Overview of the Urinary Tract
The urinary tract is divided into 2 parts:
The function of the upper urinary tract is to produce urine (eliminate excess water, waste products and electrolytes), adjust blood pressure, help in the production of red blood cells. Characteristics of the upper urinary tract:
Urine is produced by the kidneys and then drains downstream in the following sequence (the analogy of a house is used):
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Use of these images is under the Creative Commons Attribution-Share Alike 3.0 Unported license. Author: Piotr Michal Jaworski
The basic anatomy of the penis is essentially that of 2 paired cylinders, the corpora cavernosa. Each cylinder is comprosed of an elastic vascular spongy tissue fed by single blood vessel, the cavernosal argery and is surrounded by a tough elastic vascular sheath, the tunica albuginea. The two cylinders have communications in the midline, which can allow the circulation of blood, or medication, between the cylinders.
During an erection, the inflow of blood is trapped within the corpora spongiosum. The high pressure is generated by the pumping of the heart which forces blood from the cavernosal arteries into the spongy tissue. Expansion of the spongy tissue stops once the capacity of the tunica albuginea is reached.
Men are often concerned about the length of their penis.
There is quite wide range and penile lengths. It is important to note that the length of an erect penis will vary based on how it is measured. The best way to measure is from a fixed point such as the pubic bone - which removed any of the variability introduced by the suprapubic fat pad - to the very tip of the head of the penis, ideally with an erect penis but the stretched length can closely approximate tihs. It is also important to note that pictures of penises seen on the Internet or in media (e.g. pornography) are typically skewed towards above average lengths and are not a representation of what is "normal" or "average" (just in the same way that the average height of a basketball player in the NBA is not representative of the average height and the population at large).
Several studies have measured actual penile length. In general, reported erect/stretched penile length is American and European populations is between 12.5-16.5 cm (4.9-6.5 inches). Note that 'flaccid' (non-erect) length does not correlate with erect length.