Male Fertility

THE MALE GENITAL SYSTEM

Spermatozoa are generated by the seminiferous tubules of the testes, traverse through, and are further matured in the epididymes and subsequently transported through the vas deferens and ejaculated out through the urethra. Seminal fluid is produced predominantly by the seminal vesicles, prostate, and bulbourethral glands.

THE TESTES

Oval-shaped, averaging 5x3x2cm in the three diameters. Weighs about 12gm and consists of approximately 250 lobes. Each lobe contains a seminiferous tubule of about 50cm in length with a diameter of about 0.25mm. Total tubular length per testis is about 125m. Daily sperm output by the testes equals approximately 45-280 million spermatozoa. The testis is an endocrine organ consisting of Leydig cells found between the seminiferous tubules, which are lined by Sertoli cells between which the germ cells are located. Blood and lymph vessels traverse between the seminiferous tubules.

Many subdivisions occur in the evolution of the spermatogenic cells, a total of seven steps in the transformation of spermatogonia into primary spermatocytes having been demonstrated in the human. Not all spermatogonia become spermatocytes; some of them remain unchanged to initiate the next cycle of development. There are four varieties of spermatogonia and three types of primary spermatocytes, very short-lived secondary spermatocyte, and six types of spermatids, the most mature being identified as spermatozoa.

The duration of spermatogenesis from stem cell (spermatogonia) to mature spermatozoa requires a calculated 74+/-4 days. The total duration involves four cycles. In the human testis, six distinct stages (cellular associations) have been identified.

Throughout spermatogenesis, germ cells exist as clusters (perhaps several hundred or more)of cells connected by intercellular bridges. At the time of release of the mature spermatid (to be spermatozoa), excess sperm cytoplasm is pinched off from the sperm and phagocytized by the Sertoli cells. Even the cytoplasmic droplets are in the form of clusters connected by intercellular bridges just prior to their being upgulfed by the Sertoli cells. Current speculation is that the clusters of cells connected by intercellular bridges represent a form of a syncytium related to the coordination of the differentiation of the germ cells through the cycle.

Following their release, spermatozoa are moved by peristaltic movements of the seminiferous tubules, into the rete testis which funnels into a single coiled tubule, running through the epididymis. It is believed that the spermatozoa acquire the ability to become motile within the epididymis.

SEMINAL PLASMA

Whole semen is derived from various compartments of the male reproductive tract. The order in which the secretion in an ejaculate arises begins with the bulbourethral glands, followed by the prostate. Components from the testes and epididymes are next released from storage in the ampullary region of the vas deferens. The final contribution is from the seminal vesicules. In fertile men, the prostate produces about 30%, the seminal vesicles about 60%, and the remaining structures about 5-10% of the volume of seminal plasma. Spermatozoa make up about 0.001% of the total volume. Fluid from seminal vesicles contain high levels of fructose and prostaglandins. Acid phosphatase is found in high levels in seminal fluid and is a secretory product of the prostate gland. Current evidence suggests the presence of an unidentified factor in prostatic fluid related to sperm motility. The secretions of the bulbourethral grands contain sialoprotein. The role of this gland in reproduction is unknown.

SEMEN ANALYSIS

A standard test in male fertility work-up includes the semen analysis. About 90% of fertile men have sperm counts of 10-250 million/ml. At least 40% of the cells show good forward progression, and at least 60% have normal morphology. Semen volumes normally range from 2-5ml. Less than 2ml is referred to as hypospermia, and greater than 6ml is hyperspermia. Among infertile men, semen volumes may range from 0.5-10ml. Failure to produce and ejaculate may indicate retrograde ejaculation into the bladder. Urinalysis is used to confirm this condition. Sperm counts of less than 10 million/ml are referred to as oligospermia. Counts of greater than 250 million/ml is are referred to as hyperzoospermia and are related to infertility, in some instances. Semen having no sperm (azoospermia) may indicate testicular failure or a blockage in the epididymis or vas deferens. Small testes would also be an indication of severe or complete testicular failure.

CAUSES OF MALE INFERTILITY

Apart from vasectomy and pathologies involving surgical intervention (seminoma), the most common cases of male factor infertility include the following:

ENDOCRINOLOGY OF THE TESTIS

Control of testicular function is not autonomous but, rather, it involves a system of stimulation and feedback from other centres. These regions include the hypothalamus, anterior pituitary, and the testis itself. At least two sites in the testis are involved, and these include the Leydig (interstitial) cells and the seminiferous tubules. The principle product of the Leydig cells is the male sex hormone known as testosterone (or its metabolites). The major components of the seminiferous tubules are the Sertoli cells and the germ cells, collectively known as the germinal epithelium. Hormonal products of the testis have a direct inhibitory feedback effect on both the hypothalamus and the anterior pituitary. Products of the hypothalamus are stimulatory to the anterior pituitary, which, in turn, produces hormones that are stimulatory to the testis. A hormone from the anterior pituitary may also be stimulatory to the hypothalamus. It is obvious, therefore, that maintenance of normal testicular function is predicated upon numerous factors derived from the sites involved.

Category: Pathology Notes