17 -1 Chapter 17 Urinary System. 17 -2 Introduction A.The urinary system consists of two kidneys...

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Chapter 17Urinary System

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IntroductionA. The urinary system consists of two

kidneys that filter the blood, two ureters, a urinary bladder, and a urethra to convey waste substances to the outside.

CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Kidneys

A. The kidney is a reddish brown, bean-shaped organ 12 centimeters long; it is enclosed in a tough, fibrous capsule.


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B. Location of the Kidneys1. The kidneys are positioned

retroperitoneally on either side of the vertebral column between the twelfth thoracic and third lumbar

vertebrae, with the left kidney slightly higher than the

right.


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C. Kidney Structure1. A medial depression in the

kidney leads to a hollow renal sinus into which blood vessels, nerves,

lymphatic vessels, and the ureter enter.

2. Inside the renal sinus lies a renal pelvis that is subdivided into major and minor calyces; small renal

papillae project into each minor calyx.


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3. Two distinct regions are found within the kidney: a

renal medulla and a renal cortex.

a. The renal medulla houses tubes leading to the papillae.

b. The renal cortex contains the nephrons, the functional units of the kidney.


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D. Kidney Functions 1. The kidneys function to

regulate the volume, composition, and pH of body fluids and remove metabolic

wastes from the blood in the process.

2. The kidneys also help control the rate of red blood cell formation by secreting erythropoietin, and regulate blood pressure by secreting renin.


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Urine Formation A. Urine formation involves glomerular filtration, tubular reabsorption, and tubular secretion. B. Glomerular Filtration

1. Urine formation begins when the fluid portion of the blood is filtered by the glomerulus and enters the glomerular capsule as glomerular filtrate.


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C. Filtration Pressure 1. The main force responsible

for moving substances by filtration through the glomerular capillary wall is the hydrostatic pressure of

the blood inside.2. Due to plasma proteins,

osmotic pressure of the blood resists filtration, as does hydrostatic pressure inside the glomerular capsule.


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D. Filtration Rate 1. The factors that affect the

filtration rate are filtration pressure, glomerular plasma osmotic pressure, and hydrostatic pressure

in the glomerular capsule.2. When the afferent arteriole

constricts in response to sympathetic stimulation,

filtration pressure, and thus filtration rate, declines.


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3. When the efferent arteriole constricts, filtration

pressure increases, increasing the rate of filtration.

4. When osmotic pressure of the glomerular plasma is

high, filtration rate decreases.


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5. When hydrostatic pressure inside the glomerular capsule is high, filtration rate declines.

6. On average, filtration rate is 125 milliliters per minute or 180 liters in 24 hours, most of which is reabsorbed farther down the nephron.


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E. Regulation of Filtration Rate 1. Glomerular filtration rate is

relatively constant, although sympathetic impulses may decrease the rate of filtration.


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2. Another control over filtration rate is the renin-angiotensin system, which regulates sodium excretion.

a. When the sodium chloride concentration in the tubular fluid decreases, the macula

densa senses these changes and causes the

juxtaglomerular cells to secrete renin.


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b. Secretion of renin triggers a series of reactions leading to the production of angiotensin

II, which acts as a vasoconstrictor; this may, in

turn, affect filtration rate.


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c. Presence of angiotensin II also increases the secretion of aldosterone, which stimulates

reabsorption of sodium.d. The heart can also

increase filtration rate when blood volume is high.


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F. Tubular Reabsorption1. Changes in the fluid

composition from the time glomerular filtrate is formed to when urine arrives at the collecting duct are largely the result

of tubular reabsorption of selected substances.

2. Most of the reabsorption occurs in the proximal convoluted tubule, where cells possess microvilli with

carrier proteins.


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3. Carrier proteins have a limited transport capacity, so excessive amounts of a substance will be excreted into the urine.

4. Glucose and amino acids are reabsorbed by active

transport, water by osmosis, and proteins by pinocytosis.


