Anatomy of Urinary System PAN 201 Anatomy of Urinary System

URINARY SYSTEM ORGANS Kidneys (2) Ureters (2) Urinary bladder Urethra

KIDNEY FUNCTIONS Control blood volume and composition

KIDNEY FUNCTIONS Filter blood plasma, eliminate wastes Regulate blood volume, pressure Regulate fluid osmolarity Secrete renin Secrete erythropoietin (EPO) Regulate PCO2, Acid-Base balance Synthesize calcitriol (Vitamin D) Detoxify free radicals, drugs Gluconeogenesis

EXCRETION Removal of wastes Respiratory system Integumentary system CO2, water Integumentary system Water, salts, lactic acid, urea Digestive system Water, salts, CO2, lipids, bile pigments, cholesterol, etc. Urinary system Metabolic wastes, toxins, drugs, hormones, salts, H+, water

KIDNEY ANATOMY Protected by three connective tissue layers Renal fascia Attaches to abdominal wall Adipose capsule Fat cushioning kidney Renal capsule Fibrous sac Protects from trauma and infection

KIDNEY ANATOMY Gross anatomy Renal sinus Renal parenchyma

KIDNEY ANATOMY Renal sinus Surrounded by renal parenchyma Contains blood & lymph vessels, nerves, urine-collecting structures

KIDNEY ANATOMY Renal parenchyma Glandular tissue Forms urine Two zones Outer cortex Inner medulla

KIDNEY ANATOMY Renal parenchyma Renal pyramids Extensions of cortex (renal columns) divide medulla into 6 – 10 renal pyramids Pyramid + overlying cortex = Lobe Point of pyramid = Papilla Papilla nested in cup (minor calyx) 2 – 3 minor calices  Major calyx 2 – 3 major calices  Renal pelvis Renal pelvis  Ureter

KIDNEY ANATOMY: NEPHRONS Functional units of kidney ~1.2 million per kidney Three main parts Blood vessels Renal corpuscle Renal tubule

NEPHRONS Blood vessels servicing kidney Supplied by renal artery ~21% or cardiac output (Mass in only ~ 0.4%)   Afferent arterioles  Capillary cluster (glomerulus)

NEPHRONS Blood vessels servicing kidney Glomerulus Fenestrated capillaries Capillary filtration in glomerulus initiates urine production Filtrate lacks cells & proteins Drained by efferent arteriole Peritubular capillaries     Renal vein

NEPHRONS Renal corpuscle Glomerulus plus capsule Glomerulus enclosed in two-layered glomerular capsule “Bowman’s capsule” Fluid filters from glomerular capillaries “Glomerular filtrate” Fluid collects in capsular space Fluid flows into renal tubule

NEPHRONS Renal tubule Leads from glomerular capsule Ends at tip of medullary pyramid ~3 cm long Four major regions Proximal convoluted tubule Nephron loop Distal convoluted tubule Collecting duct

NEPHRONS Renal tubule Proximal convoluted tubule (PCT) Arises from glomerular capsule Longest, most coiled region Prominent microvilli Function in absorption Much contact with peritubular capillaries

NEPHRONS Renal tubule Nephron loop (“Loop of Henle”) “U” – shaped, distal to PCT Descending and ascending limbs Thick segments Active transport of salts High metabolism, many mitochondria Thin segments Permeable to water Low metabolism

NEPHRONS Renal tubule Distal convoluted tubule (DCT) Coiled, distal to nephron loop Shorter than PCT Less coiled than PCT Very few microvilli Contacts afferent and efferent arterioles (regulation imparted) Contact with peritubular capillaries

NEPHRONS Renal tubules Collecting duct DCTs of several nephrons empty into a collecting duct Passes into medulla Several merge into papillary duct (~30 per papilla) Drain into minor calyx

URINE FORMATION Overview Blood plasma  Urine Four steps Glomerular filtration Tubular reabsorption Tubular secretion Water conservation

URINE STORAGE Ureters Carry urine from kidneys to urinary bladder via peristalsis Rhythmic contraction of smooth muscle Enter bladder from below Pressure from full bladder compresses ureters and prevents backflow

