The Urinary System: Fluid and Electrolyte Balance

Exchanges Affecting Plasma Content Figure 19.1 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Concept of Balance Figure 19.2 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Kidneys in Maintaining Balance Water Sodium Potassium Calcium Acid-base Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Exchange of Water Intake Output Gastrointestinal tract Metabolism Insensible loss Sweating Kidneys Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Factors Affecting Water Balance Note: Kidneys can only minimize fluid loss Intake is required in order to add fluids Figure 19.3 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Osmolarity of Fluids Osmolarity of body fluids = 300 mOsm No osmotic force for water to move between fluid compartments Kidneys compensate for changes in osmolarity of extracellular fluid by regulating water reabsorption Water reabsorption passive Based on osmotic gradient Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Water Reabsorption Proximal tubules 70% filtered water is reabsorbed Not regulated Distal tubules and Collecting ducts Most remaining water is reabsorbed Regulated by ADH Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Sodium Reabsorption Figure 19.4 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Sodium Reabsorption Na+ is actively transported across basolateral membrane, this establishes an osmotic gradient for water reabsorption Figure 19.4 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Water Reabsorption Figure 19.5 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

The Medullary Osmotic Gradient Figure 19.6 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Counter-Current Multiplier in the Loop of Henle Osmotic gradient established by counter-current multiplier Dependent on loop of Henle Ascending Limb Impermeable to water Active transport of Na+, Cl-, and K+ Descending Limb Permeable to water No transport of Na+, Cl-, or K+ Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Counter-Current Multiplier Cortex Medulla No osmotic gradient (mOsm) Fluid enters tubule Water moves out of descending limb by osmosis Active transport of Na+, Cl–, K+ ions into medullary interstitial fluid increases osmolarity Peritubular fluid Tubular fluid Iso-osmotic state in descending limb; osmotic difference between descending and ascending limbs More fluid enters tubule, pushing fluid through by bulk flow Active transport of Na+, Cl–, K+ ions into medullary interstitial fluid increases 300 Na+ Cl– K+ 400 200 H2O Osmotic established Iso-osmotic state in descending limb; osmotic difference between descending and ascending limbs More water enters tubule and process continues System is in steady state 350 150 500 100 900 700 1 1200 1100 1400 2 3 4 5 6 7 Figure 19.7 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Vasa Recta: Countercurrent Exchanger Figure 19.8 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Regulated Water Reabsorption When membrane of late DCT and CD is impermeable to water Water cannot leave the tubules No water reabsorption More water is excreted in urine Figure 19.9a Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Regulated Water Reabsorption ADH stimulates the insertion of water channels (aquaporin-2) into apical membrane Water is reabsorpbed by osmosis Maximum urine concentration is 1400 mOsm Figure 19.9b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Minimum volume of water that must be excreted in the urine per day Obligatory Water Loss Minimum volume of water that must be excreted in the urine per day Max osmolarity urine = 1400 mOsm Some solute must be excreted Minimum water loss = 440 mL Obligatory water loss Necessary to eliminate non-reabsorbed solutes Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Effects of ADH on Principal Cells Figure 19.10 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Response: Increase in ECF Osmolarity Figure 19.11 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Response: Decrease in Blood Volume Figure 19.12 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Proximal Tubule Sodium Reabsorption Coupled to the reabsorption of other solutes Figure 19.13a Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Distal Tubule Sodium Reabsorption Coupled to the secretion of K+ and H+ Figure 19.13b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Effects of Aldosterone Figure 19.14 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Renin-Angiotensin-Aldosterone Figure 19.15 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Angiotensin II Effect on MAP Adrenal cortex Systemic arterioles Posterior pituitary Hypothalamic neurons Aldosterone secretion Sodium reabsorption in late distal tubules and collecting ducts Water reabsorption Extracellular fluid osmolarity Thirst stimulation ADH secretion Vasoconstriction MAP Plasma volume Kidneys Angiotensin II Figure 19.16 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Stimulation of Renin Release Baroreceptor reflex Sympathetic activity Afferent arteriole pressure GFR [Na+] and [Cl–] in distal tubules Macula densa Renin release Juxtaglomerular cells of afferent arteriole MAP Paracrine secretion Figure 19.17 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Role of Atrial Natriuretic Peptide Figure 19.18 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

PCT: Potassium Reabsorption Figure 19.19a Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

DCT: Potassium Secretion Figure 19.19b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Routes of Calcium Exchange Figure 19.20 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

PTH and Calcium Balance [PTH] in plasma PTH secretion [1,25-(OH2)D3] in plasma Ca2+ resorption Phosphate reabsorption Calcium excretion in urine Ca2+ reabsorption 1,25-(OH2)D3 activation Parathyroid glands Kidneys Ca2+ absorption Gastrointestinal tract Bone [Ca2+] in plasma Negative feedback Figure 19.21 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Role of Vitamin D Figure 19.22 Conversion of vitamin D3 to 25-OH D3 Vitamin D3 absorption 7-dehydrocholesterol Sunlight [Vitamin D3] in plasma [25-OH D3] in plasma [1,25-(OH2)D3] in plasma Conversion of 25-OH D3 to 1,25-(OH2)D3 Liver Kidney Ca2+ absorption Kidneys Gastrointestinal tract [Ca2+] in plasma [PTH] in plasma [Ca2+] in Skin Negative feedback Figure 19.22 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Inputs and Outputs of Acid Figure 19.23 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Response to Decrease in pH Figure 19.24 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Bicarbonate Reabsorption Figure 19.25 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Hydrogen Ion Secretion Figure 19.26 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Glutamine Metabolism in the PCT Figure 19.27 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Metabolic Alkalosis Cause: decreased H+ independent of CO2 Compensation: respiratory and renal (unless renal problem) Respiratory compensation Decrease ventilation  increase CO2 Renal compensation Decrease H+ secretion Decrease HCO3- reabsorption Decrease synthesis of new bicarbonate Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Acid-Base Disturbances/Compensation Arterial pH Acidosis pH < 7.35 Alkalosis pH > 7.45 PCO 2 < 40 mm Hg Respiratory compensation Metabolic acidosis [HCO3–] < 24 mM [HCO3–] > 24 mM Renal Respiratory acidosis > 40 mm Hg Metabolic alkalosis Respiratory alkalosis OR Figure 19.28 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.