Development, Parturition, Genetics and Inheritance

Nestor T. Hilvano, M.D., M.P.H.(Illustrations Copyright by Frederic H. Martini, Pearson Publication Inc., and The McGraw-Hill Companies Inc.)

Learning Objectives 1. Describe the process of fertilization. 2. Describe the events that transform a fertilized

egg into an embryo. 3. Describe fetal development. 4. Describe the formation and function of

placenta.5. Identify the major tissues derived from the

primary germ layers.6. Discuss the stages of labor.7. Describe the fetal circulation and the changes

at birth.8. Discuss inheritance and mutation. Cite

common causes of genetic abnormalities.

Introduction

• Development – modification of structural and functional characteristics from fertilization to maturity.

• Fertilization – conception

• Embryo – first 2 months after fertilization

• Fetus – start of 9th week until birth

• Prenatal – embryological and fetal development

• Postnatal – from birth to aging process.

Gestation • First Trimester

– Period of embryo and early fetal development

– Rudiments of all major organ

systems appear

• Second Trimester– Development of organs and organ

systems

– By end, fetus looks distinctively human

• Third Trimester– Rapid fetal growth and deposition of

adipose tissue

– Most major organ systems are fully functional

4th month

Fertilization• Events of Spermatozoa prior

to fertilization

a) Capacitation of sperm –

sperm membrane becomes

fragile and permeable to

Ca2+ upon contact w/ seminal gland’s

secretion and exposure in vagina

b) Acrosomal reaction –

release of enzymes from

sperm • penetrates granulosa cells

then zona pellucida • hyaluronidase and acrosin

Fertilization

• Secondary oocyte completes meiosis if fertilized = called a zygote

• Zygote undergoes cleavage and blastocyst formation• Implantation occurs 7 days after fertilization at ______

Ectopic Pregnancy

• Blastocyst implants outside uterus– 1 out of 300

pregnancies– most cases occur

in _____________– Tube ruptures by

12 weeks

Twins• Dizygotic twins

– 2 eggs are ovulated and fertilized (2 zygotes)

• Monozygotic twins– 1 egg is fertilized (1

zygote) but splits into 2

• Conjoined twins

Gastrulation & Organogenesis• What is gastrulation? • Formation of organs

from primary germ layers– at 8 weeks, all organs are

present

• Derivatives of ectoderm– epidermis, nervous system,

lens and cornea, internal ear

• Derivatives of mesoderm– skeleton, muscle, cartilage, blood, lymphoid tissue, gonads and

ducts, kidneys and ureters

• Derivatives of endoderm– gut and respiratory epithelium and glands, bladder and urethra

Placenta

• Surface facing fetus is smooth and connected to fetus by umbilical cord

• Uterine surface

consists of

chorion frondosum

(fetal part) and

decidua basalis

(maternal part)

Fetal Development and Circulation

• Fetus = from 9 weeks until birth– organs mature to support external life

• Fetal circulation– umbilical-placental circuit via umbilical cord– circulatory shunts

• ductus venosus connects to inferior vena cava• foramen ovale connecting right and left atria• ductus arteriosus connects pulmonary trunk to

aorta

Blood Circulation Before and After Birth

Pregnancy and Childbirth

• Gestation: pregnancy– lasts an average of 266 days (38 weeks) from

conception to childbirth– gestational calendar measured from first day

of the woman’s last menstrual period (LMP)

• Birth predicted 280 days (40 weeks) from LMP

• Premature delivery – birth at 28 – 36 weeks.

3 Stages of Labor• Cervical dilatation –

usually last over 8 hrs., water breaks

• Delivery of infant – less than 2 hrs.

• Passage of placenta -

Stages of Labor

Puerperium• First 6 weeks after delivery

• Anatomy and physiology return to normal– involution of uterus

• to pre-gravid weight in 4 weeks• accomplished by autolysis by lysosomal enzymes

– vaginal discharge called lochia

– breastfeeding promotes involution• suppresses estrogen secretion• stimulates oxytocin which causes myometrial

contraction

Mutagens and Genetic Anomalies• I________ – transfer of

genetically determined characteristics

• G_______ – study of mechanisms responsible for inheritance.

• Mutagen = is any agent that alters DNA or chromosome structure

• Most common genetic disorders - nondisjunction of chromosomes during meiosis. - can be detected prior to birth with amniocentesis (examining fetal cells from amniotic fluid) or chorionic villus sampling (examine placental cells)

Down Syndrome• Trisomy 21• Occurs in

proportion to age of mother

• Effects include:

- ____________

Male Klinefelter Syndrome

• 47 XXY• Effects include

___________

Homework 1. Define terms: ectopic pregancy, cleavage,

capacitation, acrosomal reaction, blastocyst, puerperium, chorion frondosum, decidua basalis, gastrulation, genetic, inheritance, trisomy 21, and klinefilter syndrome.

2. Describe the 3 stages of labor.

3. Review blood circulation during fetal life and identify fate of fetal structures after birth.

4. Identify the primary germ layers and name an example/s of each.