Urinary System Notes PDF

RNB 10702 ANATOMY AND PHYSIOLOGY 2 THE URINARY SYSTEM  LEARNING OUTCOMES At the end of this session, the students should be able to: Identify the organs associated with the kidneys; state the functions of the kidneys; outline the gross structure of the kidneys; described...

RNB 10702 ANATOMY AND PHYSIOLOGY 2 THE URINARY SYSTEM  LEARNING OUTCOMES At the end of this session, the students should be able to: Identify the organs associated with the kidneys; state the functions of the kidneys; outline the gross structure of the kidneys; described the structure of a nephron; explain the process involved in urine formation; explain the structure of ureter, urinary bladder and urethra in the urinary system; explain the process of micturition.  THE URINARY SYSTEM The urinary system is the main excretory system Plays a vital part in maintaining homeostasis of water & electrolyte within the body Kidney produce urine that contains carbon dioxide, ammonia, urea, uric acid, creatinine and inorganic salts The system consists of  2 kidneys  2 ureters  urinary bladder  urethra  Functions of the Urinary System Excretion of waste products from blood Regulation of blood volume and blood pressure Regulation of blood solute concentrations Regulation of extracellular fluid pH Regulation of red blood cell synthesis Regulation of Vitamin D synthesis  Kidneys Location Posterior abdominal wall Each side of the vertebral column Extend from 12th thoracic vertebra to 3rd lumbar vertebra Behind the peritoneum Below the diaphragm Right kidney slightly lower from left due to liver occupied the space Bean shape organs, about 11 cm long, 6 cm wide, 3cm thick & weigh 150 gm  Gross structure of the Kidney Renal hilum  Renal artery and nerves enter and renal vein and ureter exit kidneys  Opens into renal sinus (cavity filled with fat and loose connective tissue)  Gross structure of the Kidneys…cont Adipose capsule – protects kidney from trauma & acts as cushioning Renal fascia – thin layer of connective tissue that anchors kidney to surrounding structures and abdominal wall  Gross structure of the Kidneys (Clinical application) Nephroptosis - an inferior displacement of the kidneys It most often occurs in thin people This condition is dangerous because the ureters may kink and block urine flow  Microscopic Structure of the Kidney Internally, the kidneys consist of cortex, medulla, pyramids, papillae, columns, calyces, and renal pelvis Renal cortex & renal pyramids - constitute the functional portion or parenchyma of the kidney Nephron - the functional unit of the kidney  Microscopic Structure of the kidney…cont Renal cortex – outer light-red region Renal medulla – darker red-brown inner region Renal pyramids – cone-shaped in the renal medulla Renal columns – extension of renal cortex that fill the space between renal pyramids Renal papillae – base of renal pyramids that directed toward the center of kidney  Microscopic Structure of the kidney…cont Minor calyx – surround the renal papillae of each pyramid & collect urine from that pyramid Major calyx – form from several minor calyx Renal pelvis – cavity that collect the urine & continuous with the ureter From the major calyx the urine flows into the renal pelvis then the ureter  Nephron PATH OF URINE DRAINAGE: Collecting duct Renal hilum Minor calyx Renal cortex Major calyx Renal artery Renal medulla Renal pelvis Renal vein Renal column Renal pyramid in renal medulla Renal papilla Renal capsule Ureter Urinary bladder (a) Anterior view of dissection of right kidney  Blood and Nerve Supply of the Kidney Blood enters the kidney through the renal artery and exits via the renal vein The nerve supply to the kidney is derived from the renal plexus (sympathetic division of ANS- Autonomic Nervous System,)  NEPHRONS A functional unit of kidney When a nephron damage – they are not replaced Consists of 2 parts Renal corpuscle Renal tubule Functions Glomerular filtration Tubular reabsorption Tubular secretion  Functional Unit of the Kidney – the Nephron  Nephron…cont Renal corpuscle – filters blood plasma Located in the cortex of the kidney Glomerulus – network of tiny arterial capillary Glomerular (Bowman’s) capsule – surrounded the glomerulus  Nephron…cont Blood enter glomerulus capsule through afferent arteriole (for filtration) → the filtrate enters the glomerular capsule & continuous to renal tubule Blood leave renal corpuscle through efferent arteriole → peritubular capillaries → renal vein → inferior vena cava  Nephron…cont Renal tubule – filtered fluid Carried fluid away from the glomerular capsule Consists of; Proximal convoluted tubule (PCT) Descending and ascending loop of Henle (nephron loop) Distal convoluted tubule (DCT)  Nephron (clinical application) Glomerulonephritis (GN) Inflammatory condition of glomerulus Impaired glomerular filtration Symptom – oliguria, hypertension, hematuria & uraemia Nephrotic syndrome Increase permeability of glomerular membrane due to glomeruli damage Cause plasma protein pass through into the filtrate Symptom - edema  RENAL TUBULES Proximal convoluted tubule (PCT) Arise from glomerular capsule Filtrate pass first Great absorption occur here  Renal tubules…cont Loop of Henle A long U-shaped portion of the renal tubule Contains descending limb & ascending limb Heavily engage in active transport of salt Distal convoluted tubule (DCT) Short & less coil