Urinary System

Urinary System

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 constantly needs to 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 (mick ter RIH shun).

Succinctly phrased by Homer William Smith in 1939, “It is no exaggeration to say that the composition of the blood is determined not by what the mouth ingests but by what the kidneys keep; they are the master chemists of our internal environment, which, so to speak, they synthesize in reverse.”

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 (pair EN kuh mul) tissue. The kidneys function to filter the blood and eliminate waste through the passage of urine. The ureters (YOOR eh turs) 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 (yoo REE thrah) is the tube that conducts the urine out of the bladder. The opening of the urethra is called the urinary meatus (YOOR in nair ee mee ATE us). The triangular area in the bladder between the ureters’ entrance and the urethral outlet is called the trigone (TRY gohn). The ureters, bladder, and urethra are all stromal (STROH mul) 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. If a kidney were sliced open, the outer portion, the cortex (KORE tecks) (pl. cortices), and the inner portion, called the medulla (muh DOO lah) (pl. medullae), would be visible (Fig. 6-3). The renal pelvis and calyces (KAL ih seez) (sing. calyx) are an extension of the ureter inside of the kidney. The term renal means pertaining to the kidneys.

The hilum (HYE lum) (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 (NEFF rons) (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.

Fig. 6-4 The nephron.

The Nephron

The nephrons filter all of the blood in the body approximately every 5 minutes. The renal afferent arteries transport unfiltered blood to the kidneys. Once in the kidneys, the blood travels through small arteries called arterioles (ar TEER ree ohls) and finally into tiny balls of renal capillaries, called glomeruli (gloh MER yoo lye) (sing. glomerulus). These glomeruli cluster at the entrance to each nephron. It is here that the process of filtering the blood to form urine begins.

The nephron consists of four parts: (1) the renal corpuscle (KORE pus sul), which is composed of the glomerulus and its surrounding Bowman’s capsule; (2) a proximal convoluted tubule; (3) the nephronic loop, also known as the loop of Henle; and (4) the distal convoluted tubule. As blood flows through the capillaries, water, electrolytes, glucose, and nitrogenous wastes are passed through the glomerular membrane and collected. The most common electrolytes are sodium (Na), chloride (Cl), and potassium (K). Blood cells and proteins are too large to pass through the glomerular membrane. Selective filtration and reabsorption continue along the renal tubules, with the end result of urine concentration and subsequent dilution occurring in the renal medulla. From there, the urine flows to the calyces and exits the kidney, flowing through the ureter into the bladder, where it is stored until it can be expelled from the body through the urethra.

image Exercise 1 The Urinary System

Match the combining form with its term.

Decode the terms.


image Exercise 3 Urinary Signs and Symptoms

Fill in the blank.

1. Urinary ______________________ is the inability to release urine.

2. If a patient complains of an accumulation of fluid around her ankles, she may be exhibiting ______________________.

3. A patient with a renal ______________________ has a cavity containing pus and surrounded by inflamed tissue in the kidneys.

4. A sign of kidney failure may be excessive urea in the blood, called ______________________.

5. A concerned parent calls in to discuss her 4-year-old son’s inability to remain dry during the night. This bed-wetting may be diagnosed as ______________________.

6. Caffeine and alcohol are substances that cause an increase in the volume of fluids excreted from the body, causing ______________________.

7. A feeling of a need to urinate immediately is called ______________________.

8. The elderly gentleman was seen by his physician because he was unable to control his urination. He was suffering from urinary ______________________.

Build the terms.

Decode the terms.

Terms Related to Urinary System Disorders, Stones, and Diabetes

Term Word Origin Definition
diabetes insipidus (DI)   Deficiency of antidiuretic hormone (ADH), which causes the patient to excrete large quantities of urine (polyuria) and exhibit excessive thirst (polydipsia).
dye ah BEE teez
in SIP ih dus
diabetes mellitus (DM)   A group of metabolic disorders characterized by high glucose levels that result from inadequate amounts of insulin, resistance to insulin, or a combination of both. (See Chapter 14).
dye ah BEE teez
meh LYE tus
nephrolithiasis nephr/o kidney
lith/o stone
-iasis condition, presence of
Stones in the kidney.
neff roh lih THIGH uh sis
polycystic kidney disease poly- excessive, many
cyst/o sac
-ic pertaining to
Inherited disorder characterized by an enlargement of the kidneys caused by many renal cysts bilaterally that reduce functioning of renal tissue (Fig. 6-5).
pah lee SIS tick
renal colic ren/o kidney
-al pertaining to
Severe pain associated with kidney stones lodged in the ureter. The term “colic” means pain.
REE null
KAH lick
urinary tract infection (UTI) urin/o urine, urinary system Infection anywhere in the urinary system, caused most commonly by bacteria, but also by parasites, yeast, and protozoa (sing. protozoon). Most frequently occurring disorder in the urinary system.
urolithiasis ur/o urine, urinary system
lith/o stone
-iasis condition, presence of
Stones anywhere in the urinary tract, but usually in the renal pelvis or urinary bladder. Usually formed in patients with an excess of the mineral calcium. Also called urinary calculi (KAL kyoo lye) (Fig. 6-6).
yoo roo lih THIGH uh sis

Oct 6, 2017 | Posted by in GENERAL SURGERY | Comments Off on Urinary System
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