Items 80-82

Experimental vascular perfusion of the testis with lanthanum nitrate ( an electron dense, low molecular weight tracer ) is followed by fixation of seminiferous tubules. Subsequently, seminiferous tubules are prepared for transmission electron microscopy.

80. Lanthanum nitrate would be found in all of the following locations EXCEPT:

( A ) interstitial tissue
( B ) surrounding Leydig cells
( C ) around primordial germ cells
( D ) around immature primary spermatocytes
( E ) around spermatids

81. What structural arrangement prevents penetration of lanthanum nitrate into the adluminal compertment?

( A ) desmosomes
( B ) zonula adherens
( C ) tight junctions
( D ) gap junctions
( E ) basement membrane of the seminiferous epithelium

82. These structural elements also function in the formation of all the following morphology barriers EXCEPT:

ANSWERS AND TUTORIAL ON ITEMS 80-82

The answers are: 80-E, 81-C; 82-A. Tight junctions are an essential feature of many epithelial layers. Epithelia line cavities and cover surfaces. They have tight lateral junctions that allow them to serve as boundary tissues, separating one compartment in the body from another. For example, intestinal epithelial cells are joined together by apical junctional complexes. The junctional complex consists of an apical zonula occludens or tight junctions, a zonula adherens just deep to the zonula occludens and a macula adherens ( desmosome ) deep to the zonula adherens. The tight junction is a region of fussion of the outer leaflets of the plasma membranes fo adjacent cells. It provides a hydrophobic barrier preventing the contents of the intestinal lumen ( digestive enzymes ) from diffusing into the lateral spaces between cells. Tight junctions are also present between capillary endothelial cells in continous capillaries where they serve as the anatomical basis for the bloos-brain and between liver parenchymal cells where they serve as the anatomical basis for the blood-bile barrier. The blood-urine barrier in the kidney is more complex. The glomerular basement membrane and the filtration slit diaphragms between podocyte foot processes serve as the anatomical barrier between blood and urine. In the seminiferous epithelium, Sertoli cells form a continous epithelial layer. The spermatogenic cell line is lodged in the spaces between Sertoli cells. A complex web of tight junctions between adjacent Sertoli cells divides the seminiferous epithelium into a basal compartment containing only spermatogonia, preleptotene primary spermatocytes and leptotene primary spermatocytes. Later stages in spermatogenesis including late primary spermatocytes, secondary spermatocytes, spermatids and spermatozoa are contained within the adluminal compartment apical to the web of tight junctions. This elaborate system of tight junctions prevents exposure of the immune system to foreign antigens of mature gametes. During fetal development the male gonad becomes equipped with spermatogonia prior to the time in development when the immune system gains the ability to discriminate between native and foreign antigens. Thus, spermatogonia are recognized as native antigens. Spermatogenesis does not begin until puberty, long after to establishment of the immunological sense of native and foreign antigens. Consequently, the surface antigens peculiar to spermatozoa would be recognized as foreign antigens were it not for the tight junctions excluding these foreign antigens from immune surveillance. Other mechanisms also ensure that there is no contact between seminal antigens and the male circulatory system. Ore Microscopes Phase Contrast Microscopes Polarizing Microscopes