Urinary System Anatomy and Function

Urinary System - Anatomy

• It is also known as the excretory system
• It includes two kidneys, two ureters, one urinary bladder, and one urethra, which gets rid of urine

Functions of Kidneys

• Remove waste products from the blood
• Maintain fluid and electrolyte balance
• Secrete substances that regulate blood pressure and affect other bodily functions
• Kidneys usually excrete 1 to 2 L of urine per day

Urinary System - Excretory System

• Pelvicalyceal system is calyces, urine-draining branches in the kidney, plus the renal pelvis, an expanded portion connected to the ureters
• Ureters consist of two long tubes that extend from the pelvis of each kidney all the way down to posterior bladder
• Urinary bladder receives the distal portion of the ureters and serves as a reservoir for urine.
• Urethra is a smaller tubular portion which conveys the urine to the exterior of the body

Urinary System - Suprarenal Glands

• It is also known as adrenal glands
• Ductless endocrine glands have no functional relationship with the urinary system
• Each consists of a small, flattened body that includes an internal medullary portion and an outer cortical portion
• Situated in the retroperitoneal area, overlying the medial and superior aspects of the upper pole of the kidney
• Adrenal glands furnish two important substances: epinephrine secreted by the medulla, and cortical hormones secreted by the cortex
• Suprarenal glands are not usually shown on scout images but delineated when using CT

Urinary System - Kidneys (1 of 5)

• The kidneys are bean-shaped bodies
• They have convex lateral borders and concave medial borders
• The kidneys are divided into upper and lower poles
• Each kidney is approximately 4 ½" long, 2 to 3" wide, and 1 ½" thick
• The left kidney is slightly longer and narrower than the right kidney
• The kidneys are located retroperitoneally, in contact with the posterior abdominal wall
• Each is on one side in the same coronal plane of L3, close to the iliac crest and rib margin
• The superior aspect of the kidney lies more posterior than the inferior aspect
• Each lies in an oblique plane approximately 30 degrees anteriorly toward the aorta
• Doing a 30-degree RPO/LPO results in an elevated kidney that is demonstrated without distortion

Urinary System - Kidneys (2 of 5)

• Kidneys normally extend from the superior border of T12 to transverse processes of L3
• Right kidney is slightly lower/caudal than the left kidney
• Renal Capsule is the outer covering of the kidney that remains continuous with the outer coat of the ureter
• Adipose capsule is the fatty tissue surrounding each kidney, embedded to protect against friction
• The capsule and kidney are enveloped in a sheath of superficial fascia, the renal fascia, which is attached to the diaphragm, L spine, peritoneum, and adjacent structures
• Kidneys are supported in a fairly fixed position, through the fascial attachments and the surrounding organs
• Kidneys have approximately 1" of respiratory movement, and normally drop no more than 2" in the change from supine to upright

Urinary System - Kidneys (3 of 5)

• Hilum includes a longitudinal slit located at the medial border of each kidney
• Hilum is for transmission of the blood and lymphatic vessels, nerves, and ureter
• Hilum expands into body of the kidney to form a central cavity called the renal sinus, a fat-filled space surrounding the renal pelvis and vessels
• Renal cortex is the outer layer of the renal tissue
• Renal medulla is the inner layer of renal tissue
• Renal medulla is composed of 8 to 15 cone-shaped segments of collecting tubules, the renal pyramids
• Renal columns are extensions of the cortex between renal pyramids

Urinary System - Kidneys (4 of 5)

• Nephron: main component of tissue of kidney
• It is an essential microscopic component of the kidney
• Each kidney has approximately 1 million nephrons
• Subdivided into the renal corpuscle and the renal tubule
• Renal corpuscle consists of a double-walled membranous cup called the glomerular or Bowman capsule and a cluster of blood capillaries called the glomerulus
• Glomerulus serves as a filter for the blood, permitting water and finely dissolved substances to pass through the walls of the capillaries into the capsule
• Afferent arteriole is the vessel entering the capsule
• Efferent arteriole is the vessel exiting the capsule

Urinary System - Kidneys (5 of 5)

• Renal tubule is separated into three main distinct areas
• These areas are the proximal convoluted tubule, the nephron loop (loop of Henle) which has a descending and ascending portion, and the distal convoluted tubule
• Distal convoluted tubule opens into collecting ducts that begin in the cortex
• Flow of urine=distal convoluted ducts -->collecting ducts -->renal papilla -->minor calyces -->major calyces -->renal pelvis -->ureter -->bladder -->urethra

Urinary System - Ureters

• The ureteropelvic junction (UPJ) is the junction of the renal pelvis and ureter
• Each ureter is 10 to 12" (25 to 30 cm) long
• Ureters descend behind the peritoneum and in front of the psoas muscle and transverse processes of L spine
• Pass inferiorly and posteriorly in front of sacral wing
• Ureters enter the posterolateral surface of the urinary bladder at approximately the level of the ischial spine
• They convey urine from the renal pelves to the bladder by slow, rhythmic peristaltic contractions

