Mitosis and Meiosis

In MITOSIS, the 2 daughter cells formed in the division have the same in genetic makeup as the parent cell. They have the same DNA and thus make the same proteins and behave the same.
In MEIOSIS the cells are not identical. The gametes, eggs and sperm, are products of meiosis. There is a blend of genetic material from the mother via the egg and father via the sperm. Meiosis is necessary for genetic diversity. It also explains why an individual may have traits from a grandparent. The parent may not have that trait but carries it in their genes.
Meiosis can be a complicated subject because we have 2 of every chromosome and therefore 2 of every gene even before the DNA replication that preceeds mitosis. As well, there's a chance that 2 copies of the same gene are different. An example is a trait which appears in both a grandparent and a grandchild although the parent does not have the same trait. The parent was a carrier of said trait although he or she does not present with it.
The mixing of genetic material comes about after the DNA replicates in preparation for cell division. This involves chromosomes breaking apart and joining back together.
Here is an animated movie of meiosis at http://www.biology.yale.edu/animatedMeiosis.nclk Note the red and green chromosomes at the beginning and the mixed ones at the end.

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cellular respiration

This site breaks down the process of cellular respiration. It is written in a way that a person with some understanding of biology will be able to learn the process. I appreciated it because the chapter in my textbook was a bit convoluted.

Exciting Info about Reproduction

Sexual reproduction provides genetic diversity through recombination. This genetic diversity may serve the population well as the environment changes or as the population expands into new environments. The adaptability resulting from genetic diversity is the major advantage of sexual reproduction over asexual reproduction, although sexual reproduction can also break up well-adapted combinations of alleles through the same process of recombination.
Asexual reproduction is the only way of raising plants such as navel oranges, all of which have been reproduced from a single tree found in on a plantation on the Brazilian coast in the early 19th century.
http://www.filefarmer.com/2/successus/Books/Ch39.pdf

Alkalinity and acidosis of the blood

In humans, a normal pH of all tissues and fluids of the body is slightly alkaline. The most critical pH is in the blood. All other organs and fluids fluctuate in their range in order to keep the blood at between 4.35 and 7.45 pH

If the blood becomes too acidic then it robs some of the alkaline forming elements from the enzymes in the small intestine to maintain homeostasis. The small intestine then becomes to acidic to digest foods properly. The pancreas, gallbladder and liver must then work harder to make up for this deficiency in order to metabolize foods properly. This negatively impacts metabolic enzyme production, resulting in lowered immune function, fatigue, hormonal imbalances and absorption and digestive problems.

The bones begin to leach calcium when pH is too acidic, resulting in bone density problems.

Insulin levels increase and fat is stored rather than being metabolized.

Electrolyte imbalances occur that can negatively impact the nerve, heart and muscle cells.

A hyperalkaline state can cause muscle cramps and weakness.

Amoebas

Come look at some excellent photographs of the most famous one-celled animal.

Chemical Overuse

Here is a discussion post that I created for my biology class.

Chemicals can be useful in that they can eradicate disease carrying and crop destroying pests. But there may be ways to do this that do not involve chemicals. In terms of crops, natural predators can be introduced to eat the pests, as long as these predators are native to the areas they are being introduced to and won't disrupt the ecosystem. Praying mantises have long been favored for eating pests such as potato bugs. Ladybugs eat aphids. And dragonflies consume mosquito larvae.
Another problem with chemicals is the fact that they don't discriminate between which bugs are helpful and which are pests. They kill everything. Populations of natural predator insects have been badly damaged by the widespread use of chemicals to control garden pests and weeds. The time may be right to start re-introducing these natural predators and to cut back on the use of chemicals to control pests.
The chemicals used are not healthy for animals either, and this includes humans. If enough of them are introduced into the system of a larger animal such as a human, over time they will begin mutating cells into cancer cells. The lymph system will be overwhelmed, unable to trap and destroy all of these cancer cells, and the affected organism will develop cancer. And, as in the case of DDT, the shells of birds in areas exposed to the pesticide over a long period of time became thin and fragile due to mutations.
According to the Agency for Toxic Substances and Disease Registry
"Exposure to DDT, DDE, and DDD occurs mostly from eating foods containing small amounts of these compounds, particularly meat, fish and poultry. High levels of DDT can affect the nervous system causing excitability, tremors and seizures. In women, DDE can cause a reduction in the duration of lactation and an increased chance of having a premature baby. DDT, DDE, and DDD have been found in at least 441 of the 1,613 National Priorities List sites identified by the Environmental Protection Agency (EPA)."
Cutting back on the use of toxic substances in agriculture will reduce contamination of ground water and may in the long run reduce the incidence of cancer.

