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EXCRETORY
SYSTEM
What is Excretion?
The process of ridding the body of waste in
order to maintain homeostasis.
Excretory System
How does the excretory
system maintain
homeostasis?
–It regulates heat, water, salt,
acid-base concentrations and
metabolite concentrations
ORGANS OF EXCRETION
Skin and associated glands:
– sweat is removed by skin as a waste
product trying to Remove heat and salts
Lungs: Removes carbon dioxide
Liver:
– get rid of unneeded wastes in the body. It changes toxic
ammonia, which is a poisonous gas , to urea, a harmless
fluid.
Kidneys; removes nitrogenous waste (urea)
What is the Function of the Human
Excretory System?
Maintain proper water balance in the body and to
also remove liquid waste (urine)
Kidneys filter approximately200L of blood or
filtrate everyday
Remove approximately 1-2 L of fluid everyday
Parts of the human excretory System
Kidneys
Ureters
Urinary bladder
urethra
Urinary System
Kidneys
Kidneys:
– filter blood to produce urine.. Maintain
water balance and rid body of nitrogenous
waste (urine) created by the liver
The kidney is a lima bean shaped
structure found on both sides of the
spinal column in the lower back
The Kidney
KIDNEY PARTS
Kidney has three distinct regions
Cortex:
– the outer part
– Function: filter blood
Medulla:
– the middle part made up of collecting ducts
– Function: collect filtrate (filtered materials from the
blood) and carries it to the renal pelvis
Pelvis:
– the inner cavity where urine collects. It is connected to
the ureters
– Function: Filtrate (now called urine) drains from the
pelvis into the ureters for removal
MAJOR FUNCTIONS
OF KIDNEYS
1. Filters blood of:
 Urea – formed in the liver from the
breakdown of ammonia
 Creatinine – formed in the muscles
 Uric Acid – formed as a result of the
breakdown of nucleic acids (DNA and
RNA)
2. Controls the balance of
water in our bodies
3. Regulates pH of the blood
4. Regulates the
concentration of dissolved
ions in the blood
5. Secretes a hormone that
causes a production of red
blood cells
6. Activates Vitamin D
production in the skin
Parts of Excretory system
cont’d
Urinary Bladder:
– hollow muscular pouch located in the pelvis
– Function: hold urine until it is released from the body. A
typical bladder is able to hold up to about 500ml of
urine.
Urethra:
– hollow tube leading from the bladder to the outside of the human
body
– function: carries urine from the bladder to the outside of the body.
Ureters:
– hollow tubes connecting the renal pelvis to the urinary bladder
– Function: carry urine from the kidney to the urinary bladder
IMPORTANT BLOOD
VESSELS
Renal Artery: carries
contaminated blood into the
kidney.
Renal Vein: carries purified
blood from the kidney and
returns it back into circulation by
way of the inferior vena cava.
NEPHRONS
Tiny filtering units called nephrons fill the
cortex and medulla of the kidney.
Basic functional unit of kidney responsible
for filtering the blood and maintaining proper
water balance
Extends from renal cortex (glomerulus/
Bowman's capsule) into the renal medulla
(loop of Henle)
Each kidney contains 1 to 1.25 million
nephrons.
Parts of the Nephron
Renal artery:
– this is the artery that carries blood TO the kidney to be filtered
Renal vein:
– this is the vein that carries blood FROM the kidney AFTER it has been filtered
Glomerulus;
– A tight ball of blood capillaries located in the Bowman's capsule of Nephron.
– Blood pressure created here causes material to be filtered from the blood
Bowman's capsule:
– A cup shaped structure that receives filtrate from the Glomerulus
Proximal tubule:
– tube connected to the Bowman's capsule.
– Filtrate enters the proximal tube from the Bowman's capsule.
– Reabsorption of Amino Acids and Glucose occurs here
Loop of henle:
– long u shaped tube that extends into the renal medulla.
Responsible for maintain salt balance by reabsorption or releasing
salt in the filtrarte
Distal tubule;
– tube extending from the loop of henle.
– It also reabsorbs materials from the filtrarte . Tubular secretions
occurs here. Materials such as creatinine and drugs are added to
the filtrate
Collecting tubule:
– tube that extends from the distal tubule to the renal pelvis. This
portion of the nephron is mainly responsible for reabsorption of
water
Nephron Function (4 stages)
1. Filtration:
Blood travels from the renal
artery, to an arteriole and then
into the glomerulus, a mass of
capillaries surrounded by the
Bowman’s capsule.
Blood pressure forces some
plasma of the blood, containing
both waste and useful material,
into the Bowman’s capsule.
This material is called the
nephric filtrate.
The filtrate contains such
things as: water, urea, uric
acid, salt, glucose, amino
acids, ions and vitamins.
1. Filtration
Filtration – Hydrostatic pressure (blood pressure)
forces
water and dissolved substances out of the
glomerular blood into Bowman’s capsule.
H2O, glucose, amino acids, electrolytes, wastes
Averages 125 ml/min for both kidneys
Æ180 liters/day
The vast majority of the filtrate must be taken
back
2. Re-absorption:
From the Bowman’s capsule
the filtrate is pushed into the
proximal tubule. The process of
re-absorption, of useful
materials within the filtrate, into
the capillary network that
surrounds the nephron than
begins.
