Anatomy The Urinary System

The urinary system Functions of the urinary system  Components: 2 kidneys, 2 ureters, bladder, and urethra  Kidneys have several functions o Filter blood plasma and excrete wastes o Regulate blood volume and blood pressure o Regulate osmolarity o Regulate electrolyte and acid-base balance o Secrete erythropoietin for red blood cell production o Help synthesize vitamin D for calcium homeostasis o Clear hormones and drugs; detoxify free radicals o Provide blood glucose during starvation  Excretion o Extracting waste from bodily fluids and eliminating them  Nitrogenous wastes  Organic nitrogen – containing molecules  Urea – most common o Azotemia – condition developed from dysfunction of kidneys; may lead to uremia Kidney protection  3 layers of connective tissues o Renal fascia, perirenal fat capsule, and fibrous capsule Gross anatomy of the kidney  Hilum – slit  Renal sinus – cavity with vessels and urine-collecting structures  Renal cortex – outer zone o Extensions of cortex toward sinus  Renal medulla – inner zone o Renal pyramids, each with a renal papilla  Urine-collecting structures o One minor calyx per pyramid o Two or more minor calyces form a major calyx o Major calyces merge to form renal pelvis within sinus The nephron  Renal corpuscle o Filters blood plasma  Renal tubule o Converts filtrate into urine Basic steps in the formation of urine  Glomerular filtration creates a plasma-like filtrate of the blood  Tubular reabsorption removes useful solutes from the tubular fluid, returns them to the blood Tubular secretion removed additional wastes from the blood, adds them to the tubular fluid  Water conservation removes water from the urine and returns it to blood; concentrates wastes The renal corpuscle  Renal corpuscle – glomerulus – glomerular (Bowman) capsule  Podocytes wrap around capillaries with foot processes o Filtration slits are between processes  After passing through filtration membrane, filtrate collects in capsular space  Filtration membrane o Capillary endothelium o Basement membrane o Filtration slits The renal tubule  Proximal convoluted tubule (PCT)  Nephron loop o Descending limb o Ascending limb o Types of nephrons  Cortical – short  Juxtamedullary – long  Distal convoluted tubule (DCT)  Collecting ducts o Intercalated cell – acid-base balance o Principal cells – reabsorb sodium and water  Papillary ducts o Merger of several collecting ducts  Juxtaglomerular apparatus o Macula densa o Granular (juxtaglomerular) cells o Mesangial cells The ureters  Ureter – tube that extends 25 cm from kidney to bladder  Three-layered wall o Mucosa has urothelium o Muscularis has multiple layers of smooth muscle  Inner muscle is longitudinal; next layer is circular; outermost layer of lower urethra is longitudinal muscle o Adventitia is connective tissue binding to surrounding organs The urinary bladder  Sac on the floor of pelvic cavity  Detrusor muscle – muscular layer of bladder wall  Rugae – wrinkles of mucosa  Trigone – triangular region on floor of bladder defined by two ureter inlets and one urethra outlet The urethra  Internal urethral sphincter – smooth m. at bottom of bladder  External urethral sphincter – skeletal m. at pelvic floor  External urethral orifice – opening  Female urethra is short tube anterior to vagina  Male urethra has three divisions o Prostatic urethra o Membranous urethra o Spongy (penile) urethra The aging urinary system  Kidneys atrophy with age – become less efÏcient o Reduced renal function means drugs are not cleared from the body as quickly (dosages must be adjusted)  Kidneys become less sensitive to antidiuretic hormone o Water balance becomes precarious  Bladder control becomes problematic o Urine retention o Urinary incontinence 