Bedbugs

I was reading where the incidence of bedbug infestation has been on the rise in the United States and it crosses class barriers. It seems to be due to increased international travel and decreased use of certain pesticides. On the upside, these pesticides are carcinogenic, so less is better. Also, bedbugs, though vile, are generally not vectors for disease the way fleas, ticks and mosquitoes are.

I work in an upscale retirement community and we do have folks here who still travel frequently. We have had a few instances of bedbugs. The interesting thing about bedbugs is that they do not hide in mattresses the way many people think. They hide in the cracks of the bed, or in surrounding furniture. There are nontoxic powders containing diatoms that can be sprinkled in the cracks of furniture.

My ex husband rides the bus that comes from the airport when he comes to visit our son on the weekends. A couple of times bedbugs have hitched a ride on his backpack. I've eradicated them using this type of powder a couple of times. But it's kind of like a Stephen King story. They come back. I'll know they're back when I find itchy bites on my arms. Bastards!

For all their persistence, bedbugs are not high on the intelligence scale. At work last night I was doing something on the computer. I turned around to look at my lab book and there, bold as brass, sat a bedbug. Right in the middle of the lab book. Big sucker it was too. (For a bedbug, big is about the size of a pin head.) Had gotten fat and happy feasting off the blood of the elderly and was now coming to see me. I grabbed a Kleenex, plucked it off my book, and squashed it. That will teach it to be cocky!

It's nice to know that there are non-poisonous methods of dealing with these miniature vampires. Perhaps my next book should be titled Night of the Bedbug. Now that's a real vampire, and a real nightmare!

Thumb Dominance Experiment

DOMINANT THUMB EXPERIMENT

ABSTRACT
The hypothesis of the experiment states that when people clasp their hands, the thumb of the dominant hand may overlap the thumb of the non-dominant hand. The experiment is conducted to determine whether there is a correlation between which thumb is on top when the hands are clasped and hand dominance.

HYPOTHESIS
In theory, the thumb of the dominant hand should be on top when the hands are clasped.

RESEARCH DESIGN AND TESTING
Fifty volunteers were located to participate in the study.

PROCEDURES
The subjects were asked to state which was their dominant hand, then to clasp their hands together and see which thumb ended up on top.

SUMMARY OF DATA
SUBJECTS NUMBER % OF TOTAL SUBJECTS
Right handed with right thumb dominant (7) 14%
Right handed with left thumb dominant (34) 68%
Left handed with right thumb dominant (4) 8%
Left handed with left thumb dominant (5) 10%
Total number of experimental subjects (50) 100
Number of subjects per category divided by total subjects 100

RESULTS
As is shown in the table, 68% of subjects were right hand dominant with left thumb dominant. 14% were right handed with right thumb dominant. 10% were left handed with left thumb dominant and 8% were left handed with right thumb dominant. The majority of people in the world are right handed and that was reflected in this experiment. It is interesting to note that overall, thumb dominance is seen to be the opposite of hand dominance. This is overwhelmingly true with the right handed subjects. However, in the left handed subjects, a small majority had left thumb dominance. It is uncertain why this would be the case.
Overall, the hypothesis that thumb dominance should match hand dominance was disproven. However, the question remains as to why it appears that in left handed persons, thumb dominance generally matches hand dominance.

