Lecture 17 - Urinary System PDF

THE URINARY SYSTEM DR. MARIA CRISELDA M. BONIFACIO-UY, RN, AFPAAAMMI  KIDNEYS Dark red organs Kidney-bean shape Lie retroperitoneally in the superior lumbar region Extend from T12 to L3 vertebra Protected by the lower part of the rib cage Rig...

THE URINARY SYSTEM DR. MARIA CRISELDA M. BONIFACIO-UY, RN, AFPAAAMMI  KIDNEYS Dark red organs Kidney-bean shape Lie retroperitoneally in the superior lumbar region Extend from T12 to L3 vertebra Protected by the lower part of the rib cage Right kidney is slightly lower than the left  KIDNEYS Kidney Structure Adult kidney Length 12cm (5in), width 6cm (2.5in), thickness 3cm (1in) Convex laterally Renal Hilum A medial indentation Ureter, renal blood vessels and nerves  KIDNEYS Kidney Structure 3 protective layers: (deep to super cial) 1. Fibrous capsule Transparent; encloses each kidney and responsible for its glistening appearance 2. Perirenal fat capsule Fatty mass; surrounds each kidney and cushions it against blows 3. Renal fascia Most super cial later made of dense brous connective tissue; anchors kidney and adrenal gland fi fi fi  KIDNEYS Kidney Structure Renal Cortex Light outer region Renal Medulla Darker reddish brown inner region Renal pyramids/medullary pyramids - triangular regions with a striped appearance Broad base of each pyramid faces towards the cortex; Apex points toward the inner region Renal Columns - cortexlike tissue that separates the pyramids;  KIDNEYS Kidney Structure Renal Pelvis a at, funnel shaped tube lateral to the hilum Continuous with the ureter leaving the hilum Renal Calyces (calyces) A cup-shaped drain that enclose the tips of the pyramids Collects urine Continuously drains from the tips of the pyramids into the renal pelvis Urine ows from the pelvis to the ureter to the bladder for temporary storage until it leaves the body. fl fl  KIDNEYS BLOOD SUPPLY Renal Artery supplies each kidney; as it approaches the hilum it divides into Segmental arteries which gives o several branches called Interlobar arteries, which travel through the renal columns to reach the cortex; as it reach the cortex-medulla junction it gives o the Arcuate arteries which arch over the medullary pyramids. Small Cortical radiate arteries branch o the arcuate arteries to supply the renal cortex ff ff ff  KIDNEYS BLOOD SUPPLY Venous drainage Cortical radiate vein to arcuate vein to interlobar vein to renal vein —> emerges from the hilum and empties to the IVC  NEPHRONS The structural and functional units of the kidneys and are responsible for forming urine. Each kidney contains over a million tiny lters Collecting ducts - collect uids from several nephrons and conveys in to the renal pelvis; run downward through the medullary pyramids, giving the pyramids a striped appearance; deliver the nal urine product into the calyces and the renal pelvis fl fi fi  NEPHRONS 2 main structures: 1. RENAL CORPUSCLE consists of: glomerulus - a knot of capillaries Bowman’s capsule - a cup shaped hollow structure that completely surrounds the glomerulus Podocytes - highly modi ed octopus-like cells; have long branching extensions called foot processes that intertwine with one another and cling to the glomerulus Filtration slits - openings between foot processes; it allows podocytes to form a porous or leaky membrane around the glomerulus ideal for ltration fi fi  NEPHRONS 2 main structures: 2. RENAL TUBULE Makes up the rest of the nephron About 3 cm (1.25in) long From the Bowman’s capsule it coils and twist before forming a hairpin loop and then again becomes coiled and twisted before entering a collecting duct. Regions: Proximal convoluted tubule (PCT) Loop of Henle Distal convoluted tubule (DCT)  NEPHRONS Cortical nephrons - nephrons found in the cortex Juxtamedullary nephrons - located close to the cortex- medulla junction  NEPHRONS Capillary beds: 1. Glomerulus Supplied by the a erent arteriole from the cortical radiate artery; E erent arteriole receives the blood as it leaves the glomerulus Specialized for ltration A erent arteriole has a larger diameter than e erent arteriole, resulting in a much higher blood pressure in the glomerular capillaries than the other capillary beds