The Urinary System

The urinary system functions to cleanse the blood of wastes and to insure a proper balance of electrolytes and water in the blood plasma.

The primary organs of the urinary system are the two kidneys. They are bean-shaped and located retroperi-toneally, i.e., behind the peritoneum (see chapter 20). Each kidney receives blood through a renal artery. Blood leaves the kidney through the renal vein. The blood vessels enter and leave the kidney through a depression termed the hilus.

The outer fibrous covering of the kidney is the capsule. Deep to the capsule is the cortex. Deeper yet is the medulla. The medulla is divided into cone-shaped renal pyramids which are separated by extensions of the cortex called renal columns.

Each renal pyramid terminates in a renal papilla which projects into a cavity called a calyx (pi. - calyces). The calyces are cavities which take the urine from the papillae and empty it into the large, funnel-like renal pelvis.

The functional unit of the kidney is the nephron. Nephrons are located primarily in the cortex, though portions of the nephrons can extend into the medulla. It is estimated that there are approximately one million nephrons per kidney! Each nephron is composed of four major parts, the renal corpuscle, two convoluted tubules, and Henle's loop.

The renal corpuscle is a spherical structure composed of an inner ball of blood capillaries, the glomerulus, and an outer, double-walled, cap-like structure, Bowman's capsule. The arteriole entering a glomerulus is an afferent arteriole, while an efferent arteriole carries blood from a glomerulus.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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