Transcript Stages of development

Anatomy & Physiology
SIXTH EDITION
Lecture 29, Development and
Inheritance
Lecturer: Dr. Barjis
Room: P313
Phone: (718) 260-5285
E-Mail: [email protected]
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Frederic H. Martini
Fundamentals of
Learning Objectives
• Explain the relationship between differentiation
and development and specify the various stages
of development
• Describe the process of fertilization
• List the three prenatal periods and describe the
major events associated with each
• Discuss the importance of the placenta as an
endocrine organ
Learning Objectives
• Discuss the structural and functional changes in
the uterus during gestation
• List and discuss the events that occur during
labor and delivery
• Relate basic principles of genetics to the
inheritance of human traits
Differentiation and development
• Development involves:
• 1) Cell division and differentiation
• Differentiation is the creation of different
types of cells
• 2) changes in anatomical structures
• Anatomical changes include gradual
modification of physical and physiological
characteristics
• Development begins at fertilization
Stages of development
• Development can be divided into: Prenatal and postnatal
development
• Prenatal development begins at fertilization and ends with
birth
• Prenatal development includes:
• Embryological development
• Changes occurring during the first two months
after fertilization
• Fetal development
• Begins at the start of the ninth week and
continues until birth
• Postnatal development
• Commences at birth and continues to maturity
Fertilization (conception)
• Fertilization is fusion of two haploid gametes (egg
and sperm) each with 23 chromosome to produce
a zygote that contains 46 chromosomes
• Fertilization occurs in the uterine tubes
• Within a day of ovulation
• Spermatozoa cannot fertilize an ovum until after
capacitation
Fertilization
Fertilization Steps
• Step 1 Ovulation
• At ovulation the oocyte is in
metaphase of meiosis II
• Both the occyte and the polar
body is surrounded by corona
radiate
• Step 2 Fertilization
• Oocyte is surrounded by the
sperms
• Acrosomal enzyme from
several sperms creates gaps in
corona radiata
• One sperm makes contact with
the oocyte membrane
• Sperm and oocyte fused
• The process of meiosis will
complete
Fertilization
The Oocyte at Ovulation
• Ovulation occurs before the oocyte is completely mature i.e. oocyte is
ovulated before the process of meiosis is completed
• Ovulated oocyte is in metaphase of meiosis II
• If the egg is fertilized the process of meiosis will complete
• If fertilization does not occur, the oocyte disintegrate without
completing the process of meiosis
• Oocyte is surrounded by the corona radiate
• Spermatozoa release hyaluronidase and acrosin
• Enzymes required to penetrate corona radiate
• Single spermatozoan contacts oocyte, fertilization begins
• Oocyte activation
• Polyspermy prevented by membrane depolarization and cortical
reaction
The Stages of Prenatal Development
Embryonic and Fetal Periods
• Induction
• During prenatal development differences in
cytoplasmic composition trigger changes in
genetic activity
• Gestation periods
• The gestation period is divided into three
integrated trimesters
The First Trimester
• The first trimester is the period of embryological and
early fetal development
• Four processes occur during the first trimeter
• 1) Cleavage
• 2) Implantation
• 3) Placentation
• 4) Embryogenesis
The First Trimester
Cleavage
• Cleavage - cleavage is the first cell division
• Zygote becomes a preembryo then a blastocyst
• Blastocyte includes:
• Trophoblast – outer layer of cells
• Inner cell mass – cluster of cells at one end of
blastocyst
Cleavage and Blastocyst Formation
The First Trimester
Implantation and Placentation
• Implantation
• Attachment of blastocyst into the uterine
endometrium
• Occurs about 7 days after fertilization
• Placentation
• Blood vessels form around blastocyst and
placenta develops
• The placenta is a complex organ that permits
exchange between the maternal and embryonic
circulatory systems
Stages in Implantation
Animation: Location of the Endometrium (see tutorial)
The First Trimester
Embryogenesis
• Embryogenesis
• Formation of a viable embryo
• This process establishes the foundations for all
major organ systems
• Gastrulation
• Embryonic disc composed of germ layers
