Urinary System PDF

Functions of the Kidneys Filter blood and excrete toxic metabolic wastes Regulate blood volume, pressure, and osmolarity Regulate electrolytes and acid-base balance Secrete erythropoietin, which stimulates the production of red blood cells Help regulate calcium levels by participating in...

Functions of the Kidneys Filter blood and excrete toxic metabolic wastes Regulate blood volume, pressure, and osmolarity Regulate electrolytes and acid-base balance Secrete erythropoietin, which stimulates the production of red blood cells Help regulate calcium levels by participating in calcitriol synthesis Clear hormones and drugs from blood Detoxify free radicals In starvation, they synthesize glucose from amino acids  Nitrogenous Waste Waste- any substance that is useless to the body or present in excess of the body’s needs Metabolic waste – waste substance produced by the body, proteins and nucleic acids contain nitrogen. When broken down mostly stored as carbs and fats but have access nitrogen, which forms ammonia. – Urea Catabolism of proteins forms ammonia (very toxic) Liver converts ammonia to urea – Uric Acid Catabolism of alcohol and seafood, shellfish, and other meats – Creatinine From normal wear and tear of muscle Excretion  Kidney Anatomy Retroperitoneal with ureters, bladder, & adrenal glands Right kidney is lower than left, why? Covered with 3 layers of connective tissue 1. Fibrous capsule = encloses kidney protects from infection and trauma 2. Perirenal fat = cushions & holds in place 3. Renal fascia = binds to abdominal wall  Gross Anatomy Outer Renal cortex Inner Renal medulla – Medullary (renal) pyramids separated by renal columns – Renal papilla = projects into sinus – Renal columns = separate pyramids Renal Sinus (internal cavity) – Cavity that contains vessels, nerves &urine collecting structures Lobe of kidney: – one renal pyramid, surrounding cortex, and adjacent columns Minor calyx – Cup that holds papilla of each pyramid; collects its urine Major Calyces – Convergence of 2 or 3 minor calyces Renal Pelvis – Formed by 2-3 major calyces Gross Anatomy of the Kidney  Blood and Nerve Supply Renal arteries deliver ~ 1/4 (1200 ml) of cardiac output to the kidneys each minute Renal Arterial flow into and venous vein flow out of the kidneys follow similar paths Renal artery Nerve supply is via sympathetic fibers from the renal plexus  Ureters Convey urine from kidneys to bladder via peristalsis Retroperitoneal Enter the base of the bladder through the posterior wall – No sphincters. pressure increases from distal ends prevents backflow Three layers of wall of ureter – Mucosa: transitional epi. & lamina propria – No submucosa – Muscularis externa: includes longitudinal & circular layers of smooth muscle – Adventitia: connective tissue  Urinary Bladder Muscular sac for temporary storage of urine (up to 1 liter) Retroperitoneal 3 layers of the bladder wall – Mucosa : Transitional epithelial & lamina propria – Muscularis externa: thick detrusor muscle (3 layers of smooth muscle) – Adventitia Sphincters – Internal (smooth) – External (skeletal) Rugae Trigone – Smooth triangular area outlined by openings of ureters & urethra – Infections tend to persist in this region  Urinary Bladder Urine storage reflex: – Stretch receptors in bladder wall send sensory impulses to sacral spinal cord when contains about 200 mL Urine Voiding (completely empty) reflex: – Parasympathetic motor neurons stimulate muscle wall of bladder (detrusor muscle) to contract and the internal urethral sphincter to relax Bladder Histology  Peritoneum Left ureter Right ureter Uterus Urinary bladder Urinary bladder Prostate External urethral sphincter Internal urethral sphincter Spongy urethra Urethra External urethral sphincter Urethra External urethral [see part c] orifice Vagina Male Female Ureter Detrusor Rugae Ureteric orifices Internal urethral sphincter Prostate External urethral Prostatic urethra sphincter Membranous urethra Urinary bladder in male  Urethra Muscular tube – Epithelium mostly pseudostratified columnar Transitional near bladder Stratified squamous near external urethral orifice Female urethra (Short) – Angled forward (continence supported) Becomes more vertical in older women (incontinence) Male urethra (longer) 1. Prostatic urethra – Can hypertrophy constricting urethra (retention) 2. Membranous urethra 3. Spongy urethra  Nephron Structural and functional units ~1.2 million per kidney Functions 1. Filtration 2. Reabsorption 3. Secretion Two main parts – Renal