Human Anatomy for AP Biology
Practice problems for these concepts can be found at: Human Reproduction Review Questions for AP Biology
What are the biologic differences between a man and a woman? For the purposes of this exam, you should keep in mind that one of the first distinctions is that boys have a Y chromosome in the nuclei of their cells, and girls do not. Another major difference lies in the sex characteristics. Primary sex characteristics are the internal structures that assist in the vital process of procreation. Among these are the testes, ovaries, and uterus. Secondary sex characteristics are the noticeable physical characteristics that differ between males and females such as facial hair, deepness of voice, breasts, and muscle distribution. These characteristics come into play as indicators of reproductive maturity to those of the opposite sex.
Since we males tend to be a bit impatient, I will cover male anatomy first. The male sexual anatomy is designed for the delivery of sperm to the female reproductive system. Let's follow the journey of a sperm from the beginning to the end.
Sperm's "Wild Ride"
Here we stand in the testis. The male has two testes, located in a sac called the scrotum. This is the sperm factory—a portion of the testis called the seminiferous tubules is where the sperm are actually made. We return later to look at how these sperm are created. Notice in the other corner of the testis a structure called the interstitial cells. These are the structures that produce the hormones involved in the male reproductive system. Remember that the testis is the site of sperm and hormone production in the male reproductive system.
We are going to move along the production line to the epididymis—the coiled region that extends from the testes. The epididymis is where the sperm completes its maturation and waits until it is called on to do its duty. From here, when called into action, the sperm moves through a tunnel called the vas deferens. Each epididymis connects to the urethra via this tunnel. The urethra is the passageway through which the sperm exits during ejaculation. Yes … that is indeed the same tunnel that the urine uses to get out … good observation in back.
We're not done yet—let's look at some other important players in this process (see also Figure 16.1). I am sure you have all heard about the prostate gland and how prostate cancer is currently one of the major cancers among men. But do you know what the prostate gland does? Here we are standing by this fine structure whose function in the male reproductive system is to add a basic (pH >) liquid to the mix to help neutralize any urine that may remain in the common urethral passage. It also helps to combat the acidity of the vaginal region of the female toward which the sperm is heading.
Follow me, everyone, more to see, more to see. … Here on either side of us are the structures called the seminal vesicles. These characters play an important role in the success of the sperm on its way to the female ovum. When the male ejaculates, the seminal vesicles dump fluids into the vas deferens to send along with the sperm. Think of the seminal vesicle as a convenience store. It provides three important goods to the sperm: energy by adding fructose; power to progress through the female reproductive system by adding prostaglandins (which stimulates uterine contraction); and mucus, which helps the sperm swim more effectively.
The sperm is ready to enter the female reproductive system at this point, but before we observe the sperm as it does so, I want to take a quick tour of the female reproductive structures.
We begin in the ovary, the site of egg production. Females have two ovaries—one on either side of the body. The egg leaves the ovary before it has fully matured and enters a structure called the oviduct. The oviduct is also known as the fallopian tube—you may be more familiar with that term. Eggs travel through here from the ovary to the uterus. When fertilized by an incoming sperm in the fallopian tube, after several days' transit from the tube to the uterus, the egg usually attaches itself to the inner wall of the uterus, which is known as the endometrium. The uterus connects to the vaginal opening via a narrowed portion called the cervix. As we pass through the cervical area, we now find ourselves in the vagina, and it is here that the sperm enters the female reproductive system.
As the sperm enters, it must survive the different environment that the female body presents (Figure 16.2). Its task is to find its way to the fallopian tube, where it must meet the egg and penetrate its outer surface to achieve successful fertilization. The sperm works its way through the vaginal region, up through the cervix, through the uterus, and into the fallopian tube. Here, if the timing is appropriate, there will be a willing and waiting egg that is hoping to meet with a sperm to produce a new diploid zygote. After successful fertilization, the new happy couple moves down to the uterus and builds a nice house along the endometrium where it will develop into an embryo and remain until it is ready to be born.
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