Transcript The Urinary System

The Urinary System
also known as
The Excretory System
Function
Function
- To remove waste products that have
accumulated in blood.
- Maintain the pH of blood at about 7.2
- Produce the hormone erythropoeietin (EPO).
The Urinary System
• Cells produce water and carbon dioxide as byproducts 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.
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.
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.
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.
Structures
Gross Anatomy
Organs
The Urinary System
• The urinary system is composed of the
following organs;
– two kidneys,
– two ureters,
– one urinary bladder and
– one urethra.
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!
The Kidneys
Gross Anatomy of Kidney
Cortex
Medulla
Pelvis
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.
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
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
Excretion of Cellular Waste
The main metabolic waste products all
have nitrogen as a major component.
- Urea
- Uric Acid
- Creatinine
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
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
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 20–25% of the total arterial blood
pumped by the heart.
– Each contains from one to two million
nephrons.
The Ureters
The Urinary Bladder
The Urethra
Micturition Reflex
• This animation shows how urination,
medically referred to as micturition, is
accomplished.
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter27/animati
on__micturition_reflex.html
Microanatomy
Microscopic Structures
The Nephron
Structure
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…
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
The Nephron
Each nephron consists of five parts:
- Bowman’s Capsule and Glomerulus
- Proximal Convoluted Tubule
- Loop of Henle
(ascending & descending)
- Distal Convoluted Tubule
- Collecting Duct
The Nephron
The Nephron
Kidney to Nephron
The Nephron
The Nephron
Function
The Nephron
•
Filtration begins in the glomerulus of
Bowman’s capsule.
•
Blood enters Bowman’s 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
The Nephron
•
The fluid in Bowman’s 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.
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
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.
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.
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
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
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
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.
Control of Urine
Output
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.
Kidneys & Blood pH
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.
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
Blood pH
•
H+ + HCO31-
•
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.
•
H2CO3
H2O + CO2
Diseases of the
Excretory System
Diseases
Some diseases of the Excretory System are…
•
•
•
•
•
Gout
Kidney stones
Urinary Tract Infections (UTI)
Diabetes insipidus
Liddle’s syndrome
(the following descriptions come from Wikipedia)
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.
Gout
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?v=YevE6rYV2MA
http://www.youtube.com/watch?v=4UM90RxVbno&NR=1
Kidney Stones
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.
UTI
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.
Diabetes insipidus
Liddle’s 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).
Liddle’s syndrome
The Excretory System
also known as
The Urinary System
THE END