1. Excretory Organs

A. Excretion is removing products from the body. Water volume in body stays constant. The amount coming in and out varies to keep water volume constant.

  1. Skin excretes perspiration
    1. Sweat glands in the skin produce solution of water, salt and urea. This evaporates and cools the body. When the kidney fails urea is excreted by sweat glands.
  1. Liver excretes bile pigments (from gallbladder).
    1. Yellow pigment in urine is called urochrome and is derived from heme.
  1. Lungs remove carbon dioxide and water.
  2. Kidneys produce urine.
    1. In 1500 ml of urine, 95 % water, 30 g urea, 1-2 grams of creatine, 1 g of uric acid, 25 g salts (Na, K, Mg, ammonium, calcium, chlorine, and phosphate).
    2. Urea comes from amino acid metabolism. Nucleotides become uric acid (when crystals of uric acid in joints produce gout). Creatine phosphate becomes creatine.
  1. Path of Urine
  1. Urine made by kidneys.
    1. A tough fibrous capsule of connective tissue covered with adipose tissue covers the kidney.
    2. Blows to the back can hurt kidney.
    3. Kidneys maintain homeostasis of body fluid.
  1. Ureters are muscular tubes that move urine to the bladder by peristalsis.
    1. 5 jets of urine enter bladder per minute.
    2. Urinary bladder can hold up to 600 ml of urine.
    3. The bladder is a hollow muscular organ.
  1. Urethra goes from bladder to external opening.
    1. Urethra in female is 4 cm long and more prone to urinary tract infections.
    2. Urethra in male is 20 cm long.
    3. In male urethra is encircled by prostate gland which can enlarge in older men preventing urination.
  1. Urination and the Nervous System
  1. Bladder fills
  2. Stretch receptors send nerve impulse to spinal cord.
  3. The bladder contract.
  4. Sphincters relax.
  5. Brain controls this.

i. Potty training can not occur until brain is developmentally capable.

  1. Kidney Structure
  1. Three regions
    1. Renal cortex is the outer layer
    2. Renal medulla is a cone shaped tissue with masses called renal pyramids.
    3. Renal pelvis is the central space continuous with ureter.
    4. One million nephrons in a kidney
  1. Nephrons
    1. A structure composed of Bowmanís capsule (containing glomerulus, a tuft of capillaries), proximal convoluted tubule, loop of Henle, and distal convoluted tubule.
    2. Many nephrons enter one collecting duct.
    3. Collecting ducts carry urine to renal pelvis.
    4. Bowmanís capsule and convoluted tubules lie in renal cortex.
    5. Loop of Henle dips into renal medulla.
    6. Peritubular capillaries surround the nephron.
  1. Urine Formation
  1. Pressure filtration divides the blood.
    1. Blood enters afferent arteriole to glomerulus.
    2. Water and small molecules can filter into Bowmanís capsule.
    3. Large molecules and formed elements canít enter.
    4. Filterable ( water, nitrogenous wastes, nutrients, and salts) components form the glomerular filtrate.
    5. Non filterable components (blood cells, platelets, proteins)
    6. Exit via the efferent arteriole.
    7. If urine were the same as filtrate the body would die from dehydration, starvation, and low blood pressure.
  1. Selective reabsorption
    1. Both passive and active reabsorption of molecules from the nephron to the blood occurs at the proximal convoluted tubule.
    2. Cells lining the proximal convoluted tubule are anatomically adapted for active reabsoption.
    1. Lots of microvilli increase surface area for reabsorption.
    2. Cells have lots of mitochondria, which make ATP needed for active transport.
    3. Active transport is selective reabsoption.
    1. Useful products return to the blood.
    2. Water is passively reabsorbed.
    3. Sodium and chloride ions are actively reabsorbed, which encourages water to follow.
    4. Amino acids and glucose are reabsorbed to blood.
    5. Many carriers for glucose. The reabsorption rate is 400-mg/100ml plasma. The rest of the glucose is in the urine. In diabetes mellitus, excess glucose is in the blood.
    6. Part of the filtrate is reabsorbed, part is not.
  1. Tubular excretion
    1. Certain molecules are actively secreted from the peritubular capillary into the distal convoluted tubule.
    2. Excreted products such as drugs, Creatine, and hydrogen ions are then found in urine.
    3. Blood pH can be regulated this way.
  1. Reabsorbing water
    1. Water is reabsorbed all along the nephron.
    2. Urine becomes hypertonic (salty) because of the loop of Henle and the collecting duct.
    3. Loop of Henle

