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Chapter 11

 

Chapter 11: Urinary System

 

11.1 Urinary System Overview

  • ___________________________________ is created as food is broken down from energy
  • The role of the urinary system is to remove that waste
    • Waste in the digestive system is eliminated in the feces
  • When the products of digestion get into tissues, wastes accumulate and diffuse into the bloodstream, including ammonia, acids, and salts
    • These must be eliminated to maintain homeostasis

 

  • Most metabolic wastes are eliminated by urinary system resulting in ___________________________
    • ______________________________ are the primary organs of the urinary system
  • Kidneys regulate salt excretion in order to maintain water balance between tissues and the blood
  • Kidneys keep pH levels of the blood within normal levels by adjusting ion levels

 

  • The major organs of the urinary system:
    • ________________________ filter and cleanse blood brought by renal arteries
    • ________________________ carry waste from kidneys to the __________________, which stores the waste for excretion via the ______________________________
    • Blood that has passed through the kidneys returns to the circulation via renal veins

 

  • The paired, fist-sized kidneys sit in the upper abdominal cavity behind the liver
  • A tough, connective tissue renal capsule protects the kidney

 

  • The kidney is made up of three layers:
    • Outer _________________________________
    • Inner _________________________________
    • A hollow center, the _______________________________
  • Within the cortex and medulla are ______________________________, do the actual filtering
    • Each kidney has about 1.25 nephrons

 

  • Each kidney filters 1,000 liters of blood daily with the end product of _________
  • The urine moves via muscular contractions of the ureters to the bladder, which can store about 1 liter
  • The bladder walls are made of muscle, which contracts to expel urine through the __________________________________, a ring muscle at the top of the urethra

 

  • The __________________________________ controls urine flow out of the urethra
    • The urethra in females is 3-4 cm long and carries only urine
    • The urethra in males is 18-20 cm long and carries both urine and sperm

 

  • _________________________ relies on a positive feedback loop
    • Urine flow through the urethra stimulates muscle contractions to fully empty the bladder
    • Once empty, urine flow ceases and muscle contractions stop

 

11.2 Excretion

  • ______________________ is  a water-based solution including ________________, a waste product of protein metabolism
    • Ammonia is produced when proteins are used from cellular respiration
      • The liver converts it to urea
      • Toxic to cells
    • Uric acid results from DNA metabolism and is found in low levels in urine

 

  • Urine also contains sodium, potassium, chloride, calcium and hydrogen ions
    • Kidneys excrete these ions to maintain homeostasis of blood volume and acidity
    • Trace amounts of other materials are also found in urine, e.g., toxins and drugs
  • Urine’s yellow color comes from bilirubin (degraded hemoglobin) waste products

 

  • Creatinine is also found in urine and comes from intense muscle activity
    • Creatinine forms when creatine phosphate is used to make ATP to power muscles, a process which generates ADP

 

  • There are three phases to the processing of waste by the kidney:
    • ______________________________________________________
    • ______________________________________________________
    • ______________________________________________________

 

  • ______________________________ is the first step of urine formation
    • Blood pressure forces plasma from the capillaries into the glomerulus
  • The _________________________________ (Bowman’s capsule) is the nephron’s receiving end
    • The capsule surrounds a capillary mass, the ___________________________
    • Fluid filtered from the glomerulus into the capsule flows through the proximal convoluted tubule which is embedded in the renal cortex

 

  • 20% of nephrons have a long _________________________ (loop of Henle) which brings the tubule into the renal medulla
    • The other 80% stays in the cortex
  • Each nephron ends in a _______________________________
  • The distal tubules drain into a common ___________________________________, shared by several nephrons
  • The collecting ducts empty waste into the renal pelvis

 

  • __________________________________ is the second step of urine formation
  • The glomerular filtrate contains wastes to be excreted and essential materials to be reabsorbed
  • Most of the water, sodium, glucose and amino acids are reabsorbed, along with 50% of the urea

 

  • ___________________________________ is the third step in urine formation
  • The proximal and distal tubules permit secretion of some low concentration substances in the plasma, such as creatinine
    • These wastes move from capillaries into nephrons via active transport
  • Tubular secretion is used to remove many drugs, food additives, inorganics and even hydrogen ions from the body

 

  • The proximal tubules are lined with microvilli, finger-like projections that greatly increase surface area to facilitate reabsorption
    • The process uses ATP to actively transport sodium from the nephron into the renal cortex
    • This causes chloride, water, glucose and amino acids to be removed from the filtrate

 

  • Since sodium is positively charged, its transport into the renal cortex creates an electrical gradient between the nephron lumen (inside space) and the outside
  • As a result, chloride (negatively charged) diffuses out to equalize the charge on both sides of the nephron cell membrane

 

  • The sodium and chloride ions in the renal cortex create an osmotic gradient
    • Fluids in the nephrons are hypotonic to the renal cortex
    • Water diffuses out of the nephron into the cortex
  • Aquaporines (membrane proteins) facilitate the water’s movement, making for the rapid reabsorption of two-thirds of the water in the filtrate

 

  • The active transport of sodium from the tubule cells creates a difference in sodium concentration between the tubule epithelial cells and the filtrate in the lumen
  • This results down its concentration gradient into the epithelial cells

 

11.3 Water, pH, and Salt Balance

  • The loss of too much water results in a decline in blood volume and a decrease in blood pressure, which impairs metabolic processes
  • Water loss also makes the blood hypertonic to tissues, which lose water to the blood
    • _________________________ is the loss of too much water, resulting in dry mouth, sunken eyes and lethargy as a result of brain cell shrinkage

 

  • ___________________________________ permeability determines the final urine concentration that is excreted into the renal pelvis
  • A slightly dehydrated person recaptures much of the water in the filtrate by increasing the permeability of the collecting ducts to water

 

  • Water conservation at this level occurs because the collecting ducts pass into the solute-rich medulla interior on the way to the renal pelvis
    • This is a hyperosmotic environment, so any water in it diffuses out, leaving a highly concentrated urine

 

  • Metabolic activities produce acid, which is measured as an increase in hydrogen ions or a decrease in pH
  • Blood must be in the range of pH 7.35 – 7.45
  • Acid produced by metabolism must be neutralized

 

  • ____________________ in the blood are the main mechanism for pH maintenance
  • The bicarbonate ion is the main buffer
  • Absorbs excess hydrogen ions when the pH is low and releases it into the bloodstream when pH is high

 

11.4 When Kidneys Fail

  • A number of issues can affect normal kidney function; many can be corrected
    • ________________________________ (masses of crystals of calcium, phosphorus, uric acid and proteins) may block a ureter
    • Nephrons can be destroyed by urinary tract infections and by chronic high blood pressure
    • Diabetes causes nearly 50% of kidney failures

 

  • Protein in the urine is a first sign of kidney failure
    • The protein has slipped through the glomerulus
  • If kidney damage continues, the results is ________________________________________
    • ESRD suffers have less than 10% normal kidney function

 

  • The demand for kidney transplants far exceeds the supply, so __________________ is used as a measure to keep the patient alive
    • The most effective form of dialysis circulates a patient’s blood through an artificial kidney machine
    • The machine has membranous tubes bathed in clean fluid
      • Metabolic wastes diffuse from the blood through the membranes and into the fluid
    • A single dialysis treatment may take 3-6 hours and may be needed 3-4 times a week

 

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