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Chapter 18

Chapter 18. The URINARY SYSTEM. 4 FUNCTIONS OF THE URINARY SYSTEM. Regulating blood volume and blood pressure Regulating plasma concentrations of ions Helping stabilize blood pH Conserving valuable nutrients. THE ORGANIZATION OF THE US. Kidneys : produce urine

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Chapter 18

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  1. Chapter 18 The URINARY SYSTEM

  2. 4 FUNCTIONS OF THE URINARY SYSTEM • Regulating blood volume and blood pressure • Regulating plasma concentrations of ions • Helping stabilize blood pH • Conserving valuable nutrients

  3. THE ORGANIZATION OF THE US • Kidneys: produce urine • Ureter: transports urine from the kidneys to the urinary bladder • Urinary Bladder: temporarily stores urine prior to elimination • Urethra: conducts urine to exterior • Urine: liquid composed of water, ions, small soluble compounds

  4. The Kidneys • Ren: Latin for kidney • Nephron: basic functional unit of the kidney. Has 2 primary parts: • Renal corpuscle • 50mm renal tubule of 2 convoluted segments (in the cortex) separated by a U-tube (U-tube goes partially/completely into the medulla). • Medulla – inner layer/core • Cortex – rind • Juxta – close/nearby

  5. The Nephron (continued, I) • Renal corpuscleconsists of 2 components: • Glomerulus (glomus: ball): capillary network • Bowman’s capsule: outer wall of renal corpuscle and encapsulates the glomerulus. • Renal tubulesplit into 3 sections: • PCT: Proximal Convoluted Tubule • DCT: Distal Convoluted Tubule • Loop of Henle (has 2 limbs joined at a “U”, the lowest point of the nephron): • Descending: active secretion of ions, acids, drugs, toxins; selective reabsorption of Na+ • Ascending: impermeable to water and solutes • Filtrate: protein-free solution from filtration of blood that goes through the glomerulus. As the filtrate travels along the renal tubule, it is called the tubular fluid.

  6. The Renal Tubule • 2 convoluted tubules (CT) (twisted/coiled little tubes) • Proximal – close to(the glomerulus) • Distal – distant from(the glomerulus) • Functions of the Renal Tubule: • Reabsorbing all the useful organic molecules, plasma proteins, ions, and +90% of the water in the filtrate. (Proximal CT) • Secreting wastes missed by filtration; the secretion empties into the tubular fluid. (Distal CT)

  7. The Renal Corpuscle • Consistsof 2 components: • Glomerulus (glomus: ball): capillary network • Bowman’s capsule: outer wall of renal corpuscle and encapsulates the glomerulus

  8. Collecting system • PRIMARY FUNCTION: Reabsorption of H2O, Na+ and HCO3- ions. • 2 ducts: • Collecting: takes tubular fluid from nephrons; these ducts merge to form a papillary duct. • Papillary: delivers urine to minor calyx.

  9. BASIC PRINCIPLES OF URINE PRODUCTION • Excretion of 3 metabolic wastes: • 1. Urea • From: catabolizing amino acids • Make: 21g per day. • 2. Uric Acid • From: recycling RNA • Make: .480g per day. • 3. Creatinine • From: skeletal muscle tissue’s catabolism of creatine phosphate, used in muscle contraction. • Make: 1.8g per day.

  10. BASIC PRINCIPLES OF URINE PRODUCTION • Kidney performs 3 distinct functions: • Filtration (renal corpuscle only) • Reabsorption (mostly in PCT) • Secretion (mostly in DCT) • Also, the regulation of the amounts of H2O, Na+ and K+ ions happens between Loop of Henle and collecting system.

  11. BASIC PRINCIPLES OF URINE PRODUCTION • Glomerularfiltrationoccurs as fluids move across the wall of the glomerular capillaries in to the capsular space. • That movement is the response to blood pressure in those capillaries. • GFR – is the rate of filtrate produced per minute • Things that affect filtration (blood) pressure alter GFR and kidney function. • Declining filtration pressures simulate the juxtaglomerular apparatus to release renin. • RENIN release  increased blood volume and blood pressure

  12. BASIC PRINCIPLES OF URINE PRODUCTION • Reabsorption and Secretion along the RT: • PCT reabsorbs 60-70% of the volume of the filtrate produced in the renal corpuscle: nutrients, ions, H2O • Loop of Henle: ions and water • Ascending limb pumps out Na+ and Cl- into the medulla • Descending limb pumps out H2O into the medulla • DCT • Changes in filtrate only occur via active transport by pumps that respond to the presence of the hormone aldosterone, which responds to low Na+ or high K+concentrations. • More aldosterone = Na+ kept in blood; K+ lost to urine.