This high pressure forces uid and small solutes out of the blood into the glomerular capsule ff ff fi ff fl ff  NEPHRONS Capillary beds: 2. Peritubular capillary bed Arises from the e erent arteriole that drains the glomerulus Has low-pressure, porous vessels adapted for absorption instead of ltration Lie closely to the renal tubules where it receives solutes and water from the tubule cells and are reabsorbed from the ltrate percolating through the tubule. Drain into the cortical radiate vein, arcuate vein and into the interlobar vein leaving the cortex fi ff fi  Urine Formation and Characteristics GLOMERULAR FILTRATION A nonselective, passive process in which uid passes from the blood into the glomerular capsule part of the renal tubules Filtrate - a uid, which is essentially blood plasma without the blood proteins. Proteins and blood cells are too large to pass through the ltration membrane - if these are present in urine there is usually a problem with the glomerular lters If arterial blood pressure drops too low, glomerular pressure becomes inadequate to force substance out of the blood into the tubules and ltrate formation stops fi fl fi fi fl  Urine Formation and Characteristics TUBULAR REABSORPTION Begins as the ltrate enters the proximal convoluted tubule. Tubule cells are transporters of substances from the ltrate and passes it to the posterior aspect in to the extracellular space where they are absorbed into the peritubular capillary blood Waste and excess ions must be removed from the blood Filtrate, contains water, glucose, amino acids and ions, must be reclaimed from the ltrate and returned to the blood fi fi fi  Urine Formation and Characteristics TUBULAR REABSORPTION Reabsorption Passive transport - water Active transport - uses membrane carriers, requires ATP and very selective PCT - NaCl, HCO3, H2O, Glucose and Amino acids Loop of Henle - H2O, NaCl DCT - NaCl Collecting duct - H2O, Urea  Urine Formation and Characteristics TUBULAR SECRETION Substances such as hydrogen and potassium ions and creatinine also move from the blood of the peritubular capillaries through the tubule cells or from the tubules cells themselves into the ltrate to be eliminated in urine Important in removing substances not in the ltrate, such as certain drugs or excess potassium ions or as means in controlling blood pH fi fi  Urine Formation and Characteristics NITROGENOUS WASTE PRODUCTS Waste products are poorly reabsorbed Remain in the ltrate and are found in high concentrations in urine excreted in the body Common nitrogenous waste: Urea - formed by the liver as an end product of protein breakdown when amino acids are used to produce energy Uric acid - released when nucleic acids are metabolized Creatinine - associated with creatine metabolism in muscle tissue fi  Characteristics of Urine 1 to 1.8L of urine is produced every 24 hours Color: Clear and pale to deep yellow - freshly voided urine Normal yellow color is due to UROCHOME, a pigment that results from the body’s destruction of hemoglobin Deeper yellow - more solutes Pale, straw color - dilute urine Other than yellow - eating certain food, or presence of bile  Characteristics of Urine Urine is STERILE; odor is slightly aromatic If it is allowed to stand it takes on an ammonia odor caused by the action of bacteria on the urine solutes Some vegetables and diseases (DM) alter the order of urine  Characteristics of Urine Urine pH - slightly acidic (around 6) High protein diet causes it to be more acidic Vegetarian diet and bacterial infection makes it alkaline Speci c gravity 1.001 to 1.035 (dilute to concentrated urine) Dilute urine - when a person drinks excessive uids, used diuretics or has chronic renal failure (kidney loses its ability to concentrate urine) Concentrated urine - inadequate uid intake, fever, and kidney in ammation (pyelonephritis ) fl fi fl fl  Characteristics of Urine Solutes found in urine: Sodium ion (Na+) Potassium ion (K+) Urea Uric acid Creatinine Ammonia Bicarbonate ions  Characteristics of Urine Substances not normally found in urine: Glucose Blood proteins RBC Hemoglobin White blood cells (pus) Bile Characteristics of Urine  Ureter, Urinary Bladder, and Urethra