The Urinary System also known as The Excretory System

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The Urinary Systemalso known asThe Excretory
System
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Function
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Function
- To remove waste products that have
accumulated in blood. - Maintain the pH of
blood at about 7.2 - Produce the hormone
erythropoeietin (EPO).
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The Urinary System

• Cells produce water and carbon dioxide as
  by-products of metabolic breakdown of sugars,
  fats, and proteins.
• Chemical groups such as nitrogen, sulfur, and
  phosphorous must be stripped from the large
  molecules, to which they were formerly attached,
  as part of preparing them for energy conversion.

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The Urinary System

• The continuous production of metabolic wastes
  establishes a steep concentration gradient across
  the plasma membrane causing wastes to diffuse out
  of cells and into the extracellular fluid (ECF)
  also known as interstitial fluid.

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The Urinary System

• Multicellular organisms, and animals in
  particular, must have a specialized organ system
  to concentrate and remove wastes from the
  interstitial fluid into the blood capillaries and
  eventually deposit that material at a collection
  point for removal entirely from the body.
• In animals, it is the job of the kidneys to do
  this.

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Homeostatic Functions

• In addition to filtering blood to remove toxic
  waste products, the kidneys also control water
  balance, pH, and levels of sodium, potassium,
  bicarbonate, and calcium ions in the blood.
• They also secrete a hormone (erythropoietin
  EPO) that stimulates red blood cell production
  and activate vitamin D production in the skin.

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Structures
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Gross Anatomy
Organs
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The Urinary System

• The urinary system is composed of the following
  organs
• two kidneys,
• two ureters,
• one urinary bladder and
• one urethra.

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Gross Anatomy

• The following is a series of cross sections
  through a human cadaver showing the placement of
  organs in the body.
• Look for the excretory system organs!

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The Kidneys
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Gross Anatomy of Kidney
Cortex
Medulla
Pelvis
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Gross Anatomy of Kidney
FEATURE CHARACTERISTICS
Kidney Capsule Thin connective tissue sheath surrounding kidney.
Cortex Outer region of kidney that surrounds medulla and contains specific nephron segments.
Medulla Inner region of the kidney, surrounded by cortex, and containing specific nephron segments.
Hilus Point of entry in kidney for ureter, renal artery, and renal vein.
Ureter Thin walled tube, ensheathed in smooth muscle, that acts ast he conduit for urine to the bladder.
Renal Pelvis Cavity in center of kidney where newly-formed urine collects before entering the ureter.
Nephron Functional unit of the kidney. There are 1 million nephrons in each kidney that function independently of one another.
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Major Functions of Kidney

• Ion regulation and osmoregulation
• - regulation of salt and water balance
• - ensure body maintains proper fluid volume
  composition of the ECF
• Waste management
• - excretion of metabolic wastes and blood borne
  foreign chemicals
• Hormone production
• - function as endocrine glands producing and
  releasing hormones such as vitamin D

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The Kidney

• Humans have two fist sized kidneys located in the
  lower back on either side of the spine
• Kidneys release their waste product (urine) into
  tubes called ureters
• Ureters carry urine to the urinary bladder where
  it is temporarily stored
• Drainage from the bladder is controlled by
  sphincters
• Urine exits the bladder through a tube called the
  urethra

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Excretion of Cellular Waste

• The main metabolic waste products all have
  nitrogen as a major component.
• - Urea
• - Uric Acid
• - Creatinine

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Urea

• Produced in the liver from the breakdown of
  excess amino acids that are the building blocks
  of proteins
• Amine group (NH2) is removed to release the rest
  of the amino acid molecule which can then be
  converted into carbohydrates or fats
• The amine group can combine with a hydrogen ion
  to form toxic ammonia
• Ammonia is transformed in the liver into less
  toxic urea before being released into the
  bloodstream

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Uric Acid and Creatinine

• Uric Acid is usually produced by the breakdown of
  nucleic acids such as DNA and RNA
• Creatinine is a waste product of muscle action

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The Kidney

• The human kidneys
• are two bean-shaped organs, one on each side of
  the backbone.
• Represent about 0.5 of the total weight of the
  body,
• but receive 2025 of the total arterial blood
  pumped by the heart.
• Each contains from one to two million nephrons.

