HUMAN DEVELOPMENT

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HUMAN DEVELOPMENT

• Introduction
• Fertilization
• Cleavage
• Implantation
• Stages of development
• Placenta and umbilical cord
• Hormones of pregnancy
• Parturition and labor
• Adjustments at birth

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INTRODUCTION
What is pregnancy (gestation)? Sperm migration
fertilization occurs in ampulla of
oviduct 0.001 of sperm (2,000 3,000) in
ejaculate reach the ovum How do they get there
within 5 10 minutes of ejaculation?
flagellar action of sperm mucous strands in
cervical canal uterine contractions chemical
attractant from ovum (?)
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FERTILIZATION
Acrosomal reaction
arrested in metaphase II
corona radiata
hyaluronidase acrosin (a protease)
zona pellucida
Barriers to penetration
corona radiata zona pellucida ovum cell membrane
oötid membrane
Genetic events
oötid completes meiosios male pronucleus joins
female pronucleus chromosomes line up for first
mitosis (now a zygote)
Blocks to polyspermy
fast block depolarization of oötid membrane
slow block cortical reaction formation if
impenetrable fertilization membrane
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CLEAVAGE
male and female pronuclei
fertilization
corona radiata
oötid
zygote
ovulation
implantation
2 cell
morula
4 cell
8 cell
cleavage
trophoblast
blastocyst
inner cell mass
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IMPLANTATION
Location in uterus
fundus or posterior wall, usually
Role of the trophoblast
invasion of stratum functionalis formation of the
chorion (fetal placenta) human chorionic
gonadotropin (hCG) secretion
uterine gland
invading trophoblastic cells
trophoblast becoming chorion
chorion pushing into maternal placenta
uterine cavity
uterine cavity
inner cell mass
maternal blood spaces
stratum functionalis
DAY 7
DAY 14
DAY 16
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STAGES OF DEVELOPMENT
Predifferentiation stage (0 2
weeks) Embryonic stage (3 8 weeks)
amnion
ectoderm
chorion
mesoderm
gastrulation formation of the germ layers
ectoderm mesoderm endoderm
yolk sac
extraembryonic membranes
endoderm
amnion and amniotic fluid yolk sac allantois chori
on and chorionic villi
endometrium
Fetal stage (9 38 weeks)
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PLACENTA AND UMBILICAL CORD
Fetal placenta Maternal placenta Functions
exchange Umbilical cord
WEEK 10
remnants of yolk sac and allantois
placenta
umbilical cord
amniotic cavity
2 umbilical arteries 1 umbilical vein Whartons
jelly umbilicus (navel)
uterine cavity
maternal arterioles
maternal venule
umbilical cord
maternal blood
fetal capillaries in chorionic villi
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HORMONES OF PREGNANCY
Human chorionic gonadotropin (hCG) Estrogens Proge
sterone Human chorionic somatomammotropin
(hCS) Relaxin
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PARTURITION AND LABOR
Uterine contractility
false labor (Braxton Hicks contractions) true
labor parturition
Positive feedback theory of labor
begin 30 minutes apart ? progress to every 1 3
minutes cervical stretch ? neuroendocrine reflex
? oxytocin secretion ? uterine contraction ?
more stretch ? repeat
Stages of labor
dilation expulsion placental
DILATION (FIRST) STAGE
EXPULSION (SECOND) STAGE
PLACENTAL (THIRD) STAGE
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ADJUSTMENTS AT BIRTH
Respiratory Cardiovascular
foramen ovale ? fossa ovalis ductus
arteriosus ? ligamentum arteriosum ductus
venosus ? ligamentum arteriosum umbilical
vein ? ligamentum teres umbilical arteries
? median umbilical ligaments
FETAL CIRCULATION
ADULT CIRCULATION
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LACTATION
What is lactation?
Milk ejection (let-down) reflex
tactile stimulation of nipple/areolae initiates
neuroendocrine reflex ? sensory input to
hypothalamus ? secretion of oxytocin and
prolactin from anterior pituitary gland ?
oxytocin stimulates contraction of myoepithelial
cells around acini, causing milk
letdown prolactin stimulates renewed milk
synthesis by acinar cells
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