Urinary System Kidneys Urinary tract Ureter Bladder urethra 2013 Pearson Education, Inc.
Functions of the Urinary System Primary functions Filter blood plasma and produce urine Removing metabolic wastes, toxins, drugs Regulating blood volume and pressure Via regulating blood osmolarity Secondary functions Endocrine functions Renin: regulation of blood pressure EPO: RBCs Metabolism of vitamin D Regulate ph
Kidney Anatomy Retroperitoneal Vertebrae T11 to L3 Adrenal gland renal hilum Ureters, renal blood vessels, lymphatics, and nerves Support layers Renal fascia fat fibrous capsule
Regions Renal cortex renal columns Renal medulla 5-11 pyramids Lobe of kidney Renal Sinus Drainage system Minor calyces Major calyces: 2-3 renal pelvis Internal Anatomy
Trace the flow of urine Kidney Nephrons: ~1millions Collecting ducts: ~1000 Papillae: depend on pyramids Drainage system Ureter Bladder urethra
Blood Supply Renal arteries 20-25% of cardiac output pathway of renal blood flow Glomerulus filtration peritubular capillaries reabsorption and secretion 2013 Pearson Education, Inc.
Nephrons Structural and functional units Renal corpuscle Renal tubule > 1 million per kidney Cortical nephrons: urine formation Juxtamedullary nephrons: concentrated urine Objective: filters plasma => urine formation
Nephron Capillary Beds 2 capillary beds Glomerulus: fed and drained by arteriole Peritubular capillaries or vasa recta
Glomerulus fed and drained by arteriole Afferent arteriole => glomerulus => efferent arteriole Filtration Glomerulus => bowman s capsule Mechanism High blood pressure: Driving force for filtration Diameter: afferent arteriole > efferent arteriole
Peritubular capillaries or vasa recta Peritubular capillaries: Empty into venules Reabsorption: H2O & solutes Renal tubule => peritubular capillaries Mechanisms Low blood pressure, porous capillaries (<< renal tubule) High osmotic pressure vasa recta formation of concentrated urine
Kidney Physiology
Mechanisms of Urine Formation Synopsis of events: plasma => filtrate => urine Filtration: 180 L fluid processed daily Modification: 99% Reabsorption Urine: 1.5 L Urea: by-product of protein metabolism Creatinine: product of the breakdown of creatine in the muscle Uric acid from nitrogenous bases of nucleotides 2013 Pearson Education, Inc.
Overview of Kidney Functions Glomerular filtration: blood => filtrate Filtration membrane glomerular capillaries: (-)-charged surface basal lamina: (-)-charged glycoprotein Reabsorption: Filtrate => blood Secretion: blood => filtrate
main processes involved in converting filtrate into urine glomerular filtration tubular reabsorption tubular secretion
Pressures Movement depends on net pressure Hydrostatic pressure = blood pressure Osmotic pressure = protein concentration "Pull" of proteins in blood 2013 Pearson Education, Inc.
Passive process Glomerular Filtration Net filtration pressure (NFP): Sum of forces NFP = [HPG HPBC] [πg] glomerulus: ~55mm Hg body capillaries: 18-26mm Hg Hydrostatic Pressure forces fluids and solutes through filtration membrane Protein osmotic pressure "Pull" of proteins in blood NFP = (55-15) 30 NFP = 10mm Hg
Glomerular Filtration Rate (GFR) GFR = rate of filtrate formation by both kidneys GFR = 125 ml/min or 180L/day directly proportional to Net Filtration Pressure Total surface area available for filtration Filtration membrane permeability
How Does Vasodilation or vasoconstriction of afferent arteriole affect GFR?
Glomerular Filtration Rate (GFR) Constant GFR allows kidneys to make filtrate Objective: to maintain extracellular homeostasis Mechanism: intrinsic controls maintain GFR Act locally within kidney GFR affects systemic blood pressure Objective: to maintain systemic blood pressure GFR => urine output => blood pressure Mechanism: extrinsic controls Via sympathetic nervous system & renin-angiotensin mechanism
2 Intrinsic control mechanisms Objective maintain GFR and hydrostatic pressure GFR remains constant over a wide range of MAP myogenic mechanism adjustment of diameter of the afferent arteriole tubuloglomerular feedback mechanism Directed by macula densa
myogenic mechanism adjustment of diameter of the afferent arteriole High BP: pressure on afferent arterioles => reflexive constriction of afferent arterioles Low BP: pressure on afferent arterioles => reflexive dilation of afferent arterioles
Tubuloglomerular Feedback Mechanism Flow-dependent mechanism directed by macula densa cells In response to filtrate NaCl concentration GFR => filtrate flow rate => reabsorption time => high filtrate NaCl levels Juxtaglomerular apparatus Results: constriction of afferent arteriole => NFP & GFR more time for NaCl reabsorption 2013 Pearson Education, Inc.
extrinsic control mechanism GFR affects systemic blood pressure GFR => urine output => blood pressure (Emergency) Objective: to maintain systemic blood pressure Via sympathetic nervous system & reninangiotensin mechanism
Extrinsic control mechanism Under normal conditions at rest Renal blood vessels dilated Renal autoregulation mechanisms prevail extracellular fluid volume extremely low (blood pressure low) Emergency: maintain fluid volume in the body to stabilize blood pressure Activation of Sympathetic NS EPI: Vc afferent arterioles => GFR => urine output ( blood volume and pressure) Renin-angiotensin-aldosterone
Renin-angiotensin-aldosterone Angiotensin-II: ADH, thirst, aldosterone low A-II: Vc efferent arterioles high A-II: Vc afferent & efferent arterioles
PCT Reabsorption Kidney Functions 70% H2O and Na+ 100% glucose, amino acids Loop of Henle Descending loop: H2O reabsorption Ascending loop: Na+ reabsorption DCT Reabsorption: Na+, K+, Ca2+, Cl- tubular secretion: H+, K+
Diuretics Medications Fusoremide (Lasix) Thiazide Alcohol Inhibits ADH release Caffeine inhibits renal sodium reabsorption