Urinary System - Urinary Bladder (1 of 2)

• It is a musculomembranous sac that serves as a reservoir for urine
• Located immediately posterior and superior to the pubic symphysis
• It is anterior to the rectum in the male and the vaginal canal in the female
• Apex: At the anterosuperior aspect, adjacent to the superior aspect of the pubic symphysis
• Most fixed part is the neck--rests on the prostate in the male, and on the pelvic diaphragm in the female--has an internal urethral orifice
• Base: Where ureters enter the posterior wall of the bladder at the lateral margins of the superior part
• It varies in size, shape, and position according to its content

Urinary System - Urinary Bladder (2 of 2)

• Freely movable, held in position by folds of the peritoneum
• When empty, it is located in the pelvic cavity
• As it fills, it gradually assumes an oval shape, expanding superiorly and anteriorly into the abdominal cavity
• Adult bladder can hold approximately 500 mL of fluid when completely full
• The urge for micturition (urination) occurs when there is 250 mL of urine in the bladder
• Ureterovesical junctions (UVJs) are junctions of the ureter with the bladder
• Two openings equidistant from the internal urethral orifice
• Trigone is the triangular area between the three orifices (2 UVJs + internal urethral orifice)
• Rugae are folds of the bladder that form when it is empty

Urinary System - Urethra

• Urethra conveys urine out of the body
• The urethra is a narrow musculomembranous tube with a sphincter at the neck of the bladder
• Incontinence is a result of inability to control the sphincter
• The female urethra measures 1 1/2" (3.8 cm), and the male urethra measures 7 to 8" (17.8 to 20 cm)
• The male urethra extends from the bladder to the end of the penis and is divided into prostatic, membranous, and spongy portions
• Distal prostatic, membranous, and spongy parts of the male urethra also serve as the excretory canal of the reproductive system

Urinary System - Prostate

• The prostate is a small glandular body surrounding the proximal part of male urethra
• Situated just posterior to the inferior portion of the pubic symphysis
• Considered part of the male reproductive system
• Base is conical and attached to the inferior surface of the bladder
• Apex in contact with the pelvic diaphragm
• Approximately 1" (2.5 cm) long
• The prostate secretes a milky fluid that combines with semen from the seminal vesicles and vas deferens and enters the urethra via ducts in the prostatic urethra

Pathology

• Benign prostatic hyperplasia (BPH): Enlargement of the prostate which is noncancerous
• Calculus: Abnormal concretion of mineral salts, often called a stone
• Carcinoma is cancerous : Malignant new growth composed of epithelial cells
• Bladder carcinoma: Carcinoma located in the bladder
• Renal cell carcinoma: Carcinoma located in the kidney
• Congenital anomaly: Abnormality present at birth
• Duplicate collecting system: Two renal pelves or ureters from the same kidney
• Horseshoe kidney: Fusion of the kidneys, usually at the lower poles
• Pelvic kidney: Kidney that fails to ascend and remains in the pelvis
• Cystitis is another name for bladder: Inflammation of the bladder
• Fistula: Abnormal connection between two internal organs or between an organ and the body surface
• Glomerulonephritis: Inflammation of the capillary loops in the glomeruli of the kidney
• Hydronephrosis: Distention of renal pelvis and calyces with urine
• Nephroptosis: Excessive inferior displacement of the kidneys or kidney prolapse
• Phleboliths: Pelvic vein calcifications
• Polycystic kidney: Massive enlargement of the kidney with the formation of many cysts
• Pyelonephritis: Inflammation of the kidney and renal pelvis
• Renal hypertension: Increased blood pressure to the kidneys
• Renal obstruction: Condition preventing normal flow of urine through the urinary system
• Stenosis: Narrowing or contraction of a passage with reproduction
• Tumor: New tissue growth where cell proliferation is uncontrolled
• Wilms tumor: Most common pediatric abdominal neoplasm
• Ureterocele: Ballooning of the lower end of the ureter
• Vesicoureteral reflux: Backward flow of urine from the bladder into the ureters

Abnormal Congenital Conditions

• Duplicating collecting system=Two renal pelves or ureters from the same kidney, and are a duplication in the collecting system
• Horseshoe kidney=Fusion of the kidneys, usually at the lower poles
• Pelvic Kidney = Kidney that fails to ascend and remains in the pelvis
• Glomerulonephritis=Inflammation of the capillary loops in the glomeruli of the kidney
• Pyelonephritis=Inflammation of the kidney and renal pelvis
• Hydronephrosis=Distention of renal pelvis and calyces with urine
• Nephroptosis=Excessive inferior displacement of the kidneys or kidney prolapse
• Polycystic Kidney=Massive enlargement of the kidney with the formation of many cysts
• Wilms Tumor=Most common pediatric abdominal neoplasm usually shows the nephroblastoma involving the kidney
• Ureterocele=Ballooning of the lower end of the ureter into the bladder
• Vesicoureteral Reflux=Backward flow of urine from the bladder into the ureters