Excretory

 Homeostasis is the process of maintaining the ideal internal
conditions (i.e. correct temperature, right amount of water

and glucose & other solutes) for the body to work at it’s
optimum.
 Excretion is the process of removing metabolic waste
products and other toxins.
 Secretion is the release of useful substances, e.g. hormones,
from the body. Thus, it is not excretion. Egestion, i.e.
defecation, is also not excretion.
 Metabolic wastes are by product of metabolism
Metabolism- is the sum total of chemical reaction that
kept an organism alive.
 Osmoregulation is maintaining the correct balance
between water and solutes.
 Excretion, which includes osmoregulation, is thus
extremely important in maintaining homeostasis.
INVERTEBRATE EXCRETION
 Protozoans or known as one-celled organisms excrete

their waste products directly into their surrounding
environment.
 Ex. Euglena and amoeba eliminate most of their
excretory matter, including urea and CO2 through the
cell membrane
 Certain waste products would become highly toxic if
they were to accumulate. This could damage tissues.
 An excess of water could also lead to a number of
complications.
 Thus, the waste products must be removed – they
continually move into the bloodstream, which carries
them to the excretory organs.
Raw Materials
(Food and 02)
Useful Materials
Useless Materials
Egested (faeces) Metabolised
Metabolic Waste
Useful Products Products (urea and
CO2)
Excreted
VERTEBRATES EXCRETORY
 There are four main excretory organs:
 Lungs
 Colon
 Skin
 Kidneys
 The liver is not an excretory organ, but produces many

products which are excreted elsewhere. Toxins and drugs as
well as alcohol, is broken down in the liver. Hence, an excess
of smoking, medication and alcohol is extremely harmful to
the liver.
 The carbon dioxide released from cellular respiration is
carried to the lungs in the blood. It then diffuses across the
respiratory membrane and is exhaled.
 A small amount of heat and water is excreted this way.
 Bile pigments, from the break down of haemoglobin, and

cholesterol are synthesised in the liver.
 They pass into the small intestine as bile and are finally
excreted in the faeces as bile salts, from the colon.
 Mucus and bacteria are too excreted through the colon.
 Sweat, which is excreted through the skin, contains
water, salts and some urea.
 As the water in the sweat is excreted, heat is lost and
the body is cooled.
 Sweat is a form of excretion as it rids the body of
waste, as well as a form of secretion as it maintains
the body temperature.
 When amino acids and nucleic acids are broken down,
nitrogenous wastes are released as ammonia, urea, uric acid and
creatinine. Ammonia is toxic if it accumulates and is therefore
converted to less toxic urea in the liver.
 The regulatory functions of the normal kidney are enumerated as

follows:
 1. The excretion of waste products of metabolism

 2. The regulation of acid-base alkaline substances
 3. The regulation of the composition of blood and body fluids.
 4. The regulation of water balance of the tissues by elimination
of excess H2¬0
 5. The secretion of certain hormones, rennin and
erythropoietin that help in the maintenance and in controlling the
production of red blood cells.
 The kidneys aid in:
 excretion as they filter waste out of the blood
 regulate the water and salt balance in the body.
 One kidney – the right kidney – is slightly lower than the left as it is
pushed down by the liver, which is larger on the right.
 Each kidney contains:
 A renal artery (a branch of the abdominal aorta), which carries waste
products to the kidney and supplies the kidneys with oxygen and
nutrients.
 A renal vein that contains the purest blood in the body. It carries CO2
to the inferior vena cava.
 Ureter that carries urine from the kidney to the bladder.
The Kidneys
 The following substances are made in the liver and excreted by

the kidneys:
 Urea, the main nitrogenous waste compound secreted. It is
formed by the breakdown of excess amino acids in the process
of deamination.
 Uric acid, the nitrogenous end product of nucleic acid
metabolism.
 Creatinine is formed from creatinine phosphate, found in the
muscle cells.
 Non-nitrogenous waste, e.g. CO2, excess water, ions, hormones,
poisons and drugs.
 The main function of the urinary system is to maintain
homeostasis by regulating the volume and
concentration of body fluids. It filters and reabsorbs
certain materials from the blood.
 The urinary system is made up of the following parts:

A) Two kidneys
B) A bladder
C) An urethra
 Stores urine
 Is stimulated by impulses from a motor nerve, to contract to
expel the urine.
 Has sphincter muscles at the base to control the flow of urine
 Carries urine from the bladder to outside the body

