Testes and Seminiferous Tubules

Testis (testes, plural)

Let’s look inside the testis. Like other important organs, the testes are surrounded by a serous membrane. This membrane includes a parietal layer and a visceral layer. There is a space in between them. The outer layer is called the tunica vaginalis. It helps form the scrotal cavity. It covers the anteriorThe front of the body or toward the front when standing in the anatomical position. and lateralAway from the midline of the body. faces of the testes. This same structure is also present around the ovariesThe female gonads that produce eggs and hormones..

The tunica albugineaA fibrous layer surrounding the ovary. (albuginea meaning “white”) is an egg-shaped connective tissue mass that directly covers the testis. It dips down between lobes of the testis to form septa, similar to the visceral pleuraThe double-layered membrane surrounding the lungs and lining the thoracic cavity. in the lungs.  These septa can create 250 to 300 lobules and one testis can have 1, 2, or even 3 lobules. 

Seminiferous Tubules

The seminiferous tubules make up the bulk of the testis. These are tightly coiled structures where spermatogenesis occurs. This process involves producing sperm from stem cellsThe basic structural and functional units of life., leading to the formation of the flagellaLong, whip-like structures used by some cells (e.g., sperm) for movement.. These tubules converge into straight portions that channel sperm toward the epididymis.

In histological views, these tubules appear as round or oval structures with a central lumenThe inside space of a hollow organ or structure.. Sperm develop from the outer wall toward the lumen, eventually detaching and moving into the epididymis. Inside each tubule are many different types of cells, not just the developing sperm.

All of the seminiferous tubules straighten out and converge on a site called the rete testis.  Here, they merge together and kind of get intentionally clogged, allowing them more time to mature.  The flagella of the sperm is not fully developed so these efferent ductules have ciliated epithelium to help with movementA fundamental property of life involving motion of the body or its parts..  The rete testis then distributes the spermatozoa to the epididymis using efferent ductules.  After traversing the rete testis, spermatozoa move to the epididymis through efferent ductules that are straight.

Sperm Cells of the Seminiferous Tubules

Spermatogenesis is a process of cell division. It takes a stem cell and makes a spermatid. The spermatid will then mature into a spermatozoon.  This is the process that takes place in the seminiferous tubules.  Spermatogonia are stem cells that do mitosis.  One cell replaces this stem cell and the other cell goes on to do meiosis and become spermatids.  The mitosis of the stem cell occurs every 16 days. It takes 64 days for it to divide and mature into a spermatozoon. 

At any given time, a tubule is hosting 5 different cohorts of developing sperm.  Before this lecture, you may have thought that sperm is produced continuously. However, it is produced in waves as these cohorts mature.  The rete testis is always controlling movement into the epididymis in accordance with these waves of sperm.

Non-Sperm Cells of the Seminiferous Tubules

Several cell types support the function of the seminiferous tubules:

Myoid cells are smooth muscle-like cells surrounding the tubules, helping move sperm along.

Interstitial (Leydig) cells are found between tubules and produce testosterone.

Nurse (Sertoli) cells act like a gelatinous matrix that developing spermatocytes are embedded in—like fruits in gelatin. These cells provide nourishment and structural support.

Blood Testes Barrier

The blood-testis barrier is a structure within the nurse cells. It separates the basal compartment, which contains stem cells, from the luminal compartment, where developing sperm reside. This barrier protects developing sperm from immune system attacks, as the body does not recognize them as “self” cells.

While it’s not a distinct physical line like the respiratory membrane, this barrier plays a critical role. The basal compartment contains your own stem cells. In contrast, the luminal compartment contains developing sperm cells. These sperm cells are antigenically different and could trigger an immune response without the barrier.

The blood testis barrier results form tight junctions between nurse cells that prevent autoantibodies from harming the sperm.