Corpuscle Filters the blood plasma – Glomerulus – Glomerular capsule – Renal tubule Converts filtrate into urine  Filtration Membrane Glomerular capsule has 2 layers: – Parietal (outer) layer: simple squamous epithelium – Visceral (inner) layer: Cells called podocytes Capsular space between two layers Filtration slits allow filtrate into capsular space but prevents larger cells Negatively charged basement membrane repels large anions such as plasma proteins  The Renal Tubule Renal tubule—duct that leads away from the glomerular capsule & ends at tip of medullary pyramid Divided into four regions – Proximal convoluted tubule (PCT) – Nephron loop – Distal convoluted tubule (DCT) – Collecting duct receives fluid from many nephrons  The Renal Tubule Proximal convoluted tubule (PCT)—arises from glomerular capsule – Longest & coiled region w/Simple cuboidal epithelium with microvilli for absorption Nephron loop (U-shaped portion) – Descending limb and ascending limb – Thick segments have simple cuboidal epithelium Initial part of descending limb and part or all of ascending limb – Thin segment has simple squamous epithelium Forms lower part of descending limb = permeable to water  The Renal Tubule Distal convoluted tubule (DCT)—begins after ascending limb – Shorter and less coiled than PCT w/Cuboidal epithelium w/o microvilli – Reabsorption of water and ions – Secretion of undesirable wastes Collecting duct—receives fluid from the DCTs of several nephrons as it passes back into the medulla – Papillary duct: formed by several collecting ducts  The Renal Tubule Glomerular capsule: parietal layer Renal cortex Basement Renal medulla membrane Renal corpuscle Podocyte Renal pelvis Glomerular capsule Fenestrated Glomerulus endothelium Distal of the glomerulus Ureter convoluted Glomerular capsule: visceral layer tubule Kidney Microvilli Mitochondria Proximal convoluted tubule Highly infolded plasma membrane Cortex Proximal convoluted tubule cells Medulla Thick segment Distal convoluted tubule cells Thin segment Loop of Henle Descending limb Ascending limb Collecting Loop of Henle (thin-segment) cells duct Principal cell Intercalated cell Collecting duct cells  Urine flow within the Renal Tubule Flow of fluid from the point where the glomerular filtrate is formed to the point where urine leaves the body: glomerular capsule → PCT→ nephron loop → DCT→ collecting duct → papillary duct → minor calyx → major calyx → renal pelvis → ureter → urinary bladder → urethra  Types of Nephron Cortical nephrons: – 85% of nephrons; almost entirely in the cortex – Short tubules – Delivers to peritubular capillaries (surround entire loop) Juxtamedullary nephrons – Long loops of Henle deeply invade the medulla – Connect to the vasa recta (long, straight capillaries) – Important in the production of concentrated urine Juxtamedullary and Cortical Nephrons  Check Point Can you… – List and describe the functions of the kidney? – Label and describe the anatomical structures of the kidney including the outer layers. – Describe the function, anatomical structure, walls (histology) of the ureter, bladder and urethra. – Explain what a nephron is? What are the functions? What are the 2 main parts? What are the 4 regions of the renal tubules and their histology? Describe the 2 types of nephron.  Nephron Loop = Countercurrent Multiplier Nephron loop – Descending loop (thin segment) very permeable to water (not NaCl) – Ascending loop permeable to NaCl (but not water) – Multiplier = multiplies osmolarity (saltiness) deep in medulla – Countercurrent = fluid flows in opposite direction in adjacent tubules Allows collecting duct to concentrate urine – By creating a “salty medulla”…….conserves water  Concentrated Urine (salty urine) Interstitial fluid near the papilla of the medullary pyramid is very salty (4X as salty of the blood) Juxtamedullary nephrons help establish salty medulla – Vasa recta (blood vessels) fluid flows in opposite direction to the urine filtrate Water will be reabsorbed from collecting duct to equilibrate with interstitial fluid in the medulla Creates a urine 4X as salty as the blood = water conservation  Urine Formation: Glomerular Filtration Kidneys convert blood plasma to urine in four stages 1. Glomerular filtration 2. Tubular reabsorption 3. Tubular secretion 4. Water conservation Glomerular filtrate—the fluid in the capsular space – Similar to blood plasma except that it has almost no protein Urine—fluid that enters the collecting duct – Undergoes little alteration beyond this point except