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Excretory System

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Title: Excretory System


1
Excretory System
2
Excretion
  • is the process by which the body rids itself of
    metabolic wastes.
  • The lungs eliminate carbon dioxide
  • The large intestine eliminates toxic digestive
    waste
  • The liver changes toxin and products of protein
    metabolism into soluble compounds that the kidney
    can collect and eliminate.

3
The role of the liver
  • Excess protein is converted to carbohydrates by a
    process called deamination. This involves the
    removal of an amino group from amino acids to
    produce a carbohydrate and ammonia (a toxic gas).
  • Two molecules of toxic ammonia react with carbon
    dioxide to produce urea. Urea is about 100,000 x
    less toxic than ammonia and can be safely
    transported through the bloodstream.
  • Nucleic acids are also broken down into uric
    acid. Excess uric acid can cause kidney stones
    or gout.
  • All of the waste products made by the liver
    travel through the blood and are then filtered by
    the kidney.

4
The role of the kidneys
  • 1. Main role Removal of poisonous nitrogenous
    wastes
  • 2. Maintenance of blood pH
  • Maintenance of water balance
  • Maintain blood pressure

5
Urinary System
  • Blood is carried to the paired kidneys from renal
    arteries that branch off the aorta. The kidneys
    can hold as much as 25 of the entire blood
    supply at any given time. Wastes are then
    filtered by the kidneys and taken to the urinary
    bladder via the ureters.
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6
Urinary System Anatomy
7
  • A sphincter muscle at the base of the urinary
    bladder acts as a valve and released stored urine
    through the urethra when the muscles relax. The
    signal to urinate is relayed to the brain when
    the bladder is about 200 mL full of urine. The
    liquid in the bladder cause the walls to stretch,
    stimulating receptors. At 400 mL volume, the
    signal will be of increasing strength and
    urgency, and at a 600 mL volume, the sphincter
    muscles relax, voluntary bladder control is lost
    and urination occurs.
  • Howstuffworks "Urination"

8
  • Remember, that when you drink fluids, the fluid
    goes to your stomach first, and is then absorbed
    by the body. The loss of bladder control only
    occurs when much more than 600 mL is processed,
    absorbed, filtered and finally collected in the
    bladder.
  • The bottom line
  • You wont lose bladder control from drinking a
    Big Gulp or Slurpee. Input doesnt equal output
    when it comes to excretion. Your body retains
    much of the fluid it consumes for normal
    processes.

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The Kidneys
Cortex
  • A cross section of the kidney reveals the anatomy
    of three major structures
  • 1. The cortex
  • 2. The medulla
  • 3. The renal pelvis

Renal Pelvis
Medulla
11
Detailed Kidney Structure
  • A cross-section of the kidney reveals the anatomy
    of three major structures cortex, medulla, and
    renal pelvis
  • ureters tubes that conduct urine from the
    kidneys to the bladder
  • renal artery - delivers blood to the kidney
  • renal vein sends blood back to the body
  • renal calyces outer extensions of the renal
    pelvis that filter blood
  • cortex outer layer of connective tissue
  • medulla inner layer beneath the cortex, hold
    the major part of the nephron
  • renal pelvis hollow chamber that joins the
    kidney with the ureter

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The Nephron
  • Blood Pathway
  • The nephron is the functional unit of the
    kidney. There are about 1 million of these
    slender tubules in the kidney. These tubules are
    supplied with blood from the afferent arterioles
    which branch from the renal artery. They lead
    into a high pressure capillary bed called the
    glomerulus. This is where filtration occurs.
    Blood leaves the glomerulus via the efferent
    arterioles and is carried to a capillary network,
    called the peritubular capillaries, that wraps
    around the kidney tubule. Blood is then
    transferred to a renal vein. Then back to the
    venous blood system
  • http//www.wisc-online.com/objects/AP2504/AP2504.
    swf

14
  • Filtrate Pathway
  • The glomerulus is surrounded by a cup-like
    portion of the nephron called Bowmans capsule.
    The cortex contains Bowmans capsule, afferent
    and efferent arterioles. Fluids to be processed
    into urine enter Bowmans capsule from the
    glomerulus. Next, fluids move through the
    proximal/distal tubules and then into the
    collecting ducts which collect urine from many
    different nephrons and merge into the renal
    pelvis.
  • kidney patient guide - healthy kidney

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Urine Formation- Removal of Wastes
  • Formation of urine depends on filtration,
    re-absorption and secretion.
  • Filtration is accomplished by the movement of
    fluid into Bowmans capsule. Blood moves through
    the afferent arteriole to the glomerulus and
    small dissolved solutes (glucose, aa, urea, uric
    acid, ammonia, and salts) and water pass into
    Bowmans capsule (much lower pressure). The
    pressure gradient allows only some substances to
    be filtered. Red blood cells, plasma proteins,
    white blood cells, platelets are too large to
    pass through.
  • Nephron Information Center

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  • Re-absorption involves the transfer of
    essential solutes (glucose, aa, vitamins, salts,
    K,and H) and water from the nephron, back into
    the blood. This is very important in maintaining
    the bodys water balance. About 85 of filtrate
    is re-absorbed. (Remember the Big Gulp If you
    drink a 1L Big Gulp, about 850 mL of the fluid is
    reabsorbed, and only 150 mL is collected in the
    bladder. You dont even feel like you have to
    go yet.)
  • -Re-absorption mostly occurs in the proximal
    tubule, with some minor solutes being re-absorbed
    in the distal tubule
  • -Most water re-absorption occurs in the
    descending limb of the Loop of Henle

