Transcript Chapter 29 - Martini: Developmen

Pregnancy & Human
Development
Chapter 29
Fertilization: It’s all in the timing!
• Oocyte is only viable for ~ 24 hours.
• Sperm is viable for 12 – 24 hours (some
“super sperm” may be viable for up to 72
so be careful!)
• Therefore, usually, coitus must occur
within a 24 hour window on either side of
ovulation.
Barriers to fertilization
• Low vaginal pH
• Getting lost (50/50 chance of getting the
right uterine tube)
• Numerous defective sperm
• Uterine contractions
• Phagocytes
• By the time they get to the oocyte, there
are only a few dozen to a couple hundred
Capacitation
• Must occur before spermatozoa can
fertilize secondary oocyte:
– contact with secretions of seminal vesicles
– exposure to conditions in female reproductive
tract
Penetration
Secondary
oocyte
Head of
sperm
1650X
Fertilization
Figure 29–1
Fertilization
Figure 29–1b (1 of 2)
Fertilization
Figure 29–1b (2 of 2)
Fusion
Of the
pronuclei
Cleavage and Blastocyst Formation
Figure 29–2
What’s this thing called, Love?
• Zygote – a the single cell after fusion of
the pronuclei of the oocyte & the sperm.
• Conceptus – covers the period of develop
following first cleavage and differentiation
of cells into an embryo.
– Morula – the conceptus as a solid ball of 16
cells (about day 3).
– Blastocyst – a hollow ball of cells, from day 4.
“Hatching” occurs at this stage, when the
blastocyst emerges from the zona pellucida.
Development from zygote to
implantation.
Then what ?
• The blastocyst differentiates into:
– the trophoblast, the outer ball of cells that
eventually becomes the placenta and
“extraembryonic” membranes.
– the inner cell mass (ICM) becomes the
embryo.
• The above occurs over the course of the
second week following conception.
• Implantation – occurs on about day 6 or
so, as the blastocyst burrows into the
endometrium.
Stages in
Implantation
Figure 29–3
Day 6
Implantation
Implantation – Day 8
Implantation
Days 9 - 13
and early
placentation
Ectopic Pregnancy
• Implantation occurs outside of uterus
• Do not produce viable embryo
• Can be life threatening
The Inner Cell Mass and Gastrulation
Figure 29–4
The Primary Germ Layers
ECTODERM
MESODERM
ENDODERM
All nervous tissue
Muscle
Epidermis &
Derivatives
Cornea & lens
Connective tissue Digestive glands
Oral, nasal & anal
epithelium
Endothelium of
blood vessels
Tooth enamel
Serosae
Urethra & bladder
epithelium
Pineal, pituitary &
adrenal medulla
Eye’s fibrous &
vascular tunics
Respiratory tract
epithelium
Melanocytes
Synovia
Lymphoid tissue
Flat bones of cranium Urogenital organs
G.I. epithelium
Reproductive ducts &
gland epithelium
Thyroid, thymus &
parathyroid
The Fates of the Germ Layers
Table 29–1
Extraembryonic
Membranes
and Placenta
Formation
Figure 29–5 (1 of 3)
Figure 29–5 (2 of 3)
Placenta Formation
Figure 29–5 (3 of 3)
View of
Placental
Structure
Figure 29–6a
Placental Structure
Figure 29–6b
Decidua:
Decidua Capsularis
• Thin portion of endometrium
• No longer participates in nutrient exchange and
chorionic villi in region disappear
Decidua Basalis
• Disc-shaped area in deepest portion of
endometrium
• Where placental functions concentrated
Decidua Parietalis
• Rest of the uterine endometrium
• No contact with chorion
Hormones of Placenta
• Synthesized by syncytial trophoblast,
released into maternal bloodstream:
– human chorionic gonadotropin
– human placental lactogen
– placental prolactin
– relaxin
– progesterone
– estrogens
Human Placental Lactogen (hPL)
• Helps prepare mammary glands for milk
production
• Stimulatory effect on other tissues
comparable to growth hormone (GH)
Placental Prolactin
• Helps convert mammary glands to active
status
Relaxin
• Is a peptide hormone
• Is secreted by placenta and corpus luteum
during pregnancy
• Increases flexibility of pubic symphysis,
permitting pelvis to expand during
deliveryCauses dilation of cervix
• Suppresses release of oxytocin by
hypothalamus and delays labor
contractions
An Overview of
Prenatal Development
Table 29–2 (1 of 4)
An Overview of
Prenatal Development
Table 29–2 (2 of 4)
An Overview of
Prenatal Development
Table 29–2 (3 of 4)
An Overview of
Prenatal Development
Table 29–2 (4 of 4)
Embryogenesis
• Body of embryo begins to separate from
embryonic disc
• Body of embryo and internal organs start
to form
• Folding, differential growth of embryonic
disc produce bulge that projects into
amniotic cavity:
– projections are head fold and tail fold
The First Trimester
Figure 29–7a, b
The First Trimester
Figure 29–7c, d
Organogenesis
• Process of organ formation
The Second and Third
Trimesters
Figure 29–8
Second Trimester
• Fetus grows faster than surrounding