URETERS Two slender tubes 25 to 30 cm (10 to 12 inches) long and 6 mm (1/4in) in diameter Each ureter runs behind the peritoneum from the renal hilum to the posterior aspect of the bladder, it enters at a slight angle The superior end of each ureter is continuous with renal pelvis Its mucosal lining is continuous with the mucosa lining of the renal pelvis and the bladder inferiorly  Ureter, Urinary Bladder, and Urethra URETERS Carry urine from the kidneys to the bladder Smooth muscle layers in their walls contract to propel urine by peristalsis Once urine has entered the bladder, it is prevented from owing back into the ureters by small valvelike folds of bladder mucosa that cover the ureter opening fl  Ureter, Urinary Bladder, and Urethra URINARY BLADDER Smooth, collapsible, muscular sac that sores urine temporarily Located retroperitoneally in the pelvis just posterior the symphysis pubis Has 3 openings 2 ureteral ori ces 1 internal urethral ori ce - drains the bladder Trigone a smooth triangular region of the bladder base outlined by these 3 openings Important clinically because infections tend to persist in this region fi fi  Ureter, Urinary Bladder, and Urethra URINARY BLADDER In males, the prostate surrounds the neck of the bladder where it empties into the urethra. The bladder wall contains 3 layers of smooth muscle called the detrusor muscle Its mucosa is the transitional epithelium When the bladder is empty, it is collapsed, 5 - 7.5cm (2-3in) long, with thick walls Moderately full bladder - 12.5cm (5in) long and holds about 500ml of urine. It is capable of holding more than twice that amount Distended bladder is rm, pear-shaped and may be felt in the symphysis pubis fi  Ureter, Urinary Bladder, and Urethra URETHRA A thin walled tube that carries urine by peristalsis from the bladder to the outside of the body. 2 sphincters: 1. Internal urethral sphincter Formed by smooth muscles Location: bladder-urethra junction Involuntary sphincter that keeps urethra closed when urine is not being passed. 2. External urethral sphincter Formed by skeletal muscle Location: pelvic oor at the urogenital triangle Voluntarily controlled fl  Ureter, Urinary Bladder, and Urethra URETHRA Male Urethra Length: 20 cm (8 in) Has 3 regions 1. Prostatic 2. Membranous 3. Spongy/Penile Opens at the tip of the penis after traveling down its length Has double function: carries both urine and sperm; but never at the same time Female Urethra Length: 3 to 4 cm (1 1/2 in) External ori ce or opening lies anterior to the vaginal opening Only function is to conduct urine from the bladder to the body exterior fi  Ureter, Urinary Bladder, and Urethra MICTURITION Voiding - the act of emptying the bladder The two sphincter control the ow of urine from the bladder The bladder continues to collect urine until about 200ml have accumulated —> activates stretch receptors Impulses transmitted to the sacral region of the spinal cord and then back to the bladder via the pelvic splanchnic nerves cause the bladder to go into the re ex contractions. fl fl  Ureter, Urinary Bladder, and Urethra MICTURITION As the contractions become stronger, stored urine is forced past the internal urethral sphincter into the upper part of the urethra —> the urge to void Upon additional of 200 to 300ml more have been collected the micturition re ex occurs again. fl  Fluid, Electrolyte and Acid Base Balance Four major roles of the Kidneys Excreting nitrogen-containing wastes Maintaining water balance of the blood Maintaining electrolyte balance of the blood Ensuring proper blood pH  Maintaining Water Balance of Blood Body Fluids and Fluid Compartments Water accounts for half or more of your body weight 50% in women; 60% in men, 75% in babies Water occupies three uid compartments Intracellular uid (ICF) 2/3 of body uid Extracellular uid (ECF) Blood plasma, interstitial uid between cells, lymph Transcellular uid CSF and serous uids humors of the eyes and others fl fl fl fl fl fl fl  Maintaining Water Balance of Blood Water intake comes from uids and food we Ingest in our diet Small amount is produced during cellular metabolism Thirst mechanism - the driving force for water intake An increase in plasma