Alcohol and other teratogens in pregnancy: my experience

Alcohol is the most common teratogen in developed nation. Children with fetal alcohol syndrome tend to have specific facial deformities including widely spaced eyes and an abnormally thin upper lip. They often have developmental delays, both physically and mentally. They tend to have learning disabilities.
The amount of alcohol consumed in pregnancy has an effect on how badly affected the child will be.
When I became pregnant I had been told that I could not get pregnant. I was drinking fairly heavily at the time. Once I discovered I was pregnant I quit drinking and smoking. However, I was also taking synthyroid and Inderal, which I continued to take throughout the pregnancy. I was somewhat angry when I later discovered that the Inderal was probably unnecessary. It had not been prescribed for high blood pressure but for a mild tremor in my hands, which in monitoring myself I discovered only happens during my period.
My son wasn't technically low birth weight. He was born two weeks early by induced labor and, as it turned out, cesarean section, because I had toxemia. This is fortunate because I had also contracted campylobacter from chicken I had eaten at a restaurant and while a healthy adult can recover from this, it can kill a fetus. It was lucky that he was delivered by c-section because he could have contracted it if he had been delivered normally and could have died from the resulting infection. As it was I became very dehydrated due to the horrific diarrhea caused by this vile microbe, and I am not a small person. For a tiny infant, the loss of fluid and electrolyte imbalance would likely have been deadly.
I am not sure how much effect my drinking and smoking before realizing I was pregnant had on my son's birth weight. He was 5 pounds 12 ounces and there didn't seem to be any fat on his body. I ate well enough but wasn't particularly good about taking my calcium supplements and I think he must have been leeching calcium from my bones because I constantly craved dairy products, particularly chocolate milk and chocolate pudding.
I do know that Inderal can cause low birth weight, which is why I'm angry that the doctors thought I should continue taking it. I haven't read of any detrimental affects from taking synthyroid during pregnancy.

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999 Eyes Sideshow

There are those that will disagree with me, but after hearing the freaks speak out on the Discovery health channel show, I say that they have every right to earn THEIR OWN LIVING showcasing their different physiotypes. I do not use the term "freak" disparagingly. This is what they call themselves, and this term describes anyone who doesn't fit the "norm." Although I look "normal" on the outside, I too am a freak. More on this in a moment.

999 Eyes is a sideshow in the old style tradition. But let me borrow this paragraph from the home page because it says it better than I can.

The 999 EYES Authentic Freakshow explicitly celebrates real genetic diversity by showcasing amazing feats performed by LIVING HUMAN ODDITIES! The freaks share real stories of what it is like to be born truly different from the average 10 fingered and 10 toed genetic blueprint for humanity – giving folks from all corners a chance to realize that what is different in beautiful. We present as guests Human Marvels and Sideshow artists, such as the Leopard Man and the Human Blockhead for their fantastically adorned bodies and wondrous sideshow skills. In this show, one must be born physically and obviously different from the vast majority of humanity to be considered a true freak. The 999 EYES freaks are performers who choose by their own free will to celebrate their medical anomaly on stage. The 999 EYES supports rights for differently-abled people, and we play only in wheelchair accessible venues.

Thank you for doing it! It isn't only the so called "beautiful" people who should be able to excel in this world. Why not the truly different? Why not the "handicapped?" I usually hate P.C. terms, but these people are true illustrations of what it means to be "differently abled." I hate the idea that the world has to be a place enslaved by a very constrained definition of beautiful and those who do not fit this definition should do a favor to those whose eyes and delicate sensibilities would be offended and hide away.

