Urinary System PDF

URINARY SYSTEM RENAL HIUM Located on medial side of each kidney I. FUNCTIONS OF THE URINARY SYSTEM Entry and exit si...

URINARY SYSTEM RENAL HIUM Located on medial side of each kidney I. FUNCTIONS OF THE URINARY SYSTEM Entry and exit site for structures that supply kidney FUNCTIONS Renal artery Production, storage, and transportation of urine Renal vein Filtration of blood and waste removal Renal nerve pH regulation of bodily fluids Ureter Blood pressure regulation Lymphatics Regulation of solute concentration in blood Stimulation of erythrocyte production NEPHRONS AND BLOOD SUPPLY Vitamin D synthesis Nephron—functional unit of kidney Arteries—renal, segmental, interlobar, arcuate, II. GROSS AND MICROSCOPIC ANATOMY OF THE KIDNEY interlobular KIDNEY Nephron—afferent arterioles, glomeruli, efferent Paired, retroperitoneal organs located on either side of the arterioles, peritubular capillaries vertebral column Veins—interlobular, arcuate, interlobar, renal Not within abdominal cavity Left kidney sits slightly lower than right because it is displaced by the liver Protected by muscle, adipose, and ribs Adrenal glands located on superior margin BLOOD FLOW IN THE NEPHRONAfferent arterioles deliver blood to nephron Within nephron, glomerular capillaries filter blood Fenestrated capillaries Bloods exits via efferent arterioles Peritubular capillaries accomplish exchange of nutrients and wastes EXTERNAL LAYERS OF THE KIDNEYS Vasa recta drains peritubular capillaries Fibrous capsule maintains shape of kidney Perinephric fat absorbs shock and provides protection Renal fascia anchors kidneys to posterior abdominal wall INTERNAL ANATOMY Superficial renal cortex covers deeper renal medulla Renal medulla includes the renal pyramids and the renal columns Renal columns separate renal pyramids of medulla Also divide kidney into 6 to 8 renal lobes Renal papillae drain urine into minor calyces Minor calyces merge to form major calyces Major calyces merge to form renal pelvis NEPHRONS Functional units of the kidney that make urine Two components Renal corpuscle Composed of glomerulus and glomerular capsule Tubular system Proximal convoluted tubule, nephron loop, distal convoluted tubule, collecting ducts RENAL CORPUSCLE Responsible for filtration of blood Forms filtrate Composed of: Glomerulus = fenestrated capillary Glomerular capsule—captures filtrate Parietal layer made of simple squamous epithelium Visceral layer made of podocytes GLOMERULUS A fenestrated capillary Collecting ducts Fenestrations located in Not part of nephron but can influence solute and endothelium of glomerulus water reabsorption Allow additional Usually occurs under hormonal influences volume of blood and DCTs of several nephrons empty into the same larger substances to collecting duct be filtered in same amount of time AQUAPORINS Membrane proteins that allow FILTRATION MEMBRANE water through Limits filtration of blood cells, Water movement occurs via platelets and large plasma osmosis proteins Water moves toward Negative charge of membrane limits filtration of negatively area of greater charged molecules osmolarity Composed of: Not all sections of renal tubule Fenestrated endothelium of glomerulus contain aquaporins Basement membrane Filtration slits formed by pedicels of podocytes RENAL CORTEX VS RENAL MEDULLA Renal cortex Contains majority of nephron structures Glomeruli/renal corpuscles Most proximal and distal convoluted tubules Renal medulla Contains parts of nephron loops and collecting ducts CORTICAL VS JUXTAMEDULLARY NEPHRONS Cortical nephrons are the majority of the nephrons in the kidney TUBULAR SYSTEM (85%) Refines filtrate into urine Renal corpuscles located closer to renal capsule Proximal convoluted tubule (PCT) Shorter nephron loops Actively secretes and reabsorbs solutes Juxtamedullary nephrons (15%) have renal corpuscles closer to Nephron loop medulla Divided into descending limb and ascending limb Longer nephron loops with vasa recta Each limb