Urinary System PDF

The Urinary System An Introduction to the Urinary System Figure 26–1 3 Functions of the Urinary System 1. Excretion: – removal of organic wastes from body fluids 2. Elimination: – discharge of waste products 3. Homeostatic regulation: – of blood...

The Urinary System An Introduction to the Urinary System Figure 26–1 3 Functions of the Urinary System 1. Excretion: – removal of organic wastes from body fluids 2. Elimination: – discharge of waste products 3. Homeostatic regulation: – of blood plasma volume and solute concentration  Kidneys Organs that excrete urine Urinary Tract Organs that eliminate urine: – ureters (paired tubes) – urinary bladder (muscular sac) – urethra (exit tube) Urination or Micturition Process of eliminating urine Contraction of muscular urinary bladder forces urine through urethra, and out of body  5 Homeostatic Functions of Urinary System 1. Regulate blood volume and blood pressure: – by adjusting volume of water lost in urine – releasing erythropoietin and renin 2. Regulate plasma ion concentrations: – sodium, potassium, and chloride ions (by controlling quantities lost in urine) – calcium ion levels (through synthesis of calcitriol) 3. Help stabilize blood pH: – by controlling loss of hydrogen ions and bicarbonate ions in urine 4. Conserve valuable nutrients: – by preventing excretion of organic nutrients 5. Assist liver to detoxify the blood The Position of the Kidneys Are located on either side of vertebral column: – left kidney lies superior to right kidney – superior surface capped by adrenal gland Position is maintained by: – overlying peritoneum – contact with adjacent visceral organs – supporting connective tissues Figure 26–2  Is protected and stabilized by 3 concentric layers of connective tissue: 1. renal capsule 1. A layer of collagen fibers 2. Covers outer surface of entire organ 2. adipose capsule 1. A thick layer of adipose tissue 2. Surrounds renal capsule 3. renal fascia 1. A dense, fibrous outer layer 2. Anchors kidney to surrounding structures Connective Tissue layers of the Kidney Renal Capsule  Typical Adult Kidney Is about 10 cm long, 5.5 cm wide, and 3 cm thick Weighs about 150 g  Hilum Point of entry for renal artery and renal nerves Point of exit for renal vein and ureter  Renal Sinus Internal cavity within kidney Lined by fibrous renal capsule  Renal Capsule Bound to outer surfaces of structures in renal sinus Stabilizes positions of ureter, renal blood vessels, and nerves  Renal Cortex Superficial portion of kidney in contact with renal capsule Reddish brown and granular  Renal Pyramids 6 to 18 distinct conical or triangular structures in renal medulla: – base abuts cortex – tip (renal papilla) projects into renal sinus  Renal Columns Bands of cortical tissue separate adjacent renal pyramids Extend into medulla Have distinctly granular texture  Renal Lobe Consists of: – renal pyramid – overlying area of renal cortex – adjacent tissues of renal columns Produces urine  Renal Papilla Ducts discharge urine into minor calyx: – cup-shaped drain Renal Lobe showing Renal Papilla  Major Calyx Formed by 4 or 5 minor calyces  Renal Pelvis Large, funnel-shaped chamber Consists of 2 or 3 major calyces Fills most of renal sinus Connected to ureter, which drains kidney Blood Supply to the Kidneys Kidneys receive 20– 25% of total cardiac output 1200 ml of blood flows through kidneys each minute Kidney receives blood through renal artery Figure 26–5  Segmental arteries receive blood from renal artery Interlobar arteries deliver blood to arcuate arteries and empty into interlobular (cortical) arteries Afferent arterioles branch from each interlobular artery and deliver blood to capillaries supplying individual nephrons  Cortical and Juxtamedullary Nephrons Figure 26–7 Cortical Nephrons (1 of 2 types) 85% of all nephrons Located mostly within superficial cortex of kidney Loop of Henle is relatively short Efferent arteriole delivers blood to a network of peritubular capillaries: – which surround entire renal tubule Juxtamedullary Nephrons 15% of nephrons Have long loops of Henle that extend deep into medulla Efferent Arteriole delivers to Vasa Recta  Nephron Consists of renal tubule and renal corpuscle Microscopic, tubular structures in cortex of each renal lobe Where urine production begins Renal Tubule Long tubular passageway Begins at renal corpuscle Renal Corpuscle Spherical structure consisting of: – Bowman’s capsule – cup-shaped chamber – capillary network (glomerulus) Glomerulus Consists of 50 intertwining capillaries Blood delivered via afferent arteriole Blood leaves in efferent arteriole  The Bowman’s Capsule Is connected to initial segment of renal tubule Forms outer wall of renal corpuscle Encapsulates glomerular capillaries Podocytes Podocytes with Pedicels  The Filtration Membrane Fenestrated Endothelium – no RBCs pass Lamina