems

• Error in meiosis called nondisjunction
• chromosomes fail to separate properly
• cell with one or more extra or missing
  chromosomes is called an aneuploid
• (2n-1) is missing a chromosome
• (2n1) has an extra chromosome
• Error in meiosis called translocation
• location of chromosome segment is moved
• crossing-over between 2 nonhomologous chromosomes
• Down syndrome results from a portion of
  chromosome 21 becoming part of another chromosome
  
• individuals have 3 copies of that part of
  chromosome 21

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Incomplete Dominance

• Neither member of an allelic pair is dominant
  over the other --- resulting phenotype is
  intermediate
• Sickle-cell trait individuals have both HbA HbS
• suffer from only minor problems with anemia since
  have both normal sickle-cell hemoglobin
• Sickle-cell anemic individuals have 2HbS alleles
• produce sickle-cell hemoglobin
• suffer from severe anemia

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Sickle-Cell Inheritance

• 1 normal
• 2 embryos will be sickle-cell trait
• 1 sickle-cell anemia

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Multiple-Allele Inheritance

• Genes with more than two alternate forms
• 3 different alleles of the I gene
• IA, IB, or i
• A and B alleles are codominant since both genes
  are expressed equally
• 6 possible genotypes produce 4 blood types
• 4 phenotypes of the ABO blood groups are (A, B,
  AB O)

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Polygenic Inheritance

• Traits controlled by many genes
• continuous gradations ofsmall differences
• body build, height andskin, hair eye color
• Skin color controlled by3 genes (Aa, Bb, Cc)
• person with genotype ofAABBCC is dark
• person aabbcc is light
• Parental generation F1and F2 generation

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Autosomes Sex Chromosomes

• Each of us has a pair of sex chromosomes
• Females XX
• Males have XY
• Y is smaller
• Y is needed to produce male development

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Human Chromosomes

• 22 pairs of autosomes
• 1 pair of sex chromosomes

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Sex-Linked Inheritance

• Genes found only on X chromosomes
• Red-Green color blindness
  is lack of either red or
  greencones, so seen as same color
• XCXC is normal, XCXc is carrier
• XcXc is color blind
• XCY is normal, XcY is color blind
• Hemophilia is sex-linked traitwhere blood fails
  to clot
• Other sex-linked traits
• absence of incisors, night blindness, juvenile
  glaucoma, and some types of deafness, diabetes,
  cataracts, and muscular dystrophy

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X-Chromosome Inactivation

• Females have double dose of X chromosome in all
  cells
• One X chromosome is randomly permanently
  inactivated early in development
• Visible as dark-staining Barr body easily seen in
  nucleus of neutrophils as drumstick
• tightly coiled even in interphase cell

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Environmental Influences

• Phenotype is result of environment effects on
  genetic makeup
• more influential on polygenic traits such as
  height
• Teratogens cause developmental defects
• Chemicals Drugs
• fetal alcohol syndrome slow growth, facial
  features, defective heart CNS
• cocaine attention problems, hyperirritability,
  seizures
• Cigarette Smoking
• low birth weight, cleft lip palate, SIDS
• Irradiation or radioisotopes during first
  trimester
• mental retardation, microcephaly

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Infertility

• Female
• 10 of reproductive age U.S. population
• ovarian disease or obstruction of uterine tubes
• inadequate or excessive body fat
• Male
• definition is production of adequate quantities
  of viable, normal sperm transport through ducts
• seminiferous ducts sensitive to x-rays,
  infections, toxins, malnutrition high scrotal
  temperatures

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Alternative Fertilization Techniques

• Fertilization in a laboratory dish -- 16 cell
  stage placed into uterus
• in vitro fertilization
• mother given FSH to produce multiple oocytes
  (surgically removed)
• mixed with solution containing sperm
• intracytoplasmic sperm injection into oocyte
• Embryo transfer
• artificial insemination of oocyte donor
• blastocyst transfer to infertile woman for
  pregnancy
• Gamete intrafallopian transfer
• FSH LH stimulate multiple oocytes---aspiration
  fertilization outside the body---reimplantation
  into uterine tubes (whole procedure is to skip
  vagina)

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Down Syndrome (DS)

• Nondisjunction of chromosome 21 causes one of
  daughter cells to end up with extra copy
• trisomy 21---2 copies from mom one from dad
• More common in older mothers
• more exposure to radiation chromosome-damaging
  chemicals
• kinetochore microtubules that pull chromosomes
  apart sustain damage
• 1 in 800 infants is born with Down syndrome
• mental retardation, distinctive facial structures
  malformation of the heart, ears, hands feet

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Fragile X Syndrome

• Defective gene on X chromosome
• broken tip of X chromosome
• Causes mental retardation in some of males with
  this gene
• learning difficulties, oversized ears, enlarged
  testes double jointedness
• may be involved with autism
• Unaffected males may pass gene onto daughters
  whose children may suffer