EXCRETION IN HUMAN
EXCRETION
Excretion
is a biological process where cellular metabolic waste products are removed
from the body.
Or
Is a
removal of unwanted substances (metabolic products) from the body as fast as
they exceed a certain concentration.
Or
Is a
process by which metabolic waste products is eliminated from the body of an
organism.
Metabolic
wastes are produced as the result chemical reactions taking place in the cells
e.g. cellular respiration. Metabolism produces useful products as well as toxic
(poisonous) by-products. The toxic substances have to be removed as they are
harmful if allowed to accumulate.
NOTE
Metabolism
is the chemical processes that occur within a living organism in order to
maintain life example respiration, digestion and photosynthesis.
THE
IMPORTANCE OF EXCRETION
ü It helps to remove waste product
and toxic materials e.g. urea, carbon dioxide gas etc.
ü It eliminates the excess
materials from our body, like, soluble vitamins, drugs.
ü Maintain the pH of body fluids by
removing excess bile pigment through liver.
ü Maintains water balance in the
body. Excess water is removed as sweat or urine.
ü Regulation of blood pressure by
removing excess salt and water in the body.
ü It gives chance for absorption of
other materials.
ü Regulates the salt content in the
body.
MAJOR
EXCRETORY PRODUCTS
The
major excretory products eliminated by
organisms are carbon dioxide, excess water, and nitrogenous.
1.
Carbon dioxide gas and excess water
•
These
wastes are produced during the cellular respiration.
•
In
this process, glucose is broken down to release energy, carbon dioxide gas and
excess water.
2.
Nitrogenous waste
•
Nitrogenous
wastes are waste formed from the breakdown of proteins and amino acids.
•
Excess
protein and amino acid are broken down in the liver to form ammonia.
•
The
process where amino acid is broken down to form ammonia in the liver is called Deamination.
Types of Nitrogenous waste
The main
nitrogenous wastes excreted by living things are ammonia, urea and
uric acid.
a.
Ammonia
waste
This
waste is the results of broken down proteins and amino acid in the liver.
Ammonia wastes
are highly poisonous nitrogenous waste product.
Ammonia
is excreted mostly by aquatic organisms e.g. fish.
Ammonia
dissolves in water and is eliminated from the body in soluble form.
Those
animals which excrete their nitrogenous waste in form of ammonia are known as Ammonotelic
b.
Urea
Urea is
formed when ammonia combine with carbon dioxide in the liver.
Urea is
less toxic and is soluble in water.
Urea is
excreted by many aquatic and terrestrial animals include human being.
Those animal that excrete their nitrogenous waste
mainly inform of urea know as Ureotelic and phenomena know as
Ureotelism
c.
Uric
acid
Uric
acid is insoluble nitrogenous waste excreted main by birds, reptiles, and
insects.
Elimination
of uric acid requires lesser amount of water comparatively less soluble in
water and less toxic as compared to ammonia.
Animals
which excrete their nitrogenous waste in form of uric acid know as Urecotelic and phenomena know as Urecotelism
Other metabolic waste
The
other waste products eliminate by living things are
Hormone; this waste is result of excess production of
hormone especially to female during the pregnancy
Cholesterol; This waste is result from excess intake of fat
especially by mammals.
Bilirubin; This waste is from breaking down of haemoglobin
compound in mammals.
EXCRETION
IN HUMAN
Excretion
in human being is done through Lungs, Skin, Liver and Kidneys.
1. Lungs:
The
lungs help in getting rid of carbon dioxide, formed as a result of cellular respiration,
through exhalation.
2. Skin:
The skin
has sweat glands which excrete small amount of excess water and salts.
3. Liver:
The livers
excrete bile, which contains bile pigments. Bile pigments are produced by
breakdown old red blood cells in the liver. The liver also excretes
cholesterol.
4. Kidneys
The
kidneys are the main organs of excretion. It helps to remove excess water and
dissolved urea in form of urine from the blood.
