Ejaculation is the process by which semen, the fluid containing sperm, is expelled from the male reproductive tract through the urethra. This biological event is a complex, involuntary physical reflex involving coordinated muscular contractions and specific nerve signals. It represents the culmination of the male sexual response cycle, serving the primary biological function of delivering genetic material.
The Physiological Process
The act of ejaculation is governed by a spinal reflex arc that operates largely outside of conscious control. Sensory stimulation triggers signals that travel to the lumbar region of the spinal cord, initiating the preparatory stage. This signal cascade prepares the reproductive organs for the movement of fluid through two distinct, synchronized phases.
Emission
The first phase is known as emission, where the various components of semen are collected in the prostatic urethra. This stage is controlled by the sympathetic nervous system, which directs the smooth muscle surrounding the accessory glands to contract. These contractions propel sperm from the epididymis and fluids from the seminal vesicles and prostate gland into the urethral bulb.
During emission, a crucial protective reflex occurs where the internal sphincter muscle at the neck of the bladder contracts tightly. This involuntary closure prevents semen from flowing backward into the bladder, a condition known as retrograde ejaculation. The simultaneous contraction of the vas deferens and the seminal vesicles completes the pooling of fluid, readying it for the subsequent expulsion phase.
Expulsion
The second phase, expulsion, begins once the urethra is distended with the collected seminal fluid, triggering further somatic nerve signals. These signals cause powerful, rhythmic contractions of the striated muscles located in the pelvic floor, primarily the bulbospongiosus muscle. These muscular spasms generate the pressure necessary to forcibly eject the semen from the urethral opening.
The force and distance of the expulsion are directly related to the strength and frequency of these pelvic muscle contractions. Initially, the contractions are rapid, occurring at intervals of about 0.8 seconds, producing the greatest volume of fluid. The intensity and frequency of these muscle spasms gradually diminish until the reflex ceases entirely.
Composition of Seminal Fluid
Semen is a complex biological fluid composed of cellular elements, primarily spermatozoa, suspended in a nutrient-rich plasma called seminal plasma. While sperm cells originate in the testes and are stored in the epididymis, they account for less than five percent of the total ejaculate volume. The remaining majority of the fluid is produced by the accessory glands, which provide the environment necessary for sperm motility and survival.
Seminal Vesicles
The seminal vesicles are the largest contributors to the fluid volume, typically providing between 50 and 70 percent of the total ejaculate. Their secretion is a viscous, yellowish fluid rich in the simple sugar fructose, which serves as the primary energy source for the sperm cells’ flagellar movement. They also contribute prostaglandins and clotting factors that help semen temporarily coagulate after ejection.
Prostate Gland
The prostate gland contributes approximately 20 to 30 percent of the total seminal fluid. It produces a thin, milky, slightly acidic fluid that becomes alkaline upon mixing with vesicular fluid. This prostatic fluid contains citrate, zinc, and specialized enzymes. One of the most notable components is prostate-specific antigen (PSA), an enzyme that acts hours after ejaculation to break down the temporary gel-like clot.
The initial alkaline nature of the combined seminal fluid helps neutralize the natural acidity of the male urethra and the female vaginal tract. This pH adjustment creates a more hospitable environment, protecting the sperm from immediate degradation. Zinc concentration within the prostatic fluid plays a role in stabilizing sperm chromatin and regulating fertility.
Bulbourethral Glands
Trace amounts of fluid, known as pre-ejaculate, are contributed by the bulbourethral glands, which are located near the base of the penis. This clear, mucus-like secretion helps to lubricate the urethra and neutralize residual acidity before the main semen volume passes through. While small in volume, this fluid can sometimes contain small amounts of sperm.
Indicators of Ejaculate Health
The volume of fluid expelled can be a basic indicator of accessory gland function, particularly the seminal vesicles and prostate. A typical volume for a healthy adult male ranges between 1.5 and 5.0 milliliters. Volumes consistently falling below this range, known as hypospermia, may signal issues with gland secretion or potential duct blockage.
The time elapsed since the last ejaculation is the largest factor influencing the volume of the next release. Periods of abstinence usually result in a higher volume due to the accumulation of fluids and sperm. Factors such as age, hydration level, and overall hormonal health also play a role in determining both volume and frequency.
Semen naturally appears as a cloudy, whitish-gray fluid, often with a slightly gelatinous consistency immediately after expulsion due to the clotting factors. Within minutes, the PSA enzyme from the prostate causes liquefaction, making the fluid thinner and more watery. Variations in color, such as a yellowish tint, can sometimes be attributed to diet, vitamin intake, or prolonged periods of abstinence.
The appearance of a reddish or brown color, known as hematospermia, indicates the presence of blood, which may stem from inflammation or infection in the reproductive tract. A noticeable decrease in volume or the persistence of a thick, non-liquefied consistency should prompt a consultation with a healthcare provider to rule out underlying conditions.