My handicap is not obvious from the outside. I have a mental handicap and I do have a physical handicap which isn't obvious. I have bipolar disorder. Often I can function "normally," whatever that may be. But at other times I wrestle with a mind that seems hell bent on killing me and although I take Lithium to control my mood swings, nothing is perfect and, in the same way that a diabetic's medications sometimes fail them, Lithium sometimes fails to do the job for me. Before diagnosis I was at the mercy of my mood swings. I know that I'm different from other people and there are those who want a "perfect" world who would say that a person like me should keep away from "normal" people. But I have the right to make a living and maybe even make an impact.

I also deal with fibromyalgia, which while it does not in any way distort the limbs can occasionally be, if not crippling, physically compromising. I have a relatively mild case, but sometimes it makes me very tired and I have difficulty concentrating. The muscle soreness is of the low grade variety, but it is from head to toe. It was worse when I was working a job that was very physically demanding. I would be sore and tired for days and missed a lot of work. I was ashamed of how "lazy" I appeared to be.

I am not ashamed of my handicaps but most of my co workers still do not know that I am bipolar. They know about the fibromyalgia and the hypothyroidism. These are "acceptable" diagnoses. Mental illness is still shrouded in shame. Which is why the world needs a freak like me to tell it like it is.

So, far from saying "those poor people" regarding the side show performers, I say "let them speak out! Let them tell it like it is! Let them show off their unique body types, their unique abilities. Right on, Freaks!"

Besides, for fuck's sake, they're a hell of a lot more interesting than Paris Hilton or Lindsay Lohan on their worst day!

This freak is trying to make an extra buck or two with some affiliate marketing. I find programs I think that people really might be interested in and insert them at the bottom of my posts. No, I won't come to your house in the middle of the night with a gun and make you order anything. But I might send Axe Man to your house naked. So...the choice is yours!

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KCKmedical.com is America's leading online medical retailer. We deliver non-prescription medications and health related products at substantial savings direct to the consumer. We service thousands of customers nationwide from one location.

Phreequeshow

I am currently taking Human Growth and Development and we are studying genetics and congenital abnormalities. Phreequeshow is a site which educates about various genetic abnormalities in a way that is at once entertaining, educational and respectful.
I once watched a program about "Freaks" and was struck by the fact that many of the sideshow performers were upset about the people who were trying to protect them from exploitation. As one man said, "these people are trying to take away my means of making a living!"
Many "freaks" stated that they were well treated and respected as performers and that in many ways they called the shots. They were not "owned" by the carnival management, they were contract performers.
As long as we are respectful of others, why not allow them to make their living by capitalizing on their differences? Then instead of a handicap, it can be an asset. They can educate others that one doesn't need to be perfect or even "normal" to be a valid and valuable member of society even as they entertain and amaze. I am often inspired when I see a person with what might seem monumental handicaps triumph. In this world we have to use the abilities that we've been given, and sometimes those abilities are disguised as disabilities.
Besides, I think that Aloa the Alligator Boy would be a far more interesting person than Paris the Attention Whore.
From what I've found, I say let the "Freaks" have their show. They deserve to be in show business as much as the so-called "Beautiful" people!

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Hypochondriac

You Are 43% Hypochondriac

You can deal well with being sick - even if your symptoms are a little scary.
You're occasionally prone to worry about your health, but only when you have pretty strange symptoms.

Are You a Hypochondriac?
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Ear Wax

Who would have thought a little ear wax could cause so many problems?

At the end of December, I ended up in the emergency room. I felt dizzy and was walking like I was drunk. My blood pressure was 180/100. I was nauseated. I thought that I was having a neurological problem.

I had hardened wax jammed against the ear drum.

When the wax was removed with a jet of water (a very uncomfortable sensation!) by the ER nurse, my blood pressure came back down to an acceptable 140/80.

Some people produce more ear wax than others. If ear wax were a commodity, I'd be in high demand!

Sometimes people think they're losing their hearing, but their ears just have too much wax. When the wax is removed, they can hear just fine.