has unique permeability for solute and water Distal convoluted tubule (DCT) Farther away from renal corpuscle Reabsorbs and secretes fewer solutes and less water  NFP = HPg – (OP + HPc) Under typical conditions, glomerular hydrostatic pressure promotes filtration Directly influenced by systemic blood pressure INFLUENCE ON GFR GFR influenced by various factors Hypertension damages glomeruli and filtration membrane Larger openings allow filtration of additional solutes including plasma proteins Disease: Nephritis = inflammation of nephron May be caused by infection May harden and narrow the lumen of the tubules Interferes with flow of filtrate through tubule and decreases GFR III. PHYSIOLOGY OF URINE FORMATION PROCESS OF URINE FORMATION TUBULAR REABSORPTION AND SECRETION Production of urine depends on three processes carried out by Filtrate must be refined into urine by: the kidneys: Tubular reabsorption—filtered substances Filtration reabsorbed from tubules back into blood Accomplished by renal corpuscles Tubular secretion—wastes secreted from blood into Plasma is filtered by glomerulus to form tubular fluid to become part of urine filtrate Most filtered materials are reabsorbed Reabsorption and secretion Materials not reabsorbed become part of urine Accomplished by renal tubule Reabsorption returns filtered materials to REABSORPTION AND SECRETION WITHIN RENAL TUBULE blood Kidneys form ~180 liters of filtrate per day Secretion removes additional materials Most water and solutes are reabsorbed from blood into renal tubule PCT, nephron loop, and DCT reabsorb most water GLOMERULAR FILTRATION Collecting ducts vary in amount of water Filtration occurs as plasma is filtered into capsular space reabsorbed Nonspecific process based on size Solutes reabsorbed at various points in tubule Occurs via bulk driven by net filtration pressure (NFP) Molecules secreted become a part of urine Influenced by glomerular hydrostatic pressure, blood colloid osmotic pressure, and capsular hydrostatic pressure Glomerular filtration rate (GFR)—volume of filtrate formed per minute by both kidneys Average is 80–140 mL/minute at rest Highly variable to due gender, age, diet, metabolism PRESSURES THAT INFLUENCE GLOMERULAR FILTRATION Glomerular hydrostatic pressure promotes filtration into the capsule Capsular hydrostatic pressure and blood colloid osmotic pressure promote movement into glomerulus Movement occurs in the direction of lower pressure NET FILTRATION PRESSURE (NFP) NFP determined by interaction of glomerular hydrostatic, blood colloid osmotic, and capsular hydrostatic pressures SUBSTANCES SECRETED OR REABSORBED IN THE NEPHRON Different forms of transport used for each surface REABSORPTION AND SECRETION IN PCT Most solute and water reabsorption occurs in PCT All glucose and amino acid reabsorption occurs in PCT Sodium, bicarbonate, and calcium reabsorption occurs too Sodium (Na+) symporters provide energy for secondary active transport of glucose and amino acids Diffuse through basolateral membrane after entering tubular cells Water passively follows solutes via osmosis Secretion of excess urea, ammonia, creatinine, and acid SODIUM REABSORPTION Luminal transport occurs via facilitated diffusion No energy input required Basolateral transport occurs via active transport Sodium ions are transported from low to high concentration Sodium-potassium pumps in basolateral surface MECHANISMS OF REABSORPTION AND SECRETION Mechanisms include Simple diffusion, facilitated diffusion, primary active transport, secondary active transport, and osmosis If transport requires use of membrane channel or protein, it is subject to Specificity—can only transport specific molecules Transport maximum (Tmax)—maximal rate of transportation if all transporters occupied Competition—similar molecules may compete for transporter ANATOMY OE MEMBRANE TRANSPORT REABSORPTION OF GLUCOSE AND WATER Sodium symporters in luminal surface transport sodium and glucose into tubular cell Sodium moves