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G. Sodium and Water Reabsorption 1. Sodium ions are reabsorbed

by active transport, and negatively charged ions follow passively.

2. As sodium is reabsorbed, water follows by osmosis.


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H. Regulation of Urine Concentration and Volume

1. Most of the sodium ions are reabsorbed before

the urine is excreted, and sodium is concentrated in the renal medulla by the countercurrent mechanism.

2. Normally the distal convoluted tubule and collecting duct are impermeable to water unless the

hormone ADH is present.


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I. Urea and Uric Acid Excretion 1. Urea is a by-product of amino

acid metabolism; uric acid is a by-product of nucleic acid

metabolism.2. Urea is passively reabsorbed

by diffusion but about 50% of urea is excreted in the urine.

3. Most uric acid is reabsorbed by active transport and a small amount is secreted into the renal tubule.


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J. Tubular Secretion1. Tubular secretion transports

certain substances from the plasma into the renal tubule.

2. Active transport mechanisms move excess hydrogen ions into the renal tubule along with various organic compounds.


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3. Potassium ions are secreted both actively and passively into the distal convoluted tubule and the collecting

duct.


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K. Urine Composition1. Urine composition varies from

time to time and reflects the amounts of water and solutes that the kidneys eliminate to maintain homeostasis.

2. Urine is 95% water, and also contains urea, uric acid,

a trace of amino acids, and electrolytes.


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Urine Elimination A. After forming in the nephrons, urine passes from the collecting ducts to the renal papillae, then to the minor and major calyces, and out the renal pelvis to the ureters, urinary bladder, and finally to the urethra, which conveys urine to the outside.


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B. Ureters 1. The ureters are muscular

tubes extending from the kidneys to the base of the urinary bladder.

2. The wall of the ureter is composed of three layers: mucous coat, muscular coat, and outer fibrous coat.


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3. Muscular peristaltic waves convey urine to the urinary bladder where it passes through a flaplike valve in

the mucous membrane of the urinary bladder.


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C. Urinary Bladder1. The urinary bladder is a

hollow, distensible, muscular organ lying in the pelvic cavity.

2. The internal floor of the bladder includes the trigone, which is composed of the openings of the

two ureters and the urethra.


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3. The wall of the urinary bladder is made up of four coats: inner mucous coat, submucous coat, muscular coat made up of detrusor

muscle, and outer serous coat.

a. The portion of the detrusor muscle that surrounds the neck of the bladder forms an internal sphincter muscle.


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D. Micturition1. Urine leaves the bladder by

the micturition reflex.2. The detrusor muscle

contracts and the external urethral sphincter (in the urogenital diaphragm) must also

relax.


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3. Stretching of the urinary bladder triggers the micturition reflex center located in the sacral portion of the spinal cord.

4. Return parasympathetic impulses cause the detrusor muscle to contract in waves, and an urge to urinate is sensed.


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5. When these contractions become strong enough, the internal urethral sphincter is forced open.

6. The external urethral sphincter is composed of skeletal muscle and is under conscious control.


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E. Urethra1. The urethra is a tube that

conveys urine from the urinary bladder to the outside.

2. It is a muscular tube with urethral glands that secrete mucus into the urethral canal.


Kidney Stones

A kidney stone is a solid mass made up of tiny crystals. One or more stones can be in the kidney or ureter at the same time.

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Symptoms

The main symptom is severe pain that starts suddenly and may go away suddenly:

Pain may be felt in the belly area or side of the back

Pain may move to groin area (groin pain) or testicles (testicle pain)

Other symptoms can include:

Abnormal urine color

Blood in the urine

Chills

Fever

Nausea

Vomiting

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TreatmentThe goal of treatment is to relieve symptoms and prevent further symptoms. (Kidney stones that are small enough usually pass on their own.) Treatment varies depending on the type of stone and how severe the symptoms are. People with severe symptoms might need to be hospitalized.

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Treatment

When the stone passes, the urine should be strained and the stone saved and tested to determine the type.