Here is a page all about ear wax.

And now you know more than you ever wanted to?

Glucophage and PCOS

I have just started taking glucophage, not for diabetes but to combat the symptoms of polycystic ovarian syndrome. It is a last-ditch effort to try and help me lose weight. I have cut back on chowing down, doing things that most people would have responded to such as no longer snacking on candy from the vending machine at night and watching how many calories I consume at meals. I do exercise, not anything over the top but yoga three times a week, walking at least an hour a day plus extra walking on the treadmill twice a week. I wouldn't expect to be skinny because I do like to eat and sometimes I don't eat as well as I should, but I also wouldn't expect to weigh 240 pounds.

Stubborn weight gain is but one of the joys of PCOS. Many women who suffer from this condition have irregular periods. I have regular periods but they are extremely heavy. I have very thick hair on my head, which I'm glad of because some women who suffer from PCOS start losing their hair due to elevated androgen levels. However, I also have extremely thick hair on my arms and legs. I have to shave my arms as well as my legs and the hair is so thick that I go through a razor every time I shave, if I let the hair grow at all. The hair is extremely dark. Not very becoming, to say the least. I also have some trouble with facial hair growth but fortunately it is easily controlled with one of those small ladies' razors (Finishing Touch) and doesn't grow back as quickly as a man's beard would. My mother told me about one of my great aunts who had to shave daily or she would grow a beard like a man. I'm sure this poor woman must have had PCOS. My great grandmother was five feet tall and weighed 300 pounds. I'm 5'5" tall and currently weigh 240. I don't want to follow in her footsteps.

My mother has PCOS, as does my aunt. It does run in families.

I did have trouble with infertility and for all I know I still might if I tried to conceive a child again. My (now ex) husband and I were together for six years and never used any kind of birth control before my son was conceived. Interestingly enough, we had been planning to try adopting. My son was a surprise for us.

Ladies, if you are trying to conceive a child and having trouble, and if you are also experiencing any of the above symptoms, have your doctor check you out for PCOS.

Read this informative Article from IVF.com

I hope that the glucophage therapy works for me. So far the only side effects I've experienced were a very mild headache within ten minutes of taking it that went away on its own, and mild dry mouth. I would be thrilled if my weight loss efforts finally started working. I have been frustrated by a weight gain of 5-10 pounds every year and as I currently need to lose 90 pounds to get to a weight I find acceptable, I certainly don't need to gain more!

Keeping my fingers crossed...

What happens to a baby at birth

Before birth, oxygenated blood from the placenta flows into the child’s inferior vena cava and mixes with blood returning from the lower part of the body. The atria are, in effect, one chamber due to the open foramen ovale; however, laminar blood flow tends to supply the left atrium and ventricle (and hence the upper body) with more placental (oxygenated) blood than the right atrium receives. The ventricles also act as one and pump blood around the body. Blood from the right ventricle bypasses the lungs, flowing through the ductus arteriosus and joining blood from the left ventricle in the descending aorta. A large portion of this blood flow goes to the placenta through the umbilical arteries.

Although the pulmonary vessels are fully developed in the fetus, only a tiny amount of blood (about 5% of cardiac output) flows through them due to intense vasoconstriction of the pulmonary arterioles. The nutritive blood supply to the lungs is from the bronchial arteries that arise from the aorta. The collapsed alveoli (air sacs) are filled with amniotic fluid.

Oxygenated blood is red, de-oxygenated blood is blue, and at the moment of birth, a normal newborn is circulating a mixture of blue and red blood. The color (lips and tongue) of a healthy newborn at birth is a pinkish purple; the child has been this color for nine months and normal placental function (cord pulsating) will maintain this color until the lungs function.

