BIOLOGY 2D03 Study Guide - Pulmonary Artery, Aorta, Umbilical Vein

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30 Jan 2013
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Early Development of the Zygote to a Blastocyst (1st Week)
Ovulation releases ovum/secondary oocyte
Fertilization in the oviduct → produces zygote
Zygote undergoes cleavage as it moves along oviduct → produces morula
o As zygote divides, cells become smaller \ Morula stays same size
o Movement by cilia and peristalsis present in oviduct walls
Morula develops into a blastocyst
o Trophoblast (outer layer of blastocyst) → nourishes future embryo
o Inner cell mass → will become fetus
o Fluid filled cavity → for protection (absorbs shocks, resists compression, ...)
Blastocyst (≈100cells) implants itself in uterus lining
o Nourished by secretion from uterus
o Microvilli provide large surface area (→gas + nutrients exchange)
Implantation Of The Blastocyst Into The Uterine Lining
(2nd Week)
Trophoblast secretes enzymes → digest tissues and blood vessel of endometrium
Embryo uses released nutrients/products from digestion
Blastocyst becomes buried within endometrium
Microvilli are replaced by placenta
Trophoblast secretes human chorionic gonadotrophin (hCG) hormone
The Developing Fetus
During gestation (→length of pregnancy) growth rate is in excess
Placenta is the first organ to develop when blastocyst embeds itself in uterine lining
o Growth faster than embryo in early pregnancy
Development increases in complexity
o Differentiating of inner cell mass of blastocyst
o First month → beginning of a gut, developed kidney, brain, beating heart
o Second month → all main organ systems present; embryo is called a fetus
At the end of gestation placenta is discarded, but essential for the 1st 9 month of life
Features of the Circulatory System of the Developing Fetus:
Placenta is the Fetal Gas Exchange Organ → Fetal Lungs are Non-Functional
Umbilical vein carries oxygenated blood from placenta to vena cava
Blood in the heart bypasses through foramen ovale
Oxygenated blood flows from right into left atria / flap valve prevents back flow of blood
Some blood in right atria passes to right ventricle into pulmonary artery (to lungs)
Blood bypasses lungs through ductus arteriosus
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