male, female essentials for reproduction
gametes, 5 parts of sperm, ovum, ovaries, follicles, corpus luteum, projesterone,
fallopian tubes, fimbriae, uterus, endometrium, zygote

Friday, 9/17 - Film - The Miracle of Life

Chapter 3:

DNA, mitosis, meiosis, monozygotic/dizygotic, dominant/recessive traits,
genotype/phenotype, homozygous/heterozygous alleles, PKU,
polygenetic inheritance, X-linked genes, behavioral genetics,
karyotype, amniocentesis, CVS, ultrasound,
Temperament, multifactorial transmission, infertility,
artificial insemination, in vitro fertilization,

Interaction of nature and nurture
Twin studies, adoption studies
influence on intelligence, influence of genes and environment on personality,
influence on psychological disorders

9/13/00 - Film: The Miracle of Life

The Woman:

By the fifth month of her own prenatal development, all the eggs a woman will ever produce (5 million) have already formed in the ovaries of the fetus.

If the woman’s mental state is in equilibrium, the pituitary gland (in the brain) is instructed (by the hypothalamus) to secrete special hormones into the blood stream, which reach the ovaries.

The ovaries respond by increasing their production of the female sex hormone estrogen.

Simultaneously, an ovum (egg) starts to ripen in one of the ovaries.  This will lead to ovulation.  The release of the ovum from the capsule-like structure which contains it: the follicle.

As ovulation approaches, vaginal mucus becomes more abundant.  At the time of ovulation, the mucus becomes capable of forming a thread.

Checking these changes in mucus, and body temperature, are at the heart of natural family planning.

Two weeks after the beginning of the menstrual period, the follicle containing the ovum is ripe.

Suddenly the follicle ruptures, and the ovum is discharged through the surface of the ovary where it is caught up by the fallopian tube. The fallopian tube "pulls" the ovum in because the cilia lining the fallopian tube are creating a "current" of abdominal fluid that travels into and down the fallopian tubes.

It may be fertilized within the next 24 hours – if it is not it begins to disintegrate and die.

Once the follicle has ruptured, it is transformed into a structure known as the corpus lutheum, which forms large quantities of progesterone for the next two weeks.  This hormone enters the blood stream, altering the endometrium, the lining of the uterus, preparing it to receive the fertilized ovum.

In this way the uterus is prepared for pregnancy every month.  If fertilization does not occur, the outer layers of the endometrium are shed, causing the superficial capillary damage and the bleeding that we call menstruation.

These changes will occur monthly until about age 50, when ovulation ceases, a phase we call menopause.

Ovulation

When the egg is ripe, the portion of the follicle facing the abdominal cavity ruptures and the fluid and egg run out.

The fallopian tube has received signals as to the location of the bulging follicle; the fimbriae, finger-like projections at the end of the fallopian tube, sweep across the ovary near the bulging follicle, awaiting its rupture. The fimbriae actually "know" where to position themselves by detecting hormones secreted by the follicle.

After the follicle ruptures, it seals itself and transforms into a hormone-producing gland known as the corpus luteum.

A change in the information sent to the ovary by the brain and pituitary glad can result in more than one ovum being released at the time of ovulation:  either one ovum from each of the ovaries or two (or more) from the same ovary.  Twins or triplets are the result. If this happens, the result is always non-identical (fraternal or dizygotic) twins, which may be of different sexes.  They are no more alike than any other two siblings.  Identical (or monozygotic) twins, on the other hand, result from the fertilization of a single egg cell that then divides into two equal parts; thus the fetuses are of the same sex and are genetically identical.

