Anatomic and Physiologic Overview

The urinary system comprises the kidneys, ureters, bladder, andurethra.

A thorough understanding of the urinary system is necessaryfor assessing individuals with acute or chronic urinary dysfunctionand implementing appropriate nursing care.

Anatomy of the Upperand Lower Urinary Tracts

The urinary system—the structures of which precisely maintainthe internal chemical environment of the body—perform variousexcretory, regulatory, and secretory functions.

Kidneys

The kidneys are a pair of brownish-red structures located retroperitoneally (behind and outside the peritoneal cavity) on the posterior wall of the abdomen from the 12th thoracic vertebra to the 3rd lumbar vertebra in the adult

Kidneys• An adult kidney weighs 120 to 170 g (about 4.5 oz) and is 12 (about 4.5 inches) long, 6 cm wide, and 2.5 cm thick.

•The kidneys are well protectedby the ribs, muscles, Gerota’s fascia, perirenal fat, and therenal capsule, which surround each kidney.

KidneysThe kidney consists of two distinct regions:

Renal Parenchyma

Renal Pelvis

Kidneys Renal Parenchyma

The renal parenchyma is divided intothe cortex and the medulla.

The cortex contains the glomeruli, proximal and distal tubules, and cortical collecting ducts and their adjacent peritubular capillaries.

The medulla resembles conical pyramids. The pyramids are situated with the base facing theconcave surface of the kidney and the apex facing the hilum, or pelvis

Kidneys Renal Pelvis

The hilum, or pelvis, is the concave portion of the kidney through which the renal artery enters and the renal vein exits. The renal artery (arising from the abdominal aorta) divides into smaller and smaller vessels, eventually forming the afferent arteriole.

Kidneys Renal Pelvis

The afferent arteriole branches to form the glomerulus, which is the capillary bed responsible for glomerular filtration. Blood leaves the glomerulus through the efferent arteriole and flows back to the inferior vena cava through a network of capillaries and veins.

Kidneys

Each kidney contains about 1 million nephrons, the functional units of the kidney. Each kidney is capable of providing adequate renal function if the opposite kidney is damaged or becomes nonfunctional.

Nephrons

Kidneys

• The nephron consists of a glomerulus containing afferent and efferent arterioles, Bowman’s capsule, proximal tubule, loop of Henle, distal tubule, and collecting ducts.

• Collecting ducts converge into papillae, which empty into the minor calices, which drain into three major calices that open directly into the renal pelvis.

Nephrons

Kidneys

Nephrons are struturally divided into two types: cortical and juxtamedullary.

KidneysThe glomerular membrane normally allows filtration of fluid and small molecules yet limits passage of larger molecules, such as blood cells and albumin. Kidney function begins to decrease at a rate of approximately 1% each year beginning at approximately age 30.

The glomerulus is composed of three filtering layers: the capillary endothelium, the basement membrane, and the epithelium.

Kidneys• Urine formation

• Excretion of waste products

• Regulation of electrolytes

• Regulation of acid–base balance

• Control of water balance

• Control of blood pressure

• Renal clearance

• Regulation of red blood cell production

• Synthesis of vitamin D to active form

• Secretion of prostaglandins

Ureters

Urine, which is formed within the nephrons, flows into the ureter, a long fibromuscular tube that connects each kidney to the bladder.

The ureters are narrow, muscular tubes, each 24 to 30 cm long, that originate at the lower portion of the renal pelvis and terminate in the trigone of the bladder wall.

UretersThere are three narrowed areasof each ureter:

ureteropelvic junction

ureteral segment

ureterovesical junction

Uretersureterovesical junction

The angling of the ureterovesical junction is the primary means of providing antegrade, or downward, movement of urine, also referred to as efflux of urine.

This angling prevents vesicoureteral reflux, which is the retrograde, or backward, movement of urinefrom the bladder, up the ureter, toward the kidney.

Uretersureterovesical junction

The angling of the ureterovesical junction is the primary means of providing antegrade, or downward, movement of urine, also referred to as efflux of urine.

This angling prevents vesicoureteral reflux, which is the retrograde, or backward, movement of urinefrom the bladder, up the ureter, toward the kidney.

During voiding (micturition), increased intravesical pressure keeps the ureterovesical junction closed and keeps urine within the ureters. As soon as micturition is completed, intravesical pressure returns to its normal low baseline value, allowing efflux of urine to resume.

Therefore, the only time that the bladder is completely empty is in the last seconds of micturition before efflux of urine resumes.

Uretersureterovesical junction

The angling of the ureterovesical junction is the primary means of providing antegrade, or downward, movement of urine, also referred to as efflux of urine.

This angling prevents vesicoureteral reflux, which is the retrograde, or backward, movement of urinefrom the bladder, up the ureter, toward the kidney.

“The left ureter is slightly shorter than the right”

DidYOUknow?

UretersThe lining of the ureters is made up of transitional cell epithelium called urothelium. As in the bladder, the urothelium prevents reabsorption of urine.

The movement of urine from the renal pelves through the ureters into the bladder is facilitated by peristaltic waves (occurring about one to five times per minute) from contraction of the smooth muscle in the ureter wall (Walsh, Retik, Vaughan & Wein, 1998).

Ureters

Ureters functions as tubes that actively convey urine from the kidneys to the bladder.

BladderThe urinary bladder is a muscular, hollow sac located just behind the pubic bone.

The bladder is characterizedby its central, hollow area called the vesicle, which has two inlets(the ureters) and one outlet (the urethrovesical junction), whichis surrounded by the bladder neck.

BladderAdult bladder capacity is about 300 to 600 mL of urine. In infancy, the bladder is found within the abdomen. In adolescence and through adulthood, the bladder assumes its position in the true pelvis.

BladderThe wall of the bladder comprisesfour layers:

adventitia

detrusor

lamina propria

urothelium

Bladderurothelium

The urothelium layer is specialized, transitional cell epithelium, containing a membrane that is impermeable to water.

The urothelium prevents the reabsorption of urine stored in the bladder

BladderThe bladder neck contains bundles of involuntary smooth muscle that form a portion of the urethral sphincter known as the internal sphincter.

The portion of the sphincteric mechanism that is under voluntary control is the external urinary sphincter at the anterior urethra, the segment most distal from the bladder (Walsh et al., 1998).

BladderThe urinary bladder functions as a muscular sac that expands as urine is produced by the kidneys to allow storage of urine until voiding is convenient.

Urethra

The urethra arises from the base of the bladder: In the male, it passes through the penis; in the female, it opens just anterior to the vagina.

In the male, the prostate gland, which lies just below the bladder neck, surrounds the urethra posteriorly and laterally.

UrethraThe urethra is a muscular tube that drains urine from the body; it is 3–4 cm long in females, but closer to 20 cm in males.

Thankyou.