Urinary System Lecture Notes Part 1

Urinary System Kidney Functions •Regulating total water volume and total solute concentration in water •Regulating ECF ion concentrations •Long-term acid-base balance •Removal of metabolic wastes, toxins, drugs •Endocrine functions –Renin – regulates blood pressure –Erythropoietin – regulates RBC production •Layers of surrounding supportive tissue –Renal fascia •Anchoring outer layer of dense fibrous connective tissue –Perirenal fat capsule •Fatty cushion –Fibrous capsule •Prevents spread of infection to kidney The __________ cushions the kidney and helps attach it to the posterior body wall. perirenal fat capsule The perirenal fat capsule is a transparent capsule that prevents infections in surrounding regions from spreading to the kidney. False fibrous capsule Renal column (between the renal medulla)- interlobar artery ( space in between each lobe) The __________ is the darker, reddish-brown area of the kidney that exhibits cone-shaped tissue masses called renal pyramids. Renal medulla Renal tubule functions Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting Duct Reabsorption and secretion Reabsorption only Mostly secretion –2 Cell types –Principle Cells •Maintain water and Na+ balance –Intercalated Cells •Maintain acid-base balance of blood Types of Nephrons + Associated Blood Vessels Cortical nephrons 85% of nephrons Large CT Mostly in cortex Short loop Efferent arteriole becomes Peritubular capillaries Juxtamedullary nephrons Long loop deep into medulla Efferent Arteriole becomes Vasa recta Important in production of concentrated urine Juxtaglomerular Complex (JGC) •Involves modified portions of Ascending Loop of Henle and the Afferent arteriole •Important in regulation of rate of filtrate formation and blood pressure •3 Cell Populations •Macula Densa cells –Chemoreceptors - sense NaCl content of filtrate •Granular cells –Mechanoreceptors - sense BP in Afferent Arteriole –Secrete Renin •Mesangial cells The blood supply to the nephron is the __________. Afferent arteriole Which of the following is the countercurrent multiplier in the kidney? the loop of Henle of a juxtamedullary nephron Kidney Physiology: Mechanisms of Urine Formation 3 major renal processes •Glomerular filtration –produces cell- and protein-free filtrate •Tubular reabsorption –Selectively returns 99% of substances from filtrate to blood in renal tubules and collecting ducts •Tubular secretion –Selectively moves substances from blood to filtrate in renal tubules and collecting ducts All of the following functions are carried out in the renal tubules, EXCEPT __________. Filtration Kidney Physiology: Glomerular Filtration •Filtrate (produced by glomerular filtration) –Blood plasma minus cells and proteins Kidneys filter body's entire plasma volume 60 times each day consume 20-25% oxygen used by body at rest •Urine –<1% of original filtrate –Contains metabolic wastes and unneeded substances •Passive process – no energy required •Hydrostatic pressure forces fluids and solutes through filtration membrane Filtration membrane Porous membrane between blood and the glomerular capsule space Three layers Fenestrated endothelium of glomerular capillaries Basement membrane Foot processes of podocytes with filtration slits All of the following are layers of the filtration membrane in the glomerular membrane, EXCEPT the ____ renal capsule fenestrated endothelium visceral layer basement membrane Which of the following is NOT part of the filtration membrane? extraglomerular mesangial cells Net filtration pressure (NFP) Glomerular filtration rate (GRF) •The pressure responsible for filtrate formation (10 mm Hg) •The volume of filtrate formed per minute by both kidneys (normal = 120–125 ml/min) •Hydrostatic pressure in glomerular capillaries (HPgc) = Glomerular blood pressure •Factors controlling GFR at filtration membrane •Osmotic pressure in glomerular capillaries (OPgc)= colloid osmotic pressure of blood –Total surface area available for filtration –Filtration membrane permeability •Hydrostatic pressure in capsular space (HPcs) = pressure of fluids in glomerular capsule –Net Filtration Pressure – Most Significant NFP = HPgc minus the pressures resisting it, i.e. OPgc and HPcs In other words: forward pressure – backward pressures •Changes in GFR usually results from changes in blood pressure within the glomerular capillaries •GFR is directly proportional to NFP •If BP drops GFR drops. If BP rises GFR rises •GFR needs to be kept constant and balanced NFP = (HPgc) – (OPgc+ HPcs) The most important factor affecting the glomerular filtration rate is __________. Net filtration rate Which of the following substances is the standard substance used to measure the GFR? Inulin The net filtration pressure (NFP) is the chief force pushing water and solutes out of the blood and across the filtration membrane. True Regulation of glomerular filtration •Why regulate GFR? –High GFR = filtrate moves too quickly,reabsorption cannot occur optimally and too much urine excreted →systemic BP drops –Low GFR = filtrate moves too slowly, too much is reabsorbed and very little urine is excreted •How is GFR regulated? –Autoregulation (Intrinsic) – locally by the kidney itself •Myogenic Mechanism and TubuloglomerularMechanism –Hormones (Extrinsic) – alter systemic BP –Neural control (Extrinsic) – alters systemic BP If the efferent arteriole constricts while the afferent arteriole remains unchanged, the glomerular filtration rate __________. increases Intrinsic controls Myogenic mechanism Tubuloglomerular feedback mechanism •Myogenic means it is a mechanism generated a muscle reflex •Macula densa cells respond to levels of NaCl in filtrate •Smooth muscle of afferent arteriole contracts when stretched •GFR ↑ , [NaCl] of the 