Seminiferous Tubules in the Testis在线视频

Hello, everyone!

Today we will look at the structures

and functions of the seminiferous tubule

in the testis.

Let's begin with a clinical case.

John 29 years' old and 28-year-old Rose

have been married for 3 years.

They wanted a baby,

but Rose could not get pregnant.

After examination,

doctor told them there were anti-sperm antibodies

in John's blood,

which could be the reason for the infertility.

The questions are,

what is the normal process

and circumstance for the development of sperms?

How does the body normally prevent the production

of anti-sperm antibodies?

At the end of this session,

you should be able to answer above questions,

list the general structures

and functions of the testis,

describe the circumstance

for the development of sperm,

and explain some associated clinical changes.

In the testis,

besides the capsule and septa constituted

by connective tissue,

the main structure of testis

is convoluted seminiferous tubules,

short straight tubules,

and dilated rete testis.

The main functions of the testis

are to produce male gamete-sperms,

and male hormone-androgen.

The seminiferous tubule in the testicular lobules

is the key place for these two functions.

Shown here are the seminiferous tubules

stained by hematoxylin and eosin.

Androgen is produced by the interstitial Leydig cells

found between the seminiferous tubules

while sperms are developed

within the seminiferous tubules.

The lining cells of the seminiferous tubules

comprise the complex stratified

seminiferous epithelia,

with two basic cell populations,

spermatogenic cells and Sertoli cells.

Before puberty,

the spermatogenic cells

are all at the stage of diploid spermatogonia.

After puberty,

the spermatogonia began to undergo differentiation.

From the basal membrane to lumen,

we can find the different developmental stages

of the sperm,

spermatogonium, primary spermatocyte,

secondary spermatocyte, spermatid

and the mature sperm.

The Sertoli cells are not part of

the spermatogenic cell lines,

but they provide support

or nurture the development of sperms.

They are easily identifiable by their nuclei

in hematoxylin and eosin stained slides.

The nucleus is pale and oval to pyramidal in shape,

with one or two prominent nucleoli.

The Sertoli cells have a very extensive

and branching cytoplasmic structure.

Little of its outline can be seen

under light microscope.

However,

the extensive branching nature of its cytoplasm

can be identified under electron microscope.

This diagram shows us

the ultra-microstructure of Sertoli cells,

and their relationship to the wall of the tubule

and to other cells in the seminiferous epithelia.

In this picture,

we can easily identify the cytoplasmic outline

and the tight connection between them.

The connection between adjacent Sertoli cells

divide the wall of the tubules in to 2 parts,

luminal compartment and basal compartment.

The basal compartment,

near the peripheral region,

is sealed off from the luminal compartment

by processes of adjacent Sertoli cells.

The diploid spermatogonia

are found in the basal compartment.

After the spermatogonia start

division and differentiation,

the Sertoli cells send out new processes

to "undermine" the forming primary spermatocytes,

and seal off a new layer below them,

then break the barrier above.

This effectively transfers

the differentiated haploid cells

to the luminal compartment.

Why is this elaborate mechanism

for separating the tubule

into two compartments necessary?

The basal compartment has access to the blood stream

and all the immune components it carries.

The spermatogonia and Sertoli cells

have been there from embryonic stage,

so the immune cells are familiar with them.

When a boy reaches puberty,

the diploid spermatogonium differentiates

into haploid primary spermatocyte,

secondary spermatocyte and so on.

The differentiated haploid cells express

novel proteins on their surfaces.

There is a risk that

the immune system might recognize them as"non-self"

and produce antibodies against them.

So,

for self-protection,

the blood-testis barrier is created

by the junctions of adjacent Sertoli cells.

Maintenance of two separated compartments

allows the different stages of the spermatogenic cells

to exist under optimal conditions.

The blood-testis barrier consists of

the tight junctions between Sertoli cells,

basement membrane of tubules,

interstitial connective tissue,

endothelium, and the capillary basement membrane.

Among the structures of blood-testis barrier,

the tight junction between Sertoli cells

plays the most important role.

However,

the blood-testis barrier can be disrupted

by physical or chemical injury

or by infection.

When this barrier is broken,

differentiated sperm antigens escape from their

immunologically protected environment

and come into contact with blood elements.

That may initiate the lymphocytes

to produce anti-sperm antibodies

which immunologically "attack"

the differentiated haploid cells

in the seminiferous tubules.

Anti-sperm antibodies can be present in many men

without necessarily inducing infertility.

However,

some of them may have reproductive problems,

for example,

John in our case.

Besides being involved in the formation

of blood-testis barrier,

Sertoli cells also have other functions.

Firstly,

the cytoplasm of Sertoli cells

can form a network to provide general support,

protection, and nutritional supply

for sperm development.

Secondly,

they have the function of phagocytosis.

During spermatogenesis,

excess spermatid cytoplasm

is shed off as residual bodies.

These cytoplasmic fragments are phagocytosed

and cleared by Sertoli cells.

The third function of Sertoli cells

is to secrete inhibin, activin, and ABP.

Androgen-binding-protein (ABP),

can serve to concentrate androgen

in the seminiferous tubules,

which is necessary for the development of sperms.

Let's summarize the structures and functions

of the seminiferous tubules in the testis.

Seminiferous tubules are highly convoluted structures

within testicular lobules.

The lining epithelium is mainly composed of

spermatogenic cells

at different developmental stages,

spermatogonium, primary spermatocyte,

secondary spermatocyte, spermatid, and sperm.

The Sertoli cells are also within the

lining epithelium of seminiferous tubule

and play important functions in spermatogenesis.

These are the references for this session.

Thank you for your attention.