Urology is the branch of medicine concerned with the urinary tract of both sexes and genital tract of the human male. This site contains information on the anatomy, physiology and disorders or dysfunctions of the male urogenital system, subjects relating to specific parts of the male reproductive system such as the prostate, penis or testicles and that all important androgen, testosterone.
Development
Men and women are different from the get-go. The genetic (chromosomal) differentiator of an embryo, a pair of sex chromosomes, can be either XX or XY. Males result from the XY configuration. The differentiation of the primitive gonads are genetically determined. In a genetically male embryo, the primitive gonads begins to develop into testicles during the 7th and 8th week of gestation when placental gonadotropic hormones cause the differentiation of the center portion of the gonad while the outer portion regresses. This medullary region begins to produce testosterone and a female-characteristic-inhibiting substance. This substance promotes the regression of the primordial female duct system. At 7 weeks the external and internal genitalia are bipotential, but by the 8th week the committment to the male form is made under the influence of testosterone. The embryonic interstitial cells remain differentiated up to 4 months of gestation after which they regress and remain quiescent until stimulated by pituitary luteinizing hormone (LH) at puberty. Male sexual behavior is due to the action of male hormones on the brain in early development. Secondary sexual characteristics typical of the adult male are a result of the action of testosterone at puberty and throughout adulthood.
Anatomy
Testes
These paired ovoid glands are suspended in the scrotum beneath the penis. Each testicle consists of many lobules of coiled seminiferous tubules and interstitial cells of Leydig. Spermatogenesis occurs in the seminiferous tubules and the interstital cells make and secrete the hormone testosterone.
Epididymis
This genital duct serves as a passageway for sperm. Sperm are stored in the epidydmis for 18 hours up to 12 days during which they mature, become motile, and capable of fertilization.
Vas deferens
This duct (one for each testis) carries sperm from the epididymis into the abdomen, passing over the bladder, and joins the duct from the seminal vesicle to form the ejaculatory duct. The ejaculatory ducts desend through the prostate and terminate in the prostatic urethra. The vas deferens serves as another storage site for sperm.
Prostate
This gland is located just below the bladder and surrounds the ejaculatory ducts and prostatic urethra. It secretes a milky, alkaline fluid that makes up about 30% of the seminal fluid volume. The alkalinity helps to neutralize the acidity of the male urethra and female vagina. The cells of the prostate and prostate cancer produce a protein called prostate specific antigen, a common biomarker for metastatic cancer of the prostate.
Seminal vesicles
These glandular sac-like organs reside behind the bladder. The thick alkaline fluid secreted by the glandular epithelium of the seminal vesicle contributes about 60% of the seminal fluid volume. This fluid is rich in fructose, citric acid, amino acids, proteins, and prostaglandins for the health and nutrition of the sperm.
Urethra
This tubular passageway for seminal fluid to the outside world is 18-20 cm in length and passes through the prostate and the penis. Glands along the urethra secrete mucous and fluid from the Cowper’s glands is added here.
Bulbourethral (Cowper) glands
These paired pea-sized glands lie just below the prostate gland and secrete about 5% of the total seminal fluid volume.
Penis
Three areas of erectile tissue are housed within a loose layer of skin and connective tissue. There are two corpra cavernosa and the corpus spongiosum. The spongiosum is smaller, houses the urethra and lies under the paired cavernosa. The corpus spongiosum expands distally to form the glans penis. Circumcision removes a fold of loose skin that covers the glans. The erectile tissue is spongelike and contains a large vascular bed. The penis serves as a passageway for urine, by virtue of the urethra, and serves as the copulatory organ to deliver semen.
Erection & Ejaculation
This hemodynamic event is controlled by neural input. The flaccid state is maintained by continuous sympathetic (alpha adrenergic) nervous system stimulation of the penile blood vessels and trabecular smooth muscle. Erection occurs when vasodilator impulses are delivered by the parasympathetic nervous system which also causes the relaxation of the penile smooth muscle. Dialation of the arterioles of the penis causes the erectile tissue of the penis to fill with blood. The veins are compressed so that outflow is blocked. The effect of these vascular changes is an increase in penile turgor or a ballooning effect. The neural pathways involved in erection are integrated in the lumbar segments of the spinal cord from inputs from sensory endings in the genitalia and descending tracts carrying impulses generated from erotic psychological stimuli. Erection is mediated via the parasympathetic nervous system and terminated via the sympathetic nervous stimulation causing the constriction of penile arterioles.
A two-part spinal reflex controls ejaculation. The first phase, emission, is the movement of semen into the urethra. This is followed by the propulsion of the semen out of the urethra at orgasm. Sensory nerve endings in the glans penis travel over the pudendal nerves to the upper lumbar segments of the spinal cord where they are integrated and semen emission is initiated. At the same time the bladder neck contracts by closure of the internal sphincter thus preventing the expulsion of urine. Signals from the upper sacral and lowest lumbar regions initiate ejaculation. Efferent nerve impulses are sent to the vas deferentia, seminal vesicles and bulbocavernosus and ischiocavernosus muscles causing muscle contraction and the rythmic expulsion of the semen.
