The male reproductive system is a network of external and internal organs that function to produce, support, transport, and deliver viable sperm for reproduction. Prenatally, the male sex organs are formed under the influence of testosterone secreted from the fetal testes; by puberty, the secondary sex organs further develop and become functional. Sperm is produced in the testes and is transported through the epididymis, ductus deferens, ejaculatory duct, and urethra. Concomitantly, the seminal vesicles, prostate gland, and bulbourethral gland produce seminal fluid that accompany and nourish the sperm as it is emitted from the penis during ejaculation and throughout the fertilization process (see image below).
The scrotum is a fibromuscular pouch divided by a median septum (raphe) forming 2 compartments, each of which contains a testis, epididymis and part of the spermatic cord. Layers of the scrotum consist of skin, dartos muscle, external spermatic fascia, cremasteric fascia and internal spermatic fascia, which is in close contact with the parietal layer of the tunica vaginalis. 
The skin and dartos layers of the scrotum are supplied by the perineal branch of the internal pudendal artery in addition to the external pudendal branches of the femoral artery. The layers deep to the dartos muscle are supplied by the cremasteric branch of the inferior epigastric artery. The veins of the scrotum accompany the arteries, eventually draining into the external pudendal vein and subsequently the greater saphenous vein. Lymphatic drainage of the skin of the scrotum is by the external pudendal vessels to the medial superficial inguinal lymph nodes.
The scrotum has a rich sensory nerve supply that includes the genital branch of the genitofemoral nerve (anterior and lateral scrotal surfaces), the ilioinguinal nerve (anterior scrotal surface), posterior scrotal branches of the perineal nerve (posterior scrotal surface), and the perineal branch of the posterior femoral cutaneous nerve (inferior scrotal surface).
The testes are the primary male reproductive organ and are responsible for testosterone and sperm production. Each testis is 4-5-cm long, 2-3-cm wide, weighs 10-14 g and is suspended in the scrotum by the dartos muscle and spermatic cord. Each testis is covered by the tunica vaginalis testis, tunica albuginea, and tunica vasculosa. The tunica vaginalis testis is the lower portion of the processus vaginalis and is reflected from the testes on the inner surface of the scrotum, thus forming the visceral and parietal layers. Beneath the visceral layer of the tunica vaginalis is the tunica albuginea, which forms a dense covering for the testes.
Internal to the tunica albuginea is the tunica vasculosa, containing a plexus of blood vessels and connective tissue. Bilateral testicular arteries originating from the aorta, just inferior to the renal arteries, provide arterial supply to the testes. The testicular arteries enter the scrotum in the spermatic cord via the inguinal canal and split into two branches at the posterosuperior border of the testis.
Additionally, the testes receive blood from the cremasteric branch of the inferior epigastric artery and the artery to the ductus deferens. The pampiniform plexus drains both the testis and epididymis before coalescing to form the testicular vein, usually above the spermatic cord formation at the deep inguinal ring. Lymphatic drainage via the testicular vessels passes into the abdomen, ending in the lateral aortic and pre-aortic nodes. The tenth and eleventh thoracic spinal nerves supply the testes via the renal and aortic autonomic plexuses
The testes are divided into approximately 400 segments called lobules each of which
is occupied by 2-4 seminiferous tubules, which are responsible for producing spermatozoa.  Each testis has 600-1200 seminiferous tubules with a total length of 280-400-m.  At the mediastinum testis, on the posterior border of the testis, the seminiferous tubules empty spermatozoa into the tubuli recti and rete testis, eventually coalescing to form 6-8 efferent ductules.  The efferent ductules drain spermatozoa into the epididymis (see image below).
In the relaxed state (non-contracted dartos and cremasteric muscles), the scrotum is smooth and pendulous. However, when the dartos and cremasteric muscles contract secondary to cold or emotional stimuli, the scrotum becomes smaller, rounder and more wrinkled.
Although the shape of the testis varies little, the variation in size may be considerable. Contributing factors may include overall body habitus and race; however, certain conditions (ie. Fragile X syndrome) are associated with larger (macro-orchidism) and smaller (micro-orchidism -Klinefelter syndrome) testicles.
The 2 most common natural variations for the epididymis are the size and the rigidity with which the structure is attached to the testicle.
