Back To CourseBiology 105: Anatomy & Physiology
19 chapters | 240 lessons
Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.
The testes is where it all begins - sperm production, that is. The fate of a man's future generation all lies inside these two, golf-ball-sized organs that hang precariously just below his abdomen. In this lesson, we will look inside the testes to see what the organ that produces a male's sperm looks like. How is it that these two small organs produce the billions of sperm that are made over a lifetime?
To start, each testis is located inside a scrotal cavity and is covered by a layer of connective tissue known as the tunica albuginea. This covering is not only on the outside of the testis but also forms the partitions inside the testis known as septa. The septa are partitions of connective tissue that subdivide each testis into several smaller sections known as lobules, and it is inside these lobules where the magic of sperm production begins.
Now, let's start with all those spaghetti-looking tubes. Those are known as seminiferous tubules, and believe it or not, all the seminiferous tubules combined in the male's testes would measure more than 2.5 times the length of a football field!
The seminiferous tubules are located inside each lobule and are the location of spermatogenesis, or the creation of new sperm. So, if we go even further inside the testes and take a look at individual tubules, we will see that each tubule is surrounded by a membrane. And, inside each tubule, there are sperm in all different stages of development, while in between the membranes of adjacent tubules, you have spaces that are filled with something called areolar tissue, which is a type of loose connective tissue.
It is in these tubules, and the spaces in between the tubules, where the two main functions of the testes take place. The first, spermatogenesis, or sperm production, occurs within the tubules, while the second, hormone production, specifically the production of androgens, occurs between the tubules.
First, let's talk about what happens within the tubules. If you look at a cross-section of a single tubule, you will see that all the stages of spermatogenesis are present as well as some other cells that aid in the maturation of sperm. These cells, known as Sertoli cells, or nurse cells, are located within the tubules and aid in the process of spermatogenesis by providing both nutrition and protection to the developing sperm.
Now, if you take a closer look at the organization of the tubule, you will see that these tubes are actually organized. Notice that the cells closer to the wall of the tubule look different than the ones closest to the lumen - that's the space in the middle. That is because as they mature, they move away from the wall and towards the lumen. So that means that the cells closest to the wall of the tubule are the most immature cells and those closest to the center, or the lumen, are the most mature.
Okay, so now that we know they are organized, the next question is why? Well, this layout allows the spermatozoa produced in the later stages of production to be closer to the lumen of the tubule. That way, when the spermatozoa in the latest stages of development are released from the wall, they enter into the lumen and can be transported to the next stage.
You can think about it this way. You know when you ride those water slides at the water park that look like big pipes? And there's always a bunch of entrances at the top of the platform, and then they all end in a pool at the bottom of the platform? Well, imagine that the side of the pipe is the wall of the tubule and the hollow center of the pipe is the lumen.
When the sperm let go of the wall, they follow the slide all the way down to the pool, where all the slides converge. This structure is called the rete testis, and it's where the tubules from each lobule in the testicle converge before entering the ducts that lead to the epididymis.
The rete testis is located in the portion of the testicle closest to the head of the epididymis. That way, when sperm enter the rete testis, they can continue on into the epididymis, where they complete the final stages of maturation before being transported through the rest of the male reproductive tract.
So now that we have covered what goes on inside the tubules, let's look at what happens in the spaces in between the tubules. This is where the production of the male hormone testosterone occurs. Importantly, these spaces contain cells known as Leydig cells, or interstitial cells. These cells are responsible for the production of androgens - most importantly, the androgen testosterone.
Testosterone production is triggered when the Leydig cells receive hormone signals from the pituitary gland - that's located up where your brain is. Once produced, testosterone travels into the seminiferous tubules, where it acts on the Sertoli (nurse) cells to aid in spermatogenesis.
Importantly, without the correct levels of testosterone, sperm production would not occur. If the testosterone is too low, it won't stimulate the Sertoli (nurse) cells enough, but if it is too high, the pituitary senses this and inhibits further production of testosterone. So the amount of testosterone produced needs to be just the right amount for sperm production to occur.
So there you have it - the structure and main functions of the testes. Remember, each of these main functions takes place in a different part of the testis. The production of sperm takes place within the seminiferous tubules and with the aid of the Sertoli (nurse) cells, and the production of testosterone takes place in the Leydig (interstitial) cells located in between the tubules.
As you can see, both of these functions work together - without the production of testosterone by the Leydig cells, the Sertoli cells wouldn't be able to aid in spermatogenesis.
Each of these functions is also aided by the structure of the testis. The seminiferous tubules and rete testis provide a safe place for sperm production and transport, while the areolar tissue in between allows for blood and nutrient flow in and out of the testis.
These in turn are divided and protected by the connective tissue membrane, the tunica albuginea, which keeps all the tubules inside the testis. And remember, the testes are just the first step in sperm production - other structures in the male reproductive tract will control the maturation, the mobility, and the transportation of sperm.
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Back To CourseBiology 105: Anatomy & Physiology
19 chapters | 240 lessons