Excretory System

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Excretory System
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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.

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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.

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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

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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.
• 0000template2

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Urinary System Anatomy
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• 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"

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• 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
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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

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• 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

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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

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• 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.

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• 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.

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• 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

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• 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.

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• 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.

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• 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