BSC2086 A&P II Final Exam Study Guide – Lesson 19 1 Lesson 19: The Urinary System Part I Urinary System Functions • Three (3) Functions of the Urinary System: o Excretion: Removal of organic wastes from body fluids o Elimination: Discharge of waste products o Homeostatic regulation of blood plasma volume & solute concentration • Kidneys: Organs that produce urine • Urinary Tract: Organs that eliminate urine o Ureters – paired tubes o Urinary Bladder – muscular sac o Urethra – exit tube • Urination (Micturition): Process of eliminating urine o Contraction of muscular urinary bladder forces urine through urethra & out of body • Homeostatic Functions of the Urinary System: o Regulates blood volume & blood pressure By adjusting volume of water lost in urine Releasing erythropoietin & rennin o Regulates plasma ion concentrations Sodium, potassium, & chloride ions • Controls quantities of these ions lost in urine Calcium ion levels • Through synthesis of calcitriol o Parathyroid hormone (PTH) stimulates calcitriol release from kidneys Increases Ca2+ absorption o Helps stabilize blood pH By controlling loss of hydrogen ions & bicarbonate ions in urine o Conserves valuable nutrientsBSC2086 A&P II Final Exam Study Guide – Lesson 19 2 By preventing their excretion while excreting organic waste products o Assists liver in… Detoxifying poisons During starvation • Deaminates amino acids so other tissues can metabolize them for energy The Kidneys • Kidneys – located on either side of vertebral column o Left kidney = superior to right kidney o Superior surface capped by adrenal gland o Position is maintained by: Overlying peritoneum Contact with adjacent visceral organs Supporting connective tissues • Floating Kidney: Suspensory fibers damaged & kidney displaced o Can cause pain, distortion, of ureter/blood vessels during movement • Kidneys protected & stabilized by three (3) concentric layers of connective tissue o Fibrous Capsule (innermost layer) Layer of collagen fibers Covers outer surface of entire organ o Perinephric Fat Capsule (middle layer) Thick layer of adipose tissue Surrounds renal capsule o Renal Fascia (outermost layer) Dense, fibrous outer layer Anchors kidney to surrounding structures • Typical adult kidney: o 10 cm (4 in) long o 5.5 cm (2.2 in) wide o 3 cm (1.2 in) thick o Weighs ~150 g (5.25 oz) • Hilum o Point of entry for renal artery & renal nerves o Point of exit for renal vein & ureter • Renal Cortex: Superficial portion of kidney in contact with renal capsule o Reddish brown & granular • Renal Pyramids: 6-18 conical or triangular structures in renal medulla o Base adjacent to cortex o Renal papilla (tip) projects into renal sinus • Renal Columns: Bands of cortical tissue separate adjacent renal pyramids o Have distinct granular texture o Extend into medulla • Renal Lobe o Consists of: Renal pyramidBSC2086 A&P II Final Exam Study Guide – Lesson 19 3 Overlying area of renal cortex Adjacent tissues of renal columns o Produces urine • Renal Papilla o Ducts discharge urine into minor calyx – cup-shaped drain • Major Calyx: Formed by 4-5 minor calyces • Renal Pelvis: Large, funnel-shaped chamber o Consists of 2-3 major calyces o Fills most of renal sinus o Connected to ureter (which drains kidney) Blood Supply to the Kidneys • Kidneys receive 20-25% of total cardiac output • 1,200 mL blood flows through kidneys each minute • Kidney receives blood through renal artery • Blood Flow: o Renal artery o Segmental arteries o Interlobar arteries o Arcuate arteries o Cortical radiate (interlobular) arteries o Afferent arterioles o Glomerulus efferent arteriole o Peritubular capillaries o Venules o Cortical radiate (interlobular) veins o Arcuate veins o Interlobar veins o Renal veinBSC2086 A&P II Final Exam Study Guide – Lesson 19 4 • Renal Nerves: Innervate kidneys & ureters o Enter each kidney at hilum o Follow tributaries of renal arteries to individual nephrons o Sympathetic Innervation: Adjusts rate of urine formation by changing blood flow & blood pressure at nephrons Stimulates release of renin • Restricts losses of water and salt in urine by stimulating reabsorption at nephron • Renin-angiotensin system stimulates aldosterone release from adrenal cortex • Nephron – functional unit of the kidney o Microscopic, tubular structures in cortex of each renal lobe Each kidney has ~1.25 million nephrons o Where urine production begins o Consists of renal tubule & renal corpuscle Renal Corpuscle: Spherical structure consisting of:BSC2086 A&P II Final Exam Study Guide – Lesson 19 5 • Glomerular Capsule (Bowman’s Capsule): Cup-shaped chamber • Capillary network (glomerulus) o Glomerulus: Consists of 50 intertwining capillaries Blood delivered via afferent arteriole Blood leaves in efferent arteriole • Flows into peritubular capillaries • Drain into small venules • Return blood to venous system Blood leaves the capillary network through the efferent arteriole and NOT through a venule! • Filtration occurs in renal corpuscle o Blood pressure – forces water & dissolved solutes out of glomerular capillaries into capsular space o Produces filtrate – protein-free solution Similar to blood plasma, but lacks proteins Renal Tubule: Long tubular passageway that begins at the renal corpuscle • Three (3) Functions of the Renal Tubule: o Reabsorb useful organic nutrients that enter filtrate o Reabsorb more than 90% of water in filtrate o Secrete waste products that failed to enter renal corpuscle through filtration at glomerulus • Segments of Renal Tubule: o Located in cortex Proximal Convoluted Tubule (PCT) Nephron Loop (Loop of Henle) • U-shaped tube • Extends partially into medulla • In juxtamedullary nephrons – nephron loop extends deeper into medulla o Important to their function Distal Convoluted Tubule (DCT)BSC2086 A&P II Final Exam Study Guide – Lesson 19 6 o Organization of the Nephron: Filtrate (tubular fluid) gradually changes composition as it travels along the tubule • Due to reabsorption & secretion of substances Changes vary with
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