Untitled Quiz

Urinary System Organs

• Depicts the primary organs of the urinary system and their anatomical relationships within the body

Epithelia: Transitional

• Displays the transitional epithelium lining in the urinary bladder under relaxed state

Urinary System

• Acts as the main blood filtration system within the body
• Responsible for forming filtrate and excreting it as urine

Kidney Functions

• Filters around 50 gallons of blood per day for toxin removal
• Regulates blood volume and chemical composition
• Crucial in maintaining the water-salt and acid-base balance
• Performs gluconeogenesis during prolonged fasting, regulating blood glucose levels
• In charge of renin production, which helps with regulating blood pressure
• Erythropoietin is produced which stimulates red blood cell production
• Activates vitamin D

Kidney Anatomy: Supportive Tissues

• Renal fascia is the outermost layer
• Perirenal fat capsule is a protective layer of fat
• Fibrous renal capsule is the innermost layer

Internal Anatomy of Kidney

• The cortex is the outermost region
• The medulla contains renal pyramids.
• The renal pelvis contains major calyx and is the innermost region
• The renal artery and vein enter/exit at hilus
• The ureter drains urine

Blood and Nerve Supply of Kidney

• Approximately 1200 ml, or one-fourth, of systemic cardiac output flows through the kidneys each minute
• Arterial and venous flow follows similar paths
• Nerve supply is via the renal plexus.
• Sympathetic input regulates vasoconstriction/dilation; sympathetic activation constricts, decreasing filtration

The Nephron

• Nephrons are structural and functional units
• Each kidney contains ~1 million nephrons
• Nephrons form urine

Nephron Structure

• Renal corpuscle includes the glomerular capsule and glomerulus
• Proximal convoluted tubule exists directly after the glomerular capsule
• Thick and thin segments exist within the nephron loop, which is after the proximal convoluted tubule
• Descending and ascending loop are part of the nephron loop
• Distal convoluted tubule exists directly after the nephron loop
• Collecting duct receives input from the distal convoluted tubule

Anatomy of the Glomerular Capsule

• Glomerulus tuft of capillaries associates with renal tubule.
• Glomerular endothelium has fenestrated epithelium that allows filtrate passage.
• Glomerular (Bowman's) capsule is the blind, cup-shaped end of a renal tubule that surrounds the glomerulus.
• The Bowman's capsule collects the filtrate
• The capsule contains podocytes with filtration slits

Renal Tubule

• Filtrate passes through regions after forming in the Bowman's capsule
• Proximal convoluted tubule reabsorbs water/solutes/secretes substances
• has cuboidal cells with microvilli
• Loop of Henle is a hairpin shaped loop with Cuboidal - simple squamous - cuboidal cells
• Distal convoluted tubule makes final adjustments regarding secretion and reabsorption of electrolytes; Has cuboidal cells

Renal Tubule Features

• Glomerular capsule has parietal and visceral (glomerular) layers
• Podocytes and basement membrane are located within the glomerulus
• Distal convoluted tubule has apical microvilli and mitochondria
• The Nephron loop (thin segment) cells
• Intercalated cells and principal cells

DCT and Collecting Duct Junction

• The distal convoluted tubule nears collecting ducts at its end
• Intercalated cells, at the junction, maintain the body's acid-base balance
• Principal cells at the junction maintain salt and water balance

Nephrons: Two Main Types

• Cortical nephrons make up 85% of nephrons, they are located in the cortex
• Juxtamedullary nephrons

Capillary Beds of the Nephron

• Every nephron has two capillary beds: glomerulus capillaries and peritubular capillaries
• Filtrate formation occurs in the glomerulus capillaries
• Peritubular capillaries are porous, adapt for absorption, and are purple

Juxtaglomerular Complex (JGC)

• Includes macula densa cells of the ascending limb of the nephron loop
• Extraglomerular mesangial cells
• Granular cells

Filtration Membrane

• A filter lies between blood and the interior of the glomerular capsule
• The filtration membrane is formed by capillary endothelium, basement membrane, and foot processes of podocyte of glomerular capsule

Mechanisms of Urine Formation

• The kidneys filter the body's entire plasma volume every 22 minutes
• Water, nutrients, and ions are "removed" from filtrate and put back into circulation, producing urine

Urine Formation Mechansims

• Urine formation and blood composition adjustment involve three major processes
• Glomerular filtration
• Tubular reabsorption
• Tubular secretion

Glomerular Filtration

• Passive, non-selective process, due to high BP in capillaries
• Net Filtration Pressure ~10 mm Hg, result of osmotic/hydrostatic pressures
• Glomerular Filtration Rate (GFR) is the total amount of filtrate formed per minute by kidneys
• A normal GFR is 120-125 ml/min
• Changes in GFR are normally due to changes in blood pressure
• Outputs result in about 50 gallons of filtrate per day
• ~1.5L pass as urine

Regulation of Glomerular Filtration

• If GFR is too high, needed substances cannot be reabsorbed quickly enough and will be lost in the urine, resulting in high filtrate osmolality
• If GFR is too low, everything reabsorbed including wastes that are normally disposed of resulting in low filtrate osmolality