Densa – large plasma proteins inhibited Filtration slits – no small plasma proteins  Filtration Occurs in renal corpuscle Blood pressure: – forces water and dissolved solutes out of glomerular capillaries into capsular space – produces protein- free solution (filtrate) similar to blood plasma  Glomerular Filtration Hydrostatic Pressure – Glomerular Hydrostatic Pressure – Capsular Hydrostatic Pressure Colloid Osmotic Pressure – Blood Colloid osmotic Pressure Glomerular Hydrostatic Pressure Pushes water and solutes out of plasma Higher than in other capillaries GHP – 50mmHg  Capsular Hydrostatic Pressure Opposes GHP by pushing filtrate into plasma CsHP – 15mmHg  Net Hydrostatic Pressure GHP – CHP = NHP 50mmHg – 15mmHg = 35mmHg Plasma from glomerulus flows into capsular space  Colloid Osmotic Pressure Osmotic pressure resulting from the presence of suspended proteins BLOOD COLLOID OSMOTIC PRESSURE – Opposes filtration – Plasma proteins attract water – 25 mmHg  Net Filtration Pressure (NFP) NFP = NHP – BCOP NFP = 35 mmHg – 25 mmHg NFP = 10 mmHg  Colloid Osmotic Pressure CAPSULAR COLLOID OSMOTIC PRESSURE – Only develops if plasma proteins enter the capsular space – Promotes filtration and increases fluid loss in urine  3 Functions of Renal Tubule 1. Reabsorb useful organic nutrients that enter filtrate 2. Reabsorb more than 90% of water in filtrate 3. Secrete waste products that failed to enter renal corpuscle through filtration at glomerulus  Reabsorption and Secretion REABSORPTION is the process by which the nephron tubule moves water and solutes from the filtrate to the blood in general circulation SECRETION is the process by which substances in the peritubular capillaries are moved into the tubular fluid Filtration, Reabsorption, Secretion, Excretion Renal Tubule Segments Located in cortex: – proximal convoluted tubule (PCT) – distal convoluted tubule (DCT) Separated by loop of Henle: – U-shaped tube – extends partially into medulla Nephrons Travelling along tubule, filtrate (tubular fluid) gradually changes composition Changes vary with activities in each segment of nephron Empties into the collecting system: – a series of tubes – carries tubular fluid away from nephron The Proximal Convoluted Tubule (PCT) Is the first segment of renal tubule Entrance to PCT lies opposite point of connection of afferent and efferent arterioles with glomerulus Reabsorption & Secretion at the PCT PCT reabsorbs 60 – 70 % of the filtrate 1. Reabsorption of organic nutrients More than 99% glucose, amino acids etc Facilitated and cotransport mechanism Reabsorption & Secretion at the PCT 2. Active Reabsorption of Ions Na+, K+, HCO-3,Mg, PO4, SO4 Causes tubular fluid to become dilute Reabsorption & Secretion at the PCT 3. Reabsorption of water water reabsorbed by osmosis Causing tubular fluid to become concentrated Reabsorption & Secretion at the PCT 4. Passive Reabsorption of Ions Urea and Chloride ions diffuse passively into peritubular fluid Filtrate becomes dilute causing more water to be reabsorbed Reabsorption & Secretion at the PCT 5. Secretion Hydrogen secreted in exchange for Sodium Helps to increase blood pH and acidifies filtrate Important in lactic acidosis and ketoacidosis The Loop of Henle Also called nephron loop Renal tubule turns toward renal medulla: – leads to loop of Henle Descending limb: – fluid flows toward renal pelvis Ascending limb: – fluid flows toward renal cortex Each limb contains: – thick segment – thin segment  The Thick Descending Limb – Has functions similar to PCT: pumps sodium & chloride ions out of tubular fluid Ascending Limbs – Of juxtamedullary nephrons in medulla: create high solute conc. in peritubular fluid The Thin Segments – Are freely permeable to water, not to solutes – Water movement helps conc. tubular fluid The Thick Ascending Limb – Ends at a sharp angle near the renal corpuscle - where DCT begins  The Countercurrent Multiplication System Occurs in the loop of Henle Reabsorbs 1/2 of the water in the filtrate and 2/3 of the Sodium Chloride Thin descending limb permeable to water Thick ascending limb allows active transport of sodium chloride only  The Countercurrent Multiplication System 1. Sodium chloride moves into interstitial fluid from filtrate of thick ascending limb 2. A concentration gradient develops between the thin descending limb and the peritubular fluid  The Countercurrent Multiplication System 3. Water moves from the thin descending limb into the peritubular fluid by osmosis As filtrate passes through the descending limb it loses more water because of the sodium chloride and urea in the interstitial fluid of the medulla  The Countercurrent Multiplication System 4. Fluid entering the thick ascending limb is highly concentrated. Sodium chloride is actively lost from thick ascending limb The Countercurrent Multiplication System (Urea also reabsorbed along