compare to PCT End of nephron Collecting Ducts Receive fluids from the DCT of several nephrons Fluid flow from the collecting ducts into the minor calyces  Juxtaglomerular Apparatus Specialized structure near glomerulus Juxtaglomerular cells – ring of smooth muscle in the afferent arteriole where the latter enters Bowman’s capsule - produce renin for blood pressure regulation Macula densa - specialized tubule cells of the distal tubule that – monitors sodium in urine  Overview of Renal Physiology (Urine formation) Glomerular filtration Tubular reabsorption Tubular secretion Renal corpuscle Renal tubule and collecting duct Afferent Glomerular arteriole capsule Fluid in Urine 1 Filtration from blood renal tubule (contains plasma into nephron excreted substances) 2 Tubular reabsorption 3 Tubular secretion Efferent from fluid into blood from blood into fluid arteriole Blood (contains reabsorbed Peritubular capillaries substances)  Filtration Movement of fluid, derived from blood flowing through the glomerulus, across filtration membrane Through semipermeable walls of glomerulus & glomerular capsule Filtrate – water, ions & small molecules Not filtrated - plasma proteins, blood cells & platelets 19% of plasma become filtrate 150-180 liters filtrate produced daily – more than 99% returned to blood plasma via tubular reabsorption 1.8 liter of filtrate become urine  Filtration…cont Filtration pressure: pressure gradient responsible for filtration; forces fluid from glomerular capillary across membrane into lumen of Bowman’s capsules Pressures that contribute to filtration pressure: Glomerular capillary pressure (GCP): blood pressure inside capillary tends to move fluid out of capillary into Bowman’s capsule Capsule hydrostatic pressure (CHP): pressure of filtrate already in the lumen Blood colloid osmotic pressure (BCOP): osmotic pressure caused by proteins in blood  Filtration…cont Glomerular filtration rate – amount of filtrate formed in all the renal corpuscles of both kidneys each minute 1 GLOMERULAR BLOOD 2 CAPSULAR HYDROSTATIC HYDROSTATIC PRESSURE PRESSURE (CHP) = 15 mmHg (GBHP) = 55 mmHg 3 BLOOD COLLOID OSMOTIC PRESSURE Afferent arteriole (BCOP) = 30 mmHg Proximal convoluted tubule Efferent arteriole NET FILTRATION PRESSURE (NFP) =GBHP – CHP – BCOP = 55 mmHg 15 mmHg 30 mmHg = 10 mmHg Glomerular (Bowman's) Capsular capsule space  Filtration…cont Renal autoregulation Protect renal blood flow & glomerular filtration Involves changes of constriction in afferent arterioles As systemic BP increases, afferent arterioles constrict and prevent increase in renal blood flow Juxtaglomerular apparatus - detect if there is increased rate of blood flow of filtrate past cells of macula densa – caused afferent arteriole constricts In severe dehydration or hemorrhage → sympathetic simulation constricts small arteries & afferent arterioles → decrease renal blood flow and filtrate formation  Renin also secreted from juxtaglomerular cells → stimulates vasoconstriction and maintains GFR Tubuloglomerular feedback  Reabsorption Return of most of the filtered water and many solutes to the bloodstream About 99% of filtrate is reabsorbed - sodium, potassium, calcium, bicarbonate, chloride Mostly in PCT– the walls are line with microvilli to increase surface area for absorption Using active and passive processes  Reabsorption…cont Passive process Not using any energy to transport molecules By diffusion or osmosis Glucose, urea, salt & H2O diffuse in Bowman’s capsule H2O diffuse back in PCT & loop of Henle by osmosis Salt passively diffused back from ascending loop of Henle into medulla Active process Using energy to transport molecules Use carrier proteins binding to molecules Reabsorption of glucose, amino acids, vitamins, mineral & some H2O back into blood within PCT & DCT  Reabsorption…cont Sodium reabsorption is the key of creating osmotic & electrical gradient that drive the reabsorption of water & other solutes About 180 liters of filtrate are formed in 24 hours & 1 to 2 liters of urine produced  Reabsorption…cont Place of reabsorption 65% in proximal convoluted tubule 15% in nephron loop 19% in distal convoluted tubule 1% will excreted as urine Most of solutes reabsorbed by active transport mechanism uses carrier molecules  Reabsorption…cont Water & other substance are reabsorbed by osmosis in all part of tubules except at ascending limb which is impermeable to water  Secretion Secretion – remove some substance from blood into renal tubules Helps control blood pH Helps eliminate substances from the body Takes place along the renal tubules & collecting ducts Occurs via both passive diffusion & active transport Summary of urine formation  Hormonal Actions Parathyroid hormone Secreted by parathyroid gland Action - together with calcitonin, regulates the reabsorption of Ca2+ & phosphate in DCT → maintain blood level Increase Ca2+ level & calcitonin lower it Aldosterone Secreted by adrenal cortex – due to renin act on angiotensin l → convert to angiotensin ll → act on renal cortex to produce aldosterone Action - Increase reabsorption of Na+ and H2O and secrete more K+ Regulated through negative feedback mechanism Aldosterone Actions Negative feedback regulation of Aldosterone  Hormonal Actions …cont Antidiuretic hormone (ADH) Secreted by anterior pituitary Action - increase water reabsorption in DCT and collecting duct → decrease urine volume → maintain normal blood volume & blood pressure Secretion – negative feedback Atrial natriuretic peptide (ANP) Secreted from cardiac muscle in the right atrium of the heart when blood pressure increase Action - decreases reabsorption of Na+ and water in PCT and collecting ducts Secretion – negative feedback Negative feedback regulation of secretion of ADH and ANP  Urine Concentration and Dilution The kidneys possess the unique property of changing the volume & osmolality of the urine by concentrating & diluting as per body needs Hypothalamus is sensitive to the blood composition & sends responses which affect the kidney If concentration of solutes in blood is high than normal – kidneys secrete small amount of concentrated urine to conserve water in the body & eliminates solutes to restore normal blood osmolality By diluting urine – kidney conserve solutes & remove excessive water  Urine Concentration and Dilution…cont Formation of diluted urine Low ADH makes late DCT and collecting duct have low water permeability → more water is reabsorbed from tubular fluid → diluted urine Formation of concentrated urine High level ADH caused large volume of water is reabsorbed from the tubular fluid into interstitial fluid → less water is reabsorbed from tubular fluid → concentrated urine  Urine Concentration and Dilution (Clinical application) Diuretics are drugs that increase urine flow rate They work by a variety of mechanisms The most potent ones are the loop diuretics, such as furosemide, which inhibits the symporters in the thick ascending limb of the loop of Henle Urine Transportation, Storage & Elimination  Ureters Transports urine from renal pelvis of kidney to the urinary bladder About 25 to 30 cm long, diameter 3mm Urine move by peristaltic waves, hydrostatic pressure & gravity No anatomical valve at the opening of the ureter into bladder – when bladder fills it compresses the opening and prevents backflow  Urinary Bladder Hollow, distensible muscular organ Located in the pelvic cavity, posterior to the symphysis pubis & below parietal peritoneum Capacity averages 700-800mL Micturition – discharge of urine from bladder  Combination of voluntary and involuntary muscle contractions  When volume increases stretch receptors send signals to micturition center in spinal cord triggering spinal reflex – micturition reflex  Urinary bladder…cont Wall of the bladder Mucosal membrane - the inner lining that continuous from ureter  When the bladder is empty - the inner lining is arranged in folds/rugae  The rugae is to allow the bladder to expand as it fills Submucosa – support the mucosal membrane Muscularis – composed smooth muscle fiber called detrusor muscle that able to expel urine when it contract  Urinary bladder…cont Trigone A triangular area that formed by 3 openings in the floor of urinary bladder 2 opening from ureter – small flap cover the opening to allow urine to enter the bladder & prevent backflow to ureters 1 opening into urethra – encircle by internal urethral sphinter Bladder is distensible; the desire to urinate appears when urine ≈300 to 400 mls Bladder capacity ≈600 mls  Urethra Tube that exits the bladder The opening to the outside is external urethral orifice Internal urethral sphincter – the beginning of the urethra that leave the bladder (smooth involuntary muscle) External urethral sphincter – skeletal (voluntary) muscle that encircle urethra where it pass through the pelvic floor The 2 sphincters control the flow of the urine through urethra  Urethra…cont Male urethra - about 20 cm long - transports both urine & semen Female urethra - about 3 - 4 cm long  Urethra (clinical application) Urinary tract infection (UTIs) occur more frequent in women The opening of the urethra (female) is closed to proximity to the anal opening – gives intestinal bacteria easy to assess the urethra The female urethra is short – allow any infection to spread to the urinary bladder Urethritis – infection of the urethra Cystitis – infection to urinary bladder  Micturition Reflex Accumulation of urine in the bladder → stretch receptor in the bladder wall activated → triggers sensory impulse & transmitted to the spinal cord → spinal reflex initiated → stimulates involuntary contraction of detrusor muscle & relaxation of internal urethral sphincter → urine enter the urethra → micturition occur  Micturition reflex…cont When bladder control is stablish, sensory impulse that transmitted to the spinal cord also pass upward to the brain for awareness to pass urine as bladder fills (300-400mls) By learn & conscious effort, contraction of external sphincter & muscle of the pelvic floor can inhibit micturition – in adult Over-distension bladder – involuntary relaxation may occur  Micturition (clinical application) Urinary incontinence It is inability to control urination & to retain urine in the bladder Temporary incontinence may result when the muscles around the bladder & urethra become weakened & lose muscle tone May due to stretching of the muscle during childbirth A cough & sneeze may increase pressure within the bladder that sufficient to force urine to escape Permanent incontinence may caused by damage of central nervous system or extensive damage to the bladder or urethra  Composition of Urine Urine is clear & amber in color due to presence of urobilinogen, a bile pigment altered in the intestine, reabsorbed then excreted by the kidneys 60