When the lungs are functioning, the umbilical vessels close, the ductus venosis closes, the hepatic portal vein is open, the foramen ovale closes, the heart is two sided, the cardiac output from the right ventricle (blue blood) goes through the lungs and is oxygenated, the left ventricular output (red blood) goes through the body, the ductus arteriosus closes, the pulmonary arterioles are open, the alveoli are full of air and the child turns from purple to pink. All of this complicated process is coordinated and controlled by the child’s reflexes; it usually happens within three or four minutes of birth. What makes it happen?

All babies are born soaking wet, and on meeting the atmosphere, the skin cools; this triggers two reflexes:

The cold crying reflex - cold, wet diapers produce the same result, crying.
The cold pressor reflex - cold skin raises blood pressure.
In order to cry, the child must first take a deep breath, and an inspiratory "gasp" is often the first sign, triggered by cold, that a child is going to cry or breathe. Contraction of the diaphragm and intercostal muscles increase thoracic volume and create negative intra-thoracic pressure. Once air is in the lungs, another reflex is triggered that relaxes the pulmonary arterioles; this causes an enormous increase in pulmonary blood flow.

The cold pressor reflex increases the blood pressure in the aorta, and this may be sufficient to reverse blood flow through the ductus arteriosus causing more blood to flow through the lungs.

The cord is also cooling, and the cord is a well-designed self-refrigerator. It has no skin and blubber to keep it warm like the child. It contains only the cord vessels surrounded by a watery gel, Wharton’s jelly, covered by a single layer of cells, the amnion. Water evaporation cools it rapidly, causing the vessels, especially the muscular arteries, to constrict; this further helps to raise systemic blood pressure and to reverse ductus arteriosus flow.

At the same time, a large transfusion of placental blood is being forced into the child by gravity and/or by uterine contraction, greatly increasing cardiac output and pulmonary blood flow. The net result of these changes is a large amount of blood flowing into the left atrium from the lungs, which raises left atrial pressure and closes the foramen ovale - the heart changes from one-sided to two-sided. The lungs are now oxygenating blood that is pumped round the body by the left ventricle - the child turns pink.

If the child has not taken the first breath, or is depressed and cannot breathe, the massive increase in pulmonary blood flow generated by the placental transfusion may, of itself, initiate ventilation. Jaykka [1,2] showed that the fetal lungs are erectile tissues; by injecting serum through the pulmonary artery of excised animal fetal lungs, the engorged capillaries around the alveoli erected them and caused air to enter through the trachea. With establishment of pulmonary blood flow, the high colloid osmotic pressure of blood causes absorption of amniotic fluid from the alveoli and "dries out" the lungs, filling the "erected" alveoli with air.

Cold will eventually cause the cord vessels to close; however, a high arterial blood oxygen concentration is probably a key factor in umbilical artery closure - they close before the umbilical vein closes; it may also cause ductus arteriosus closure. After umbilical artery closure, the placental transfusion may continue through the cord vein in a very measured and controlled manner.

Information found at: http://whale.to/a/morley4.html

Powerful Picture

Click the title link to view the photo in a larger scale at its original location. This is a five-week-old embryo found in the case of an ectopic pregnancy. Ectopic pregnancies cannot survive and present great danger to the mother's health. The embryo was removed shortly after the photo was taken. The details in the photograph are amazing. At this stage it is difficult to distinguish a human fetus from the fetuses of other animals. Apologies as I reveal the horror movie lover in me, but we do look a bit like alien chestbursters during our earliest stages of development.

