Anatomy Urinary -The organs of the urinary system

The Urinary System Chapter 26 The organs of the urinary system include: Functions of the urinary system (all done by kidneys):  Regulate the volume, concentration, pH and content of blood  Eliminate metabolic wastes as urine 3 processes occur within the kidneys to accomplish these goals Filtration (F) – Pressure (blood pressure) forces some fluid (plasma) and small substances from blood to renal (kidney) tubules. Results in the formation of “filtrate” in the renal tubules; approx. 180 liters filtrate/day Reabsorption (R) – Movement (by passive & active means) of most fluid & many solutes from renal tubules back into the blood; approx. 99% filtate reabsorbed Secretion (S) – Selective movement of specific substances (e.g. H +, K+) from blood to tubules blood Blood vessels (capillaries) Filtered blood F filtrate R Renal tubules S urine Gross Anatomy of the Kidneys  Retroperitoneal organs  Left kidney more superior than right (due to liver)  Notch at medial border (hilus) for renal artery & vein, ureter Each kidney surrounded by 3 layers of CT:  renal capsule – innermost layer of dense CT  adipose capsule – middle layer protecting & insulating kidneys  renal fascia – outer layer holding kidneys in place in abdominal cavity Internal Anatomy of the Kidneys  Cortex  Medulla where urine formation occurs  pyramids  renal papillae  renal columns  Pelvis - collecting basin  minor calyces  major calyces  renal pelvis Microscopic Anatomy of the Kidneys Functional unit of the kidneys is the “Nephron” Nephron = renal corpuscle + renal tubules Most (85%) nephrons classified as “cortical nephrons” – corpuscle located within cortex Some (15%) classified as “juxtamedullary nephrons” – corpuscle at junction of cortex & medulla Renal corpuscle – 1st part of the nephron; site of filtration; comprised of  glomerulus – capillary network  Bowman’s capsule – double layered capsule of epithelial tissue (inner visceral layer/outer parietal layer), surrounding glomerulus Bowman’s capsule (parietal (capsular) layer) capsular space Visceral layer of Bowman’s capsule (podocytes) Filtration occurs across “endothelial capsular (filtration) membrane” – junction between glomerular endothelium & podocytes; results in formation of “filtrate” in capsular space glomerulus Representative Nephron proximal convoluted tubule distal convoluted tubule reabsorption Filtrate from renal corpuscle will move into PCT  loop of Henle DCT; and then into a collecting system of tubes (connecting tubule  collecting duct  papillary duct  minor calyx) NEPHRON Secretion, some reabsorption renal corpuscle filtration COLLECTING SYSTEM collecting duct variable secretion &/or reabsorption Loop of Henle H2O Connecting tubule solutes more reabsorption papillary duct delivery of urine to minor calyx filtrate Blood supply to kidneys Efferent arteriole glomerulus Afferent arteriole Efferent arterioles branch into a second capillary network, the peritubular capillaries, which surround the renal tubules. The peritubular capillaries which surround the tubules of juxtamedullary nephrons are longer & straighter, therefore known as vasa recta Reabsorption & secretion occur between the renal tubules & peritubular capillaries Peritubular capillaries  venules  interlobular veins  arcuate veins  interlobar veins  (segmental veins) renal vein Juxtaglomerular Apparatus (JGA) Extremely important to regulate the rate of filtration that occurs at the glomerulus (glomerular filtration rate “GFR”) To regulate glomerular BP, we have a feedback system – the juxtaglomerular apparatus (JGA) Macula densa JGA = Juxtaglomerular cells  juxtaglomerular cells of the afferent arteriole – recognize if renal BP is too low & then can respond  macula densa cells of the distal convoluted tubule – recognize if decreased filtrate produced or too many solutes within filtrate & then can respond Histology of the kidneys Once urine is formed, it will move from the pelvis of the kidneys into the ureters  retroperitoneal, muscular tubes running from kidneys to urinary bladder  lined with transitional epithelium  transports urine primarily by peristalsis  Hollow muscular organ that temporarily stores urine prior to “micturition”  Lined with mucosa of transitional epithelium with rugae  Muscularis of 3 layers of smooth muscle known as “detrussor muscle” Urinary bladder  Internally have “trigone” – triangular area formed by openings of ureters & urethra  Micturition reflex – stretch receptors in wall of bladder stimulate smooth muscle of detrussor muscle (involuntary); stimulation of internal urethral sphincter (involuntary) & external urethral sphincter of skeletal muscle (voluntary) Histology of bladder & ureters muscularis Transitional epithelium Ureter Urinary bladder Urethra  Transports urine out of body  Inner urethral sphincter of smooth muscle; external urethral sphincter of skeletal muscle  Anatomically different in men & women