Glomerular Filtration Regulation

• GFR is controlled by two mechanisms, including intrinsic and extrinsic
• Intrinsic regulates from renal autoregulation
• Extrinsic regulates from neural controls and the hormonal mechanism which includes the renin-angiotensin system

Tubular Reabsorption

• Tubular reabsorption flows through tight junctions and follow a transcellular and paracellular route

Tubular Reabsorption in PCT

• Sodium ions actively reabsorbed causes all organic nutrients to be reabsorbed and water reabsorption
• Approximately 65% of filtrate is reabsorbed in the PCT

Sodium Reabsorption

• Happens in the PCT, ascending loop, and DCT
• The active transport moves Na into the interstitial fluid along the basolateral membrane
• Tubular cell concentration [Na] decreases and diffuses down into the tubular cells via the luminal membrane
• Sodium reabsorption provides the energy and means for reabsorbing most other solutes

Water Reabsorption by PCT Cells

• Active pumping of Na+ drives water reabsorption by osmosis
• An osmotic gradient is created and water diffuses passively from filtrate into the interstitial fluid

Tubular Secretion

• The opposite of reabsorption, wastes and excess ions move from blood to filtrate
• Urine will contain both filtered and secreted substances.
• Main site is PCT, with activity also in DCT and collecting ducts

Tubular Secretion Importance

• Disposing of substances not already in filtrate
• Eliminating undesirable substances such as urea and uric acid
• Ridding the body of excess potassium ions
• Controlling blood pH

Regulation of Urine Concentration and Volume

• Osmolality is the concentration of solutes, higher mOsm = higher concentration
• The kidneys maintain the solute load of body fluids constant at 300 mOsm
• Kidneys regulate urine concentration and volume to regulate the solute load
• This regulation is done via the countercurrent mechanism of the Loop of Henle and vasa recta

Osmotic Gradient in the Renal Medulla

• Osmotic gradients established in the renal medulla help to concentrate urine
• This is essential to water conservation
• The pelvis is the center

Descending Loop of Henle

• Impermeable to solutes
• Permeable to water
• Filtrate becomes more concentrated approaching the medulla

Ascending Loop of Henle

• Is permeable to solutes
• Is impermeable to water
• Filtrate is more diluted than under normal body conditions (~100 mOsm)
• A concentration gradient is created

Countercurrent Multiplier and Vasa Recta

• Allows the formation of concentrated urine
• Countercurrent exchanger also called vasa recta

Final Processing: Collecting Ducts

• Collecting duct activity is under direct physiological control
• Cells of the collecting ducts "fine tune" filtrate
• Intercalated cells use H+ ions for pH balance
• Principal cells are hormone regulated.
• Aldosterone stimulates additional Na+ and K+ transport
• ADH stimulates increased water osmosis from filtrate to interstitial fluid

Formation of Urine: Normal Conditions

• Stable, low concentrations of aldosterone and ADH exist
• Some water is reabsorbed.
• Overall: urine is slightly more concentrated, ~600 mOsm than normal body conditions, ~300 mOsm

Forming Concentrated Urine

• ADH levels increase leading to aquaporin production causing an increase in water reabsorption
• Filtrate equilibrates with interstitial fluids
• Urine may be concentrated up to 1200 mOsm, with low overall volume

Forming Dilute Urine

• Decreases in ADH leading to decreased water reabsorption
• Filtrate kept as dilute as possible
• Urine volume increases greatly with these processes
• Diuretic substances (e.g. caffeine and alcohol) and disease conditions, like diabetes insipidus, trigger these same effects

Physical, Chemical Characteristics of Urine

• Urine is 95% water and 5% solutes
• Fresh urine is clear and pale to deep yellow; the yellow colour is due to urochrome
• Nitrogenous wastes include urea, uric acid, and creatinine
• Other normal solutes include sodium, potassium, phosphate, bicarbonate, and other ions
• Abnormal concentrations of any urinary constituents may indicate a pathology

Other Urinary System Organs: Ureters

• Paired, slender tubes transport urine from kidneys to bladder
• Ureters actively propel urine to the bladder in response to smooth muscle stretch

Other Urinary System Organs: Urinary Bladder

• Smooth, collapsible, muscular sac stores urine temporarilly, for up to 1 liter
• The bladder expands without significant rise in internal pressure when urine accumulates

Urinary Bladder Structure

• The trigone is a triangular area outlined by the openings for the ureters and urethra
• It is clinically important because infections tend to persist in this region

Other Urinary System Organs: Urethra

• A muscular tube that drains urine from the bladder and conveys it out of the body
• Sphincters keep the urethra closed when urine is not being passed

Micturition

• Also called urination or voiding, is the act of emptying the bladder
• It is under autonomic control
• Sympathetic activity inhibits bladder muscles and stimulates the internal sphincter
• Parasympathetic activity stimulates bladder muscles and inhibits the internal sphincter
• The external sphincter is skeletal muscle, so it is under voluntary control

Imbalances of the Urinary System

• Kidney stones, also called renal calculi, are deposits of mineral salts (calcium, uric acid) that precipitate in the pelvis

Urinary System Diseases

• Renal carcinoma: cancer of kidney

Urinary System Diseases

• Giant Kidney Worm, Dioctophyma renale, can grow up to 1 meter long with a width of 12 mm