Download Excretory System PPT File

2A.6 EXCRETION
This is explained well in your
textbooks – and the diagrams in here
are great too
So make sure to read through the
Chapter & make your own notes!!
Excretion
There are many chemical reactions taking place in
the body – these produce by-products, some of
which are able to be used by the body, while others
are wastes.
Most wastes are toxic and would be harmful if
allowed to accumulate.
The removal of metabolic wastes from the body is
called Excretion
Removing wastes also allows the body to maintain
equilibrium within the body (this is called
Homeostasis)
Organs of Excretion
• Kidneys – filter blood to
maintain a constant
concentration of materials in
the body fluids, excrete/remove
nitrogenous wastes like urea,
uric acid & creatinine
• Liver – deamination &
synthesis of urea
• Lungs – CO2
• Skin – sweat glands secrete
sweat (contains salts, urea &
lactic acid)
Kidney
Objectives:
• Label the components of the Urinary system &
relationship with the CV system
• Label structures of a kidney (cut-in half)
• Label the nephron (the microscopic structure)
• Explain the kidney’s function in relation to the
nephron
– filtration & selective reabsorption to form urine)
• Use a table to show the composition of blood
plasma & urine = to assess the kidney’s ability to
filter & reabsorb some substances and let others
pass out.
Functions of the kidneys
To rid the body of wastes,
especially nitrogenous wastes
such as urea.
To regulate the balance of
fluid, salt and pH.
Functions of the kidneys
They achieve these outcomes by
filtering the blood as it passes
through the kidneys.
Waste substances are removed by
the processes of filtration and
tubular secretion.
Useful substances are returned to
the body by the process of selective
reabsorption.
Structure
The major structural components
of the urinary system are:
Kidneys x2
Urinary bladder x1
Ureters x2
Urethra x1
Components of the urinary
system & the kidney (external)
US Govt - NIH
What is the function of the….
Bladder?
Ureters?
Urethra?
Frontal section through the
kidney (*need to know)
Renal artery
supplies
blood to
kidney
Renal vein
takes blood
away from
kidney
US Govt - NIH
Nephron*
• The functional (microscopic) unit of
the kidneys is the nephron.
• A nephron consists of a Bowman’s
capsule, a renal tubule and their
associated blood supply.
• Each kidney contains approximately
one million nephrons.
The renal tubule (*need to know
how to label)
Bowman’s capsule
Proximal
convolute
tubule
(PCT)
Common
collecting duct
Distal convolute
tubule (DCT)
Loop of Henle (LOH)
Processes that occur in the
production of urine
1. Filtration
2. Reabsorption (some is selective)
3. Tubular secretion
(explained well in textbook – and there is a
summary table as well!)
The renal corpuscle
Filtration takes place in the renal
corpuscle.
the renal corpuscle consists of the
Bowman’s capsule and a mass of
blood capillaries – the glomerulus.
The renal corpuscle
Afferent
arteriole (blood
coming in)
Bowman’s
capsule
Efferent arteriole
(blood leaving)
Glomerulus
Proximal
convolute
tubule
1. Filtration
Urea
Water,
Glucose
Amino acids
Vitamins
Salts (mainly
sodium & chlorine)
Filtration
Process
Structure
Filtration
Renal
corpuscle
Substance
Active or
passive
Filtrate
Water
Urea, Glucose,
Amino acids,
Vitamins, Salts
(mainly sodium
& chlorine
Passive
(mass flow)
Passive
2. Reabsorption
Water, Glucose,
Amino acids,
Vitamins, Salts
(mainly sodium
& chlorine)
Water
Salts (mainly
sodium & chlorine)
Urine
- Water
- Urea
- Salts
The proximal tubule
• Microvilli line the
proximal tubule
and create a
brush border,
which greatly
increases the
surface area for
reabsorption.
Microvilli
L Slomianka ANHB - UWA
Reabsorption
Structure
PCT
Loop of
Henle
DCT
Collecting
duct
Substance
Active/passive
Water (60-70%)
Salts (60-70%)
Glucose (100%)
Amino acids (100%)
Vitamins (100%)
Water (25%)
Na+/Cl- (25%)
Water (5%)
Na+/Cl- (5%)
Passive (osmosis)
Water (5%)
Passive (osmosis)
All active
Passive (osmosis)
Active
Passive (osmosis)
Active
3. Tubular secretion
H+
NH4+ (ammonium)
Creatinine
Toxins
Drugs
Neurotransmitters
Tubular secretion
Process
Tubular
secretion
Structure
PCT
&
DCT
Substance
Mode
H+
Active
NH4+ (ammonium)
Creatinine
Toxins
Drugs
Neurotransmitters
So, why is it well suited to its function?
• Glomerular capsule surrounds the glomerulus to
collect the fluid filtered out of the blood capillaries
• The efferent arteriole leading out of the glomerulus
has a smaller diameter – raising blood pressure – so
that more fluid is filtered
• The tubule has two sets of convolutions (PCT, DCT)
and a loop so that each tubule has a large surface
area for reabsorption and secretion
• Each kidney has over a million nephrons so the total
surface area available for reabsorption and secretion
is extremely large
Urine
• Urine is a clear, transparent fluid. It
normally has an amber colour (to
presence of some bile pigments).
• It is collected in the bladder and
eliminated through the urethra.
• The average amount of urine
voided (passed) in 24 hours is
about 1.5 litres (varies with diet,
environment etc)
Composition of urine
• The composition of urine varies (usually
due to diet/water intake)
• Typically, urine contains:
– approx. 95% water
– approx 5% other solutes (incl. organic
molecules such as urea, creatinine and uric
acid), ions (mainly sodium & chloride ions)
and other metabolic wastes.
– There should be no blood cells in urine (too
large to pass through glomerulus)
– It does not normally contain proteins and
glucose
Terms
•
•
•
•
Fluid intake
Urine output
Total Volume
Concentration (concentrated or dilute)
Impacts
• If water intake is low, urine is very
concentrated. (opposite = diluted)
• Sleeping – kidney function slows down at
night – so less urine produced (and
therefore higher concentration in the
morning)
• If blood cells present in urine – could be
sign of infection or disease (should not be
present)
• Alcohol – increases urine output
• Read Kidney Failure and Kidney Dialysis
(in textbook)