Drink at least 6 - 8 glasses of water per day to produce a large amount of urine. Some people might need to get fluids through a vein (intravenous).

Pain relievers can help control the pain of passing the stones (renal colic). For severe pain, you may need to take narcotic pain killers or nonsteroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen.

Depending on the type of stone, your doctor may prescribe medicine to decrease stone formation or help break down and remove the material that is causing the stone. Medications can include:

Allopurinol (for uric acid stones)

Antibiotics (for struvite stones)

Diuretics

Phosphate solutions

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Treatment

Surgery is usually needed if:

The stone is too large to pass on its own

The stone is growing

The stone is blocking urine flow and cuasing an infection or kidney damage

Today, most treatments are much less invasive than in the past.

Extracorporeal shock-wave lithotripsy is used to remove stones slightly smaller than a half an inch that are located near the kidney. This method uses ultrasonic waves or shock waves to break up stones. Then, the stones leave the body in the urine.

Percutaneous nephrolithotomy is used for large stones in or near the kidney, or when the kidneys or surrounding areas are incorrectly formed. The stone is removed with an endoscope that is inserted into the kidney through a small opening.

Ureteroscopy may be used for stones in the lower urinary tract.

Standard open surgery (nephrolithotomy) may be needed if other methods do not work or are not

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Urinary Tract Infections

Urinary tract infections are a serious health problem affecting millions of people each year.

Infections of the urinary tract are the second most common type of infection in the body. Urinary tract infections (UTIs) account for about 8.3 million doctor visits each year.* Women are especially prone to UTIs for reasons that are not yet well understood. One woman in five develops a UTI during her lifetime. UTIs in men are not as common as in women but can be very serious when they do occur.

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What are the causes of UTI?

Normally, urine is sterile. It is usually free of bacteria, viruses, and fungi but does contain fluids, salts, and waste products. An infection occurs when tiny organisms, usually bacteria from the digestive tract, cling to the opening of the urethra and begin to multiply. The urethra is the tube that carries urine from the bladder to outside the body. Most infections arise from one type of bacteria, Escherichia coli (E. coli), which normally lives in the colon.

In many cases, bacteria first travel to the urethra. When bacteria multiply, an infection can occur. An infection limited to the urethra is called urethritis. If bacteria move to the bladder and multiply, a bladder infection, called cystitis, results. If the infection is not treated promptly, bacteria may then travel further up the ureters to multiply and infect the kidneys. A kidney infection is called pyelonephritis.

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What are the causes of UTI?

Microorganisms called Chlamydia and Mycoplasma may also cause UTIs in both men and women, but these infections tend to remain limited to the urethra and reproductive system. Unlike E. coli, Chlamydia and Mycoplasma may be sexually transmitted, and infections require treatment of both partners.

The urinary system is structured in a way that helps ward off infection. The ureters and bladder normally prevent urine from backing up toward the kidneys, and the flow of urine from the bladder helps wash bacteria out of the body. In men, the prostate gland produces secretions that slow bacterial growth. In both sexes, immune defenses also prevent infection. But despite these safeguards, infections still occur.

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How is UTI diagnosed?

To find out whether you have a UTI, your doctor will test a sample of urine for pus and bacteria. You will be asked to give a "clean catch" urine sample by washing the genital area and collecting a "midstream" sample of urine in a sterile container. This method of collecting urine helps prevent bacteria around the genital area from getting into the sample and confusing the test results. Usually, the sample is sent to a laboratory, although some doctors' offices are equipped to do the testing.

In the urinalysis test, the urine is examined for white and red blood cells and bacteria. Then the bacteria are grown in a culture and tested against different antibiotics to see which drug best destroys the bacteria.

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How is UTI treated?

UTIs are treated with antibacterial drugs. The choice of drug and length of treatment depend on the patient's history and the urine tests that identify the offending bacteria. The sensitivity test is especially useful in helping the doctor select the most effective drug.

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17 -1 Chapter 17 Urinary System. 17 -2 Introduction A.The urinary system consists of two kidneys...

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