across basolateral surface by sodium-potassium pumps; glucose by facilitated diffusion Amino acids reabsorbed in similar way As osmolarity of IF and blood increases, water reabsorbed by osmosis via aquaporins TRANSPORTATION ROUTES Reabsorption may occur between tubular cells or through them Luminal surface = surface of cell that faces lumen of renal tubule Basolateral surface = surface that faces interstitial fluid/peritubular capillaries REABSORPTION OF BICARBONATE Sodium-hydrogen antiporter in luminal surface transports sodium ions into tubular cell and hydrogen ions into tubular lumen  Carbonic anhydrase combines hydrogen and bicarbonate ions to form carbonic acid Carbonic acid dissociates to form carbon dioxide and water Carbon dioxide enters tubular cell and is converted back into bicarbonate for reabsorption UNDERSTANDING THE COUNTERCURRENT MULTIPLIER Actions of nephron loop referred to as countercurrent multiplier Multiplies osmolarity of REABSORPTION AND SECRETION IN NEPHRON LOOP IF Descending limb contains aquaporins for water reabsorption Countercurrent multiplier train Ascending limb actively reabsorbs solute ions, especially Na + analogy and Cl- Solutes pulled out Builds osmotic gradient for water reabsorption from from earlier cars descending limb Influences latter cars Countercurrent multiplier system Creates As filtrate moves through nephron loop solute pumps osmotic in ascending multiply osmotic gradient to increase gradient water reabsorption that pulls Structure of vasa recta allows nutrient and waste exchange water from without disruption of osmotic gradient descending nephron DESCENDING AND ASCENDING NEPHRON LOOP loop Descending loop contains permanent aquaporins Osmolarity of tubular fluid increases as water moves REABSORPTION AND SECRETION IN DCT into interstitium Reabsorption varies according to physiological needs Thick ascending loop impermeable to water Sodium and chloride ion reabsorption occurs Symporters transport sodium and chloride ions Water passively follows sodium and chloride into interstitium Parathyroid hormone (PTH) will increase calcium reabsorption Osmolarity of tubular fluid decreases here Creates osmotic gradient for movement of water JUXTAGLOMERULAR APPARATUS Juxtaglomerular apparatus (JGA) regulates glomerular blood hydrostatic pressure Allows kidneys to autoregulate glomerular filtration rate (GFR) Composed of: Macula densa—cells in the DCT Regulates release of renin to control blood pressure Responds to elevated GFR by decreasing release of nitric oxide Lowers GFR as afferent arteriole constricts Juxtaglomerular (JG) cells—smooth muscle cells in afferent arteriole Respond to elevated GFR by constricting afferent arteriole to reduce GFR EPITHELIAL CELLS OF ASCENDING NEPHRON LOOP Thick ascending limb transports solutes Sodium and chloride ions are transported into epithelial cell Movement of chloride ions builds up negative COLLECTING DUCTS AND RECOVERY OF WATER charge in interstitial fluid (IF) Collecting ducts regulate urine volume, urine osmolarity, and Attracts additional cations for blood osmolarity reabsorption Principal cells – reabsorb sodium ions and secrete potassium ions Intercalated cells – reabsorb potassium and bicarbonate ions; secrete hydrogen ions  Alters osmolarity of blood by varying reabsorption of water Kidney releases erythropoietin (EPO) in response to hypoxemia If blood is hyperosmotic, reabsorption of water EPO stimulates production of red blood cells increases Production occurs in red bone marrow If blood is hypoosmotic, reabsorption of water Kidney damage may lead to anemia decreases Regulated by hormones CALCIUM REABSORPTION DCT contains receptors for PTH IV. HOMEOSTASIS AND CONTROL OVER THE FORMATION OF PTH causes cells in DCT to upregulate calcium channels URINE Increased calcium channels lead to increased RENIN-ANGIOTENSIN-ALDOSTERONE PATHWAY reabsorption of calcium Increases blood pressure to maintain GFR Active forms of vitamin D aids b transporting calcium