solute content of only 2 to 3 percent excites highly sensitive cells in the hypothalamus called osmoreceptors, which in turn activate the hypothalamic thirst center Water leaves the body by several routes. Some water vaporizes out of the lungs (insensible water loss), some is lost in perspiration, and some leaves the body in the stool fl  Maintaining Water Balance of Blood Other Kidney functions: Ensure proper concentrations of various electrolytes in both intracellular and extracellular uids Most electrolytes enter the body in food and hard (mineral rich) water Reabsorption of water and electrolytes by the kidneys is regulated by hormones fl  Maintaining Water Balance of Blood Antidiuretic hormone (ADH) Released during blood volume depletion eg: Hemorrhage, excessive water loss (sweating or diarrhea); Arterial blood pressure drops which in turn decreases the amount of ltrate formed by the kidneys. Travels in the blood the collecting ducts, where it causes the ducts to reabsorb more water, resulting in normalization of blood volume and pressure and small amount of concentrated urine is formed fi  Maintaining Electrolyte Balance Aldosterone Produced by the adrenal cortex A second hormone that helps regulate blood composition and blood volume by acting on the kidneys A major factor regulating sodium ion content of the ECF and regulate the concentration of other ions (K, Cl, Mg) Increase water reabsorption by the tubule cells; as sodium ions are reclaimed water follows passively back into the blood “WATER FOLLOWS SALT”  Maintaining Electrolyte Balance Sodium ion Are electrolyte responsible for osmotic water ow Low sodium = water leaves blood; water enters tissue -> EDEMA 80% in the ltrate are reabsorbed in the PCT High Aldosterone levels = sodium ions are actively reabsorbed in the DCT and collecting ducts Increasing Na ion in blood -> Decreases K ion fi fl  Maintaining Electrolyte Balance Renin Angiotensin Mechanism Most important trigger for aldosterone Mediated by the juxtaglomerular (JG) apparatus of the renal tubules. JG apparatus consist of a complex of modi ed smooth muscle cells (JG cells) in the a erent arteriole plus some modi ed epithelial cells forming part of the DCT fi ff fi  Maintaining Acid Base Balance of Blood Blood pH: 7.35 -7.45 Alkalosis: arterial pH above 7.45 Acidosis: arterial pH below 7.35 Because a pH of 7.0 is neutral; any pH between 7.0 and 7.35 is not acidic, it represents a lower than optimanl pH for the functioning of most cells. This is called PHYSIOLOGICAL ACIDOSIS  Maintaining Acid Base Balance of Blood BLOOD BUFFERS Chemical bu ers are systems of one or two molecules that act to prevent dramatic changes in the hydrogen ion concentration when acids or bases are added A drop in pH -> binds to hydrogen ion A rise in pH -> releases hydrogen ion ff  Maintaining Acid Base Balance of Blood BLOOD BUFFERS Acids are proton (H) donors; acidity of a solution re ects only on the free hydrogen ions, not those still bound to anions. Strong acids (HCl) dissociate completely and liberate all their hydrogen ions in water; causes large change in pH Weak Acids (Carbonic Acid H2CO3) release only some of their H+ and have lesser e ect on pH; e ective at preventing pH changes because they are forced to dissociate and release more H+ when pH rises over the desirable pH range ff ff fl  Maintaining Acid Base Balance of Blood BLOOD BUFFERS Bases are proton or hydrogen ion acceptors Strong bases (Hydroxides) dissociate easily in water and quickly tie up H+ Weak bases (bicarbonate ion HCO3 and ammonia NH3) are slower to accept H+ As pH drops the weak bases become stronger and begin to tie up more H. Weak acids and weak bases are valuable members of the chemical bu er systems ff  Maintaining Acid Base Balance of Blood BLOOD BUFFERS Three major chemical bu er system BICARBONATE, PHOSPHATE and PROTEIN BUFFER SYSTEMS Each helps to maintain the pH in one or more of the uid compartments All three operate in a similar way ff fl  Maintaining Acid Base Balance of Blood BLOOD BUFFERS BICARBONATE BUFFER SYSTEM A mixture of Carbonic acid (H2CO3) and its salt, Sodium bicarbonate (NaHCO3). H2CO3 is a weak acid, it does not dissociate in neutral or