The blood–testis barrier is a physical barrier between the
blood vessel
Blood vessels are the tubular structures of a circulatory system that transport blood throughout many Animal, animals’ bodies. Blood vessels transport blood cells, nutrients, and oxygen to most of the Tissue (biology), tissues of a Body (bi ...
s and the
seminiferous tubule
Seminiferous tubules are located within the testicles, and are the specific location of meiosis, and the subsequent creation of male gametes, namely spermatozoa.
Structure
The epithelium of the tubule consists of a type of sustentacular cells k ...
s of the animal
testes
A testicle or testis ( testes) is the gonad in all male bilaterians, including humans, and is homologous to the ovary in females. Its primary functions are the production of sperm and the secretion of androgens, primarily testosterone.
The ...
. The name "blood-testis barrier" is misleading as it is not a blood-organ barrier in a strict sense, but is formed between
Sertoli cell
Sertoli cells are a type of sustentacular "nurse" cell found in human testes which contribute to the process of spermatogenesis (the production of sperm) as a structural component of the seminiferous tubules. They are activated by follicle-sti ...
s of the seminiferous tubule and isolates the further developed stages of germ cells from the blood. A more correct term is the Sertoli cell barrier (SCB).
Structure
The walls of seminiferous tubules are lined with primitive germ layer cells and by
Sertoli cells.
The barrier is formed by
tight junction
Tight junctions, also known as occluding junctions or ''zonulae occludentes'' (singular, ''zonula occludens''), are multiprotein Cell junction, junctional complexes between epithelial cells, sealing and preventing leakage of solutes and water. Th ...
s,
adherens junction
In cell biology, adherens junctions (or zonula adherens, intermediate junction, or "belt desmosome") are protein complexes that occur at cell–cell junctions and cell–matrix junctions in epithelial and endothelial tissues, usually more basa ...
s and
gap junction
Gap junctions are membrane channels between adjacent cells that allow the direct exchange of cytoplasmic substances, such small molecules, substrates, and metabolites.
Gap junctions were first described as ''close appositions'' alongside tight ...
s between the
Sertoli cell
Sertoli cells are a type of sustentacular "nurse" cell found in human testes which contribute to the process of spermatogenesis (the production of sperm) as a structural component of the seminiferous tubules. They are activated by follicle-sti ...
s, which are
sustentacular cell
A sustentacular cell is a type of cell primarily associated with structural support, they can be found in various tissues.
* Sustentacular cells of the olfactory epithelium (also called supporting cells or Sertoli cells) have been shown to be inv ...
s (supporting cells) of the
seminiferous tubules
Seminiferous tubules are located within the testicles, and are the specific location of meiosis, and the subsequent creation of male gametes, namely spermatozoa.
Structure
The epithelium of the tubule consists of a type of sustentacular cells ...
, and divides the seminiferous tubule into a basal compartment (outer side of the tubule, in contact with blood and lymph) and an endoluminal compartment (inner side of the tubule, isolated from blood and lymph). The tight junctions are formed by
intercellular adhesion molecules in between cells that are anchored to actin fibers within the cells. For the visualization of the actin fibers within the seminiferous tubules see Sharma et al.'s immunofluorescence studies.
Function
The presence of the SCB allows Sertoli cells to control the adluminal environment in which germ cells (spermatocytes, spermatids and sperm) develop by influencing the chemical composition of the luminal fluid.
The barrier also prevents passage of
cytotoxic
Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are toxic metals, toxic chemicals, microbe neurotoxins, radiation particles and even specific neurotransmitters when the system is out of balance. Also some types of dr ...
agents (bodies or substances that are
toxic
Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...
to
cell
Cell most often refers to:
* Cell (biology), the functional basic unit of life
* Cellphone, a phone connected to a cellular network
* Clandestine cell, a penetration-resistant form of a secret or outlawed organization
* Electrochemical cell, a de ...
s) into the seminiferous tubules.
The fluid in the lumen of seminiferous tubules is quite different from plasma; it contains very little protein and glucose but is rich in androgens, estrogens, potassium, inositol and glutamic and
aspartic acid. This composition is maintained by blood–testis barrier.
The barrier also protects the germ cells from blood-borne noxious agents,
prevents antigenic products of germ cell maturation from entering the circulation and generating an
autoimmune
In immunology, autoimmunity is the system of immune responses of an organism against its own healthy cells, tissues and other normal body constituents. Any disease resulting from this type of immune response is termed an " autoimmune disease" ...
response,
and may help establish an osmotic gradient that facilitates movement of fluid into the tubular lumen.
[
]
Note
Steroids
A steroid is an organic compound with four fused rings (designated A, B, C, and D) arranged in a specific molecular configuration.
Steroids have two principal biological functions: as important components of cell membranes that alter mem ...
penetrate the barrier.
Some proteins
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, re ...
pass from Sertoli cells to Leydig cells to function in a paracrine
In cellular biology, paracrine signaling is a form of cell signaling, a type of cellular communication (biology), cellular communication in which a Cell (biology), cell produces a signal to induce changes in nearby cells, altering the behaviour of ...
fashion.
Clinical significance
Auto-immune response
The blood–testes barrier can be damaged by trauma to the testes (including torsion or impact), by surgery or as a result of vasectomy
Vasectomy is an elective surgical procedure that results in male sterilization, often as a means of permanent contraception. During the procedure, the male vasa deferentia are cut and tied or sealed so as to prevent sperm from entering into ...
. When the blood–testes barrier is breached, and sperm enters the bloodstream, the immune system
The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...
mounts an autoimmune
In immunology, autoimmunity is the system of immune responses of an organism against its own healthy cells, tissues and other normal body constituents. Any disease resulting from this type of immune response is termed an " autoimmune disease" ...
response against the sperm, since the immune system has not been tolerized against the unique sperm antigens that are only expressed by these cells. The anti-sperm antibodies
An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that caus ...
generated by the immune system can bind to various antigen
In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response.
...
ic sites on the surface of the developing sperm within the testes. If they bind to the head, the sperm may be less able to fertilize an egg
An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the ...
, and, if they bind to the tail, the motility of the sperm can be reduced.
See also
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References
External links
*
Overview at okstate.edu
{{DEFAULTSORT:Blood-testis barrier
Animal reproductive system
Animal physiology
Testicle