The Reproductive System

I've already predicted that this is going to be a challenging post to write. Not so much in terms of content, because it's basically what we learned in Year 8-10 Health and Year 10 Science, but with a little bit more depth. No, the challenge here will be trying not show off exactly how immature I am. I'll probably shove in a few immature jokes here and there- let's face it, sometimes the awkwardness makes it easier to remember this stuff- but I'll try not to go overboard... if I can help it!

First a brief intro to what I'll be talking about. Basically, males and females each have different sex cells, called gametes. When the different gametes (sperm from the male, ovum from the female) meet up, they fertilise and result in a single cell, called a zygote, which then develops into a baby. What follows is an overview of the gonads (sex organs) in males and females.

Male Reproductive System

The spermatozoa (a.k.a. sperm) are produced in the testes (singular testis) of the male reproductive system. The testes are located in a skin-covered pouch called the scrotum, which is actually not just one skin-covered pouch. It's divided into two sacs, each containing a single testis. Sperm production requires a temperature slightly lower than normal body temperature, so the testes-containing scrotum hangs outside of the body cavity, where it is slightly cooler. The scrotum also contains some smooth muscle fibres, which allow the scrotum to move towards or away from the body, depending on the outside temperature.

Each testis is oval in shape, and is around 4.5cm long, 2.5cm wide and 3cm thick. It contains 200-300 lobules (compartments) which are filled with seminiferous tubules, which in turn are lined with cells that can divide to produce sperm. This is known as spermatogenesis. Between these tubules are interstitial cells, which secrete testosterone (a.k.a. the male sex hormone).

The seminiferous tubules eventually join together to form short, straight tubules, which then join into ducts, which leave the testis and enter the epididymis, which is... wait for it... ANOTHER TUBULE. It's around 5-6m in length, but it's highly folded, so it fits. Its length allows it to store lots of sperm for up to a month, while they mature.

The epididymis then continues into... YET ANOTHER DUCT. This time it's called the vas deferens, or sperm duct. This takes the sperm away from the testis, into the abdominal cavity, across the upper surface of the bladder and around to the back of the bladder, where it meets up with the other vas deferens from the other testis and joins another tube, called the urethra. The urethra transports both urine and sperm to the outside world.

I'm going to pause for a moment now to talk about other stuff that happens while the sperm passes through the urethra. There are three glands that secrete different fluids that make up the semen (or seminal fluid), a liquid that nourishes and aids the transport of sperm. The seminal vesicles, located behind the urinary bladder, secrete a thick sugar-rich fluid that makes up 60% of the volume of semen. The prostate gland (which is apparently shaped like a doughnut, according to my book) surrounds the urethra just below the bladder, and secretes a thin, milky, alkaline fluid. Finally, the bulbo-urethral glands, a.k.a. Cowper's glands, are two small yellow glands located beneath the prostate gland. They secrete a clear mucus which mainly acts as a lubricant, though a small amount does get included in the semen as well.

Oh yeah and now for the bit that I bet the more immature among you really wanted to know. The penis contains a type of connective tissue, called erectile tissue, which has a very rich blood supply. You can see where I'm going from here can't you...! Well, the erectile tissue contains a large number of sponge-like spaces, which can fill with blood, causing an erection.

That's all from me on the male reproductive system. Now it's time to talk about the...

Female Reprodctive System

The ova (singular ovum) in females are produced in the ovaries. Each almond-shaped ovary is around 3cm long. The ovaries are located within the body, on either side of the pelvic cavity, and are supported by ligaments.

The ovaries are composed of connective tissue called stroma, which is surrounded by a layer of cells containing some germ cells. These cells are enclosed in follicles, and eventually develop into ova. As the follicle matures, it moves closer and closer to the surface of the ovary, before rupturing, releasing the egg into the uterine tube (also known as the Fallopian tube or oviduct). There are two of these tubes that carry the egg from each ovary to the uterus. In order to help guide the egg into the uterine tube, the opening of the tube near the ovary has small projections called fimbriae.

The fallopian tubes themselves are lined with epithelial tissue complete with cilia, which help carry the egg towards the uterus.

The uterus is sometimes called the womb. I'm pretty sure that a slang term for it is "oven," but don't write that on your test paper- it's not very scientific! The uterus is held behind the urinary bladder and in front of the rectum by ligaments. The ligaments do not hold the uterus tightly, so there is allowance for some slight movement. The wall of the uterus is mainly made up of smooth muscle, and has a soft mucous membrane lining called the endometrium, which protects and nourishes the foetus during pregnancy.

At the lower end of the uterus is the cervix, which contains a narrow passage known as the cervical canal. The cervix protrudes into the vagina, which leads to the outside of the body. The vagina is muscular and is lined with mucous membranes. It is quite capable of stretching, which is good considering that babies are meant to be able to come out through there.

The external opening of the vagina is partially covered by a fold of tissue called the hymen. Loss of virginity is associated with the breaking of the hymen, but this isn't quite accurate- the hymen can be stretched and torn through various means, sexual intercourse being only one of them.

