Chapter 9

Medical Terminology – Urinary System

Functions of the Urinary System:

The urinary system performs many functions that are important for maintaining Homeostasis.

Homeostasis – refers to a state of equilibrium that produces a constant internal environment throughout the body.  The Nervous System also plays a key role in the maintenance of Homeostasis.  It’s the body’s attempt to maintain a stable internal environment.

The Urinary system maintains Homeostasis via the following mechanisms:

• Maintains the proper balance of water, salts and acids
• Constantly filters the blood to remove waste materials from the blood.  Urea, an example of waste material, made from protein metabolism
• Converts these waste products and excess fluids into Urine in the kidneys and excretes them from the body via the urinary bladder

Negative Feedback – not in Chapter

Most homeostatic processes which occur in the body, occur thru what is known as a Negative Feedback Mechanism. This means that for various situations, body temperature being an example, a Set Point, or normal value, is established. Thus, in the case of Body temperature, as the body's temperature falls below the Body's Set Point, the Homeostatic mechanism is Turned ON . This will raise the Body's temp to maintain a consistency. Once the set point is reached, the homeostatic mechanism is turned off.

The Major components of this feedback mechanism include:

• Receptor - Sensor which responds to changes in the environment.  Receptors send information further into the body, to an area known as the Control Center .

• Control Center - This area determines, along with other peripheral areas in the body, the Set Point & determines the appropriate response necessary to maintain homeostasis.  The flow of information toward the Control Center is occurring in an Afferent, or Inward direction.  When the information is traveling away from the Control Center , it is occurring in an outward, or Efferent direction.

• Effector - This is the 3^rd component of Negative Feedback, and provides the means for the Control Center 's response to stimulus, which affects the Receptor.  Information now travels away from the Control Center , along and Efferent or Outward (away from) direction.

All these components establish a Feedback Loop, allowing for a turning on or turning off of the response to the initial stimuli.

Anatomy of the Urinary System (See Figures 9.1, Page 250)

The urinary system, also referred to as the Urinary Tract, consists of the following (See Figures 9.1, Page 250):

• Kidneys (2)
• Ureters (2)
• Urinary Bladder (1)
• Urethra (1)

An important part of the Endocrine System, the Adrenal Gland, sits on top of each Kidney.

Kidneys – the Kidneys constantly filter the blood to remove waste products and excess water.  These are excreted as Urine, which is 95% water and 5% other waste materials.

• The outer layer of the Kidneys is known as the Renal Cortex.  It contains over 1 million microscopic units called Nephrons. 
• The inner layer of the Kidneys is called the Medulla and contains most of the urine-collecting tubules.  A Tubule is a small tube.
• The Renal Pelvis is the funnel-shaped area within each kidney that is surrounded by the Cortex and Medulla layers.

 Nephrons – are the functional units of the kidneys.  They form urine by the processes of: (See Figure 9.2b, Page 251):

• Filtration
• Reabsorption
• Secretion

Blood flows into the kidney through the renal artery.  It is filtered in the capillaries of the Glomerulus and leaves the kidney through the renal vein.  The Glomerulus is a cluster of capillaries surrounded by a membrane called the Bowman’s capsule.

Waste products pass through a series of urine-collecting tubules and are transported to the Renal Pelvis before entering the Ureters.

The Color of Urine is determined by the pigment that gives urine its normal yellow-amber or straw color.  This pigment is known as Urochrome.  The color of urine can be influenced by normal factors such as:

• Amount of liquid consumed
• Any Diseases present
• Any Medications being taken

Ureters – are narrow tubes that carry urine from a kidney to the urinary bladder

Urinary Bladder – is a hollow muscular organ that is a reservoir for urine.  It is located in the Anterior portion of the pelvic cavity behind the Pubic Symphysis and stores about 1 pint of urine.

Urethra - is the tube extending from the urinary bladder to the outside of the body.  Be careful not to confuse the following terms:

• Ureter
• Urethra

In addition to the Urinary System, in Males, the Urethra plays a role in the males’ Reproductive System.  In males, the Urethra carries both Urine and Semen.  In Females, the Urethra only carries Urine.

Excretion of Urine

As the Urinary Bladder fills up, pressure is placed on the base of the urethra, resulting in the urge to urinate, also known as Micturate.  Urination is also known as Micturition or Voiding.

Urination requires the coordinated contraction of the urinary bladder muscles and relaxation of the sphincters.  This forces urine through the urethra and out through the Opening to the Urethra (Urinary Meatus).

The Urinary Sphincters are muscles which help to control the flow of urine from the urinary bladder.

Medical Specialties Related to the Urinary System

• Nephrologist
• Urologist

Pathology of the Urinary System

The book presents a laundry list of related conditions to the Urinary System.  Please refer to the definition list for some examples.

Renal Failure – inability of one or both of the kidneys to perform their functions.

Kidney Stones – also known as Calculus, is an abnormal mineral deposit.  (Minerals are an example of an Organic substance required by the body, like Proteins.)  These stones vary in size from small sand-like granules to the size of marbles and are named for the organ or tissue where they are located. 

Nephrolithiasis – is a disorder characterized by the presence of stones in the kidney.

Table 9.1, Page 255 lists some examples of Stones and their locations:

• Cystolith – stones found in the Urinary bladder
• Nephrolith – Stones found in the Kidney
• Ureterolith – Stones found in the Ureter

Diuresis – increased excretion of urine.  A disorder found in the brain, Diabetes Insipidus may cause this, as would drinking too much alcohol.

Incontinence – refers to the inability to control excretory functions.

Diagnostic Procedures of the Urinary System

• Urinalysis – is the examination of urine to determine the presence of abnormal elements.  Usually done at the same time blood tests are being performed.

• Cystocsopy – is the visual examination of the urinary bladder.

• Catheterization – is the insertion of a sterile catheter through the urethra and into the urinary bladder.  This is most commonly performed to withdraw urine, relieve urinary retention pressures, etc.

• KUB (kidneys, Ureters, bladder) – is a radiographic study of these structures without the use of a contrast medium.

• Intravenous Pyelogram – referred to as an IVP – is a radiographic (x-ray) study of the kidneys and Ureters in which iodine is injected into a vein as a contract medium to make these structures appear more clearly.

Common Treatments of the Urinary System

Examples include:

• Diuretics – medications administered to increase urine secretion to rid the body of excess sodium and water

• Dialysis – is a procedure to remove waste products from the blood of patients whose kidneys no longer function

• Hemodialysis – also known as HD – filters waste products from the patient’s blood.

• Renal Transplantation – also known as a Kidney Transplant – is the grafting of a donor kidney into the body to replace the recipient’s failed kidneys.  (Graft refers to implanting - living tissue - surgically)

• Lithotripsy – also known as ESWL (extra corporeal shockwave lithotripsy)– is the destruction of a kidney stone with the use of ultrasonic waves (high energy sound waves) traveling through water.  Extracorporeal means situated or occurring outside of the body

Catherization – is a procedure to:
(See Figure 9.12, Page 260)

• Withdraw urine for diagnostic purposes

• Control incontinence

• Place fluid into the bladder