The Man

Sperm cells originally have 46 chromosomes, but divide during development to have only 23 chromosome each.  Since all male cells have an X and a Y sex chromosome (which makes them male), when these sperm cells divide (meiosis), one chromosome is taken by one of the sperm cells, and one chromosome is taken by the other sperm cell. As such, each sperm cell ends up with one sex chromosome – either an X or a Y chromosome.  If a sperm cell with an X sex chromosome fertilizes an ovum, the baby will be female; if a sperm cell with a Y sex chromosome fertilizes an ovum, the baby will be male. There is some evidence that "male" sperm cells are lighter and therefore swim faster, making it more likely that a male sperm cell will fertilize the egg; this might explain why there are more males conceived than females.

As with the woman, hormones from the pituitary gland in the brain are primarily responsible for sexual maturation and the initiation of sperm production.  The pituitary is controlled by the hypothalamus, which is sensitive to different hormones in males and females. In males the hypothalamus is sensitive to testosterone.

At puberty, the pituitary gland secrets hormones into the blood stream that are sensed by the testicles, which increase the production of testosterone.

Testosterone is responsible for secondary sex characteristics, such as the voice “cracking”, body growth, and body hair.  It also causes the sperm to mature and the sex organs to become fully operative.

Every day, a healthy young male produces nearly 100 million sperm, or 1,000 sperm per second.  The sperm are produced in the long, convoluted passageways of the testes known as the seminiferous tubules.

Each sperm is made of a head, which contains the genetic material and is covered by a cap-like structure, called an acrosome, which contains enzymes that help the sperms to penetrate the wall of the ovum.

In each ejaculation, perhaps 500 million sperm are discharged.  But about half of the sperm produced have small defects that prevent them from fertilizing an ovum.

At ejaculation, the sperm (which account for less than 1% of the volume of semen, the fluid which is ejaculated) are thrust at great speed through the vas deferens and the urethra.  There they mix with a secretion from the prostate gland containing substances that facilitate their long journey to the female ovum.

Fertilization

The moment the sperm and egg fuse.

If the ovum is not fertilized, it degenerates and travels down the fallopian tube into the uterus and then the vagina.  The woman then has her menstrual period two weeks later.

During intercourse, sperm are ejaculated against the opening of the cervix at the far end of the vagina.  The journey of about 6-7 inches from vagina to fallopian tubes generally takes several hours.

If no egg is available for fertilization, the sperm swim around the fallopian tubes, some spilling out into the abdominal cavity among the intestines and other organs.

Sperm and egg cells may or may not be attracted to each other by chemicals. New evidence suggest they might send signals that serve to attract each other.

The long survival time of sperm, especially in the folds of the cervix, means that intercourse four to eight days before ovulation can result in fertilization.  But conception is far more likely if intercourse occurs while a woman is ovulating.

The sperm must swim up current, for the cilia that are beating in rhythm to send to ovum down to the uterus and waving in the opposite direction that the sperm want to go.

About 50 to 100 sperm reach the ovum (50 out of the 500 million that were ejaculated!).

The enzyme cap of the sperm, upon reaching the ovum, now acts to strip away the protective covering of the ovum.  The enzymes come off the head of the sperm and create an opening in the egg.

At the time when one sperm penetrates the inner cell plasma of the ovum, a chemical change occurs in the ovum wall, and all other sperm are shut out.  After 20,000 tail thrashings, one sperm is the winner!

The excluded sperm continue to jostle around the ovum with undiminished strength for several days.

After gaining entry, the sperm drops its tail.  All that is left is the head with the genetic material.

The inner substance of the ovum moves vigorously, forcing together the head of the sperm and the nucleus of the ovum, each containing genetic material, 23 chromosomes each.  When they reach each other, they fuse, and the outer walls of the nuclei dissolve.This one cell now has 46 chromosomes, and is called a zygote.

Roughly 12 hours after the fusion of chromosomes, the first cell division takes place, and divisions then continue at intervals of 12 to 15 hours.

With each cell division, the 46 chromosomes split and recombine with material available in the environment to make two cells from one, each with 46 chromosomes.

