The Urinary System

Urinary or Excretory SystemFunctions:

Removes certain wastes and excess water from the body

Maintains the acid-base balance of the body

Parts include two kidneys, 2 ureters, the bladder, and the urethra

KidneysTwo bean-shaped organs Located on either side of the vertebral column

behind the upper part of the abdominal cavity and separated from this cavity by the peritoneum

Protected by the ribs and a heavy cushion of fat Connective tissue helps hold the kidneys in

position Each kidney is enclosed in a mass of fatty tissue

called the adipose capsule Cover externally by a tough, fibrous tissue called

the renal fascia or fibrous capsule

Kidney Sections:Cortex(1) Outer section of the kidney(2) Contains most of the nephrons

that aid in the production of urine

Medulla (1) Inner section of the kidney (2) Contains most of the collecting

tubules that carry the urine from the nephrons on through the kidney

Hilum of Kidney:Notched or indented area on each kidney

Area where ureter, nerves, blood vessels, and lymph vessels enter and leave the kidney

NephronsMicroscopic filtering

units located in the kidney

Over one million per kidney

Each nephron consists of a glomerulus, Bowman’s capsule, a proximal and distal convoluted tubule, and a collecting duct (tubule)

Renal arteries carry blood to the kidneyBranches of the renal artery pass

through the medulla to the cortex where the blood enters the first part of the nephron, the glomerulus

Glomerulus of the Nephron:(1) Cluster of

capillaries(2) As blood

passes through water, mineral salts, sugar, metabolic products and other substances are filtered out of the blood

(3) Red blood cells and proteins are not filtered out

Glomerulus continued:Filtered blood leaves the glomerulus and eventually is carried to the renal vein, which carries it away from the kidney

Substances filtered out in the glomerulus enter the next section of the nephron, Bowman’s capsule

Bowman’s Capsule: (1) C-shaped

structure that surrounds the glomerulus

(2) It is the start of the convoluted tubule

(3) Picks up the materials filtered from the blood in the glomerulus

(4)Passes the materials into the convoluted tubule

As these materials pass through the various sections of the tubule, substances needed by the body are reabsorbed and returned to blood capillaries

At the end, most of the water, sugar, vitamins, and mineral salts have been reabsorbed

Excess sugar and salts, some water, and wastes, including urea, uric acid, and creatinine, remain in the tubules and become known as the concentrated liquid called urine

Convoluted Tubules:

Collecting Ducts:Urine now enters

collecting ducts or tubules located in the medulla

Collecting tubules empty into a funnel-shaped structure, the renal basin or pelvis, which is the first section of the ureter

UretersTwo muscular tubes about 10

to 12 inches longOne extends from the renal

pelvis of each kidney to bladder

Peristalsis, a rhythmic wavelike motion of the involuntary muscle, moves the urine through the ureter from the kidney to the bladder

BladderHollow muscular sacLies behind the symphysis

pubis at the midline of the pelvic cavity

Has lining of mucous membrane

Arranged in a series of folds called rugae

Rugae disappear as muscles of the bladder allow it to expand and fill with urine

Three layers of visceral (smooth) muscle form the walls

Bladder Functions:Receives the urine from the ureters

Stores the urine until it is eliminated from the body

Urge to void (urinate or micturate) occurs when the bladder contains about 250 cc (1 cup) of urine, but bladder can hold much more urine

Circular Sphincter Muscles:Control the bladder opening to prevent emptying

When bladder is full, receptors in the bladder will send out a signal for a reflex that will open the muscle

Reflex action cannot be controlled by infants, but as children get older, they learn to control this reflex

Urethra:Tube that carries the urine from bladder to the outside

External opening is called the urinary meatus

Different in females than males

Urethra cont.FemalesTube about 1 ½ inches

(3.75cm) longOpens in front of the

vaginaCarries only urine to

the outside

Urethra cont:MalesS-shaped tube about 8

inches (20 cm) longPasses through the

prostate gland and out through the penis

Carries both urine from the urinary system and semen from the reproductive system

Urine1. Liquid waste product produced by the urinary

system2. About 95 percent water3. Waste products dissolved in this water are urea,

uric acid, creatinine, mineral salts, and various pigments

4. Excess useful products, such as sugar, can also be found in urine but their presence usually indicates disease

5. About 1,500 to 2,000 cc (1½ to 2 quarts) of urine are produced daily from the approximately 150 quarts of liquid that is filtered through the kidneys

 

Conditions affecting urination

1. Polyuria: excessive urination2. Oliguria: below normal amounts of

urination3. Anuria: absence of urination4. Hematuria: blood in the urine5. Pyuria: pus in the urine6. Nocturia: urination at night7. Dysuria: painful urination8. Retention: inability to empty the bladder9. Incontinence: involuntary urination

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