昀椀ltrate will rise because it has passed thru the tubules too quickly to be reabsorbed • ↑BP → muscle stretch → constriction of afferent arterioles → reduces blood 昀氀ow into glomerulus •In response to ↑ [NaCl], the macula densa cells →↑ GFR prevented stimulate constriction of a昀昀erent arteriole, thus ↓ blood 昀氀ow into glomerulus and ↓ NFP & •Opposite happens with ↓ BP in the a昀昀erent GFR arteriole Opposite occurs for ↓GFR Extrinsic controls Hormones Ex: Systemic Blood Pressure drops (↓GFR) Granular cells experience less stretch and secrete the enzyme Renin into blood Renin catalyzes the production of the hormone Angiotensin Angiotensin causes systemic vasoconstriction and water retention → Systemic BP rises and GFR Sympathetic nervous system Ex: Systemic Blood Pressure drops (↓GFR) Systemic baroreceptors activate the Sympathetic Nervous System SNS activity results in an increase in systemic BP which increased blood flow to the glomerulus – GFR returns to normal goes back to normal Which process results in increased blood pressure in response to hormone release? renin-angiotensin-aldosterone mechanism All of the following would stimulate the release of renin from granular cells, EXCEPT __________. reduced stretching of the granular cells hemorrhaging or dehydration inhibition by the macula densa cells stimulation of the granular cells by the sympathetic nervous system •The primary goal of the intrinsic controls is to maintain a steady GFR in kidney •The primary goal of the extrinsic controls is to maintain steady systemic blood pressure In situations where there is an extreme change of blood pressure (e.g., mean arterial pressure of less than 80 mm Hg), extrinsic controls take precedence over intrinsic blood pressure controls. True Tubular reabsorption (2 routes) •A transepithelial process whereby most tubule contents are returned to the blood •Paracellular – between cells •Transcellular – through cells Tubular reabsorption- PCT •Majority of reabsorption occurs in the PCT •Blood vessel leaving glomerulus surrounds PCT (peritubular capillaries) Na+ – Active Transport •active transport at basolateral membrane •this draws Na from PCT lumen into tubule cells Water – Flows through Aquaporins •follows movement of Na (obligatory water reabsorption) •Less water in filtrate (increases concentrations of Other substances Down concentration gradient •Secondary active transport (co-transported with Na at luminal membrane) solutes) •Passive process but pulled by Na+ movement + How is Na reabsorbed? By active transport The energy needed for secondary active transport is provided by the __________. concentration gradient established by Na Tubular reabsorption Loop of henle DCT and Collecting Ducts •Only water leaves the descending limb •Reabsorption here is regulated by hormones •Only solutes (Na, Cl) leave the ascending limb •Hormones alter tubule permeability •Important when forming concentrated urine •Antidiuretic hormone (ADH) – Water Causes more aquaporins to be inserted into the luminal membranes of the collecting ducts •Water reabsorption •Aldosterone – Na+ (therefore water also) More luminal Na and K channels on luminal membrane •More Na-K ATPases on basolateral membrane •Na reabsorption •Water follows Na (if it can) •Atrial natriuretic peptide (ANP) – Na+ (water also) •Released by cardiac atrial cells •High blood volume / pressure •Inhibits Na reabsorption •Increases glomerular filtration rate •PTH – Ca2+ Urea transport into the medullary collecting duct is enhanced by __________. ADH Water can leave the ascending limb of the loop of Henle. False, descending What types of molecules are not reabsorbed? •Waste products (urea, uric acid, creatinine) •Substances in excess •Why are some things not reabsorbed? •Lack carriers or channels •Not lipid soluble •Too large to pass through tight junctions •Substance that “saturates” its transport mechanism (exceeds the transport maximum) Tubular secretion •Why is secretion necessary? •Not all “waste” products are filtered from the blood in glomerular filtration (Ammonium (NH4+), Creatinine) •Some “waste” products are reabsorbed •Controlling blood pH (secrete either H+ or HCO3-) •What needs to be secreted? •Waste products not filtered •Excess amounts of K+ Removing some drugs and metabolites Diuretics •Chemicals that enhance the urinary output 3 types: Osmotic diuretics •Any substance not reabsorbed Loop diuretics •Inhibit Na reabsorption Thiazides •Inhibit water reabsorption so that water stays in the urine –Caffeine •High glucose levels in urine –Lasix and Diuril –Alcohol: inhibits the release of ADH Act on DCT Alcohol and many drugs prescribed for hypertension are all examples of diuretics. True Clinical Evaluation of Kidney Function- Renal Clearance •The volume of plasma that is cleared of a particular substance in a given time •RC tests monitor insulin, determine GFR and detect glomerular damage RC = UV/P RC = renal clearance rate U = concentration (mg/ml) of the substance in urine V = flow rate of urine formation (ml/min) P = concentration of the same substance in plasma Physical Characteristics of Urine •Color and transparency –Clear, pale to deep yellow (due to urochrome) –Cloudy urine may indicate infection of the urinary tract •Urochrome = pigment from destruction of hemoglobin •Concentrated urine has a deeper yellow color Drugs, vitamin supplements, and diet can change the color of urine •Odor –Fresh urine is slightly aromatic –Standing urine develops an ammonia odor •Ammonia odor = bacteria metabolize urea •Uncontrolled diabetes mellitus = fruity smell (acetone) Some drugs and vegetables (asparagus) alter the usual odor •pH –Slightly acidic (pH 6) with a range of 4.5 to 8.0 •Diet can alter pH •Specific gravity –A measure of how concentrated the urine is