Transcript Excretion - Salisbury Composite High School

Excretion
The process by which the body
rids itself of metabolic wastes
1.
2.
Lungs eliminate carbon dioxide
Large intestine eliminates toxic
digestive waste
3. Liver deaminates amino acids to
form ammonia (NH3)
-Ammonia is toxic so it is converted into
urea.
-Nucleic acids break down into uric
acid.
4. Kidneys-remove urea and uric acid
The Urinary System
Two kidneys
 Ureters – tubes
from kidney to
bladder
 Bladder – stores
urine
 Urethra – from
bladder to exterior

The Kidneys


Function: to remove
metabolic wastes
from blood
Also regulate pH
and water balance
of blood
The Nephron

Microscopic
filters – 1
million in
each kidney!
Each kidney has 3 regions:
1)
Cortex – outermost

Contains most parts of
nephrons
2) The medulla:
middle region

Contains loops of
Henle, collecting
ducts of nephrons
3) The renal pelvis:
the mostly hollow
innermost region

Collecting ducts
merge to form
ureter
The Urinary System


Ureters have
muscular walls –
peristalsis
About 25 cm
long
The Urinary System

The urinary
bladder – holds
up to 600 mL
Urinary System

Urethra is longer
in males (20 cm
vs. 4 cm)– thus
less infections
get to bladder
The Urinary System


Micturition: the voluntary
release of sphincters
controlling the urine
output from bladder
Also aided by contraction
of bladder wall
Formation of Urine


done by the nephrons
three stages: filtration, absorption and
secretion.
Filtration


High blood pressure in the glomerulus
forces small molecules out of the
blood and into Bowman’s Capsule
Water, ions like Na+, Cl- and H+,
amino acids, urea and glucose can
pass into Bowman’s capsule
Filtration


Red blood cells, white blood cells and
platelets can not move into Bowman’s
capsule.
(If they do it is a sign that something
is wrong.)
Filtration


About 45 gallons (180 L ) per day
passes through Bowman’s capsule.
But only 1-2 L of urine is formed so
what happens next?
Reabsorption



Essential nutrients and water are
reabsorbed into the blood stream and
distributed to the body.
main site: proximal convoluted
tubule
also occurs in the loop of Henle, distal
tubule and collecting ducts
Reabsorption



Na+ is moved back into the blood by
active transport- requires energy
Negative ions like Cl- will follow the
Na+ due to charge attraction
Glucose and amino acids are also
reabsorbed by active transport
Active transport may form vesicles
Reabsorption

The movement of solutes back into
the blood creates an osmotic gradient
so that water also moves into the
blood by osmosis.
Secretion
Secretion – actively transporting
materials back into urine from the
blood.
Ex) nitrogenous waste, water

Occurs in the proximal and distal
tubules.
Secretion

Proximal tubule
secretes H+ which
helps maintain pH
balance

Blood is neutral
and H+ makes it
acidic so it must
be removed.
Secretion

Other things secreted
include ammonia,
potassium ions,
penicillin, histamines,
creatine, etc.
Penicillin capsules
Histamine release from a WBC
Hormonal Control
1) Aldosterone is
secreted from
the cortex of the
adrenal glands
when blood
pressure is low.
Hormonal Control

Low B.P is
monitored by
kidneys
(juxtaglomerular
complex)
Hormonal Control
Aldosterone
causes the DCT
and collecting
ducts to increase
Na+ transport
into blood
 Chloride ions and
water follow
passively

Hormonal Control

Net result: Blood pressure increases
and urine output decreases
Hormonal Control
2) Antidiuretic
Hormone (ADH)
 Produced by
hypothalamus,
stored in posterior
pituitary gland
Hormonal Control


Hypothalamus
monitors water
content of blood
(osmoreceptors)
When the body is
dehydrated, ADH
is released.
Hormonal Control



ADH makes the nephron more
permeable to water so more water is
reabsorbed into the blood.
As a result, the urine becomes more
concentrated.
When the body is well hydrated, the
hypothalamus does not release ADH


Diuretics like alcohol and caffeine
inhibit ADH production
So urine output increases
Diabetes Mellitis


inadequate secretion of insulin
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.
Sugar is found in the urine
Diabetes Insipidus



lack of ADH
production
urine output
increases up to
20L/day
no sugar in urine
Nephritis
inflammation of the nephrons
 Protein in the urine is a common
symptom
 The osmotic gradient also causes an
increase in urine production.
 Nephritis can lead to irreversible
kidney damage and eventual kidney
failure.

Dialysis
Hemodialysis
 Artificial kidney
machine connects
to a vein and
pumps blood
through
semipermeable
tubes submerged
in a solution to
remove waste
Dialysis
Peritoneal
dialysis-a
catheter is
inserted through
abdominal lining.
 Fluid is injected
to collect waste
and is drained

Kidney Stones
Crystallized oxalic
acid and/or
calcium and/or
phosphate
 Painful!

Kidney Stones
Treatment:
 Surgical removal
 Drugs to dissolve
 Lithotripsy-shock
waves
Kidney Transplant

In 2002 there
were 48
transplants done
in Edmonton.