Reabsorption occurs by
osmosis, diffusion, and active
transport
Reabsorbed materials include
water, glucose, amino acids,
ions and vitamins
When the filtrate reaches the
end of the distal tubule the
solution is isotonic (the filtrate
and the surrounding cells have
the same concentration of water
and solutes).
The filtrate then moves down
the descending loop of Henle;
as the loop descends further
into the inner medulla, sodium
concentrations in the
surrounding tissue increase
which draws water out of the
filtrate (by osmosis).
At the bottom of the loop
sodium ions in the filtrate are
at high concentration and
therefore diffuse out of the
tubule.
Positive sodium ions are
followed by negative chloride
ions
Water cannot reenter the
ascending loop because this
loop is impermeable to water
H2O - osmosis
NaCl - active transport
Glucose, amino acids - active co-transport
3. Secretion
Occurs in the distal tubule
Involves active transport of
substances from the capillaries
into the tubule
Substances include hydrogen
ions, creatinine and drugs
4. Elimination
The fluid than enters the
collecting duct as urine. It passes
through the pelvis into the ureter.
Most of the water, ions and useful
nutrients (glucose, amino acids)
have been reabsorbed.
Path of filtrate through
nephron:
Bowman’s capsule - proximal tubule
- loop of Henle - distal tubule collecting duct
Control of Water Balance
When water levels are too low:
1) The hypothalamus stimulates
the pituitary gland to secrete a
hormone called anti-diuretic
hormone (ADH) or
Vasopressin. ADH travels
through blood to kidneys.
2) ADH increases the
permeability of the tubules
and collecting ducts
3) More water is reabsorbed
into the blood so the urine
is more concentrated
When water levels are too high:
1)Hypothalamus doesn’t stimulate
ADH secretion
2)Little water is reabsorbed into the
blood so the urine is more dilute.
Other
Aldosterone: affects distal tubule and collecting
tubule to reabsorb sodium ions
ANP( atrial natruuretic peptide: increase
glomerulus filtration rate by dilating the arterioles
and inhibits the collecting ducts from reabsorbing
sodum.
Excretory System Disoders
These are problems associated with the kidneys,
bladder , or ureters
We will examine the following disorders:
– 1. Urinary tract Infections
• Cystitus
• Ureyhritis
• Pyelonephritis
– 2. Kidney stones
– 3. Kidney Failure
Urinary Tract Infections UTI’s
These are Bacterial Infections of the kidneys,
bladder or Urethra
There are 3 types of UTI’s
– 1. Cystitis- infection of the bladder
– 2. Urethritis- infection of the urethra (tube leading
from the bladder to the outside of the body)
– 3. Pyelonephritis- infection of the kidney
Causes of UTI’s
Bacteria from the anus (females
Blocked prostate (men)
Bacterial infection from other areas of the body
Note: UTI’s are more common in females
than males
Symptoms of UTI’s
Painful urination
Burning sensation
Bloody or brown urine
Chills, fever, nausea
Danger and Treatments
Danger of UTI’s
– Permanent damage to the kidneys and possible
kidney failure.
Treatments of UTI’s
– antibiotics
2. Kidney Stones
What are Kidney Stones?
– These are hard crystals of calcium oxalate or uric
acid that foem in the kidney bladder or ureter/urethra
– Kidney stones form when materials in the urine
solidify
– Kidney stones are more common in men than
women
Causes of Kidney Stones?
Urinary tract infections
Not drinking enough water
Too much vitamin C and D
Symptoms of Kidney Stones
Severe pain in abdomen and back
Blood in urine
Nausea
vomiting
Treatments of Kidney Stones
Change diet
Drink lots of water
Ultrasound( breaks them up so they can pass)
called lithotripsy
Surgery (open)
Incision through the back (nephrolithotomy
Insertion of thin telescopic instrument into
urinary tract( ureteroscopsy)
Kidney Failure
When the kidneys are not working correctly,
waste products and excess fluid can build up
and the levels of sodium, potassium, phosphate
and calcium are not regulated correctly.
symptoms of kidney disease, which can include
high blood pressure,
excessive tiredness,
fluid retention and
possibly lower back pain.
Causes
Kidney damage can occur for a number of reasons
diabetes,
high blood pressure,
infections and a group of diseases that affect the
glomerulus.
The kidneys also need an adequate supply of blood,
so if there is something wrong with the blood vessels
to the kidney, such as a narrowing, this will prevent
the kidneys from working efficiently.
Treatments
dialysis
– cleans and filters your blood using a machine to temporarily
rid your body of harmful wastes, extra salt, and extra water.
Hemodialysis helps control blood pressure and helps your
body keep the proper balance of important chemicals such as
potassium, sodium, calcium, and bicarbonate.
– Dialysis can replace part of the function of your kidneys. Diet,
medications, and fluid limits are often needed as well. Your
diet, fluids, and the number of medications you need will
depend on which treatment you choose.
Kidney transplantation
– surgically places a healthy kidney from another
person into your body. The donated kidney does
enough of the work that your two failed kidneys used
to do to keep you healthy and symptom free.