Health Sciences 2711A/B Chapter Notes -Erythropoiesis, Microcephaly, Embryonic Disc
This preview shows pages 1-2. to view the full 7 pages of the document.
September 28, 2009 Readings
Berk pp. 60-77
•ovum is a tiny sphere, measuring 1/175 inch in diameter
•although it is invisible to the naked eye, it is a giant to the microscopic world.
•sperm is 1/500 inch
•if the ovum is not contacted by the sperm, pregnancy does not occur and it is
discarded 2 weeks later by menstruation.
•sperm is produced 300 million a day in the testes
•sperm live up to 6 days and can lie and wait for the ovum
•corpus luteum: the spot on the ovary from which the ovum was released
•secretes hormones that prepare the lining of the uterus to receive a fertilized ovum.
•ovum only survives for 1 day after being released into the fallopian tube
•38 weeks of pregnancy divided into three stages:
•lasts about 2 weeks (from fertilization in the fallopian tube until the cell is released
into the uterus)
•by the 4th day, 60-70 cells ﬁll the hollow, ﬂuid-ﬁlled ball called a blastocyst
•inside the blastocyst, are embryonic disks, which are the cells inside
•the outer ring of cells are called the trophoblast
•Implantation: between 7th and 9th days after fertilization, this is when the
blastocyst buries itself deep into the uterus lining.
•trophoblast multiples and forms a membrane called the amnion, that closes the
organism in amniotic ﬂuid (helps keep temperature and provides cushion)
•yolk sac emerges and produces red blood cells until the liver, spleen, and the
bone marrow are mature enough to take over this function.
•30% of zygotes do not survive these ﬁrst 2 weeks
•The Placenta and the Umbilical Cord:
•trophoblast forms another membrane called the chorion, where tiny blood
vessels (villi) emerge.
•as the villi buries itself into the uterine wall, the placenta forms.
•placenta permits food and oxygen to reach the organism and waste products to
be carried away
•placenta is connected to the organism by the umbilical cord (contains one large
vein, and two arteries)
•vein: delivers blood with nutrients
•arteries: remove waste products
•last from implantation to the 8th week of pregnancy (in a span of 6 weeks)
•groundwork of all body structures and organs are done
•The Last Half of the First Month:
Only pages 1-2 are available for preview. Some parts have been intentionally blurred.
•in the ﬁrst week of this period (3rd week of the month) the embryonic disk forms
three layers of cells:
•ectoderm --> nervous system and skin
•mesoderm --> muscles, skeleton, circulatory system, and other internal
•endoderm --> digestive system, lungs, urinary tract, and glands
•ectoderm folds over to become the neural tube --> spinal cord and brain
•neurons form, heart begins to pump blood, and the muscles, digestive tract,
backbone, and ribs appear
•embryo is only 1/4 inch long at this point
•The Second Month:
• the eyes, ears, nose, jaw and neck form
•intestines grow, heart develops separate chambers
•liver and spleen take over the production of making red blood cells
•embryo can now move, but still too tiny to be sensed by the mother
•9th week to the end of the pregnancy
•The Third Month:
•brain starts to signal, fetus starts to kick, bend its arms, etc
•tiny lungs start to work
•by 12th week, external genitals begin to form, sex of fetus can be determined
•heartbeat can now be heard
•1st trimester of the pregnancy is complete at the end of the 3rd month
•The Second Trimester:
•between 17-20 weeks
•vernix forms - protects skin from chapping during the long months spend
bathing in the amniotic ﬂuid.
•lanugo forms - white, downy hair covering the entire body, helping the vernix
stick to the skin
•brains neurons are in place
•organs are well-developed
•glial cells are still forming (still continues to even after birth)
•brain growth = new behavioural capacities
•The Third Trimester:
•age of viability - the point at which fetus can ﬁrst survive, between 22 and 26
•cerebral cortex enlarges
•greater responses to stimulation
•temperament begins (fetus may get a fever = active in ﬁrst year of life)
•during the ﬁnal two months, fetus can distinguish tone and rhythm
•gains 5 pounds and grows 7 inches
•Teratogens: an environmental agent that causes damage to the baby during the
•harm of the teratogen is dependent on dosage, heredity, age, and other negative
You're Reading a Preview
Unlock to view full version