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 ...

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

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 ...

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

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.

References

External links

*
Overview at okstate.edu
{{DEFAULTSORT:Blood-testis barrier Animal reproductive system Animal physiology Testicle