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The Ureters
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The Urinary Bladder
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The Urethra
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Micturition Reflex

• This animation shows how urination, medically
  referred to as micturition, is accomplished.

http//highered.mcgraw-hill.com/sites/0072495855/s
tudent_view0/chapter27/animation__micturition_refl
ex.html
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Microanatomy
Microscopic Structures
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The Nephron
Structure
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Nephrons

• The kidney is composed of one million to two
  million nephrons.
• It is in the nephrons that the blood is cleaned
  of its waste products
• Water, minerals, uric acid, glucose, protein,
  lipids, bilirubin (breakdown product of
  erythrocytes), alkaline phosphatase, etc

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The Nephron

• The tubes of the nephron are surrounded by cells,
  and a network of blood vessels spreads throughout
  the tissue
• By controlling what enters or leaves the
  nephrons, the kidneys keep the levels of water,
  ions, and other materials in our body fluids
  relatively constant

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The Nephron

• Each nephron consists of five parts
• - Bowmans Capsule and Glomerulus
• - Proximal Convoluted Tubule
• - Loop of Henle
• (ascending descending)
• - Distal Convoluted Tubule
• - Collecting Duct

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The Nephron
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The Nephron
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Kidney to Nephron
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The Nephron
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The Nephron
Function
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The Nephron

• Filtration begins in the glomerulus of Bowmans
  capsule.
• Blood enters Bowmans Capsule through a tiny
  artery that branches to form a network of thin
  walled capillaries called the glomerulus
• Under the influence of blood pressure, some blood
  plasma small particles are forced out of the
  capillaries into the surrounding capsule
• Larger blood components remain in the capillaries

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The Nephron

• The fluid in Bowmans capsule is called the
  nephric filtrate and is pushed into the
  proximal tubule
• Nephric filtrate is simply blood plasma, minus
  almost all of the plasma proteins.
• Essentially it is no different from interstitial
  fluid (the fluid that floats between the cells of
  our tissues) also known as extra cellular fluid
  (ECF).
• Approximately 180L of filtrate is made per day
  125mL/min.

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The Nephron

• Reabsorption begins in the proximal tubule
• Reabsorption is the process by which materials
  required by the body are removed from the nephric
  filtrate and returned to the bloodstream
• Both active and passive transport mechanisms draw
  water, glucose, amino acids, and ions from the
  filtrate into surrounding cells
• The lining of the proximal tubule is covered with
  tiny projections to increase the surface area for
  reabsorption
• When the filtrate reaches the end of the proximal
  tubule, the fluid is isotonic with the
  surrounding cells

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The Nephron

• The filtrate now moves into the Loop of Henle
  which acts to remove water from the filtrate by
  the process of osmosis
• Its descending limb is permeable to water but
  completely impermeable to salt.
• As the filtrate descends deeper into the
  hypertonic interstitium of the renal medulla,
  water flows freely out of the descending limb by
  osmosis until the tonicity of the filtrate and
  interstitium equilibrate.
• Longer descending limbs allow more time for water
  to flow out of the filtrate, so longer limbs make
  the filtrate more hypertonic than shorter limbs.

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The Nephron

• Unlike the descending limb, the ascending limb of
  Henle's loop is impermeable to water, a critical
  feature of the countercurrent exchange mechanism
  employed by the loop.
• The ascending limb actively pumps sodium out of
  the filtrate, generating the hypertonic
  interstitium that drives countercurrent exchange.
• In passing through the ascending limb, the
  filtrate grows hypotonic since it has lost much
  of its sodium content. This hypotonic filtrate is
  passed to the distal convoluted tubule in the
  renal cortex.

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The Nephron

• Chloride ions follow the sodium ions because of
  electrical attraction
• Also, as the water concentration in the filtrate
  decreases, the chloride ion concentration in the
  filtrate increases
• This results in the diffusion of even more
  chloride ions out of the ascending loop

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The Nephron

• Secretion begins in the distal convoluted tubule.
• It is the release by active transport of
  substances into the filtrate. It is accomplished
  by the tubular lining cells.
• It is done for three purposes
• Removal of toxins, vitamins, hormones and drugs.
• Electrolyte balance.
• Acid-base balance

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The Nephron

• The fluid from a number of nephrons moves from
  the distal tubules into a common collecting duct
• The permeability of the distal tubule and
  collecting duct is under hormonal control
• Antidiuretic hormone (ADH) is secreted by the
  anterior pituitary gland and increases the
  permeability of the distal tubule and collecting
  duct
• ADH allows more water to be removed from the
  filtrate when the body needs to conserve water

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The Nephron

• By the time the filtrate comes to the end of the
  distal tubule, 99 of the water (180 L per day)
  and nearly 100 of the glucose have been
  reabsorbed.
• The filtrate now goes to the collecting tube
  where it is now called urine.