to Renin released by JG cells when BP is low basolateral membrane for exocytosis Converts angiotensinogen into angiotensin I Angiotensin I converted to angiotensin II by ACE in lungs VI. GROSS AND MICROSCOPIC ANATOMY OF THE URINARY Angiotensin II causes vasoconstriction and aldosterone release TRACT (URETERS, URINARY BLADDER, AND URETHRA) Aldosterone increases Na+ and water reabsorption URINARY TRACT Urine flows from kidneys to: Ureters Exit kidneys and transport urine to urinary bladder Urinary bladder Temporarily stores urine Urethra Allows urine to exit body ANTIDIURETIC HORMONE Increases water reabsorption by the kidney Promotes insertion of aquaporins in collecting duct Increased water reabsorption leads to higher blood pressure Vasoconstriction also leads to increased blood pressure NATRIURETIC HORMONES Main example is atrial natriuretic hormone (ANH) Stimulates excretion of sodium Excretion of sodium increases water loss in urine Leads to lower blood pressure HORMONES THAT INFLUENCE GFR AND RBF URETERS Transport urine from kidneys to urinary bladder Retroperitoneal location Lined by transitional epithelium Urine moves through ureters by peristalsis and gravity Physiological sphincter prevents reflux of urine URINARY BLADDER Receives urine via ureteral openings Stores urine until eliminated from body V. ADDITIONAL ENDOCRINE ACTIVITIES OF THE KIDNEY Lined by transitional epithelium VITAMIN D SYNTHESIS Walls contain detrusor muscle Vitamin D synthesized by skin in response to UV radiation Internal urethral orifice Most active form of vitamin D is calcitriol Surrounded by internal urethral sphincter, which is Kidney coverts precursor from skin to calcitriol composed of smooth muscle and is involuntary Aids in absorption of calcium from digestive tract and External urethral sphincter is composed of skeletal muscle and is reabsorption of calcium by kidneys under voluntary control ETYTHROPOIESIS  Sympathetic hypogastric inhibits detrusor muscle contraction Parasympathetic pelvic increases contraction of detrusor muscle URINARY BLADDER AND URETHRA IN BIOLOGICAL FEMALES Urinary bladder anterior and inferior to uterus Uterus may compress bladder in pregnancy MALE URETHRA Shorter urethra increases risk of cystitis (urinary tract infection) Biological male urethra is substantially longer than biological female urethra Divided into three sections: Prostatic, membranous, and spongy urethra VII. URINE CHARACTERISTICS AND ELIMINATION CHARACTERISTICS OF URINE Characteristics of urine change depending on factors like water intake, exercise, and nutrient intake URINARY BLADDER AND URETHRA IN BIOLOGICAL MALES pH range is 4.5–8.0 Urinary bladder located superior to prostate gland Glucose, blood, and protein not found in normal urine Enlargement of prostate gland may restrict flow of urine into urethra Longer urethra passes through prostate gland, floor of pelvis, and penis Longer urethra decreases risk of cystitis MICTURITION REFLEX Proper term for urination Urine entering bladder causes distention (stretching) of bladder Parasympathetic stimulation causes detrusor muscle to URINALYSIS contract Urinalysis—a test that evaluates materials found in urine Relaxation of internal urethral sphincter allows urine to flow into Abnormal components of urine: urethra Protein—usually indicates damage to filtration External urethral sphincter is skeletal muscle membrane Spinal reflex relaxes it to allow urine to continue to Glucose—usually indicates diabetic condition flow and exit urethra Blood—indicates structural damage to urinary tract Control achieved during “potty training” Leukocytes—indicates urinary tract infection Ketones—indicates body is using fat as energy NERVES INVOLVED IN URINATION source Pudendal nerve regulates voluntary micturition (urination) by regulating external urethral sphincter ----------------------------------------------------END-------------------------------------------------- Pelvic and hypogastric nerves innervate urinary bladder