Human Development and Heredity

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Chapter 24

• Human Development and Heredity

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Overview

• Fertilization
• Early embryonic period
• Embryonic period
• Fetal period
• Labor and delivery

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• Pregnancy
• Gestation begins with fertilization and ends with
  delivery
• Approximately 38 weeks
• All fetal tissues differentiate from single
  fertilized egg

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• Fertilization and the Start of
• Pregnancy
• Vagina receives semen
• Sperm dissolve egg cell coating, penetrate plasma
  membrane
• Sperm, egg combine in single cell (zygote)
• Zygote divides into cell cluster, moves to uterus
• Cluster becomes embryo

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Zygote ? Implantation
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The female reproductive system. Arrows show the
pathway of the spermatozoa and ovum and also of
the fertilization and implantation of the
fertilized ovum.   Zooming In u Where is the ovum
fertilized?
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• The Placenta
• Organ of nutrition, respiration, excretion for
• developing offspring
• Embryonic cluster forms villi (projections)
• Projections invade uterine wall, maternal blood
  channels (venous sinuses)
• Embryonic layer and uterine lining form placenta

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Extraembryonic membranes
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Placenta
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Fetal circulation and section of placenta. Colors
show relative oxygen content of blood.   Zooming
In u What is signified by the purple color in
this illustration?
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• The Umbilical Cord
• Connects embryo to placenta
• Carries blood to and from fetus
• Fetus has special circulatory features

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• Placental Hormones
• Placenta is an endocrine organ
• Human chorionic gonadotropin (hCG)
• Progesterone
• Estrogen
• Human placental lactogen (hPL) or human chorionic
  somatomammotropin
• Relaxin

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Checkpoint 24-1 What organ nourishes the
developing fetus? Checkpoint 24-2 What is the
function of the umbilical cord?
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• Development of the Embryo
• Embryology is study of growth during first eight
• weeks of life
• Nervous system begins to form
• Heart and blood vessels originate
• Limb buds form
• Human appearance

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Checkpoint 24-3 All body systems originate
during the early development of the embryo. At
what time in gestation does the heartbeat first
appear?
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• The Fetus
• Offspring from month three until birth
• Organs grow and mature
• Ovaries form
• Most rapid growth months four to six (second
  trimester)
• Can determine sex
• Amniotic sac
• Vernix caseosa

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Checkpoint 24-4 What is the name of the
fluid-filled sac that holds the fetus?
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Diagnostic tests
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Midsagittal section of a pregnant uterus with
intact fetus.   Zooming In u What structure
connects the fetus to the placenta?
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• The Mother
• Heart pumps more blood
• Lungs increase respiration
• Kidneys excrete waste from fetus and mother
• Digestive system supplies additional nutrients
• Nausea and vomiting common
• Urinary frequency and constipation common

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Checkpoint 24-5 What is the approximate duration
of pregnancy in days?
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• The Use of Ultrasound in Obstetrics
• Safe, painless, noninvasive method used to
• Diagnose pregnancy
• Judge fetal age
• Determine location of placenta
• Show presence of excess amniotic fluid and fetal
  abnormalities

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• Childbirth
• Factors that start labor
• Uterine muscle stretching stimulates
  prostaglandin production
• Pressure on cervix stimulates posterior pituitary
  to release oxytocin
• Placenta changes
• Fetal cortisol inhibits mothers progesterone
• Increase of estrogen relative to progesterone

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• The Four Stages of Labor
• Parturition (labor and delivery)
• Onset of regular uterine contractions
• Cervix dilates, fetus passes to outside
• Afterbirth is expelled
• Bleeding is controlled

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Checkpoint 24-6 What is parturition?
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• Cesarean Section
• Incision made in abdominal wall and uterine wall
  for
• fetal delivery may be required for
• Placental abnormality
• Abnormal fetal position
• Disproportion between head of fetus and mothers
  pelvis

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Checkpoint 24-7 What is a cesarean section?
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• Multiple Births
• Two types of twins
• Fraternal
• Two different ova
• Two placentas and surrounding sacs
• Identical
• Single ovum
• Embryonic cells separate into two units
• Usually single placenta
• Separate umbilical cords

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• Termination of Pregnancy
• Live birth
• Immature (premature) infant
• Abortion
• Spontaneous (miscarriage)
• Induced
• Fetal death
• Stillbirth

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Checkpoint 24-8 What does the term viable mean
with reference to a fetus?
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• The Mammary Glands and Lactation
• Mammary gland (breast) structure
• Lobes
• Glandular tissue
• Fat
• Lactiferous ducts
• Papilla (nipple)
• Lactation
• Placental lactogen (hPL)
• Prolactin (PRL)
• Colostrum
• Oxytocin
• Breast milk