for changes in water content  Proximal Convoluted Tubule Distal Convoluted Tubule Reabsorption of water, ions, Secretion of ions, acids, drugs, toxins and all organic nutrients Variable reabsorption of water, sodium ions, and calcium ions (under hormonal control) Renal Corpuscle Production of filtrate Glomerulus Glomerular capsule Collecting Duct Collecting duct Variable reabsorption of water and reabsorption Nephron Loop or secretion of sodium, Descending thin limb potassium, hydrogen, Further reabsorption and bicarbonate ions of water Thick ascending limb Reabsorption of sodium and chloride ions KEY Papillary Duct Filtration occurs exclusively in the renal corpuscle, across the filtration membrane. Delivery of urine to minor calyx Water reabsorption occurs primarily along the PCT and the descending thin limb of the nephron loop, but also to a variable degree in the DCT and collecting system. Urine storage and elimination Variable water reabsorption occurs in the DCT and collecting system. Solute reabsorption occurs along the PCT, the thick ascending limb of the nephron loop, the DCT, and the collecting system. Variable solute reabsorption or secretion occurs at the PCT, the DCT, and the collecting system.  1. Filtration Pressure Filtration pressure depends on hydrostatic and osmotic pressures on each side of the filtration membrane Blood hydrostatic pressure (BHP) – High in glomerular capillaries 60 mm Hg compared to 30 in most other capillaries Because afferent arteriole is larger than efferent arteriole: a large inlet and small outlet Hydrostatic pressure in capsular space – 18 mm Hg due to high filtration rate and continual accumulation of fluid in the capsule 1. Filtration Pressure Forces Involved in Glomerular Filtration  1. Filtration Large amounts of blood filtered every day – 50-60X amount of blood in body – only a small amount becomes urine Glomerular filtration rate (GFR) = 125ml/min or about 45 gallons a day! – we reabsorb a lot! – 99% of filtrate is reabsorbed Filtration depends on good blood flow and on normal filtration pressures 1. Glomerular Filtration Regulation 3 mechanisms to control ensure GFR is maintained: – Renal Autoregulation (locally) : Nephron adjust their own blood flow – Smooth muscle contract when stretched – Glomerulus gets feedback and adjusts filtration rate – Sympathetic Control: Sympathetic nervous system (vasoconstriction) – Innervate renal blood vessels – Constrict afferent arterioles (reduces urine output) – Parasympathetic does not regulate – Hormonal Control: Renin (RAAS) – Reabsorption of water and salt  Hormonal Regulation Renin secreted when blood flow to the nephron is reduced – Increases blood pressure which increases urine production Secreted by Juxtaglomerular Apparatus (JGA) – Granular cells on afferent arteriole When blood pressure is low – Macula densa on DCT When blood sodium levels are low  What does RENIN do? Stimulates the RAAS pathway – renin–angiotensin system (renin–angiotensin–aldosterone) Once secreted, renin travels to the liver and catalyzes the reaction: – Converts Angiotensinogen (in liver)à to Angiotensin I – Angiotensin I travels to the lung converted to Angiotensin II by the enzyme, ACE (angiotensin converting enzyme)  Then what? Angiotensin II causes 4 responses 1. Systemic vasoconstriction Increase in blood pressure which will increase urine filtration 2. Secretion of ADH Hypothalamus (posterior pituitary) Increases water reabsorption to increase blood pressure 3. Secretion of aldosterone Adrenal gland Increases Na+ reabsorption and increased blood pressure 4. Stimulate feeling of “thirst” hypothalamus  Check Point Can you… – What is the countercurrent multiplier and what is it’s purpose? – What are the 4 mechanisms of urine formation? – How does glomerular filtration occur? – How do filtrate move out of the glomerulus into the capsular space? – What are 3 ways that glomerular filtration rate is regulated? Or How do we insure sufficient blood flow into the kidneys? – What is renin? Where is it secreted? Why is it secreted? – What is the pathway of the RAAS system? – What are the 4 results of the RAAS system?  