CH 16 Urinary System
Chapter 16: The Urinary System and Excretion
16.1 Introduction to the Urinary System
Excretion: The process of removing metabolic wastes and toxins to maintain homeostasis.Kidneys: Primary organs of the urinary system filtering blood and producing urine through nephrons, regulating fluid, electrolyte balance, and waste removal.
16.2 Functions of the Urinary System
Overview of Functions
Excretion of Metabolic Wastes:
Urea: Nitrogenous waste from amino acid metabolism, synthesized in the liver.
Creatinine: Waste from creatine phosphate breakdown, indicative of kidney function.
Uric Acid: Breakdown product of purines; excess can lead to gout.
Urochrome: Pigment giving urine its yellow color from hemoglobin breakdown.
Preservation of Water-Salt Balance:
The kidneys regulate hydration and electrolyte levels, influencing osmotic pressure and blood volume.
Maintenance of Blood Pressure:
By controlling blood volume and producing renin, the kidneys aid in blood pressure regulation.
Maintenance of Acid-Base Balance:
Excreting hydrogen ions and reabsorbing bicarbonate to regulate blood pH.
Secretion of Hormones:
Renin: Activates blood pressure regulation pathways.
Erythropoietin (EPO): Stimulates red blood cell production.
Active Vitamin D: Promotes calcium and phosphate absorption in the intestines.
Kidney Filtering Capacity: Each kidney filters about 180 liters of blood daily, with <1% excreted as urine.
16.3 Organs of the Urinary System
Structure and Location
Kidneys: Bean-shaped organs located retroperitoneally, containing over a million nephrons.
Ureters: Muscular tubes transporting urine from kidneys to bladder via peristalsis.
Urinary Bladder: Stores urine temporarily; composed of smooth muscle and controlled by sphincters.
Urethra: Tube leading from the bladder to the external opening; varies in length by gender.
16.4 Urination
Micturition
The urination process is controlled by nerve signals reacting to bladder fullness, causing detrusor muscle contractions and sphincter relaxation.
16.5 Anatomy of the Kidney
Renal Cortex: Outer layer containing renal corpuscles and tubules.
Renal Medulla: Inner portion with renal pyramids collecting urine.
Renal Pelvis: Connects kidneys to ureters, collecting urine.
16.6 Urine Formation
Steps in Urine Formation
Glomerular Filtration: Blood is filtered; water and small solutes enter the glomerular capsule.
Tubular Reabsorption: Water and nutrients are reabsorbed into the bloodstream, especially in the proximal convoluted tubule.
Tubular Secretion: Active transport of substances into tubular fluid for excretion.
Final Urine Product: Composed of unabsorbed filtered substances and secreted substances.
16.7 Regulatory Functions of the Kidneys
Managing fluid (60% in males, 50% in females) and electrolyte balance is vital for health. Intake must match output through urine, sweat, and respiration.
16.8 Hormonal Regulation
ADH: Increases water reabsorption during dehydration.
Aldosterone: Promotes sodium reabsorption, regulating blood pressure.
ANH: Decreases blood pressure by promoting sodium and water excretion.
16.9 Acid-Base Balance
Blood pH is maintained between 7.35 and 7.45; kidneys excrete hydrogen ions and reabsorb bicarbonate for equilibrium.
16.10 Problems with Kidney Function
Altered urine composition can signal renal issues; common problems include diabetes, hypertension, infections, kidney stones, and glomerular damage.
16.11 Treatment for Kidney Problems
Hemodialysis: Machine filters blood when kidneys fail.
Renal Transplantation: Surgical implantation of a kidney requiring immunosuppressive therapy to prevent rejection.
16.12 Aging Effects on the Urinary System
Aging leads to reduced kidney function, shrinkage, fewer nephrons, and increased risk of kidney stones and UTIs, requiring monitoring.
16.13 Homeostasis
Kidneys are essential for excretion and maintaining homeostasis, regulating water-salt balance, blood pressure, and pH, supporting overall body function.