The cells divide every 12 to 15 hours. The cilia of the fallopian tube continue to propel (with the help of the "loser" sperm) the zygote toward the uterus. If the zygote implants in the fallopian tube, or in the abdominal cavity, it is called a tubal or ectopic pregnancy.

The ovum remains in the fallopian tube for about 3 days after fertilization.  Passing into the uterus, it must now attach itself to the uterine wall.

When the blastocyst implants on the endometrium, the blastocyst releases hormones that enter the woman’s bloodstream.  These can be detected through a blood test, and as such pregnancy can be detected with a high degree of certainty well before the first menstrual period has been missed.

Other proteins released by the blastocyst weaken the woman’s immune system in the uterus, so that the woman’s body will not reject this object, which is made up of foreign material (foreign is anything that doesn't have the woman's own protein "signature," or that which her own body cells have). Ever since the genes of the ovum and the genes of the sperm combined, the “tissue” that is the zygote is a totally new set of material, just as if foreign tissue had been inserted into the woman’s body.

The whole lining of the uterus, the endometrium, becomes thicker once the blastocyst has implanted.  The passage way out of the cervix becomes sealed with a plug of mucus.

Until about the 8-cell stage, all the cells are exactly alike.  Then differentiation begins, as cells begin to form that are different from each other.

By the 12th day, the cells are dividing roughly twice a day and number a couple of thousand.

Early miscarriages, which the woman is unaware of, are common.  This normally occurs when there is a serious chromosomal problem.  This is nature’s way of protecting itself from abnormalities.

Hormonal Changes

The woman knows she is pregnant often as early as a week after ovulation.  The first signs are often swelling, tender breasts, slight nausea, and heightened sensitivity to odors and flavors. Tiredness is also common.

The blastocyst divides into two groups of cells: one will form the embryo (blastocyst) and the other the placenta (trophoblast).  The first thing the placental cells do is send a hormonal signal to the ovaries that no more ovulations are needed for a long time. This coincides with the "death" of the corpus luteum (so, the placenta takes over the job the corpus luteum was performing - telling the body to NOT produce more mature eggs and to NOT go through menstruation).  Also, the ovary then secretes more progesterone, which causes the endometrium to grow and flourish.

The growing placenta also secretes progesterone, and by 7 or 8 weeks the ovaries are no longer needed to produce progesterone.

At three weeks, the neural tube begins to form.  This tube will close and form the spinal cord and brain.  Three different layers of cells differentiate into cells that will form the (1) backbone, brain, nerve cells, skin (2) bones, muscles, blood, lymph vessels, heart, ovaries, testicles, kidney (3) intestinal tube, lungs, urinary tract.

The yolk sac produces red blood cells and stem cells, which will become the immune system’s white blood cells; the embryo has its own blood, separate from the mother’s.

At four weeks, the heart starts beating.

Five weeks after fertilization, the embryo is roughly ½ an inch long.

At six weeks, the spinal cord shimmers through the thin skin, while the vertebra are beginning to develop.

The cells of the placenta penetrate the blood vessels of the endometrium in order to gain access to the nutrients in the mother’s blood.  The placental barrier also protects embryo from any dangerous substances in the mother’s blood.

The umbilical cord carries oxygenated blood and nutrients to the embryo, and transports deoxygenated blood and waste products back from the embryo.

As early as the seventh week, dendrites of neurons in the brain have begun to make contact with one another. 100,000 new neurons are created each minute, and at birth there will be some 100 billion neurons.

At 8 weeks, all organs are in place, and the embryo is still only 1 ½ inches long.  At this point, biologists and pediatricians refer to the being as a FETUS.  Hormonal changes in the mother become less dramatic, and nausea gradually subsides.

Tests used to determine the health of the fetus include amniocentesis, in which a sample of amniotic fluid is extracted from the amniotic sac via the mother’s abdomen, and the chromosomes examined.

The average pregnancy lasts 280 days. Births two weeks late or two weeks early are common.  A weight increase of 25-30 pounds by the end of pregnancy is the optimum goal.

