Page 116 - 86 human physiology part-2

Pregnancy and Birth

Second Trimester

20 Weeks

• By 20 weeks the fetus will be about 6 1/3" long and weighs 12 oz. Movements are for more
coordinated. The sexual organs are well developed and are usually visible on ultra sound.
• The fetus is growing very quickly. At this stage, the mother should feel the movements of
the fetus. Movements are more noticeable as the fetus's leg bones achieve their final relative
proportions in a process called quickening. Quickening is the process of muscles contracting
that cause movement at the fetus's sinovial joints. The joint movement enhances the nutrition of
the articular cartilage and prevents the fusion of connective tissues within the joint. It also
promotes bone hardening.
• From now on, the fully developed placenta will provide all the fetus' needs until birth;
oxygen, nutrients and protective antibodies.

Third Trimester

29 Weeks

• By 29 weeks the baby is about 10" long and weighs about 2 lbs. 7 oz.
• The brain grows much larger, and fatty protective sheath covers the nerve fibers; this
important development allows brain impulses to travels faster, enhancing the ability to learn.
The lungs have developed most of their airways and air sacs. The placenta is quite selective in
what it allows to pass from the mother to the baby's blood, stopping some harmful substances,
such as certain drugs, from crossing over.

40 Weeks

• The baby is now ready to be born. When the head of the baby moves down from high in the
mother's abdomen and settles deeper into her pelvis in preparation for birth, it is called
engagement. This can happen any time between 36 weeks and labor.
• In the last four weeks of pregnancy the baby puts on a lot of weight and develops a thick
layer of fat. All organs are completely formed and functioning.

Umbilical Cord

This is the life support for a growing embryo. The umbilical cord stretches between the placenta
and the fetus. This cord contains the umbilical arteries and vein. The umbilical cord forms by week 5 of
conception. The average cord is close to 22 inches long and may have the appearance of a coil. The
umbilical cord is very rich in stem cells and is often used for parents who choose to store their stem
cells in a blood bank or donate it to a blood bank. These stem cells can be used to treat over 45
disorders and is an alternative from extracting the stem cells from a donor.

• Umbilical Arteries

Wikibooks | 331