Urinary System 03 17 2011 Functions of the Urinary System Regulate aspects of homeostasis o Water balance with Antidiuretic Hormone ADH o Acid base balance in the blood by regulating plasma pH o Regulate plasma ionic composition electrolytes with aldosterone o Regulate blood pressure and blood volume by regulating plasma volume and plasma osmolarity o Red blood cell production secrete erythropoietins stimulates RBC production when low oxygen levels are detected and renin aka angiotensinogenase released in low blood pressure Activates vitamin D3 calcitrol Elimination of waste products o Nitrogenous wastes o Toxins o Drugs Organs of the Urinary System Kidneys Ureters Urinary bladder Urethra Structures of the Urinary System Kidneys form urine Ureters transplant urine from kidneys to bladder Bladder stores urine Urethra excretes urine from bladder to outside of body Ureters Slender tubes attaching the kidney to the bladder o Continuous with the renal pelvis o Enter the posterior aspect of the bladder Runs behind the peritoneum Peristalsis is aided by gravity in urine transport Urinary Bladder Smooth collapsible muscular sac Temporarily stores urine a moderately full bladder is about 5 inches long and holds about 500 mL of urine Trigone is a triangular region of the bladder base o Three openings Two from the ureters One to the urethra o In males the prostate gland surrounds the neck of the bladder Position and Shape of a Distended and an Empty Urinary Bladder in an Adult Male Can hold up to 500 ml of urine Urinary Bladder Wall Three layers of smooth muscle collectively called the detrusor muscle Mucosa made of transitional epithelium Walls are thick and folded in an empty bladder Bladder can expand significantly without increasing internal pressure Urethra Thin walled tube that carries urine from the bladder to the outside of the body by peristalsis Release of urine is controlled by two sphincters o Internal urethral sphincter involuntary and made of smooth muscle o External urethral sphincter voluntary and made of skeletal muscle Urethra Gender Differences Length o Females is 3 4 cm 1 5 inch o Males is 20 cm 8 inches Location Function o Females next to the wall of the vagina o Males through the prostate and penis o Females only carries urine o Males carries urine and is a passageway for sperm cells Location of the Kidneys Against the dorsal body wall At the level of the T12 to L3 vertebrae The right kidney is slightly lower than the left due to position of the liver Regions of the Kidney Renal cortex is the outer region Renal medulla inside the cortex Renal pelvis is the inner collecting tube Kidney Features Renal hilum is a medial indentation where several structures enter or exit the kidney ureters renal blood vessels and nerves An adrenal gland sits atop each kidney Covering of the Kidneys Renal Fibrous capsule surrounds each kidney Renal fascia is the outermost capsule that helps hold the kidney in place against the muscles of the trunk wall This renal fascia also divides the fat that surrounds the kidney into two layers 1 inside the renal fascia is perirenal fat between the capsule of the kidney fascia Perirenal fat capsule surrounds the kidney and cushions against blows and helps attach it to the body wall 2 outside the renal fascia is the pararenal fat Macroscopic Anatomy of the Kidney Kidney Structures Renal or medullary pyramids triangular regions of tissue in the Renal columns extensions of cortex like material inward that medulla separate the pyramids Calyces cup shaped structures that funnel urine towards the renal pelvis Blood Supply One quarter of the total blood supply of the body passes through the kidneys each minute Renal artery provides each kidney with arterial blood supply Renal artery divides into segmental arteries interlobar arteries arcuate arteries cortical radiate arteries Venous blood flow cortical radiate veins arcuate veins interlobar veins renal vein Nephron Anatomy and Physiology The structural and functional units of the kidneys are nephrons Responsible for forming urine Renal tubule extends from glomerular capsule and ends at the collecting duct o Glomerular Bowman s capsule o Proximal convoluted tubule PCT o Loop of Henle o Distal convoluted tubule DCT Nephron Anatomy Glomerulus o Knot of capillaries o Capillaries are covered with podocytes from the renal tubule o Glomerulus sits within a glomerular Bowman s capsule the first part of the renal tubule o Urine is not called urine until it is processed it is called filrate before that Nephron Anatomy Nephrons are associated with two capillary beds o Glomerulus o Peritubular capillary beds Peritubular Capillary Beds Arise from efferent arteriole of the glomerulus Normal low pressure capillaries Adapted for absorption instead of filtration Cling close to the renal tubule to reabsorb reclaim some substances from collecting tubes Renal Corpuscle Renal Corpuscle o Bowman s capsule inflow end of renal tubules o Glomerulus tuft of capillaries Site of filtration movement from capillaries to tubules Glomerulus Fed and drained by arterioles o Afferent arteriole arises from a cortical radiate artery and o Efferent arteriole receives blood that has passed through the feeds the glomerulus glomerulus Specialized for filtration High pressure forces fluid and small solutes out of blood and into the glomerular capsule Types of Nephrons Cortical nephrons o Located entirely in the cortex o Includes most nephrons Juxtamedullary nephrons found at the boundary of the cortex and medulla Collecting Duct Receives urine from many nephrons Run through the medullary pyramids Delivers urine into the calyces and renal pelvis More nephrons than collecting ducts because nephrons share collecting ducts Urine Formation Sites of Filtration Reabsorption and Secretion in a Kidney Basic Renal Processes Glomerular filtration is from glomerulus to Bowman s capsule Reabsorption is from tubules to peritubular capillaries Secretion is from peritubular capillaries to tubules Excretion is from tubules out of body Glomerular Filtration Mostly nonselective passive process size of solute Water and solutes smaller than proteins are forced through capillary Proteins and blood cells are normally too large to pass through the walls filtration membrane Filtrate is collected in the glomerular capsule and leaves via the renal tubule GFR 125 mL min or 180 liters day Reabsorption blood Movement from tubules into peritubular capillaries returned to o Most
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