2. Tubular Reabsorption Tubular reabsorption returns nutrients to the blood Filtrate: glucose, amino acids, water and sodium Glucose and amino acids must be reabsorbed at 100% Reabsorption happens in: 1. Proximal Convoluted Tubule = 65% of filtrate 2. Nephron Loop = 25% of filtrate Na, K, & Cl 15% water 3. DCT = 7% initial filtrate 20% of water  2. Transport Maximum 100% of Glucose & Amino Acids are Reabsorbed due to facilitated diffusion by microvilli in PCT, water will follow – Limited number of carriers – When glucose levels exceed the number of carriers (as in diabetics) glucose will “spill” into the urine Transport maximum = – The maximum rate of reabsorption – Reached when transporters are saturated  2. Tubular Reabsorption of Na+ Water follows sodium Symports: both reabsorbed – Glucose & Na+ – Amino acid & Na+ – lactate – Na/K/Cl into the blood Antiports: – Na+ into blood H+ out of blood (secretion) – Na+ into blood K+ out of blood (secretion)  2. Tubular Reabsorption Nitrogenous wastes – Urea: nephron reabsorbs about half Concentration remaining in blood is safe Helps to create concentrated urine by – Uric Acid: PCT reabsorbs, but later portions of the nephron secrete – Creatinine: not reabsorbed – it is passed in urine  3. SECRETION Most secretion happens in the DCT – Potassium secretion Trade Na+ ions – Hydrogen secretion Also trade Na+ ions Carbonic acid + carbonic anhydrase = bicarbonate – Other ions, compounds, and drugs  4. Water Conservation Collecting duct conserves water Medullary portion is more permeable to water – Making urine 4x more concentrated As urine passes through salty medulla, water leaves concentrating urine Basic Stages of Urine Formation Hormones effecting reabsorption & secretion Aldosterone (Adrenal cortex) – Water and sodium reabsorption, K+ secretion – Increase BP to normal – Urine volume reduced (with elevated K+) Parathyroid hormone (Parathyroid gland) – Increase calcium reabsorption when blood levels low ANP (rt atrium) – Sodium secretion, water follows – Decreases BP – Salty & dilute urine ADH (Hypothalamus) – Water reabsorption in ascending limb, DCT and CT – Increases BP  How does ADH work? ADH causes vesicles with aquaporins to merge with the epithelial cell membrane of the DCT ADH present – aquaporins insert into membrane (water reabsorption) ADH not present – aquaporins are taken back into the vesicles (water secreted – dilute urine – Diabetes insipidus: patients unable to produce ADH lose water & dehydrate rapidly – Alcohol and caffeine inhibit ADH secretion Summary of Reabsorption and Secretion  Check Point Can you – Describe where reabsorption occurs along the nephron? – Define transport maximum? – Explain how sodium is reabsorbed along the nephron? – Describe where secretion occurs along the nephron? – Explain the affects of the following hormones on the nephron? ADH, Parathyroid hormone, ANP, aldosterone  Urine flow Urine fine-tuned in DCT and the collecting duct Urine flow: – minor calyx – major calyx – renal pelvis – ureter (peristalsis) – bladder (via “functional valve”) prohibiting reflux Internal urethral sphincter constricted to hold urine in the bladder  Characteristics of Urine Urinalysis: examination of physical & chemical properties Color: normally pale yellow, but depends on concentration or dyes in the urine – Dark yellow = concentrated – Urochrome = yellow color from break down of hemoglobin – Hematuria : high levels of red blood cells in urine – Pyuria: “pus” in urine due to infection and increase in WBCs pH: 4.5-8.0 (usually 6.0) depending on diet  Characteristics of Urine Specific gravity: measure of “stuff” in the urine (density of urine relative to density of water) Osmolartity of urine: may be dilute or concentrated urine depending on how dehydrated a person is Chemical Composition: 95% water, 5% solutes – Normal: urea, uric acid, creatinine, NaCl, K, Ca, Mg, phosphates, urochrome, bilirubin – Abnormal: glucose, albumin, ketones (in diabetics = metabolic acidosis) bile pigments v Proper concentration otherwise crystals & stones can form.  Urine Volume Normal for average adult - 1-2 L/day – Polyuria – output in excess of 2 L/day Causes: diabetes mellitus (high glucose levels) or insipidus (ADH) – Oliguria – output of less than 500 mL/day – Anuria – 0-100 mL/day Causes: kidney disease, dehydration, circulatory shock, prostate enlargement Less than 400 mL/day is not safe Characteristics of Urine  Renal Function Tests Test for diagnosing kidney disease – Evaluate severity, monitor progress, – Determine Renal Clearance Volume of blood plasma form which a particular waste is completely removed in one minute – Determine Glomerular filtration rate Assess kidney disease Substance that is not secreted nor absorbed  Check Point Can you… – Explain urine flow? – Describe the normal characteristics of urine? – Describe abnormal components of urine? – Properly apply the terms that describe urine amounts.