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The Urinary System Function • Maintain the consistency of fluids in the body • Similar to a water purification plant Facts • Kidneys filter 200 liters of fluid every day • Removes metabolic waste, ions, toxins from the bloodstream • Help regulate blood pressure and secretes erythropoietin Organs • Kidneys • Ureters • Urinary bladder • Urethra Kidney Location • Superior lumbar region • T12 to L3 • Receive some protection from the lower ribs • Right kidney is crowded by liver so it lies slightly lower than left kidney • Weighs 150g (0.33 lbs) • 12cm long, 6cm wide, 3cm thick (about size of large bar of soap) Internal Anatomy • Three regions: – Cortex – Medulla • Contains renal pyramids – Pelvis • Collects urine to send down ureter to bladder Blood Supply • Under normal conditions, the renal arteries deliver approximately ¼ of blood supply to the kidneys every minute Nephrons • Each kidney contains over one million tiny processing units called nephrons • They carry out the process of making urine • Each consists of: Glomerulus – mass of capillaries Bowman’s capsule – structure that collects filtrate from glomerulus Glomerulus • Endothelium is very porous • Large amounts of solute-rich, protein free fluid pass from the blood to the Bowman’s capsule • This fluid (or filtrate) is raw material that is processed by the renal tubules to form urine Renal Tubule • Filtrate leaves the glomerulus and travels through a set of small tubes = tubules • About 3 cm long • Three parts: 1) Proximal convoluted tubule (closer to glomerulus) 2) Loop of Henle 3) Distal convoluted tubule Collecting Ducts • Receive filtrate from many nephrons • Give renal pyramids striped appearance 2 1 1 3 1 4 1 5 6 7 Quiz • Click Here Kidney Physiology • Of the approximately 1000mL of blood that passes through the glomeruli each minute, 650mL is plasma • About of 120mL of plasma is forced into the renal tubules • Equivalent to filtering entire blood plasma 60 times a day = 47 gallons • Kidneys consume 20-25% of all oxygen used by body at rest Filtrate vs. Urine • Once filtrate has moved through the collecting ducts, it has lost most of its water, nutrients and essential ions • What remains is called urine and contains mostly metabolic wastes • About 1.5L of the 180L of filtrate leaves the body as urine • Rest is returned to circulation Urine Formation Three processes: 1) Glomerular filtration 2) Tubular reabsorption 3) Tubular secretion Glomerular Filtration • For the most part, filtration is a passive, nonselective process in which fluids and solutes are forced through a membrane by hydrostatic pressure • Very efficient because of high permeability and high blood pressure • 55mm Hg in contrast to other capillaries in body at 18mm Hg Tubular Reabsorption • Our total blood volume is filtered into the renal tubules about every 45 minutes • If some was not reclaimed, all of our plasma would be drained away within an hour • This reclaiming process is called tubular reabsorption Tubular Reabsorption • All organic nutrients (glucose, amino acids) are completely reabsorbed but the reabsorption of water and ions are regulated by hormones • Which hormone regulates the reabsorption of water by adjusting the permeability of the collecting ducts? Antidiuretic hormone • Reabsorption of: – Cations (Na+, K+, Mg2+, Ca2+) – Anions (HCO3-, Cl-) HCO3- is bicarbonate; where did that come from? Small Intestine Tubular Secretion • Disposing of certain drugs (penicillin, phenobarbital – seizures and anxiety) • Eliminates urea – CO(NH2)2 – How body eliminates nitrogen • Eliminates uric acid – C5H4N4O3 – Uric acid is a product of the breakdown of purine nucleotides. Which ones are purines? adenine (A) and guanine (G) – High blood concentrations of uric acid can lead to a type of arthritis known as gout GOUT Gout Formation of Dilute Urine • Simple process because no water is absorbed in the renal tubules Formation of Concentrated Urine • Antidiuretic hormone (ADH) inhibits urine output by increasing reabsorption of water • During maximum ADH secretion, 99% of water is reabsorbed and returned to blood Diuretics • Chemicals that increase urinary output – Alcohol inhibits ADH release – Caffeine, drugs for hypertension and edema from congestive heart failure inhibit sodium ion reabsorption which inhibits water reabsorption Characteristics of Urine • Generally clear and pale to deep yellow in color • Color results from the body’s destruction of hemoglobin and creation of by-product bilirubin • More water = pale urine, and vice versa • Pink or brown urine can result from foods like beets or rhubarb or due to bile pigments or blood in urine • Cloudy urine may indicate infection of some part of urinary tract Characteristics of Urine Odor – Fresh urine has a slight odor – Urine that is allowed to stand develops an ammonia odor due to bacteria – Some foods or drugs can create unusual odor – In persons with diabetes, urine can smell fruity when glucose is high Chemical Composition • 95% of urine is water • 5% is solutes – Urea • breakdown of amino acids – Creatinine • Helps regenerate ATP, more in skeletal muscles – Uric acid • Breakdown of purines Kidney Stones • Caused by Ca, Mg, or uric acid salts crystallizing in kidney • Most are smaller than 5mm so they pass without problems • Larger crystals can obstruct ureter • Prevention includes adequate hydration • Treatment includes shock wave lithotripsy (using ultrasound to break up stones) Pyelonephritis • Infection of entire kidney • In females, usually caused by E. coli bacteria from anal area into urinary tract • Severe cases can result in abscesses that cause kidney to fill with pus • If left untreated, kidneys can be damaged • Causes: Renal Failure – Repeated damage from infections – Physical injury to kidneys – Crush injury to skeletal muscles (releases myoglobin that clogs renal tubules) – Heavy metal poisoning (Hg or Pb) – Organic solvent poisoning (paint thinner, acetone, dry-cleaning fluid, etc.) – Inadequate blood supply (can occur in arteriosclerosis) Physiology of Renal Failure • Filtrate formation decreases or stops • Nitrogen waste builds up • Blood pH becomes more acidic Hemodialysis • Artificial kidney • Patient’s blood is passed through membrane tubing that is permeable and wastes diffuse out of blood • Usually done 3-4 times per week and each session takes 4-8 hours • Life threatening kidney failure only becomes obvious after about 75% of renal function has been lost • Only permanent solution is kidney transplant Ureters • Tubes that take urine from each kidney to bladder • Each begins at L2 • Stretching of ureters causes peristalsis to push urine down Urinary Bladder • Smooth, collapsible, muscular sac that temporarily stores urine • A moderately full bladder holds about 500mL of urine (2 cups) Urethra • Thin walled muscular tube that drains urine from the bladder to outside the body • Has sphincters: Internal – involuntary sphincter keeps urethra closed when urine is not being passed External – voluntary sphincter that relaxes during voiding of urine Urinary Tract Infections • Overall, 40% of all women get UTIs –Urethra is only 3-4 cm long –Proximal to anal opening –Improper toilet habits –Sexual intercourse can cause vaginal bacteria to move into urethra Incontinence • Inability to control urination – Infants have not learned to control external sphincter – In older adults, the sphincter malfunctions Crash Course • Video About 12 minutes