19
Steps involved in re-absorption
  • 1. Na is actively transported out of the
    nephron.
  • 2. Cl- and HCO3- follow Na by charge
    attraction.
  • 3. The resulting osmotic gradient draws water
    from the nephron into the blood. (Remember, water
    follows salt)
  • 4. An additional osmotic gradient is created by
    plasma proteins that stay in the blood. (They
    were too big to pass through Bowmans capsule)
  • 5. Urea and uric acid may diffuse out as well,
    but will be reabsorbed later

20
  • Re-absorption occurs until a threshold level of
    substance is reached. Excess amounts of glucose
    and salts in the blood will not be re-absorbed
    and will be excreted in the urine. This is why
    urine tests can tell us about our blood
    chemistry.

21
  • Tubular Secretion involves the movement of
    materials from the blood back into the nephron.
    Nitrogen containing wastes (urea, uric acid),
    histamines, excess H (that regulate pH),
    minerals, drugs, penicillin, etc. are all removed
    from the body by the cells in the distal tubule,
    which actively transports these substances back
    to the nephron. The distal tubule contains loads
    of mitochondria to keep up with this energy
    demand.
  • http//cpharm.vetmed.vt.edu/VM8314/NephronMovie.s
    wf

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Regulating Water Balance
  • Antidiuretic Hormone (ADH) helps regulate the
    osmotic pressure of body fluids by causing the
    kidneys to increase water re-absorption,
    producing more concentrated urine. ADH makes the
    distal tubules more permeable to the last 15 of
    water can be re-absorbed into the blood.

25
  • Special nerve receptors called osmoreceptors
    located in the hypothalamus in the brain detect
    changes in the osmotic pressure of the blood and
    stimulate or inhibit the secretion of ADH. These
    receptors also elicit the thirst response,
    inspiring you to increase fluid consumption.
    Substances such as alcohol and caffeine decrease
    the release of ADH, resulting in increased urine
    output and dehydration.

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Blood Pressure
  • The kidneys regulate blood pressure by regulating
    the amount of fluid in the blood. More fluid
    means higher pressure. The hormone aldosterone,
    acts on the nephrons to increase sodium (salt)
    re-absorption from the distal tubule, back into
    the blood. Chloride ions and water will follow,
    causing the blood volume to increase.
    Aldosterone is secreted by the adrenal cortex,
    just above the kidney. A drop in blood pressure
    is detected by the juxtaglomerular apparatus,
    located near the glomerulus. This causes the
    release of liver proteins, angiotensinogen and
    rennin, which stimulate the release of
    aldosterone from the adrenal gland.
  • http//www.wisc-online.com/objects/AP2204/AP2204.s
    wf

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pH Balance
  • Despite the variety of foods and fluids with
    different pH levels we consume, our bodies
    maintain a relatively constant pH between about
    7.3 and 7.5. A relatively stable pH is
    maintained by a buffer system that absorbs excess
    H ions or basic ions. Bicarbonate ions (HCO3-)
    are key components of this system
  • HCO3- H ?? H2CO3 ?? H2O CO2

30
  • Bicarbonate ions in the blood remove excess H
    ions, but the buffer must be restored for this
    system to continue working indefinitely. The
    kidneys reverse this reaction. Carbon dioxide is
    actively transported from the peritubular
    capillary and combines with water to produce
    HCO3- and H ions. The bicarbonate ion diffuses
    back into the blood and the H ions combine with
    phosphate or ammonia and are excreted in the
    filtrate.
  • The pH balance is mostly controlled by the distal
    tubule of the nephron
  • Acid-Base Balance

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Kidney Dysfunction
  • Diabetes Mellitis is caused by the inadequate
    secretion of insulin from the pancreas. Without
    insulin, blood glucose levels are extremely high,
    and excess glucose remains in the nephron. The
    high osmotic gradient prevents water
    re-absorption and increases urine production.
  • Diabetes Insipidus is caused by inadequate
    production of Anti-Diuretic Hormone (ADH).
    Without ADH, urine input increases dramatically,
    as much as 20 L per day and the patient will be
    extremely thirsty.

33
  • Nephritis Brights Diseases is inflammation
    of the nephrons which can have a variety of
    causes. Protein in the urine is a common symptom
    of nephritis. The osmotic gradient also causes
    an increase in urine production. Nephritis can
    lead to irreversible kidney damage and eventual
    kidney failure.
  • Kidney Stones are caused by
  • the precipitation of mineral solutes
  • form the blood. The stones lodge in the
  • renal pelvis or the ureter, causing major pain
    and bleeding. Stones can be removed by surgery
    or by using ultrasonic waves that blast the
    stones into smaller fragments.

34
  • Dialysis is used for patients whose kidneys no
    longer function properly.
  • Hemodialysis a machine is connected to the
    patients circulatory system by a vein. Blood is
    pumped through a series of tubes submerged in
    solutes that removed waste from the blood.
  • kidney patient guide - Haemodialysis animation
  • Peritoneal Dialysis is done through the lining
    of the abdominal cavity. A catheter tube is
    inserted and solution is fed into the abdominal
    cavity for two to six hours. This fluid collects
    wastes from the body and is drained from the
    catheter when the process is complete.
  • kidney patient guide - How Peritoneal Dialysis
    works animation

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Kidney Transplant
  • kidney patient guide - Kidney Transplant animation
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