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Human Development and Pregnancy Chapter 28
Required Figs 28.1, 28.4, 28.6
Developmental Terms
Pregnancy – events that occur from fertilization until the infant is born
Conceptus – the developing offspring
Gestation period – from the last menstrual period until birth
Stages of Development
Preembryo – conceptus from fertilization until it is two weeks old
Embryo – conceptus during the third through the eighth week
Fetus – conceptus from the ninth week through birth
After ovulation, the secondary oocyte is viable for __12__to __24__hours, while
sperm is viable for __24___ to __48__ hours.
Penetration of the secondary oocyte by sperm involves the release of acrosomal
enzymes that digest holes through the transparent layer of the oocyte called the zona
pellucida. This is called the ________acrosomal________reaction.
_______Fertilization____ is when a sperm fuses with an egg (secondary oocyte) and
the chromosomes combine to form a zygote.
To ensure only one sperm enters an oocyte, Ca2+ is released by the oocyte ER, which
causes the _____cortical____reaction, in which release of granules containing enzymes
(ZIPs) destroy sperm receptors, preventing further sperm entry.
Events of Embryonic Development
The first cleavage produces two daughter cells called ____blastomeres_____.
Morula – the 16 or more cell stage (72 hours old)
By the fourth or fifth day the pre-embryo consists of 100 or so cells called a
_____blastocyte____ , which is a fluid-filled hollow sphere composed of:
A single layer of trophoblasts-take part in placenta formation
The inner cell mass-becomes the embryonic disc (future embryo) and some of the
cells develop into a transparent membrane filled with amniotic fluid called the
______amnion________.
Implantation
Implantation begins six to seven days after ovulation when the trophoblasts adhere to a
properly prepared ____uterine endometrium_____________.
-The implanted blastocyst is covered over by endometrial cells
-____human Corionic Gonadotroin (hCG)_______ secreted by tropoblasts prompts the
corpus luteum in ovary to continue to secrete progesterone and estrogen. hCG is
detectable in the blood about _1__ week after fertilization. (Basis for most pregnancy
tests)
-___chorion____ – developed from trophoblasts after implantation, continues
this hormonal stimulus, which develops into part of the placenta.
-Implantation is completed by the __12th__day after ovulation
Gastrulation
The blastocyst develops into a gastrula during the 3rd week with three primary germ layers
which develop into all the tissues and organs of the body and are called:
1. endoderm
2. ectoderm
3. mesoderm
Organogenesis
Organogenesis is the formation of ___body organs & organ systems______.
By the end of the ___8th__ week of development, all organ systems are recognizable.
Placentation
Placentation is the formation of the tempory organ called the _____placenta______from:
Embryonic trophoblastic tissues
Maternal endometrial tissues
Placentation begins at approximately 12 days of development.
The chorion develops fingerlike villi, which:
Become vascularized
Extend to the embryo as umbilical arteries and veins
Lie immersed in maternal blood
By the second to third month, the placenta:
Assumes the role of progesterone and estrogen production
Is providing nutrients and removing wastes
The placenta is formed and fully functional by the end of the ______3rd______ month
*Note that plancentation overlaps with some other processses of development.
Changes During Pregnancy
The placenta secretes______human Placental Lactogen____ (hPL) which stimulates
maturation of the breasts for lactation and promotes growth of the fetus.
_human Chorionic Thyrotropin___ (hCT) increases maternal metabolism
Morning sickness can occur due to elevated levels of estrogen and progesterone.
Maternal blood volume increases _____25-40%_________%
Urine production increases to handle additional fetal wastes.
As birth nears, ____oxytocin______ and __________prostaglandins________cause
uterine contractions of labor.
False labor contractions are called ___Braxton Hicks____ contractions.
The proces of giving birth to a baby is called_____parturition_______ ,and the 3
stages that expel the infant from the uterus are called ___labor________.
Hopefully, the birth goes smoothly and the baby is born healthy .
What are teratogens?
Factors that may cause severe congenital abnormalities or even fetal death.
In addition to nicotine and alcohol, what 4 classes of drugs can be teratogens?
1. Anticoagulants
2. Sedatives
3. Anti-hypertensives
4. Some antibiotics