• Endoderm
• Mesoderm
• Ectoderm
The Inner Cell Mass and Gastrulation
Germ layers
• Gastrulation
• By day 12 surface cells move toward the
primitive streak
• A third germ layer forms
• The three germ layers are:
• Ectoderm – superficial cells that did not
migrate
• Endoderm – cells facing the blastocoele
• Mesoderm – migrating cells between ectoderm
and endoderm
Extraembryonic Membranes
• Four extraembryonic membranes:
• Yolk sac
• Amnion
• Allantois
• Chorion
Extraembryonic Membranes and Placenta
Formation
Extraembryonic Membranes and Placenta
Formation
Extraembryonic Membranes and Placenta
Formation
Embryo Anatomy
• Yolk sac
• Important site of blood cell formation
• Amnion
• Encloses fluid that surrounds and cushions
developing embryo
• Allantois
• Eventually becomes bladder
• Chorion
A Three-Dimensional View of Placental
Structure
Placentation
• Chorionic villi extend into maternal tissue
• Forms intricate branching network for
maternal blood
• Umbilical cord connects fetus to placenta
Hormones of the placenta
• Trophoblast secretes hormones to maintain
pregnancy
• HCG
• Estrogens
• Progesterone
• hPL
• Placental prolactin
• Relaxin
Second and Third Trimesters
• Second trimester
• Organ systems increase in complexity
• Third trimester
• Many organ systems become fully functional
• Fetus undergoes largest weight change
• At end of gestation fetus and uterus push
maternal organs out of position
The Second and Third Trimesters
Growth of the Uterus and Fetus
Growth of the Uterus and Fetus
Developing fetus totally dependent on maternal
organs
• Maternal adaptations include increased
• Respiratory rate
• Tidal volume
• Blood volume
• Nutrient and vitamin uptake
• Glomerular filtration rate
Animation: Anatomy comparison of pregnant and non-pregnant (see tutorial)
Structural and Functional Changes in the Uterus
• Progesterone inhibits uterine muscle contraction
• Opposed by estrogens, oxytocin and
prostaglandins
• Multiple factors interact to produce labor
contractions in uterine wall
Factors Involved in the Initiation of Labor and
Delivery
Labor and Delivery
Goal of labor is parturition
• Stages of labor
• Dilation
• The cervix dilates and fetus moves toward
cervical canal
• Expulsion
• The cervix completes dilation and fetus
emerges
• Placental
• Ejection of the placenta
The Stages of Labor
Other labor and delivery situations
• Premature labor
• True labor begins before fetus has completed
normal development
• Difficult deliveries
• When the fetus faces the pubis rather than the
sacrum
• The legs or buttocks enter the vaginal canal
first (breech births)
• Multiple births
• Twins, triplets, etc.
• Dizygotic or monozygotic situations
Postnatal Development
Postnatal life stages
• Neonatal period
• Infancy
• Childhood
• Adolescence
• Maturity
• Senescence begins at maturity and ends in
death
The neonatal period
• From birth to one month
• Respiratory, circulatory, digestive and urinary
systems adjust
• Infant must thermoregulate
• Maternal mammary glands secrete colostrum
first few days
• Milk production thereafter
• Both secretions are released via the milk letdown reflex
• Body proportions change during infancy and
childhood
The Milk Let-Down Reflex
Growth and Changes in Body Form
Adolescence
• Begins at puberty
• The period of sexual maturation
• Ends when growth is completed
Puberty marked by
• Increased production of GnRH
• Rapid increase in circulating FSH and LH
• Ovaries and testes become sensitive to FSH / LH
• Gamete production initiated
• Sex hormones produced
• Growth rate increases
Hormonal changes at puberty produce gender
specific differences in system
• Differences are retained throughout life
• Adolescence continues until growth completed
• Further changes occur when sex hormones
decline
• Menopause
• Male climacteric
Senescence
• Aging affects functional capabilities of all system
You should now be familiar with:
• The relationship between differentiation and
development, and the various stages of
development
• The process of fertilization
• The three prenatal periods and describe the
major events associated with each
• The importance of the placenta as an endocrine
organ
You should now be familiar with:
• The structural and functional changes in the
uterus during gestation
• The events that occur during labor and delivery
• The basic principles of genetics as they relate to
the inheritance of human traits