The seminal vesicles show considerable variation in size, most notably when the vesicle is in the full or empty state.
In the flaccid state, the penis varies in length from 8-12 cm and in width from 3-4.5 cm.  Factors influencing size may include race and physiological differences. For example, when the temperature is cold, contraction of the dartos muscle causes the penis to decrease in size. In the erectile state, the penis varies in length from 12-18 cm and in width from 4-5 cm. 
A developmental defect may occur that allows the tunica vaginalis to retain direct communication with the peritoneum and the possibility of subsequent bowel herniation. A congenital inguinal hernia can be differentiated from an acquired inguinal hernia by the intraoperative finding of bowel in contact with the testis. Bifid scrotum occurs when the two halves of the scrotum are separated by a cleft due to failed fusion of the paired genital swellings and is commonly associated with severe degrees of hypospadias or ambiguous genitalia. 
Anorchidism is a rare condition consisting of bilateral absence of the testis. Monorchidism is the presence of one testis and polyorchidism is the presence of a supernumerary testis.
Cryptorchidism (undescended testes) is one of the most frequent anomalies of the congenital organs and may occur in up to 1 of 500 male births,  as well as unilaterally or bilaterally. Undescended testis are usually small, atrophic and often non-functional. Arrested migration may occur at any point during testis descent. Abdominal cryptorchidism occurs when the testis arrest superior to the inguinal canal, inguinal cryptorchidism occurs within the inguinal canal and subinguinal cryptorchidism occurs between the superficial inguinal ring and the scrotum.
Patients with undescended testis are at increased risk of testicular malignancy, most commonly testicular seminoma. The incidence of a testicular tumor in the general population is 1 in 100,000 and in men with a cryptorchid testis is 1 in 2550, resulting in an overall relative risk of greater than 40. 
Ductus (vas) deferens
The ductus deferens may be congenitally absent, a condition known as vasal aplasia. This condition has been linked to cystic fibrosis, resulting in azoospermia even though the process of spermatogenesis is often normal.
A short spermatic cord occurs when the growth of the spermatic cord does not keep pace with the rest of the body’s growth. In these instances, the testis may be higher in the scrotum often referred to as an ascending or retractile testis.
See the list below:
A hydrocele (communicating) is a collection of peritoneal fluid that accumulates between the layers of the tunica vaginalis when the processus vaginalis fails to obliterate between the deep inguinal ring and the superior border of the scrotum. Most communicating hydroceles are smaller in the morning and increase in size throughout the day when the individual is in the upright position. Diagnosis is based on physical examination and transillumination of the hydrocele sac.
Fournier’s gangrene is a form of necrotizing fasciitis affecting the scrotum and often extending to the perineum, penis and abdominal wall. Patients with diabetes mellitus, local trauma, periurethral extravasation of urine and perianal infection are predisposed to Fournier’s gangrene. The initial diagnosis can be made based on a swollen, erythematous and tender infection of the scrotum and the most common pathogens are facultative organisms, anaerobes and group-A streptococcus.
See the list below:
Testicular torsion may occur if the testis twists on the suspending spermatic cord. This is a surgical emergency, as the blood supply needs to be restored to the testis within six hours of symptom onset in order decrease the risk of testis infarction. The testis should subsequently be sutured to the scrotal wall (orchiopexy) to prevent recurrence, in addition to orchiopexy of the contralateral testis.
Most acute presentations of scrotal pain and swelling can be attributed to epididymitis, testicular torsion, or torsion of a testicular appendage. In many cases, torsion of a testicular appendage, although a benign condition, may present identically to testicular torsion, a true urologic emergency. Ultrasound may be used to aid in diagnosis, however a normal clinical exam of a non-tender testis in the presence of a paratesticular nodule at the superior pole may be more diagnostic for appendical torsion. Classically, a blue-dot appearance (Blue Dot sign) may be seen in the area of the injury, however this is only present in 20% of cases.
Varicocele is a common condition characterized by enlargement and thickening of the pampiniform plexus in the spermatic cord. Varicocele is most commonly causes by defective venous valves but also may be due more serious causes such as testicular vein compression secondary to an abdominal tumor. Symptoms of varicocele include a dull, aching pain in the scrotum, testicular heaviness, testicular atrophy and visible and palpable veins in the scrotum commonly referred to as feeling like “a bag of worms.”