Alcohol and nicotine are dangerous to the fetus, and both cause abnormalities.  Nicotine and carbon monoxide pass through the placental barrier and into the fetal bloodstream.

Ultrasound is usually performed in the 16th or 17th week.

Fetal Development

In the third month, the organ systems are becoming interconnected

As early as the 11th week, the yolk sac ceases to be necessary; thereafter blood cells are formed in the liver and spleen, and bone marrow.

At 11 weeks old, the fetus can move its arms and legs.

By 11 to 12 weeks the face is beginning to look human,

A fetus begins to react to sound between the 4th and 5th month.  It can hear and respond to sounds outside and inside of the womb.

In the third month the entire fetus is covered by hair called lanugo.  The lanugo disappears before birth and we still do not know its purpose. It is probably a vestige of our "uncivilized" or primate-like past.

During the first 1 1/2 months of fetal development, it is impossible to tell boys from girls with the naked eye.

A fetoscope may also be used to look at the fetus in the womb.

About halfway though the pregnancy (18-20 weeks), the woman will first notice the movements of the fetus.

During the last two months of prenatal development, the fetus gains ½ a pound per week.

At about the 7th month the fetus runs out of available room to move around.

Toward the end of the pregnancy, weight gain (25-35 lbs.) begins to be a problem for the mother.

In 97% of the cases, the fetus is positioned head down. If it isn't, the doctor can try to turn the baby, called external cephalic version (ECV).

Babies positioned in breech position are often best delivered by cesarean section.

Labor and Delivery

Three definite signs that delivery is imminent: regular contradictions, water breaking, and a “show” of mucus sometimes mixed with blood.

Contractions at intervals of less than 10 minutes are a reliable indication that labor has begun.  At about 5 minutes apart, it is time for admission to the hospital.

Labor sometimes begins with amniotic fluid gushing out of the vagina - water breaking – amniotic sac.

Labor is usually divided into 3 stages:

dilation stage: begins when contractions start or the membranes rupture.  The cervix gradually opens, until it is fully dilated at about 10 centimeters, or about 4 inches.  At the same time the baby’s head pushes and rotates downward toward the pelvis.  This stage takes 6-20 hours, the longest stage.

expulsion stage: lasts from the time the cervix is fully dilated and the baby’s head becomes engaged in the pelvis until the baby is born,  This is the pushing stage, and varies from just a few minutes to just over an hour.

An epidural anesthetic is commonly used to lessen the mother's pain during delivery.  Using a needle, an anesthetic is injected directly into the spinal canal, numbing the nerves as they exit the spinal canal.  This may lessen the mother’s ability to bear down, which may result in the doctor having to use forceps.

After birth

The umbilical cord is cut shortly after birth, although the placenta remains in the uterus, where it gradually begins to come loose.

The mother must bear down and push out the placenta.  The uterus can now contract and return to original size. In fact, breast feeding triggers the uterus to begin to return to normal size.  The doctor checks to see if there is any tearing in the vagina or perineum, and sew this up if so.

Within an hour the infant will show it is hungry by exhibiting the rooting reflex, showing that it is seeking the breast.

The newborn baby can and will suckle milk from the breast. The baby’s sucking is also necessary to "jump start" milk prodution in the mother. A nerve reflex from the nipples causes the brain to instruct the pituitary gland to secrete prolactin, from the pituitary milk production. Another hormone, oxytocin, from the pituitary simultaneously affects the milk gland and ducts, causing the milk to be squeezed out of the breast.

In the first few days, the milk contains colostrum, which is important for "jump starting" the baby’s immune system.  After two or three days, the mother's milk begins to flow more regularly.

Breastmilk contains all the nutrients and minerals the baby needs, superior than any that can be manufactured. Plus, it's always the right temperature!

Newborns see best at a distance of 8-10 inches, about the distance at which they see their mother’s face when breast feeding.