BMS100 - Chapter 17 Outline
    Nitrogenous Wastes (wastes that contain nitrogen)
  1. Protein catabolism (breakdown) produces amino acids.
  2. The “amino group” (-NH2) may be removed from the amino acid and, if so, it becomes ammonia (NH3), which is a "waste" and very toxic.
  3. Ammonia enters the blood and some of it enters the liver.
  4. The liver converts ammonia to urea, which is much less toxic.
  5. Urea enters the blood and is excreted (along with ammonia) by the urinary system.
    Urinary System
  1. kidneys - produce urine (contains wastes filtered from blood)
  2. ureters (2) – carry urine from each kidney to urinary bladder
  3. urinary bladder - stores urine and forces it through the urethra
  4. urethra (1) - conveys urine from the urinary bladder to outside the body
    Kidneys (p. 454)
  1. Each kidney is divided into a cortex, a medulla, and a sinus (to which the ureter is connected)
  2. Renal artery: attached to aorta, carries blood into kidney.
  3. Renal vein: attached to inferior vena cava, carries blood out of kidney.
  4. Renal blood flow is approx. one liter per minute.
  5. Nephrons - the functional unit of the kidneys
    1. one nephron includes one renal corpuscle + one renal tubule
    2. each corpuscle consists of one glomerulus (ball of capillaries) and a capsule that surrounds the glomerulus
    3. renal tubule
      1. receives fluid from renal corpuscle (is continuous with capsule)
      2. is surrounded by blood capillaries
      3. water, ions, etc. may be exchanged between tubule and capillaries
      4. each tubule leads to the renal sinus
        • any fluid that enters the tubule and stays there becomes urine and is excreted
    4. blood supply to a nephron: renal artery > branches of renal a. > afferent arteriole > glomerular capillaries > efferent arteriole
    5. afferent arteriole has a larger diameter than does the efferent arteriole
      • pressure in glomerulus is approx. 2X pressure in a typical capillary
    I. FILTRATION
  1. Water and dissolved materials are forced by pressure out of glomerular capillaries.
  2. The fluid produced by filtration is called filtrate.
  3. Filtrate includes water, sodium, chloride, glucose, amino acids, urea, ammonia, and other substances.
  4. Filtration rate - the kidneys produce about 125 ml. of filtrate per minute (or approx. 150-180 liters per day).
  5. Filtrate is collected in the capsule then passes into the tubule.
  6. True or false? Most of the filtrate becomes urine and is excreted.
    II. REABSORPTION
  • Valuable substances are reabsorbed from filtrate and returned to blood. Such substances are transported out of the tubule and into the surrounding capillary.
    1. Active transport (by molecular "pumps”) reabsorbs sodium.
    2. As sodium ions (positively charged) are pumped out of the tubule, chloride and other negatively charged ions “follow” them.
    3. Glucose and amino acids are reabsorbed by special carriers.
    4. Water is reabsorbed by osmosis (water “follows” solutes).
  • Not reabsorbed:
    1. Ammonia is not reabsorbed.
    2. Approx. half of the urea is not reabsorbed.
    3. Substances that are filtered but not reabsorbed are eventually excreted.
  • Per 100 ml. of filtrate that enters the renal tubule, approx. what percent is reabsorbed? Approx. what percent is excreted, i.e., approx. how much urine is produced per minute?
      III. SECRETION
  • Secretion transports substances from the blood to the tubule so they can be excreted.
    Chapter 17 Questions at OLC - 4,6, 7, 8, 9, 10, 11, 12, 14, 15, 17, 20, 22, 30, 31, 34, 35, 37, 39, 40, 41
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    Spring 2011