placenta
Third Trimester
•
•
•
•
Most of the organ systems become ready
Growth rate starts to slow
Largest weight gain
Fetus and enlarged uterus displace many
of mother’s abdominal organs
Growth of the Uterus and Fetus
Figure 29–9a, b
Growth of the Uterus and Fetus
Progesterone
• Released by placenta
• Has inhibitory effect on uterine smooth
muscle
• Prevents extensive, powerful contractions
Opposition to Progesterone
• 3 major factors:
– rising estrogen levels
– rising oxytocin levels
– prostaglandin production
Initiation of Labor and Delivery
Figure 29–10
False Labor
• Occasional spasms in uterine musculature
• Contractions not regular or persistent
True Labor
• Results from biochemical and mechanical
factors
• Continues due to positive feedback
Hormone
levels
throughout
pregnancy
Placental hormones
Contractions
• Begin near top of uterus, sweep in wave
toward cervix
• Strong, occur at regular intervals, increase
in force and frequency
• Change position of fetus, move it toward
cervical canal
Stages of Labor
1. Dilation stage
2. Expulsion stage
3. Placental stage
Dilation Stage
•
•
•
•
Begins with onset of true labor
Cervix dilates
Fetus begins to shift toward cervical canal
Highly variable in length:
– typically lasts over 8 hours
Dilation Stage
• Frequency of contractions steadily
increase
• Amniochorionic membrane ruptures (water
breaks)
The Stages of Labor
Figure 29–11 (1 of 2)
Expulsion Stage
• Begins as cervix completes dilation
• Contractions reach maximum intensity
• Continues until fetus has emerged from
vagina:
– typically less than 2 hours
The Stages of Labor
Figure 29–11 (2 of 2)
Delivery
• Arrival of newborn infant into outside world
Episiotomy
• Incision through perineal musculature
• Needed if vaginal canal is too small to
pass fetus
• Repaired with sutures after delivery
Fetal circulation
The Beginning
Next - Inheritance
Cesarean Section
• Removal of infant by incision made
through abdominal wall
• Opens uterus just enough to pass infant’s
head
• Needed if complications arise during
dilation or expulsion stages
Placental Stage
• Muscle tension builds in walls of partially
empty uterus
• Tears connections between endometrium
and placenta
• Ends within hour of delivery with ejection
of placenta, or afterbirth
• Accompanied by a loss of blood
Actual
placenta
Premature Labor
• Occurs when true labor begins before
fetus has completed normal development
• Newborn’s chances of surviving are
directly related to body weight at delivery
Immature Delivery
• Refers to fetuses born at 25–27 weeks of
gestation
• Most die despite intensive neonatal care
• Survivors have high risk of developmental
abnormalities
Premature Delivery
• Refers to birth at 28–36 weeks
• Newborns have a good chance of
surviving and developing normally
Forceps Delivery
• Needed when fetus faces mother’s pubis
instead of sacrum
• Risks to infant and mother are reduced
using forceps:
– forceps resemble large, curved salad tongs
– used to grasp head of fetus
Breech Birth
• Legs or buttocks of fetus enter vaginal
canal first instead of head
• Umbilical cord can become constricted,
cutting off placental blood flow
• Cervix may not dilate enough to pass head
• Prolongs delivery
• Subjects fetus to severe distress and
potential injury
5 Life Stages
1. Neonatal period - Extends from birth to 1
month
2. Infancy - 1 month to 2 years of age
3. Childhood - 2 years until adolescence
4. Adolescence - Period of sexual and
physical maturation
5. Maturity
Colostrum
• Secretion from mammary glands
• Ingested by infant during first 2–3 days
• Contains more proteins and less fat than
breast milk:
– many proteins are antibodies that help ward
off infections until immune system is
functional
Colostrum
• Mucins present inhibit replication of
rotaviruses
• As production drops, mammary glands
convert to milk production
Breast Milk
• Consists of:
–
–
–
–
–
–
–
water
proteins
amino acids
lipids
sugars
salts
large quantities of lysozymes—enzymes with
antibiotic properties
Milk Let-Down Reflex
• Mammary gland secretion triggered when
infant sucks on nipple
• Continues to function until weaning,
typically 1–2 years
The Milk
Let-Down
Reflex
Figure 29–12
Benefits of Breast-feeding
• Acquired immune defenses
– Neutrophils, macrophages, T and B cells
– Immunoglobulin A
• Reduced incidence of later diseases in child
– Lymphoma, heart disease, gastrointestinal
disorders, diabetes mellitus & meningitis
• In mother
– Reduced incidence of osteoporosis and breast
cancer
– Stronger bonding, less post-partum depression,
– More rapid weight loss, uterine recovery
Growth and Changes in
Body Form and Proportion
Figure 29–13
From embryo to fetus