N30.0 Acute cystitis

Excludes1 irradiation cystitis (N30.4-)

trigonitis (N30.3-)

Pyeloileostomy, urinary diversion

Pyeloplasty

Pyelorrhaphy

Pyeloscopy

Pyelostomy

Pyelotomy

Functions of the Urinary System

The major function of the urinary system is to continually maintain a healthy balance of the amount and content of extracellular fluids within the body. Biologists use the term homeostasis to describe this important process. The process of metabolism changes food and liquid (with its requisite fats, carbohydrates, and proteins) into building blocks, energy sources, and waste products. To operate efficiently, the body needs to constantly monitor and rebalance the amounts of these substances in the bloodstream. The breakdown of proteins and amino acids in the liver leaves chemical wastes, such as urea, creatinine, and uric acid, in the bloodstream. These wastes are toxic, nitrogenous substances that must be excreted in the urine. The act of releasing urine is called urination, voiding, or micturition.

Anatomy and Physiology

The urinary system is composed of two kidneys, two ureters, a urinary bladder, and a urethra (Figs. 6-1 and 6-2). The work of the urinary system is done by a specialized tissue in the kidneys called parenchymal tissue. The kidneys function to filter the blood and eliminate waste through the passage of urine. The ureters are thin, muscular tubes that move urine in peristaltic waves from the kidneys to the bladder. The urinary bladder is the sac that stores the urine until it is excreted. The bladder is lined with an epithelial mucous membrane of transitional cells. Underneath, a layer termed the lamina propria is composed of connective tissue that holds the blood vessels and nerves. The detrusor muscle is the final coat; it normally contracts to expel urine. The urethra is the tube that conducts the urine out of the bladder. The opening of the urethra is called the urinary meatus. The triangular area in the bladder between the ureters’ entrance and the urethral outlet is called the trigone. The ureters, bladder, and urethra are all stromal tissue, which is a supportive tissue.

The Kidney

Because the kidneys are primarily responsible for the functioning of the urinary system, it is helpful to look at them in greater detail. Each of the two kidneys is located high in the abdominal cavity, tucked under the ribs in the back and behind the lining of the abdominal cavity (retroperitoneal). The normal human kidney is about the size of a fist. The tough outer covering of the kidney is the renal capsule. If a kidney were sliced open, the outer portion, the cortex (pl. cortices), and the inner portion, called the medulla (pl. medullae), would be visible (Fig. 6-3). The renal pelvis and calyces (sing. calyx) are an extension of the ureter inside the kidney. The renal pyramids are triangular sections that extend from the renal medulla toward the renal pelvis. The downward point of the pyramid is referred to as the papilla. The term renal means “pertaining to the kidneys.” The ureteropelvic junction (UPJ) is the area where the ureter joins the renal pelvis. It is a common site of obstruction of the outward flow of urine from the kidney.

The hilum (pl. hila) is the location on the kidney where the ureter and renal vein leave the kidney and the renal artery enters. The cortex contains tissue with millions of microscopic units called nephrons (Fig. 6-4). Here in the tiny nephrons, blood passes through a continuous system of urinary filtration, reabsorption, and secretion that measures, monitors, and adjusts the levels of substances in the extracellular fluid.

14. transurethral ____________________________________________________________________________________

15. paranephric _____________________________________________________________________________________

16. retroperitoneal __________________________________________________________________________________

17. suprarenal ______________________________________________________________________________________

18. perivesical ______________________________________________________________________________________

Anatomy and Physiology

Both male and female anatomy can be divided into two parts: parenchymal, or primary tissue, which produces sex cells for reproduction; and stromal, or secondary tissue, which includes all of the glands, nerves, ducts, and other tissues that serve a supportive function in producing, maintaining, and transmitting these sex cells. Together these types of reproductive tissue, in either sex, are called genitalia. The parenchymal organs that produce the sex cells in both sexes are called gonads. The sex cells themselves are called gametes.

In the male, the gonads are the testes (sing. testis) or testicles, paired organs that produce the gametes called spermatozoa (sing. spermatozoon). The testes are suspended in a sac called the scrotum (pl. scrota) outside the body’s trunk (Fig. 6-12).

At puberty, the stage of life in which males and females become functionally capable of sexual reproduction, the interstitial cells in the testicles begin to produce testosterone, a sex hormone responsible for the growth and development of male sex characteristics. The spermatozoa are formed in a series of tightly coiled, tiny tubes in each testis called the seminiferous tubules. The formation of sperm is called spermatogenesis. The serous membrane that surrounds the front and sides of the testicle is called the tunica vaginalis testis. From the seminiferous tubules, the formed spermatozoa travel to the epididymis (pl. epididymides), where they are stored.

When the seminal fluid is about to be ejected from the urethra (ejaculation), the spermatozoa travel through the left and right vas deferens, also called the ductus deferens, from the epididymides, around the bladder. The spermatic cord is an enclosed sheath that includes the vas deferens, along with arteries, veins, and nerves.

To survive and thrive, the sperm are nourished by fluid from a series of glands. The seminal vesicles, Cowper’s (or bulbourethral) glands, and the prostate gland provide fluid either to nourish or to aid in motility and lubrication. The sperm and the fluid together make up a substance called semen. The ejaculatory duct begins where the seminal vesicles join the vas deferens, and this “tube” joins the urethra. Once the sperm reach the urethra, they travel out through the shaft, or body, of the penis, which is composed of three columns of highly vascular erectile tissue. There are two columns of corpora cavernosa and one of corpus spongiosum that fill with blood through the dorsal veins during sexual arousal. Two leglike extensions of the corpus cavernosa, the crura, attach the penis to the pubic bone on either side. During ejaculation, the sperm exit through the enlarged tip of the penis, the glans penis. At birth, the glans penis is surrounded by a fold of skin called the prepuce, or foreskin. The removal of this skin is termed circumcision.

When ejaculation occurs during sexual intercourse (coitus or copulation), the sperm then race toward the female sex cell, or ovum. If a specific sperm penetrates and unites with the ovum, conception takes place, and formation of an embryo begins.