The Male Reproductive System
A system block diagram is provided below in figure 1 to simplify description using easily understood mechanical and electrical devices. Basically, the system comprises a number of fluid stores, fluid pumps, ducts and a senor/probe. Not shown is the processor (brain) that controls the operation of the system.
The main component parts of the reproductive system are the prostate gland (A), the seminal vesicle (B) the bulbourethral glands (C) the testes (D) and the penis depicted as sensor probe (10). Although not an essential part of the reproductive system, the bladder is depicted as fluid store (1).
- The prostrate gland comprises a valve (2), an Alkaline Fluid Store (3) and a Pump (5)
- The seminal vesicle comprises a nutrient fluid store (4)
- The bulbourethral glands comprise a lubricating store (8) and pump (6).
- The testes comprise fertiliser store (9) and pump (7).
The dark lines are fluid ducts and the arrows show the direction of fluid flow.
When the reproductive system is not in operation all pumps are inoperative and valve (2) is open. Also, all fluid stores are full, assuming sufficient time for replenishment since the system was last used.
From sexual arousal to ejaculation of semen the following events take place.
Figure 1: Simplified Block Diagram of the Male Reproductive System
Event 1: The penis (10) becomes erect and the surface area becomes more sensitive to stimulus.
Event 2: After sexual arousal reaches a high state, valve (2) is closed to prevent flow of urine from the bladder (1) and any semen flow into the bladder. Also, the lubricating fluid (8) is secreted by pump (6) through the open pump (5) down the fluid duct to discharge from the end of the penis (10).
Event 3: At the point of ejaculation, pump (7) become operational along with the main ejaculatory pump (5), to combine and force the nutrient (4) and alkaline fluids (3) along with sperm from the fertiliser store (9) out of the penis (10).
Event 4: After ejaculation has occurred, the penis becomes placid and the system returns back to its rest state to allow replenishment of the fluid stores to take place.
The ejaculated fluid discharged from the penis at is known as semen and is a combination of the alkaline, nutrient and lubricating fluids as well as the sperm.
The constituent parts of semen are shown in figure 2 below.
Figure 2: Constituent Parts of Semen
Although simplified, the constituent parts of semen basically comprise nutrients to feed the sperm on its journey (70%), an alkaline (antacid) solution (25%) to protect the sperm from the acidity of the virginal tract and a lubricant (1%) to cleanse and smooth the way for the semen along the urethra. The actual sperm content represents less than 4% of the fluid ejaculated from the penis.
The prostate gland
The main function of the prostate is to store and secrete the alkaline fluid. The prostate also contains some smooth muscles that help expel semen during ejaculation.
A small amount of the alkaline fluid (les than 1%) includes proteolytic enzymes, prostatic acid phosaphatases and Prostate Specific Antigen (PSA). This fluid also contains zinc.
Table 1, below describes the four zones and the constitution of the zones in a percentage of the prostate as a whole.
| Zone | Constitution (%) | Description |
| Peripheral Zone (PZ) | Composes up to 70% of the normal prostate gland in young men. | The sub-capsular portion of the posterior aspect of the prostate gland which surrounds the distal urethra. It is from this portion of the gland that more than 64% of prostatic cancers originate. |
| Central Zone (CZ) | Constitutes approximately 25% of the normal prostate gland. | This zone surrounds the ejaculatory ducts. The central zone accounts for roughly 2.5% of prostate cancers although these cancers tend to be more aggressive and more likely to invade the seminal vesicles. |
| Transition Zone (TZ) | Responsible for 5% of the prostate volume at puberty. | Prostate cancer originates in this zone in roughly 34% of patients. The transition zone surrounds the proximal urethra and is the region of the prostate gland which grows throughout life and is responsible for the disease of benign prostatic enlargement. |
| Anterior fibro-muscular zone (or stroma) | Accounts for approximately 5% of the prostatic weight. | This zone is usually devoid of glandular components, and composed only, as its name suggests, of muscle and fibrous tissue. |
To work properly, the prostate needs male hormones (androgens), which are responsible for male sex characteristics. The most significant male hormone is testosterone, which is produced mainly by the testes. Some male hormones are produced in small amounts by the adrenal glands. A healthy prostate is slightly larger than a walnut. It surrounds the urethra just below the urinary bladder and can be felt during a Digital Rectum Examination (DRE).
The prostate gland has four distinct glandular regions, two of which arise from different segments of the prostatic urethra.
The Central Zone accounts for the most aggressive prostate cancers which are more likely to invade the seminal vesicles. Although this zone only represents approximately 2.5% of cancers compared with the Peripheral Zone which represents 64% of cancers, the actual percentage of the aggressive cancers compared with all life threatening cancers is higher because 34% of all growths (those mainly originating in the Transition Zone) are benign.
The seminal vesicles
The seminal vesicles are posterior to the urinary bladder and just above the prostate gland. About 65-75% of the semen originates from the seminal vesicles, which contain proteins, enzymes, fructose, mucus, vitamin C, flavins, phosphorylcholine and prostaglandins. High fructose concentrations provide nutrient energy for the spermatozoa as they travel through the female reproductive system.
Loading ...