Aorta
Adrenal Gland Carries oxygenated blood,
Regulates Salt food and waste from the
heart
Renal Artery
Renal Vein Carries blood from body to
Carries blood from kidneys kidneys
to inferior vena cava
Kidney
Excretory and
Inferior vena cava osmoregulatory organ.
Carries deoxygenated Ureter
blood and other Carries urine from
substances back to the kidneys to bladder
heart
Motor Nerve
Stimulates bladder
nerve
Bladder
Stores urine
Urethra
Carries urine from
bladder to outside the
body
 Found in abdominal cavity below the diaphragm, near the
posterior, on either side of the vertebral column.
 Kept in position with connective tissue, the peritoneum, as
well as renal blood vessels. They are wedged in with other
organs.
 Externally they are bean-shaped, dark red and the size of a
large bar of soap.
 The inner, concave border is called the hilum.
 Surrounded by three layers of protective tissue:
 A tough, fibrous renal capsule on the surface protects them from
disease.
 A middle layer of adipose tissue cushions them against blows.
 An outer layer of fibrous connective tissue, the renal fascia, anchors
the kidneys to surrounding structures.
Nephro
n
Renal Capsule
Protects kidney
Papilla
Tips of each pyramid, fits into
calyx
Renal artery
Carries blood to kidneys
Renal vein
Carries blood fromkidneys
Pyramid
Made up of collecting
ducts
Calyx
Collects urine from collecting
ducts
Medulla
Made up of pyramids
Ureter
Carries urine from pelvis to
bladder for storage
The kidney needs to have a constant supply of blood in order
to control the composition of body fluids.
 The renal artery, a branch from the aorta, enters the
kidney at the hilum. It supplies blood rich in nitrogenous
waste, oxygen and nutrients.
 The renal vein carries purified, deoxygenated blood to the
inferior vena cava, and then to the heart.
 A passive, non selective process.
 Fluids and solutes are forced through the glomerular
membrane by hydrostatic pressure.
 The glomerular filtrate has the same composition as blood,
without the blood cells and plasma proteins. These are too
large to fit through the glomerular membrane.
 Substances in glomerular filtration: Blood plasma without
protein molecules which includes:
 Useful substances – water, glucose, amino acids, vitamins, hormones,
and ions.
 Waste substances – e.g. nitrogenous waste such as urea, uric acid and
creatinine.
 Glomerular Filtration
 The fluid part of the blood is filtered from the glomerulus into
the cavity of the Bowman’s capsule.
 Tubular Reabsorption
 As the fluid flows along the renal tubule, useful substances
are reabsorbed back into the bloodstream according to the
body’s needs.
 Tubular Excretion
 In addition, certain unwanted substances in the blood are
actively excreted into the tubules.
 Occurs in the loop of Henle.
 Substances are reabsorbed in the following ways:
 Active reabsorption
 Passive reabsorption
This is the process by which substances are reabsorbed.
 Carrier molecules on the microvilli join up with certain
molecules from the filtrate and actively transport them
through the epithelial cells to the blood.
 Energy from ATP is used to join the molecule to the
carrier molecule. The following are actively reabsorbed:
 All organic nutrients such as glucose, amino acids and water
soluble vitamins are completely reabsorbed.
 Sodium ions and fat soluble vitamins are selectively reabsorbed,
according to the needs of the body.
 Passively = no energy needed.
 About 65% of the water is passively reabsorbed from
the filtrate in the proximal convoluted tubule by
osmosis.
 Chloride ions passively follow the path of sodium
ions.
 Urea, uric acid and creatinine is not reabsorbed.
 Takes place in proximal and distal tubules and is
reabsorption in reverse.
 The following molecules and ions are taken from the
blood and deposited into the filtrate:
 Hydrogen and potassium ions (secreted directly)
 Creatinine and uric acid
 Drugs, preserves and colourants (actively excreted)
 About 96% of urine is water.
 1.5% is salts, mainly sodium chloride.
 Urea makes up 2%
 Small quantities of drugs, colourants, hormones and
preservatives.
 About 1.5 litres of urine is produced daily.
Maintain homeostasis in the following ways:
 Excreting nitrogenous waste
 Osmoregulation – water and salts
 Maintain pH of body fluids
 Maintain electrolytic (salt) balance of body fluids by
absorbing and/or secreting ions.
Common Kidney Diseases
 Chronic Kidney Dse- long term condition that does

not improve overt time; commonly caused by high BP
and diabetes.
 Kidney Stones- occur when minerals and other
substances in blood crystallize in the kidney forming
solid masses(sotnes).Passing of kidney stone can be
extremely painful and cause rarely other problems
 UTI – are bacterial infections of any part of urinary
system. Infection is present in bladder and urethra
THE END

Excretory

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Excretory

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 Homeostasis is the process of maintaining the ideal internal

conditions (i.e. correct temperature, right amount of water

 Protozoans or known as one-celled organisms excrete

Egested (faeces) Metabolised

 The liver is not an excretory organ, but produces many

 Bile pigments, from the break down of haemoglobin, and

 The regulatory functions of the normal kidney are enumerated as

 1. The excretion of waste products of metabolism

 The following substances are made in the liver and excreted by

 The urinary system is made up of the following parts:

 Carries urine from the bladder to outside the body

 Chronic Kidney Dse- long term condition that does

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