THE HUMAN URINARY SYSTEM
The
urinary system is the system consists of all the organs involved in the
formation and release of urine. This system filters the blood, remove waste and
extra water which become a component of urine.
Parts of urinary system
1.
Kidneys
2.
Ureters
3.
Bladder
4.
Urethra
The urinary system consists
of the kidneys, the ureters, bladder, and the urethra.
Diagram of human urinary system
1.
kidneys
The
bean-shaped organs which help the body to eliminate urea in form of urine. The
urinary system consists of two kidneys such as the right kidney and the left
kidney.
2.
Ureters
The pair
of ducts or tubes that carries urine from the kidneys to the bladder. Ureters
wall consist of smooth muscles which contract to force urine downward, away
from the kidneys.
3.
Bladder(Urinary
bladder)
The
muscular sac that keep or stores urine temporary before excreted out of the
body. The bladder also is known as the urinary bladder and is located in
the lower abdominal. The bladder walls relax (expand) to store urine, and also
contract and to remove urine from the body.
4.
Sphincter
muscles
The
circular muscles help to keep urine from leaking by closing tightly around
the opening of the bladder.
5.
Urethra
Urethra
is a tube like structure which carries urine from the bladder to outside the
body. In female, urethra carry urine outside the body while in male; urethra
carry urine and sperm outside the body.
The
Internal structure of a kidney
From
the diagram above,
The
internal structure of kidney is composed of three basic regions such as
1. Cortex,
2. Medulla and
3. Pelvis.
1. Cortex
The
cortex is the outer part of the kidney where blood is filtered. This part
contains Billions of glomeruli that help in filtration of blood contents.
2. Medulla
The
medulla is the inner part of the kidney where the amount of salt and water are
controlled. It consists of billions of loops of Henle. The surface of medulla
is folded to form projection called pyramids.
3. Pelvis
This is
a part of the kidney where urine is collected after formed in the kidney. This
part is connected to the ureters which carry urine from the kidney to the
bladder.
FUNCTIONS
OF KIDNEY IN EXCRETION
ü Maintain volume of extracellular
fluid (fluid outside the cell).
ü Maintain ionic balance in
extracellular fluid
ü Maintain pH of the extracellular
fluid.
ü Excrete toxic metabolic
by-products such as urea, and uric acid.
ü Filtering blood and producing
urine.
ü Absorbing minerals.
NEPHRON
Nephron
is the structural and functional unit of the kidney. It act as filters and
remove the waste products from blood and forms urine. Each kidney possesses a
large number of nephrons approximately one million.
Structure
of the Nephron
Afferent arteriole and Efferent
arteriole
Afferent
arteriole is the branch of renal artery which carries blood to the glomerulus
capsule while Efferent arteriole carries blood away from the glomerulus to
different part of the body.
Bowman’s capsule
A round
cup like structure which surrounds or encloses a glomerulus. It serves as a filter to remove
organic wastes, excess inorganic salts, and water.
Glomerulus
A
network of capillaries surrounded by the Bowman's capsule. It receives and
filter blood from afferent arteriole. The blood with large particles is taken
from the glomerulus through efferent artery to different parts of body.
Proximal convoluted tube
This is
the first convoluted tube extended from Bowman’s capsule to the descending loop
of Henle. It helps in reabsorption of glucose, amino acid, potassium and
calcium ions.
Loop of Henle
The
U-shaped part of the nephron, located between the proximal and distal
convoluted tubules. Loop of Henle helps to reabsorb water and salt (Nacl). Animals
with long loop of Henle store large amount of water in their body for long
period of time. It is one of the adaptive features for animals living in desert
area.
Parts of loop of Henle
It is
divided into two parts such as descending and ascending.
i.
Descending loop of Henle
This
part is permeability to water. Therefore, water is reabsorbed.
ii. Ascending part loop of Henle
This
part is permeability to sodium ions. Therefore, sodium ions are reabsorbed.
