The Human Reproductive

System

Most animals are either male or female. Male animals produce only male gametes (sperm) and females only female gametes (eggs.)

Sperm are produced in a pair of organs known as the testes.

Eggs are produced in a pair of organs known as the ovaries.

Human females release one egg or ovum from their ovaries approximately every 28 days. If the egg is not fertilized by a male sperm cell within about 72 hours, the egg dies and the thin, temporary mucous membrane of the uterus is passed from the female during a process known as menses or menstruation.

Ovulation with fertilization

Ovulation without

fertilization.

Remember that CELLS are the smallest unit of life. They are the building blocks of larger organisms.

How did you start out?

Well, once upon a time…..

Fertilization occurs when a haploid male gamete (sperm) joins with the haploid female gamete (egg).

The egg will receive only one sperm cell. Once one sperm cell is able to penetrate the egg, the egg doors are locked and bolted shut, so to speak.

As the two gametes join, they become a fully diploid cell called a zygote. Still only one cell, the zygote will begin to undergo mitosis as the process of building YOU begins!

http://www.youtube.com/watch?v=_2MFFzldkYQ&feature=related

(Pause after development of zygote)

One cell becomes two…

Two become four…

At first, all these new cells forming through mitosis are exactly alike. But after a few weeks, the new cells start changing and forming into new types of cells that will eventually become the various types of cells that make up the tissues of our body.

This new cell is known as an embryo.

After a few weeks, the cells begin to specialize. The human form begins to materialize…..well, sort of. At this point of development the organism is transforming from an embryo to a fetus.

By week 8, you are really starting to take shape. You

still have that whole “alien baby” look happening. At around this point, the organism is

considered to be a fetus.

By week 14, your organs and systems are developing quickly.

And you have already become an expert “thumb thucker.”

By week 24 you have hair and fingernails. All your organs and systems are developed, but not ready yet for the real world. At this point you weight about 1.3 pounds.

By week 32, you have developed your senses, and..Oh my, it’s a boy! You weigh about 4 pounds.

OK. Let’s see this in action…http://www.youtube.com/watch?v=_2MFFzldkYQ&feature=related (finish the YouTube video up to 5:55.

At 36 weeks, you could easily handle the real world. But it’s so warm and comfy in there. Mom may not be so comfy, though. And she has another month to go! What do you look like at this point?

http://www.youtube.com/watch?v=sVB0qTiq5jU&feature=related

But the new 3D ultrasound imaging uses advanced computer software that makes images pop…http://www.youtube.com/watch?v=sVB0qTiq5jU&feature=related

In older ultrasound technology images, it was sometimes hard to make out the features. You needed specialized training in some cases…

Finally, the day arrives. Human babies have a 40 week gestation period. Forty plus weeks in the warm, cozy womb comes abruptly to an end. Your fully formed, slimy, screaming little body experiences the blinding light and feels the cold are of the delivery room for the first time.

Dude! Put me

baaaaack!!!

For the time being, it’s sleep, eat, cry, pee. Sleep, eat, cry, poo poo…

And, you get introduced to the rest of the family.

Now all those cells in your body have specialized. Some became blood, some became fingernails…you get the picture. Most became a form of tissue such as

1. Epithelial tissue- this tissue covers the outer layer of your body (as skin) and the outer layer of the organs inside your body. The epithelial layer acts as a boundary. It is the first line of defense against invading pathogens.

2. Nerve tissue- nerve tissue makes up the network of pathways in your body that carry messages to your brain.

3. Muscle tissue- muscles control our movement, both voluntarily and involuntarily.

4. Connective tissue- these tissues hold our body together, provide us with protection from injuries

These tissues form the organs of our body: brain, heart, liver, kidney, stomach, skin, etc.

Certain organs function as parts of a system: digestive, circulatory, muscular, endocrine, etc.

Let’s take a look first at the skeletal system.