Chapter 18 Development - Histopathology Service•Muscle, bones, blood, gonads, etc. •Endoderm:...
Transcript of Chapter 18 Development - Histopathology Service•Muscle, bones, blood, gonads, etc. •Endoderm:...
Chapter 18
Development
Fertilization, Cleavage, and
Implantation
• Sperm and egg unite: 6-24 hours after
intercourse, sperm survives days in female
reprod. tract
• One sperm fertilizes one egg
– Occurs in upper oviduct
– Acrosome: contains digestive enzymes
– Sperm digests thru follicle cells and zona pellucida
– Sperm membrane fuses with egg membrane
– Zona pellucida made impermeable to other sperm
Fertilization
How many sperm normally fertilize a
single egg?
A. 1
B. 2
C. 4
D. More than a million
• Cleavage involves: cell division without cell
growth, up to about day four
– Function is to restore cell size to normal (i.e.
smaller than the egg cell)
– Produces a “morula” – a solid ball of cells
Early Development
Blastocyst
• Inner cell mass cells form embryo
proper
– Source of embryonic stem cells
• Outer (trophoblast) cells form placenta
– Secrete hCG (human chorionic
gonadotropin) after implantation
– Extends life of corpus luteum
– Basis of pregnancy test
Implantation
Implantation
The cells of the blastocyst that produce
the embryo proper are called:
A. Zona cells
B. Trophoblast cells
C. Inner cell mass
D. Amnion
Gastrulation
• Cells migrate to produce a three layered embryo
• Ectoderm: outermost layer
• Forms nervous system, skin, etc.
• Mesoderm: middle layer
• Muscle, bones, blood, gonads, etc.
• Endoderm: innermost layer
• Viscera, gut, etc.
Neurulation Forms Neural Tube
• The neural tube forms the CNS (brain &
spinal cord)
• Inductive interactions between tissues
– Chemical signals influence development of
nearby tissue
– Ex: Neural tube induced by notochord
Somites: form bone & muscle
The neural tube develops into:
A. The digestive tube
B. Reproductive tract
C. Brain and spinal cord
Extraembryonic Membranes and
Placenta
• Extra-embryonic membranes
– Amnion: lines amniotic cavity, filled with
amniotic fluid
– Chorion: makes human chorionic
gonadotropin (hCG)
Placenta
• Functions
– Nutrient exchange with mother
• Umbilical cord connects fetus to placenta
• Filters nutrients, waste, and provides
antibodies for fetus
• No mixing of mother and fetal circulations
– Endocrine organ: produces hormones
• hCG
• Estrogen and Progesterone
The following are functions of the
placenta
A. Nutrient exchange with the mother
B. Produces hormones required for
pregnancy
During the first stage of labor, the cervix opens (dilates) and thins out (effaces) to allow
the baby to move into the birth canal. In figures A and B, the cervix is tightly closed. In
figure C, the cervix is 60 percent effaced and 1 to 2 cm dilated. In figure D, the cervix is
90 percent effaced and 4 to 5 cm dilated. The cervix must be 100 percent effaced and 10
centimeters dilated before a vaginal delivery.
Factors That Contribute to Labor
• Estrogen: Progesterone ratio
– High P promotes uterine quiescence (early
pregnancy)
– High E promotes uterine contractility (late
pregnancy)
• Oxytocin promotes uterine contractions
via neuroendocrine reflex
Lactation
• During Pregnancy:
– High E and P during pregnancy promote
breast development but inhibit milk prodn.
• After Childbirth:
– E & P levels plummet
– Prolactin promotes milk synthesis
– Oxytocin induces milk ejection via
neuroendocrine reflex
Environmental Disruptions During the
Embryonic Period Cause Major Birth
Defects
Lower limbs
Spina bifida
Spina bifida baby