  13. BASIC PRINCIPLES OF URINE PRODUCTION • Reabsorption along the collecting duct: • In the presence of ADH, the collecting duct reabsorbs H2O back into the medulla, sending away a small volume of urine. But, because the H2O was already absorbed, it is highly concentrated. • In the absence of ADH, the collecting duct simply passes along the regular volume of urine. It is diluted, since H2O was not reabsorbed.

  14. URINE TRANSPORT, STORAGE, AND ELIMINATION • Filtrate modification and urine production end at the renal pelvis. • The rest is responsible for transporting, storing, and eliminating the urine. Components: • Ureters • Urinary bladder • Internal urethral sphincter

  15. FLUID, ELECTROLYTE, AND ACID-BASE BALANCE • Intracellular fluid: 60% of total body water • Extracellular fluid: 40% of total body water Electrolyte balance is important because total electrolyte concentrations affect water balance. • Problems are usually Na+ related. • Gained from diet, lost through urine and sweat. Reabsorbed via aldosterone in the DCT. • K+ imbalance can also occur and is more dangerous, but is rare. • Generally low concentrations in ECF. Losses occur when Na+ declines, ECF K+ rises (aldosterone)

  16. ACID-BASE BALANCE • Normal pH is 7.35-7.45 • ACIDOSIS: pH too low • ALKILOSIS: pH too high • Cation: ion with + charge. CA+ION: “see a positive ion”. • Anion: ion with – charge. ANegativeION.

  17. ACID-BASE BALANCE • 3 major buffer systems of the body: • H2CO3/HCO3− : primary affecter of ECF pH • PO43− : primary affecter of ICF pH • Protein: in the ICF/ECF, amino acids respond to changes in H+ concentrations. • Blood plasma proteins and hemoglobin in RBCs prevent major blood pH changes.

  18. ACID-BASE BALANCE H2CO3/HCO3− : the most important factor affecting pH of ECF CO2+ H2O  H2CO3 H2CO3  H+ + HCO3− CO2 + H2O↔ H2CO3 ↔ H+ + HCO3− CO2 + H2O ↔ H++ HCO3− • ↓ pH  ↑CO2while↑pH  ↓CO2 (inverse relationship) • With the exception of RBCs, all cells produce CO2 24hrs/day. • Spontaneous reaction • Carbonic anhydrase speeds up this in RBCs, liver cells, kidney cells, parietal cells of the stomach.

  19. ACID-BASE BALANCE PO43− : primary affecter of ICF pH. Technically also plays a role in ECF, but only supporting, since ICF pH is dominated by H2CO3/HCO3−. Really, this is the dihydrogen phosphate buffer system. • H2PO4-↔ H+ + HPO42-

  20. ACID-BASE BALANCE • Protein: Organic/metabolic acids • Made primarily from metabolic processes • Examples: • Lactic acid (from anaerobic metabolism of pyruvic acid) • Ketone bodies (from metabolism of fatty acids) • These are either recycled or excreted rapidly, so significant buildups of these do not occur. If pH goes up, carboxyl group (– COOH) releases a H+. If pH goes down, an amino group (– NH2) takes a H+ for –NH3+.

  21. ACID-BASE BALANCE • Respiratory: lungs help by affecting the H2CO3/HCO3−buffer system. Changing the respiratory rate can change the CO2 pressure in the fluids, affecting the buffer capacity. • Renal: vary rates of H+ secretion and HCO3−absorption depending on the ECF pH. • Why these also? • Buffer systems only provide a temporary solution by tying up excess H+. • For homeostasis, the H+ needs to be removed from the body. • If all the buffer molecules are tied up with that excess H+, then the ECF can no longer deal with excess H+, leaving pH unmaintained. • Therefore, there must be a combo between the 3 buffer systems and these 2 additional mechanisms. • These 2 mechanisms do this by: • Secreting or absorbing H+ • Controlling acid/base excretion • Generating more buffers

  22. ACID-BASE DISORDERS • Respiratory acidosis/alkilosis • Metabolic acidosis/alkilosis

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