acidic solutions When a strong acid HCl is added most of the H2CO3 remains intact HCO3 of the salt act as bases to tie up the H+ ions released by the stronger acid forming more H2CO3 HCl + NaHCO3 —> H2CO3 + NaCl Strong base + weak base —> weak acid + salt  Maintaining Acid Base Balance of Blood BLOOD BUFFERS If a strong base such as sodium hydroxide (NaOH) is added to a solution containing the bicarbonate bu er system, NaHCO3 will not dissociate further under such alkaline conditions. Carbonic Acid (H2CO3) will be forcd to dissociate further by the presence of the strong base releasing more H+ to bind with the OH- released by NaOH NaOH + H2CO3 —> NaHCO3 + H2O Strong base + weak acid —> weak base + water ff  Maintaining Acid Base Balance of Blood Respiratory Mechanism Respiratory system eliminates carbon dioxide from the blood while it loads oxygen into the blood When carbon dioxide (CO2) enters the blood from the tissue cells, most of it enters the red blood cells, where it is converted to bicarbonate ion (HCO3) for transport in the plasma  Maintaining Acid Base Balance of Blood Renal Mechanism Only kidneys can rid the body of other acids generated during metabolism and have the power to regulate blood levels of the alkaline substances Most potent of the pH-regulating mechanisms The most important means by which the kidneys maintain acid-base balance of the blood are by excreting bicarbonate ions and reabsorbing or generating new bicarbonate ions.  Maintaining Acid Base Balance of Blood Renal Mechanism Increase in blood pH, bicarbonate ions are excreted and hydrogens ions are retained by the tubule cells Decrease in blood pH, bicarbonate is reabsorbed and generated and hydrogen is secreted Urine pH varies from 4.5 to 8.0 which re ects the ability of the renal tubules to excrete basic or acidic ions to maintain blood pH homeostasis fl READ ON THE DEVELOPMENTAL ASPECTS OF THE URINARY SYSTEM  Diseases of the Urinary System Hydronephrosis - a condition where urine backs up into the kidney, causing it to stretch. It can be caused by a blockage in the ureter or chronic kidney disease. Oliguria - abnormally low urinary output; between 100 and 400ml/day; indicates glomerular blood pressure is too low to cause ltration Anuria - less than 100ml/day; result from transfusion reactions and acute in ammation or from crushing injuries to the kidneys fi fl  Diseases of the Urinary System Renal Calculi - crystals formed when urine becomes extremely concentrated, solutes such as uric acid salts that precipitate in the renal pelvis Nephrolithiasis, Ureterolithiasis, Cystolithiasis Symptoms: ank pain, frequent bacterial infections, urinary retention and alkaline urine Treatment: Lithotripsy fl  Diseases of the Urinary System Renal Calculi - crystals formed when urine becomes extremely concentrated, solutes such as uric acid salts that precipitate in the renal pelvis Nephrolithiasis, Ureterolithiasis, Cystolithiasis Symptoms: ank pain, frequent bacterial infections, urinary retention and alkaline urine Treatment: Lithotripsy fl  Diseases of the Urinary System Urinary Tract Infection Urethritis Cystitis Pyelonephritis or Pyelitis Symptoms: dysuria, urinary urgency, frequency, fever, cloudy or blood tinged urine. When kidneys are involved: back pain and severe headache  Diseases of the Urinary System Incontinence - occurs when a person is unable to voluntarily control the external sphincter Normal in children 2 years old or younger because they have not yet gained control over their voluntary sphincter Urinary retention - opposite of incontinence. The bladder is unable to expel its contained urine; cause: General anesthesia and older men who has prostate enlargement or hyperplasia  Diseases of the Urinary System Adult polycystic kidney disease - degenerative condition that appears to run in families. One or both kidneys enlarge, sometimes to the size of a football, and have many blister like sacs (cysts) containing urine. Hypospadias - a condition found in male babies only. Occurs when the urethral ori ce is located on the ventral surface of the penis Glomerulonephritis - in ammation of the glomerulus; a sequelae to untreated childhood strep infection. fi fl