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Checkpoint 24-9 What is lactation?
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• Disorders of Pregnancy,
• Childbirth and Lactation
• Ectopic pregnancy
• Tubal ectopic pregnancy
• Placenta previa
• Abruptio placentae

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• Pregnancy-Induced Hypertension
• Preeclampsia (toxemia of pregnancy)
• Caused by hormone imbalance
• May lead to eclampsia
• Kidney failure
• Convulsions
• Coma

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Checkpoint 24-10 What is an ectopic pregnancy?
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• Postpartum Disorders
• Puerperal infections
• Infections related to childbirth
• Develops in about 6 of maternity patients
• Hydatidiform mole
• Benign overgrowth of placental tissue
• May invade wall of uterus, causing rupture
• Choriocarcinoma
• Malignant tumor of placental tissue
• Rare, spreads rapidly

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Checkpoint 24-11 What is puerperal infection?
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Breast
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• Lactation Disturbances
• Causes can vary
• Malnutrition or anemia
• Emotional disturbances
• Abnormalities in or injuries to mammary glands
• Mastitis (inflammation of breast) caused by
  infection

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Its a girl Its a boy
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• Genes and Chromosomes
• Genes are DNA segments
• Thousands of genes per chromosome
• Gene carries code for specific trait
• Cell contains 46 chromosomes (except sex cell)
• 1 pair sex chromosomes
• 22 pairs autosomes

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• Dominant and Recessive Genes
• Dominant gene
• Always expresses effect
• Need from one parent only
• Recessive gene
• No effect unless paired allele also recessive
• Need from both parents
• Heterozygous alleles
• Homozygous alleles

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Checkpoint 24-12 What is the difference between
a dominant and a recessive gene?
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• Distribution of Chromosomes
• To Offspring
• Meiosis
• Produces gametes with 23 chromosomes
• Cells receive chromosomes at random from parents
• Punnett square

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• Sex Determination
• Sex chromosomes not matched in size, appearance
• Female (X) chromosome larger
• Male (Y) chromosome smaller
• Femalestwo X chromosomes
• MalesX, Y chromosomes
• SpermX or Y chromosome, determines offspring sex

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Sex determination. If an X chromosome from a male
unites with an X chromosome from a female, the
child is female (XX) if a Y chromosome from a
male unites with an X chromosome from a female,
the child is male (XY).
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• Sex-Linked Traits
• Traits carried on sex chromosomes
• Most are carried on X (X-linked)
• Appear almost exclusively in males

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• Hereditary Traits
• Determined by single pair of genes
• Less common
• Determined by gene pairs acting together
• More common
• Multifactorial inheritance

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• Gene Expression
• Gene effects on phenotype are influence by many
• factors
• Sex
• Presence of other genes
• Environment

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• Genetic Mutation
• Genes or chromosomes that do not replicate
  exactly
• Changes in genes or chromosomes
• Chromosomal breakage or loss, gene fragment
  rearrangement
• May occur during cell division
• Spontaneous
• Induced by mutagen

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• Genetic Diseases
• Gene disorders
• All are genetic
• Some are hereditary
• Passed from parent to offspring
• Genetic research can identify some causes

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• Congenital Versus Hereditary Diseases
• Congenital
• Present at birth
• Possible causes
• Maternal infections
• Environmental toxins
• Maternal alcohol, cigarette consumption
• Maternal nutrition
• Hereditary
• Genetically transmitted or transmissible
• Not always evident at birth

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• Examples of Genetic Diseases
• Down syndrome (trisomy 21)
• Huntington disease
• Marfan syndrome
• Phenylketonuria (PKU)
• Sickle cell disease
• Cystic fibrosis
• Tay-Sachs disease
• Progressive muscular atrophies
• Albinism
• Osteogenesis imperfecta
• Neurofibromatosis
• Some cancers

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• Treatment and Prevention of
• Genetic Diseases
• More than 400 genetic diseases identified
• List is growing as science advances

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• Genetic Counseling
• Family history (pedigree)
• Laboratory studies
• Amniocentesis
• Chorionic villus sampling (CVS)
• Karyotype analysis
• Counseling prospective parents

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Amniocentesis. A sample of amniotic fluid is
removed from the amniotic sac. Cells and fluid
are tested for fetal abnormalities. (Reprinted
with permission from Cohen BJ. Medical
Terminology. 4th ed. Philadelphia Lippincott
Williams Wilkins, 2004.)