Transcript water - naturalsciencesekcat

Excretory system –
Urinary system
Water and Waste
Water Balance
• 3 Ways we gain water:
• Drinking
• Food
• Chemical Reactions
Water Balance
4 Ways we lose water:
Sweat
Breath
Urine
Faeces
Maintenance of water balance
• To maintain water balance, water gain
must be equal to water loss.
• About 70% human body made up of water
• Kidneys regulate the water content of
body
Water balance
Water Gain
• 2150 ml in drink &
food
• 250 ml from chemical
reactions
• 2500 ml = total
gain
Water loss
• 500 ml in sweat
• 400ml in breath
• 1500 ml in urine
• 100ml in faeces
• 2500 ml = total
loss
Maintenance of water balance
If large volume water consumed, kidneys
produce large volume of urine
If small volume water consumed, kidneys
produce small volume of urine
Role of ADH
Anti-diuretic hormone
The kidneys are controlled by ADH
ADH is released by pituitary gland and
controls the volume of water reabsorbed &
returned to bloodstream by the kidneys
The kidneys
Blood is brought to the kidney in the
renal artery. The kidneys filter the blood
and then reabsorb useful materials such
as glucose. After it has been purified the
blood returns to the circulation through
the renal vein.
Urine is taken from the kidneys to the
bladder by the ureters. The bladder
stores the urine until it is convenient to
expel it from the body. The main waste
product removed in the urine is urea.
Urea is a waste product produced in the
liver when surplus amino acids are
broken down to be used for energy. It is
released into the bloodstream until it is
filtered out and removed by the kidney.
Waste Disposal
 Many harmful wastes such as urea are produced in
the body, following chemical reactions
 Urea is a poisonous nitrogenous waste made in liver
by breakdown of excess amino acids
 Urea passes from liver to blood & transported to
kidney where it is removed during filtration
 Urea dissolved in excess water forms urine and
passes to the bladder
The Kidney
Filtration & Absorption
• The renal artery containing unpurified blood
enters a kidney & divides into many tiny
branches
• The blood in each is filtered by a special filtering
unit (nephron)
• Useful substances are reabsorbed in blood
vessels which unite to leave kidney as renal vein
(contains purified blood)
Nephron
• Each filtering unit in a kidney
• Consists of cup-shaped Bowman’s capsule
leading into long tubule
• The renal artery supplying each kidney with
blood divides into about a million tiny branches,
each of which leads to a glomerulus
• The glomerulus is a tiny knot of blood capillaries
surrounding a Bowman’s capsule
NEPHRON DIAGRAM
From renal
artery
Glomerulus
Bowman’s capsule
•Water
•Glucose
•Urea
all filtered
out.
Collecting
duct
GLUCOSE
reabsorbed.
WATER
reabsorbed.
Urea +
excess
water
to renal
vein
To the URETER
The Nephron
What is urine?
• Excretion from the body
• Mainly consists of
– UREA
– Excess salt
– Water
• Sterile
Urine production
• Plasma fluid filters out through pores in the
capillary walls & collects in Bowman’s capsule
• This glomerular filtrate contains glucose, salts,
urea & water
• As it passes though kidney tubule, useful
substances are reabsorbed into capillaries
surrounding tubule
• Further water is reabsorbed from liquid flowing
down collecting duct
Urine production
Is so effective 99% water originally present in
glomerular filtrate is reabsorbed
Final urine contains the urine originally
present in the filtrate & excess salts
Problems
• Too high salt and minerals in diet
–  Solids precipitating out – Kidney stones
• Physical assault on kidneys
–  damage to kidney tissue resulting in blood in
urine
• Too much water
–  Renal failure as kidneys cannot cope with
workload