Following orgasm, blood is rapidly removed from the penile erectile tissues and the penis becomes flaccid. There is a variable refractory period that must occur prior to the sequence being repeated.
Semen contains sperm and secretions of the seminal vesicles, prostate, Cowper’s glands, and urethral glands. The average volume expelled is about 2-3 mililiters containing about 100 million sperm per mililiter.
Both the volume and sperm count decrease with successive ejaculations. Upon ejaculation the semen becomes less viscous due to proteolysis of certain proteins by enzymes. Human sperms travel at about 3 mm/min in the female genital tract taking some 30-60 minutes for sperm to reach the Fallopian tubes (where fertilization normally occurs).
Common Disorders
Impotence
Erectile dysfunction may occur with or without associated disturbances in libido or ejaculation. It is likely that all men experience occasional episodes of impotence sometime in their lives. The causes of erectile dysfunction can be pathological, pharmacological or psychogenic. Most organic causes boil down to disturbances in neural pathways involved in erection or blood supply to the penis. Drugs and psychogenic factors diminish libido (desire for sex), interfere with neural pathways and blood flow. In some patients, the cause of erectile dysfunction has many contributing factors.
Symptoms of erectile dysfunction are, alone or in combination, a constant or episodic inability to maintain an erection, decreased penile pressure and decreased libido. Signs and symptoms of the underlying pathological or psychological cause may also be seen. In psychogenic or drug-induced cases there is often a rapid onset of the dysfunction. Patients with organic impotence generally have had a more gradual loss of potency without any decrease in libido. However, those patients with a systemic cause, such as cirrhosis or cardiac insufficiency, may have a concurrent loss of libido and potency.
Behavioral therapy, reassurance, explanation and psychotherapy are effective 40-70% of the time in psychogenic impotence. Removing the causitive drug usually results in a return to potency in drug-induced impotence. Effective therapy for the underlying organic cause will similarly effect a cure to erectile dysfunction in many cases. For those with permanent neuronal damage, surgically implanted prostheses are available. These devices have been satisfactory in 85-90% of cases.
Treatments for erectile dysfunction include intercavernous injections or oral medications. Approved oral treatments include sublingual apomorphine, oral sildenafil (ViagraTM), and alpha adrenergic antagonists (yohimbine, phentolamine, and prazosin). Apomorphine is a centrally-acting non-opiod dopamine agonist with proven erectogenic activity and no effect on libido. It has fewer systemic side effects than some of the other treatments. Oral sildenafil has adverse drug interactions and side effects associated with it. Alpha adrenergic antagonists such as are also effective treatments for erectile dysfunction in some men. However, these are general alpha adrenergic antagonists and therefore have a much broader action than is needed and some unwanted side effects.
Infertility
Male fertility is dependent on the quantity of semen ejaculated, the number of sperm per mililiter, and the motility and morphology of the sperm. On average some 400 million sperm are ejaculated in a fluid volume of 3 ml. When the number of sperm drops below 20-50 million infertility (defined as the inability to conceive after 12 months of adequate exposure in unprotected sex) and/or sterility results. About 15% of married couples are infertile for one or more reasons. Male factors are responsible for some 40% of the infertility seen in married couples and 20% is due to combined male and female factors.
About 9% of males evaluated for infertility have a disturbance of the hypothalamus, pituitary, adrenal or thyroid glands. Sex chromosome abnormalities, cryptorchidism and adult seminiferous tubule failure are found in 18% of infertile males. About 4% of male infertility cases are associated with varicoclele and less than 10% have a congenital or acquired ductal abnormalities. Autoimmune disturbances, ejaculation disturbances and anatomic abnormalities are much less common causes. In some cases, (5-6%) no causitive factor can be defined.
Gynecomastia
Male breast development is common during the neonatal peiod and is present in about 70% of pubertal males. The causes are numerous, but include drug-induced (marijuana, methyldopa, digitalis, phenothiazines), endocrine, systemic disease, tumors of endocrine cells, familial or idiopathic causes. Proposed mechanisms for this disorder involve an imbalance between estrogen and androgen concentration or an abberation in response at the mammary gland level. Chronic gynecomastia is usually asymptomatic. Acute gynecomastia often presents with nipple or breast pain and tenderness, enlarged breasts and sometimes a discharge. Patients may be more at risk for breast cancer. Treatment is by removing the underlying cause or drug. Antiestrogens are useful for relieving pain and reversing gynecomastia in some patients. For cosmetic reasons, surgical reduction may be considered. Pubertal gynecomastia usually spontaneously regressess over 1-2 years. Drug-induced breast enlargement is easily corrected by removal of the causitive agent in the early stages of the disorder. After 6 months to a year very little regression takes place.