The fundamental elements of the urinary apparatus are the kidneys (french: les reins) - two glandular organs situated in the loins behind the peritoneum, each of which is provided with a duct - the ureter - for the passage of the secretion to a reservoir - the bladder - by which it is periodically expelled from the body through a tube of outlet - the urethra.
Physical characters of the kidneys
The kidney in its typical form is bean-shaped. It is elongated from above downwards, compressed between its parietal and abdominal surfaces, and presents at its anterior and internal aspect a cleft, the hilum, leading to a cavity, called the sinus, in which lie the renal vessels, nerves, and duct. The gland in the male averages about four and three-quarter inches in length, an | inch and an eighth, m thickness and weighs about five ounces. The dimensions of the female kidney differ little from those of the male, but its weight is from one-seventh to one-fifth less. In the child the organ is relatively large, but its permanent elation to the body weight is usually attained by the end of the tenth year of life.
It offers for description two surfaces, two extremities, and two borders. The anterior or visceral surface is convex, and looks obliquely forwards and outwards ; the posterior or parietal surface, less convex than the anterior, looks inwards and backwards ; the rounded upper extremity is usually somewhat larger than the lover, and is placed about half an inch nearer to the median sagittal plane of the body. The external border is narrow and convex. The internal border (or surface) ,looking forwards, inwards, and slightly downwards, is relatively broad, and is ssured vertically in the middle third of its length by the hilum. The hilum is a slit -like aperture bounded by two rounded lips of variable and jLiequal thickness. The posterior lip is nearer to the middle line than the anterior,, id between the two pass the renal vessels and nerves, the duct, and a quantity of :,t-bearing connective tissue. The sinus (fig. 609), occupied by the structures just kmed, is narrowest near its entrance, and about an inch in depth. Its fundus is perced by the renal vessels and nerves, and by the uriniferous tubules ; and gives attachment to the primary branches (calices) of the duct.
Investment and fixation
The entire organ is enveloped and supported by a lid of capsule of fat -bearing connective tissue derived from the parietal layer of subperitoneal fascia (fig. 608). The adipose element may be in large or small quantity. In the latter case the investment often appears as a transparent fascial pile, which in renal operations may be mistaken for peritoneum, or fascia transversalis ; or, if the fat be excessively developed, it may form a kind of hernial protrusion into the parietal incision. Should the sustentacular power of the fatty capsule become impaired from any cause, the phenomenon of movable or wandering kidney is established, the organ tending to shift its place as far and in such flection as the attachment of its vessels to the main trunk will permit. A partial Cjering of peritoneum is loosely adherent to its anterior surface.