a. The descending limb of the loop of Henle canít absorb salt, and the ascending limb canít absorb water.

    1. Salt passively diffuses out of the lower portion of the ascending limb.
    2. The upper part of ascending limb actively transports salt into tissue of the renal medulla.
    3. Increase in salt in the direction of the inner medulla.
    4. Urea leaks from the lower portion of collecting duct and contributes to a high solute (salt) concentration.
    5. Water leaves descending limb of the loop of Henle, returning to the blood.
    6. Urine is hypertonic to blood.
  1. Regulatory Functions of the Kidneys
  1. Regulates pH and salt balance

i. Blood pH is 7.4

    1. Nephron excretes H+ and NH3. Nephron reabsorbs Na+ and HCO3-. When blood is acidic this happens at a greater rate, when blood is basic this happens less.
    2. Nephron can also excrete or reabsorb ions such as K+, and Magnesium.
  1. Blood volume (and salt balance)

i. Under control of hormones (antidiuretic hormone, also called ADH, and aldosterone).

    1. ADH is secreted by posterior pituitary.
    1. ADH acts to increase the permeability of the collecting duct to water which increases water reabsorption into the blood.
    2. Secretion of ADH depends on whether the blood volume needs to be increased or decreased.
    3. Alcohol inhibits the secretion of ADH. Water lost in urine which contributes to hangover.
    1. Caffeine increases glomerular filtration rate and decreases the tubular reabsoption of Na. Leads to loss of water in urine.
    2. Diuretics (drugs that cause water loss in urine) are prescribed for high blood pressure, pulmonary edema and congestive heart failure. However salts are lost also.
    3. Aldosterone is secreted by the adrenal cortex and is involved in maintaining Na and K balance.
    1. Aldosterone acts on the ascending arm of the loop of Henle to increase Na reabsorption into kidney and excretion of K.
    2. More Na means more water returns to blood.
    3. Blood pressure monitored by juxtaglomerular apparatus.
    4. When blood pressure is not high enough to promote filtration the afferent arteriole cells secrete renin.
    5. Renin turns angiotensinogen into angiotensin 1.
    6. Angiotensin1 is turned into angiotensin II by an enzyme (ACE).
    7. Angiotensin II is a vasoconstrictor that also stimulates the adrenal cortex to release aldosterone.
    8. Blood volume and blood pressure go up.
    9. This process is always on in patients with hypertension.
    10. ACE inhibitor is used to counteract this process.
  1. Problems with Kidney Function
  1. Urethritis is the infection of the urethra.
  2. Cystitis involves the bladder.
  3. Pyelonephritis is an infection of the kidneys.
  4. Damage to the glomeruli may lead to blockage or leakage.
  5. Uremia is when 2/3 rd of nephrons is inoperative.
  6. Imbalance in ionic composition of body fluids can lead to loss of consciousness and heart failure.
  7. Kidney transplant used in cases of renal failure.
  8. Dialysis
    1. Blood shunted into tube with semi-permeable membrane that allows wastes to diffuse out but keeps necessary components in blood.
    1. Can remove waste products (urea), chemicals, toxins, drugs etc.
    2. Can add bicarbonate if blood is acidic.
    3. Can be hooked up to machine (about 2 x a week) or can use a bag stored in abdominal cavity.