Distal convoluted tubule
This is
the second convoluted or coiled tube that extended from the loop of Henle to
the collecting duct. At distal convoluted tubule also Sodium ions and water are
reabsorbed
Collecting ducts
The
collecting ducts are small tubes that direct or drainage urine into the renal
pelvis for drainage into the ureter. Once in the ureter, the urine can be
pushed into the bladder for elimination.
Questions
1) Why proximal and distal
convoluted tubule is highly convoluted?
2) Give reason, why camel adapts
well in desert?
MECHANISM OF URINE
FORMATION
The process
of urine formation in the body involves three process steps such as Filtration,
Reabsorption and Secretion.
1.
Filtration
Filtration
takes place in the glomerulus when the kidneys receive blood contents under
high pressure through renal artery. In the glomerulus, filtration of amino
acid, water, salt, glucose, and urea from the blood is done. At glomerulus,
blood speed slow down to allow more absorption of materials. This is called
glomerular ultra filtration.
2.
Reabsorption
Reabsorption
is the movement of substances out of the renal tubules back into the blood
capillaries. It occurs in different parts of the nephron such as proximal
convoluted tubes, loop of Henle, distal convoluted tube and collecting duct.
i.
Reabsorption at proximal convoluted tube
In this
region, Glucose, amino acid, potassium and calcium ions are reabsorbed
ii. Reabsorption
at loop of Henle
In
descending part of loop of Henle, water is reabsorbed while in ascending part
loop of Henle, sodium ions are reabsorbed.
iii Reabsorption at Distal convoluted tube
In this
region, Sodium ions and water also are reabsorbed.
iv Reabsorption at collecting duct
In this
region, more water are absorbed
3.
Secretion
The
process where substances move out of the blood into the renal tubules (nephron).Secretion
takes place at distal convoluted tubule where potassium and acid in the form of
hydrogen ions, are removed from the blood by the distal convoluted tubule, and
are then added to the urine.
URINATION
Is the
release of urine from the urinary bladder through the urethra to the outside of
the body. It’s the urinary system form of excretion.
COMPOSITION
OF URINE
ü
Water
ü
Urea
ü
Salt
eg sodium chloride
ü
Creatinine
COMPLICATION
AND DISORDERS OF EXCRETORY SYSTEM
Complication
and disorders of excretory system is inability of excretory system to carry out
their normal function such as excreting wastes. Some of complication and
disorders of excretory system are Kidney stones and Kidney failure.
KIDNEY
STONES
Kidney
stones are deposit of calcium salt and other salt in the urinary system. Kidney
stones can damage urinary system resulting to severe pain as well as blood in
urine when urinating.
CAUSES
ü Kidney stones are caused due to
crystallization of salt around the blood or dead tissue.
ü Stones commonly have been found
in those that drink less than the recommended eight to ten glasses of water a
day.
SYMPTOMS OF KIDNEY STONES
ü Blood in urine - This may be
caused by the stone scratching the kidney or ureter
ü Pain during the urination
ü Men may have pain in
the testicles and scrotum.
ü Periods of intense pain in the
back or side of your abdomen which may last for minutes or hours
ü Feeling restless and unable to
lie still
ü Nausea
ü Needing to urinate more often
than normal
HOW TO PREVENT KIDNEY STONES
ü Drink plenty of water to dilutes
the substances in urine that lead to stones.
ü Make sure to take in amount of
calcium appropriate to your age.
ü Reduce stone forming foods: such
as chocolate, spinach, tea, and most nuts
ü Reduce sodium: Low sodium diet is
recommended for the stone prone.
ü Limit animal protein: Eating too
much animal protein, such as red meat, eggs, and seafood, boosts the level of
uric acid and could lead to kidney stones.
TREATMENT FOR KIDNEY STONES
ü Surgical treatments which may
involve kidney transplant
KIDNEY
FAILURE
Kidney
failure occurs when the kidneys partly or completely lose their ability to
carry out normal function such as filter water and waste from the blood. Kidney
fail can be categorized into acute kidney failure and chronic kidney failure.