collecting duct deep in medulla; not shown)  Benefits of the Countercurrent Multiplication System Efficient reabsorption of water and solutes before reaching the DCT and collecting duct system Establishment of a concentration gradient for the reabsorption of water in the presence of ADH from the collecting duct system The Distal Convoluted Tubule (DCT) The third segment of the renal tubule Initial portion passes between afferent and efferent arterioles Has a smaller diameter than PCT Epithelial cells lack microvilli  Reabsorption & Secretion in the Distal Convoluted Tubule 1. Active Reabsorption of sodium and chloride ions Sodium is reabsorbed in exchange for potassium using ion pumps controlled by Aldosterone 2. Calcium reabsorption in the presence of Parathyroid hormone and Calcitrol  Reabsorption & Secretion in the Distal Convoluted Tubule 3. Secretion of : potassium in exchange for sodium hydrogen in exchange for sodium reabsorption (pump also sensitive to Aldosterone, therefore, prolonged aldosterone secretion can result in alkalosis)  ADH – antidiuretic hormone Hormone causes special water channels to appear Increases rate of osmotic water movement Higher levels of ADH increases: – number of water channels – water permeability of DCT and collecting system No ADH, water is not reabsorbed – All fluid reaching DCT is lost in urine producing large amounts of dilute urine  Diuretics Are drugs that promote water loss in urine (diuresis) Diuretic therapy reduces: – blood volume – blood pressure – extracellular fluid volume  Buffering of Urine In the cells of the PCT and DCT the NH2 group from amino acids (deamination) bind to 2 hydrogen ions to produce NH4 NH4 passes into the tubular fluid The Collecting System The distal convoluted tubule: – opens into the collecting system Individual nephrons: – drain into a nearby collecting duct Several collecting ducts: – converge into a larger papillary duct – which empties into a minor calyx The Collecting System: Transports tubular fluid from nephron to renal pelvis Adjusts fluid composition Determines final osmotic concentration and volume of urine  Reabsorption and Secretion in the Collecting Duct System Sodium reabsorption controlled by aldosterone Bicarbonate reabsorption in exchange for chloride ions Urea reabsorbed at papillary duct making medulla concentrated Secretion of hydrogen ions or bicarbonate ions  The Concentration of components – in a urine sample depends on osmotic movement of water Normal Urine Is a clear, sterile solution Yellow colour (pigment urobilin) generated in kidneys from urobilinogens  Urine Transport, Storage, and Elimination Takes place in the urinary tract: – ureters – urinary bladder – urethra Organs for the Conduction and Storage of Urine Figure 26–18a Organs for the Conduction and Storage of Urine Figure 26–18b Organs for the Conduction and Storage of Urine Figure 26–18c  The Ureters Are a pair of muscular tubes Extend from kidneys to urinary bladder Begin at renal pelvis attached to posterior abdominal wall Penetrate posterior wall of the urinary bladder Pass through bladder wall at oblique angle Ureteral openings are slit-like rather than rounded Shape helps prevent backflow of urine: – when urinary bladder contracts  Peristaltic Contractions Begin at renal pelvis Sweep along ureter Force urine toward urinary bladder Every 30 seconds  The Urinary Bladder Is a hollow, muscular organ Functions as temporary reservoir urine storage Full bladder can contain 1 liter of urine Bladder Position Is stabilized by several peritoneal folds Posterior, inferior, and anterior surfaces: – lie outside peritoneal cavity Ligamentous bands: – anchor urinary bladder to pelvic and pubic bones  The Urethral Entrance Lies at apex of trigone: – at most inferior point in urinary bladder  The Neck of the Urinary Bladder Is the region surrounding urethral opening Contains a muscular internal urethral sphincter (sphincter vesicae- Smooth muscle fibers of sphincter provide involuntary control of urine discharge)  The Urethra Extends from neck of urinary bladder To the exterior of the body The Male Urethra Extends from neck of urinary bladder To tip of penis (18–20 cm)  3 Parts of the Male Urethra 1. Prostatic urethra: – passes through center of prostate gland 2. Membranous urethra: – short segment that penetrates the urogenital diaphragm 3. Spongy urethra (penile urethra): – extends from urogenital diaphragm – to external urethral orifice  The Female Urethra Is very short (3–5 cm) Extends from bladder to vestibule External urethral orifice is near anterior wall of vagina  The External Urethral Sphincter In both sexes: – is a circular band of skeletal muscle – where urethra passes through urogenital diaphragm Acts as a valve Is under voluntary control: – via perineal branch of pudendal nerve Has resting muscle tone Voluntary relaxation permits micturition