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Control of Urine Output
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Urine Output

• The permeability of the distal and collecting
  tubes is controlled by a hormone called
  anti-diuretic hormone (ADH) also known as
  vasopressin.
• When it enters the kidney, ADH makes the walls of
  the renal tubules and collecting ducts more
  permeable to water, so that more water is
  reabsorbed into the bloodstream. Less urine is
  formed, more water is retained.
• Alcohol and caffeine block the release of ADH
  leading to low permeability and therefore
  increased urine production.

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Kidneys Blood pH
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Blood pH

• Blood pH should be around 7.4.
• This is maintained by active transport of H out
  of the blood into the nephric filtrate.
• Urine pH can vary from 4.5 to 8.0 normal urine
  pH is 6.0.

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Blood pH

• Respiratory system works together with kidney to
  control blood pH.
• There are buffers in our blood that control blood
  pH.
• H HCO31- H2CO3 H2O CO2

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Blood pH

• H HCO31- H2CO3 H2O CO2
• Breathing rate will affect the equilibria of the
  reactions above.
• High rate of breathing will shift reactions to
  the right and increase pH.
• Low rate of breathing will shift reactions to the
  left and increase pH.

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Diseases of the Excretory System
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Diseases

• Some diseases of the Excretory System are
• Gout
• Kidney stones
• Urinary Tract Infections (UTI)
• Diabetes insipidus
• Liddles syndrome
• (the following descriptions come from Wikipedia)

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Gout (also called metabolic arthritis) is a
disease due to an inborn disorder of the uric
acid metabolism. In this condition monosodium
urate crystals are deposited on the articular
cartilage of joints and in the particular tissue
like tendons. This provokes an inflammatory
reaction of these tissues. These deposits often
increase in size and burst through the skin to
form sinuses discharging a chalky white
material. Normally, the human bloodstream only
carries small amounts of uric acid. However, if
the blood has an elevated concentration of uric
acid, uric acid crystals are deposited in the
cartilage and tissue surrounding joints. Elevated
blood levels of uric acid can also result in uric
kidney stones.
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Gout
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Kidney stones, also known as nephrolithiasis,
urolithiasis or renal calculi, are solid
concretions (crystal aggregations) of dissolved
minerals in urine found inside the kidneys or
ureters. They vary in size from as small as a
grain of sand to as large as a grapefruit. Kidney
stones typically leave the body in the urine
stream if they grow relatively large before
passing (on the order of at least 2-3
millimeters), obstruction of a ureter and
distention with urine can cause severe pain most
commonly felt in the flank, lower abdomen and
groin. Such pain, called renal colic, often comes
in waves and can be particularly severe. Nausea
is associated with this particular pain primarily
due to the embyrological association of the
kidneys and the intestinal tract. Recurrence
rates are estimated at about 10 per year. Kidney
stones are totally unrelated to gallstones.
http//www.youtube.com/watch?vYevE6rYV2MA http//
www.youtube.com/watch?v4UM90RxVbnoNR1
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Kidney Stones
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A urinary tract infection (UTI) is a bacterial
infection that affects any part of the urinary
tract. Although urine contains a variety of
fluids, salts, and waste products, it usually
does not have bacteria in it. When bacteria get
into the bladder or kidney and multiply in the
urine, they cause a UTI. The most common type of
UTI is a bladder infection which is also often
called cystitis. Another kind of UTI is a kidney
infection, known as pyelonephritis, and is much
more serious. Although they cause discomfort,
urinary tract infections are usually quickly and
easily treated by seeing a doctor promptly.
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UTI
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Diabetes insipidus (DI) is a disease
characterized by excretion of large amounts of
severely diluted urine, which cannot be reduced
when fluid intake is reduced. It denotes
inability of the kidney to concentrate urine. DI
is caused by a deficiency of antidiuretic hormone
(ADH), or by an insensitivity of the kidneys to
that hormone.
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Diabetes insipidus
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Liddles syndrome is caused by a single mutant
allele (therefore the syndrome is inherited as a
dominant trait) encoding the aldosterone-activated
sodium channel in the collecting tubules. The
defective channel is always "on" so too much Na
is reabsorbed and too little is excreted. Where
Na goes, water goes. The resulting elevated
osmotic pressure of the blood produces
hypertension (high blood pressure).
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Liddles syndrome
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The Excretory Systemalso known asThe Urinary
SystemTHE END