Anyway the vagina opens up to a region called the vulva, which is made up of the labia majora, the labia minora, and the clitoris. The labia majora are two fleshy folds of skin which are comprised of fat and fibrous tissue, which in turn is comprised of many sebaceous glands (oil-producing glands, according to Google). Between and beneath the labia majora are the labia minora, which are two smaller folds of skin, which lack fat and are a pinkish in colour. They do, however, also contain sebaceous glands. The labia minora surround the openings of the urethra, vagina and the clitoris, which is like the female equivalent of a penis in that it also contains erectile tissue, blood vessels and nerves.

Now onto my next topic!

The Ovarian Cycle

The ovarian cycle mainly involves the maturation of an egg and its release into a fallopian tube. It's around 20-40 days long (28 being average), and coincides with the menstrual cycle, which I'm going to talk about a bit later.

At birth, the ovaries contain around 400 000 immature eggs (waste of space if you ask me, since apparently only around 400 of these eggs actually reach maturity throughout a woman's lifetime). Anyway each egg is initially surrounded by a single layer of cells. This whole unit is called a primary follicle.

After hitting puberty, some of the primary follicles undergo further development. The cells surrounding the primary follicle begin to grow, divide, and secrete fluids, forming a fluid-filled space that forces the egg to move towards the edge of the follicle. Now it's a secondary follicle. w00t!

Each month, one of these secondary follicles (sometimes more, but usually one) will develop further. The others will normally break down to be reabsorbed into the ovary. More and more fluid accumulates within the follicle, causing it to grow and move towards the surface of the ovary. When it reaches the surface (roughly 10-14 days after the primary follicle started developing), the follicle is mature, and is referred to as a Graafian follicle.

When the mature follicle bursts, the egg is expelled into the uterine tube. This is known as ovulation. Normally only one egg is released at a time, but occasionally multiple eggs may be released at the same time. If the egg doesn't meet up with sperm, the next group of follicles begin developing.

After ovulation, the ruptured Graafian follicle collapses. The blood within the follicle bgins to clot, and the clot is then absorbed by the remaining follicle cells, which then form a cream coloured body called the corpus luteum. ("Luteum" means "yellow" in Latin- apparently an embryologist called Regnier de Graaf saw a yellow coloured body when observing cow ovaries.) The corpus luteum secretes hormones that influence the development of the lining of the uterus. The lifetime of the corpus luteum varies depending on whether pregnancy has occurred or not. If pregnancy has not occurred, the corpus luteum reaches its maximum development after around 8-10 days, before degenerating into a fibrous mass of scar tissue called corpus albicans (which eventually degenerates... I think). However, if pregnancy has occurred, the corpeus luteum continues to develop, reaching the peak of its development around three months later before degenerating very slowly (it's still present by the time the child is born).

The Menstrual Cycle

The menstrual cycle involves the changes in the lining of the uterus (the endometrium, remember?) and the vagina. These are closely linked to ovulation, as the changes in the lining are in preparation for childbirth.

While the follicle is maturing, the endometrium of the uterus becomes thicker and softer, and the number of blood vessels and mucus-secreting glands increases.

After ovulation, the endometrium continues to thicken, and the glands begin to secrete a watery mucus rich in glycogen, which is thought to assist the sperm as they travel to the fallopian tubes.

If the egg isn't fertilised, the corpus luteum degenerates, decreasing the hormonal messages to the endometrium. This results in the endometrium degenerating. Around 14 days later, blood from broken-down capillaries, mucous secretions and cell debris from the uterine lining all come out through the vagina. This is known as menstruation.

Menarche is when a woman first begins to menstruate. This normally occurs between 9-16 years of age. Menopause, normally occurring between the ages of 40 and 50, is when menstruation no longer occurs. Normally, there is around 35 years between menarche and menopause.

What Can Go Wrong?

First of all, there are several cancers that can affect the sex organs- see my previous post on cancer for more details.

There are many types of menstrual abnormalities. Primary amenorrhoea is when menstruation doesn't begin during adolescence, while secondary amenorrhoea is when one or more periods are missed. Secondary amenorrhea is quite common, and happens to nearly all women at some point. Dysmenorrhoea is painful menstruation caused by strong contractions of the uterus. Abnormal uterine bleeding involves very heavy periods, periods that are too frequent, bleeding during non-menstrual phases and bleeding after menopause. Premenstrual syndrome, or PMS for short, encompasses a whole range of crazy symptoms that some of us women experience before having our period. They're quite varied, ranging from mood swings to bloating to joint pain, and so on.

Ovarian cysts are fluid-filled tumours in the ovary that are usually not cancerous.

Pelvic inflammatory disease (PID) is an infection of the pelvic organs of the female reproductive tract.

Yay! Now the awkwardness is over... or not. Next post is on reproduction, and there is a very interesting diagram in this book of the path the sperm takes to get to the egg. w00t w00t!!