Renal (Urinary) System Chapter 17

Function Maintains homeostasis in ECF Removing metabolic waste (except CO2) e.g. ammonia, urea, uric acid Removing foreign compounds e.g. drugs, food additives, pesticides Regulating salt concentrations, fluid volume, and pH

Anatomy Fig 17.1 Kidneys (2) Ureters (2) Urinary bladder Urethra process plasma into urine Ureters (2) tubes that carry urine to bladder Urinary bladder storage of urine Urethra carries urine to exterior Fig 17.1

Anatomy Fig 17.2 Cortex Medulla Renal Pelvis Renal artery and vein outer granular region Medulla inner striated region renal pyramids Renal Pelvis central collecting cavity Renal artery and vein Fig 17.2

Anatomy Fig 17.2 Nephron 1 million per kidney functional unit of the kidney smallest unit capable of forming urine Fig 17.2

Nephron Fig 17.5 Vascular Component Renal Artery Afferent Arteriole conducts blood Renal Artery Afferent Arteriole Glomerulus Efferent Arteriole Peritubular Capillaries Venules Renal Vein Fig 17.5

Nephron Fig 17.5 Tubular Component Bowman’s capsule forms urine Bowman’s capsule Proximal Convoluted Tubule Loop of Henle Distal Convoluted Tubule Collecting duct Fig 17.5

Urine Formation Urine - water and waste solutes Nephrons conduct three processes to convert blood plasma into urine filtration filter blood plasma to retain cells/proteins reabsorption remove valuable materials from filtrate secretion transfer additional wastes to filtrate

Filtration Figs 17.8-17.10 Occurs in the glomerulus Fenestrated capillaries 3 layers of podocytes form capillary walls Small pores (fenestrae) filters plasma proteins + cells stay in blood forms ultrafiltrate Figs 17.8-17.10

Filtration Fig 17.10 Filtration driven by blood pressure Glomerular filtration is non-selective Small particles pass (glucose, Na+, urea, H2O) Large ones do not 20% of plasma enters tubule plasma filtered 65x/day Fig 17.10

Reabsorption Fig 17.12 Occurs in remainder of nephron tubule Selective movement of substances from tubule into plasma Return of valuable substances to peritubular caps Active or passive Passive (no energy) Active transport (requires energy) Fig 17.12

Secretion Fig 17.21 Also occurs in tubules Additional materials transported from plasma in peritubular capillaries into tubule excess K+, Ca2+ and H+, uric acid foreign compounds By passive diffusion or active carrier transport Fig 17.21

Proximal Tubule Figs 17.2, 17.5 Proximal Tubule Reabsorbs: 2/3 of plasma Na+ 2/3 of plasma Cl- 2/3 of plasma H2O 100 % of plasma glucose Figs 17.2, 17.5

Active Transport in the Proximal Tubule Na+ actively transported from cell to blood Creates Na+ gradient favoring Na+ flow from lumen Na+ gradient used to transport glucose against concentration gradient (cotransport) Glucose diffuses into blood passively Fig 17.13

Passive Reabsorption in the Proximal Tubule Cl- to be reabsorbed passively along electrical gradient Water reabsorbed along osmotic gradient Fig 17.14

Acid Base Balance Proximal tubule also secretes H+ and absorbs HCO3- used to regulate pH with  pH,  H+ secretion and HCO3- reabsorption Fig 17.28

Loop of Henle Fig 17.16 Kidneys produce a hyperosmotic urine less H2O than blood plasma concentrating mechanism occurs in the Loop of Henle Fig 17.16

Loop of Henle Countercurrent Multiplication generates osmotic gradient that draws H2O out of the tubules to be reabsorbed due to active reabsorption of Na+ & Cl- Exchange = 30 Exchange = 50

Loop of Henle Fig 17.16 descending limb ascending limb permeable to water no active transport ascending limb impermeable to water lined w/ Na+-K+ pumps Fig 17.16

Loop of Henle Pumping of ions out of ascending limb creates osmotic gradient Water flows out of descending limb Absorbed by peritubular capillaries Fluid becomes more concentrated as it passes down descending limb Figs 17.16, 17.17

Loop of Henle Removal of ions without water causes fluid to become less concentrated in the ascending limb Less concentrated than blood in distal convoluted tubule 25% of initial Na+ and water reabsorbed by loop of Henle Fig 17.16

Distal Convoluted Tubule and Collecting Duct Secretion of K+ and H+ Reabsorption of Na+ and water Generation of hyperosmotic urine final ~8% of water and Na+ reabsorbed Figs 17.19, 17.27

Hormonal Regulation of Reabsorption Aldosterone increases Na+ reabsorption and K+ secretion by distal & collecting tubules  salt retention and BP (H2O retention) ADH induces implantation of aquaporins (water channels) into tubule cell membranes  permeability of Distal and Collecting tubules to water  H2O reabsorption =  urine volume

Triggering of Aldosterone Release release induced by juxtaglomerular apparatus region of afferent arteriole that comes into contact w/ascending limb of Loop of Henle releases renin (enzyme) into blood in response to BP renin converts angiotensinogen  angiotensin I Fig 17.26

Triggering of Aldosterone Release angiotensin I converted to angiotensin II (fully activated) by angiotensin converting enzyme in lungs angiotensin II stimulates aldosterone release Fig 17.26

Urination Fig 17.1 Ureters Urinary Bladder Two sphincters transfer urine to pelvic region Urinary Bladder Stores urine smooth muscle, stretchable walls Two sphincters internal urethral sphincter (involuntary) external urethral sphincter (voluntary) Fig 17.1

Urination Fig 17.1 Urination Reflex: Stretch receptors in bladder wall  spinal cord efferents to smooth muscle  contraction Internal sphincter relaxes External sphincter relaxes Fig 17.1