Ovarian Follicles

An ovarian follicle consists of a developing oocyte surrounded by one or more layers of cells called follicular cells. At the same time that the oocyte is progressing through meiosis, corresponding changes are taking place in the follicular cells. Primordial follicles, which consist of a primary oocyte surrounded by a single layer of flattened cells, develop in the fetus and are the stage that is present in the ovaries at birth and throughout childhood.
Beginning at puberty follicle-stimulating hormone stimulates changes in the primordial follicles. The follicular cells become cuboidal, the primary oocyte enlarges, and it is now a primary follicle. The follicles continue to grow under the influence of follicle-stimulating hormone, and the follicular cells proliferate to form several layers of granulose cells around the primary oocyte. Most of these primary follicles degenerate along with the primary oocytes within them, but usually one continues to develop each month. The granulosa cells start secreting estrogen and a cavity, or antrum, forms within the follicle. When the antrum starts to develop, the follicle becomes a secondary follicle. The granulose cells also secrete a glycoprotein substance that forms a clear membrane, the zona pellucida, around the oocyte. After about 10 days of growth the follicle is a mature vesicular (graafian) follicle, which forms a "blister" on the surface of the ovary and contains a secondary oocyte ready for ovulation.

Ovulation
Ovulation, prompted by luteinizing hormone from the anterior pituitary, occurs when the mature follicle at the surface of the ovary ruptures and releases the secondary oocyte into the peritoneal cavity. The ovulated secondary oocyte, ready for fertilization is still surrounded by the zona pellucida and a few layers of cells called the corona radiata. If it is not fertilized, the secondary oocyte degenerates in a couple of days. If a sperm passes through the corona radiata and zona pellucida and enters the cytoplasm of the secondary oocyte, the second meiotic division resumes to form a polar body and a mature ovum

After ovulation and in response to luteinizing hormone, the portion of the follicle that remains in the ovary enlarges and is transformed into a corpus luteum. The corpus luteum is a glandular structure that secretes progesterone and some estrogens. Its fate depends on whether fertilization occurs. If fertilization does not take place, the corpus luteum remains functional for about 10 days then it begins to degenerate into a corpus albicans, which is primarily scar tissue, and its hormone output ceases. If fertilization occurs, the corpus luteum persists and continues its hormone functions until the placenta develops sufficiently to secrete the necessary hormones. Again, the corpus luteum ultimately degenerates into corpus albicans, but it remains functional for a longer period of time.

http://training.seer.cancer.gov/module_anatomy/unit12_3_repdt_female1_ovaries.html

Meiosis

Normally, meiosis causes a halving of chromosome material, so that each parent gives 23 chromosomes to a pregnancy

A cool site about meiosis for you to enjoy:
http://www.sciencecases.org/mitosis_meiosis/mitosis_meiosis2.asp

Testes! One, two...three???

We are currently studying the reproductive system in class. Here is some fun trivia about the testes. The information was gathered from Wikipedia.

In land mammals, with the exception of the elephant the testes are located outside of the body, as they are suspended by the spermatic cord and within the scrotum. This is due to the fact that The cremasteric muscle is part of the spermatic cord. When this muscle contracts, the cord is shortened and the testicle is moved closer up toward the body, which provides slightly more warmth to maintain optimal testicular temperature. When cooling is required, the cremasteric muscle relaxes and the testicle is lowered away from the warm body and are able to cool. This phenomenon is known as the cremasteric reflex. It also occurs in response to stress (the testicles rise up toward the body in an effort to protect them in a fight), and there are persistent reports that relaxation indicates approach of orgasm. There is a noticeable tendency to also retract during orgasm.

The testicles can also be lifted voluntarily using the pubococcygeus muscle, which partially activates related muscles. This can sometimes be triggered by tightening or sucking in the stomach or abdomen.

Animals other than mammals do not have externalized testicles. Birds, despite having very high core body temperatures have internal testes: it was once theorized that birds used their air sacs to cool the testes internally, but later studies revealed that birds' testes function at core body temperature.[1] Marine mammals also have internal testes, but it has recently been shown (eg, for dolphins) that they use elaborate vascular networks to provide the necessary temperature lowering for proper operation.

The seminiferous tubules of the testes are the starting point for the process of spermatogenesis, where stem cells adjacent to the inner tubule wall divide in a centripetal direction - beginning at the walls and proceeding into the lumen to produce immature sperm.