Arterial Supply Ureter is supplied by multiple arteries throughout its course From above downward, these are:: Renal artery Gonadal artery Common iliac artery Internal iliac artery 1 2 3 4

URINE STORAGE Ureters Small diameter A 25 – 30 cm long muscular tube transporting urine from kidney to urinary bladder. Begins as a continuation of renal pelvis. Easily obstructed or injured by kidney stones (renal calculi)

URINE STORAGE Urinary bladder Muscular sac Wrinkles termed rugae Openings of ureters common site for bladder infection

Urinary Bladder Located immediately behind the pubic symphysis Shape and relations vary according to the amount of urine it contains An empty bladder: In adults, is entirely a pelvic organ; as it fills, rises up into the hypogastric region. In young children, it projects above the pelvic inlet

An empty bladder is pyramidal in shape having: An apex A base (posterior surface) A superior surface Two infrolateral surfaces A neck

Apex Directed forward Lies behind the upper margin of the symphysis pubis Is connected to umbilicus by the median umbilical ligament (remnant of urachus)

Base or Posterior surface Triangular in shape Upper part covered by peritoneum Lower part related to: In males: vas deferentia and seminal vesicles In females: vagina

Superior surface Completely covered by peritoneum. Related to the coils of ileum or sigmoid colon in males and to uterus in females Male pelvis Female pelvis

Infrolateral surfaces: Related in front to the retro pubic pad of fat & the pubic bones Posteriorly lie in contact with the obturator internus above and levator ani below Retropubic fat Accommodates distention of bladder Continuous with anterior abdominal wall. Rupture of bladder results in escape of urine to anterior abdominal wall

Neck: Lies inferiorly, and is the most fixed part of the bladder Is related to lower border of symphysis pubis In male, rests on the upper surface of prostate. Here, the smooth muscle fibers of the bladder are continuous with those of the prostate The circular muscle fibers thickened to form the sphincter vesicae

Interior of the Urinary Bladder Mucous membrane thrown into folds except in the triangular region in the base of bladder, between the openings of the two ureters and the urethra. This region is called the ‘trigone’. Here The mucous membrane is always smooth even when the bladder is empty Uvula vesicae, a small elevation located just behind the urethral orifice, It is produced by the median lobe of prostate.

Blood & Nerve Supply Arterial supply: from internal iliac artery Venous drainage: into internal iliac vein Lymphatics: into internal iliac lymph nodes The nerves form the vesical nerve plexus that contains: Sympathetic fibers derived mainly from L1,2 Parasympathetic fibers derived from pelvic splanchnic nerves S2,3,4 Sensory fibers from the bladder are visceral and transmit pain sensation resulting from overdistention

The normal capacity of bladder is about 300-500ml. As bladder fills, the superior surface bulges upward into abdominal cavity. The peritoneal lining is peeled off the lower part of anterior abdominal wall and the bladder comes into direct contact with the anterior abdominal wall

URINE ELIMINATION Urethra Conveys urine from body Internal urethral sphincter Retains urine in bladder Smooth muscle, involuntary External urethral sphincter Provides voluntary control over voiding of urine

URINE ELIMINATION Urethra 3 – 4 cm long in females Bound by connective tissue to anterior wall of vagina Urethral orifice exits body between vaginal orifice and clitoris

URINE ELIMINATION Urethra ~18 cm long in males Prostatic urethra ~2.5 cm long, urinary bladder  prostate Membranous urethra ~0.5 cm, passes through floor of pelvic cavity Penile urethra ~15 cm long, passes through penis

URINE ELIMINATION Urination (micturition) ~200 ml of urine held Distension initiates desire to void Internal sphincter relaxes involuntarily Smooth muscle External sphincter voluntarily relaxes Skeletal muscle Poor control in infants Bladder muscle contracts Urine forces through urethra

Ureteric Constrictions The ureter has constrictions at three points (sites of obstruction and stone impaction) At the ureteropelvic junction At the crossing of external/common iliac artery At site of entrance to bladder 1 2 3