The prostate is a small gland that is part of the male reproductive system, primarily responsible for contributing fluid to semen. Its structure and location are unique, influencing both reproductive and urinary functions throughout a man’s life. Understanding the prostate’s physical characteristics provides insight into its function and how it changes with age.
Where the Prostate is Located
The prostate gland is situated deep within the male pelvis, immediately beneath the urinary bladder. This placement means the prostate is positioned directly in front of the rectum, which is why a physician can examine it during a digital rectal exam.
The gland’s most defining spatial relationship is with the urethra. The prostate completely encircles the initial segment of the urethra, often described as the prostatic urethra. This tight anatomical relationship explains why changes in the gland’s size can directly affect a person’s ability to urinate. It is held in place by surrounding tissues and ligaments, forming a boundary between the bladder above and the external sphincter muscle below.
The Gland’s External Appearance and Size
In a healthy, young adult male, the prostate gland is a relatively modest organ, commonly compared in size to a walnut or a chestnut. Its dimensions are typically small, measuring approximately 4 centimeters wide, 3 centimeters high, and 2 centimeters deep. This size translates to an average volume of about 25 cubic centimeters and a weight of roughly 20 to 25 grams.
The prostate’s shape is often described as an inverted cone or a flattened sphere, with a broad base facing upward toward the bladder. Its exterior is encased in a thin, fibrous covering known as the prostatic capsule. When palpated, the texture of a healthy prostate is typically smooth and firm, often likened to the consistency of a rubber ball.
Internal Structure: Zones and Lobes
The prostate is anatomically organized into distinct regions that are significant for understanding disease patterns. The most widely accepted model divides the glandular tissue into three main zones, which differ in their cell types and susceptibility to specific conditions.
The largest is the Peripheral Zone, which accounts for about 70% of the gland’s total volume and forms the posterior and lateral parts. The majority of prostate cancers originate in the cells of this zone. The Central Zone is a wedge-shaped region surrounding the ejaculatory ducts, making up approximately 25% of the glandular tissue.
The third major region is the Transitional Zone, a small area that surrounds the urethra, comprising only about 5% to 10% of the normal prostate volume. This zone is the site where benign prostatic hyperplasia (BPH), or non-cancerous enlargement, typically develops. While the zonal model is used for pathology, the prostate is also described anatomically by lobes:
- Two lateral lobes.
- Anterior lobe.
- Median lobe.
How the Prostate Changes Over Time
The physical appearance of the prostate does not remain static throughout a man’s life; it undergoes two main growth phases. A more sustained and noticeable growth phase begins around age 40 and continues for decades. This age-related increase in size is a common occurrence, with the gland steadily becoming larger and heavier.
This growth, known as hyperplasia, significantly alters the gland’s overall shape, moving it from a walnut-sized organ toward the size of an apricot or even a lemon in older individuals. The increase is largely driven by the proliferation of cells within the Transitional Zone, which expands inward, causing the gland to bulge and potentially compress the central urethra passing through it. This change in physical appearance is a normal part of aging for many men, even if the enlargement is not always accompanied by problematic symptoms.