ACUTE
KIDNEY FAILURE
Acute
kidney failure occurs when kidneys suddenly become unable to filter waste
products from your blood. Acute kidney failure also is called acute renal
failure or acute kidney injury.
CHRONIC
KIDNEY FAILURE
Chronic
kidney failure occurs when a disease slowly destroys the kidneys. Destruction
occurs over many years, usually with no symptoms until the late stage of kidney
failure.
WHAT CAUSES KIDNEY FAILURE?
ü
Loss
of blood flow to the kidneys this can be caused by heart attacks, heart
disease, dehydration, blood pressure etc.
ü
Drugs
and alcohol
ü
Blood clots in or around the kidneys
ü
Infections
ü
Physical
injured or trauma
ü
Drug
toxicity
ü
Kidney
stone
SYMPTOMS
ü
Making
more or less urine than normal.
ü
Blood
in the urine (typically only seen through a microscope)
ü
Urine
that is bubble (may be seen when protein is in the urine)
ü
Fatigue
ü
Shortness
of breath
ü
Weakness
ü
Mental
confusion
ü
Nausea
and vomiting
HOW TO PREVENT KIDNEY FAILURE
ü Take Balanced diet to avoid heart
diseases e.g. Blood pressure.
ü Drink alcohol only in moderate
ü Drink lots of water every
day
ü Reduce the intake of salt: Salt
increases the amount of sodium in diet which may lead to kidney stone.
ü Manage diabetes, high blood
pressure and heart disease
ü Drink healthy beverages: Including
fresh juices is another way of drinking more fluids and keeping your kidneys
healthy
TREATMENT FOR KIDNEY FAILURE
ü Kidney failure is treated by
Kidney transplant.
ü A kidney transplant involves
surgically placing a healthy kidney from a donor into the patient.
REVISION QUESTIONS
Q n. Draw the cross-section part of the skin and label
all parts correctly
Qn. Give
brief explanation not more than three lines in each of the following:
(i)
How
the skin is the excretion surface?
(ii)
How
the skin is used in regulation?
(iii)
Justify
why the skin is a sense
Qn (a) Define the following terms;
(i)
Homeostasis
(ii) Osmoregulation
Qn. Animal A with 36oC body
temperature and animal B with 30oC body temperature were put into a
refrigerator switched to 10oC at about 15 minutes. When temperature
(s) of animal A and B were taken again (after 15 minutes) the temperature of
animal A was averagely the same but the temperature of animal B was 10oC.
Qn. Give the biological terms used to describe
animal A and B with respect to temperatures control
Qn. Briefly explain how mammals overcome
overheating.
Qn. (a) Describe the following terms
i.
Hypoglycemia
ii.
Hyperglycemia
iii.
Polyuria
iv.
Deamination
Qn. Distinguish between diabetes mellitus and
diabetes insipidus.
Qn. Describe the behavioral and physiological
mechanisms of temperature regulation in mammals.
Qn. Name four organism mammal body involved
in regulation.
Qn. Urea, ammonia, and uric acid are all
excretory products. Which of these substances requires?
i)
Least
water to eliminate
ii)
Most
water to eliminate
iii)
Is
major excretory products in Birds, Amoeba, Insects and Man
Qn. The following are the main waste products
excreted in man; carbon dioxide, water and urea.
i) Name the major organs through which
each is excreted.
ii) Name the organs where each is produced
Qn. Name two substances that the body would
be deficient after sweating.
Qn. Explain the main parts internal
structures of the kidney and its function.
Qn. Differentiate between diamination and
detoxification.
Qn. Explain the common urinary disorder in
human being.
Qn. Explain the function of the following
i.
Loop
of Henle
ii.
Bowman’s
capsule
iii.
Proximal
convoluted tubule
iv.
Collecting
duct.
